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V2S/V3R Index Distinguishes LVOT from RVOT Origins Introduction Although several ECG criteria have been proposed for differentiating between left and right origins of idiopathic ventricular arrhythmias (VA) originating from the outflow tract (OT-VA), their accuracy and usefulness remain limited. This study was undertaken to develop a more accurate and useful ECG criterion for differentiating between left and right OT-VA origins. Methods and Results We studied OT-VAs with a left bundle branch block pattern and inferior axis QRS morphology in 207 patients who underwent successful catheter ablation in the right (RVOT; n = 154) or left ventricular outflow tract (LVOT; n = 53). The surface ECGs during the OT-VAs and during sinus beats were analyzed with an electronic caliper. The V2S/V3R index was defined as the S-wave amplitude in lead V2 divided by the R-wave amplitude in lead V3 during the OT-VA. The V2S/V3R index was significantly smaller for LVOT origins than RVOT origins (P < 0.001). The area under the curve (AUC) for the V2S/V3R index by a receiver operating characteristic analysis was 0.964, with a cut-off value of ≤1.5 predicting an LVOT origin with an 89% sensitivity and 94% specificity. In the AUC and accuracy, the V2S/V3R index was superior to any previously proposed ECG criteria in an analysis of all OT-VAs. This advantage of the V2S/V3R index over the V2 transition ratio and other indices also held true for a subanalysis of 77 OT-VAs with a lead V3 precordial transition. Conclusion The V2S/V3R index outperformed other ECG criteria to differentiate left from right OT-VA origins independent of the site of the precordial transition. [ABSTRACT FROM AUTHOR]

Cardiovascular Implantable Electronic Device Implantation with Uninterrupted Dabigatran Background While continuation of oral anticoagulation (OAC) with warfarin may be preferable to interruption and bridging with heparin for patients undergoing cardiovascular implantable electronic device (CIED) implantation, it is uncertain whether the same strategy can be safely used with dabigatran. Objective and Methods To determine the risk of bleeding and thromboembolic complications associated with uninterrupted OAC during CIED implantation, replacement, or revision, the outcomes of patients receiving uninterrupted dabigatran (D) were compared to those receiving warfarin (W). Results D was administered the day of CIED implant in 48 patients (age 66 ± 12.4 years, 13 F and 35 M, 21 ICDs and 27 PMs), including new implant in 25 patients, replacement in 14 patients, and replacement plus lead revision in 9 patients. D was held the morning of the procedure in 14 patients (age 70 ± 11 years, 4 F and 10 M, 5 ICDs and 9 PMs). W was continued in 195 patients (age 60 ± 14.4 years, 54 F, and 141 M), including new implant in 122 patients, replacement in 33 patients, and replacement plus lead revision or upgrade in 40 patients. Bleeding complications occurred in 1 of 48 patients (2.1%) with uninterrupted dabigatran (a late pericardial effusion), 0 of 14 with interrupted D, and 9 of 195 patients (4.6%) on W (9 pocket hematomas), P = 0.69. Fifty percent of bleeding complications were associated with concomitant antiplatelet medications. Conclusions The incidence of bleeding complications is similar during CIED implantation with uninterrupted D or W. The risks are higher when OAC is combined with antiplatelet drugs. [ABSTRACT FROM AUTHOR]

Dabigatran versus Warfarin for AF Ablation Background Uninterrupted oral anticoagulant (OA) therapy with warfarin has become the standard of care at many centers performing catheter ablation of atrial fibrillation (AF). Compared with warfarin, dabigatran, a direct thrombin inhibitor, has been demonstrated to reduce the risk of stroke in nonvalvular AF with similar bleeding risk. Few data exist on the safety profile of uninterrupted dabigatran therapy during AF ablation. Methods We compared the safety and efficacy of uninterrupted OA therapy with either warfarin or dabigatran in all patients undergoing AF catheter ablation at the University of Alabama at Birmingham between November 1, 2010 and January 31, 2012. All patients underwent a transesophageal echocardiogram (TEE) on the day of their ablation procedure to assess for the presence of intracardiac thrombi. All complications were identified and classified as bleeding, thromboembolic events, or other. Results There were 212 patients in the dabigatran group and 251 patients in the warfarin group. The groups were well matched. There were 3 complications in the dabigatran group and 6 in the warfarin group (P = 0.45). There were 2 bleeding complications in the dabigatran group and 6 in the warfarin group (P = 0.23). There was one thromboembolic complication (a possible TIA) in the dabigatran group and none in the warfarin group (P = 0.28). Conclusion The administration of dabigatran is as safe and effective as warfarin for uninterrupted OA therapy during catheter ablation of AF. [ABSTRACT FROM AUTHOR]

A 72-year-old man with nonischemic cardiomyopathy was referred because his implantable cardioverter defibrillator had failed to terminate spontaneous ventricular fibrillation (VF). Defibrillation threshold (DFT) testing confirmed that 830-V shocks failed to defibrillate VF despite optimization of the biphasic waveform and reversal of shock polarity. The placement of a new right ventricular lead and the addition of a subcutaneous array failed to defibrillate VF at 830 V. The combination of a subcutaneous array and azygos vein coil successfully defibrillated VF. The mechanism for successful DFT reduction was likely greater current supplied to the posterior basal left ventricle by the azygos vein lead. (PACE 2012; 35:e173-e176) [ABSTRACT FROM AUTHOR]

A 55-year-old man underwent catheter ablation of ventricular tachycardia (VT) after anterior myocardial infarction. Although electrophysiological study suggested that the VT originated from the septum, biventricular endocardial irrigated radiofrequency ablation failed to interrupt the VT. Epicardial ablation at the site located halfway between the lesions in the right and left ventricles via a pericardial approach eliminated the VT, suggesting that the VT likely originated from the top of the septum. When VTs originating from the upper septum are refractory to endocardial ablation, epicardial mapping and ablation may be considered because only that site may be accessible with an epicardial approach. (PACE 2012; 35:e116-e119) [ABSTRACT FROM AUTHOR]

A 39-year-old man with idiopathic monomorphic premature ventricular contractions (PVCs), exhibiting a right bundle branch block and inferior axis QRS morphology, underwent electrophysiological testing. After a radiofrequency (RF) application to the anterior mitral annulus (MA) eliminated the spontaneous PVC morphology, a second PVC morphology occurred. Pacing from the first ablation site exhibited an excellent match to the second PVCs with a long stimulus to QRS interval. An RF application delivered near the first lesion eliminated all PVCs. The MA PVCs in this case exhibited a single origin with multiple breakouts and preferential conduction that were unmasked by RF ablation. (PACE 2012; 35:e112-e115) [ABSTRACT FROM AUTHOR]

A 62-year-old man with severe coronary artery disease and a left ventricular aneurysm underwent catheter ablation of ventricular tachycardia (VT) with right bundle branch block QRS morphology. Endocardial bipolar voltage mapping with standard threshold settings demonstrated no low-voltage areas within the aneurysm. Catheter ablation of the epicardial surface of the aneurysm eliminated the VT. Endocardial bipolar voltage mapping with any other settings could not predict the site of the epicardial arrhythmogenic substrate whereas endocardial unipolar voltage mapping could. Endocardial unipolar voltage mapping may be helpful for predicting epicardial arrhythmogenic substrates. (PACE 2012; 35:e13-e16) [ABSTRACT FROM AUTHOR]

A 62-year-old man with idiopathic ventricular tachycardia (VT) exhibiting left bundle branch block and left inferior axis QRS morphology with a Qr in lead III underwent electrophysiological testing. Successful ablation was achieved in the left ventricle (LV) at a site with an excellent pace map, adjacent to the His bundle electrogram recording site. At that site, the sequence of the ventricular electrogram and late potential recorded during sinus rhythm reversed during spontaneous premature ventricular contractions with the same QRS morphology as the VT. This case shows that VT can arise from the LV ostium adjacent to the membranous septum. (PACE 2010; 33:e114-e118) [ABSTRACT FROM AUTHOR]

