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Background Electrophysiological predictors of atrioventricular (AV) block after transcatheter aortic valve replacement (TAVR) are unknown. Objective We sought to assess the value of electrophysiology study before and after TAVR. Methods Seventy-five consecutive pacemaker-free patients undergoing TAVR at the Montreal Heart Institute were prospectively studied. Results Eleven patients (14.7%) developed AV block during the index hospitalization and 3 (4.0%) after hospital discharge over a median follow-up of 1.4 years (interquartile range 0.6–2.1 years). AV block developed in 5 of 6 patients with preprocedural right bundle branch block (83.3%), 8 of 30 patients with new-onset left bundle branch block (LBBB; 26.7%), and 1 of 7 patients with preexisting LBBB (14.3%). In multivariate analysis that considered all patients, the delta-HV interval (HV interval after TAVR minus HV interval before TAVR) was the only factor independently associated with AV block. In the subgroup of patients with new-onset LBBB, the postprocedural HV interval was strongly associated with AV block. By receiver operating characteristic analysis, a delta-HV interval of ≥13 ms predicted AV block with 100.0% sensitivity and 84.4% specificity and an HV interval of ≥65 ms predicted AV block with 83.3% sensitivity and 81.6% specificity. In multivariate analysis, the HV interval after TAVR (hazard ratio 1.073 per ms; 95% confidence interval 1.029–1.119; P = .001) was also independently associated with all-cause mortality. Conclusion A prolonged delta-HV interval (≥13 ms) is strongly associated with AV block after TAVR. In patients with new-onset LBBB after TAVR, a postprocedural HV interval of ≥65 ms is likewise predictive of AV block.

Atrial fibrillation recurs in ∼30%-40% of patients after pulmonary vein (PV) isolation (PVI) procedures, often because of restored PV-left atrial (LA) conduction. Adenosine or isoproterenol are used clinically to reveal dormant PV conduction and guide additional ablation.The purpose of this study was to assess the differential efficacy of adenosine and/or isoproterenol in revealing dormant PV conduction.In 25 patients undergoing PVI, dormant conduction was assessed sequentially in response to intravenous adenosine, isoproterenol, and adenosine plus isoproterenol in 100 PVs. To study mechanisms, PVs were isolated by radiofrequency ablation in coronary-perfused canine LA-PV preparations. After PVI, resting membrane potential from PV cells was recorded before and after 1 mM adenosine, 1 μM isoproterenol, 1 μM isoproterenol plus 1 mM adenosine, or no drug (controls).Clinical PVI was successful in all 100 PVs, with dormant conduction in 31. Sensitivity for dormant conduction was isoproterenol 10%; adenosine 87% (P.001 vs. isoproterenol); and isoproterenol + adenosine 100% (P = .13 vs. adenosine). Dormant PV conduction in vitro was revealed with adenosine (53%) and adenosine + isoproterenol (60%) but not with isoproterenol alone or in controls (P.01). Radiofrequency lesions producing PVI depolarized resting membrane potential, causing inexcitability. Postablation, resting membrane potential hyperpolarized after both adenosine and isoproterenol, but adenosine-induced changes were greater (9.1 ± 0.6 mV, vs. 3.8 ± 0.6 mV; P0.001), with no significant additional effect when isoproterenol was added to adenosine.Adenosine is superior to isoproterenol in revealing dormant PVs clinically and experimentally because of more effective adenosine-induced hyperpolarization. Adding isoproterenol to adenosine had no significant additional value.

Further-more, the procedure is complex, time consuming, andhighly dependent on operator competency given the diffi-culties associated with creating contiguous curvilinear le-sions with focal ablation. As such, considerable effort hasbeen directed toward deriving more effective and saferapproaches.Balloon-based ablation systems potentially offer a sim-pler and faster means of achieving pulmonary vein isolation(PVI) that, theoretically, is less reliant on operator dexterity.Concurrently, cryothermal energy offers advantages overRF energy, including increased catheter stability, less endo-thelial disruption with lower thromboembolic risk, and min-imal tissue contraction with healing, an observation thoughtto result in less esophageal damage and PVS.

