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Background: The purpose of this study was to evaluate serial changes in QRS duration in the 12-lead electrocardiogram (ECG) and their prognostic value in patients with atrial fibrillation (AF). Methods: Retrospective evaluation of the 12-lead ECG was performed in 822 patients with AF. Inclusion criteria included AF in two sequential ECGs and an echocardiogram obtained within 7 days of the second ECG. The mean age of the 228 patients enrolled in the study was 71.2 ± 12.9 and 45.6% were females. Nearly half of the patients had hypertension (49.5%) and a history of heart failure (44.7%). The patients were followed for 21 ± 19 months, and the end point was all-cause mortality. Results : Cox proportional hazards analysis demonstrated that the independent predictors of mortality in AF patients were age, renal insufficiency, a history of stroke, heart rate, incremental QRS prolongation (P = 0.0418), and the absence of warfarin use. Patients with QRS prolongation >15 ms had a worse prognosis than those with QRS prolongation ≤15 ms (P = 0.0019). Conclusions: A progressive increase in QRS duration predicted a poor prognosis in patients with AF in our study. A prospective study is needed to substantiate the prognostic value of QRS prolongation in AF patients. [ABSTRACT FROM AUTHOR]

The author discusses various problems with the implementation of the QRS duration (QRSd) in patients who were hospitalized with worsening heart failure (HF). He claimed that QRSd is being used by physicians as an index of severity and disease progression in patients with HF. The author argued that automation needs to be based on QRSd values since such electrocardiogram (ECG) variable cannot be measured to the nearest 1.0 ms, like how the ECG machine does.

KATSOURAS, C.S., et al.: Localization of Accessory Pathways by the Electrocardiogram: Which Is the Degree of Accordance of Three Algorithms in Use? We evaluated the extent of agreement among three algorithms used for the localization of accessory pathways in patients with overt preexcitation. By the use of one algorithm, three independent couples of observers localized the accessory pathway in 95 consecutive patients showing overt preexcitation in the 12-lead surface electrocardiogram. We defined the following regions: Left atrioventricular ring (LAVR), Right atrioventricular ring (RAVR), Left lateral/left anterolateral (LL/LAL), Left posterior/left posterolateral (LP/LPL), Left posteroseptal (LPS), Right midseptal (RMS), Right posteroseptal (RPS), Right posterior/right posterolateral (RP/RPL), Right lateral/right anterolateral (RL/RAL), and Right anterior/right anteroseptal (RA/RAS). The extent of agreement in each region was evaluated and compared with the expected one, as calculated from the reported. The extent of agreement was as expected: (1) high in the regions LAVR, RAVR, LL/LPS and (2) limited in the regions LPS, RPS, and (3) clearly lower than expected in the regions LP/LPL, RA/RAS, RMS, RL/RAL. In cases with total or partial disagreement, the number of electrocardiograms with duration of QRS complex smaller than 120 ms was greater than in cases with total agreement (30/46 vs 22/50, P < 0.05). The observed agreement among algorithms is clearly lower than the expected one. Minimal preexcitation, limited number of patients, and arbitrarily defined regions were possibly the reasons for some unexpected results. (PACE 2004; 27:189–193) [ABSTRACT FROM AUTHOR]

VERECKEI, A.: Inferior Wall Pseudoinfarction Pattern Due to Hyperkalemia. Pseudoinfarction pattern is a rare ECG manifestation of marked hyperkalemia. Case reports characteristically describe the occurrence of anteroseptal pseudoinfarction pattern and four cases of anteroseptal together with inferior wall pseudoinfarction pattern associated with hyperkalemia. We report a case with isolated inferior wall pseudoinfarction pattern due to hyperkalemia. (PACE 2003; 26:2181–2184) [ABSTRACT FROM AUTHOR]

Grom, A., et al. : A Technical Approach to Optimized Atrial Recognition in the ICD: The Intrathoracic Six-Channel Farfield ECG. --> Present‐day ICD systems offer the possibility to reconstruct an intrathoracic 6‐lead ECG (IT‐ECG), using the defibrillator coils in the right ventricle and superior vena cava and the left‐laterally positioned ICD as electrodes according to Einthoven and Goldberger. The aim of this study was to assess the feasibility of (1) automated P wave recognition in the IT‐ECG without an additional atrial electrode as the basis of AV synchronous ventricular pacing (VDD) and for improved differentiation between supraventricular tachyarrhythmias and, (2) the automated detection of pacing evoked atrial potentials (EAP) in dual chamber ICDs as the basis for atrial "autocapture"pacing systems. In 27 patients during ICD implanation intraoperatively, the IT‐ECG was digitally recorded. A recently established algorithm for automatic P wave and EAP detection correctly identified 1,663/1,672 (99.5%) P waves (oversensing rate 0.6%) and 543/554 (98.0%) EAP (no oversensing). During subthreshold atrial stimulation, 405/412 (98.3%) P waves were correctly identified (oversensing due to pacemaker spikes,n = 421, without subsequent EAP, 1.9%,n = 8). During stimulated ventricular tachycardia in 26/27 patients retrograde P wave or AV dissociation were identified. The 6‐lead IT‐ECG, easily implementable in ICD systems, is a diagnostic tool providing reliable information about atrial activation, serving as a basis for VDD pacing in single chamber ICD systems, allowing reliable EAP recognition that enables atrial "autocapture"pacing in dual chamber ICDs, and improves the differentiation between supraventricular and ventricular tachycardia. (PACE 2003; 26[Pt. I]:1472–1478) [ABSTRACT FROM AUTHOR]

This article describes a collection of ECGs from many species obtained over the past 50 years. Presented are ECGs of species in which the pacemaker is a separate contractile chamber with its own action and recovery potentials. In such species, pacemaker atrial and AV block can be produced. Shortening of the atrial refractory period and the negative inotropic effect can be produced by vagal stimulation. The cardiac electrogram and stroke volume are recorded from the turtle heart. The EGG and respiration were recorded from the snake. ECG records were obtained from the anesthetized and decapitated housefly. ECG records of the rabbit show slowing when the nose encountered irritating vapors. Records from a dog with atrial fibrillation exhibit rhythmic fibrillation frequency changes correlated with respiration. In addition, in a morphinized dog with atrial fibrillation, impulses crossed the AV node only during inspiration. The ECGs of a cow and came! exhibit long P-R intervals and biphasic P waves. Finally the elephant ECG shows a clear U wave following the T wave. [ABSTRACT FROM AUTHOR]

Acute coronary occlusion causes ST-segment elevation on the body surface ECG and on the epicardial electrogram in the territory supplied by that artery. The occurrence and significance of endocardial ST changes have not been studied. The NOGA electromechanical mapping was performed on eight anesthetized dogs at baseline, immediately after occlusion of the LAD, and again at 5 hours to assess regional changes in the ST segment. AI 3 days and 4 weeks the ventricles were remapped for comparison. Regional unipolar ST-segment elevation was measured for each zone from NOGA maps at 0, 80, and 120 .ms after the J point. ST segments rose immediately in the infarct zones, as demarcated by echocardiography, compared to remote zones, but by 3 days had dropped below, and at 4 weeks returned to baseline values. Immediately postocclusion, ST elevation at 120 ms best differentiated between normal versus abnormal echo scores (concordance = 0.80), probably by correcting for pressure reduced ST elevation. In conclusion, acute endocardial ST-segment changes occur in the infarct zone in the dog, showing a distinctive temporal evolution. [ABSTRACT FROM AUTHOR]