A 59-year-old man with two different premature ventricular contractions (PVCs) forming a couplet underwent electrophysiological testing. Although pacing from the aorto-mitral continuity (AMC) produced an excellent pace map of one type of PVCs, a radiofrequency application within the right coronary cusp (RCC) eliminated all the PVCs. This case demonstrates that a single origin with two breakout sites in the left ventricular ostium (LVos) may result in a couplet consisting of different PVCs and preferential conduction from the RCC to AMC may also occur. These possibilities should be kept in our mind when predicting sites of origin of LVos ventricular arrhythmias. (PACE 2010; 33:e88–e92) [ABSTRACT FROM AUTHOR]

Limited Response to CRT in Patients with RVD. Introduction: Patients with left ventricular dysfunction (LVD) and LV dyssynchrony may respond to cardiac resynchronization therapy (CRT). However, right ventricular dysfunction (RVD) is a predictor of decreased survival in patients with LVD, and its influence on clinical response to CRT is unknown. The purpose of this study was to examine the effect of RVD on the clinical response to CRT. Methods and Results: A retrospective cohort of consecutive patients who underwent implantation of a CRT implantable cardioverter-defibrillator (ICD) were included and deemed to have RVD based on a RV ejection fraction <0.40. A lack of response to CRT was defined as: death, heart transplantation, implantation of an LV assist device, absent improvement in NYHA functional class at 6 months or hospice care. Among 130 patients included (mean age 58 ± 11 years, 68.5% male, 87.7% Caucasian, 51.5% nonischemic cardiomyopathy), 77 (59.2%) had no response to CRT as defined above. Of the nonresponders, 43 (56%) had RVD and 34 (44%) did not have RVD (P = 0.02). After adjustment for age, race, gender, cardiomyopathy type, atrial fibrillation, serum sodium, and severe mitral regurgitation, RVD (adjusted OR = 0.34, 95%CI 0.14–0.82), female gender (adjusted OR = 0.36, 95%CI 0.14–0.95), and serum creatinine (adjusted OR = 0.25, 95%CI 0.09–0.71) were independently associated with decreased odds of response to CRT. There was a significant difference in survival of patients with and without RVD after CRT (log rank P = 0.01). Conclusion: RVD represents a strong predictor of lack of clinical response to CRT in patients with CHF due to LVD and should be considered when prescribing CRT. (J Cardiovasc Electrophysiol, Vol. 21, pp. 431–435, April 2010) [ABSTRACT FROM AUTHOR]

IVT Arising Adjacent to the Left Sinus of Valsalva. Background: Idiopathic ventricular arrhythmias (VAs) may be amenable to catheter ablation within or adjacent to the left sinus of Valsalva (LSOV). However, features that discriminate these sites have not been defined. The purpose of this study was to determine the electrocardiographic and electrophysiological features of VAs originating within or adjacent to the LSOV. Methods and Results: We studied 48 consecutive patients undergoing successful catheter ablation of idiopathic VAs originating from the left coronary cusp (LCC, n = 29), aortomitral continuity (AMC, n = 10) and great cardiac vein or anterior interventricular cardiac vein (Epi, n = 9). A small r wave, or rarely an R wave, was typically observed in lead I during the VAs and pacing in these regions. An S wave in lead V5 or V6 occurred significantly more often during both the VAs and pacing from the AMC than during that from the LCC and Epi (p < 0.05 to 0.0001). For discriminating whether VA origins can be ablated endocardially or epicardially, the maximum deflection index (MDI = the shortest time to the maximum deflection in any precordial lead/QRS duration) was reliable for VAs arising from the AMC (100%), but was less reliable for LCC (73%) and Epi (67%) VAs. In 3 (33%) of the Epi VAs, the site of an excellent pace map was located transmurally opposite to the successful ablation site (LCC = 1 and AMC = 2). Conclusions: The MDI has limited value for discriminating endocardial from epicardial VA origins in sites adjacent to the LSOV probably due to preferential conduction, intramural VA origins or myocardium in contact with the LCC. (J Cardiovasc Electrophysiol, Vol. 21, pp. 170-176, February 2010) [ABSTRACT FROM AUTHOR]

A 65-year-old man with frequent premature ventricular contractions (PVCs) underwent electrophysiological testing. Although an excellent pace map was obtained from the right coronary cusp (RCC), radiofrequency ablation at that site interrupted the PVCs transiently. Successful ablation was achieved in the left coronary cusp with earlier local ventricular activation during the PVCs than that in the RCC. These findings suggest that preferential conduction within the aortic root may exist and cause ventricular arrhythmias (VAs) arising from this region to exhibit variable electrocardiographic features, thereby limiting the reliability of electrocardiographic algorithms and pace mapping to predict the site of the VA origin. (PACE 2010; e10–e13) [ABSTRACT FROM AUTHOR]

Idiopathic VAs Originating from the LV Papillary Muscles. Introduction: Idiopathic ventricular arrhythmias (VAs) can originate from the left ventricular (LV) papillary muscles (PAMs). This study investigated the prevalence, electrocardiographic and electrophysiological characteristics, and results of catheter ablation of these VAs, and compared them with other LV VAs. Methods and Results: We studied 71 patients with VAs originating from the LV anterolateral and posteroseptal regions among 159 patients undergoing successful catheter ablation of idiopathic LV VAs. PAM VAs were uncommon, rare in a sustained form, and more common from the posterior papillary muscle (PPM) than anterior papillary muscle (APM). A younger age was a good predictor for differentiating left posterior fascicular VAs from PPM VAs. There were several electrocardiographic features that accurately differentiated PAM and LV fascicular VAs from mitral annular VAs. However, an R/S ratio ≤1 in lead V6 in the LV anterolateral region and a QRS duration >160 ms in the LV posteroseptal region were the only reliable predictors for differentiating PAM VAs from LV fascicular VAs. A sharp ventricular prepotential was recorded at the successful ablation site during 42% of the PAM VAs. Radiofrequency current with an irrigated or conventional 8-mm tip ablation catheter was required to achieve a lasting ablation of the PAM VA origins whereas that with a nonirrigated 4-mm tip ablation catheter produced excellent results in LV fascicular and mitral annular VAs. Conclusions: There are differences in the electrocardiographic and electrophysiological features among VAs originating from these regions that are helpful for their diagnosis and effective catheter ablation. (J Cardiovasc Electrophysiol, Vol. 21, pp. 62–69, January 2010) [ABSTRACT FROM AUTHOR]

A 54-year-old woman with idiopathic premature ventricular contractions (PVCs) underwent electrophysiological testing. Three-dimensional (3D) geometries of the papillary muscles and chamber of the left ventricle (LV) were reconstructed using a CARTO-based 3D ultrasound imaging system (Biosense Webster Inc., Diamond Bar, CA, USA) during the PVCs. Activation mapping in the LV was then performed during the PVCs and the activation map revealed the earliest ventricular activation on the anterior papillary muscle. An irrigated radiofrequency current delivered at that site with guidance from that system eliminated the PVCs. This case may suggest that the guidance system may be feasible and useful for catheter ablation of PVCs arising from uncommon sites. [ABSTRACT FROM AUTHOR]

