Cardiovascular morbidity after allogeneic haematopoietic stem cell transplantation according to conditioning intensity: a single-centre retrospective analysis

Background Allogeneic haematopoietic stem cell transplantation (HSCT) is increasingly offered to older and comorbid patients through reduced-intensity conditioning (RIC). However, contemporary data on cardiovascular complications according to conditioning intensity remain limited. Purpose To compare early and late cardiovascular events between myeloablative conditioning (MAC) and reduced-intensity conditioning (RIC) regimens in patients undergoing allogeneic HSCT. Methods We conducted a single-centre retrospective cohort study including adult patients undergoing allogeneic HSCT between 2013 and 2024. Patients were classified according to conditioning intensity (MAC vs RIC). Baseline cardiovascular risk factors, early cardiovascular complications (≤100 days), late cardiovascular events (>100 days), and mortality were collected. A composite endpoint of net adverse cardiovascular events (NACE) was analysed. Comparisons between groups were performed using appropriate statistical tests. Results A total of 486 patients were included (MAC n=296; RIC n=190). Patients receiving RIC were significantly older and had a higher prevalence of cardiovascular risk factors, including hypertension, hypercholesterolaemia, coronary artery disease, and prior stroke. Acute cardio-toxicity within 100 days occurred more frequently in RIC compared with MAC (41.6% vs 25.3%, p=0.0002), mainly driven by a higher incidence of acute left ventricular dysfunction (9.5% vs 3.7%, p=0.008) and early pericardial effusion (32.3% vs 22.6%, p=0.02), while early atrial arrhythmias were numerically higher but not statistically different. During follow-up beyond 100 days, late cardiovascular events were uncommon overall. Pericardial effusion remained more frequent in RIC (4.2% vs 1.4%, p=0.07), and myocardial infarction occurred exclusively in the RIC group (3.2% vs 0.0%, p=0.003). The composite NACE rate was significantly higher in RIC (54.0% vs 33.7%, p<0.0001). Cardiovascular mortality was low and comparable between groups (1.6% vs 1.7%, p=0.9), as was 100-day mortality. Conclusions Reduced-intensity conditioning, generally used in patients with increased frailty, is associated with a higher burden of early and late cardiovascular morbidity after allogeneic HSCT, particularly driven by acute dysfunction and pericardial effusion. However, these complications do not translate into increased early or cardiovascular mortality, suggesting a more complex but not more lethal cardiovascular phenotype in RIC patients.