Dynamic systolic dysfunction in patients after heart transplantation: analysis using exercise cardiac magnetic resonance imaging

Background Exercise intolerance remains a crucial problem in patients post-heart transplantation (HTx). Therefore, evaluating dynamic cardiac function is essential to understand the pathophysiology of exercise intolerance in HTx. Purpose To investigate the dynamic cardiac function in HTx using exercise cardiac magnetic resonance imaging (exCMR). Methods ExCMR was performed in 8 consecutive males who underwent HTx between April 2024 and October 2024, 4 to 6 months after HTx. ExCMR was performed in 8 healthy males as Controls. Transthoracic echocardiography (TTE) and cardiopulmonary exercise test (CPX) were performed within two weeks prior to exCMR. The cine of short-axis views were scanned at rest, during exercise at 25% maximal workload (MWL) from CPX (Ex1) and at 40% MWL (Ex2) while subjects pedaling in a supine position. Images using Aquarius software provided left ventricular end-diastolic volume index (LVEDVI) and end-systolic volume index (LVESVI). Cardiac index (CI) was calculated by multiplying heart rate (HR) and LV stroke volume index (LVSVI), which is the difference between LVEDVI and LVESVI. Data are presented as mean ± SD. Statistical analysis was performed using two-way repeated measures ANOVA with post-hoc Tukey’s multiple comparison or unpaired t-test. Results Compared to Controls, the mean age was significantly higher in HTx (44 ± 12 vs. 36 ± 5 years-old, p<0.001), while no differences were observed in body surface area (1.7 ± 0.2 vs. 1.8 ± 0.1 m², p=0.815) or body mass index (23 ± 4 vs. 23 ± 2 kg/m², p=0.796). TTE revealed no difference in LV ejection fraction (LVEF; 60 ± 5 vs. 59 ± 9 %, p=0.843), while E/e’ (11 ± 3 vs. 7 ± 2, p=0.008) and LV global longitudinal strain (-12 ± 1 vs. -20 ± 1 %, p<0.001) were higher, suggesting the presence of diastolic dysfunction. CPX showed lower %peak VO2 (55 ± 10 vs. 104 ± 12 %, p<0.001) and Δheart rate (HR)/ΔWR (0.3 ± 0.1 vs. 0.5 ± 0.1 bpm/watt, p<0.001) suggesting exercise intolerance and poor HR response in HTx. ExCMR demonstrated that the HR at rest was higher, and the peak HR at Ex2 was lower in HTx compared to Controls (Figure A). While no difference in LVEF was observed at rest, the response of LVEF to exercise was reduced in HTx, and no further increase was observed at Ex2 (Figure B). LVSVI was significantly lower at each step (Figure C). Exercise did not change LVEDVI in Controls but increased in HTx (Figure D). Exercise decreased LVESVI until Ex2 in Controls but remained unchanged in HTx (Figure E). There was no difference in CI at rest; however, CI increased significantly during exercise in Controls, while it only increased to Ex1, and no further increase was observed in HTx (Figure F). Conclusion Exercise decreased LVESVI in Controls but increased LVEDVI in HTx. The augmentation of CI during exercise was hampered in HTx. These findings suggest that, together with poor HR response, dynamic systolic dysfunction may contribute to exercise intolerance in the early period of HTx.exCMR in post-heart transplantation