Identifying and Managing Premature Ventricular Contraction-Induced Cardiomyopathy: What, Why, and How?

Premature ventricular contraction (PVC)-induced cardiomyopathy is increasingly being recognized as a reversible cause of left ventricular (LV) systolic dysfunction (LVSD). The diagnosis of PVC-induced cardiomyopathy is considered in subjects with high PVC burdens (> 10,000 per 24 hours) after excluding other known causes of LVSD. PVC suppression is the mainstay of the management of PVC-induced cardiomyopathy, in addition to proven evidence-based medical therapy recommended for subjects with LVSD. Management strategies for PVC-induced cardiomyopathy include medical therapy and/or catheter ablation, with an increasing role for catheter ablation as a first-line therapy in view of the potential for permanent suppression of PVCs. Recovery of LVSD is typically a gradual process over months after effective suppression of PVCs. Last, asymptomatic patients with high PVC burdens and preserved LV systolic function appear to be at low risk over the intermediate term for developing LVSD. However, it is prudent to monitor LV function periodically because of the potential for deterioration of LV function observed during long-term follow-up in some subjects.

Outcome of Apparently Unexplained Cardiac Arrest: Results From Investigation and Follow-Up of the Prospective Cardiac Arrest Survivors With Preserved Ejection Fraction Registry

BACKGROUND

The Cardiac Arrest Survivors with Preserved Ejection Fraction Registry (CASPER) enrolls patients with apparently unexplained cardiac arrest and no evident cardiac disease to identify the pathogenesis of cardiac arrest through systematic clinical testing. Exercise testing, drug provocation, advanced cardiac imaging, and genetic testing may be useful when a cause is not apparent.

METHODS AND RESULTS

The first 200 survivors of unexplained cardiac arrest from 14 centers across Canada were evaluated to determine the results of investigation and follow-up (age, 48.6±14.7 years, 41% female). Patients were free of evidence of coronary artery disease, left ventricular dysfunction, or evident repolarization syndromes. Advanced testing determined a diagnosis in 34% of patients at baseline, with a diagnosis emerging during follow-up in 7% of patients. Of those who were diagnosed, 28 (35%) had an underlying structural condition and 53 (65%) had a primary electric disease. During a mean follow-up of 3.15±2.34 years, 23% of patients had either a shock or an appropriate antitachycardia pacing from their implantable cardioverter defibrillator, or both. The implantable cardioverter defibrillator appropriate intervention rate was 8.4% at 1 year and 18.1% at 3 years, with no clear difference between diagnosed and undiagnosed subjects, or between those diagnosed with a primary electric versus structural pathogenesis.

CONCLUSIONS

Obtaining a diagnosis in previously unexplained cardiac arrest patients requires systematic clinical testing and regular follow-up to unmask the cause. Nearly half of apparently unexplained cardiac arrest patients ultimately received a diagnosis, allowing for improved treatment and family screening. A substantial proportion of patients received appropriate implantable cardioverter defibrillator therapy during medium-term follow-up.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00292032.

Strategy of continued vs interrupted novel oral anticoagulant at time of device surgery in patients with moderate to high risk of arterial thromboembolic events: The BRUISE CONTROL-2 trial

BACKGROUND

Patients who require perioperative anticoagulation during cardiac implantable electronic device surgery are at increased risk for bleeding complications. The BRUISE CONTROL trial demonstrated that continuing warfarin was safer than heparin bridging, reducing the incidence of clinically significant pocket hematoma. Novel oral anticoagulants are being increasingly prescribed in place of warfarin. The best perioperative management of these new anticoagulants is unknown.

METHODS/DESIGN

A randomized controlled trial to investigate whether a strategy of continued vs interrupted novel oral anticoagulant (dabigatran, rivaroxaban, or apixaban) at the time of device surgery, in patients with moderate to high risk of arterial thromboembolic events, reduces the incidence of clinically significant hematoma (defined as a hematoma requiring reoperation and/or resulting in prolongation of hospitalization, and/or requiring interruption of anticoagulation). The secondary outcomes include components of the primary outcome, composite of all other major perioperative bleeding events, thromboembolic events, all-cause mortality, cost-effectiveness, patient quality of life, perioperative pain, and satisfaction. Planned analyses include descriptive statistics of all baseline variables. For the primary outcome, interrupted vs continued novel oral anticoagulant arms will be compared using the χ(2) test. If any clinically significant differences are identified, a logistic regression analysis will be conducted. Quality of life will be assessed using EuroQol-5D, and perioperative pain using a visual analog scale.

DISCUSSION

BRUISE CONTROL-2 is a randomized trial evaluating the best strategy to manage novel oral anticoagulants at the time of device surgery. We hypothesize that device surgery can be performed safely without interruption of these medications.