The incidence and prevalence of atrial fibrillation (AF) increase with age. Catheter ablation has been suggested to improve the quality of life of patients with AF. However, in order to expand the indications for AF ablation to the elderly, several important questions should be answered as to whether safety and efficacy of AF ablation in elderly patients are similar to those in younger populations, whether the AF mechanisms in elderly patients are similar to those in younger patients so that the same ablation techniques can be used in both groups, and whether anticoagulation strategies should be the same for elderly patients as for younger patients after AF ablation. Recent studies reported that the risk of complications from AF ablation did not vary with age, nor was the AF recurrence rate age-dependent for any type of AF, suggesting that the AF mechanisms in elderly patients were similar to those in younger patients. On the other hand, the feasibility of discontinuation of anticoagulation in the elderly after successful AF ablation has not been established since it is difficult to be certain whether AF has been truly cured and since many elderly people are likely to be considered as high-risk based on their CHADS2 score. In addition, the elderly patients who have been included in published trials of AF ablation may not represent an unselected population of individuals in this age group. Randomized trials of catheter ablation will be necessary before this procedure can be promoted for wider use in the elderly. [ABSTRACT FROM AUTHOR]

The article describes the case of a 65-year-old woman with paroxysmal supraventricular tachycardia (SVT) who developed atrioventricular nodal reentrant tachycardia. She was referred for catheter ablation. Results of the programmed ventricular stimulation showed a decremental retrograde ventriculoatrial (VA) conduction with a concentric retrograde atrial activation. It was observed that during the tachycardia, the VA conduction was brief with oscillation.

Introduction: Focal ventricular arrhythmias (VAs) have been reported to arise from the posterior papillary muscle in the left ventricle (LV). We report a distinct subgroup of idiopathic VAs arising from the anterior papillary muscle (APM) in the LV. Methods and Results: We studied 432 consecutive patients undergoing catheter ablation for VAs based on a focal mechanism. Six patients were identified with ventricular tachycardia (VT, n = 1) or premature ventricular contractions (PVCs, n = 5) with the earliest site of ventricular activation localized to the base (n = 3) or middle portion (n = 3) of the LV APM. No Purkinje potentials were recorded at the ablation site during sinus rhythm or the VAs. All patients had a normal baseline electrocardiogram and normal LV systolic function. The VAs exhibited a right bundle branch block (RBBB) and right inferior axis (RIA) QRS morphology in all patients. Oral verapamil and/or Na+ channel blockers failed to control the VAs in 4 patients. VT was not inducible by programmed electrical stimulation in any of the patients. In 4 patients, radiofrequency current with an irrigated or conventional 8-mm-tip ablation catheter was required to achieve a lasting success. Two patients had recurrent PVCs after a conventional radiofrequency ablation with a 4-mm-tip ablation catheter had initially suppressed the arrhythmia. Conclusions: VAs may arise from the base or middle portion of the APM and are characterized by an RBBB and RIA QRS morphology and focal mechanism. Catheter ablation of APM VAs is typically challenging, and creation of a deep radiofrequency lesion may be necessary for long-term success. [ABSTRACT FROM AUTHOR]

A 49-year-old woman with dextrocardia and situs inversus underwent catheter ablation of paroxysmal atrial fibrillation (AF). During the electrophysiologic study, AF triggered by frequent premature atrial contractions (PACs) with a short coupling interval exhibiting a “P on T” pattern occurred. Pulmonary vein mapping revealed that those PACs originated from right-sided (anatomic left) or left-sided (anatomic right) pulmonary veins. In this case with mirror-image dextrocardia, the P-wave morphologies in leads I and aVL and the II/III ratio of the P-wave amplitude were helpful for predicting a right- or left-sided pulmonary vein origin. [ABSTRACT FROM AUTHOR]

A 55-year-old man with arrhythmogenic right ventricular cardiomyopathy underwent catheter ablation of ventricular tachycardia (VT) with left bundle branch block and left superior axis QRS morphology with an early precordial transition. Endocardial mapping during the VT revealed a focal activation pattern from a small region of low voltage in the left ventricular (LV) septum. Despite earliest endocardial activation in the LV septum, epicardial mapping demonstrated a macro-reentrant circuit with successful catheter ablation at an inferior peritricuspid annular site. Activation from the reentrant circuit propagated through the scar area in the epicardial right ventricle to the remote endocardial LV breakout site. [ABSTRACT FROM AUTHOR]

A 32-year-old woman with a history of nonischemic dilated cardiomyopathy, left bundle branch block, left ventricular ejection fraction of 0.15, and New York Heart Association Class III congestive heart failure, despite optimal medical treatment, was referred for cardiac resynchronization therapy with implantation of an implantable cardioverter defibrillator. The patient had prior chemotherapy for non-Hodgkin's lymphoma and was shown to have chronic total occlusion of the superior vena cava (SVC) by magnetic resonance imaging. Cardiac resynchronization was accomplished with an iliofemoral approach without complications resulting in marked clinical improvement. We conclude that the iliofemoral approach allows transvenous implantation of cardiac resynchronization therapy in patients with superior vena cava occlusion. [ABSTRACT FROM AUTHOR]

A 61-year-old woman with typical atrial flutter underwent an electrophysiologic study and radiofrequency catheter ablation. The electroanatomic mapping revealed two contiguous lines of distinct double potentials (DPs) extending anteriorly/posteriorly from the coronary sinus ostium to the inferior vena cava (IVC) border. A large part of the anterior line of the DPs was close and parallel to the tricuspid annulus (TA). An initial discrete radiofrequency application at the very narrow preexisting isthmus between the TA and anterior line of the DPs completed the IVC-TA isthmus conduction block. [ABSTRACT FROM AUTHOR]

A 64-year-old man with atrial tachycardia (AT) 3 years after a superior vena cava (SVC) isolation for atrial fibrillation underwent electrophysiologic testing. SVC mapping with a basket catheter revealed a more frequent activation in the SVC than in either of the atria during the AT and consequently the recovered conduction between the SVC and right atrium. The conduction improved from 3 or 4–1 conduction to 2–1 conduction after adenosine was administered. Ectopic firing in the SVC persisted even after restoration of sinus rhythm by the successful SVC isolation, which was confirmed by adenosine. [ABSTRACT FROM AUTHOR]

STEINHAUS, D., et. al.: Implant Experience with an Implantable Hemodynamic Monitor for the Management of Symptomatic Heart Failure. Introduction: Management of congestive heart failure is a serious public health problem. The use of implantable hemodynamic monitors (IHMs) may assist in this management by providing continuous ambulatory filling pressure status for optimal volume management. Methods and Results: The Chronicle® system includes an implanted monitor, a pressure sensor lead with passive fixation, an external pressure reference (EPR), and data retrieval and viewing components. The tip of the lead is placed near the right ventricular outflow tract to minimize risk of sensor tissue encapsulation. Implant technique and lead placement is similar to that of a permanent pacemaker. After the system had been successfully implanted in 148 patients, the type and frequency of implant-related adverse events were similar to a single-chamber pacemaker implant. R-wave amplitude was 15.2 ± 6.7 mV and the pressure waveform signal was acceptable in all but two patients in whom presence of artifacts required lead repositioning. Implant procedure time was not influenced by experience, remaining constant throughout the study. Conclusion: Based on this evaluation, permanent placement of an IHM in symptomatic heart failure patients is technically feasible. Further investigation is warranted to evaluate the use of the continuous hemodynamic data in management of heart failure patients. (PACE 2005; 28:747–753) [ABSTRACT FROM AUTHOR]