The presence, frequency, and duration of episodes of paroxysmal atrial fibrillation (PAF) is difficult to establish. This is caused by the limited duration of standard Holter recordings and to the unsatisfactory yield of patient-triggered event recorders, because of asymptomatic events and of an inconsistent use of the patient dependent triggering function. A prospective cohort of 65 consecutive patients with recurrent palpitations and a negative 24-hour ECG Holter was investigated by means of a cardiac event recorder bearing continuous automatic arrhythmia analysis and storage. Over a mean duration of 77 ± 36 hours, episodes of PAF were diagnosed in 20 (31%) patients, who had a total of 37 episodes; mean duration of PAF episodes was 7 hours 50 minutes ± 8/hours 45 minutes (minimum 45 minutes, maximum 28 hours). Eleven (55%) of these 20 patients were asymptomatic and would have remained undiagnosed without the automatic mode of the event recorder. Asymptomatic PAF episodes were longer than symptomatic ones (10 hours 30 minutes ± 6 hours 30 minutes vs 4 hours 50 minutes ± 4 hours, P < 0.05). In addition, episodes of sustained paroxysmal supraventricular tachycardia (PSVT) were diagnosed in 39 (57%) patients, of whom 34 (87%) were symptomatic. In this prospective cohort, a second standard 24-hour monitoring would have missed 44% of the patients with PAF or PSVT and a classical patient-triggered event recorder 13%. In patients still complaining of palpitations after one negative 24-hour Holter, numerous, prolonged, and often asymptomatic episodes of PAF can be revealed by long-term automatic event recorders. These devices should help clarify the clinical consequences of such episodes. [ABSTRACT FROM AUTHOR]

Arrhythmogenic right ventricular dysplasia (ARVD) is a syndrome characterized by recurrent ventricular tachycardia. However, cases of ARVD have also presented as dilated cardiomyopathy later associated with ventricular arrhythmias. Histologically, this syndrome manifests as a fibrofatty replacement of the RV myocardium, predisposing the heart to ventricular arrhythmias. ARVD was once considered a disease of the young, but may be underrecognized in the older population. This report presents two cases of elderly men with newly symptomatic ARVD, believed to represent the oldest patients with ARVD described in the literature to date. The diagnosis of ARVD should be considered in individuals of all ages who present with a clinical syndrome consistent with ARVD and supportive evidence on ECG. [ABSTRACT FROM AUTHOR]

Multichannel magnetocardiography (MCG) noninvasively measures variations in magnetic field strength from many sites at the body surface, potentially providing useful regional information about ventricular repolarization. MCGs contain features similar to ECGs, and although errors associated with repolarization measurement have been quantified for ECGs, no comparative data exists for MCGs. In this study, errors in manual measurement of repolarization interval in the MCG were determined. Sixteen MGG channels and three ECG leads were recorded simultaneously in eight healthy subjects. Each recording was displayed in a random order on a computer screen, in presentations with different noise levels, time display widths, and amplitude display heights. In total, manual measurement of repolarization intervals in 2,048 (eight subjects × 16 channels × eight presentations × two repeats) MCGs were made by each of four analysis. Measured repolarization intervals were reduced by 3 ms when noise was added and by a further 3 ms when this noise was doubled. Intervals were shortened by 9 ms when the time display width was doubled and by a further 10 ms when the display width was doubled again. Measurements increased by 7 ms for a doubling of amplitude display height, equivalent to a doubling of T wave height. There were also consistent differences between analysts; amounting to a greatest mean difference of 24 ms. Display characteristics, added noise, and different analysts thus affect manual repolarization interval measurements in MCG. The errors detected demonstrate the importance of a standard presentation for repolarization measurement in the MCG. [ABSTRACT FROM AUTHOR]

If not diagnosed by history, examination, or ECG, the diagnosis of syncope can be difficult with a low yield from echocardiography, ambulator ECG recording. electrophysiological study, and tilt table testing. During 2 years, 48 patients with unexplained syncope or presyncope from three hospitals in one city underwent the implantation of a Medtronic Reveal implantable loop recorder capable of cardiac monitoring for 14 months. All patients had at least two prior episodes of syncope or presyncope. Fifty-two percent of patients had electrophysiological studies, all of which were negative. The implantable loop recorder remained implanted until a diagnostic event was recorded, or until the end of the battery life. After a mean follow-up of 5.6 ± 5.7 months, symptoms reoccurred in 25 (52.1%) patients at a mean of 2.8± 2.1 months after insertion of an implantable loop recorder. No further symptoms occurred in 23 (47.9%) patients. Of the 25 patients who had a symptom and recorded an event, an arrhythmia was seen in 10 (40%) patients. Seven patients had bradycardia; 4 with profound sinus bradycardia/sinus arrest, 1 with complete heart block. and 2 in association with the cardioinhibitory component of vasovagal syncope. Three patients had tachycardias: two with supraventricular tachcardia and one with atrial flutter. Fifteen (60%) of the 25 patients who activated their device due to syncope or presyncope were in sinus rhythm during the event. The implantable loop recorder was effective in making a cardiological or noncardiological diagnosis for unexplained syncope or presyncope in 52.1% of the patients. [ABSTRACT FROM AUTHOR]

Technically related noise in 12-lead ECGs recorded with ambulatory recorders has never been systematically compared with that in ECGs recorded with conventional ECGs. This study compared serial 10-second ECGs obtained in ten healthy men, age 22-45 years, who were recorded in the supine resting position using a (1) MAG VU recorder, (2) digital ambulatory SEER MG recorder with a Multi-Link detachable EGG cable, and (3) digital ambulatory SEER MC recorder with a light ambulatory EGG cable. In each EGG, averaged sinus rhythm cycles of the entire recording were realigned with the native signal and subtracted. The resulting "residuum" was quantified by computing its standard deviation and root mean square of successive differences (RMSSD). While the RMSSD residuum values were significantly tower with the MAG VU recorder (6.27 ± 0.98 μV) than with the SEER MG recorder with either EGG cables (7.29 ± 1.31 and 7.17 ± 1.31 μV, P < 0.003 and p < 0.02), the difference was practically negligible and there was no detectable difference in the standard deviation residuum values. The study concludes that valid ECG investigations of serial EGG testing may be conducted using the ambulatory SEER MG recorders providing the biological sources of EGG noise are controlled. The available technology for noise assessment suggests that studies involving advanced analysis of serial EGGs (e.g., of drug related changes), should incorporate objective characterisation of EGG quality. [ABSTRACT FROM AUTHOR]

This study was designed to prospectively assess ventricular de- and repolarization by the QRS, QT, and JT intervals, and their dispersion in the 12-lead ECG during right ventricular pacing at 60. 70, and 80 beats/min during the first month after AV junctional RE ablation. Previous reports have found early polymorphic ventricular arrhythmia after RF AV junctional ablation. Our hypothesis was that there is a proarrhythmic state following this procedure, which depends on the paced rate and time after ablation. The analysis of the immediate changes was based on 17 patients (10 men) with a mean age of 64 years (SD 14) (range 38-82 years). A 12-lead ECC was recorded during right ventricular pacing at 60, 70, and 80 beats/min within 24 hours (day 1), between 24 and 48 hours (day 2), and 1 week after ablation (day 7). For analysis of changes beyond 1 week, 13 additional patients with a mean age of 73 years (SD 8) (range 62-90 years) were analyzed on days 1, 7, and 30. All intervals were measured with a digitizing table. The mean QRS duration shortened by 2.4% at 60 beats/min (P < 0.01), and the mean QT and JT intervals shortened by 5-7% between days 1 and 7 (P < 0.001), The mean QT was 9% shorter and the mean QT interval was 13% shorter at 80 compared to 60 beats/min on day 1 (P < 0.001). QT dispersion was reduced by 13% when the stimulation rate was increased from 60 to 80 beats/min on day 1 (P < 0.05). There were no significant changes beyond the first week. The study results point to the induction of a proarrhythmic state immediately after AV junctional RE ablation resolving during the first week, Repolarization shortened gradually between 80 and 60 beats/min to an extent that is suggestive of a clinically important antiarrhythmic effect at the higher rate, which was supported also by clinical experience. [ABSTRACT FROM AUTHOR]