Management of antithrombotic therapy during cardiac implantable device surgery

Anticoagulants are commonly used drugs that are frequently encountered during device placement. Deciding when to halt or continue the use of anticoagulants is a balance between the risks of thromboembolism versus bleeding. Patients taking warfarin with a high risk of thromboembolism should continue to take their warfarin without interruption during device placement while ensuring their international normalized ratio remains below 3. For patients who are taking warfarin and have low risk of thromboembolism, either interrupted or continued warfarin may be used, with no evidence to clearly support either strategy. There is little evidence to support continuing direct acting oral anticoagulants (DOACs) for device implantation. The timing of halting these medications depends largely on renal function. If bleeding occurs, warfarin׳s anticoagulation effect is reversible with vitamin K and activated prothrombin complex concentrate. There are no DOAC reversal agents currently available, but some are under development. Regarding antiplatelet agents, aspirin alone can be safely continued while clopidogrel alone may also be continued, but with a slightly higher bleeding risk. Dual antiplatelet therapy for bare-metal stent/drug-eluting stent implanted within 4 weeks/6 months, respectively, should be continued due to high risk of stent thrombosis; however, if they are implanted after this period, then clopidogrel can be halted 5 days before the procedure and resumed soon after, while aspirin is continued. If the patient is taking both aspirin and warfarin, aspirin should be halted 5 days prior to the procedure, while warfarin is continued.

High-intensity interval training improves cardiovascular health, exercise capacity, and quality of life in permanent atrial fibrillation: a case study

Persons with permanent atrial fibrillation experience reduced exercise tolerance, weight gain, and an associated decline in overall health. We report on a 74-year-old man with permanent atrial fibrillation who underwent a 10-week high-intensity interval training program. Substantial improvements in heart rate, blood pressure, aerobic and functional capacity, and quality of life were observed. These are desirable as these patients are not candidates for other treatment options and more effective therapies for the treatment of atrial fibrillation are needed.

Risk of pocket hematoma in patients on chronic anticoagulation with warfarin undergoing electrophysiological device implantation: a comparison of different peri-operative management strategies

OBJECTIVE

Periprocedural management of warfarin remains challenging in patients requiring electrophysiological device surgery. For patients at high risk of thromboembolic events, guidelines recommend bridging therapy with heparin; however, this strategy is associated with a high risk of pocket hematoma. This paper systematically reviews studies appraising the risk of pocket hematoma with different perioperative anticoagulation strategies.

METHODS

All relevant studies identified in MEDLINE/PubMed, The Cochrane Collaboration CENTRAL, clinicaltrials.org and in bibliographies of key articles. Estimates were combined using a fixed effects model. Heterogeneity was assessed by p values of χ2 statistics and I2. Publication bias was assessed by visual examination of funnel plots and by Egger test. Fifteen studies enrolling 5911 patients met all inclusion criteria and were included in this review.

RESULTS

Heparin bridging compared with no heparin was associated with increased risk of pocket hematoma (OR = 4.47, 95% CI 3.21-6.23, p < 0.00001), and prolonged hospital stay (9.13 ± 1.9 days vs. 5.11 ± 1 .39 days, p < 0.00001). Warfarin continuation was not associated with increased pocket hematoma compared to warfarin discontinuation (p = 0.38), but was associated with reduced risk of pocket hematoma compared with heparin bridging (OR = 0.37, 95% CI 0.2-0.69, p = 0.002). Thromboembolic complications were reduced with heparin bridging vs. no heparin (0.50% vs.1.07%, p = 0.02), and no significant differences were reported between heparin bridging vs. warfarin continuation (p = 0.83).

CONCLUSIONS

Heparin bridging is associated with a higher risk of pocket hematoma and a prolonged hospital stay. Perioperative continuation of warfarin reduces the occurrence of pocket hematoma compared with heparin bridging without any significant differences in thromboembolic complications.

Radiographic Predictors of Lead Conductor Fracture

Background—

Lead fracture is a limiting factor in high voltage lead durability. Fractures noted with the Medtronic Fidelis leads provide an opportunity to examine factors captured on implant chest x-ray that correlate with risk for lead conductor fracture. We evaluated contributory factors in a large population of fractures.

Methods and Results—

We conducted a retrospective case–control study at 8 Canadian centers that routinely capture anterior posterior and lateral chest x-rays within 2 weeks of implant. Cases were patients that experienced confirmed Medtronic Fidelis 6949 lead fracture based on standard definitions, matched one-to-one to controls for date of implant, sex, and age with normally functioning Fidelis leads from the same center. Select chart data and x-rays were collected for all patients. Radiographic measurements by ≥2 individuals per case/control were blinded to patient status. The data were analyzed using a time to failure multivariable Cox proportional hazards model with stratification for each matched pair. X-ray pairs from 111 fracture patients were compared with 111 controls (age 61.5±12.8 years, 75% male, 221 model 6949 leads). Six parameters included in the statistical analysis were significantly associated with risk of fracture, including slack/tortuosity measures, pulse generator and superior vena cava coil location, and angle of lead exit from the pocket.

