Heart rate response during cardiopulmonary exercise in heart transplant recipients

Background Denervation at heart transplant (HTx) results in attenuated heart rate (HR) control and limited exercise tolerance. Purpose The aim of this study was to assess longitudinal changes in the HR response to exercise in HTx recipients. We compared the results with those of healthy controls. Methods Seventy-four HTx recipients were enrolled in a cardiopulmonary exercise trial. The HR response to maximal exercise was tested at 11 weeks and at 1- and 3-years follow-up post HTx, and compared with the HR response 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 (CRI). Results Elleven 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 53% (41 bpm vs 62 bpm; p0.85) in 44% of the HTx recipients at 1 year and in 51% at 3 year after HTx. Conclusion The increase and decrease in HR during exercise are considerably muted in de novo HTx recipients. The HR response improves during the first year after surgery, and thereafter levels off. In contrast the decline in HR after exercise seems to increase with time, which may be related to the effect of exercise. This suggests that partial re-innervation takes place. Whether this response continues to improve in the longer term remains to be determined. Funding Acknowledgement Type of funding source: Public grant(s) – National budget only. Main funding source(s): South-Eastern Norway Regional Health Authority