Relationship between sex, body size, and cardiac resynchronization therapy benefit: A patient-level meta-analysis of randomized controlled trials

BACKGROUND

Women might benefit more than men from cardiac resynchronization therapy (CRT) and do so at shorter QRS durations.

OBJECTIVE

This meta-analysis was performed to determine whether sex-based differences in CRT effects are better accounted for by height, body surface area (BSA), or left ventricular end-diastolic dimension (LVEDD).

METHODS

We analyzed patient-level data from CRT trials (MIRACLE, MIRACLE ICD, MIRACLE ICD II, REVERSE, RAFT, COMPANION, and MADIT-CRT) using bayesian hierarchical Weibull regression models. Relationships between QRS duration and CRT effects were examined overall and in sex-stratified cohorts; additional analyses indexed QRS duration by height, BSA, or LVEDD. End points were heart failure hospitalization (HFH) or death and all-cause mortality.

RESULTS

Compared with men (n = 5628), women (n = 1439) were shorter (1.62 [interquartile range, 1.57-1.65] m vs 1.75 [1.70-1.80] m; P < .001), with smaller BSAs (1.76 [1.62-1.90] m2 vs 2.02 [1.89-2.16] m2; P < .001). In adjusted sex-stratified analyses, the reduction in HFH or death was greater for women (hazard ratio, 0.54; credible interval, 0.42-0.70) than for men (hazard ratio, 0.77; credible interval, 0.66-0.89; Pinteraction = .009); results were similar for all-cause mortality even after adjustment for height, BSA, and LVEDD. Sex-specific differences were observed only in nonischemic cardiomyopathy. The effect of CRT on HFH or death was observed at a shorter QRS duration for women (126 ms) than for men (145 ms). Indexing QRS duration by height, BSA, or LVEDD attenuated sex-specific QRS duration thresholds for the effects of CRT on HFH or death but not on mortality.

CONCLUSION

Although body size partially explains sex-specific QRS duration thresholds for CRT benefit, it is not associated with the magnitude of CRT benefit. Indexing QRS duration for body size might improve selection of patients for CRT, particularly with a "borderline" QRS duration.

CLINICALTRIALS

GOV REGISTRATION

NCT00271154, NCT00251251, NCT00267098, NCT00180271.

Benefit of cardiac resynchronization therapy among older patients: A patient-level meta-analysis

BACKGROUND

Cardiac resynchronization therapy (CRT) reduces heart failure hospitalizations (HFH) and mortality for guideline-indicated patients with heart failure (HF). Most patients with HF are aged ≥70 years but such patients are often under-represented in randomized trials.

METHODS

Patient-level data were combined from 8 randomized trials published 2002-2013 comparing CRT to no CRT (n = 6,369). The effect of CRT was estimated using an adjusted Bayesian survival model. Using age as a categorical (<70 vs ≥70 years) or continuous variable, the interaction between age and CRT on the composite end point of HFH or all-cause mortality or all-cause mortality alone was assessed.

RESULTS

The median age was 67 years with 2436 (38%) being 70+; 1,554 (24%) were women; 2,586 (41%) had nonischemic cardiomyopathy and median QRS duration was 160 ms. Overall, CRT was associated with a delay in time to the composite end point (adjusted hazard ratio [aHR] 0.75, 95% credible interval [CI] 0.66-0.85, P = .002) and all-cause mortality alone (aHR of 0.80, 95% CI 0.69-0.96, P = .017). When age was treated as a categorical variable, there was no interaction between age and the effect of CRT for either end point (P > .1). When age was treated as a continuous variable, older patients appeared to obtain greater benefit with CRT for the composite end point (P for interaction = .027) with a similar but nonsignificant trend for mortality (P for interaction = .35).

CONCLUSION

Reductions in HFH and mortality with CRT are as great or greater in appropriately indicated older patients. Age should not be a limiting factor for the provision of CRT.

Cardiac Resynchronization Therapy Improves Outcomes in Patients With Intraventricular Conduction Delay But Not Right Bundle Branch Block: A Patient-Level Meta-Analysis of Randomized Controlled Trials

BACKGROUND

Benefit from cardiac resynchronization therapy (CRT) varies by QRS characteristics; individual randomized trials are underpowered to assess benefit for relatively small subgroups.

METHODS

The authors analyzed patient-level data from pivotal CRT trials (MIRACLE [Multicenter InSync Randomized Clinical Evaluation], MIRACLE-ICD [Multicenter InSync ICD Randomized Clinical Evaluation], MIRACLE-ICD II [Multicenter InSync ICD Randomized Clinical Evaluation II], REVERSE [Resynchronization Reverses Remodeling in Systolic Left Ventricular Dysfunction], RAFT [Resynchronization-Defibrillation for Ambulatory Heart Failure], BLOCK-HF [Biventricular Versus Right Ventricular Pacing in Heart Failure Patients with Atrioventricular Block], COMPANION [Comparison of Medical Therapy, Pacing and Defibrillation in Heart Failure], and MADIT-CRT [Multicenter Automatic Defibrillator Implantation Trial - Cardiac Resynchronization Therapy]) using Bayesian Hierarchical Weibull survival regression models to assess CRT benefit by QRS morphology (left bundle branch block [LBBB], n=4549; right bundle branch block [RBBB], n=691; and intraventricular conduction delay [IVCD], n=1024) and duration (with 150-ms partition). The continuous relationship between QRS duration and CRT benefit was also examined within subgroups defined by QRS morphology. The primary end point was time to heart failure hospitalization (HFH) or death; a secondary end point was time to all-cause death.