Conclusions—

Pocket, intravascular and intracardiac lead characteristics on x-ray correlate with risk of lead conductor fracture. These observations may be useful to direct implant technique to optimize lead durability. Validation in larger populations and other lead models may inform the application of these results.

Incidence, predictors, and procedural results of upgrade to resynchronization therapy: the RAFT upgrade substudy

BACKGROUND

The resynchronization-defibrillation for ambulatory heart failure trial (RAFT) study demonstrated that adding cardiac resynchronization therapy (CRT) in selected patients requiring de novo implantable cardiac defibrillators (ICD) reduced mortality as compared with ICD therapy alone, despite an increase in procedure-related adverse events. Data are lacking regarding the management of patients with ICD therapy who develop an indication for CRT upgrade.

METHODS AND RESULTS

Participating RAFT centers provided data regarding de novo CRT-D (CRT with ICD) implant, upgrade to CRT-D during RAFT (study upgrade), and upgrade within 6 months after presentation of study results (substudy). Substudy centers enrolled 1346 (74.9%) patients in RAFT, including 644 de novo, 80 study upgrade, and 60 substudy CRT attempts. The success rate (initial plus repeat attempts) was 95.2% for de novo versus 96.3% for study upgrade and 90.0% for substudy CRT attempts (P=0.402). Acute complications occurred among 26.2% of de novo versus 18.8% of study upgrade and 3.4% of substudy CRT implantation attempts (P<0.001). The most common complication was left ventricular lead dislodgement. The principal reasons for not yet attempting upgrade in the substudy were patient preference (31.9%), New York Heart Association Class I (17.0%), and a QRS<150 ms (13.1%).

CONCLUSIONS

Among a broad group of implant physicians, CRT upgrades were performed in patients with an ICD in situ with no difference in implant success rate and a reduced acute complication rate as compared with a de novo CRT implant. Decisions to upgrade were influenced by predictors of benefit in subgroup analyses of the RAFT study and other trials.

Cardiac Resynchronization Therapy in a Patient with Persistent Left Superior Vena Cava Draining into the Coronary Sinus and Absent Innominate Vein: A Case Report and Review of Literature

Introduction

Persistent left superior vena cava (PLSVC) is a rare congenital anomaly of the superior venous system that may be discovered at the time of cardiac implantable electronic device (CIED) implantation.

Methods and Results

We present a subject who needed cardiac resynchronization therapy (CRT)-CIED implantation and was discovered to have PLSVC with absent innominate vein during the implant procedure. We were able to successfully implant a CRT-CIED using a right-sided approach via the right superior vena cava (SVC). We present a description of our implant technique and a brief review of the different aspects of CIED implantation in subjects with variants of PLSVC.

Conclusion

Superior venous anomalies such as PLSVC can make CIED implantation technically challenging. However, with increasing operator experience, cardiac imaging and appropriate tools successful CIED implantation is possible in almost all cases.

The Role Of Renin Angiotensin System In Atrial Fibrillation

Atrial fibrillation (AF) is the most prevalent arrhythmia and its incidence is on the rise. AF causes significant morbidity and mortality leading to rising AF-related health care costs. There is experimental and clinical evidence from animal and human studies that suggests a role for the renin angiotensin system (RAS) in the etiopathogenesis of AF. This review appraises the current understanding of RAS antagonism, using angiotensin converting enzyme inhibitors (ACE-I), angiotensin receptor blockers (ARB) and aldosterone antagonists (AA), for prevention of AF. RAS antagonism has proven to be effective for primary and secondary prevention of AF in subjects with heart failure and left ventricular (LV) dysfunction.However, most of the evidence for the protective effect of RAS antagonism is from clinical trials that had AF as a secondary outcome or from unspecified post-hoc analyses. The evidence for prevention in subjects without heart failure and with normal LV function is not as clear. RAS antagonism, in the absence of concomitant antiarrhythmic therapy, was not shown to reduce post cardioversion AF recurrences. RAS antagonism in subjects undergoing catheter ablation has also been ineffective in preventing AF recurrences.

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.

Evolution of clinical diagnosis in patients presenting with unexplained cardiac arrest or syncope due to polymorphic ventricular tachycardia

BACKGROUND

A systematic evaluation of patients with unexplained cardiac arrest (UCA) yields a diagnosis in 50% of the cases. However, evolution of clinical phenotype, identification of new disease-causing mutations, and description of new syndromes may revise the diagnosis.

