Changes in heart rate variability among cardiac resynchronization therapy patients

Abstract

Background: Cardiac resynchronization therapy with defibrillation (CRT-D) is a viable therapy in the treatment of congestive heart failure (CHF). A prognostic marker of CHF is heart rate variability (HRV), which is a sign of autonomic dysfunction. Small clinical studies have shown improvements in measures of HRV (e.g., mean, minimum, and maximum heart rate, and SDANN (standard deviation of average five-minute RR intervals)) after CRT-D. The present study evaluated changes in HRV measures and clinical variables in a large generalized sample of patients who received CRT-D. Design: The Heart Failure-Heart Rate Variability (HF-HRV) Registry is an ongoing study that will enroll over 1200 (currently 1179) CHF patients who receive a Guidant CONTAK RENEWAL CRT-D. CRT-D device meaures (HRV measures and physical activity levels) and quality of life (QOL; measured with the Minnesota Living with Heart Failure Questionnaire) data were measured at implant/2-weeks (n = 957), 3-months (n = 528), and 6-months (n = 216) post-implant; data were collected at 12-months but were not reported. Proc Mixed was used to evaluate changes in HRV and clinical variables over time controlling for baseline measurements. Results: The average age of the HF-HRV Registry patients at implant was 70±11 years old; 79% of the patients were male. At implant, 89% of the patients had NYHA III and 11% had NYHA IV. The table summarizes results from patients with implant/2-week data and 3- or 6-month visit data. Conclusion: This large sample of CHF patients who received CRT-D showed improvements in heart rate variability (as shown by SDANN, HRV Footprint, and increases in maximum HR and decreases in minimum HR), Activity Log, and QOL. Future analyses will evaluate how SDANN and other measures are related to CHF hospitalizations and mortality. In addition, further analyses will determine if specific patient sub-groups show differential improvements in these measures. Tabled 1 Implant/2-weeks (n) 3-Months (n) 6-Months (n) p-value SDANN 69.1±23.2 (283) 77.9±26.5 (266) 82.3±26.5 (116) <0.0001 HRV Footprint 31.6±11.5 (283) 34.0±12.5 (266) 36.7±12.2 (116) <0.0001 Mean HR 74.4±10.5 (283) 74.9±11.2 (266) 72.4±9.3 (116) 0.45 Minimum HR 63.1±9.6 (283) 62.3±10.0 (266) 60.1±8.4 (116) 0.0001 Maximum HR 94.1±12.4 (283) 97.2±13.7 (266) 94.9±11.5 (116) <0.0001 Activity Log 4.9±3.2 (416) 7.9±4.6 (389) 7.5±3.7 (165) <0.0001 QOL 60.9±23.8 (514) 53.3±23.5 (501) 51.0±22.8 (205) <0.0001 Open table in a new tab