RESULTS

Of 6264 patients included, 25% were women, the median age was 66 [interquartile range, 58 to 73] years, and 61% received CRT (with or without an implantable cardioverter defibrillator). CRT was associated with an overall lower risk of HFH or death (hazard ratio [HR], 0.73 [credible interval (CrI), 0.65 to 0.84]), and in subgroups of patients with QRS ≥150 ms and either LBBB (HR, 0.56 [CrI, 0.48 to 0.66]) or IVCD (HR, 0.59 [CrI, 0.39 to 0.89]), but not RBBB (HR 0.97 [CrI, 0.68 to 1.34]; Pinteraction <0.001). No significant association for CRT with HFH or death was observed when QRS was <150 ms (regardless of QRS morphology) or in the presence of RBBB. Similar relationships were observed for all-cause death.

CONCLUSIONS

CRT is associated with reduced HFH or death in patients with QRS ≥150 ms and LBBB or IVCD, but not for those with RBBB. Aggregating RBBB and IVCD into a single "non-LBBB" category when selecting patients for CRT should be reconsidered.

REGISTRATION

URL: https://www.

CLINICALTRIALS

gov; Unique identifiers: NCT00271154, NCT00251251, NCT00267098, and NCT00180271.

Evaluating Polygenic Risk Scores in "Lone" Atrial Fibrillation

Background

Polygenic scores incorporating varying numbers of single nucleotide polymorphisms (SNPs) have been demonstrated to exert a prominent role in atrial fibrillation (AF). We sought to compare the relative discriminatory capacities of 2 previously validated polygenic scores in "lone" AF.

Methods

A total of 186 lone AF cases of European ancestry underwent SNP genotyping. A genome-wide polygenic score (GPS) and polygenic risk score (PRS) involving 6,730,541 and 1168 SNPs, respectively, were calculated for 186 cases and 423 controls of European ancestry from the 1000 Genomes (1KG) Project. The distribution of the polygenic scores was compared between the cases and controls and their discriminatory capacities were evaluated using receiver operating characteristic (ROC) curves.

Results

A total of 34.4% of patients with lone AF had GPS scores greater than the top 10th percentile of 1KG controls, corresponding to a 4.64-fold increased odds (95% confidence interval [CI], 2.99-7.18; P < 0.001) for AF. A PRS score in the top 10th percentile of 1KG controls was observed in 26.3% of cases, which equated to a 3.16-fold increased odds (95% CI, 2.01-4.98; P < 0.001) for AF. Comparison of C-statistics from ROC curves indicated improved discriminatory capacity of the GPS (0.76) relative to the PRS (0.70) (P = 0.002).

Conclusions

Our study evaluating 2 polygenic scores for AF suggests that the GPS, containing more than 6.7 million SNPs, exhibits an improved discriminatory capacity in lone AF compared with a PRS possessing 1168 SNPs. Our findings suggest that genetic risk scores for AF that maximally leverage genomic data may provide improved predictive power.

A simple maneuver to determine if septal accessory pathway ablation requires a left atrial approach

INTRODUCTION

Septal accessory pathway (AP) ablation can be challenging due to the complex anatomy of the septal region. The decision to access the left atrium (LA) is often made after failure of ablation from the right. We sought to establish whether the difference between ventriculo-atrial (VA) time during right ventricular (RV) apical pacing versus the VA during tachycardia would help establish the successful site for ablation of septal APs.

METHODS

Intracardiac electrograms of patients with orthodromic reciprocating tachycardia (ORT) using a septal AP with successful catheter ablation were reviewed. The ∆VA was the difference between the VA interval during RV apical pacing and the VA interval during ORT. The difference in the VA interval during right ventricular entrainment and ORT (StimA-VA) was also measured.

RESULTS

The median ∆VA time was significantly less in patients with a septal AP ablated on the right side compared with patients with a septal AP ablated on the left side (12 ± 19 vs. 56 ± 10 ms, p < .001). The StimA-VA was significantly different between the two groups (22 ± 14 vs. 53 ± 9 ms, p < .001). The ∆VA and StimA-VA were always ≤ 40 ms in patients with non-decremental septal APs ablated from the right side and always greater than 40 ms in those with septal APs ablated from the left.

CONCLUSION

ΔVA and StimA-VA values identified with RV apical pacing in the setting of ORT involving a septal AP predict when left atrial access will be necessary for successful ablation.

An International Multicenter Evaluation of Inheritance Patterns, Arrhythmic Risks, and Underlying Mechanisms of CASQ2-Catecholaminergic Polymorphic Ventricular Tachycardia

BACKGROUND

Genetic variants in calsequestrin-2 (CASQ2) cause an autosomal recessive form of catecholaminergic polymorphic ventricular tachycardia (CPVT), although isolated reports have identified arrhythmic phenotypes among heterozygotes. Improved insight into the inheritance patterns, arrhythmic risks, and molecular mechanisms of CASQ2-CPVT was sought through an international multicenter collaboration.

METHODS

Genotype-phenotype segregation in CASQ2-CPVT families was assessed, and the impact of genotype on arrhythmic risk was evaluated using Cox regression models. Putative dominant CASQ2 missense variants and the established recessive CASQ2-p.R33Q variant were evaluated using oligomerization assays and their locations mapped to a recent CASQ2 filament structure.

RESULTS

A total of 112 individuals, including 36 CPVT probands (24 homozygotes/compound heterozygotes and 12 heterozygotes) and 76 family members possessing at least 1 presumed pathogenic CASQ2 variant, were identified. Among CASQ2 homozygotes and compound heterozygotes, clinical penetrance was 97.1% and 26 of 34 (76.5%) individuals had experienced a potentially fatal arrhythmic event with a median age of onset of 7 years (95% CI, 6-11). Fifty-one of 66 CASQ2 heterozygous family members had undergone clinical evaluation, and 17 of 51 (33.3%) met diagnostic criteria for CPVT. Relative to CASQ2 heterozygotes, CASQ2 homozygote/compound heterozygote genotype status in probands was associated with a 3.2-fold (95% CI, 1.3-8.0; P=0.013) increased hazard of a composite of cardiac syncope, aborted cardiac arrest, and sudden cardiac death, but a 38.8-fold (95% CI, 5.6-269.1; P<0.001) increased hazard in genotype-positive family members. In vitro turbidity assays revealed that p.R33Q and all 6 candidate dominant CASQ2 missense variants evaluated exhibited filamentation defects, but only p.R33Q convincingly failed to dimerize. Structural analysis revealed that 3 of these 6 putative dominant negative missense variants localized to an electronegative pocket considered critical for back-to-back binding of dimers.