OBJECTIVE

To assess the evolution in diagnosis among patients with initially UCA.

METHODS

Diagnoses were reviewed for all patients with UCA recruited from the Cardiac Arrest Survivors with Preserved Ejection Fraction Registry with at least 1 year of follow-up.

RESULTS

After comprehensive investigation of 68 patients (age 45.2 ± 14.9 years; 63% men), the initial diagnosis was as follows: idiopathic ventricular fibrillation (n = 34 [50%]), a primary arrhythmic disorder (n = 21 [31%]), and an occult structural cause (n = 13 [19%]). Patients were followed for 30 ± 17 months, during which time the diagnosis changed in 12 (18%) patients. A specific diagnosis emerged for 7 patients (21%) with an initial diagnosis of idiopathic ventricular fibrillation. A structural cardiomyopathy evolved in 2 patients with an initial diagnosis of primary electrical disorder, while the specific structural cardiomyopathy was revised for 1 patient. Two patients with an initial diagnosis of a primary arrhythmic disorder were subsequently considered to have a different primary arrhythmic disorder. A follow-up resting electrocardiogram was the test that most frequently changed the diagnosis (67% of the cases), followed by genetic testing (17%).

CONCLUSIONS

The reevaluation of patients presenting with UCA may lead to a change in diagnosis in up to 20%. This emphasizes the need to actively monitor the phenotype and also has implications for the treatment of these patients and the screening of their relatives.

Impact of QRS Morphology and Duration on Outcomes After Cardiac Resynchronization Therapy

Background—

The impact of QRS morphology and duration on the effectiveness of cardiac resynchronization therapy (CRT) has been usually assessed separately. The interaction between these 2 simple ECG parameters and their effect on CRT has not been systematically assessed in a large-scale clinical trial.

Methods and Results—

The Resynchronization–Defibrillation for Ambulatory Heart Failure Trial showed that implantable cardioverter defibrillator-CRT was associated with a significant reduction in the primary end point of all-cause mortality or heart failure hospitalization. For this substudy, we excluded patients in atrial fibrillation and those with a previous pacemaker. All baseline ECGs were reviewed by a panel of 3 experienced electrocardiographers. A total of 1483 patients were included in this study. Of these, 1175 had left bundle-branch block (LBBB) and 308 had non-LBBB. In patients with LBBB receiving implantable cardioverter defibrillator-CRT, there was a reduction in the primary outcome and in each individual component of the primary outcome. Furthermore, there was continuous relationship between QRS duration and extent of benefit. In patients with non-LBBB and QRS ≥160 ms, the hazard ratio for the primary outcome was 0.52 (0.29–0.96; P =0.033); in patients with QRS <160 ms, the hazard ratio was 1.38 (0.88–2.14; P =0.155).

Conclusions—

In patients with LBBB, there was a continuous relationship between broader QRS and greater benefit from implantable cardioverter defibrillator-CRT. However, our data do not support the use of implantable cardioverter defibrillator-CRT in patients with non-LBBB, especially when the QRS duration is <160 ms. There may be some delayed benefit when the QRS is ≥160 ms, but this needs further investigation.

Clinical Trial Registration—

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

Prevalence of cardiac sarcoidosis in patients presenting with monomorphic ventricular tachycardia

INTRODUCTION

Sarcoidosis is a granulomatous disease of unknown etiology, which involves the heart in 5-25% of cases. Although ventricular tachycardia (VT) has been reported as the first presentation of sarcoidosis, its prevalence has not previously been investigated. In this prospective study, we sought to systematically investigate the prevalence of cardiac sarcoidosis (CS) in patients presenting with monomorphic VT (MMVT) and no previous history of sarcoidosis.

METHODS

Consecutive patients presenting with MMVT to a tertiary care center were screened for inclusion. Patients with idiopathic VT, VT secondary to coronary artery disease, or prior diagnosis of sarcoidosis were excluded. Included patients underwent F-18-fluorodeoxyglucose positron emission tomography (PET) scan. In subjects with PET scanning suggestive of active myocardial inflammation, histological diagnosis was confirmed through extracardiac or endomyocardial biopsy (EMB).

RESULTS

A total of 182 patients presented to our institution with VT between February 2010 and September 2012 and 14 subjects met inclusion criteria. Within this group, six of 14 (42%) patients had abnormal PET scans suggesting active myocardial inflammation. Four of the six patients had tissue biopsies that were diagnostic of sarcoidosis; the remaining two patients had guided EMB indicating nonspecific myocarditis. Atrioventricular block was observed in three of four (75%) patients with CS and none in 10 of the others (P = 0.022). Three of the four patients had pulmonary sarcoidosis and one patient had isolated CS. All four patients were treated with corticosteroids.