KEYWORDS Cryoablation; Atrial fibrillation; Phrenic nerve; Electromyography; Pulmonary veins ABBREVIATIONS CMAP compound motor action potential; EMG electromyography; RSPV right superior pulmonary vein (Heart Rhythm 2011; 8:1068 –1071)

Hemidiaphragmatic paralysis is the most frequent complication associated with cryoballoon ablation for atrial fibrillation. To date, no preventive strategy has proved effective.We sought to assess the feasibility of diaphragmatic electromyography during cryoballoon ablation, explore the relationship between altered signals and phrenic nerve palsy, and define characteristic changes that herald hemidiaphragmatic paralysis.Cryoballoon ablation was performed in the right superior pulmonary vein or superior vena cava in 16 mongrel dogs weighing 37.7 ± 2.4 kg, at sites determined by phrenic nerve capture. During ablation, the phrenic nerve was paced at 60 bpm from the superior vena cava while recording diaphragmatic compound motor action potentials (CMAPs) by esophageal decapolar catheters. Diaphragmatic excursion was monitored by fluoroscopy and abdominal palpation.Before ablation, the CMAP amplitude was 592 (interquartile range 504, 566) μV, initial latency 21.5 ± 4.2 ms, peak latency 64.7 ± 21.1 ms, and duration 101.7 ± 13.3 ms. Hemidiaphragmatic paralysis was obtained in all dogs 62 ± 34 seconds into the cryoapplication. The CMAP amplitude decreased exponentially, with no patterned changes in latencies and duration. Discriminatory analyses by receiver-operating curve characteristics identified a 30% reduction in CMAP amplitude as the most predictive cutoff value for hemidiaphragmatic paralysis (c-statistic 0.965; P.0001). This criterion presaged diaphragmatic paralysis, as detected by abdominal palpation, by 31 ± 23 seconds.Diaphragmatic electromyographic signals could be reliably recorded during cryoballoon ablation. An exponential decrease in CMAP amplitude precedes diaphragmatic paralysis, with a 30% reduction yielding the best discriminatory potential. A promising safety margin was detected, which merits prospective validation.

There are many similarities between atrial effects of atrial tachycardia remodeling (ATR) and vagal nerve stimulation (VS): both promote atrial fibrillation (AF), reduce atrial effective refractory period (AERP) and AERP rate accommodation, enhance AERP heterogeneity, and increase inward-rectifier K+ current.This study sought to compare the consequences of ATR and VS at similar levels of AERP abbreviation in dogs.ATR dogs (n = 6) were subjected to 7-day atrial tachypacing at 400 beats/min, with radiofrequency-induced atrioventricular block and ventricular demand pacing (80 beats/min) to control ventricular response. VS was applied in 6 matched dogs with stimulation parameters selected to produce similar mean AERP values to ATR dogs.ATR and VS produced similarly short AERPs (79 +/- 12 and 80 +/- 12 ms, respectively), AERP rate-adaptation loss, and AERP heterogeneity increases. Although both ATR and VS increased AF duration, VS was significantly more effective in AF promotion, with mean AF duration of 992 +/- 134 seconds, versus 440 +/- 240 seconds (P.05) under ATR. The greater AF-promoting effect of VS was associated with greater mean dominant frequency values during AF (11.7 +/- 1.8 versus 10.0 +/- 1.3 Hz ATR, P.05). VS greatly enhanced the spatial dominant frequency variability, increasing the coefficient of variation to 15.2 +/- 1.9 Hz, versus 8.9 +/- 1.5 Hz for ATR (P.05), primarily by increasing the per-dog maximum dominant frequency (15.4 +/- 0.6 Hz versus 12.5 +/- 0.6 for ATR, P.01).For matched AERP values, VS promotes AF more strongly than ATR. Despite similar AERP changes, VS produces considerably greater increases in dominant frequencies, particularly maximum values, consistent with previous suggestions that inward-rectifier K+ current enhancement is particularly effective at accelerating and stabilizing spiral wave rotors that maintain AF.

