A.D. Krahn

Evaluation of Early Complications Related to De Novo Cardioverter Defibrillator Implantation : Insights From the Ontario ICD Database

OBJECTIVES This study examined the predictors of early complications after defibrillator implantation. BACKGROUND Although implantable cardioverter-defibrillators are widely used, predictors of procedural complications and the consequences of these events have not been determined. METHODS In a prospective, multicenter, population-based clinical outcomes registry of all newly implanted defibrillator patients at 18 centers in Ontario, Canada, we examined 45-day complications and all-cause mortality from February 2007 to May 2009. Complications were determined longitudinally and were categorized as direct implant-related or indirect events. RESULTS Among 3,340 patients (mean age 63.8 +/- 12.5 years, 78.5% men), major complications occurred in 4.1% of de novo procedures. Compared with those undergoing a single-chamber device, implantation of a cardiac resynchronization defibrillator (adjusted hazard ratio [HR]: 2.17, 95% confidence interval [CI]: 1.38 to 3.43, p < 0.001) or dual-chamber device (adjusted HR: 1.82, 95% CI: 1.19 to 2.79, p = 0.006) was associated with increased risk of major complications. Major complications were increased in women (adjusted HR: 1.49, 95% CI: 1.02 to 2.16, p = 0.037) and when left ventricular end-systolic dimension exceeded 45 mm (adjusted HR: 1.54, 95% CI: 1.08 to 2.20, p = 0.018). Major complications (excluding death) occurring early after defibrillator implantation were associated with increased adjusted risk of subsequent death up to 180 days after defibrillator implant (adjusted HR: 3.70, 95% CI: 1.64 to 8.33, p = 0.002). Direct implant-related complications were associated with increased risk of early death (adjusted HR: 24.89, p = 0.01), whereas indirect clinical complications conferred increased risk of near-term death (adjusted HR: 12.35, p < 0.001) after defibrillator implantation. CONCLUSIONS Complications after de novo defibrillator implantation were strongly associated with device type. Major complications were associated with increased risk of mortality.

Complications associated with defibrillation threshold testing: The Canadian experience

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.

Recommendations for the use of genetic testing in the clinical evaluation of inherited cardiac arrhythmias associated with sudden cardiac death: Canadian Cardiovascular Society/Canadian Heart Rhythm Society joint position paper.

The era of gene discovery and molecular medicine has had a significant impact on clinical practice. Knowledge of specific genetic findings causative for or associated with human disease may enhance diagnostic accuracy and influence treatment decisions. In cardiovascular disease, gene discovery for inherited arrhythmia syndromes has advanced most rapidly. The arrhythmia specialist is often confronted with the challenge of diagnosing and managing genetic arrhythmia syndromes. There is now a clear need for guidelines on the appropriate use of genetic testing for the most common genetic conditions associated with a risk of sudden cardiac death. This document represents the first ever published recommendations outlining the role of genetic testing in various clinical scenarios, the specific genes to be considered for testing, and the utility of test results in the management of patients and their families.

Differential ventricular entrainment: A maneuver to differentiate AV node reentrant tachycardia from orthodromic reciprocating tachycardia

BACKGROUND Distinguishing atrioventricular node reentry (AVNRT) from orthodromic reentrant tachycardia (ORT) utilizing an accessory pathway (AP) can sometimes be challenging. A pacing maneuver that reliably distinguishes between the two would be of value. OBJECTIVE This study sought to assess the utility of differential entrainment for the diagnosis of supraventricular tachycardia. METHODS Consecutive patients underwent prospective electrophysiological study of regular paroxysmal supraventricular tachycardia. Overdrive pacing with entrainment of tachycardia from each of the right ventricular apex and right ventricular base was performed. The post-pacing interval (PPI), PPI minus the tachycardia cycle length and corrected for AV node decrement (cPPI-TCL), and the ventriculoatrial (VA) interval (last RV pacing stimulus to last entrained high right atrial signal) were calculated at each site. RESULTS Entrainment at both RV sites was achieved in 35 patients, 16 with typical AVNRT, 1 with atypical AVNRT, and 18 with ORT (13 left free wall, 3 right free wall, and 2 septal APs). The cPPI-TCL and VA intervals were significantly longer from base than apex in AVNRT (cPPI-TCL 61 ms longer, VA 38 ms longer, both P < .0001). There was no significant difference in differential entrainment intervals in patients with ORT. A differential cPPI-TCL >30 ms or VA interval >20 ms identified patients with AVNRT with a positive predictive value, negative predictive value, sensitivity, and specificity of 100%. CONCLUSION Differential ventricular entrainment is a useful tool for diagnosing between AVNRT and ORT. A differential cPPI-TCL >30 ms or VA interval of >20 ms reliably predicts AVNRT.