CONCLUSION

In this prospective study, four of 14 (28%) patients presenting with MMVT (without idiopathic VT, ischemic VT, or known sarcoidosis) had CS as the underlying etiology. Clinicians should consider screening for CS in patients with unexplained MMVT.

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.).

Canadian Cardiovascular Society guidelines on the use of cardiac resynchronization therapy: evidence and patient selection

Recent landmark trials provided the impetus to update the recommendations for cardiac resynchronization therapy (CRT). This article provides guidance on the prescription of CRT within the confines of published data. A future article will explore the implementation of these guidelines. These guidelines are intended to serve as a framework for the prescription of CRT within the Canadian health care system and beyond. They were developed through a critical evaluation of the existing literature, and expert consensus. The panel unanimously adopted each recommendation. The 8 recommendations relate to ensuring the adequacy of medical therapy before the initiation of CRT, the use of symptom severity to select candidates for CRT, differing recommendations based on the presence or absence of sinus rhythm, the presence of left bundle branch block vs other conduction patterns, and QRS duration. The use of CRT in the setting of chronic right ventricular pacing, left ventricular lead placement, and the routine assessment of dyssynchrony to guide the prescription of CRT are also included. The strength of evidence was weighed, taking full consideration of any risks of bias, as well as 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.

Epinephrine Infusion in the Evaluation of Unexplained Cardiac Arrest and Familial Sudden Death

Background—

Epinephrine infusion may unmask latent genetic conditions associated with cardiac arrest, including long-QT syndrome and catecholaminergic polymorphic ventricular tachycardia (VT).

Methods and Results—

Patients with unexplained cardiac arrest (normal left ventricular function and QT interval) and selected family members from the Cardiac Arrest Survivors with Preserved Ejection Fraction Registry (CASPER) registry underwent epinephrine challenge at doses of 0.05, 0.10, and 0.20 μg/kg per minute. A test was considered positive for long-QT syndrome if the absolute QT interval prolonged by ≥30 ms at 0.10 μg/kg per minute and borderline if QT prolongation was 1 to 29 ms. Catecholaminergic polymorphic VT was diagnosed if epinephrine provoked ≥3 beats of polymorphic or bidirectional VT and borderline if polymorphic couplets, premature ventricular contractions, or nonsustained monomorphic VT was induced. Epinephrine infusion was performed in 170 patients (age, 42±16 years; 49% men), including 98 patients with unexplained cardiac arrest. Testing was positive for long-QT syndrome in 31 patients (18%) and borderline in 24 patients (14%). Exercise testing provoked an abnormal QT response in 42% of tested patients with a positive epinephrine response. Testing for catecholaminergic polymorphic VT was positive in 7% and borderline in 5%. Targeted genetic testing of abnormal patients was positive in 17% of long-QT syndrome patients and 13% of catecholaminergic polymorphic VT patients.

Conclusions—

Epinephrine challenge provoked abnormalities in a substantial proportion of patients, most commonly a prolonged QT interval. Exercise and genetic testing replicated the diagnosis suggested by the epinephrine response in a small proportion of patients. Epinephrine infusion combined with exercise testing and targeted genetic testing is recommended in the workup of suspected familial sudden death syndromes.

Clinical Trial Registration—

URL: http://www.clinicaltrials.gov . Unique identifier: NCT00292032.

Cardiac-resynchronization therapy for mild-to-moderate heart failure

BACKGROUND

Cardiac-resynchronization therapy (CRT) benefits patients with left ventricular systolic dysfunction and a wide QRS complex. Most of these patients are candidates for an implantable cardioverter-defibrillator (ICD). We evaluated whether adding CRT to an ICD and optimal medical therapy might reduce mortality and morbidity among such patients.

METHODS

We randomly assigned patients with New York Heart Association (NYHA) class II or III heart failure, a left ventricular ejection fraction of 30% or less, and an intrinsic QRS duration of 120 msec or more or a paced QRS duration of 200 msec or more to receive either an ICD alone or an ICD plus CRT. The primary outcome was death from any cause or hospitalization for heart failure.

RESULTS

We followed 1798 patients for a mean of 40 months. The primary outcome occurred in 297 of 894 patients (33.2%) in the ICD-CRT group and 364 of 904 patients (40.3%) in the ICD group (hazard ratio in the ICD-CRT group, 0.75; 95% confidence interval [CI], 0.64 to 0.87; P<0.001). In the ICD-CRT group, 186 patients died, as compared with 236 in the ICD group (hazard ratio, 0.75; 95% CI, 0.62 to 0.91; P = 0.003), and 174 patients were hospitalized for heart failure, as compared with 236 in the ICD group (hazard ratio, 0.68; 95% CI, 0.56 to 0.83; P<0.001). However, at 30 days after device implantation, adverse events had occurred in 124 patients in the ICD-CRT group, as compared with 58 in the ICD group (P<0.001).

