Effects of Cardiac Resynchronization Therapy on Heart Rate Turbulence

BACKGROUND: Cardiac resynchronization therapy (CRT) improves the clinical status of patients with heart failure (HF), though its effects on heart rate turbulence (HRT) are unknown. METHODS: We measured HRT indices in 58 recipients of CRT systems (mean age = 56 +/- 9 years, 41 men) in New York Heart Association HF functional class III-IV, and with a left ventricular (LV) ejection fraction < or =35%. At 6 months of follow-up, 42 patients were responders and 13 nonresponders to CRT, and three patients died suddenly. The HRT indices turbulence onset (TO%) and turbulence slope (TS ms/RR interval) were calculated from digital 24-hour electrocardiogram before and after 6 months of CRT. TO > or = 0% and TS < or = 2.5 ms/RR interval were considered abnormal. RESULTS: Mean TO in the entire population was 0.4 +/- 1.5 before CRT, and decreased to -0.8 +/- 7.0 during the 6 months of CRT (ns). TS increased significantly from 2.0 +/- 1.7 at baseline, to 3.9 +/- 3.1 (P < 0.05), and a significantly lower proportion of patients had abnormal HRT indices at 6 months. In contrast to the significant increase observed in responders, not significant change in TS was observed among the nonresponders. CONCLUSIONS: During 6 months of CRT, improvements in HRT indices and a decrease in the proportion of patients with abnormal HRT were observed. CRT may have beneficial effects on baroreflex sensitivity.