Design and implementation of a population-based registry of implantable cardioverter defibrillators (ICDs) in Ontario

BACKGROUND There are scarce population-based data on the use, complication rates, and outcomes of patients receiving implantable cardioverter defibrillators (ICDs). OBJECTIVE This study sought to describe the methodology of the Ontario ICD Database, a prospective study of all ICD recipients in Ontario, Canada. METHODS In this registry, web-based data collection will be performed in all patients referred to a cardiac electrophysiologist for consideration of an ICD. The variables included in the database were determined by consensus. Outcomes to be assessed will include defibrillator device therapies (e.g., shock or antitachycardia pacing), morbidity, and death. Preliminary statistics are reported after the first 6 months of data collection. RESULTS Of 208 total variables selected by consensus, 111 (53.4%) were referral/patient characteristics, 12 (5.8%) were implant-related, and 85 (40.9%) were outcome variables. Among 990 referred patients, 902 were accepted, with the following ICD indications: primary prevention (63.3%), secondary prevention (21.6%), and generator replacement (15.1%). The mean (SD) age of patients with implants was 63.9 +/- 12.6 years, and 79% were men. Among accepted ICD patients, 66% had ischemic heart disease, 23% had nonischemic dilated cardiomyopathy, and 11% had other cardiac conditions. Left ventricular (LV) systolic dysfunction was highly prevalent, with 82% of primary and 44% of secondary prevention patients having LV ejection fraction <or=30%. The perioperative complication rate was 3.69%. CONCLUSION The Ontario ICD Database will examine defibrillator patient characteristics and clinical and device-related outcomes. Contemporary ICDs are implanted largely for primary prevention, and the majority of these conformed with LV ejection fraction guidelines.

Atrial Response to Ventricular Antitachycardia Pacing Discriminates Mechanism of 1:1 Atrioventricular Tachycardia

Background: Inappropriate shocks from implantable cardioverter defibrillators (ICD) remain a significant clinical problem despite device discrimination algorithms. The atrial response to antitachycardia pacing (ATP) may determine the mechanism of 1:1 A:V tachycardia.

Rate-control versus conversion strategy in postoperative atrial fibrillation: trial design and pilot study results.

Atrial fibrillation (AF) remains a frequent complication of cardiac surgery. The optimal treatment strategy has not been established. Retrospective studies have suggested that a primary rate-control strategy may be equivalent to a strategy that restores sinus rhythm. Fifty patients with postoperative atrial fibrillation were randomly assigned to a strategy of antiarrhythmic therapy +/- electrical cardioversion or ventricular rate control. Anticoagulation with heparin overlapped with coumadin was administered to both arms. The primary endpoint of the study was time to conversion to sinus rhythm analyzed by the Kaplan-Meier method. The effects of strategy on hospital length of stay was examined as well as the incidence of recurrent AF. This study demonstrated no significant difference between an antiarrhythmic conversion strategy (n = 27) and a rate-control strategy (n = 23) in time to conversion to sinus rhythm (11.2 +/- 3.2 vs. 11.8 +/- 3.9 hours; p = 0.8). With Cox multivariate analysis to control for the effects of age, sex, beta-blocker usage, and type of surgery, the conversion strategy showed a trend toward reducing the time from treatment to restoration of sinus rhythm (p = 0.08). The length of hospital stay was reduced in the antiarrhythmic arm compared with the rate-control strategy (9.0 +/- 0.7 vs. 13.2 +/- 2.0 days; p = 0.05). In hospital relapse rates in the antiarrhythmic arm were 30% compared with 57% in the rate-control strategy (p = 0.24). At the termination of the study, 91% of the patients in the rate-control arm were in sinus rhythm compared with 96% in the antiarrhythmic arm. In conclusion, this pilot study shows little difference between a rate-control strategy and a strategy to restore/maintain sinus rhythm. Regardless of the strategy, majority of patients will be in sinus rhythm after two months. A larger randomized, controlled study is needed to assess the impact of restoration of sinus rhythm on length of stay.