HOYT, R.,et al.: Transvenous Catheter Cryoablation for Treatment of Atrial Fibrillation: Results of a Feasibility Study. Pulmonary vein (PV) isolation using radiofrequency (RF) ablation can induce PV stenosis. Cryoablation may offer a safer alternative energy source for PV isolation. PV isolation with cryoablation was attempted in 31 patients with paroxysmal atrial fibrillation (AF). Event monitors were used to measure the AF episode burden. Serial spiral CT scans were obtained to monitor PV stenosis pre- and postcryoablation. Cryoablation was immediately successful for PV isolation in 29 of 31 patients (94%), with 5.9± 1.2 months of follow-up. Additional RF ablation was performed for AF recurrences in seven patients. The remaining 22 patients with a single cryoablation procedure demonstrated a time-dependent, long-term reduction in the frequency of AF episodes. At 6 months of follow-up, 18 of 22 of cryo-treated only patients (82%) were free of symptomatic AF episodes, and antiarrhythmic drugs were discontinued in 12 of 22 patients. Serial spiral CT scans demonstrated no change in the cryo-treated PV ostial diameter. PV cryoablation was effective to control paroxysmal AF in most patients. Early recurrences of AF postcryoablation were common, though tended to resolve within 6 months postablation, consistent with a process of reverse atrial remodeling. Cryoablation of the PVs did not cause PV stenosis or other serious adverse events.(PACE 2005; 28:S78–S82) [ABSTRACT FROM AUTHOR]

MAYHEW, M.W., et al.: Electrical Characteristics of a Split Cathodal Pacing Configuration. Several electrical configurations can be used for biventricular pacing to achieve cardiac resynchronization. Commercially approved biventricular pacing systems stimulate the RV with an endocardial lead and the LV with a unipolar lead positioned in the cardiac venous circulation using the tip electrodes of both leads linked as a common cathode. The distribution of current with this parallel circuit, split cathodal configuration is dependent on the separate impedances of the two leads. A total of 19 patients with left bundle branch block and congestive heart failure underwent implantation of a cardiac venous lead and standard bipolar right atrial and RV pacing leads. Stimulation thresholds and impedances were measured for the RV and LV in five electrical configurations: (1) unipolar LV from the cardiac venous lead; (2) bipolar LV using the tip electrode in the cardiac vein as the cathode and the ring electrode of the RV lead as the anode; (3) bipolar RV from the RV lead; (4) unipolar split cathodal stimulation of the cardiac venous and RV leads; and (5) bipolar split cathodal stimulation of the cardiac venous and RV leads. Repeat measurements of RV and LV thresholds were made from the pulse generator at 1-year follow-up. The LV stimulation threshold increased from 0.7 ± 0.5 V in the unipolar configuration to 1.0 ± 0.8 V in the unipolar split cathodal configuration (P = 0.01) and from 1.0 ± 0.7 V in the bipolar configuration to 1.3 ± 0.9 V in the bipolar split cathodal configuration (P < 0.001). The RV stimulation threshold increased from 0.3 ± 0.2 V in the bipolar configuration to 0.5 ± 0.2 V in the bipolar split cathodal configuration (P = 0.005). The bipolar impedance measured 874 ± 299 Ω for the coronary venous lead, 705 ± 152 for the RV lead, 442 ± 87 in the split unipolar cathodal configuration, and 516 ± 64 in the bipolar split cathodal configuration. At 1-year follow-up, the LV stimulation threshold was 1.8 ± 1.6 in the unipolar split cathodal configuration and 2.4 ± 1.6 in the bipolar split cathodal configuration (P = 0.003). The RV stimulation threshold at 1 year was 0.7 ± 0.3 in the unipolar split cathodal configuration and 0.8 ± 0.3 in the bipolar split cathodal configuration (P = 0.02). The split cathodal configuration significantly increases the apparent stimulation threshold for both the LV and the RV as compared with individual stimulation of either chamber alone. Programming to the bipolar split cathodal configuration further increases the apparent stimulation threshold. These observations support the development of pacing systems with separate LV and RV output circuits for resynchronization therapy. (PACE 2003; 26:2264–2271) [ABSTRACT FROM AUTHOR]

Introduction: Ablation of muscular fascicles around the ostium of pulmonary veins (PVs) resulting in electrical isolation of the veins may prove to be an effective treatment for atrial fibrillation (AF). Correctly discriminating atrial and PV potentials is necessary to effectively isolate PVs from the left atrium in patients with paroxysmal AF. Methods and Results: A training set of 151 electrode recordings obtained from 10 patients with AF was used to develop an algorithm to discriminate atrial and PV potentials. Bipolar electrograms were collected from a multielectrode basket catheter placed sequentially into each PV. Amplitude, slope, and normalized slopes of both bipolar and quadripolar electrograms (difference between adjacent bipoles) were entered into a binary logistic regression model. A receiver operating characteristic curve was used to define a threshold able to effectively discriminate atrial and PV potentials. The normalized slopes of both domains, bipolar and quadripolar, produced a logistic function that discriminated atrial and PV potentials against a threshold (0.38) with 97.8% sensitivity and 94.9% specificity. The algorithm then was evaluated on a test set of 214 electrode recordings from four patients who also had paroxysmal AF. These patient electrograms also were evaluated by two independent electrophysiologists. The algorithm and electrophysiologists matched identification of activation origin in 84% of electrograms. Conclusion: Atrial and PV potentials acquired from a multielectrode basket catheter can be discriminated using the normalized slopes of bipolar and quadripolar electrograms. These additional parameters need to be included by physicians determining the preferential ablation site within PVs. (J Cardiovasc Electrophysiol, Vol. 14, pp. 698-704, July 2003). [ABSTRACT FROM AUTHOR]

Introduction: Fluoroscopic imaging provides limited anatomic guidance for left atrial structures. The aim of this study was to determine the utility of real-time, phased-array intracardiac echocardiography during radiofrequency ablation for atrial fibrillation. Methods and Results: In 29 patients undergoing pulmonary vein isolation (n = 16) or linear (n = 13) left atrial radiofrequency ablation for atrial fibrillation, intracardiac phased-array echocardiography was used to visualize left atrial anatomy and the pulmonary veins, as well as ablation and mapping catheters during ablation procedures. In the 16 pulmonary vein isolation patients, the mean pulmonary vein ostial diameters measured by venography and intracardiac echocardiography were similar for all veins positions, except that left common pulmonary vein diameters were larger as measured by echocardiography (2.50 ± 0.29 cm) than by venography (1.79 ± 0.50 cm, P = 0.001). The ostial diameters measured by echocardiography and venography were not correlated, however (r = 0.23, P = 0.19). As directed by echocardiography, only 1 of 25 circular mapping catheters (4%) used in 16 patients was replaced due to inappropriate sizing of the pulmonary veins. Mean pulmonary vein Doppler flow velocities increased after ablation for left-sided veins but ostial diameters were unchanged. In the linear ablation patients, the entire extent of the linear electrode array could be visualized in only 3 of 52 of catheter positions (6%) in the 13 patients. A portion of the catheter could be seen in only 50% of all target catheter positions. Conclusion: Phased-array intracardiac echocardiography (1) allows sizing and positioning of pulmonary vein mapping catheters, (2) provides measures of pulmonary vein ostial diameters, (3) continuously monitors pulmonary vein Doppler flow velocities, and (4) has limited use in positioning linear ablation catheters in the left atrium. [ABSTRACT FROM AUTHOR]

