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Background Atrioventricular reciprocating tachycardia (AVRT) utilizing a concealed accessory pathway is common. It is well appreciated that some patients may have multiple accessory pathways with separate atrial and ventricular insertion sites. Methods We present three cases of AVRT utilizing concealed pathways with evidence that each utilizing a single ventricular insertion and two discrete atrial insertion sites. Results In case one, two discrete atrial insertion sites were mapped in two separate procedures, and only during the second ablation was the Kent potential identified. Ablation of the Kent potential at this site remote from the two atrial insertion sites resulted in the termination of the retrograde conduction in both pathways. Case two presented with supraventricular tachycardia (SVT) with alternating eccentric atrial activation patterns without alteration in the tachycardia cycle length. The two distinct atrial insertion sites during orthodromic AVRT and ventricular pacing were targeted and each of the two atrial insertion sites were successfully mapped and ablated. In case three, retrograde decremental conduction utilizing both atrial insertion sites was identified prior to ablation. After mapping and ablation of the first discrete atrial insertion site, tachycardia persisted utilizing the second atrial insertion site. Only after ablation of the second atrial insertion site was SVT noninducible, and VA conduction was no longer present. Conclusions Concealed retrograde accessory pathways with discrete atrial insertion sites may have a common ventricular insertion site. Identification and ablation of the ventricular insertion site or the separate discrete atrial insertion sites result in successful treatment.

Background Atrial refractoriness may be an important determinant of atrial fibrillation (AF) risk, but its measurement is not clinically accessible. Because the QT interval predicts incident AF and the atrium and ventricle share repolarizing ion currents, we investigated the association between an individual's QT interval and atrial effective refractory period (AERP). Methods In paroxysmal AF patients presenting for catheter ablation, the QT interval was measured from the surface 12-lead electrocardiogram. The AERP was defined as the longest S1–S2 coupling interval without atrial capture using a 600-ms drive cycle length. Results In 28 patients, there was a positive correlation between QTc and mean AERP. After multivariate adjustment, a 1-ms increase in QTc predicted a 0.70-ms increase in AERP. Conclusions The QTc interval reflects the AERP, suggesting that the QTc interval may be used as a marker of atrial refractoriness relevant to assessing AF risk and mechanism-specific therapeutic strategies.

Introduction There are several methods to induce ventricular fibrillation (VF) during defibrillation threshold (DFT) testing. Delivering a shock at a critical time during the T wave (T-shock) is the conventional approach, while delivering a constant direct current voltage (DC stim) from the implantable cardioverter defibrillator is an alternative method. Only a few reports compare VF induction methods. The purpose of this study was to evaluate the effects and safety of DC stim versus T-shock. Methods We retrospectively investigated 414 consecutive patients undergoing DFT testing. We compared the two groups (DC stim and T-shock) with respect to clinical characteristics, electrocardiogram (ECG) changes, and complications. Results Ventricular arrhythmia, including ventricular tachycardia (VT) and VF, was induced by DC stim in 93 patients or T-shock in 321 patients. No more than three attempts were performed during one procedure. There was no significant difference in the baseline ECG, induced tachycardia cycle length (TCL), or complications between the two groups. However, the induced TCL was significantly shorter than the clinical TCL regardless of induction method (P = 0.001). Five patients suffered major complications (i.e., electromechanical dissociation or incessant VT). A history of atrial fibrillation was significantly greater in patients with major complications than the others (80% vs 24%, P = 0.004), and was an independent predictor on multivariate analysis. Conclusions There is no significant difference in induced TCL or complications between the DC stim and T-shock. The induced TCL is significantly shorter than clinical TCL regardless of induction method.

