Mechanisms underlying ventricular arrhythmias in idiopathic dilated cardiomyopathy: implications for management

Titin Cardiomyopathy Associated With Refractory Ventricular Tachycardia: A Case Report

Cardiomyopathy is defined as structural and functional myocardial abnormality not attributed to ischemic, valvular, hypertensive, or congenital cardiac causes. The main phenotypes of cardiomyopathy include hypertrophic, dilated, non-dilated left ventricular, restrictive, arrhythmogenic right ventricular, Takotsubo, and left ventricular noncompaction cardiomyopathies. A significant proportion of dilated cardiomyopathy (DCM) cases represents patients with genetic mutations, most commonly titin gene truncating variants (TTNtv). It has been shown that TTNtv mutation contributes to the development of certain types of DCM such as alcohol, chemotherapy, and peripartum. We present a case of DCM where genetic workup revealed TTNtv without other contributing factors. The course was complicated by multiple ventricular tachycardias (VTs) refractory to medical management, despite treatment with amiodarone, sotalol, dofetilide, mexiletine, and propranolol. Interestingly, endocardial mapping failed to delineate the substrate of tachycardia. This report underscores the importance of genetic testing in DCM and highlights the potential association of titin cardiomyopathy with refractory VTs, possibly of epicardial origin.

Association of Titin-Truncating Genetic Variants With Life-threatening Cardiac Arrhythmias in Patients With Dilated Cardiomyopathy and Implanted Defibrillators

Importance

There is a need for better arrhythmic risk stratification in nonischemic dilated cardiomyopathy (DCM). Titin-truncating variants (TTNtvs) in the TTN gene are the most common genetic cause of DCM and may be associated with higher risk of arrhythmias in patients with DCM.

Objective

To determine if TTNtv status is associated with the development of life-threatening ventricular arrhythmia and new persistent atrial fibrillation in patients with DCM and implanted cardioverter defibrillator (ICD) or cardiac resynchronization therapy defibrillator (CRT-D) devices.

Design, Setting, and Participants

This retrospective, multicenter cohort study recruited 148 patients with or without TTNtvs who had nonischemic DCM and ICD or CRT-D devices from secondary and tertiary cardiology clinics in the United Kingdom from February 1, 2011, to June 30, 2016, with a median (interquartile range) follow-up of 4.2 (2.1-6.5) years. Exclusion criteria were ischemic cardiomyopathy, primary valve disease, congenital heart disease, or a known or likely pathogenic variant in the lamin A/C gene. Analyses were performed February 1, 2017, to May 31, 2017.

Main Outcome and Measures

The primary outcome was time to first device-treated ventricular tachycardia of more than 200 beats/min or first device-treated ventricular fibrillation. Secondary outcome measures included time to first development of persistent atrial fibrillation.

Results

Of 148 patients recruited, 117 adult patients with nonischemic DCM and an ICD or CRT-D device (mean [SD] age, 56.9 [12.5] years; 76 [65.0%] men; 106 patients [90.6%] with primary prevention indications) were included. Having a TTNtv was associated with a higher risk of receiving appropriate ICD therapy (shock or antitachycardia pacing) for ventricular tachycardia or fibrillation (hazard ratio [HR], 4.9; 95% CI, 2.2-10.7; P < .001). This association was independent of all covariates, including midwall fibrosis measured by late gadolinium enhancement on cardiac magnetic resonance images (adjusted HR, 8.3; 95% CI, 1.8-37.6; P = .006). Having a TTNtv was also associated with the risk of receiving a shock (HR, 3.6; 95% CI, 1.1-11.6; P = .03). Individuals with a TTNtv and fibrosis had a greater rate of receiving appropriate device therapy than those with neither (HR, 16.6; 95% CI, 3.5-79.3; P < .001). Having a TTNtv was also a risk factor for developing new persistent atrial fibrillation (HR, 3.9; 95% CI, 1.3-12.0; P = .01).