The clinical significance of QT dispersion (QTd) measured in 12-lead ECGs is controversial. The aim of this study was to clarify factors that determine the QTd and its measurement errors in different lead arrays in patients with structural heart disease. Two blinded observers measured QT intervals on a computer screen from 120-channel ECG recordings in a retrospective set of 257 patients, comprising a group of 121 myocardial infarction (MI) survivors without ventricular tachyarrhythmia during a 6-month follow-up and a group of 136 survivors of ventricular tachyarrhythmia/fibrillation. QTd did not differ in patients with and without ventricular tachyarrhythmia/fibrillation. Eleven ventricular tachyarrhythmia/fibrillation survivors without structural heart disease bad the lowest QTd (P < 0.02). The strongest factor determining QTd and the magnitude of its measurement error was the lead array (P ≤ 0.0001). Measurement errors had two components. The smallest relative errors were in the total body surface mapping array with one component related to interobserver reproducibility (9.1 ± 7.6%), and the other component related to accuracy of measurement of the QT interval (36 ± 16%). The authors estimated that a difference of QTd of at least 50 ms between study groups is required in a 12-lead ECG to draw any conclusions from the studies. In patients with structural heart disease, QTd from limited arrays of EGG leads was not a reliable measure. It correlated with the presence of structural heart disease, but not with arrhythmogenicity. An array consisting of EGG leads covering the entire chest allowed better reproducibility and measurement accuracy of QTd. [ABSTRACT FROM AUTHOR]

The aim of this study ivas to determine the effect of recording conditions on the operator dependent measures of QT dispersion in patients with known and/or suspected repolarization abnormalities. Among several methods for risk stratification, QT dispersion has been suggested as a simple estimate of repolarization abnormalities. In a cohort of high and low risk patients, different components of the repolarization process were assessed in the 12-lead ECC using three different paper speeds and amplifier gains. To assess measurement error and reproducibility, a straight line was repeatedly measured. The operator error was 0.675 ± 0.02 mm and the repeatability of the measurement error was 31 ± 6%. The QT interval was most frequently measurable in V2-V5. Depending on the lead selected for analysis, the incidence of visible U waves was greatest in the precordial leads with high amplifier gain and low paper speed, strongly affecting QT interval measurement. The timing of the onset of the QBS complex (QRS onset dispersion) or offset of the T wave was strongly dependent on the paper speed. Paper speed, but not amplifier gain, had a significant shortening effect on the measurement of the maximum QT interval. As QT interval measurement in each ECC lead incorporates QRS onset and T wave offset (depending on the number of visible U waves), the dispersion of each of these parameters significantly affected QT dispersion. Thus, QT dispersion appears to reflect merely the presence of more complex repolarization patterns in patients at risk of arrhythmias. [ABSTRACT FROM AUTHOR]

QT dispersion has been suggested and disputed as a risk marker for ventricular arrhythmias after myocardial infarction. Delayed ventricular activation after myocardial infarction may affect arrhythmic risk and QT intervals. This study determined if delayed activation as assessed by (1) QRS duration in the 12-lead ECG and by (2) late potentials in the signal-averaged ECG affects QT dispersion and its ability to assess arrhythmic risk after myocardial infarction. QT duration, JT duration, QT dispersion, and JT dispersion were compared to QHS duration in the 12-lead ECG and to late potentials in the signal-averaged ECG recorded in 724 patients 2-3 weeks after myocardial infarction. Prolonged QRS duration {> 110 ms) and high QRS dispersion increased QT and JT dispersion by 12%-15% (P < 0.05). Presence of late potentials, in contrast, did not change QT dispersion. Only the presence of late potentials (n = 113) was related to arrhythmic events during 6-month follow-up. QT dispersion, JT dispersion, QRS duration, and QRS dispersion were equal in patients with (n = 29) and without arrhythmic events (QT disp 80 ± 7 vs 78 ± 1 ms, JT disp 80 ± 6 vs 79 ± 2 ms, mean ± SEM, P > 0.2). In conclusion, prolonged QRS duration increases QT dispersion irrespective of arrhythmic events in survivors of myocardial infarction. Presence of late potentials, in contrast, relates to arrhythmic events but does not affect QT dispersion. Therefore, QT dispersion may not be an adequate parameter to assess arrhythmic risk in survivors of myocardial infarction. [ABSTRACT FROM AUTHOR]

Bipolar recordings eliminate much of the far-field signal, while minimally filtered unipolar recordings contain substantial far-field signal components. These properties may allow the onset of the unipolar recording to serve as a timing reference for the bipolar recording obtained from the same electrode catheter during mapping of focal atrial or ventricular tachycardias. Mapping and RF ablation were performed in 26 patients with focal ventricular tachycardia and 14 patients with focal atrial tachycardia. At 205 mapping sites, simultaneous recordings of (1) minimally filtered unipolar electrograms (0.5-500 Hz), (2) high pass filtered unipolar electrograms (100 Hz), and (3) filtered bipolar recordings (30-500 Hz) were analyzed. The interval between the onset of the minimally filtered unipolar electrogram and the first peak of the bipolar electrogram (UniOn - Bip) correlated closely with the timing of the local electrogram referenced to the surface ECG (r = 0.85, P < 0.001). Of 53 sites where RF ablation was performed, UniOn - Bip was shorter at successful compared to unsuccessful sites (3.8 ± 3.5 vs 9.2 ± 5.2ms, P < 0.001) and was < 15 ms at all successful sites. In conclusion, the comparison of simultaneous unipolar and bipolar electrograms from a single catheter allows assessment of the prematurity of local electrograms from a focal source without the use of the P wave or QRS onset as a timing reference. [ABSTRACT FROM AUTHOR]

QT dispersion has been proposed to reflect the heterogeneity of ventricular repolarization, but a poor reproducibility limits its clinical usefulness. Spatial vectorcardiographic descriptors constitute a novel approach to quantify ventricular repolarization. To test the ability of vectorcardiographic descriptors to discriminate among different subsets of postinfarction patients, 50 consecutively recruited patients with acute MI, 50 patients with history of an old (> 6 months) Ml and 50 healthy controls were evaluated. The maximum and minimum QT and JT intervals and QT and JT dispersion were manually measured from a digitally recorded 12-lead ECG. X, Y, and Z leads were reconstructed from the 12-lead ECG. The amplitude of the maximum spatial T vector (spatial T amplitude), the angle between the maximum spatial QRS and T vectors (spatial QHS-T angle), and the frontal plane QBS-T angle were automatically calculated. The spatial T amplitude and the spatial QRS-T angle did not differ between patients with a recent and those with an old MI (P = 1), QT dispersion was significantly lower in patients with an old MI than in patients with a recent one (P = 0.002). The spatial repolarization descriptors showed better short-term reproducibility than the dispersion indices. In conclusion, the spatial T amplitude and the spatial QRS-T angle are accurate measures of ventricular repolarization that do not differ between patients with recent and those with old MI. The different QT dispersion values observed in this study between the two post-MI groups should be considered cautiously because of the low accuracy of the manual measurements. [ABSTRACT FROM AUTHOR]