CONCLUSIONS

Among patients with NYHA class II or III heart failure, a wide QRS complex, and left ventricular systolic dysfunction, the addition of CRT to an ICD reduced rates of death and hospitalization for heart failure. This improvement was accompanied by more adverse events. (Funded by the Canadian Institutes of Health Research and Medtronic of Canada; ClinicalTrials.gov number, NCT00251251.).

Psychological adjustment in ICD patients living with advisory fidelis leads

Psychological Adjustment and Fidelis ICD Leads. 

INTRODUCTION

Implantable cardioverter defibrillators (ICD) advisory notices present treatment dilemmas for physicians and patients. On one side, the risk of device malfunction and the likely severity of clinical sequelae have to be estimated. This estimate has to be weighed against the risks of surgery to replace the advisory component. It is unclear whether there is important psychological morbidity associated with living with an ICD under advisory and whether this should be factored into decision making. The study had 2 objectives: (1) to examine whether there is adverse psychological adjustment when an ICD is under advisory, and (2) to assess the psychological sequel of advisory ICD component malfunction.

METHODS

This study focused on the Sprint Fidelis advisory. All patients in our practice who still had an in service Medtronic Fidelis lead were included in the study. Three groups were compared: advisory group but no fracture (n = 249), advisory group with lead fracture (n = 24), and a control group (n = 143). For both objectives, we used a general anxiety and depression instrument and also device-specific measures of psychological well being.

RESULTS AND CONCLUSIONS

First, there was no evidence of differences in the psychological functioning of patients at risk of ICD lead malfunction compared to a control group. Second, patients who had experienced an ICD lead fracture had adverse psychological morbidity compared to control patients, and this appeared, primarily, to be related to receiving inappropriate shock(s) at the time of the fracture.

Characterization of a novel mutation in the cardiac ryanodine receptor that results in catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an arrhythmogenic disease that manifests as syncope or sudden death during high adrenergic tone in the absence of structural heart defects. It is primarily caused by mutations in the cardiac ryanodine receptor (RyR2). The mechanism by which these mutations cause arrhythmia remains controversial, with discrepant findings related to the role of the RyR2 binding protein FKBP12.6. The purpose of this study was to characterize a novel RyR2 mutation identified in a kindred with clinically diagnosed CPVT. Single-strand conformational polymorphism analysis and direct DNA sequencing were used to screen the RyR2 gene for mutations. Site-directed mutagenesis was employed to introduce the mutation into the mouse RyR2 cDNA. The impact of the mutation on the interaction between RyR2 and a 12.6 kDa FK506 binding protein (FKBP12.6) was determined by immunoprecipitation and immunoblotting and its effect on RyR2 function was characterized by single cell Ca(2+) imaging and [(3)H]ryanodine binding. A novel CPVT mutation, E189D, was identified. The E189D mutation does not alter the affinity of the channel for FKBP12.6, but it increases the propensity for store-overload-induced Ca(2+) release (SOICR). Furthermore, the E189D mutation enhances the basal channel activity of RyR2 and its sensitivity to activation by caffeine. The E189D RyR2 mutation is causative for CPVT and functionally increases the propensity for SOICR without altering the affinity for FKBP12.6. These observations strengthen the notion that enhanced SOICR, but not altered FKBP12.6 binding, is a common mechanism by which RyR2 mutations cause arrhythmias.

Paradigm of genetic mosaicism and lone atrial fibrillation: physiological characterization of a connexin 43-deletion mutant identified from atrial tissue

BACKGROUND

Atrial fibrillation (AF) is the most common sustained arrhythmia observed in otherwise healthy individuals. Most lone AF cases are nonfamilial, leading to the assumption that a primary genetic origin is unlikely. In this study, we provide data supporting a novel paradigm that atrial tissue-specific genetic defects may be associated with sporadic cases of lone AF.

METHODS AND RESULTS

We sequenced the entire coding region of the connexin 43 (Cx43) gene (GJA1) from atrial tissue and lymphocytes of 10 unrelated subjects with nonfamilial, lone AF who had undergone surgical pulmonary vein isolation. In the atrial tissue of 1 patient, we identified a novel frameshift mutation caused by a single nucleotide deletion (c.932delC) that predicted 36 aberrant amino acids followed by a premature stop codon, leading to truncation of the C-terminal domain of Cx43. The mutation was absent from the lymphocyte DNA of the patient, indicating genetic mosaicism. Protein trafficking studies demonstrated intracellular retention of the mutant protein and a dominant-negative effect on gap junction formation of both wild-type Cx43 and Cx40. Electrophysiological studies revealed no electrical coupling of cells expressing the mutant protein alone and significant reductions in coupling when coexpressed with wild-type connexins.