Conclusions and Relevance

Having a TTNtv was an important risk factor for clinically significant arrhythmia in patients with DCM and ICD or CRT-D devices. Having a TTNtv, especially in combination with midwall fibrosis confirmed with cardiovascular magnetic resonance imaging, may provide a risk stratification approach for evaluating the need for ICD therapy in patients with DCM. This hypothesis should be tested in larger studies.

Anti-arrhythmic therapy in patients with non-ischemic cardiomyopathy

Implantable cardiac defibrillators (ICD) are the foundation of therapy for the prevention of sudden cardiac death. While ICDs prevent SCD, they do not prevent the occurrence of ventricular arrhythmias which are usually symptomatic. Though catheter ablation has been successful in substrate modification of ventricular tachycardia in patients with ischemic cardiomyopathy, there is much less evidence to support its use in non-ischemic cardiomyopathy. Therefore, anti-arrhythmic drugs (AADs) are an essential adjunctive therapy for secondary prevention of ventricular arrhythmias in patients with non-ischemic cardiomyopathy. In patients with hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM), the prevalence of ventricular arrhythmias correlates with the volume of scar as characterized by late gadolinium enhancement. Beta-blockers forms the cornerstone of treatment to prevent ventricular arrhythmias in both HCM and DCM. Disopyramide is an important therapeutic option in HCM as it provides both negative inotropy which reduces obstruction as well as lass I anti-arrhythmic action. In DCM sotalol, through is combined beta-blocking and class III AD effects, significantly reduces the burden of ventricular arrhythmias. Though amiodarone is efficacious in the prevention of ventricular arrhythmias in both HCM and DCM, its use is limited by its side-effects profile. Evidence for AAD therapy for arrhythmogenic right ventricular dysplasia (ARVD) is limited by its low prevalence and lack of studies. ICDs have been shown to reduce SCD regardless of whether patients are receiving AAD therapy.

Implantable cardioverter defibrillators for primary prevention in patients with nonischemic cardiomyopathy: A systematic review and meta-analysis

BACKGROUND

Implantable cardioverter defibrillators (ICDs) have proved their favorable outcomes on survival in selected patients with cardiomyopathy. Although previous meta-analyses have shown benefit for their use in primary prevention, the evidence remains less robust for patients with nonischemic cardiomyopathy (NICM) in comparison to patients with coronary artery disease (CAD).

OBJECTIVES

To evaluate the effect of ICD therapy on reducing all-cause mortality and sudden cardiac death (SCD) in patients with NICM.

DATA SOURCES

PubMed (1993-2016), the Cochrane Central Register of Controlled Trials (2000-2016), reference lists of relevant articles, and previous meta-analyses. Search terms included defibrillator, heart failure, cardiomyopathy, randomized controlled trials, and clinical trials.

STUDY SELECTION

Eligible trials were randomized controlled trials with at least an arm of ICD, an arm of medical therapy and enrolled some patients with NICM. The primary endpoint in the trials should include all-cause mortality or mortality from SCD.

DATA EXTRACTION

Hazard ratios (HRs) for all-cause mortality and mortality from SCD were either extracted or calculated along with their standard errors.

DATA SYNTHESIS

Of the 1047 abstracts retained by the initial screen, eight randomized controlled trials were identified. Five of these trials reported relevant data regarding patients with NICM and were subsequently included in this meta-analysis. Pooled analysis of HRs suggested a statistically significant reduction in all-cause mortality among a total of 2573 patients randomized to ICD vs medical therapy (HR 0.80; 95% CI, 0.67-0.96; P=.02). Pooled analysis of HRs for mortality from SCD was also statistically significant (n=1677) (HR 0.51; 95% CI, 0.34-0.76; P=.001).

CONCLUSION

ICD implantation is beneficial in terms of all-cause mortality and mortality from SCD in certain subgroups of patients with NICM.