Introduction: This study evaluated an atrial automatic capture verification scheme based on atrial evoked response (AER). Atrial pacing was between Atip and Can (Atip-Can) using different coupling capacitances (CCs). Independent pairs of sensing electrodes between Aring and Vtip (Aring-Vtip) or between Aring and a separate indifferent electrode (Aring-Indiff) were used to reduce pacing-induced afterpotentials. Methods and Results: A custom-made external pacing system was used to perform automatic step-up and step-down pacing (0.1 to 7.1 V at 0.5 msec, step size of 0.1 V) using different CCs (2 or 15 µF). Intracardiac signals from Aring-Indiff and Aring-Vtip were independently recorded and analyzed both in real time and off-line to detect AER. Every paced beat also was visually inspected and compared with surface ECG to verify the captures. With the intracardiac signals properly filtered, AER detection was based on the signal within a window of 12 to 65 msec after the stimulus. Data from 27 patients (4 chronic and 23 acute implantations; age 65.6 ± 13.9 years) were analyzed. Bipolar atrial lead measurements using a standard pacing system analyzer were as follows (mean ± SD): impedance 695 ± 227 Ω, P wave amplitude 4.2 ± 2.3 mV, slew rate 1.1 ± 0.9 V/sec, and pacing threshold at 0.5 msec 1.0 ± 0.5 V. The results with CC = 2 µF showed that of 9,500 atrial paced beats, correct capture verification rates were -99.8% (Aring-Indiff) and 99.4% (Aring-Vtip). Similar results were achieved with CC = 15 µF (99.7% and 99.5%, respectively). Conclusion: AER can be reliably detected using independent pacing (Atip-Can) and sensing (Aring-Vtip or Aring-Indiff) electrodes. Therefore, atrial automatic capture verification by AER detection is feasible. [ABSTRACT FROM AUTHOR]

Sensing of the intracardiac evoked response (ER) after a pacing stimulus has been used in implantable pacemakers for automatic verification of capture. Reliable detection of ER is hampered by large residual after potentials associated with pacing stimuli. This led to the development of various technological solutions, like the use of triphasic pacing pulses and low polarizing electrode systems. This study investigated the effect of reducing the coupling capacitance (CC) in the pacemaker output circuitry on the magnitude of after potential, and the ability to automate detection of ventricular evoked response. A CC of 2.2 µF and four different blanking and recharge time settings were clinically tested to evaluate its impact on sensing of the ventricular ER and pacing threshold. Using an automatic step-down threshold algorithm, 54 consecutive patients, aged 70 ± 10 years with acutely (n = 27) OT chronically (n = 27) implanted ventricular pacing leads were enrolled for measurement testing. Routine measurements, using a standard pacing system analyzer (PSA), were (mean ± SD) impedance 569 ± 155 Ω. R wave amplitude baseline to peak 9.8 ± 3.7 mV and threshold 0.9 ±0.7 V at 0.4-ms pulse width. This new capture verification scheme, based on a CC of 2.2 µF and recharge/blanking timing setting of 10/12 ms, was successful in 52 patients which is equivalent to a success rate of 96%. In a subgroup of 26 patients implanted with bipolar ventricular leads (10 chronic. 16 acute), data were collected in unipolar (UP) and bipolar (RP) pace/sense configurations. Also, ER signals were recorded with two different band-pass filters: a wider band (VVR) of 6-250 Hz and a conventional narrow band (NB) of 20-100Hz. WR sensing from UP lead configuration yielded statistically significant larger signal to artifact ratios (SAR) than the other settings (P < 0.01). A dedicated unipolar ER sensing configuration using a small output capacitor and a wider band-pass filter enables adequate automatic capture verification, without any restrictions on pacing lead models or pacing/sensing configurations. [ABSTRACT FROM AUTHOR]

The two goals of this study were (1) to develop a closed-chest animal model of monomorphic ventricular tachycardia; and (2) to investigate the effect of dual site pacing on inducibility of ventricular tachycardia. In the first part of the study, 10 of 14 sheep underwent successful induction of myocardial infarction by temporary balloon occlusion of the left anterior descending coronary artery. After a follow-up period of 21-43 days, sustained monomorphic ventricular tachycardia could be induced during programmed electrical stimulation using a "clinical" stimulation protocol in 8 of the 10 sheep. The number of ventricular tachycardia episodes per animal varied between 5 and 70. Ventricular fibrillation was never induced during programmed electrical stimulation. Ventricular tachycardia episodes lasted from 30 seconds up to 15 minutes and were terminated by antitachycardia pacing or DC cardioversion. In the second part of the study, the effect of dual site stimulation on ventricular tachycardia inducibility was investigated. High current stimuli from an area within the infarcted zone were given with the Si programmed stimulation protocol. This dual site stimulation showed no effect on ventricular tachycardia induction during programmed electrical stimulation. This animal model shows a high induction rate of sustained monomorphic ventricular tachycardia in the chronic phase of myocardial infarction. The high incidence of ventricular tachycardia inducibility provides a reliable tool to study new techniques for the prevention of ventricular tachyarrhythmias. [ABSTRACT FROM AUTHOR]

High-Resolution Mapping and Histologic Examination. Introduction: Catheter ablation may prevent condoction of multiple atrial wavefronts and/or reduce the critical mass of atrial myocardium required to sustain fibrillation. The purpose of this study was to examine the effect of radiofrequency (RF) energy application on conduction in canine atria by performing high-density epicardial mapping and careful histologic examination of the ablation zone. Methods and Results: RF energy was applied to the right atrial endocardium in nine anesthetized mongrel dogs in an attempt to create a line of conduction block spanning the vertical length of a 504-channel epicardial mapping plaque. The mean length and width of the histologically determined ablation zone was 34 ± 4 and 7.3 ± 2.6 mm, respectively. No thrombus was present. Conduction block that spanned the mapping plaque in 6 of 9 animals was matched histologically by continuous transmural necrosis in five. in one, only a portion of the ablation zone was transmural; the remainder was wide but nontransmural. In 2 of 3 animals with conduction, a narrow region was present where continuous transmural necrosis was absent. In the other animal, conduction was present despite continuous transmural necrosis. Conclusion: Conduction block usually occurred when continuous transmural necrosis was present, and conduction usually persisted when continuous transmural necrosis was absent. However, important exceptions were observed, including block when the ablation zone was wide but nontransmural, and conduction despite a thin line of continuous transmural necrosis. [ABSTRACT FROM AUTHOR]

Two patients who survived cardiac arrest late after doxorubicin administration are described. Both patients had nonischemic, dilated cardiomyapathies and underwent electrophysiological studies during which no ventricular arrhythmias were induced. Their negative electrophysiological studies despite well documented cardiac arrests and subsequent clinical courses suggest that patients with cardiomyopathies after doxorubicin administration and dilated cardiomyopathies of other etiologies have similar natural histories. Treatment with an automatic implantable cardioverter defibrillator appears to be a reasonable therapeutic option pr patients with anthracycline associated cardiac disease who have survived their malignancy but at the price of developing life-threatening arrhythmias. [ABSTRACT FROM AUTHOR]

Morbidity (36 cases) and mortality (6 cases) have been reported in patients with Accufix J retention wire atrial leads. This has resulted in ongoing patient fluoroscopic monitoring as well as lead extractions. The estimated implanted worldwide population is 40,860. Estimating the size of the remaining population at risk is an important tool for assessing patient management guidelines. Results: The Kaplan-Meier method can be used to calculate the cumulative probability of remaining free of extraction and death for patients based on implant duration. The individual Kaplan-Meier curves for lead extraction and patient survival can also be computed. Based on the Multicenter Study (MCS) population of 2,298 patients, the probability that a patient is alive with the lead still implanted at 5 years implant duration is 52.5%. The event-free survival rate at 5 years implant duration is 81.3%. The corresponding probability of remaining free from injury due to the J-wire is 99.9% at 5 years implant duration. Assuming similar rates of death and extraction, these results can be extrapolated to the world wide population. Conclusions: The management of Accufix patients must consider patient longevity, the probability of J-wire morbidity/mortality, and the probability of extraction complication morbidity/mortality. The probability of remaining at risk as a function of time from implant can be calculated from the events known in the MCS patient population. These event-free survival estimates can be used to identify subsets of the population at greater or lesser risk based on various clinical parameters. [ABSTRACT FROM AUTHOR]

