Cardiopulmonary exercise testing has been used to measure functional capacity in children who have undergone a heart transplant. Cardiopulmonary exercise testing results have not been compared between children transplanted for a primary diagnosis of CHD and those with a primary diagnosis of cardiomyopathy despite differences in outcomes. This study is aimed to compare cardiopulmonary exercise testing performance between these two groups.

Patients who underwent heart transplant with subsequent cardiopulmonary exercise testing at least 6 months after transplant at our institution were identified. They were then divided into two groups based on primary cardiac diagnosis: CHD or cardiomyopathy. Patient characteristics, echocardiograms, cardiac catheterisations, outcomes, and cardiopulmonary exercise test results were compared between the two groups.

From the total of 35 patients, 15 (43%) had CHD and 20 (57%) had cardiomyopathy. Age at transplant, kidney disease, lung disease, previous rejection, coronary vasculopathy, catheterisation, and echocardiographic data were similar between the groups. Mean time from transplant to cardiopulmonary exercise testing, exercise duration, and maximum oxygen consumption were similar in both groups. There was a difference in heart rate response with CHD heart rate response of 63 beats per minute compared to cardiomyopathy group of 78 (p = 0.028). Patients with CHD had more chronotropic incompetence than those with cardiomyopathy (p = 0.036).

Primary diagnosis of CHD is associated with abnormal heart rate response and more chronotropic incompetence compared to those transplanted for cardiomyopathy.

Inappropriate heart rate response to exercise – chronotropic incompetence – and exercise intolerance are common in patients with a systemic right ventricle. We aimed to assess the relationship between heart rate increase, oxygen consumption, and timing of the right ventricular cardiac cycle in this cohort.

We prospectively studied nine patients with systemic right ventricles and pre-existing pacemakers using Doppler-echocardiography and treadmill exercise testing. Echocardiography was performed at increasing heart rates. Exercise tests were performed with baseline pacemaker settings and with optimised heart rate response in random order. In addition, eight age- and gender-matched controls underwent exercise testing using a similar exercise protocol.

Patients with a systemic right ventricle had significantly lower peak oxygen consumption compared to controls – 12.6 plus or minus 6.8 versus 31.4 plus or minus 6.6 metres per kilogram per minute (p = 0.0006) – at baseline and active pacemaker reprogramming failed to increase peak oxygen consumption in this cohort – 12.6 plus or minus 6.8 versus 12.4 plus or minus 4.9 millilitres per kilogram per minute (p = NS) at baseline and with reprogramming, respectively. We found not only a marked increase in total isovolumic time but also a significant reduction in total filling time and the aortic velocity time integral, p-value is less than 0.001 for all, at higher heart rates compared to baseline conditions.

This study suggests that despite chronotropic incompetence at baseline, rate-responsive pacing does not improve exercise capacity in patients with a systemic right ventricle. It further indicates that high heart rates may be detrimental in these patients by reducing diastolic filling and stroke volume. These findings may have clinical implications when considering implantation of a permanent pacemaker in this cohort.