Atrioventricular Conduction Delay Predicts Impaired Exercise Capacity in Patients with Heart Failure with Reduced Ejection Fraction
Heart failure (HF) is a major cause of morbidity and mortality, and ventricular dyssynchrony is an important contributor. The ReThinQ trial reported no improvement with cardiac resynchronization therapy (CRT) in HF patients with left ventricular ejection fraction (LVEF) <35 %, narrow QRS (<130 ms), New York Heart Association (NYHA) class III, and echocardiographically detected dyssynchrony, in spite of echocardiographic optimization. We investigated whether a subset of narrow QRS patients might derive benefit from CRT, based on baseline PR interval. We retrospectivelyanalyzed the 87 patients from ReThinQ who were randomized to CRT. Patients were divided into two groups: baseline PR interval <180 ms and baseline PR interval ≥180 ms. The primary outcome was change in VO2 max at 6 months; secondary outcomes were change in LVEF, 6-min walk distance, and change in NYHA class. Forty-six patients had PR < 180 ms and 41 had PR ≥ 180 ms. The baseline characteristics were similar in the two groups. As compared to patients with a short PR interval, at 6 months, only patients with PR ≥ 180 ms showed a statistically significant increase in VO2 max from 12.2 to 13.6 mL/kg min (P = 0.045). Similarly, LVEF was significantly improved only in the long PR group (0.26 to 0.28, P = 0.038). A greater percentage of patients in the long PR group showed improvement by at least one NYHA class (59 vs. 35 %, P = 0.033). A longer baseline PR interval may allow more efficacious delivery of CRT by allowing programming of physiologic AV delays. A short baseline PR interval may contribute to LV under-filling and CRT non-response.