Electrocardiographic remodeling in patients paced for heart failure

Congestive heart failure due to advanced coronary artery disease or dilated cardiomyopathy is often associated with intraventricular conduction delays . Electrical resynchronization is an evolving method to improve clinical an d functional status. To evaluate whether pacing-induced changes in the elec trocardiogram are related to hemodynamic changes, we analyzed electrocardio grams of patients enrolled in the Pacing Therapies in Congestive Heart Fail ure trial. The study population consisted of 42 patients, New York Heart As sociation functional class Ill-IV with a baseline QRS complex of 175 +/- 32 msec and a PR interval of 196 +/- 33 msec. The mean left ventricular eject ion fraction was 0.23. Using high-resolution computer scans, we measured QR S duration of intrinsic and paced electrocardiographs at different times du ring the study, Results of the electrocardiographic measurements were corre lated with functional results. During the crossover period, 34 episodes of biventricular pacing, 27 episodes of left ventricular pacing, and 5 episode s of right ventricular pacing occurred, each at an individual optimized atr ioventricular (AV) delay. The only significant difference was that right ve ntricular pacing increased the QRS width by 40 msec as compared with baseli ne or biventricular pacing. Functional benefit, as indicated by relative in crease of peak oxygen uptake (VO2) compared with baseline, was significantl y correlated with shortening of paced QRS width (correlation coefficient, r = 0.55; p <0.05). After 12-month follow-up of 28 patients, we saw a slight , nonsignificant decrease of intrinsic QRS width. With regard to the underl ying disease, intrinsic QRS width at baseline and at 12 months was also not significantly different between patients with coronary artery disease and dilated cardiomyopathy. This study found that right ventricular pacing caus es an increase in QRS duration in patients with left bundle-branch block, w hereas in left ventricular and biventricular pacing, QRS width remains unch anged. Shortening of QRS width is correlated with a pronounced relative inc rease of peak VO2, and thus may become a noninvasive marker of clinical eff icacy. There is no evidence of remodeling of the intrinsic electrocardiogra m after 12 months of pacing. (C) 2000 by Excerpta Medica, Inc.