CONCLUSIONS

This international multicenter study of CASQ2-CPVT redefines its heritability and confirms that pathogenic heterozygous CASQ2 variants may manifest with a CPVT phenotype, indicating a need to clinically screen these individuals. A dominant mode of inheritance appears intrinsic to certain missense variants because of their location and function within the CASQ2 filament structure.

Prediction of heart failure hospitalizations based on the direct measurement of intrathoracic impedance

Aims

OptiVol fluid index was developed as a transthoracic impedance‐based indicator of short‐term risk for heart failure hospitalization (HFH). OptiVol is calculated as the accumulating difference between daily impedance (measured impedance) and long‐term average impedance (reference impedance). Measured impedance alone was thought to have limited prognostic utility; however, measured impedance has the advantage of being simple, direct, and possibly additive to OptiVol fluid index in establishing long‐term HFH risk. We tested the hypothesis that directly measured impedance has independent prognostic value in predicting long‐term HFH risk and that changes in measured impedance result in a change in predicted long‐term HFH risk.

Methods and results

A retrospective analysis of 1719 patients studied in PARTNERS‐HF, FAST, and RAFT studies was performed. Baseline measured impedance was determined using daily values averaged over 1 month, from Month 6 to 7 post implant; change in measured impedance was determined from values averaged over 1 month, from Month 7 to 8 post implant compared with baseline. The predictive value of baseline measured impedance for HFHs was assessed beginning 7 months post implant. The predictive value of a change in measured impedance for a change in HFHs was assessed beginning 8 months post implant. Baseline measured impedance successfully predicted HFHs. For example, 3 year HFH rate for low baseline impedance < 70 Ω was 23%; for high baseline impedance ≥ 70 Ω was 15% (P < 0.001). Changes in measured impedance resulted in changes in predicted HFHs. For example, when a baseline impedance of ≥70 fell during follow‐up to <70 Ω, the subsequent HFHs were 15% compared with 4% in patients with measured impedance that remained >70 Ω (P = 0.004). In addition, when baseline measured impedance fell during follow‐up by >1%, 2%, or 3%, subsequent HFHs increased to 13%, 17%, or 18%, respectively. Finally, the prognostic value of measured impedance was additive to the prognostic value of the OptiVol fluid index.

Conclusions

Direct measurements of intrathoracic impedance using an implanted device can be used to stratify patients at varying risk of long‐term HFH. These direct measurements of impedance have practical clinical appeal because they are simple, continuous, and ambulatory.

Compared to CPAP extubation to non-invasive ventilation is associated with higher risk of bronchopulmonary dysplasia in extremely low birth weight infants

OBJECTIVE

While non-invasive ventilation (NIV) has been associated with improved extubation rates, its impact on bronchopulmonary dysplasia (BPD) remains unclear.

METHOD

In this retrospective, chart review study of infants admitted to the Cleveland Clinic, we aimed to compare the incidence of BPD among extremely low birth weight (ELBW) infants extubated to continuous positive pressure (CPAP) versus those extubated to NIV via RAM cannula or biphasic CPAP. Data collected included demographics, ventilatory modes, extubation data, and presence of complications. Infants extubated to either CPAP or NIV were compared using Wilcoxon rank- sum and Chi-square tests, and data were corrected using logistic regression models. Data are presented as medians.

RESULTS

A total of 120 infants were included, of whom 62% were extubated to NIV. The incidence of BPD was significantly lower in the CPAP group vs NIV (57% vs. 78%, p = 0.011). Infants in the CPAP group were heavier (birth weight (BWT) of 833 vs 724 grams, p = 0.005), more mature (gestation age (GA) 27 vs 25 weeks, p <  0.001) and were extubated significantly earlier (2 vs 8 days, p <  0.001). After adjusting for BWT and GA, NIV continued to be significantly associated with higher incidence of BPD among those extubated on the first day of life (odds ratio 5.9; 95% CI: 1.2-29.1, p = 0.029).

CONCLUSION

This study concludes that, as compared to CPAP, early use of NIV is associated with higher risk of BPD in ELBW infants. Further investigation using prospective studies is recommended to validate these findings.

Incremental Value of Implantable Cardiac Device Diagnostic Variables Over Clinical Parameters to Predict Mortality in Patients With Mild to Moderate Heart Failure

Background

Heart failure remains a leading cause of morbidity and mortality. Clinical prediction models provide suboptimal estimates of mortality in this population. We sought to determine the incremental value of implantable device diagnostics over clinical prediction models for mortality.

Methods and Results

RAFT (Resynchronization/Defibrillation for Ambulatory Heart Failure Trial) patients with implanted devices capable of device diagnostic monitoring were included, and demographic and clinical parameters were used to compute Meta‐Analysis Global Group in Chronic Heart Failure (MAGGIC) heart failure risk scores. Patients were classified according to MAGGIC score into low (0–16), intermediate (17–24), or high (>24) risk groups. Mortality was evaluated from 6 months postimplant in accordance with the RAFT protocol. In a subset of 1036 patients, multivariable analysis revealed that intermediate and high MAGGIC scores, fluid index, atrial fibrillation, and low activity flags were independent predictors of mortality. A device‐integrated diagnostic parameter that included a fluid index flag and either a positive atrial fibrillation flag or a positive activity flag was able to significantly differentiate higher from lower risk for mortality in the intermediate MAGGIC cohort. The effect was more pronounced in the high‐risk MAGGIC cohort, in which device‐integrated diagnostic–positive patients had a shorter time to death than those who were device‐integrated diagnostic negative.

