Aims: We aimed to evaluate within the MADIT-CRT database whether different enrollment characteristics between US and non-US centres affected the clinical course of study patients.
Methods and results: We evaluated differences in baseline characteristics, procedure-associated complications, clinical as well as echocardiographic response to cardiac resynchronization therapy with a defibrillator (CRT-D), between patients enrolled in 87 US centres (n = 1271) and 23 non-US centres (n = 549) in MADIT-CRT. Non-US patients displayed significant differences in baseline characteristics from US patients, including a higher frequency of left bundle branch block, a more advanced heart failure (HF) functional class >3 months prior to enrollment, and larger baseline cardiac volumes. Procedure-related complications occurred at a significantly higher frequency among patients enrolled in non-US centres (17%) than among those enrolled in US centres (10%; P < 0.001). During follow-up, CRT-D was associated with 42% (P = 0.003) and 38% (P < 0.001) reductions in the risk of HF or death in the two respective groups (P for the difference = 0.80), and with similar reductions in cardiac volumes (all P > 0.10). Subgroup analysis showed a more pronounced effect of CRT-D among women in the US group, including a significant 71% (P = 0.02) reduction in the risk of death, whereas CRT-D therapy was associated with a significant clinical benefit in men only in the non-US group.
Conclusion: Patients enrolled in US and non-US centres in MADIT-CRT displayed significant differences in baseline clinical and echocardiographic characteristics and in the frequency of procedure-related complications, but experienced an overall similar clinical and echocardiographic response to CRT-D.