PO-03-109 RIGHT VENTRICULAR PACING EXACERBATE ELECTRICAL DYSSYNCHRONY BEYOND INTRINSIC LEFT BUNDLE BRANCH BLOCK

Abstract

Right ventricular (RV) pacing produces an iatrogenic form of left bundle branch block (LBBB). Intrinsic LBBB (I-LBBB) can cause adverse hemodynamic effects due to ventricular dyssynchrony, mainly in patients with heart failure and reduced ejection fraction (HFrEF). Although RV pacing is thought to create a similar activation pattern as LBBB, some studies suggest RV apical pacing can be harmful even in patients with I-LBBB. Currently, the mechanism responsible for this harm is not fully understood. We aimed to quantify and compare the degree of ventricular electrical dyssynchrony, as measured on the surface ECG, during I-LBBB, and RV pacing in patients with HFrEF (left ventricular EF ≤40%) and I-LBBB. Patients with HFrEF and prophylactic defibrillator therapy were prospectively recruited. For each patient, 3-minute, high-resolution (1024 Hz), digital 12-lead ECGs were recorded during I-LBBB rhythm and then RV pacing at 60 bpm or intrinsic heart rate (whichever was higher). High-resolution ECGs were analyzed to quantify abnormal intra-QRS peaks (QRSp) as a measure of ventricular electrical dyssynchrony. QRSp was defined as the mean number of peaks detected in the QRS complex that deviated from a smoothing-filtered version of the QRS. QRSp was automatically quantified for each precordial lead using validated custom software. Mean QRSp was defined as the average of QRSp in precordial leads. Thirty patients with HFrEF (66±9 yrs, 50% male, LVEF 30±8%) and I-LBBB (QRS duration [QRSd]: 172±22 ms) were included. Changes in mean QRSp between I-LBBB and RV apical pacing are shown in (Figure1A). RV pacing increased the mean QRSp in 27 patients (90%) as compared to I-LBBB, suggesting overall more electrical dyssynchrony during RV pacing. Changes in QRSd between I-LBBB and RV pacing are shown in (Figure 1B). RV pacing resulted in QRSd widening beyond I-LBBB QRSd in 18 patients (60%), while QRSd did not change in the remaining patients. During RV pacing (versus I-LBBB), Mean QRSp changed in more patients as compared to QRSd (27 patients versus 18 patients; p = 0.007). Although RV pacing produces an iatrogenic form of LBBB, ventricular electrical activation is more dyssynchronous during RV pacing as measured by changes in mean QRSp and QRSd. Compared to QRSd, mean QRSp is a more sensitive marker of change in ventricular electrical dyssynchrony between RV pacing and I-LBBB. Our results suggest RV pacing can exacerbate ventricular electrical dyssynchrony in those with I-LBBB.