Background A recent study using an anti-plakoglobin antibody and immunofluorescence methods in endomyocardial tissue specimens found that a marked reduction in plakoglobin staining was highly sensitive and specific for the diagnosis of arrhythmogenic right ventricular cardiomyopathy (ARVC). The purpose of our study was to determine the diagnostic utility of plakoglobin immunolocalization using more standard immunoperoxidase methods suitable for clinical laboratories. Methods Between January 2007 and October 2010, all patients at our center with suspected ARVC underwent noninvasive and genetic testing, right ventricular (RV) angiography, electrophysiologic studies, and endomyocardial biopsy from the RV septum. Several studies using anti-plakoglobin antibodies were performed using standard immunoperoxidase methods at concentrations of 1:50,000 and 1:75,000 after serial dilutions. Results Among 16 patients, nine patients fulfilled the clinical criteria for ARVC, and seven patients were found to have other cardiac diagnoses. In the initial study (1:50,000) only one of nine ARVC patients showed reduced plakoglobin signal while the others had normal staining. On repeat staining (1:75,000), reduced signal was observed in three of five of the ARVC patients compared to none in controls (four patients did not have adequate tissue for the repeat experiment). Conclusion These results confirm that abnormal plakoglobin staining can differentiate biopsies from patients with ARVC from those with other myopathies, but with low sensitivity. Further, each specimen must be studied at a particular concentration due to variable antibody reactivity. The necessity for such fine-tuning of the reaction, as well as the subjectivity involved in interpretation of the results, would make this method difficult to utilize in routine hospital laboratories.

Background High-burden premature ventricular contractions (PVCs) may be an important determinant of heart failure (HF) in patients presenting for PVC ablation. The prevalence and characteristics of high-burden PVC patients outside this setting remain unknown. We, therefore, sought to determine predictors of high-burden PVCs and, among high-burden PVC patients, predictors of HF. Methods We identified all patients undergoing a 24–48-hour Holter study showing at least 20% PVCs between 2005 and 2013 at the University of California, San Francisco. Three time-matched controls undergoing Holter monitoring were selected for each high-burden PVC patient. Medical records were reviewed and test characteristics of PVC counts from 12-lead electrocardiograms (ECG) as predictors of high-burden PVC Holters were analyzed. Results Among 5,091 participants, 66 (1.3%) exhibited at least 20% PVCs. After multivariate adjustment, high-burden PVC patients had a three-fold greater odds of HF (odds ratio [OR] 3.15; 95% confidence interval [CI] 1.28–6.50; P = 0.005) and 10-fold greater odds of having a first-degree family member with sudden death (OR 9.97; 95% CI 1.78–60.8; P = 0.011). The C-statistic for the number of PVCs on 12-lead electrocardiogram as a predictor of high-burden PVCs was 0.7949. Among high-burden PVC patients, HF was associated with a history of coronary artery bypass grafting (OR 11.76; 95% CI 1.30–106.49; P = 0.028). Conclusion Among all undergoing Holter monitoring, 1.3% exhibited high-burden PVCs, a phenomenon associated with HF and a first-degree family history of sudden death. In an analysis restricted to high-burden PVC patients, a history of coronary artery bypass grafting was a predictor of HF.

Introduction Left atrial (LA) tissue characteristics may play an important role in atrial fibrillation (AF) induction and perpetuation. Although frequently used in clinical practice, computed tomography (CT) has not been employed to describe differences in LA wall properties between AF patients and controls. We sought to noninvasively characterize AF associated differences in LA tissue using CT.

Background: The axillary vein is a commonly used extrathoracic access site for cardiac rhythm device lead implantation. We sought to describe variation in axillary vein location and identify predictors of a more cranial or caudal radiographic location to facilitate blind venous cannulation. Methods: This was a single-center, retrospective study of patients undergoing lead implantation between 2006 and 2010. The cranial-caudal location of the axillary vein lateral and medial to the rib cage border was determined by reviewing peripheral contrast venograms. Multivariate linear regression was performed. Results: Of 155 patients, the majority were men (62%) and White (53%). The most frequent position of the lateral and medial axillary vein was over the third rib (40%) and top of the third rib (15%), respectively. In multivariate analysis, whites had a more caudal location of both the lateral (0.56 rib spaces lower, 95% confidence interval [CI] 0.22–0.91, P = 0.002) and medial axillary vein (0.50 rib spaces lower, 95% CI 0.85–0.91, P = 0.019). Other independent predictors included an approximate 3–4% higher rib space location for every digit increase in body mass index (BMI) (P = 0.049 for the lateral location and P = 0.016 for the medial location) and an approximate half rib space higher location for males (P = 0.015 for the lateral location and P = 0.013 for the medial location). Conclusions: The most common radiographic position of the axillary vein was over the third rib. Whites have a more caudal axillary vein location while men and patients with higher BMI have a more cranial position of the axillary vein. (PACE 2011; 34:1585–1592)