CONCLUSIONS

This study reports atrial tissue genetic mosaicism of a novel loss-of-function Cx43 mutation associated with lone AF. These findings implicate somatic genetic defects of Cx43 as a potential cause of AF and support the paradigm that sporadic, nonfamilial cases of lone AF may arise from genetic mosaicism that creates heterogeneous coupling patterns, predisposing the tissue to reentrant arrhythmias.

Evaluation of non-synonymous NPPA single nucleotide polymorphisms in atrial fibrillation

AIMS

Atrial fibrillation (AF), the most common sustained cardiac arrhythmia, is an important cause of morbidity and mortality. A genetic mutation in the NPPA gene, which encodes the atrial natriuretic peptide, has been identified as the putative causative factor in a family with an autosomal dominant pattern of inheritance for AF. Two common single nucleotide polymorphisms (SNPs) in NPPA, rs5063 and rs5065, result in amino acid changes of the primary peptide and have been previously implicated in conditions associated with AF, including stroke and hypertension. Recently, the rs5063 SNP has been reported to confer an increased risk of AF development in a Chinese population. We sought to examine the associations of both rs5063 and rs5065 with AF in two separate North American cohorts of European ancestry.

METHODS AND RESULTS

Patients with early-onset AF, along with healthy controls, were recruited at the University of Ottawa Heart Institute (UOHI) and the Massachusetts General Hospital (MGH). Study participants were genotyped for rs5063 and rs5065 using a combination of restriction fragment length polymorphism analysis and DNA microarrays. The study genotyped a total of 620 AF cases and 2446 healthy controls. The UOHI arm of the study identified an odds ratio (OR) of 0.72 [95% confidence interval (CI): 0.42-1.24] for rs5063, whereas an OR of 1.33 (95% CI: 0.80-2.21) was observed in the MGH arm. The combined OR approximated unity (OR 0.99; 95% CI: 0.54-1.80). Analysis of rs5065 revealed an OR of 1.12 (95% CI: 0.84-1.48) in UOHI, 1.08 (95% CI 0.80-1.45) in MGH, and 1.10 (95% CI 0.90-1.35) when combined.

CONCLUSION

Common non-synonymous genetic variants within NPPA in these two large North American cohorts of European ancestry are not associated with the development of AF.

Frequency and predictors of tachycardia-induced cardiomyopathy in patients with persistent atrial flutter

BACKGROUND

There are few data on the frequency and predictors of tachycardia-induced cardiomyopathy (TICM) in patients with persistent atrial flutter.

OBJECTIVES

To examine the incidence of TICM in patients undergoing ablation for persistent atrial flutter, and to examine predictors for the development of TICM.

METHODS AND RESULTS

One hundred eleven patients met the inclusion criteria for the present study. Twenty-eight of 111 (25%) patients had cardiomyopathy before ablation. Sixteen of 28 (57%) patients showed significant improvement in their left ventricular (LV) function postablation. LV function improved to normal in 12 of 16 (75%) patients. Nineteen of 28 (68%) cardiomyopathy patients had preablation LV function in the range in which they would be considered for an implantable cardioverter defibrillator for primary prevention of sudden cardiac death. In nine of 19 (47%) patients, the ejection fraction improved such that an implantable cardioverter defibrillator was no longer indicated. In multivariate analysis, average ventricular rate during atrial flutter was the only independent predictor of reversibility of cardiomyopathy (P=0.013).

CONCLUSIONS

Sixteen of 28 (57%) cardiomyopathy patients with persistent atrial flutter had significantly improved LV function postablation. In 75% of these patients, LV function improved to normal.

Canadian Registry of ICD Implant Testing procedures (CREDIT): current practice, risks, and costs of intraoperative defibrillation testing

BACKGROUND

There is uncertainty about the proper role of defibrillation testing (DT) at the time of implantable cardioverter defibrillator (ICD) insertion.

METHODS

A prospective registry was conducted at 13 sites in Canada between January 2006 and October 2007.

OBJECTIVES

To document the details of DT, the reasons for not conducting DT, and the costs and complications associated with DT.

RESULTS

DT was conducted at implantation in 230 of 361 patients (64%). DT was more likely to be conducted for new implants compared with impulse generator replacements (71% vs 32%, P = 0.0001), but was similar for primary and secondary prevention indications (64% vs 63%, P = NS). Among patients not having DT, the reason(s) given were: considered unnecessary (44%); considered unsafe, mainly due to persistent atrial fibrillation (37%); lack of an anesthetist (20%); and, patient or physician preference (6%). When performed, DT consisted of a single successful shock > or = 10J below maximum device output in 65% of cases. A 10J safety-margin was met by 97% of patients, requiring system modification in 2.3%. Major perioperative complications occurred in 4.4% of patients having DT versus 6.6% of patients not having DT (P = NS). ICD insertion was $844 more expensive for patients having DT (P = 0.16), largely due to increased costs ($28,017 vs $24,545) among patients having impulse generator replacement (P = 0.02).