To permit a more complete analysis of J-wire fracture in the Accufix series of atrial permanent pacemaker leads, the time to occurrence of all known fractures and injuries has been redefined relative to the duration of risk exposure, that is, according to the interval of time between implant and occurrence of the event. This redefinition permits application of a cumulative hazards model to the data, which previously has not been explored. Predictors of J-wire fracture can be tested using this method. This also permits parametric curve-fitting for determination of linearity or constancy of risk of events over time. Results: Among 2,063 Multicenter Study (MCS) leads analyzed, 381 fractures of the J-wire were identified. Stratified analysis based on cumulative hazard curves identified a more open shape of the J-wire as predictive of fracture, which supports the results previously reported based on logistic regression analysis. Fitting a Weibull curve to the cumulative hazard of J-wire fracture gives a shape parameter equal to 0.85. This value indicates that the instantaneous hazard of J-wire fracture decreased over time from implant. Conclusions: (1) The cumulative hazard function can be used to examine predictors of J-wire fracture and preliminary findings support the previously identified predictor of J shape; (2) Based on these analyses, the rate of J-wire fracture appears to decrease slightly as time from implant increases. [ABSTRACT FROM AUTHOR]

To make recommendations for management of potential fatal failure of the Accufix series of atrial J-wire permanent pacemaker leads, we closely monitored the number of injuries and fatalities resulting either from spontaneous fracture of the J-wire or from attempts to extract the lead. In a population of 30,357 patients, 2,298 patients are enrolled in a prospective follow-up Multicenter Study, the remainder are patients with known clinical status from voluntary reporting, and 2,992 patients died following implant. In the remaining 27,365 patients, 6 deaths have been attributed to J-wire related injury (J-inj) while 13 were complications (E-inj) associated with 4,076 lead extraction procedures (3,974 intravascular (intra)/102 primary thoracotomy (PT). The date of occurrences were from 1994 to November 1997. Conclusions: (1) Since lead extractions were not conducted in a controlled study, it is not known whether the deaths associated with lead extraction is in excess of what would have occurred if these leads hod not been removed in this specific subset. (2) Awareness of the procedure related complication rate appears to have moderated the rate of lead extraction and may ultimately lead to management that reasonably balances the risks of patient injury. [ABSTRACT FROM AUTHOR]

Mixed venous oxy-hemoglobin saturation (MvO2) is a physiological variable with several features that might he desirable as a control parameter for rate adaptive pacing. Despite these desirable characteristics, the long-term reliability of the MvO2 sensor in vivo is uncertain. We, therefore, designed a study to prospectively evaluate the long-term performance of a permanently implanted MvO2 saturation sensor in patients requiring VVIH pacing. Under an FDA approved feasibility study, eight patients were implanted with a VVIR pulse generator and a right ventricular pacing lead incorporating an MvO2 sensor. In order to accurately assess long-term stability of the sensor, patients underwent submaximal treadmill exercise using the Chronotropic Assessment Exercise Protocol (CAEP) at 2 weeks, 6 weeks, and 3, 6, 9, 12, 18, and 24 months following pacemaker implantation. Paired maximal exercise testing using the CAEP was also performed with the pacing system programmed to the VVl and VVIR modes in randomized sequence with measurement of expired gas exchange after 6 weeks and 12 months of follow-up. During maximal treadmill exercise the peak exercise heart rate (132 ± 9 vs 71.5 ± 5 beats/min. P < 0.00001) and maximal rate of oxygen consumption (1,704 ± 633 vs 1382 ± 407 mL/min, P - 0.01) were significantly greater in the WIR than in the VVl pacing mode. Similarly, the duration of exercise was greater in the VVIB than the WI pacing mode (8.9 ± 3.6 min vs 7.6 ± 3.7 min. P - 0.04). The resting MvO2 and the MvO2 at peak exercise were similar in the WI and VVIR pacing modes (P = NS). However, the MvO2 at each comparable treadmill exercise stage was significantly higher in the WIR mode than in the VVI mode (CAEP stage 1 (P = 0.005), stage 2 (P = 0.04), stage 3 (P = 0.008), and stage 4 (P = 0.04). The correlation between MvO2 and oxygen consumption (VO2) was excellent (r - -0.93). Telemetry of the reflectance of red and infrared light and MvO2 in the right ventricle during identical exercise workloads revealed no significant change over the first 12 months of follow-up (ANOVA, P - NS). The chronotropic response to exercise remained proportional to VO2 in all patients over the first 12 months of follow-up. The time course of change in MvO2 during maximal exercise was significantly faster than for VO2. At the 18- and 24-month follow-up exercise tests, a significant deterioration of the sensor signal with attenuation of chronotropic response was noted for 4 of the 8 subjects with replacement of the pacing system required in one patient because of lack of appropriate rate modulation. Rate modulated VVIR pacing controlled by right ventricular MvO2 provides a chronotropic response that is highly correlated with VO2. This parameter responds rapidly to changes in workload with kinetics that are more rapid than those of VO2. Appropriate rate modulation provides a higher MvO2 at identical workloads than does VVI pacing. Although the MvO2 sensor remains stable and accurate over the first year following implantation, significant deterioration of the signal occurs by 18-24 months in many patients. [ABSTRACT FROM AUTHOR]

The normal heart rate is linearly related to oxygen consumption during exercise. The maximum heart rate of the normal sinus node is approximated by the formula: HRmax = (220-age) with a variance of approximately 15%. However, the nominal upper rate of most permanent pacemakers is 120 beats/min, a value that remains unchanged for many patients. As this nominal setting falls well below the maximum predicted heart rate for most patients, it is possible that the chronotropic response of rate adaptive pacemakers during moderate and maximal exercise workloads may be less than optimal. The purpose of this study was to determine the effect of the upper programmed rate on oxygen kinetics during submaximal exercise workloads and maximum exercise performance during symptom-limited treadmill exercise. Exercise performance with an upper rate programmed to 220-age was compared with an upper rate of 120 beats/min. Eleven patients (5 men and 6 women, mean age 54 ± 10 years) with complete heart block following catheter ablation of the atrioventricular junction for refractory atrial fibrillation who were implanted with permanent, rate-modulating VVIR pacemakers comprised the study population. Tile tale adaptive sensors were based on activity in 8 patients, minute ventilation in 2 patients, and mixed venous oxygen saturation in 1 patient. After performing a symptom-limited treadmill exercise test to determine maximum exercise capacity and to optimize programming of the rate adaptive sensor, each subject performed two treadmill exercise tests in random sequence with a rest period of at least 1 hour between tests. During one of the tests the upper rate was programmed to a value calculated by the formula: HRmax = (220-age). During the other exercise test the upper rate was programmed to 120 beats/min. Patients were blinded as to theft programmed values and to the hypothesis of the study. A novel treadmill exercise protocol was used that consisted of a 6 minute, constant-workload phase at approximately 50% of maximum workload followed immediately by incremental, symptom-limited exercise using a modified Chronotropic Assessment Exercise Protocol (CAEP) with I minute stages until peak exertion. Breath-by-breath analysis of expired gases was performed with subjective scoring of exertional difficulty at the end of the constant workload phase and during each stage of incremental exercise using the Borg Perceived Exertion Scale. Exercise duration was significantly longer (637 ± 47 vs 611 ± 48 seconds, P < 0.005) with the higher programmed upper rate. Oxygen kinetics were also significantly improved with an age predicted upper rate with a lower O2 deficit (258 ± 88 vs 395 ± 155 mL, P = 0.002) and higher VO2 rate constant (3.6 ± 1.0 vs 2.4 ± 0.7, P < 0.001). The VO2 max during peak exertion was higher with an age predicted upper rate than with an upper rate of 120 beats/min (1807 ± 751 vs 1716 ± 702 mL/min, P = 0.01). The mean Borg score was lower during the last common treadmill stage during maximum exercise with an age predicted upper rate than with an upper rate of 120 beats/rain (15.7 ± 2.0 vs 16.5 ± 1.9, P = 0.04). The mean Borg score during submaximal, constant workload exercise was also lower with a higher upper rate (9.0 ± 2.5 vs 9.6 ± 2.2, P = 0.10). Programming the upper rate of rate adaptive pacemakers based on the age of the patient improves exercise performance and exertional symptoms during both low and high exercise workloads as compared with a standard nominal value of 120 beats/min. [ABSTRACT FROM AUTHOR]

