Abstract 17944: The Impact of Baseline PR Interval on Response to CRT in Heart Failure with Narrow QRS Complexes: A Sub-Study of the ReThinQ Trial

Background: In heart failure (HF) patients (pts) who are treated with cardiac resynchronization therapy (CRT), the programmed AV delay must be shorter than the native PR interval in order to preempt intrinsic, dyssynchronous conduction. When the native PR interval is short, such programming results in truncation of transmitral flow, especially in the presence of dilated atria and marked intraatrial (R–>L) conduction delays. Pts with longer baseline PR intervals can have longer (more physiologic) AV delay programming, thereby allowing complete left atrial emptying. Such pts may show improved response to CRT. We analyzed the impact of baseline PR interval in the ReThinQ Trial, which assessed response to CRT in pts with NYHA class III HF, QRS complex duration <130 ms, and echo-detected dyssynchrony. Methods: Pts randomized to CRT in the ReThinQ trial were divided onto 2 groups depending on baseline PR interval: PR≥180ms and PR<180ms. Outcomes at 6 months were compared in the 2 groups. Results: A total of 87 pts were randomized to CRT; 45 pts had PR≥180ms and 42 pts had PR<180ms. At baseline, age, gender, type of cardiomyopathy, LVEF and QRS duration were similar in the 2 groups. Compared to baseline, peak VO 2 at 6 months (which was the primary endpoint in the ReThinQ Trial) was significantly improved only in pts with PR≥180ms (12.1–>13.5 ml/kg/min, P =0.045) but not in pts with PR<180 ms (12.1–>12.3 ml/kg/min, P =NS). Although both groups had significant improvements in NYHA class, pts with PR≥180ms showed greater improvement at 6 months as compared to pts with PR<180 ms (2.3 vs. 2.6, P =0.017). Finally, improvement in exercise duration showed a trend toward significance in pts with PR≥180ms (9.1–>9.9 min, P =0.12), but there was no difference in pts with PR<180 ms (8.6–>8.7 min, P =0.42). There were no significant changes in LVEF. Conclusions: In the ReThinQ Trial, only pts with PR≥180ms showed significant improvements in peak VO 2 after 6 months of CRT. Similarly, NYHA class improved to a greater degree in pts with PR≥180ms as compared to pts with PR<180 ms. This suggests that some of the benefit of CRT may be negated by truncation of transmitral flow in pts with PR<180 ms. A short baseline PR may be a contributor to CRT non-response.