Background: The coronary circulation in cyanotic congenital heart disease (CCHD) includes the extramural
coronary arteries, basal coronary blood flow, flow reserve, the coronary microcirculation, and coronary atherogenesis.
Methods: Coronary arteriograms were analyzed in 59 adults with CCHD. Dilated extramural coronaries were examined
histologically in six patients. Basal coronary blood flow was determined with N-13 positron emission tomography in 14
patients and in 10 controls. Hyperemic flow was induced by intravenous dipyridamole pharmacologic stress. Immunostaining
against SM alpha-actin permitted microcirculatory morphometric analysis. Non-fasting total cholesterols were
retrieved in 279 patients divided into four groups: Group A---143 cyanotic unoperated, Group B---47 rendered acyanotic
by reparative surgery, Group C---41 acyanotic unoperated, Group D---48 acyanotic before and after operation.
Results: Extramural coronary arteries were mildly or moderately dilated to ectatic in 49/59 angiograms. Histologic examination
disclosed loss of medial smooth muscle, increased medial collagen, and duplication of internal elastic lamina. Basal
coronary flow was appreciably increased. Hyperemic flow was comparable to controls. Remodeling of the microcirculation
was based upon coronary arteriolar length, volume and surface densities. Coronary atherosclerosis was absent in both
the arteriograms and the necropsy specimens.
Conclusions: Extramural coronary arteries in CCHD dilate in response to endothelial vasodilator substances supplemented
by mural attenuation caused by medial abnormalities. Basal coronary flow was appreciably increased, but hyperemic flow
was normal. Remodeling of the microcirculation was responsible for preservation of flow reserve. The coronaries were
atheroma-free because of the salutory effects of hypocholesterolemia, hypoxemia, upregulated nitric oxide, low platelet
counts, and hyperbilirubinrmia.