A 56-year-old woman without structural heart disease had an ECG typical of Brugada syndrome. Syncope occurred due to monomorphic VT with left bundle branch block (LBBB) morphology. At electrophysiological study, VT with the same morphology was inducible. [ABSTRACT FROM AUTHOR]

In 120 consecutive patients with standard pacing indications, we tested the feasibility of RV septal lead implantation technique guided by surface ECG and the degree to which this technique reduces paced QRS duration compared to RV apical stimulation when passive-fixation leads are used. During implantation, an ECC was recorded with a paper speed of 100 mm/s using the orthogonal Frank leads, and QRS was measured from the earliest to the latest deflection in any of the Frank leads. Pace-mapping of the septum was performed until QRS was minimal. The lead was attached, where QRS, pacing threshold, lead impedance, and EGM amplitude provided the best compromise. An average of 3.7 ± 2.5 attempts (range 1–18, median 7] was needed until a final implantation site was found. There were no technical problems during implantation. QRS could be reduced by 5–55 ms (mean A QRS 19 ± 11 ms) in 83 (69%) of 120 patients. In 22 (18%) patients, QRS was identical with apical and septal pacing, and in 15 (13%) patients, QRS was 5–20 ms (10 ± 4) longer despite septal stimulation. Average QRS was significantly shorter during septal pacing compared with apical pacing (151 ± 20 vs 162 ± 23 ms, P < 0.001). There was a tendency towards greatest QRS reduction when the high septum was stimulated (22 ± 11 ms reduction) as compared with mid- (18 ± 11 ms) or apical parts of the RV septum (16 ± 10 ms). QRS reduction was most likely if apical QRS width was > 170 ms (P = 0.0002), and there was an inverse correlation between apical QRS and Δ QRS (r = 0.53, P < 10-7). During a mean follow-up of 14 months, there was no pacing or sensing problem and no lead dislodgment occurred. [ABSTRACT FROM AUTHOR]

Automatic recognition of repolarization abnormalities from the standard electrocardiogram (ECG) is of considerable clinical importance. This study examined the autonomic variations in automatically measured repolarization parameters, including maximum QT interval (QTmax), global QT dispersion (QTd), T area dispersion (T area D) and principal component analysis ratio 2 (PCA-2). Twelve-lead ECGs were recorded continuously in 40 healthy subjects during supine, sitting and standing positions, and during the Valsalva maneuver. With the exception of PCA-2, the other repolarization parameters correlated either moderately or strongly during the steady-state supine position. QTmax, PCA-2, and T area D decreased significantly between supine and sitting position (P < 0.001, P < 0.001 and P < 0.01, respectively). QTmax, QTD, and T area D decreased significantly between sitting and standing (P < 0,001, P < 0.05 and P < 0.01, respectively). All parameters significantly decreased between supine and standing position: QT- max (P < 0.001), QTD (P < 0.05), PCA-2 (P < 0.05) and T area D(P < 0.001). During Valsalva, only PCA-2 increased significantly (P < 0.001) between supine and standing position. There were no significant changes in QT dispersion and dispersion of T wave area during Valsalva, compared to baseline, in both supine and standing positions. Automatic conventional measures of repolarization heterogeneity hove limited practical value in detecting the effects of autonomic changes on ventricular repolarization. Newer concepts evaluating spatial and temporal irregularity of ventricular repolarization are still needed to reliably detect the effects of autonomic activity on ventricular repolarization. [ABSTRACT FROM AUTHOR]

Available descriptors of irregularities of ventricular repolarization are of limited clinical value. We studied the effect of autonomic variations on several new descriptors of the three-dimensional T loop. Twelve-lead digital ECGs were recorded continuously in 40 healthy subjects at baseline in the supine position, during postural changes (supine → sitting → standing → supine → standing), and during Valsalva maneuver performed three times in the supine and three times in the standing positions. A minimum dimensional space was constructed from the 12-lead ECG, using singular value decomposition, on the basis of median ECG beats constructed from 10-second consecutive ECG recordings. Temporal variations (TLA and PL, which measure the T loop area, and LD, the interlead relationship during repolarization) and wavefront direction descriptors (TCRT, the deviation between the QRS and T vectors) were calculated and expressed as normalized values. Values of TLA, PL, and TCRT were significantly lower in the sitting than in the supine position (-38139 ± 9099 vs 47133 ± 7511, -0.017 ± 0.005 vs 0.033 ± 0.005 and -0.032 ± 0.019 vs 0.071 ± 0.015, respectively, P < 0.001 for all) and decreased further in the standing position (-88288 ± 14468, -0.067 ± 0.013, -0.198 ± 0.025, respectively, P < 0.001 for all). LD increased from supine to sitting (98.7 ± 29.4 vs -87.5 ± 15.2, P < 0.001) and increased further, though nonsignificantly in the standing position (118.3 ± 35.2). TLA, PL, and TCRT decreased from baseline during Valsalva in the supine (-34118 ± 11424 vs 62234 ± 12215, -0.038 ± 0.014 vs 0.065 ± 0.010, -0.08 ± 0.03 vs 0.10 ± 0.02, respectively, P < 0.001 for all). LD was significantly increased by Valsalva in the supine position (13 ± 46 vs -153 ± 30, P < 0.001) and nonsignificantly in the standing position (99 ± 50 vs 86 ± 30, P = NS). There were significant correlations among TLA, PL, and LD, and no significant correlation between TCRT and any of the temporal variation descriptors. These new temporal and wavefront direction descriptors are sensitive and rapid detectors of autonomic effects on ventricular repolarization. [ABSTRACT FROM AUTHOR]

Recordings: The aim of the present study was to investigate the QT-RR interval relationship in ambulatory EGG recordings with special emphasis on the physiological circumstances under which the QT-RR intervals follow a linear relation. Continuous EGG recordings make it possible to automatically measure QT duration in individual subjects under various physiological circumstances. However, identification of QT prolongation in Holter recordings is hampered by the rate dependence of QT duration. Comparison of QT duration and QT interval rate dependence between different individuals implies that the nature of the QT- RB relationship is defined in ambulatory ECG. Holter recordings were performed in healthy volunteers at baseline and after administration of dofetilide, a Class III antiarrhythmic drug. After dofetilide, beat -to- beat automated QT measurements on Halter tapes were compared with manually measured QT intervals on standard EGGs matched by time. The QT-RR relationship was analyzed at baseline of individual and group data during three different periods: 24-hour, daytime, and nigh time. Data were collected under steady-state or non-steady-state conditions of cycle length and fitted with various correction formulae. Our study demonstrated an excellent agreement between manually and automated measurements. The classic Bazett correction formula did not fit the QT-RR data points in individual or group data. When heart beats were selected for a steady rhythm during the preceding minute, QT-RR intervals fit a linear relationship during the day and night periods, but not during the 24-hour period in both individual and group data. In contrast, in the absence of beat selection, data fit a more complex curvilinear relationship irrespective of the period. Our study provides the basis for comparison of QT interval durations and QT-RR relationships between individuals and between groups of subjects. [ABSTRACT FROM AUTHOR]

