Synchrotron microangiography reveals configurational changes and to-and-fro flow in intramyocardial vessels.

In 8 dogs, in situ microangiography using synchrotron radiation visualized penetrating transmural arteries (PTAs) with a diameter of >60 μm and allowed quantitation of vessel diameters of >140 μm. Myocardial contraction reduced the vascular short-axial diameters to 87 ± 17% ( n = 62, P < 0.001, paired t-test) of the end-diastolic values and increased the longitudinal dimension to 129 ± 5% ( n = 45, P < 0.001). The diameter reduction in the subendocardial PTA segments was significantly more marked than that in the subepicardial PTA segments (60 ± 12 vs. 88 ± 12%, n=13, P < 0.001, paired t-test). Intracoronary administration of dobutamine (0.1 μg ⋅ kg-1 ⋅ min-1) increased, and in contrast, partial clamping of the coronary artery (ischemia) decreased, the configurational changes. To-and-fro blood flow was clearly observed in PTAs with visual identification of capacitive backflow, resistive forward flow during ischemia on coronary arteriography, and even under baseline conditions in coronary venography. Thus this method advances our understanding of mechanical influences on the coronary circulation.