Ventricular Electrical Activation Delay and High-Frequency Electrocardiograms: Hype or Hope?

Abstract

See Article by Plesinger et al > Between too early and too late, there is never more than a moment. > > —Franz Werfel (novelist, playwright, poet) Cardiac resynchronization therapy (CRT) is undoubtedly an effective adjunctive therapy to the management of patients with symptomatic heart failure meeting certain guideline criteria. Numerous randomized clinical trials have shown improvements in heart failure hospitalization and mortality in select populations,1–5 with the suggestion that lifespan gain increases nonlinearly with time in both low- and high-risk individuals. Despite the overall gain noted in trials, a substantial proportion of patients do not derive the anticipated response. This occurs so frequently that, invariably, publications on CRT report approximately a 30% nonresponder rate. To improve patient selection for upstream CRT response, various investigators have worked to identify predictors of CRT response a priori. Reproducible clinical characteristics that predict a favorable likelihood of response form the basis for guideline recommendation and appropriate use criteria including heart failure symptoms, a reduced ejection fraction, a widened QRS complex, and left bundle branch block (LBBB); in addition, other advantageous factors include nonischemic substrate, female gender, and greater interventricular dyssynchrony.6,7 The staple measure of dyssynchrony has been the longer QRS duration with LBBB morphology representative of a greater degree of interventricular dyssynchrony. Indeed, patients with a QRS duration ≥150 ms respond more favorably than those with durations between 120–149 ms.8 The lack of benefit in some individuals despite interventricular synchronization suggests that atrioventricular and intraventricular dyssynchrony should also be optimized if possible.9,10 Given that the QRS morphology appearance is the summation of ventricular depolarization simply using the duration for measurement of interventricular dyssynchrony may be an oversimplification. As such, …