Roles and indications for use of implantable defibrillator and resynchronization therapy in the prevention of sudden cardiac death in heart failure

CNP Promotes Antiarrhythmic Effects via Phosphodiesterase 2

BACKGROUND

Ventricular arrhythmia and sudden cardiac death are the most common lethal complications after myocardial infarction. Antiarrhythmic pharmacotherapy remains a clinical challenge and novel concepts are highly desired. Here, we focus on the cardioprotective CNP (C-type natriuretic peptide) as a novel antiarrhythmic principle. We hypothesize that antiarrhythmic effects of CNP are mediated by PDE2 (phosphodiesterase 2), which has the unique property to be stimulated by cGMP to primarily hydrolyze cAMP. Thus, CNP might promote beneficial effects of PDE2-mediated negative crosstalk between cAMP and cGMP signaling pathways.

METHODS

To determine antiarrhythmic effects of cGMP-mediated PDE2 stimulation by CNP, we analyzed arrhythmic events and intracellular trigger mechanisms in mice in vivo, at organ level and in isolated cardiomyocytes as well as in human-induced pluripotent stem cell-derived cardiomyocytes.

RESULTS

In ex vivo perfused mouse hearts, CNP abrogated arrhythmia after ischemia/reperfusion injury. Upon high-dose catecholamine injections in mice, PDE2 inhibition prevented the antiarrhythmic effect of CNP. In mouse ventricular cardiomyocytes, CNP blunted the catecholamine-mediated increase in arrhythmogenic events as well as in I_CaL, I_NaL, and Ca²⁺ spark frequency. Mechanistically, this was driven by reduced cellular cAMP levels and decreased phosphorylation of Ca²⁺ handling proteins. Key experiments were confirmed in human iPSC-derived cardiomyocytes. Accordingly, the protective CNP effects were reversed by either specific pharmacological PDE2 inhibition or cardiomyocyte-specific PDE2 deletion.

CONCLUSIONS

CNP shows strong PDE2-dependent antiarrhythmic effects. Consequently, the CNP-PDE2 axis represents a novel and attractive target for future antiarrhythmic strategies.

Primary Prevention Implantable Cardioverter-Defibrillator Therapy in Heart Failure with Recovered Ejection Fraction

Given recent advances in both pharmacologic and nonpharmacologic strategies for improving outcomes related to chronic systolic heart failure, heart failure with recovered ejection fraction (HFrecEF) is now recognized as a distinct clinical entity with increasing prevalence. In many patients who once had an indication for active implantable cardioverter-defibrillator (ICD) therapy, questions remain regarding the usefulness of this primary prevention strategy to protect against syncope and cardiac arrest after they have achieved myocardial recovery. Early, small studies provide convincing evidence for continued guideline-directed medical therapy (GDMT) in segments of the HFrecEF population to promote persistent left ventricular myocardial recovery. Retrospective data suggest that the risk of sudden cardiac death is lower, but still present, in HFrecEF as compared with HF with reduced ejection fraction, with reports of up to 5 appropriate ICD therapies delivered per 100 patient-years. The usefulness of continued ICD therapy is weighed against the unfavorable effects of this strategy, which include a cumulative risk of infection, inappropriate discharge, and patient-level anxiety. Historically, many surrogate measures for risk stratification have been explored, but few have demonstrated efficacy and widespread availability. We found that the available data to inform decisions surrounding the continued use of active ICD therapies in this population are incomplete, and more advanced tools such as genetic testing, evaluation of high-risk structural cardiomyopathies (such as noncompaction), and cardiac magnetic resonance imaging have emerged as vital in risk stratification. Clinicians and patients should engage in shared decision-making to evaluate the appropriateness of active ICD therapy for any given individual. In this article, we explore the definition of HFrecEF, data underlying continuation of guideline-directed medical therapy in patients who have achieved left ventricular ejection fraction recovery, the benefits and risks of active ICD therapy, and surrogate measures that may have a role in risk stratification.

"Those Plates That Save Me": Experiences of Italian Patients With Implantable Cardioverter Defibrillator

This study aimed to investigate and understand the experiences and feelings lived by people with an ICD. Qualitative study, semi-structured interviews were conducted with a sample of 16 patients, during the annual follow-up. A hermeneutical analysis of the interviews was carried out to identify the themes. Four main themes were classified: "My heart falls asleep," highlighting a reduced awareness of the pathology and ICD installation; "But what is this thing. . .?" underlining the lack of information and fears related to the device and its functioning; "I cannot hug the microwave" which describes the changes brought about by the surgery; "And with this one I am alright for the rest of my life", involving hopes and life expectations. This study highlighted the patients' need for major support from health professionals while processing their new life conditions.

Cholinergic stimulation improves electrophysiological rate adaptation during pressure overload-induced heart failure in rats

BACKGROUND

Left ventricular (LV) electrical maladaptation to increased heart rate in failing myocardium contributes to morbidity and mortality. Recently, cardiac cholinergic neuron activation reduced loss of contractile function resulting from chronic trans-aortic constriction (TAC) in rats. We hypothesized that chronic activation of cardiac cholinergic neurons would also reduce TAC-induced derangement of cardiac electrical activity.

METHODS

We investigated electrophysiological rate adaptation in TAC rat hearts with and without daily chemogenetic activation of hypothalamic oxytocin neurons for downstream cardiac cholinergic neuron stimulation. Sprague Dawley rat hearts were excised, perfused, and optically mapped under dynamic pacing after 16 weeks of TAC with or without 12 weeks of daily chemogenetic treatment. Action potential duration (APD60) and conduction velocity (CV) maps were analyzed for regional rate adaptation to dynamic pacing.

RESULTS

At lower pacing rates, untreated TAC induced elevated LV epicardial APD60. Fitted APD60 steady state (APDss) was reduced in treated TAC hearts. At higher pacing rates, treatment heterogeneously reduced APD60 compared to untreated TAC hearts. Variance of conduction loss was reduced in treated hearts compared to untreated hearts during fast pacing. However, CV was markedly reduced in both treated and untreated TAC hearts throughout dynamic pacing. At 150msec pacing cycle length, APD60 v. diastolic interval (DI) dispersion was reduced in treated hearts compared to untreated hearts.

CONCLUSIONS

Chronic activation of cardiac cholinergic neurons improved electrophysiological adaptation to increases in pacing rate during development of TAC-induced heart failure. This provides insight into the electrophysiological benefits of cholinergic stimulation as a treatment for heart failure patients.

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.