Impaired Power Output and Cardiac Index With Hypoplastic Left Heart Syndrome: A Magnetic Resonance Imaging Study

Background Unfavorable cardiac mechanics in children with hypoplastic left heart syndrome (HLHS) when compared with other single-ventricle defects may affect long-term morbidity and outcome. Using noninvasive phase contrast magnetic resonance imaging (PC MRI), we examined cardiac mechanics in children with HLHS and compared the results to other single-ventricle defects. Methods Eighteen children with HLHS and 18 children with other single-ventricle defects were studied after the Fontan operation. Phase contrast MRI scans were obtained perpendicular to the ascending aorta, and flow was quantified using an in-house segmentation and reconstruction scheme. The total power output was determined using the modified Bernoulli equation along with cardiac output and systemic vascular resistance index. Results Compared with non-HLHS congenital heart defects, children with HLHS had significantly lower power output (1.40 ± 0.39 versus 1.78 ± 0.38 W/m2, p < 0.004) and cardiac index (3.15 ± 0.97 versus 4.09 ± 1.23 L • Min−1 • m−2, p < 0.009) with a concomitant higher systemic vascular resistance index (28.94 ± 11.5 versus 22.7 ± 8.53 WU, p < 0.03) despite generating similar systolic blood pressures (112.9 ± 22.4 versus 115.2 ± 23 mm Hg, p > 0.05). Conclusions Minimally invasive measurements with PC MRI in children with HLHS showed significantly lower power output and cardiac index when compared with other single-ventricle physiologies. Abnormal aortic flow patterns may contribute to power loss and may have long-term survival and morbidity implications associated with the Fontan procedure. Elevated systemic vascular resistance index despite similar blood pressure opens avenues for therapeutic intervention for afterload reduction.