Limitations and Challenges in Mapping Ventricular Tachycardia: New Technologies and Future Directions

Recurrent episodes of ventricular tachycardia in patients with structural heart disease are associated with increased mortality and morbidity, despite the life-saving benefits of implantable cardiac defibrillators. Reducing implantable cardiac defibrillator therapies is important, as recurrent shocks can cause increased myocardial damage and stunning, despite the conversion of ventricular tachycardia/ventricular fibrillation. Catheter ablation has emerged as a potential therapeutic option either for primary or secondary prevention of these arrhythmias, particularly in post-myocardial infarction cases where the substrate is well defined. However, the outcomes of catheter ablation of ventricular tachycardia in structural heart disease remain unsatisfactory in comparison with other electrophysiological procedures. The disappointing efficacy of ventricular tachycardia ablation in structural heart disease is multifactorial. In this review, we discuss the issues surrounding this and examine the limitations of current mapping approaches, as well as newer technologies that might help address them.

Rapid correction of hypokalemia in a patient with an implantable cardioverter-defibrillator and recurrent ventricular tachycardia

We present the case of a 74-year-old man with non-ischemic dilatated cardiomyopathy and an implantable cardioverter-defibrillator presenting with a serum potassium of 2.6 mmol/L, recurrent unstable ventricular tachycardia, and multiple defibrillations. Administration of a rapid bolus of 20 mEq KCL solution via central venous access, followed by an additional total of 80 mEq (orally and intravenously [i.v.]) over the next 2 h, resulted in immediate resolution of his recurrent unstable dysrhythmia without toxic side effects. Guidelines for rapid correction of hypokalemia quote a maximum safe administration of 20 mEq i.v./h. In addition to discussing the clinical relevance and physiologic interactions of the variables leading to this patient's presentation, we discuss the successful termination of his sustained recurrent ventricular dysrhythmia by rapid potassium repletion above currently recommended rates. The patient we present is representative of a growing population, given medical and technological advances over the years. Potassium boluses may be reasonable in such circumstances, particularly in patients with ICDs.

The mystery of sudden death: mechanisms for risks

This review addresses the possible overlapping mechanisms that may apply to the risk of sudden unexpected death occurring in epilepsy and in cardiac disease. It explores the interaction between the central and peripheral autonomic nervous systems and the cardiopulmonary systems. Included is a discussion of the potential interactive role of genetically determined subtle cardiac risk factors for arrhythmias with a predisposition for seizure-related cardiac arrhythmias. We address the possible mechanisms that are operant in producing both epileptogenic and cardiogenic arrhythmias. Finally, we speculate about potential preventive measures to minimize the risk of both sudden unexpected death in epilepsy and sudden cardiac death.

[Primary prophylaxis with the implantable cardioverter-defibrillator in heart failure: a clinical point of view]

The implantable cardioverter-defibrillator (ICD) is one of the great inventions of modern cardiology. Its use for the prevention of sudden death in patients with left ventricular dysfunction has meant that clinical cardiologists are now fully involved in decision-making on the implantation of these devices. The majority of clinical trials, which have used low ejection fraction as the only or main criterion for patient recruitment, have shown that ICD use leads to a significant improvement in survival. Three trials, two of which were carried out soon after myocardial infarction and one of which was performed at the same time as surgical revascularization, were exceptions. However, it is important to be aware that the improvements observed in the most recent trials have not been as large as those seen in the initial studies. Reduced efficacy has meant that in the Sudden Cardiac Death in Heart Failure Trial (SCD-HeFT), for instance, 25 ICDs had to be implanted to save one life over a 2-year period. The most likely explanation for this observation is that the better prognosis achieved by present-day pharmacologic treatment of heart failure has reduced the margin of benefit associated with ICD use. Another consequence is that depressed left ventricular ejection fraction has lost some of its specificity in predicting sudden death. New predictive variables are needed to improve risk stratification in this population. Without these variables, the use of ICDs in the primary prevention of sudden death in patients with left ventricular dysfunction will not seem a very attractive option from the point of view of good clinical practice.