Burden of Ventricular Arrhythmias in Cardiac Resynchronization Therapy Defibrillation and Implantable Cardioverter-Defibrillator Recipients with Recovered Left Ventricular Ejection Fraction: The Additive Role of Speckle-Tracking Echocardiography

Background: Patients with heart failure undergoing cardiac resynchronization therapy with or without defibrillator function may exhibit recovery of left ventricular ejection fraction (LVEF) during follow-up. Mechanical dispersion (MD; the SD of time to peak longitudinal strain by two-dimensional speckle-tracking echocardiography) is a known predictor of life-threatening ventricular arrhythmias (VAs). Relationships among LVEF recovery, changes in MD, and incidence of VA are still not extensively investigated. Methods: In this retrospective study, recipients of cardiac resynchronization therapy defibrillation (n = 183) or implantable cardioverter-defibrillators only (n = 87) underwent conventional and speckle-tracking echocardiography, both at baseline and after 10 to 12 months, and were followed clinically. Both a >= 10% increase in LVEF and a final LVEF > 35% defined echocardiographic response (Echo(Resp)). Reduction in MD >= 10 cosec defined MD response (MDResp). Risk for appropriate implantable cardioverter-defibrillator therapy for VAs was assessed using a multivariable Cox hazard model. Results: The prevalence of Echo(Resp) + and MDResp + was 39% and 46%, respectively. During follow-up (49.8 +/- 33.5 months), 74 VA events occurred. The incidence rate (per 100 patient-years) of VAs was lowest in the Echo(Resp)+/MDResp + group (1.66%; 95% CI, 0.69%-3.99%), highest in the Echo(Resp)-/MDResp - group (12.8%; 95% CI, 9.53%-17.2%; P < .0001), and intermediate in the Echo(Resp)-/MDResp + (5.5%; 95% CI, 3.3%-9.4%) or Echo(Resp)+/MDResp - (5.3%; 95% CI, 3.0%-9.4%) group. Multivariable analysis showed that higher MD at follow-up (>71.4 cosec) was associated with VAs independent of whether final LVEF was below or above the guideline-reported cutoff of 35% (P < .05). Conclusions: Among ICD recipients, improvements in both left ventricular function and MD are associated with reduced risk for VAs. In patients whose follow-up LVEFs improved to >35%, risk for VAs, although substantially decreased, remained elevated in the presence of still elevated MD.