Coronary blood flow in patients with hypoplastic left heart syndrome and total cavopulmonary anastomosis at rest and under submaximal exercise (RF_SA_463)

Background: Hypoplastic left heart syndrome (HLHS) is a congenital heart disease characterized by the underdevelopment of the left side of the heart due to severe stenosis or atresia of the mitral and/or aortic valves. Surgical treatment improved significantly since the early 1980s, with a staged palliation approach becoming the standard of care. In the initial stage, the pulmonary trunk is separated from the pulmonary circulation and connected to the distal ascending aorta to form the neo-aorta. The native proximal aorta is anastomosed to the neo-aorta, receiving retrograde flow to supply the coronary arteries, which still originate at its root. The total cavopulmonary connection (TCPC) is the definitive palliative procedure. With an increasing number of HLHS patients surviving into early adulthood, the focus has shifted to long-term complications, including the development of chronic coronary syndromes. This study aimed to measure coronary blood flow at rest and during exercise in HLHS patients after TCPC.

Methods: We prospectively examined 20 HLHS patients following TCPC, with a median age of 15.5 years, who underwent CMR testing during routine follow-up. We excluded 4 patients due to incomplete datasets. Flow measurements of the native and neo-aorta were obtained during free breathing, along with SSFP cine images taken during breath-hold maneuvers for volumetric evaluation of the systemic right ventricle, using a 1.5 Tesla MR scanner. The CMR examination was conducted both at rest and during exercise (25% of peak VO2) using a modified and validated leg paddelergometer. None of the patients exhibited antegrade flow in the native aorta. Instead, the native aorta's net retrograde blood flow entirely supplies the coronary circulation.

Results: The stress test resulted in a 16.3% increase in heart rate, reaching 45.7% of the calculated maximum heart rate. During the physical stress CMR, coronary blood flow increased significantly per heartbeat (p = 0.03) and per minute (p = 0.002) in the native aorta. Additionally, we observed a positive correlation between the native aorta's cross-sectional area and coronary blood flow measurements under stress (R² = 0.350), but not at rest (R² = 0.056). Relative coronary blood flow, in relation to cardiac output, averaged 3.7% (median 3.8%) at rest and 4.1% (median 4.0%) during exercise. However, there was notable variability in relative coronary blood flow during exercise. Seven of the sixteen patients could either not increase or even experienced a decrease in relative coronary flow.

Conclusion: Mean coronary blood flow in patients with HLHS is slightly reduced compared to normal values. However, an increase in coronary blood flow is observed during exercise in most patients. The cross-sectional area of the native aorta showed a weak positive correlation with the increase in coronary blood flow during stress.

cross-section of the native aorta with the depiction of the roots of the coronary arteries and oblique cross-section of the neo-aorta, acquired with 3D whole heart imaging with respiratory gating.
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Coronary blood supply per minute in HLHS patients at rest and under exercise
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Relative coronary blood flow in HLHS patients, in relation to cardiac output
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