Conclusions

Device diagnostics using a combination of fluid index trends, atrial fibrillation burden, and patient activity provide significant incremental prognostic value over clinical heart failure prediction scores in higher‐risk patients. This suggests that combining clinical and device diagnostic parameters may lead to models with better predictive power. Whether this risk is modifiable with early medical intervention would warrant further studies.

Clinical Trial Registration

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00251251.

Ankyrin-B dysfunction predisposes to arrhythmogenic cardiomyopathy and is amenable to therapy

Arrhythmogenic cardiomyopathy (ACM) is an inherited arrhythmia syndrome characterized by severe structural and electrical cardiac phenotypes, including myocardial fibrofatty replacement and sudden cardiac death. Clinical management of ACM is largely palliative, owing to an absence of therapies that target its underlying pathophysiology, which stems partially from our limited insight into the condition. Following identification of deceased ACM probands possessing ANK2 rare variants and evidence of ankyrin-B loss of function on cardiac tissue analysis, an ANK2 mouse model was found to develop dramatic structural abnormalities reflective of human ACM, including biventricular dilation, reduced ejection fraction, cardiac fibrosis, and premature death. Desmosomal structure and function appeared preserved in diseased human and murine specimens in the presence of markedly abnormal β-catenin expression and patterning, leading to identification of a previously unknown interaction between ankyrin-B and β-catenin. A pharmacological activator of the WNT/β-catenin pathway, SB-216763, successfully prevented and partially reversed the murine ACM phenotypes. Our findings introduce what we believe to be a new pathway for ACM, a role of ankyrin-B in cardiac structure and signaling, a molecular link between ankyrin-B and β-catenin, and evidence for targeted activation of the WNT/β-catenin pathway as a potential treatment for this disease.

Cardiac resynchronization is pro-arrhythmic in the absence of reverse ventricular remodelling: a systematic review and meta-analysis

Aims

Cardiac resynchronization therapy (CRT) has been shown to reduce mortality and heart failure (HF) hospitalization but its effects on the rate of ventricular arrhythmias (VAs) appears to be neutral. We hypothesize that CRT with LV epicardial stimulation is inherently pro-arrhythmic and increases VA rates in the absence of reverse ventricular remodelling while conferring an anti-arrhythmic effect in mechanical responders.

Methods and results

In this systematic review and meta-analysis, we considered retrospective cohort, prospective cohort, and randomized controlled trials comparing VA rates between cardiac resynchronization therapy-defibrillator (CRT-D) non-responders, CRT-D responders and those with implantable cardioverter-defibrillator (ICD) only. Studies were eligible if they defined CRT-D responders using a discrete left ventricular volumetric value as assessed by any imaging modality. Studies were identified through searching electronic databases from their inception to July 2017. We identified 2579 citations, of which 23 full-text articles were eligible for final analysis. Our results demonstrated that CRT-D responders were less likely to experience VA than CRT-D non-responders, relative risk (RR) 0.49 [95% confidence interval (CI) 0.41-0.58, P < 0.01] and also less than patients with ICD only: RR 0.59 (95% CI 0.50-0.69, P < 0.01). However, CRT-D mechanical non-responders had a greater likelihood of VA compared with ICD only, RR 0.76 (95% CI 0.63-0.92, P = 0.004).

Conclusion

CRT-D non-responders experienced more VA than CRT-D responders and also more than those with ICD only, suggesting that CRT with LV epicardial stimulation may be inherently pro-arrhythmic in the absence of reverse remodelling.

Effect of coronary revascularization on long-term clinical outcomes in patients with ischemic cardiomyopathy and recurrent ventricular arrhythmia

BACKGROUND

Patients with ventricular tachycardia (VT) postmyocardial infarction (MI) are a higher risk group with significant morbidity and mortality. We examined the impact of prior coronary revascularization on clinical outcomes in patients with ischemic cardiomyopathy and VT.

METHODS

The VANISH trial randomized 259 patients with prior MI and antiarrhythmic drug-refractory VT to receive escalated medical therapy or catheter ablation. Clinical outcomes were compared according to whether patients have undergone prior revascularization procedures. The primary outcome was a composite of death, appropriate implantable cardiac defibrillator (ICD) shock, or VT storm. The secondary outcomes included elements of the primary outcome, hospitalization, and any ventricular arrhythmia.

RESULTS

190 patients (73%) had prior coronary revascularization. Revascularization group had more men (97% vs 83%; P  =  0.0003) and patients in that group were older (mean age 69.3 ± 7.6 vs 66.7 ± 9.2; P  =  0.04), had more renal insufficiency (22.6% vs 8.7%; P  =  0.01), and were more likely to have an implanted cardiac resynchronization device (23% vs 10%, P  =  0.03) as compared with the nonrevascularized patients. There were no significant differences in baseline medication use. There was a trend toward fewer hospitalizations in the revascularization group (64% vs 77%; P  =  0.07); there were no differences in the individual outcomes of mortality, VT storm, ICD shocks, recurrent MI, or cardiac failure.

CONCLUSIONS

In this cohort of patients with an ischemic cause for VT, a history of prior coronary revascularization was not associated with a reduction in ventricular arrhythmia or mortality.

Clinically Significant Pocket Hematoma Increases Long-Term Risk of Device Infection: BRUISE CONTROL INFECTION Study

BACKGROUND

The BRUISE CONTROL trial (Bridge or Continue Coumadin for Device Surgery Randomized Controlled Trial) demonstrated that a strategy of continued warfarin during cardiac implantable electronic device surgery was safe and reduced the incidence of clinically significant pocket hematoma (CSH). CSH was defined as a post-procedure hematoma requiring further surgery and/or resulting in prolongation of hospitalization of at least 24 h, and/or requiring interruption of anticoagulation. Previous studies have inconsistently associated hematoma with the subsequent development of device infection; reasons include the retrospective nature of many studies, lack of endpoint adjudication, and differing subjective definitions of hematoma.