Ventricular fibrillation (VF) is the most common arrhythmia causing sudden cardiac death. However, the likelihood of successful defibrillation declines with increasing duration of VF. Because the morphology of the electrocardiogram (ECG) waveform during VF also changes with time, this study examined a new measure that describes the VF waveform and distinguishes between early and late VF. Surface ECC recordings were digitized at 200 samples/s from nine swine with induced VF. A new measure called the scaling exponent was calculated by examining the power-law relationship between the summation of amplitudes of a 1,024-point (5.12 second) waveform segment and the time scale of measurement. The scaling exponent is a local estimate of the fractal dimension of the ECG waveform. A consistent power-law relationship was observed for measurement time scales of 0.005-0.040 seconds. Calculation of the scaling exponent produced similar results between subjects, and distinguished early VF (< 4-minute duration) from late VF (≥4-minute duration). The scaling exponent was dependent on the order of the data, supporting the hypothesis that the surface ECC during VF is a deterministic rather than a random signal. The waveform of VF results from the interaction of multiple fronts of depolarization within the heart, and may be described using the tools of nonlinear dynamics. As a quantitative descriptor of waveform structure, the scaling exponent characterizes the time dependent organization of VF. [ABSTRACT FROM AUTHOR]

Although atrial signal-averaged electrocardiogram (SAECG) has been proposed for noninvasive identification of patients with atrial tachyarrhythmias, the substantial variability of the measurement limits the clinical value. The aim of the study was to assess the short- to long-term reproducibiiity of atrial SAECG and to compare it to that of the conventional ventricular SAECG in 51 healthy volunteers (30 men; age 32 ±8 years]. In each subject, SAECG recordings were obtained using MAC-VU electrocardiograph and HiRES and PHiRES software (Marquette Medical Systems) and repeated after 5 minutes, 1 day, 1 week, and 1 month. Automatically detected onset and offset of the filtered QRS complex and P wave were subsequently corrected by two independent observers, and the averaged values were used for the analysis. Conventional ventricular SAECG parameters: filtered QRS duration (QRStot), low amplitude signal duration, and root mean square voltage (RMS) of the terminal 40 ms of QRS; and 5 atrial parameters: filtered P wave duration (Ptot), RMS of the terminal 40, 30, 20 ms, and of the entire P wave were obtained. Relative errors of different pairs of measures were used to assess the intrasubject reproducibility. QRStotand Ptot were the most reproducible parameters. The relative errors after 5 minutes, 1 day, 1 week, and 1 month were 0.8% to 2.4% for QRStot, and 1.3% to 4.2% for Ptot. For RMS voltages, the relative errors exceeded 15% in short-term and 20% in long-term recordings. Although Ptot was statistically less reproducible than QRStot, the reproducibility of the former was good and comparable to that of the QRStot. The reproducibility of the voltage parameters was significantly poorer than that of the duration parameters. The study showed a satisfactory short- and long-term reproducibility of Ptot in the atrial SAECG in healthy subjects. However, low reproducibility of the voltage parameters should be considered in clinical applications. [ABSTRACT FROM AUTHOR]

A new generation of lined steroid-eluting leads featuring 1.2-mm² distal electrodes (CapSure® Z, Medtronic Inc., Minneapolis MN, USA) has the potential to reduce battery current drain and enhance pulse generator longevity by means of high pacing impedance and low pacing threshold. Forty patients aged 50-87 years (mean 72.4 years) were implanted with 33 ventricular (models 4033 and 5034) and 30 atrial-J (models 4533 and 5534) leads with 1.2-mm² electrodes. Low pacing outputs, mainly in the range from 1 V/0.20 ms to 1.6 V/0.36 ms with ⩾ 3:1 pulse width safety margins (PWSM) applied, were instituted at 3-6 months of implantation and adjusted at subsequent follow-up controls according to changes in thresholds. Cumulative follow-up period of low outputs was 1.512 months (24 months per lead, range 9-36 months), which involved 3.43 follow-up controls per lead (range 2-5). During follow-up, pulse width thresholds (PWTs) at the used amplitudes did not change in 55.5% of the leads: PWTs increased by ⩽ 100% in 36.5%, by 101%-200% in 1.6%. and by > 200% in 6.3% of the leads. Changes in PWT that would apparently exceed 3:1 PWSM over a 1-year period occurred in one atrial lead where even the nominal 3.5 V/0.4-ms output would not be effective and in one ventricular lead in the aftermath of an acute myocardial infarction (300% PWT rise at 1.6 V). Based on the present observations, pacemaker dependent patients require ⩾ 4:1 PWSM and other patients ⩾ 3:1 PWSM with output pulse widths ⩽ 0.60 ms and annual pacemaker clinic visits. Calculated battery current drain and anticipated longevity associated with a variety of pacing outputs and impedances are provided, compared, and discussed. Correlation between acute and chronic pacing impedances and pacing thresholds was weak, implying that a systematic intraoperative pacing site optimization cannot contribute significantly to the extension of average battery longevity. [ABSTRACT FROM AUTHOR]

The presence of late potentials on the body surface recording was correlated with ventricular activation maps of reentrant circuits in the postinfarction canine model of reentrant excitation. Late potentials were found to correlate with delayed myocardial activation. However, during a reentrant rhythm complete diastolic activity on the body surface could not be detected if the mass of electrically active cells was too small and/or if very slow conduction in part of the reentrant circuit generated low amplitude extracellular potentials. Myocardial zones responsible for late potentials during a basic rhythm (e.g., sinus rhythm) may not necessarily be part of the critical zone of slow conduction during reentrant activation. Dynamic changes in late potentials are not amenable to temporal signal averaging techniques but could be detected by a high resolution beat-to-beat recording. A thorough understanding of the electrophysiological limitations of late potentials in the signal-averaged ECG could result in better utilization of the technique in clinical practice as well as in the development of new approaches for the detection of the arrhythmogenic substrate. [ABSTRACT FROM AUTHOR]

A method of ECG mapping from 90 points on the chest surface is described in 41 male and 17 female patients, aged 6 to 59 years. All also underwent invasive electrophysiological investigation and intraoperative epicardial mapping. Fifty-two patients had one, three patients two, and one patient had three anomalous accessory pathways. Two patients had nodoventricular tracts (Mahaim fibers). We distinguished seven zones along the atrioventricular groove (AVG) to compare the data derived from epicardial, endocardial, and body surface mapping. A microcomputer was used for the analysis of all ECGs to construct and analyze the isopotential maps. The criterion for localization of the anomalous accessory pathways was determined after analysis of the data from all 58 patients. The localization criterion was the appearance ofa minima] deflection (-0.09 ± 0.03 mV) on the surface isopotential maps within the first 0.28 msec of the QHS complex. This criterion for localization of anomalous accessory pathways from the chest surface was proposed on the basis of comparison of data from selective coronary angiography, the ventriculogram, and the chest X ray i.e., radiographic-topographic-anatomical data. In 20 patients, 10-20 nontraditional ECG leads were recorded from the chest to reflect the atrioventricular groove. The number of nontraditional EGG leads depended on patient age, weight, and height. Localization of the accessory pathway in one of the seven zones was established by the earliest delta wave and its maximum deviation. It was possible to localize the anomalous accessory pathway and to suspect mu]tip]e pathways in 95% of cases using nontraditional EGG leads and the listed criteria. Comparison of results of body surface mapping with X ray-topographic-anatomical data made determination of the anomalous accessory pathway possible with a high degree of success. We propose a new system of 10-20 nontraditional EGG leads recording data from the AVG projection onto the chest surface for topical localization of the Kent bundle in one of the seven zones into which the AVG was divided. [ABSTRACT FROM AUTHOR]

