Effect of Cardiac Resynchronization Therapy in Patients Without Left Ventricular Dyssynchrony
Does cardiac resynchronization therapy (CRT) impact survival in patients with left ventricular (LV) dyssynchrony at baseline?
This was a cohort study of 290 patients with New York Heart Association (NYHA) class III/IV heart failure, left ventricular ejection fraction (LVEF) ≤35%, and a QRS duration ≥120 ms without LV dyssynchrony. LV dyssynchrony was measured by tissue Doppler echocardiogram prior to CRT implant, and was defined as the maximum delay between peak systolic velocities of the septal and lateral walls. All patients had maximum delay <60 ms prior to CRT implant. Atrioventricular delay but not interventricular delay was optimized 24 hours after device implant. After 48 hours of CRT, patients were divided into two groups based on sample median LV dyssynchrony measures: induced LV dyssynchrony (≥40 ms) and noninduced dyssynchrony (<40 ms). Survival was assessed based on LV dyssynchrony grouping after CRT implant.
At baseline, the median [interquartile range] baseline LV dyssynchrony measure was 22 ms [16-34], 69% had a left bundle branch block, and 45% had a QRS <150 ms. Of the 290 patients, 50% (n = 145) had induced LV dyssynchrony 48 hours after CRT. Compared with baseline, LV dyssynchrony increased to 40 ms [24-56] at 48 hours and 40 ms [24-67] after 6 months of follow-up (p < 0.001). A CRT response (≥15% decrease in LV end-systolic volume) occurred in 93% of patients without induced dyssynchrony compared with only 51% of those with induced dyssynchrony (p < 0.001). There were 73 deaths (25%) over 34 months of median follow-up. At 1 and 2 years, mortality in the induced dyssynchrony group (10% and 17%, respectively) was higher than in those without induced dyssynchrony (3% and 8%, respectively). Induced LV dyssynchrony after CRT was associated with a significantly (adjusted hazard ratio, 1.25 [1.06-1.47] per 25 ms) higher risk of death on follow-up.
The authors concluded that induction of LV dyssynchrony may lead to worse outcome in patients with systolic heart failure.
Scientists are slowly starting to unfold the mystery of CRT response in patients with heart failure. Several preimplant correlates of CRT ‘response’ have been identified, including tissue Doppler measures, QRS duration, QRS morphology, and myocardial scar quantification on magnetic resonance imaging. This analysis is novel in that it examined the impact of inducing dyssynchrony in those undergoing CRT without echocardiographic evidence of dyssynchrony preimplant. Overall, mortality for this cohort of patients (all NYHA class III/IV) was not high, and almost half had a QRS <150 ms prior to implant. Mortality was apparently higher in those with induced dyssychrony after CRT implant, and the survival curves showed marked separation after 2 years of follow-up. This study raises several questions including: Is survival worse in patients with induced dyssynchrony compared with those not receiving any CRT? If so, will V-V optimization measures impact induced dyssynchrony and outcome or should CRT be discontinued? Finally, if induced dyssynchrony is truly detrimental, can we predict who will have induced dyssynchrony after CRT implant? For many reasons, I prefer the term ‘biventricular pacing’ rather than CRT.
Keywords: Echocardiography, Doppler, Heart Failure, Cardiac Resynchronization Therapy
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