OBJECTIVES

The BRUISE CONTROL INFECTION (Bridge or Continue Coumadin for Device Surgery Randomized Controlled Trial Extended Follow-Up for Infection) prospectively examined the association between CSH and subsequent device infection.

METHODS

The study included 659 patients with a primary outcome of device-related infection requiring hospitalization, defined as 1 or more of the following: pocket infection; endocarditis; and bloodstream infection. Outcomes were verified by a blinded adjudication committee. Multivariable analysis was performed to identify predictors of infection.

RESULTS

The overall 1-year device-related infection rate was 2.4% (16 of 659). Infection occurred in 11% of patients (7 of 66) with previous CSH and in 1.5% (9 of 593) without CSH. CSH was the only independent predictor and was associated with a >7-fold increased risk of infection (hazard ratio: 7.7; 95% confidence interval: 2.9 to 20.5; p < 0.0001). Empiric antibiotics upon development of hematoma did not reduce long-term infection risk.

CONCLUSIONS

CSH is associated with a significantly increased risk of infection requiring hospitalization within 1 year following cardiac implantable electronic device surgery. Strategies aimed at reducing hematomas may decrease the long-term risk of infection. (Bridge or Continue Coumadin for Device Surgery Randomized Controlled Trial [BRUISE CONTROL]; NCT00800137).

Canadian Cardiovascular Society guidelines on the use of cardiac resynchronization therapy: implementation

Recent studies have provided the impetus to update the recommendations for cardiac resynchronization therapy (CRT). This article provides guidance on the implementation of CRT and is intended to serve as a framework for the implementation of CRT within the Canadian health care system and beyond. These guidelines were developed through a critical evaluation of the existing literature, and expert consensus. The panel unanimously adopted each recommendation. The 9 recommendations relate to patient selection in the presence of comorbidities, delivery and optimization of CRT, and resources required to deliver this therapy. The strength of evidence was weighed, taking full consideration of any risk of bias, and any imprecision, inconsistency, and indirectness of the available data. The strength of each recommendation and the quality of evidence were adjudicated. Trade-offs between desirable and undesirable consequences of alternative management strategies were considered, as were values, preferences, and resource availability. These guidelines were externally reviewed by experts, modified based on those reviews, and will be updated as new knowledge is acquired.

Pacemaker or defibrillator surgery without interruption of anticoagulation

BACKGROUND

Many patients requiring pacemaker or implantable cardioverter-defibrillator (ICD) surgery are taking warfarin. For patients at high risk for thromboembolic events, guidelines recommend bridging therapy with heparin; however, case series suggest that it may be safe to perform surgery without interrupting warfarin treatment. There have been few results from clinical trials to support the safety and efficacy of this approach.

METHODS

We randomly assigned patients with an annual risk of thromboembolic events of 5% or more to continued warfarin treatment or to bridging therapy with heparin. The primary outcome was clinically significant device-pocket hematoma, which was defined as device-pocket hematoma that necessitated prolonged hospitalization, interruption of anticoagulation therapy, or further surgery (e.g., hematoma evacuation).

RESULTS

The data and safety monitoring board recommended termination of the trial after the second prespecified interim analysis. Clinically significant device-pocket hematoma occurred in 12 of 343 patients (3.5%) in the continued-warfarin group, as compared with 54 of 338 (16.0%) in the heparin-bridging group (relative risk, 0.19; 95% confidence interval, 0.10 to 0.36; P<0.001). Major surgical and thromboembolic complications were rare and did not differ significantly between the study groups. They included one episode of cardiac tamponade and one myocardial infarction in the heparin-bridging group and one stroke and one transient ischemic attack in the continued-warfarin group.

CONCLUSIONS

As compared with bridging therapy with heparin, a strategy of continued warfarin treatment at the time of pacemaker or ICD surgery markedly reduced the incidence of clinically significant device-pocket hematoma. (Funded by the Canadian Institutes of Health Research and the Ministry of Health and Long-Term Care of Ontario; BRUISE CONTROL ClinicalTrials.gov number, NCT00800137.).

Reduced septal glucose metabolism predicts response to cardiac resynchronization therapy

BACKGROUND

Up to 50% of patients do not respond to Cardiac Resynchronization Therapy (CRT). Recent work has focused on quantifying mechanical dyssynchrony and left ventricular scar. Septal reverse-mismatch (R-MM) (reduced FDG uptake vs perfusion) has been observed in patients with cardiomyopathy and prolonged QRS duration. We hypothesized that a greater quantity of septal R-MM would indicate a greater potential for reversibility of the cardiomyopathy, when the dyssynchrony is improved with CRT. Therefore, this study's objective was to assess whether greater septal R-MM pattern predicts response to CRT.

METHODS AND RESULTS

Forty-nine patients had pre-implant Rubidium-82 and Fluorine-18-fluorodeoxyglucose PET scanning. Total and regional left ventricular scar size and extent of R-MM were calculated. Response to CRT was defined as ≥10% improvement in left ventricular end-systolic volume or ≥5% absolute ejection fraction improvement. In the non-ischemic cardiomyopathy subset non-responders had significantly less septal R-MM than responders (13.1% compared to 27.1%, P = .012). There were correlations between the extent of septal R-MM and the increase in ejection fraction (r = 0.692, P = .0004) and reduction in left ventricular end-systolic volume (r = -0.579, P = .004). For each 5% absolute increase in extent of septal R-MM the odds ratio of being a responder was 2.17 (95% CI 1.15, 4.11, P = .017). Extent of septal R-MM displayed high sensitivity and specificity (area under curve = 0.855, P = .017) to predict response.

