Heart rate variability in isolated rabbit hearts

Clinical evidence for the presence of heart rate variability (HRV) in patients with cardiac denervation after heart transplantation raised our interest in HRV in an isolated heart preparation. Therefore hearts of seven adult white ELCO rabbits were transferred to a perfusion apparatus. After a stabilization of 30 min in the Langendorff mode, the hearts were perfused in the working heart mode and in the Langendorff mode for 20 min each. HRV was analyzed in the frequency domain. A computer simulated ECG at a constant heart rate of 2 Hz was used for error estimation of the system. In the isolated heart, HRV was of random, broad-band fluctuations, different from the well characterized oscillations at specific frequencies in intact animals. Mean was 423/spl plusmn/51 ms in the Langendorff, 406/spl plusmn/33 ms in the working heart mode and 500 ms in the computer simulated ECG, total power was 663/spl plusmn/207 ms/sup 2/, 817/spl plusmn/318 ms/sup 2/ and 3.7 ms/sup 2/, respectively. There was no significant difference in any measure of HRV between Langendorff and working heart mode. These data show the presence of HRV in isolated, denervated hearts. Left atrial filling, i.e. the working heart mode, did not alter HRV, indicating that left atrial stretch did not influence sinus nodal discharge rate.