Can cardiac resynchronization therapy be used as a tool to reduce sudden cardiac arrest risk?
Introduction
Patients with cardiomyopathy and reduced left ventricular (LV) ejection fraction (LVEF) are at risk of heart failure (HF) symptoms and ventricular arrhythmias (VA), leading to sudden cardiac arrest (SCA).1,2 In selected HF patients with LVEF impairment and wide QRS, cardiac resynchronization therapy (CRT) has been shown to decrease mortality, morbidity and to improve quality of life (QoL).3., 4., 5., 6., 7., 8. Indeed, in CRT-responders, resynchronization positively impacts the failing heart, leading to LV reverse remodeling and improving the cellular and molecular function,9,10 and leading to improvement in symptoms.
Controversial results have been published regarding the effect of CRT on the residual VA risk. Some studies demonstrated a reduction of appropriate implantable cardioverter device (ICD) therapy,5,11., 12., 13. mostly related to positive LV remodeling. However, the decrease in VA risk is inconsistent, influenced by pre- and post-implantation factors (such as baseline echocardiography parameters or cardiac fibrosis).14 Furthermore, proarrhythmic effect of CRT has been raised in some cases, mediated by heterogeneous trans-mural myocardial repolarization and prolonged action potential duration.15,16
This review aims at focusing on the residual VA and SCA risk in HF patients after CRT implantation, and describing the parameters influencing this response and discussing the requirement of a concomitant ICD implantation in patients likely to be super-responders.
Section snippets
Impact on morbidity and mortality
Numerous landmark trials established the efficacy of CRT in patients with HF. The MUSTIC (Multisite Stimulation in Cardiomyopathies) trial was the first to evaluate the benefit of CRT in 67 severe HF patients (New York Heart Association/NYHA functional class III). Indeed, biventricular pacing significantly improved exercise tolerance, QoL and decreased by two thirds the hospitalization rate.3 Similarly, the MIRACLE (Multicenter Insync Randomized Clinical Evaluation) trial assessed the benefit
VA risk in HF patients
VAs are common in HF patients with reduced LVEF. For instance, among the >5000 patients implanted with an ICD in primary prevention included in the DAI-PP (Défibrillateur Automatique Implantable-Prévention Primaire) study, 22.3% of those experienced at least one VA episode during 3-year follow-up.27 Additionally, the related VA risk does not seem to be related to the etiology of the underlying cardiomyopathy, a similar incidence of appropriate ICD therapy having been described in patients with
Is CRT without defibrillator sufficient to protect HF candidates to CRT?
In HF patients with reduced LVEF and prolonged QRS, CRT-P alone or combined with defibrillators (CRT-D) will induce LV remodeling, improve symptoms/survival and is a class I recommendation under current guidelines.17 Currently, most candidates for CRT implantation also meet ICD criteria and up to 80% of patients are implanted with CRT-D in primary prevention in clinical practice.51 However, among these patients, CRT-P could be sufficient to reduce the rate of VAs and protect from SCA.
Conclusions
CRT has substantially improved the prognosis of HF patients who are candidates for the therapy. LV reverse remodeling and especially super-response with LVEF normalization are undeniably associated with a decrease in VAs and SCA risk. Data suggest that CRT-P is a sufficient tool to protect selected HF patients from SCA. However, identifying CRT candidates who do not need concomitant ICD implantation remains challenging. Cardiac imaging and myocardial scar analysis seems promising to evaluate
Acknowledgements
This research was supported by the French Federation of Cardiology and the Rennes University Hospital. There are no other COI/Disclosures.
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Echocardiography parameter for evaluation of various effects of cardiac resynchronization therapy
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