Gold, Michael R.

AbstractCardiac physiologic pacing (CPP), encompassing cardiac resynchronization therapy (CRT) and conduction system pacing (CSP), has emerged as a pacing therapy strategy that may mitigate or prevent the development of heart failure (HF) in patients with ventricular dyssynchrony or pacing‐induced cardiomyopathy. This clinical practice guideline is intended to provide guidance on indications for CRT for HF therapy and CPP in patients with pacemaker indications or HF, patient selection, pre‐procedure evaluation and preparation, implant procedure management, follow‐up evaluation and optimization of CPP response, and use in pediatric populations. Gaps in knowledge, pointing to new directions for future research, are also identified.

Background Cardiac resynchronization therapy results in improved ejection fraction in patients with heart failure. We sought to determine whether these effects were mediated by changes in contractility, afterload, or volumes. Methods and Results In 610 patients with New York Heart Association class I/ II heart failure from the Re synchronization Reverses Remodeling in Systolic Left Ventricular Dysfunction ( REVERSE ) study, we performed detailed quantitative echocardiography assessment prior to and following cardiac resynchronization therapy. We derived measures of contractility (the slope [end‐systolic elastance] and the volume intercept of the end‐systolic pressure–volume relationship, stroke work, and preload recruitable stroke work), measures of arterial load and ventricular–arterial coupling, and measures of chamber size (volume intercept, end‐systolic and end‐diastolic volumes). At 6 and 12 months, cardiac resynchronization therapy was associated with a reduction in the volume intercept and end‐systolic and end‐diastolic volumes ( P <0.01). There were no consistent effects on end‐systolic elastance, stroke work, preload recruitable stroke work, or ventricular–arterial coupling. In the active cardiac resynchronization therapy population, baseline measures of arterial load were associated with the clinical composite score (odds ratio 1.30, 95% CI 1.04 to 1.63, P =0.02). The volume intercept was associated with mortality (hazard ratio 1.90, 95% CI 1.01 to 3.59, P =0.047) and more modestly with the combined end point of mortality or heart failure hospitalization (hazard ratio 1.48, 95% CI 0.8 to 2.25, P =0.06). In contrast, end‐systolic elastance, stroke work, preload recruitable stroke work, and ventricular–arterial coupling were not associated with any outcomes. Conclusion In patients with NYHA Class I/ II heart failure, cardiac resynchronization therapy exerts favorable changes in left ventricular end‐systolic and end‐diastolic volumes and the volume intercept. The volume intercept may be useful to gain insight into prognosis in heart failure. Clinical Trial Registration URL : https://www.clinicaltrials.gov/ . Unique identifier: NCT 00271154.

Background — The Multicenter Unsustained Tachycardia Trial (MUSTT) was designed to evaluate an antiarrhythmic treatment strategy, including drugs and implantable defibrillators (ICDs), guided by electrophysiological (EP) testing. We performed several statistical analyses to assess the contribution of defibrillators to the observed treatment benefit. Methods and Results — First, the effects of defibrillators were indirectly examined by comparing the randomized treatment arms (EP-guided therapy versus no antiarrhythmic therapy) within subgroups that varied according to ICD usage. Use of ICDs increased during the trial; hence, the randomized treatments were compared according to date of enrollment. There were also site-specific differences in ICD use; hence, the randomized arms were compared within groups of sites defined by level of ICD use. There was a distinct “dose response” in relation to ICD use. Where ICD use was high, EP-guided therapy produced significant reductions in arrhythmic death or cardiac arrest ( P <0.004). Where ICD use was low, there was no benefit of EP-guided therapy. Finally, outcomes of EP-guided therapy patients who received an ICD were directly compared with outcomes of other patients using the Cox proportional hazards model with receipt of an ICD as a time-dependent covariate. Adjusted for other prognostic factors, patients who received an ICD had risk reductions of >70% in arrhythmic death or cardiac arrest and >50% in total mortality ( P <0.001 for both end points). Conclusions — The benefit of EP-guided antiarrhythmic therapy observed in MUSTT was due to improved outcomes among patients who received an ICD but not among patients who received antiarrhythmic drugs.