Immediate cardiovascular responses to orthostasis in the early and late months after cardiac transplantation

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Immediate post-standing (< 30 s) heart rate and blood pressure regulation was studied in patients in the early (2 ± 2 months, n = 10) and late months (49 ± 18 months, n = 30) after orthotopic heart or heart and lung transplantation with continuous non-invasive blood pressure (Finapress) and ECG recordings, and was compared to 15 healthy subjects. Heart rate acceleration on standing was absent in the early post-transplantation period. Modest, delayed heart rate acceleration (maximum 12 ± 8 beats/min) was seen late post-transplantation. Subgroup analysis showed that 15 patients late post-ttransplantation had limited (maximum 6 ± 3 beats/min) heart rate acceleration, 11 patients showed maximum heart rate acceleration between 11 and 19 beats/min and 4 patients showed heart rate acceleration comparable in magnitude with that of normal subjects (maximum 28 ± 5 beats/min). The blood pressure transients were comparable in the 3 groups, with a tendency for greater drop and smaller overshoot in systolic blood pressure in transplant subjects. The findings of normal blood pressure transients in the setting of extensive afferent cardiac denervation questions the role of intracardiac (intraventricular) receptors in reflex blood pressure regulation. The development of heart rate responsiveness is compatible with sympathetic reinnervation in many patients in the late post-transplantation period; however, an intrinsic cardiac mechanism may also be possible.