CONCLUSIONS

In patients with non-ischemic cardiomyopathy, greater extent of septal glucose metabolic R-MM pattern, predicted response to CRT. This parameter may be useful for identifying patients who benefit from CRT.

Successful ablation of a concealed parahisian accessory pathway using a remote magnetic navigation system following failure by conventional methods

OBJECTIVE

Using conventional catheters, ablation of concealed parahisian accessory pathways may be difficult and high risk for heart block.

METHODS AND RESULTS

We describe the case of a concealed parahisian accessory pathway with three prior attempts to ablate using conventional methods (RF and cryotherapy). Using a remote magnetic navigation system, successful ablation occurred following a single RF lesion (total fluoroscopy time 17 min). In contrast to previous attempts, the patient remained asymptomatic during follow-up (12 months).

CONCLUSIONS

This is the first report of successful remote magnetic catheter ablation of a concealed parahisian AP. Magnetic catheter stability during RF application likely contributed to the success of this procedure and may have minimized the risk of AV block.

Appropriate Result from an Inappropriate ICD Shock

A case of inappropriate detection of an ungrounded external AC current by an implantable cardioverter defibrillator (ICD) is reported. The resultant ICD shock dislodged the patient from the electrical source, thus preventing injury or electrocution.

Canadian Cardiovascular Society/Canadian Heart Rhythm Society position paper on implantable cardioverter defibrillator use in Canada

The Canadian Heart Rhythm Society in conjunction with the Canadian Cardiovascular Society is committed to the promotion of evidence-based practice in Canada. Since the last Canadian guidelines on the management of sudden cardiac death were published in 2000, several well-conducted clinical trials evaluating the implantable cardioverter defibrillator have been completed and published. The Canadian Cardiovascular Society Council has granted permission to review and update guidelines for the indications for implantable cardioverter defibrillators. Furthermore, data are emerging on the potential benefits of biventricular pacing therapy (cardiac resynchronization) for heart failure; recommendations for the use of this therapy have been included in the present paper. Ethical considerations and the economic implications of these recommendations are also included. Canada's heart rhythm specialists, represented by the Canadian Heart Rhythm Society, have been joined by two heart failure specialists, a medical ethicist and an economist, to develop the present position paper. Members of the Canadian Heart Rhythm Society participated in the discussion of these recommendations in open forum meetings and by electronic communication.

Vasopressin versus epinephrine for inhospital cardiac arrest: a randomised controlled trial

BACKGROUND

Survival rates for cardiac arrest patients, both in and out of hospital, are poor. Results of a previous study suggest better outcomes for patients treated with vasopressin than for those given epinephrine, in the out-of-hospital setting. Our aim was to compare the effectiveness and safety of these drugs for the treatment of in-patient cardiac arrest.

METHODS

We did a triple-blind randomised trial in the emergency departments, critical care units, and wards of three Canadian teaching hospitals. We assigned adults who had cardiac arrest and required drug therapy to receive one dose of vasopressin 40 U or epinephrine 1 mg intravenously, as the initial vasopressor. Patients who failed to respond to the study intervention were given epinephrine as a rescue medication. The primary outcomes were survival to hospital discharge, survival to 1 h, and neurological function. Preplanned subgroup assessments included patients with myocardial ischaemia or infarction, initial cardiac rhythm, and age.

FINDINGS

We assigned 104 patients to vasopressin and 96 to epinephrine. For patients receiving vasopressin or epinephrine survival did not differ for hospital discharge (12 [12%] vs 13 [14%], respectively; p50.67; 95% CI for absolute increase in survival 211.8% to 7.8%) or for 1 h survival (40 [39%] vs 34 [35%]; p50.66; 210.9% to 17.0%); survivors had closely similar median mini-mental state examination scores (36 [range 19-38] vs 35 [20-40]; p50.75) and median cerebral performance category scores (1 vs 1).

INTERPRETATION

We failed to detect any survival advantage for vasopressin over epinephrine. We cannot recommend the routine use of vasopressin for inhospital cardiac arrest patients, and disagree with American Heart Association guidelines, which recommend vasopressin as alternative therapy for cardiac arrest.

Relationship between pacemaker dependency and the effect of pacing mode on cardiovascular outcomes

BACKGROUND

A recently completed trial, the Canadian Trial of Physiological Pacing (CTOPP), showed that physiological pacing did not significantly reduce mortality, stroke, or heart failure hospitalization, but it did show that atrial fibrillation occurred less frequently in patients with physiological pacing. Many pacemaker patients experience only transient bradyarrhythmias with an adequate unpaced heart rate (UHR) and are not pacemaker-dependent. The purpose of the present analysis was to determine if pacemaker-dependent patients have an increased benefit from physiological pacing compared with non-pacemaker-dependent patients.

METHODS AND RESULTS

Of 2568 patients included in the CTOPP trial, 2244 patients had a pacemaker dependency test performed at the first follow-up visit. The yearly event rate of cardiovascular death or stroke steadily increased with decreasing UHR in the ventricular pacing group, but it remained constant in the physiological pacing group. When the patients were subdivided to UHR </=60 bpm or >60 bpm, there was an interaction between pacing mode treatment and UHR subgroup. The Kaplan-Meier plot confirmed a physiological pacing advantage only in the UHR </=60 bpm subgroup. This differential effect was also present for the outcomes of cardiovascular death and total mortality.

CONCLUSIONS

This study demonstrated that UHR at first follow-up has an important influence on how pacing mode selection affects cardiovascular death and total mortality. Pacemaker-dependent patients with low UHR will probably be paced frequently and will likely benefit from physiological pacing. In contrast, non-pacemaker-dependent patients will likely be paced infrequently and may not benefit from physiological pacing.