Although high thoracic left sympathectomy via an anterior surgical approach is a highly efficacious treatment for refractory ventricular arrhythmias in patients with the long QT syndrome, the degree of sympathetic denervation has been variable, success of the operation is influenced by anatomical differences between patients, and Homer's syndrome may result. We hypothesized that interruption of sympathetic input to the heart could be accomplished using a posterior thoracic approach to this variable and often complex anatomy by division of the sympathetic chain rather than by direct destruction of the stellate and superior thoracic ganglia with the more conventional anterior, supraclavicular approach. In addition, the posterior approach should decrease the risk of Horner's syndrome by avoiding the ocular sympathetic efferent nerves. This posterior approach is described in five patients with the long QT syndrome and recurrent ventricular arrhythmias. After a mean follow-up of 18 ± 12 months, all are alive without Horner's syndrome. [ABSTRACT FROM AUTHOR]

Background: Oxygen uptake during constant workload exercise increases exponentially from its resting value before reaching a steady state. The difference between the actual rate of oxygen consumption at the onset of exercise and the steady state is an oxygen deficit. Similarly, the normal sinus node increases its rate at the onset of exercise before achieving a steady state, thereby producing a heart rate deficit. The purpose of this study was to test the hypothesis that elimination of the heart rate deficit by an instantaneous increase in heart rate at the onset of constant workload exercise to the steady-state level would reduce the oxygen deficit and improve the perceived difficulty of exertion as compared with the chronotropic response of the normal sinus node. Methods and Results: Ten subjects with normal sinus node function who had DDD pacemakers implanted for AV block completed a symptom-limited maximal treadmill exercise test using the Ghronotropic Assessment Exercise Protocol (GAEP) to assess sin us node function, maximal heart rate, and VO2 max. The subjects then performed constant workload exercise tests (6-mm duration) at a workload equal to approximately 50% of metabolic reserve with the pacemaker randomly programmed to each of three patterns of chronotropic response: (1) DDD (lower rate 60 beats/ min); (2) Fast (lower rate abruptly programmed to the expected value at 50% metabolic reserve); and (3) Overpaced (lower rate at least 80% of the age predicted maximum). The oxygen deficit was lower with the fast chronotropic response (434 ± 238 mL O2) than with either the DDD (512 ± 233; P - 0.02). or overpaced chronotropic patterns (488 ± 238; P = 0.02 vs fast). The rate constant for change in VO2 was highest with the fast chronotropic pattern (2.85 ± 1.38) compared with either the DDD (2.25 ± 0.64; P = 0.01) or overpaced (2.38 ± 0.43; P = 0.02) patterns. The Borg perceived exertion rating was lowest with the fast chronotropic response (P = 0.02 vs DDD and P = 0.02 vs overpaced). Conclusions: The results of this study suggest that oxygen kinetics and exertional symptoms are hit proved by an abrupt increase in pacing rate at the onset of exercise to a value that is appropriate for metabolic demand as compared with the DDD pacing mode in patients with normal sinus node function. In contrast, an overly aggressive chronotropic response was not associated with improved oxygen kinetics or exertional symptoms. [ABSTRACT FROM AUTHOR]

Background: The sin us node is considered to be the model of chronotropic response for pacemakers that use artificial rate modulating sensors. Maximal metabolic exercise testing with measurement of oxygen consumption (VO2) is frequently used to evaluate chronotropic response. Since activities of daily living are generally transient and involve submaximal effort, maximal exercise testing may not provide the most clinically relevant method of assessing rate modulation. The purpose of this study was to determine if an abrupt increase in heart rate (HR) at the onset of submaximal exercise provides improved oxygen kinetics compared with a linear response. Methods and Results: Thirteen patients with complete heart block and permanent rate modulating pacemakers implanted following catheter ablation of the atrioventricular junction for refractory atrial fibrillation were chosen for study. The patients first completed a maximal treadmill exercise test using the chronotropic assessment exercise protocol with breath-by-breath analysis of expired gases. The expected HR at 50% of metabolic reserve was calculated for each patient. Three submaximal constant workload exercise tests were then performed at 50% of each patient's metabolic reserve, with the pacemaker randomly programmed to provide three different patterns of chronotropic response: linear (in which HR increased from 70 beats/min to the expected HH at 50% of metabolic reserve), fast (in which HR was abruptly increased to the expected HR at 50% of metabolic reserve), and slow (VVI at 70 beats/min). Oxygen kinetics were compared for the three patterns of chronotropic response. Cumulative oxygen (O2) consumption was significantly greater for the fast pattern (3610 mL) as compared with the linear (3487 mL, P = 0.004) or slow pattern (3277 mL). The O2 deficit was lower for the fast (361 ± 139 mL) than for the linear (539 ± 225mL,P = 0.003) or slow chronotropic pattern (559 ± 194). Similar improvements in the rate constant of O2 uptake and Borg perceived exertion scores were observed with the fast chronotropic response pattern. Conclusion: A rapid increase in pacing rate at the onset of exercise improves oxygen kinetics and results in less perceived exertion as compared to a more gradual rate increase that is more characteristic of sinus node behavior. [ABSTRACT FROM AUTHOR]

An increased interest has developed in active fixation leads for several reasons. Exit block is an uncommon complication that is seen with both active and passive fixation leads. Exit block has not been a significant problem with passive fixation steroid-eluting leads and has been treated with these leads. A new steroid-eluting active fixation lead was examined for its performance in patients in whom exit block had previously occurred. The lead function was evaluated prospectively in 24 patients with a history of exit block (15 ventricular and 9 atrial). The results in patients with atrial exit block are encouraging with an average chronic stimulation threshold of 0.19 msecs at 2.5 volts. Results in the ventricle are less encouraging with 3 occurrences of recurrent exit block in 15 patients; however, the remaining patients had a good mean threshold of 0.21 ±0.11 msecs at 2.5 volts. There were a remarkable number of nonlead related complications suggesting that this is a substantially different group than routine implantations. [ABSTRACT FROM AUTHOR]

Right ventricular contractility increases in response to catecholamine stimulation and greater ventricular preload, factors that increase with exercise workload. Thus, the maximum systolic dP/dt may be a potentially useful sensor to control the pacing rate of a permanent pacing system. The present study was designed to test the long-term performance of a permanent pacemaker that modulates pacing rate based on right ventricular dP/dt and to quantitatively analyze the chronotropic response characteristics of this sensor in a group of patients with widely varying structural heart diseases and degrees of hemodynamic impairment. A permanent pacing system incorporating a high fidelity pressure sensor in the lead for measurement of right ventricular dP/dt was implanted in 13 patients with atrial arrhythmias and AV block, including individuals with coronary artery disease, hypertension, severe obstructive pulmonary disease with prior pneumonectomy, atrial septa! defect, dilated cardiomyopathy, restrictive cardiomyopathy, and mitral stenosis. Patients underwent paired treadmill exercise testing in the VVI and VVIR pacing modes with measurement of expired gas exchange and quantitative analysis of chronotropic response using the concept of metabolic reserve. The peak right ventricular dP/dt ranged from 238-891 mmHg/sec with a pulse pressure that ranged from 19-41 mmHg. There was a positive correlation between the right ventricular dP/dt and pulse pressure (r = 0.70, P = 0.012). The maximum pacing rate and VO2max were 72 ± 6 beats/min and 12.61 ± 4.0 cc Oz/kg per minute during VVI pacing and increased to 124 ± 18 beats/min and 15.89 ± 5.9 cc O2/kg per minute in the WIR pacing mode (P < 0.0003 and P < 0.002, respectively). The integrated area under the normalized rate response curve was 96.7 ± 45.7% of expected during exercise and 100.1 ± 43.4% of expected during recovery. One patient demonstrated an anomalous increase in pacing rate in response to a change in posture to the left lateral decubitus position. Thus, the peak positive right ventricular dP/dt is an effective rate control parameter for permanent pacing systems. The chronotropic response was proportional to metabolic workload during treadmill exercise in this study population with widely varying forms of structural heart disease. [ABSTRACT FROM AUTHOR]

