Heart Rate Response after Heart Transplantation

Abstract

Denervation after heart transplantation (HTx) results in attenuated heart rate (HR) control and limited exercise tolerance. The aim of this study was to assess HR response changes to exercise with time in HTx recipients, compared with healthy controls. The HR response to maximal cardiopulmonary exercise was tested in 50 de novo HTx recipients at 11 weeks (range 7-16) after surgery, at 1-year follow-up and in 50 age and gender matched controls. The HR was measured at rest, at 25-, 50-, 75-, and 100% of VO2peak, and 30 sec, 1, 2, and 4 min after peak exercise on a treadmill or bicycle ergometer. We also assessed the HR reserve and the chronotropic response index. 11 weeks after HTx, the HR response to exercise was blunted, but improved significantly during follow-up. The change in HR from rest to peak exercise increased by 32% (46 bpm vs 68 bpm; p&lt0.001) from inclusion to the 12 months' follow-up (Figure). In comparison, the change in HR during exercise in controls was 115 bpm. In HTx recipients, approximately 50 % of the total increase in HR occurred between rest and 25% of VO2peak (figure). In the controls, roughly 40% of the total increase in HR occurred during the initial 25% of VO2peak. The HTx recipients had a significantly higher change in HR between 75- and 100% of VO2peak at inclusion than at 1-year follow-up (p=0.004) and this delayed change in HR was higher than in controls (p = 0.001). The chronotropic response index increased during follow-up (0.48 ± 0.2 vs 0.79 ± 0.2; p&lt0.001) and normalized in 50% of the HTx recipients at 1 year. Finally, the HR declined more rapidly after exercise at follow-up than at inclusion, however, the decline remained slower than in controls (Figure). The increase and decrease in heart rate during exercise are considerably reduced in de novo HTx recipients, but improve during the first year after surgery. Whether this response continues to improve during longer follow-up remains to be determined.