Identification of a gene responsible for familial Wolff-Parkinson-White syndrome

BACKGROUND

The Wolff-Parkinson-White syndrome, with a prevalence in Western countries of 1.5 to 3.1 per 1000 persons, causes considerable morbidity and may cause sudden death. We identified two families in which the Wolff-Parkinson-White syndrome segregated as an autosomal dominant disorder.

METHODS

We studied 70 members of the two families (57 in Family 1 and 13 in Family 2). The subjects underwent 12-lead electrocardiography and two-dimensional echocardiography. Genotyping mapped the gene responsible to 7q34-q36, a locus previously identified to be responsible for an inherited form of Wolff-Parkinson-White syndrome. Candidate genes were identified, sequenced, and analyzed in normal and affected family members to identify the disease-causing gene.

RESULTS

A total of 31 members (23 from Family 1 and 8 from Family 2) had the Wolff-Parkinson-White syndrome. Affected members of both families had ventricular preexcitation with conduction abnormalities and cardiac hypertrophy. The maximal combined two-point lod score was 9.82 at a distance of 5 cM from marker D7S636, which confirmed the linkage of the gene in both families to 7q34-q36. Haplotype analysis indicated that there were no alleles in common in the two families at this locus, suggesting that the two families do not have a common founder. We identified a missense mutation in the gene that encodes the gamma2 regulatory subunit of AMP-activated protein kinase (PRKAG2). The mutation results in the substitution of glutamine for arginine at residue 302 in the protein.

CONCLUSIONS

The identification of this genetic defect has important implications for elucidating the pathogenesis of ventricular preexcitation. Further understanding of how this molecular defect leads to supraventricular arrhythmias could influence the development of specific therapies for other forms of supraventricular arrhythmia.

Dynamic changes of QT interval and QT dispersion in non-Q-wave and Q-wave myocardial infarction

QT interval and QT dispersion both prolong early postinfarction. Non-Q wave (NQMI) and Q-wave myocardial infarction (QMI) differ in the extent of transmural necrosis, which may influence these measures of myocardial repolarization. This study compared dynamic changes in QT interval and QT dispersion early postinfarction between NQMI and QMI. In 40 patients with NQMI and 69 patients with QMI, maximum QTc (QTc(max)) and QT dispersion (QTD) were measured during the first 4 days postinfarction. Infarct size was assessed daily by using the Selvester QRS score. In both infarct types, QTc(max) and QTD were prolonged on day 1 of infarction, peaking over the next 2 days before returning toward baseline by day 4. NQMI patients had significantly longer QTc(max) and QTD by days 2 to 3 when compared with QMI patients. Multivariable linear regression identified "infarct type x QRS score" as the only independent predictor of QTc(max) (R(2) =.32, P <.0001) and QTD (R(2) =.19, P <.0001) on day 2. In conclusion, dynamic changes of QTc(max) and QTD occur in both infarct types. Large NQMI is associated with greater prolongation of QTc(max) and QTD, which may be due to greater M cell uncoupling and exposure when compared with QMI.

Circadian variation of paroxysmal atrial fibrillation. PA3 Investigators. Atrial Pacing Peri-ablation for Prevention of Atrial Fibrillation Trial

The circadian variation of paroxysmal atrial fibrillation (AF) was studied in 67 patients who received a dual-chamber pacemaker 3 months before a planned atrioventricular node ablation. A distinct circadian variation of AF was observed with 2 time peaks in initiation (1 in the early morning and 1 in the early evening hours), which was modulated by atrial pacing, the duration of AF, and the use of beta-adrenergic blocking agents.

Permanent pacing from a left ventricular vein in a patient with persistent left and absent right superior vena cava

Persistent left superior vena cava with coexisting absent right superior vena cava is rare with less than 150 cases in the literature. Various techniques for pacemaker implantation have been described in this situation. We report a 40-year-old man with sinus and atrioventricular nodal dysfunction who underwent dual chamber pacemaker implantation. We elected to implant the ventricular electrode down a left ventricular branch of the coronary sinus and the lead is stable at 4-month follow-up.

Interatrial conduction of atrial tachycardia in heart transplant recipients: potential pathophysiology

Surgical suture lines formed at the site of anastamosis have been considered to be electrically inert and thus present a line of block to conduction. However, a number of reports have suggested that conduction is occasionally possible across suture lines. Most of these cases have reported conduction between donor and recipient atria following cardiac transplantation. We report an illustrative case successfully treated with radiofrequency ablation, and present pathology findings that may give insight into the pathophysiology.

Effects of physiologic pacing versus ventricular pacing on the risk of stroke and death due to cardiovascular causes. Canadian Trial of Physiologic Pacing Investigators

BACKGROUND

Evidence suggests that physiologic pacing (dual-chamber or atrial) may be superior to single-chamber (ventricular) pacing because it is associated with lower risks of atrial fibrillation, stroke, and death. These benefits have not been evaluated in a large, randomized, controlled trial.

METHODS

At 32 Canadian centers, patients without chronic atrial fibrillation who were scheduled for a first implantation of a pacemaker to treat symptomatic bradycardia were eligible for enrollment. We randomly assigned patients to receive either a ventricular pacemaker or a physiologic pacemaker and followed them for an average of three years. The primary outcome was stroke or death due to cardiovascular causes. Secondary outcomes were death from any cause, atrial fibrillation, and hospitalization for heart failure.

RESULTS

A total of 1474 patients were randomly assigned to receive a ventricular pacemaker and 1094 to receive a physiologic pacemaker. The annual rate of stroke or death due to cardiovascular causes was 5.5 percent with ventricular pacing, as compared with 4.9 percent with physiologic pacing (reduction in relative risk, 9.4 percent; 95 percent confidence interval, -10.5 to 25.7 percent [the negative value indicates an increase in risk]; P=0.33). The annual rate of atrial fibrillation was significantly lower among the patients in the physiologic-pacing group (5.3 percent) than among those in the ventricular-pacing group (6.6 percent), for a reduction in relative risk of 18.0 percent (95 percent confidence interval, 0.3 to 32.6 percent; P=0.05). The effect on the rate of atrial fibrillation was not apparent until two years after implantation. The observed annual rates of death from all causes and of hospitalization for heart failure were lower among the patients with a physiologic pacemaker than among those with a ventricular pacemaker, but not significantly so (annual rates of death, 6.6 percent with ventricular pacing and 6.3 percent with physiologic pacing; annual rates of hospitalization for heart failure, 3.5 percent and 3.1 percent, respectively). There were significantly more perioperative complications with physiologic pacing than with ventricular pacing (9.0 percent vs. 3.8 percent, P<0.001).