Background Cryoablation is increasingly used to treat atrioventricular nodal reentrant tachycardia (AVNRT). It is unknown whether larger electrode-tip cryocatheters improve outcomes without compromising safety. Objective This study sought to compare acute and long-term success with 4-mm versus 6-mm electrode-tip cryocatheters for AVNRT. Methods We conducted a 2-group cohort study on 289 patients, age 45.5 ± 15.9 years (76.8% female), who underwent transcatheter cryoablation as a first-time procedure for AVNRT with 4-mm (N = 152) or 6-mm (N = 137) electrode-tip catheters. Results Acute procedural success was achieved in 90.7% (95% confidence interval 86.9% to 93.7%) with no difference between the 2 electrode-tip sizes. A shorter fluoroscopy time (16.1 ± 11.3 versus 20.3 ± 14.9 minutes, P = .0096) and trend toward briefer procedural duration (166.6 ± 49.1 versus 173.5 ± 53.0 minutes, P = NS) were noted with 6-mm electrode tips. Transient AV block occurred in 5.2%, with complete recovery in 4.4 ± 2.6 seconds. Over a median follow-up of 155 days, recurrences were less common with 6-mm electrode tips. Actuarial event-free survival rates at 1, 3, 6, and 12 months with 6-mm versus 4-mm electrode-tip cryocatheters were 96.7%, 93.4%, 91.9%, and 88.5% versus 89.9%, 87.0%, 84.1%, and 77.1%, respectively, with no recurrence thereafter (P = .0457). In multivariate analyses adjusting for baseline imbalances and medical therapy postablation, cryoablation with a 4-mm-tip catheter incurred a 2.5-fold increased risk of recurrence (hazard ratio 2.5, 95% confidence interval 1.0 to 6.1, P = .0420). Conclusion In patients with AVNRT, cryoablation with 6-mm electrode-tip catheters is safe and is associated with fewer recurrences on long-term follow-up compared with 4-mm electrode-tip cryocatheters.

Background The impact of revascularization on recurrent ventricular arrhythmias (VAs) in patients with coronary artery disease and relatively preserved left ventricular ejection fraction (LVEF) is unknown. Objective The purpose of this study was to determine the impact of revascularization on recurrent VAs or death. Methods A cohort study was conducted on consecutive patients with prior myocardial infarction and LVEF ≥40% presenting with a first clinical sustained VA in the absence of an acute coronary syndrome. The impact of revascularization on recurrent VAs and all-cause mortality was assessed. Results A total of 274 patients (mean age 66.1 ± 9.7 years, 85.4% male, mean LVEF 48.3% ± 7.2%) were included in the study. Eight-eight patients (32.1%) underwent coronary revascularization. During mean follow-up of 6.2 ± 5.1 years, 140 (51.1%) died or had recurrent sustained VAs or appropriate implantable-cardioverter defibrillator therapy. Revascularization was not associated with a significantly lower rate of recurrent VAs or death (multivariable hazard ratio [HR] 0.86, 95% confidence interval [CI] 0.60–1.24, P = .43) regardless of whether it was complete or incomplete (HR 0.65, 95% CI 0.25–1.69, P = .37) or was performed by percutaneous or surgical means (HR 1.02, 95% CI 0.53–1.94, P = .96). An implantable-cardioverter defibrillator was associated with a significant reduction in mortality (HR 0.23, 95% CI 0.09–0.55, P = .001). Conclusion Patients with prior myocardial infarction and LVEF ≥40% who present with sustained VAs in the absence of an acute coronary syndrome remain at high risk for recurrent VAs and all-cause death. Coronary revascularization does not systemically mitigate this risk.

An elevated resting heart rate has been associated with adverse cardiovascular outcomes. Its prognostic value has not specifically been examined in patients with atrial fibrillation.The purpose of this study was to assess the relationship between resting heart rate measured in sinus rhythm and in atrial fibrillation and subsequent hospitalizations and death.An analysis of individual patient-level data from subjects enrolled in the AFFIRM and AF-CHF trials was conducted to determine the impact of resting heart rate on hospitalizations and mortality. Separate analyses were performed in atrial fibrillation and sinus rhythm. A total of 7159 baseline ECGs (4848 in atrial fibrillation, 2311 in sinus rhythm) were analyzed in 5164 patients (34.8% female, age 68.2 ± 8.3 years).During mean follow-up of 40.8 ± 16.3 months, 1016 patients died (668 cardiovascular deaths), and 3150 required at least 1 hospitalization (2215 cardiovascular). An elevated baseline heart rate in sinus rhythm was associated with increased all-cause mortality [hazard ratio (HR) 1.24 per 10 bpm increase, 95% confidence interval (CI) 1.14-1.36, P.0001]. In contrast, a baseline heart rate in atrial fibrillation was not associated with mortality. However, compared to heart rates 90-114 bpm in atrial fibrillation, a heart rate114 bpm was independently associated with all-cause (HR 1.18, 95% CI 1.06-1.31, P = .0018) and cardiovascular (HR 1.25, 95% CI 1.10-1.42, P = .0005) hospitalizations.In patients with a history of atrial fibrillation, an elevated baseline heart rate in sinus rhythm is independently associated with mortality. In contrast, the baseline heart rate in atrial fibrillation is not associated with mortality but predicts hospitalizations.