Delayed and inhomogeneous ventricular depolarization is found in patients with ventricular tachycardia. This abnormal activity may be discerned as a ventricular late potential (LP) by applying special signal-averaging techniques to the surface electrocardiogram. The presence of LPs after acute myocardial infarction (AMI) is associated with an increased risk of serious ventricular arrhythmias and sudden cardiac death during the subsequent year. Thus the signal-averaged ECG (SAECG) can identify a high risk subset of patients following AMI for whom more intensive diagnostic and/or therapeutic measures are indicated. Patients with findings ordinarily indicative of a relatively poor prognosis, such us reduced left ventricular ejection fraction, may be more precisely classified into high or low risk based on the presence or absence of LPs. The SAECG may be helpful in selecting patients with other types of presentations, such as syncope, who are likely to benefit from electrophysiological testing. [ABSTRACT FROM AUTHOR]

We examined the hypothesis that a ≥2 second pause detected on 24-hour Holter monitoring in patients with persistent atrial fibrillation and complaints of syncope or dizziness lacked sufficient specificity to warrant implantation of a permanent pacemaker. We retrospectively reviewed cases from our 24-hour electrocardiographic (Holter) monitoring data base. A total of 411 consecutive Holter monitoring records demonstrating persistent atrial fibrillation obtained during a 5-year period (1982 to 1987) were examined. One hundred and five (26%) patients had cerebral symptoms (dizziness or syncope) as a primary indication for monitoring 80 (76%) patients were identified with documented ventricular pauses of ≥2 seconds. Three hundred and six patients (74%) underwent 24-hour monitoring without cerebral symptoms as an indication and 209 (68%) patients had ≥2-second pauses. Clinical information was available in 164 (50 symptomatic and 114 asymptomatic) patients. There were no significant differences in the clinical or Holter findings between the two groups. Of the 50 symptomatic patients, 15 (30%) underwent permanent pacemaker placement and the remaining 35 (70%) were managed conservatively during a mean follow-up of 23 ± 5 months. Eleven of 15 paced (73%) and 31 of 35 (89%) nonpaced patients experienced resolution of their cerebral symptoms (NS). The sensitivity of Holter monitoring in detecting pauses of ≥2 seconds in patients with cerebral symptoms was high (76%), but the specificity (32%) and positive predictive values (28%) were low. In conclusion, the finding of a 2-second pause interval on Holter monitoring lacks sufficient specificity to identify symptomatic patients with persistent atrial fibrillation. In addition, there is a high rate of spontaneous resolution of cerebral symptoms in this group without the use of a pacemaker. These findings suggest that in patients with persistent atrial fibrillation in the presence of a 2-second pause on a Holter recording, a clear association between cerebral symptom and the pause interval is necessary before the use of a permanent pacemaker is recommended. [ABSTRACT FROM AUTHOR]

The occurrence of atrial fibrillation in patients with paroxysmal supraventricular tachycardia (PSVT) has been well documented when PSVT is secondary to atrioventricular reentry, but not when PSVT is secondary to atrioventricular nodal reentry (AVNRT). Seventeen patients with AVNRT were followed using transtelephonic electrocardiogram monitoring to document symptomatic tachycardias. The median length of telephone monitor surveillance was 357 days. Fifteen of 17 patients transmitted electrocardiograms that showed PSVT. Three of 17 patients (18%) transmitted electrocardiograms that showed atrial fibrillation. A transition from PSVT into atrial fibrillation was not recorded, but all three did have PSVT recorded on other days of follow-up. We report the occurrence of atrial fibrillation in patients with AVNRT and that its incidence is higher than expected for the general population. [ABSTRACT FROM AUTHOR]

This article presents a subject index for Volume 12 of the journal "Pace." Some of the subjects of various articles published in the journal are: Catheter ablation, atrial pacing, ambulatory electrocardiography, anticoagulants, anxiety, arrhythmias, and catecholamines.

Presented are three patients with Wenckebach type second degree AV block that was complicated with AV nodal reentry producing different arrhythmias. The common presentation of manifest AV nodal reentry is an incomplete Wenckebach periodicity, whereby the retrograde impulse interrupts the Wenckebach cycle; rarely, the retrograde impulse initiates an AV junctional reentrant tachycardia. The documentation of concealed AV nodal reentry is more difficult and should be considered if there is a sudden increase of the PR interval in the Wenckebach cycle. [ABSTRACT FROM AUTHOR]

Interpretation of signal-averaged electrocardiograms (SAECG) in the young could be of value in detecting those at risk for episodic ventricular tachycardia, but suffers from a lack of data in normal young people. The purpose of this study is to determine normal values for QRS duration and the duration and amplitude of terminal potentials on the SAECG in young adults, Thirty-two normal medical students were examined. With high pass filtering at 25 Hz, normal total QRS duration (QRS) varied as a function of sex and body size whereas low amplitude signal duration (LAS) did not. Ninety-five percent confidence limits are: QRS (male) 85-117 msec, QBS (female) 76-102 msec, and LAS 6-35 msec. Boot mean square voltage of the terminal QRS showed a broad scatter, however none was <20 microvolts. High pass filtering at 40 Hz did not change the QHS duration, but resulted in significantly longer LAS duration and diminished RMS voltage. Because of the longer QHS and shorter LAS previously reported in the presence of right bundle branch block, the normal values reported here should not be applied in the presence of intraventricular conduction delay following surgical repair of congenital heart disease. They will, however, provide a basis for interpretation of SAECG in young adults with normal QHS duration. [ABSTRACT FROM AUTHOR]

The influence of pacemaker output on the morphology of the paced QHS complex was studied from standard lead electrocardiograms in 69 patients with bipolar pacemakers. In 40 of the 69 patients (58%), there was a significant (P < 0.001) change in electrical axis, from -75° at the low output setting (2.7 V, 0.15 msec) to -67° at the high output setting (8.1 V, 2.29 msec). In 30 patients, these changes were also associated with changes in the QRS morphology and in the T-wave. This phenomenon may be explained by additional stimulation from the proximal electrode at high output, thus altering the pattern of depolarization. [ABSTRACT FROM AUTHOR]

Overdrive stimulation of reentrant ventricular tachycardias (VT) may result in entrainment and/or termination of these arrhythmias. We investigated whether surface ECG criteria of entrainment can also be observed in nonreentrant VT. For this purpose ouabain-induced tachycardias were used that are considered to be based on delayed afterdepolarizations. In nine conscious dogs, having surgically induced complete AV block, pacing was performed using trains of 20 stimuli from a site distant to the origin of the VT. The pacing intervals were shortened in steps of 5-10 msec, until complete capture from the pacing site or termination of the VT was obtained. During stimulation variable fusion was seen and complete capture of the ventricles from the pacing site occurred just after a slight decrease in pacing cycle length (20 ± 10 msec). Overdrive stimulation resulted only in 1 out of 58 stimulation trains in termination of VT. Following stimulation it was observed that: (1) The length of the first postpacing interval was significantly longer (P < 0.001) than both the mean prepacing VT cycle length and interstimulus interval; (2) A change in QRS configuration occurred after 57% of the stimulation trains; (3) The VT accelerated slightly in comparison to the prepacing rate (P < 0.05); and (4) The length of the first postpacing interval and the mean R-R interval of the VT postpacing were directly related to the interstimulus interval (r = 0.82 and 0.97, respectively). In conclusion, overdrive stimulation of ouabain-induced arrhythmias did not result in entrainment or in termination of the tachycardia. Instead, other responses were seen that may be of help in differentiating between arrhythmias caused by delayed afterdepolarizations and reentry. [ABSTRACT FROM AUTHOR]