CONCLUSIONS

DT was not performed in a third of ICD implants, usually due to a perceived lack of need or relative contraindication.

Formation of a national network for rapid response to device and lead advisories: The Canadian Heart Rhythm Society Device Advisory Committee

The Canadian Heart Rhythm Society (CHRS) Device Advisory Committee was commissioned to respond to advisories regarding cardiac rhythm device and lead performance on behalf of the CHRS. In the event of an advisory, the Chair uses an e-mail network to disseminate advisory information to Committee members broadly representative of the Canadian device community. A consensus recommendation is prepared by the Committee and made available to all Canadian centres on the CHRS Web site after approval by the CHRS executive. This collaborative approach using an e-mail network has proven very efficient in providing a rapid national response to device advisories. The network is an ideal tool to collect specific data on implanted device system performance and allows for prompt reporting of clinically relevant data to front-line clinicians and patients.

Systematic Assessment of Patients With Unexplained Cardiac Arrest

Background— Cardiac arrest without evident cardiac disease may be caused by subclinical genetic conditions. Provocative testing to unmask a phenotype is often necessary to detect primary electrical disease, direct genetic testing, and perform family screening.

Methods and Results— Patients with apparently unexplained cardiac arrest and no evident cardiac disease (normal cardiac function on echocardiogram, no evidence of coronary artery disease, and a normal ECG) underwent systematic evaluation that included cardiac magnetic resonance imaging, signal-averaged ECG, exercise testing, drug challenge, and selective electrophysiological testing. Diagnostic criteria were based on accepted criteria or provocation of the characteristic clinical features for long-QT syndrome, catecholaminergic polymorphic ventricular tachycardia, Brugada syndrome, early repolarization, arrhythmogenic right ventricular cardiomyopathy, coronary spasm, and myocarditis. Sixty-three patients in 9 centers were enrolled (age 43.0±13.4 years, 29 women). A diagnosis was obtained in 35 patients (56%): Long-QT syndrome in 8, catecholaminergic polymorphic ventricular tachycardia in 8, arrhythmogenic right ventricular cardiomyopathy in 6, early repolarization in 5, coronary spasm in 4, Brugada syndrome in 3, and myocarditis in 1. Targeted genetic testing demonstrated evidence of causative mutations in 9 (47%) of 19 patients. Screening of 64 family members of these patients identified 15 affected individuals who were treated (24%). The remaining 28 patients (44%) were considered to have idiopathic ventricular fibrillation.

Conclusions— Systematic clinical testing, including drug provocation and advanced imaging, results in unmasking of the cause of apparently unexplained cardiac arrest in >50% of patients. This approach assists in directing genetic testing to diagnose genetically mediated arrhythmia syndromes, which results in successful family screening.

Rapid genetic testing facilitating the diagnosis of short QT syndrome

Short QT syndrome (SQTS) is a rare genetic disease with a risk of sudden cardiac death. The present report describes syncope in a young man that resulted in a motor vehicle accident. An electrocardiogram and initial investigations were unremarkable, but treadmill testing showed a lack of adaptation of the QT interval, which has been described in SQTS. To evaluate the possible diagnosis of SQTS, DNA sequencing of genes known to be associated with SQTS was performed and identified a novel mutation in the KCNH2 gene. Consequently, the patient was diagnosed with SQTS and the recommendation of implantable cardioverter defibrillator implantation was accepted by the patient before discharge from the hospital.

Gain-of-function mutation of Nav1.5 in atrial fibrillation enhances cellular excitability and lowers the threshold for action potential firing

Genetic mutations of the cardiac sodium channel (SCN5A) specific only to the phenotype of atrial fibrillation have recently been described. However, data on the biophysical properties of SCN5A variants associated with atrial fibrillation are scarce. In a mother and son with lone atrial fibrillation, we identified a novel SCN5A coding variant, K1493R, which altered a highly conserved residue in the DIII-IV linker and was located six amino acids downstream from the fast inactivation motif of sodium channels. Biophysical studies of K1493R in tsA201 cells demonstrated a significant positive shift in voltage-dependence of inactivation and a large ramp current near resting membrane potential, indicating a gain-of-function. Enhanced cellular excitability was observed in transfected HL-1 atrial cardiomyocytes, including spontaneous action potential depolarizations and a lower threshold for action potential firing. These novel biophysical observations provide molecular evidence linking cellular "hyperexcitability" as a mechanism inducing vulnerability to this common arrhythmia.