Functional restitution of cardiac control in heart transplant patients

Abstract

Cardiovascular control is fundamentally altered after heart transplantation (HT) because of surgical denervation of the heart. The main goal of this work was the noninvasive characterization of cardiac rate control mechanisms after HT and the understanding of their nature. We obtained 25 recordings from 13 male HT patients [age = 28-68 yr, time after transplant (TAT) = 0.5-62.5 mo]. The control group included 14 healthy men (age = 28-59 yr). Electrocardiogram, continuous blood pressure (BP), and respiration were recorded for 45 min in the supine position and then during active change of posture (CP) to standing. The signals were analyzed in the time domain [mean and variance of heart rate (HR) and rise time of HR in response to CP] and the frequency domain [low and high frequency (LF and HF)]. Our principal finding was the consistent pattern of evolution of the HR response to standing: from no response, via a slow response (>40 s, TAT > 6 wk), to a fast increase (<20 s, TAT > 24 mo). HR response correlated with TAT (P < 0.001). LF correlated with HR response to CP (P < 0.0001); HF and HR did not. An important finding was the presence of very-high-frequency peaks in the power spectrum of HR and BP fluctuations. Extensive arrhythmias tended to appear at the TAT that corresponds to the transition from slow to fast HR response to CP. Our results indicate a biphasic evolution in cardiac control mechanisms from lack of control to a first-order control loop followed by partial sympathetic reinnervation and, finally, the direct effect of the old sinoatrial node on the pacemaker cell of the new sinoatrial node. There was no indication of vagal reinnervation.

Wavelet analysis of instantaneous heart rate: a study of autonomic control during thrombolysis

“…Again, as for the HF peak, sympathetic denervation, either surgical (14,15,56,57) or pharmacological (6,8,31), results in a markedly reduced, yet still measurable, LF peak. In the case of sympathetic denervation, the LF peak is probably caused by the mechanical effect of LF fluctuations in the arterial pressure (50,56). Intense sympathetic activation, such as during an exercise test (15,49), results in a diminished LF peak, similar to the one found in the denervated system.…”

“…A more extreme condition, in which vagal activity is uncorrelated with the HF peak, is the case of vagal denervation, either surgical or by pharmacological means. Denervation results in a markedly reduced HF peak (14,56,57); the residual HF peak is then essentially caused by the mechanical stretching effect of respiration on the sinoatrial (SA) node (50). Lack of correlation between vagal activity and the HF peak has also been observed in conditions that involve a strong vagal activation.…”

“…56). Therefore, we may choose to trade frequency resolution for time resolution in this frequency range.…”

Decreased heart rate and blood pressure in a recent cardiac transplant patient after spinal anesthesia

“…Because the patient underwent transplantation using the bicaval anastomosis technique, changes in donor HR could not have been mediated by altered rate of contraction of remnant innervated atrial tissue. [27][28][29] Possibly, the hypotension produced by spinal block resulted in cardiac ischemia with decreased perfusion of the SA node of the donor heart. Such a mechanism has been suggested to account for a lethal bradyarrhythmia 30 and for bradycardia following protamine-induced hypotension 31 in transplanted patients.…”

Heart transplantation-spectral and bispectral analysis

“…Statistical properties of HR -Statistical properties of the HR were significantly different between the HT and control subjects. The 〈HR〉 was higher in the HT group, whereas the 〈STD〉 was much lower (see [5] for details). There was no correlation between 〈HR〉 and 〈STD〉 with TAT, nor with the HR response to CP.…”