Background Atrial fibrillation (AF) recurrence after pulmonary vein isolation (PVI) is associated with PV to left atrium reconduction. Effective lesion creation necessitates adequate contact force between the ablation catheter and myocardium. Objective The purpose of this study was to study the utility of contact force–guided ablation on immediate and long-term outcomes. Methods Seventy-five patients with highly symptomatic paroxysmal AF underwent wide circumferential PVI using an irrigated-tip radiofrequency catheter. In 25 patients, ablation was guided by real-time contact force measurements (CF group; SmartTouch, Biosense Webster). A control group of 50 patients underwent PVI using a standard nonforce sensing catheter (standard group; ThermoCool, Biosense Webster). After PVI, all patients underwent adenosine testing to unmask dormant conduction. Patients were followed up at 3, 6, and 12 months and by transtelephonic monitoring as well. Results Dormant conduction was unmasked and subsequently eliminated in 4 PV pairs (8%; 16% of patients) in the CF group and 35 PV pairs (35%; 52% of patients) in the standard group ( P = .0004 per PV pair; P = .0029 per patient). The single-procedure, off–antiarrhythmic drug freedom from recurrent atrial arrhythmias at 1 year was 88% in the CF group vs 66% in the standard group ( P = .047). Procedure duration and fluoroscopy time were significantly longer in the CF group ( P = .0038 and P = .0001, respectively). Conclusion The use of real-time contact force guidance results in a significant reduction in the prevalence of dormant conduction with improved long-term freedom from recurrent arrhythmias. The utility of a contact force–guided approach requires evaluation in a long-term prospective randomized study.

c A Introduction Focal radiofrequency (RF) ablation guided by 3-dimesnional (3D) mapping systems has shown considerable success in treating paroxysmal and persistent atrial fibrillation (AF). Unfortunately, the procedure remains complex, timeonsuming, and highly dependent on operator competency. ultielectrode catheters were developed to address technial difficulties. The pulmonary vein (PV) ablation catheter PVAC, Medtronic Ablation Frontiers, Carlsbad, CA) is a F deflectable circular multielectrode catheter that enables apping and circumferential PV ablation. For persistent F, 2 additional catheters, that is, the multiarray septal atheter (MASC) and the multiarray ablation catheter MAAC), were developed to facilitate left atrial mapping nd substrate modification. The accompanying GENius ultichannel, duty-cycled RF generator (Medtronic Ablaion Frontiers) enables the delivery of energy in a unipolar r bipolar configuration to all electrodes simultaneously or ndividually. During an RF application, energy delivery to ndividual electrodes is temperature controlled by a softare algorithm that modulates power to reach the userefined target temperature (maximum 8 W per electrode ith the PVAC in a 4:1 power setting or 10 W in all other ettings). Our objective was to systematically review the

Background Defibrillation threshold (DFT) testing has traditionally been a routine part of implantable cardioverter-defibrillator (ICD) implantation, despite a lack of compelling evidence that it predicts or improves outcomes. In the past, when devices were much less reliable, DFT testing seemed prudent; however, modern ICD systems have such a high rate of successful defibrillation that many electrophysiologists now question whether DFT testing is still worthwhile, particularly since DFT testing may now be the highest acute risk component of ICD implantation. Objective The purpose of this study was to systematically document complications directly attributable to intraoperative DFT testing. Methods We obtained data on DFT-related complications from all 21 adult ICD implant centers in Canada, covering the period from January 1, 2000, to September 30, 2006. Results There were a total of 19,067 ICD implants in Canada during the study period. There were three DFT testing–related deaths, five DFT testing–related strokes, and 27 episodes that required prolonged resuscitation. Two patients had significant clinical sequelae after prolonged resuscitation. Conclusions The risk of severe complications from intraoperative DFT testing appears small, even allowing for the underestimation of its true rate with the current study methodology. These slight but measurable risks must be considered when assessing the risk-benefit ratio of the procedure. Additional data from ongoing prospective ICD registries and/or clinical trials are required.