The effect of encainide on chronic pacing thresholds was evaluated in 10 patients, age 64-89, who were exposed to weekly increased encainide dosing (25 mg TID, 50 mg TID, 75 mg TID). Median pacing threshold (μjoules) increased modestly at each period compared to placebo and returned rapidly to baseline after discontinuation. ... No patient experienced a pacing-related clinical event. One patient had a large threshold increase (566%), but no failure to capture on 24-hour EGG, and one patient whose threshold increased minimally had clinically insignificant capture failure, the longest event being 3 beats. No other failure to capture was noted. Thus, encainide, like a number of other antiarrhythmic drugs, appears to affect pacing thresholds. At the highest dose of 225 mg/day (75 mg TID, which exceeds the generally recommended dose of 50 mg TID), but not at lower doses, some patients may experience loss of capture that does not appear related to the change in threshold energy required. Increases in the duration of the paced QRS induced by encainide did not predict increases in threshold. Therefore, when higher doses of encainide are required in patients with pacemakers, clinical observation and ambulatory electrocardiographic monitoring should be carried out. [ABSTRACT FROM AUTHOR]

A mathematical model for pure parasystole and modulated parasystole leads to a number of quantitative predictions. The predictive power of the model is examined by confronting it with data obtained from a 16-year-old symptomatic male born with a ventricular septal defect that was surgically closed at 5 years of age. A diagnosis of ventricular parasystole and inducible ventricular tachycardia was made following a syncopal episode. The physiological variables required by the model to make specific predictions are the sinus and ectopic cycle lengths and the ventricular refractory period. From these three variables, a two-dimensional parameter space is constructed consisting of the ratio of the refractory period to the sinus cycle length and the ratio of the ectopic to sinus cycle length. For any set of parameters, predictions are made concerning the number of sinus beats between ectopic beats. The different behaviors exhibited in the electrocardiographic (ECG) data agree with theoretical predictions. [ABSTRACT FROM AUTHOR]

The presence of a nodoventricular pathway (Mahaim fiber) has been invoked to explain certain distinctive electrocardiographic and electrophysiological observations. The presence of an atrioventricular or atriofascicular fiber with decremental conduction proper- ties has been documented in many of these patients. We report the case of a patient with a Mahaim fiber and the response to conduction over this pathway after adenosine, procainamide, encainide, verapamil, edrophonium, phenylephrine and isoproterenol. Conduction over the Mahaim fiber was blocked by adenosine. but not verapamil. The time course of adenosine induced block over the Mahaim fiber differed from adenosine induced AV nodal block. Mahaim fibers are decrementally conducting pathways that are adenosine sensitive. These findings support the concept that conduction in accessory pathways manifesting decremental properties is not mediated by the calcium channel. [ABSTRACT FROM AUTHOR]

The mechanisms behind ventricular premature beats may be divided into two main categories, reentry and modulated parasystole. Although it is relatively easy to distinguish among arrhythmia generating mechanisms on the cellular level, it is far more difficult in the clinic. Modulation of ventricular parasystole by sinus beats has been shown to result in a biphasic phase response curve. Two cases are reported where the deduction of such phase response curves from long-term ECG recordings is discussed and described as a stepwise procedure. [ABSTRACT FROM AUTHOR]

Twenty patients with advanced AV block and normal sinus node function underwent pacemaker implantation, randomly receiving a CPI 910 ULTRA II model VDD pacemaker. The first 13 patients received the implantation of a single lead with a screw-in positive ventricular fixation tip and a unipolar ring floating atrial electrode spaced 13 cm from the tip. A subsequent group of seven patients received a conventional porous tinned-tip lead with a pair of unipolar ring floating electrodes. The second solution was adopted because the best atrial signal was not always in the high or mid-high atrium portion, but sometimes in the middle or mid-low position. With the modified double-electrode lead, the floating atrial electrode that detects the best signal can be selected, cutting out the pin of the one not used. The comparisons between minimal atrial slew rate and maximal ventricular slew rate, as well as those between minimal P wave amplitude and maximal B wave amplitude, show a highly significant range difference, as large as P < 0.01. Surface electrocardiograms, stress tests, and 24-hour Holter monitoring showed the correct functioning of the system with an average sensing failure from 0.05 to 1%. In conclusion, VDD stimulation is feasible with a single unipolar lead and a floating atrial electrode in conjunction with a pacemaker generator (CPI 910 ULTRA II) originally designed for permanent twin-lead implantation. [ABSTRACT FROM AUTHOR]

Dual-chamber, rate-modulated pacing (DDDR) has only recently been made available. During exercise, the pacemaker is capable of tracking not only the patient's intrinsic P wave but also the AV sequential sensor-indicated rate response, which depends on the programmed variables of the specific sensor in the DDDR pulse generator. Programmed options that affect the operation of a rate-modulated DDDR device are slope, threshold, reaction time, and recovery time. In addition, one is required to program a base or minimum pacing rate and a maximum tracking rate, as in any DDD device, as well as a maximum sensor rate. It is essential to know and understand all these programmed options if one is to correctly interpret electrocardiograms from a DDDR pacemaker. Interpreting the electrocardiograms also requires an understanding of the sensor-indicated rate of the pacemaker at any given level of exercise, which is determined by the options previously listed and the interaction between the sensor-indicated rate and the patient's intrinsic atrial and ventricular activity. This paper presents electrocardiograms typical of a new DDDR pacemaker undergoing clinical investigation. [ABSTRACT FROM AUTHOR]

The explanation and interpretation of ECGs recorded from paced patients may be very difficult because of pacemaker specification, programmed parameters, and idiosyncrasy and also because of hidden interactions between the device and its environment. Moreover, the recent development of very sophisticated pacemakers makes the heart-pacemaker interaction (HPI) difficult to understand even when the recorded ECG is accompanied by an event marker. A computer system providing an automatic analysis of the HPJ based on ECG data has been developed and implemented on an IBM PC AT computer. The system evaluates all possible combinations of HPI events and establishes whether they correspond to the pacemaker. The system inputs interactively the description of the pacemaker mode and programming, and the description of the analyzed ECG in the form of timing of "definite" and "possible" sensing events and generator pulses. The computer performs the analysis and establishes whether the device operates correctly within its permitted error. The system has been tested by evaluating different examples of paced ECGs. The presented examples confirm the ability of the system and show the potential for its future clinical use. Future development of the system and the provision of computer support for the understanding of the HPI of complex DDDR pacemakers are discussed. [ABSTRACT FROM AUTHOR]

