Purpose or Case Report: AAOCA is the second leading cause of sudden cardiac death in the young which typically occurs with exertion. With in-vitro patient-specific modeling the study aims to assess the differences in fractional flow reserve(FFR)with hyperemia(high-flow)in a patient with AAOCA with a confirmed ischemic event and compare it to a patient with normal coronaries
Methods & Materials: Patient-specific flow models were created after segmenting CT data and 3D printed using Agilus a flexible material whose compliance was matched to native aortic tissue from 2 subjects:1)11 year old male with anomalous right coronary artery(RCA)with a 12.3mm intramural course, slit-like ostium and confirmed ischemia on stress testing; 2)16 year old male with normal coronary artery anatomy. The two models were placed in a left heart duplicator under exercise conditions of 90bpm, cardiac output of 5L/min and mean aortic pressure of 100mmHg. RCA flow at baseline was set to account for 30% of 4-5% of the cardiac output. Pressure waveforms were recorded using a Millar catheter starting in the aorta, through ostium and intramural segment into RCA mediastinal segment. FFR was computed as the ratio of distal to aortic pressure. A simulated stress test was performed, increasing the aortic pressure from 100 to 240mmHg to observe effects of pressure-driven anatomical deformation on coronary flow
Results: In normal RCA, FFR measurements from the aortic position to the mediastinal segment showed no sign of ischemia(FFR>0.8). In the anomalous RCA, FFR measurements under exercise conditions showed a significant drop in FFR in the middle of the intramural course to<0.6, indicating conditions for ischemia. FFR recovered distal to the intramural segment, but remained<0.8. Exposing the models to the simulated stress illustrated an unhindered increase in coronary flow in response to aortic pressure with the normal model compared with the ischemic AAOCA model, with the latter showing a slope on the flow-pressure curve that was 2.2 times lower than that obtained with the normal coronary
Conclusions: Ischemia in AAOCA patients may manifest through dynamic biomechanically driven flow resistance related to the morphological substrate like ostial stenosis and intramural course. In AAOCA with clinically documented ischemia, FFR significantly decreases at the ostium and intramural course, and resistance to flow with increasing aortic pressure increases(absent in normal coronaries). These findings may highlight the mechanisms leading to sudden death in AAOCA