Background: An unusual 12-lead electrocardiographic pattern may be present in patients with cavotricuspid isthmus (CTI)-dependent flutter. Objective: Using baseline patient characteristics and echocardiography, we sought to study predictors of unusual electrocardiogram (ECG) characteristics in patients with CTI-dependent atrial flutter. Methods: This was a dual-center, retrospective cohort study of 147 patients undergoing electrophysiology study and ablation for CTI-dependent atrial flutter. Results: Among this cohort, 23 patients (16%) had unusual 12-lead ECG characteristics. Using multivariatelogisticregression,wefoundtwoclinicalpredictorsforhavinganunusualECGpattern.Aclockwise (CW) pattern at time of electrophysiology study was the strongest predictor of an unusual ECG pattern (odds ratio 15.3, 95% confidence interval [CI] 4.0‐59.4, P < 0.005). In addition, patients with decreased systolic function had a 3.5 greater odds (95% CI 1.1‐11.5, P = 0.037) of having an unusual ECG pattern. Conclusions: Our data demonstrate that among patients suffering from CTI-dependent atrial flutter who are referred for ablation, 16% will have unusual ECG patterns. Patients with CW atrial activation and left ventricle dysfunction have greater odds of manifesting unusual patterns by surface electrocardiogram. (PACE 2011; 34:1251‐1257)

Background: Although inappropriate shocks are known to be an important consequence of implantable cardioverter-defibrillators (ICDs), the subjective experience of pain intensity perceived by those receiving inappropriate versus appropriate shocks has not previously been examined. Methods: One hundred ICD patients underwent a standardized interview by an investigator blinded to the clinical history. Patients with a previous ICD shock were asked to describe the intensity of the associated pain on a standard 0–10 scale (10 being the worst pain they had ever experienced). Medical charts were then examined for any history of inappropriate and/or appropriate ICD discharges. Results: Thirty-five of the 100 patients had a record of at least one ICD shock, and 17 had experienced at least one inappropriate shock. Those with a history of an inappropriate shock described a significantly higher median pain scale (9, interquartile range [IQR] 8–10) compared to those with a history of only appropriate shocks (median 4, IQR 2–8, P = 0.0011). In multivariable analysis, a history of an inappropriate shock was the only predictor statistically significantly associated with an increase in shock pain: the pain scale for those with inappropriate shocks was higher by 2.8 points on average after multivariable adjustment (95% confidence interval 0.29–5, P = 0.030). Eighteen patients had considered having their device deactivated, and a history of an inappropriate shock was the only factor independently associated with this consideration. Conclusions: Compared to those who have received only appropriate shocks, inappropriate ICD shocks are associated with a recollection of greater pain and consideration of device inactivation. (PACE 2011; 34:348–353)

Background: Atrial fibrillation (AF) has been linked to an inflammatory process detected through various biomarkers, including C-Reactive Protein (CRP). Early recurrence of AF within the first 3 months after curative AF ablation is not felt to reflect success or failure of the procedure. We hypothesized that this early recurrence is due to an inflammatory response to the ablation itself. We therefore sought to evaluate levels of CRP after AF ablation. Methods: We prospectively enrolled subjects undergoing AF ablation. A control group of patients undergoing ablation for supraventricular tachycardia (SVT) was also enrolled. Each patient had CRP drawn on the day of the procedure (prior to ablation) and during their first follow-up (median 49 days, interquartile range [IQR] 37–93) and second follow-up (median 147 days, IQR 141–257) clinic visits. Patient interviews were performed and medical histories reviewed for evidence of recurrent AF prior to the first follow-up. Results: CRP levels significantly increased from baseline to first follow-up in the AF ablation group (P = 0.0017). CRP did not significantly change after SVT ablation (P = 0.92). Seventeen (45%) of the AF subjects exhibited recurrence of AF prior to first follow-up. After adjusting for multiple potential confounders, AF ablation patients with recurrent AF prior to their first follow-up had a statistically significant greater odds of having an increase in CRP (OR 21, 95% CI 1.1–417, P = 0.045). Conclusions: AF ablation generates an inflammatory response that persists for several weeks. This inflammation may explain early recurrence of AF after curative ablation.