Antiarrhythmic drugs have no consistent effects on the signal-averaged electrocardiogram (EGG) while successful surgical ablation of ventricular tachycardia is known to abolish late potentials. Ten patients with prior myocardial infarction had successful ablation of recurrent sustained ventricular tachycardia by selective ethanol infusion into a small coronary vessel supplying the tachycardia origin. Signal-averaged ECGs were performed before and after initially successful ablation in patients without pacemaker dependence or intraventricular conduction delay to assess the effects on late potentials and to determine if the signal-averaged ECG could predict ventricular tachycardia recurrence. Only four of ten patients were eligible for study and all four had late potentials prior to ethanol ablation. Late potentials were abolished in one patient who has not had an arrhythmia recurrence in 25 months. One patient with sudden death and another patient with ventricular tachycardia recurrence had persistent late potentials post procedure that were modified by a reduction in terminal voltage and lengthening of terminal low amplitude signal. The fourth patient who receives chronic amiodarone had no arrhythmia recurrence in spite of persistent but modified late potentials. Thus, the abolition of late potentials after ethanol ablation may predict freedom from arrhythmia recurrence. [ABSTRACT FROM AUTHOR]

The pathology associated with an investigational transvenous defibrillating and sensing lead is described. The lead system had delivered a total of 865 J from the time of implantation to the time of patient death from a noncardiac cause 7 months after implantation and 1 month after his last defibrillator shock. There was mild, superficial fibrous thickening on the endothelial surface of the superior vena cava adjacent to the proximal spring electrode, which did not extend into the vessel wall. The distal portion of endocardial lead was embedded in the interventricular septum near the apex of the right ventricle, surrounded by fibrous thickening, and partially covered by endocardial tissue. Microscopically, there was a thick bed of fibrous connective tissue surrounding the lead with extensive interstitial fibrous connective tissue radiating into the adjacent myocardium. Since this pattern is different from the more generalized fibrotic scarring produced by myocardial infarction, we speculate that the mechanism for the observed interstitial fibrosis is replacement fibrosis following acute myocyte injury that resulted from prior defibrillator shocks and possibly from the trauma produced by the lead compressing adjacent myocardium during systole. Potential effects on device efficacy of these fibrotic changes at the bioelectric interface include their representing a new arrhythmia substrate, the possibility that fibrosis could increase both defibrillation and pacing thresholds, and that the inflammatory reaction may cause deterioration of intracardiac electrograms and interfere with sensing and tachycardia recognition. [ABSTRACT FROM AUTHOR]

Signal-averaged electrocardiography has been used to identify patients at risk for arrhythmic death after myocardial infarction. Since patients with implantable cardioverter defibrillators (ICDs) are at high risk for arrhythmic events, they should also be expected to have a high incidence of abnormal signal-averaged electrocardiograms (SAECGs). However, whether the SAECG can discriminate patients who will have arrhythmia recurrence and receive appropriate ICD shocks from those who will have no recurrence and no shocks is unknown. This study examines the usefulness of the SAECG to separate appropriate users from non-users of the ICD. Fifty patients with ICDs participated in this study. Those who received a shock preceded by symptoms, a shock without preceding symptoms but with electrocardiographic documentation of ventricular fibrillation or ventricular tachycardia, or a shock while asleep were classified as ICD users. All other patients were classified as nonusers. The SAECG was classified as normal if the QRS duration on the standard electrocardiogram was ≤ 110 msec and if the total filtered QRS duration was < 120 msec, the root-mean square voltage of the terminal 40 msec was > 25 µV, and the terminal low amplitude signal duration measured < 38 msec. The SAECG was classified as abnormal if the QRS duration on the standard electrocardiogram was ≤ 110 msec and any one of these three criteria were outside the "normal range." The SAECG was classified as indeterminate if the QRS duration on the standard 12-lead electrocardiogram was > 110 msec. For the entire group of 50 patients, 8 (16%), 12 (24%), and 30 (60%) had normal, abnormal, and indeterminate SAECGs, respectively. Of the 22 ICD users, 1 (5%), 5 (23%), and 16 (73%) patients had normal, abnormal, and indeterminate SAECGs, respectively. Of the 28 ICD nonusers, 7 (25%), 7 (25%), and 14 (50%) patients had normal, abnormal, and indeterminate SAECGs, respectively. ICD users had lower left... [ABSTRACT FROM AUTHOR]

Active fixation leads have reduced the incidence of lead dislodgement in patients with permanent pacemakers. However, theoretic concern that the tissue trauma associated with a myocardial screw-helix may increase the chronic pacing threshold of active compared to passive fixation leads has remained. Whether active fixation leads with a stimulating electrode that is independent of the fixation mechanism are associated with a lower chronic pacing threshold than leads utilizing a screw-helix for both fixation and stimulation is unknown. The present prospective, randomized study compared the acute and chronic atrial pacing and sensing characteristics of two unipolar active fixation leads, one utilizing a screw-helix for both fixation and electrical stimulation, the other with an active porous tip electrode and an electrically inactive helix. Patients were randomized to receive either a Medtronic 6957J lead with an electrically active myocardial screw-helix or a Cordis 329-101P lead with an inactive helix arid a porous tip electrode. The baseline characteristics of the groups were comparable. At implantation, the 329-101P lead had a lower mean voltage threshold than the 6957J lead (0.61 ± 0.16 V vs 1.05 ± 0.34 V. P = 0.0004). There were no significant differences in atrial electrogram amplitude, slew rate, or lead impedance between the groups. At 6 weeks follow-up, there were no differences in the mean threshold voltage (1.85 ± 0.36 vs 1.93 ± 0.69 V), impedance (528 ± 81 vs 530 ± 118 ohms), or atrial electrogram amplitude (2.63 ± 0.50 vs 2.42 ± 0.95 mV) between the two leads. At long-term follow-up (mean 16.2 ± 2.8 months, range 13.1-20.0 months) there were no significant differences in voltage threshold (1.65 ± 0.61 vs 1.97 ± 0.64 V), impedance (565.5 ± 81.6 vs 617.7 ± 146.7 ohms), or atriul ehtctrogram amplitude (2.79 ± 0.75 vs 3.10 ± 1.53 mV). Thus, these results suggest that active fixation leads in the atrium with an electrode that is independent of the fixation mechanism do not provide chronic stimulation thresholds or electrogram amplitudes that are superior to those obtained with leads utilizing a myocardial screw-helix as both the active electrode and the fixation device. [ABSTRACT FROM AUTHOR]

The article presents a case of transient entrainment of sustained ventricular tachycardia by atrioventricular (AV) nodal reentrant tachycardia in a 74-year-old woman using rapid atrial pacing. Topics discussed include the activation sequence during the narrow QRS tachycardia, indication of long conduction time, and factors leading to spontaneous entrainment of clinical tachycardias.