When should we recommend catheter ablation for patients with the Wolff-Parkinson-White syndrome?

Purpose of review Catheter ablation has been proven as very effective and safe therapy for patients with symptomatic Wolff–Parkinson–White (WPW) syndrome. Its application in asymptomatic individuals with WPW pattern remains controversial. This review will elaborate on the role of catheter ablation in symptomatic and asymptomatic patients with WPW pattern on ECG. Recent findings Several recent prospective studies evaluated invasive risk stratification followed by prophylactic catheter ablation in asymptomatic patients with WPW pattern. Inducibility of arrhythmias in these patients during invasive electrophysiological study was shown to predict the development of future symptomatic arrhythmias. Although ablation of accessory pathways performed in ‘inducible’ patients decreased the incidence of subsequent symptomatic arrhythmias, the studies were not powered to detect a reduction in life-threatening arrhythmias. Summary Radiofrequency catheter ablation remains the first-line therapy for patients with symptomatic WPW syndrome. Invasive electrophysiological study and possible ablation of accessory pathway may be offered to well informed asymptomatic individuals with WPW if they are willing to trade the very small risk of subsequent sudden death or incapacity for a small immediate procedural risk of serious complications or death. Asymptomatic patients may require invasive risk stratification and possible catheter ablation for important social or professional reasons.

Acute Testing of the Rate‐Smoothed Pacing Algorithm for Ventricular Rate Stabilization

We evaluated the capability of a new pacemaker‐based rate‐smoothing algorithm (RSA) to reduce the irregular ventricular response of AF. RSA prevents sudden decreases in rate using a modified physiological band and flywheel feature. Twelve patients (51 ± 21 years) with hemodynamically tolerated AF of 4 months to 20 years duration were studied. Atrial and ventricular leads were connected to the external pacemaker device in the electrophysiology laboratory. Consecutive RR intervals during AF were measured at baseline and after ventricular pacing with RSA ON. Ventricular pacing with the rate smoothing algorithm reduced maximum RR intervals (1,207 ± 299 vs 855 ± 148 ms, P = 0.0005), with no significant change in the minimum RR interval (401 ± 55 vs 393 ± 74 ms, P = 0.292). A small shortening of the mean RR interval (634 ± 153 vs 594 ± 135 ms, P = 0.007) was seen with no change in the median RR interval (609 ± 153 vs 595 ± 143 ms, P = 0.388). There was a 43% reduction in RR standard deviation (145 ± 52 vs 82 ± 28, P = 0.0005), 49% reduction in mean absolute RR interval difference (MAD) (152 ± 64 vs 77 ± 34, P = 0.0005) and MAD/mean RR ratio (0.23 ± 0.05 vs 0.13 ± 0.04, P = 0.0005). We conclude that rate‐smoothed pacing effectively reduces RR variability of AF in the acute setting.

Noninvasive Assessment of Atrial Substrate Change after Wide Area Circumferential Ablation: A Comparison with Segmental Pulmonary Vein Isolation

Background: The wide area circumferential ablation (WACA) approach to atrial fibrillation is thought to result in ‘substrate modification’ perhaps related to autonomic denervation. We examined this prospectively by comparing WACA and segmental pulmonary vein isolation (PVI) using noninvasive surrogate markers.