QRS frequency characteristics help predict response to cardiac resynchronization in left bundle branch block less than 150 milliseconds.

Abstract

Baseline QRS duration (QRSd) ≥150 ms is a recognized predictor of clinical improvement by cardiac resynchronization therapy (CRT), particularly for those with left bundle branch (LBBB). Patients with QRSd <150 ms are considered less likely to respond. The purpose of this study was to test our theory that left ventricular dyssynchrony, although usually associated with wider QRSd, also exhibits lower QRS frequency characteristics and that low-frequency content predicts CRT response in LBBB patients. We retrospectively examined the QRS frequency content of 170 heart failure patients with LBBB and QRSd ≥120 ms using Fourier transformation. Ninety-four responders to CRT (defined as reduction in left ventricular end-systolic volume by ≥15% from baseline) were compared to 76 nonresponders (<15% reduction). Analysis of 3 standard ECG leads (I, aVF, and V3) representing the 3 dimensions of depolarization was performed, and V3 provided the best predictive value. The QRSd of responders (160.3 ± 17.8 ms) and nonresponders (161.8 ± 21.1 ms, P = .604) were similar. We found that the percentage of total QRS frequency power below 10 Hz that exceeded 52% was most predictive of CRT response compared to other cutoff values. However, the percentage of patients with total QRS power >52% below 10 Hz was especially predictive of response in those with QRSd <150 ms. In these patients, this power threshold was highly predictive of CRT response (positive predictive value 85.7%, negative predictive value 71.4%). In this group of CRT recipients with LBBB, retrospective analysis of QRS frequency content below 10 Hz had greater predictive value for CRT response than baseline QRSd, particularly in those with QRSd <150 ms.