CONCLUSIONS

Physiologic pacing provides little benefit over ventricular pacing for the prevention of stroke or death due to cardiovascular causes.

Radiofrequency ablation of atrial tachycardia originating from the triangle of Koch

Atrial tachycardia (AT) originating in the triangle of Koch is reported rarely and presents a potential risk of atrioventricular (AV) block during radiofrequency (RF) catheter ablation. Eight patients with AT in the triangle of Koch undergoing RF ablation are presented. There were five women and three men, ranging in age from 32 to 74 years. One patient had bicuspid aortic valve disease, and the other seven patients had no structural heart disease. At electrophysiological study, AT was inducible in all eight patients. In one patient, AV nodal re-entrant tachycardia was also inducible. The site of AT was located by recording the earliest atrial activation during AT and successful RF ablation. Fluoroscopy confirmed the corresponding site to the region of the triangle of Koch. The earliest atrial activation was 35+/-9 ms before the surface P wave, and was recorded at the apex of the triangle of Koch near the bundle of His in six patients and midway between the bundle of His and coronary sinus os in two patients. At the successful RF application site, His potential was not recorded in any patient. The mean AV ratio was 5:1 (range 1:1 to 12:1). RF ablation at the successful site resulted in accelerated junctional rhythm in four of the eight patients and successfully terminated AT in all eight patients, with first-degree AV block in one patient. In conclusion, AT from the triangle of Koch is a distinct entity and RF ablation can be successfully performed; however, a potential risk of AV block remains.

Dofetilide enhances shock-induced extension of refractoriness and lowers defibrillation threshold

OBJECTIVE

To explore the hypothesis that class III antiarrhythmics reduce defibrillation threshold (DFT) by prolonging postshock refractoriness.

ANIMALS AND METHODS

The effect of a new selective potassium channel blocker, dofetilide (DOFlow 2.5 micrograms/kg bolus plus 0.9 microgram/kg/h; DOFmed 10 micrograms/kg bolus plus 3.6 micrograms/kg/h; and DOFhigh 25 micrograms/kg bolus plus 9 micrograms/kg/h), on DFT was compared with that of placebo in anesthetized open chest dogs (n = 6 per group). The effects of dofetilide on refractory period extension (RPE) were assessed by using DFT strength shocks delivered at various stages of repolarization.

RESULTS

DFT was significantly decreased in the DOFhigh group, whether expressed as shock peak voltage or energy (P < 0.05 compared with changes in placebo). At baseline, a shock timing of ventricular effective refractory period of 25 ms resulted in RPE of 100 +/- 24 ms, 80 +/- 11 ms, 91 +/- 14 ms and 90 +/- 20 ms in the placebo, DOFlow, DOFmed, and DOFhigh groups, respectively. After infusion, these RPE values were unchanged in the placebo group but tended to increase in the dofetilide treatment groups. DOFhigh significantly increased RPE by 20 +/- 18 ms (P < 0.05 compared with baseline values and changes in placebo). Dofetilide-induced changes in RPE and DFT were significantly correlated when expressed as voltage (r2 = 0.78, P < 0.01), current (r2 = 0.80, P < 0.01) and energy (r2 = 0.53, P < 0.01).

CONCLUSIONS

These results show that dofetilide prolonged RPE at a plasma level that reduced DFT, thus providing support for the hypothesis that selective prolongation of refractoriness may synergize with shock-induced RPE to decrease the energy requirements for defibrillation.

Ventriculophasic modulation of atrioventricular nodal conduction in humans

BACKGROUND

Baroreceptor-mediated phasic changes in vagal tone have been hypothesized to cause ventriculophasic sinus arrhythmia (VPSA). The objectives of this study were to demonstrate ventriculophasic modulation of AV nodal conduction and to substantiate the role of the baroreflex on ventriculophasic AV nodal conduction (VPAVN) by pharmacological perturbation of parasympathetic tone.

METHODS AND RESULTS

Twelve patients with infra-Hisian second-degree heart block and VPSA were studied. Incremental atrial pacing was performed until AV nodal Wenckebach block at baseline, after phenylephrine infusion, and after atropine. AV nodal conduction curves were constructed for each phase and compared. At baseline, VPAVN was present in 9 of 12 patients on the steep portion of the AV nodal conduction curves. Phenylephrine increased systolic blood pressure from 149+/-33 to 177+/-22 mmHg (P<0.001) and sinus cycle length from 844+/-169 to 1010+/-190 ms (P<0.001) and shifted the AV nodal conduction curves up and to the right. Phenylephrine induced VPAVN in 2 of 3 patients in whom it was not present at baseline and in 11 of 12 total. Atropine abolished both VPSA and VPAVN in all patients.

CONCLUSIONS

VPAVN was demonstrated in patients with infra-Hisian second-degree AV block. It was accentuated by phenylephrine and abolished by atropine, suggesting a baroreflex mechanism for VPSA and VPAVN.

Safety and feasibility of same day discharge in patients undergoing radiofrequency catheter ablation

We retrospectively analyzed outcomes of radiofrequency catheter ablation in patients who were discharged the same day and compared them with patients staying overnight. For most tachyarrhythmias, it is safe and feasible to discharge patients undergoing radiofrequency ablation on the same day.