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Pathophysiology of cardiac transplantation and the challenge of exercise
1Institute of Advanced Biomedical Technologies, Section of Physiological Genomics, National Research Council, Milano, Italy. marconi@itba.mi.cnr.it
Insights
Heart transplantation in adults and children (pediatric heart recipients) shows reduced exercise capacity. Pediatric heart recipients occasionally exhibit improved heart rate response, but muscle-level impairments still limit overall exercise tolerance.
Area of Science:
- Cardiology
- Exercise Physiology
- Transplantation Medicine
Background:
- Heart transplantation is a common procedure for both adult (A-HTR) and pediatric (P-HTR) patients.
- A-HTR typically exhibit a blunted heart rate response to exercise due to cardiac denervation, influenced by catecholamines.
- Exercise tolerance is reduced in A-HTR, with peak heart rates around 140 bpm and maximal aerobic power at ~60% of healthy controls.
Purpose of the Study:
- To compare the exercise response in adult and pediatric heart transplant recipients.
- To investigate potential differences in cardiovascular and aerobic capacity between A-HTR and P-HTR.
- To identify factors limiting exercise tolerance in heart transplant recipients.
Main Methods:
- The study involved analyzing physiological responses during exercise in cohorts of adult and pediatric heart transplant recipients.
- Measurements included heart rate response to exercise onset and offset, peak heart rate, and maximal aerobic power (VO2).
- Comparison was made with age-matched healthy control subjects.
Main Results:
- A-HTR demonstrated delayed heart rate recovery and reduced peak heart rate (approx. 140 bpm) and aerobic power (~60% of controls).
- P-HTR generally mirrored A-HTR responses, but some showed faster heart rate responses and higher peak values (172 bpm).
- P-HTR had greater maximal aerobic power than A-HTR, though still ~60% of controls, suggesting residual muscle-level limitations.
Conclusions:
- While some pediatric heart transplant recipients may achieve near-normal cardiovascular responses to exercise, overall exercise tolerance remains limited.
- Functional impairments at the muscle level are likely contributors to reduced exercise capacity in both adult and pediatric heart transplant recipients.
- The precise origin of these muscle-level functional impairments in heart transplant recipients requires further investigation.
Abstract:
Heart transplantation is now currently performed in adult (A-HTR) as well as in pediatric cardiac patients (P-HTR). In A-HTR, heart denervation results in a delayed, blunted heart rate (HR) response to exercise onset, mainly sustained by the level of circulating catecholamines. At the offset of exercise HR resumes the pre-exercise level in 5-25 min, depending on the absolute work intensity. Peak HR is approximately 140 beats/min. Maximal aerobic power is 19 O2/kg x min, i.e., approximately 60% than that of healthy age-matched sedentary subjects and exercise tolerance is therefore reduced. A functional impairment at the muscle level may also be present, as suggested by the slow kinetics of the VO2 readjustment (phase II) at the onset of submaximal aerobic exercise. P-HTR generally behave as A-HTR. However, recently, in a few P-HTR a fast HR response to exercise and greater peak HR values (172 +/- 22 beats/min) were demonstrated. Maximal aerobic power of P-HTR was 32 +/- 7 ml O2/kg x min, greater than that of A-HTR, but yet approximately 60% of that of healthy age-matched controls. It may be concluded that occasionally P-HTR may resume an almost normal cardiovascular response to exercise; nevertheless, their exercise tolerance is limited, likely by functional impairment at the muscle level, whose origin is still unknown.