The analysis accuracy and susceptibility to faults of the additional diagnostic functions were tested in 16 patients (eight men, eight woman, average age 61.5 ± 10.8 years, 14 VVI, 2 AAI) with diagnostic pacemakers (Quintech DPG 921). The average observation period was 19.7 months. With 109 follow-up intervals of an average duration of 87 ± 39 days, this meant an observation period of 25.9 patient years. A stage-by-stage test structure over several intervals of time was applied in order to validate the data acquired through pacemaker Holier functions by means of control ECGs and mathematical test methods. The only fault to occur in the diagnostic/unctions was a loss of stored data. This was observed in 10% of the follow-up intervals and was on the average 28% (16%-38%) of the total events. Forty-four percent (7/16) of the pacemakers were affected by this malfunction. Our results show that the diagnostic data are certainly correctly acquired. The clinical value of the diagnostic functions is clearly reduced by this potential loss of data. [ABSTRACT FROM AUTHOR]

To examine the association between ventricular rhythm disturbances and changes in the pacemaker-induced stimulated T interval (STIM-T interval), we compared findings from monitoring of two patient groups. The first group consisted of 15 patients with QTX microprocessor pacemakers and the second group consisted of 198 patients with documented ventricular rhythm disturbances and coronary artery disease (CAD). In the first group, which was free of ventricular rhythm disturbances and manifest coronary artery disease, the STIM-T interval was measured every 4 hours over a 36-hour period at four pacemaker frequency settings (70, 80, 90, and 100) in order to observe the circadian variation of the STIM-T interval as a function of changes in autonomic nervous system (ANS) tone. The second group was comprised of patients with CAD and over 30 VES/hrs (Lown grade classification 1-5), and taking no antiarrhythmic medication. These patients were followed using 24-hour Holter monitoring over a minimum of 23 hours and with less than 5% artifact/recording. Information regarding mean hourly heart rate, total number of VES, VES pairs, VT runs, and ischemic episodes in this group was compared with changes in the STIM-T interval in the first group. The STIM-T interval was found to be shorter during the day and longer at night ai all heart rate settings. The total frequency of VES, of VES pairs, VT runs, and ischemic episodes in the second group varies in a similar circadian fashion. The greatest total number of VES, of VES pairs, VT runs, and ischemic episodes was recorded in the waking hours, at the same time when the STIM-T interval is the shortest, while this number was significantly lower during sleep, when the STIM-T interval of the first group is the longest. This coincidence of circadian variation pattern between STIM-T interval in group I, and ventricular arrhythmias and ischemic episodes in group II, suggests that alterations in ANS tone reflected in the STIM-T interval may be an important factor in the occurrence of these untoward events. [ABSTRACT FROM AUTHOR]

Masked bifascicular block (MBB) (absent or minimal S in I and VL, high R in Vi, and ÂQRS approximately -60å) is a rare condition. We have found 16 such cases in the last 12 years, thirteen male and three female, mean age 70 ± 9 years. The conventional electrocardiogram was tabulated and the clinical features and evolution of the patients were followed over 39.1 ± 32 months. Ten patients required pacemakers, nine because of complete atrioventricular (AV) block or increase in the previous AV block. Seven patients died (follow-up 27.2 ± 32 months), five from heart failure. This study shows: (1) MBB is a subgroup of patients with a high risk of advanced atrioventricular block; (2) a pacemaker implant does not significantly reduce the high mortality in this group because of the severity of the underlying disease; (3) these results should be evaluated in a larger series of patients in order to confirm our provisional results. [ABSTRACT FROM AUTHOR]

In the interpretation of electrocardiograms recorded during atrioventricular sequential pacing, uncertainty frequently arises in the assessment .for evidence of atrial capture. In the present study, electrocardiographic characterization of pacing .from the right atrial appendage as a component of atrioventricular pacing was performed on tracings obtained/ram 16 patients with bipolar dual chamber pacing units, and from 18 patients with unipolar dual chamber pacing units in which large overshoot potentials occurred following the atrial pacing spike. Atrial complexes resulting from bipolar pacing of the right atrial appendage were found to be uniformly prolonged and of diminished amplitude compared to those in sinus rhythm; they were also noted to contain sequential inferoposterior and leftward-posterior component vectors. The exponential overshoot-decay complex associated with unipolar atrial pacing appeared as a vector directed along the axis from the pulse generator to the pacing lead; the degree to which this deflection interfered with identification of atrial capture in various leads was thus largely dependent on pulse generator location. It was concluded that careful systematic inspection of multiple electrocardiographic leads will generally permit the characteristic features of pacing the right atrial appendage to be recognized, thus facilitating correct interpretation of atrial capture during atrioventricular sequential pacing. [ABSTRACT FROM AUTHOR]

The morphology of bipolar electrograms recorded in the right atrium was examined in nine patients in an attempt to discriminate retrograde from anterograde atrial signals to an extent that would be useful for physiologic pacing. Peak-to-peak amplitude, duration, √energy, maximum slew rate, mean slew rate, and polarity were examined in the time domain. Maximum frequency, half-power frequency, Fourier amplitude peak, and frequency of peak were measured in the frequency domain. There was a significant difference between anterograde and retrograde signals for all variables related to amplitude; these variables are peak-to-peak amplitude, √energy, Fourier amplitude peak, maximum slew rate and mean slew rate. In seven of nine patients there was at least one variable sufficiently discriminating to insure reliable detection of anterograde signals while systematically rejecting retrograde signals. However, no individual variable was able to effect this discrimination in more than four patients and at least three variables were needed for all seven patients: maximum frequency, one of either √energy and Fourier amplitude peak, and one of either frequency of peak or half-power frequency (six possible combinations). Thus, although differences between anterograde and retrograde atrial activity can be demonstrated in most patients, no single parameter displays sufficient discriminating power to facilitate physiologic pacing in patients exhibiting retrograde activity. [ABSTRACT FROM AUTHOR]

The electrophysiologic mechanisms of sinus dysfunction have recently been determined by direct recording of the sinus node electrogram. The association of various degrees of abnormalities in the formation of the impulse within the sinus node and of sinoatrial conduction block, represents the pathophysiological substrate of the mechanism of sinus node dysfunction. The purpose of this work is to present clinical and experimental data supporting the concept of sinus node isolation. In our clinical case, the sinus node was probably intact despite aspects of sinus node dysfunction on the surface ECG. Sinus node electrograms were recorded with a sinoatrial conduction time of 100 ms (normal values in our laboratory: 83 ms ± 38 ms). Atrial mapping demonstrated that the area depolarized by the sinus node involved a 2 cm² zone surrounding it. This perisinusal activity could not be recorded on the surface ECG. Both exit and entry blocks in the sinus node were demonstrated. Our experimental data showed o total desynchronization between the electrical activity of the sinus node and that of the atrium under hypoxic conditions. Both types of cases demonstrated that an atrial dysrhythmia was coexisting with regular sinus activity. From these data we concluded that a sinus node free from any pathological involvement could be associated with severe symptoms of sinus node dysfunction on the surface ECG. [ABSTRACT FROM AUTHOR]

The automatic termination of malignant tachyarrhythmias and of ventricular fibrillation by an implantable device requires a reliable sensing of these episodes of abnormal ECG. Therefore, we induced tachyarrhythmias and fibrillation in eleven dogs and recorded electrograms and intrainyocardial pressure. The electrograms were analyzed using the autocorrelation function and the probability density function. Intramyocardial pressure was monitored as a hemodynamic parameter. Results show that in the case of sinus rhythm, all methods are reliable, but in the case of VT and VF, electrogram processing only is insufficient. It is concluded that combined monitoring of ECG processing and a hemodynamic parameter may increase the sensitivity of an automatic tachycardia-fibrillation detection system. [ABSTRACT FROM AUTHOR]