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Coronary artery stenoses that limit blood flow below demand are considered critical. In this comparative study we investigated whether the same degree of stenosis in either the proximal third of the right coronary artery (RCA) or the proximal third of the left anterior descending artery (LAD) causes critical flow reduction. Lesions were quantified from 35-mm cinefilms in multiple projections using a vernier caliper. These morphometric measurements were correlated with various manifestations of critical flow reduction, such as angina pectoris, development of collateral vessels and segmental wall motion abnormalities. In 13 patients with anginal pain and isolated RCA stenosis, the mean degree of obstruction was 63% area stenosis, which was significantly lower (p < 0.05) than that measured in 17 symptomatic patients who had isolated obstructions of the LAD (77% area stenosis). In patients with an identical degree of obstruction (78%) in either the LAD or RCA, collateral vessels were angiographically demonstrable in 53% of the RCA stenoses but in only 29% of the LAD stenoses. Furthermore, when the stenoses were less than 63% in the RCA and LAD, regional wall motion abnormalities were more frequently (p < 0.05) associated with RCA than with LAD stenoses. These observations indicate that a significantly smaller percent area of stenosis is critical in the RCA than in the LAD.

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214 patients with single vessel disease were followed-up for 1-78 months (mean 48 months). Incidence of sudden death was studied in relation to coronary artery lesions, left ventricular wall motion and ventricular arrhythmias found during ambulatory ECG recording. Incidence of sudden death was 11% (16 of 144) in patients with lesions of the left anterior descending branch (LAD), 8% (4 of 55) in lesions of the right (RCA) and 7% (1 of 15) in those with lesions of the left circumflex (LCX) coronary artery. Coronary artery occlusion was associated with a significantly higher incidence of sudden death (15%, 18 of 123) than high-grade stenosis (3%, 3 of 91) (P less than 0.05). The risk of sudden death increased in patients with complex arrhythmias and occluded LAD or RCA (8 of 38, 21%; 2 of 12, 18%) compared with patients without complex arrhythmias (5 of 34, 15%; 1 of 18, 6%). One patient with LCX occlusion died suddenly. Our data show that the incidence of sudden death in relatively low in patients with single vessel disease. However, there is a high risk of sudden death in patients with LAD or RCA occlusion associated with akinetic left ventricular areas and complex arrhythmias.

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We studied the heterogeneity of myocardial blood flow in nine anesthetized closed-chest dogs using an indicator-dilution technique that allows the stochastic description of transport characteristics for three inert gases (helium, argon, and xenon) from the coronary inflow to outflow. The results show that under normal conditions the transcoronary transport of the tracers is spatially heterogeneous. Heterogeneity is strongly dependent on the arterial oxygen tension over a range of 40-200 Torr. This could be similarly observed with each tracer gas despite different physicochemical properties and was largely independent from the magnitude of coronary blood flow. The results are interpreted to mean that the arteriolar or intratissue PO2 influences myocardial blood flow over a broad range and possibly acts as an important integrating factor in the local regulation of coronary blood flow and flow reserve.

SUMMARY To determine the value of nondynamic computed tomography (CT) in assessing aortocoronary bypass graft patency, we studied 67 patients with 125 grafts by CT and by coronary angiography at close time intervals. CT scans were performed before and after one to three (average 1.98 + 0.65) 50-ml i.v. bolus injections of contrast material. Eighty-four of 92 grafts patent at angiography were also visualized by CT (sensitivity 91.3%); 29 of 33 grafts closed at angiography were considered to be occluded by CT (specificity 87.9%). Eleven of 13 grafts demonstrating one or more severe obstructions at angiography were considered to be patent by CT. Interobserver disagreement existed in four of 125 grafts (3.2%) and intraobserver variability was 1.6%. Although nondynamic CT allows a correct assessment of graft patency in many cases, it does not provide sufficient information on graft stenosis and function to replace angiography in patients who are symptomatic after surgery. ACCURATE determination of aortocoronary bypass graft patency requires angiography. Noninvasive methods for analyzing bypass grafts function, such as the directional Doppler flow technique,' thallium-201 myocardial perfusion scintigraphy2' and echocardiographic analysis of regional ventricular function,5 are of limited value because they indirectly assess bypass graft patency. A noninvasive method easily performed, repeatable and without special risks, visualizing the anatomy and providing direct information on graft patency, would be very useful in the postoperative evaluation of patients after bypass graft surgery. Computed tomography (CT) provides a high-resolution, cross-sectional image of the chest and may be an

The pathological mechanism of cardiac transplant vasculopathy (TVP) is uncertain. We tested the hypothesis that the endothelial function, in terms of the release of endothelium-derived relaxing factor, is impaired in patients with angiographic evidence of transplant vasculopathy. In a pilot study, the effects of the substances used (substance P, acetylcholine, nitroglycerin) were assessed as regards tone of pre-contracted human coronary arteries in vitro, obtained from recipient hearts during cardiac transplantation. The study shows that substance P is a "pure' endothelium-dependent dilator of epicardial human coronary arteries, whereas acetylcholine has a more complex effect on vascular tone involving both a direct effect on the endothelium and the smooth muscle cells. In a second pilot study, the effects of intracoronary infusions of substance P (5-100 pmol.min-1) and acetylcholine (2-50 nmol.min-1) on flow velocity were compared in 10 patients undergoing cardiac catherization after heart transplantation. Flow velocity was determined by a 3F Doppler catheter placed into the proximal segment of the left anterior descending artery (LAD). Both drugs increased concentration-dependent flow velocity; substance P and acetylcholine maximally increased flow velocity by about 85 +/- 24% and 143 +/- 15%, respectively (P < 0.05). In a third study, 23 patients undergoing diagnostic cardiac catheterization were included approximately 40 months after heart transplantation. Patients were classified into those with (n = 8) and those without (n = 15) angiographic evidence of TVP. Coronary flow velocity (by Doppler) and epicardial coronary diameter (by quantitative angiography) were determined after intracoronary injections of substance P (20 pmol), nitroglycerin (0.1 mg), and papaverine (8 mg). Substances were injected through the central lumen which was placed into the LAD. Increases in flow velocity in response to substance P were significantly less in patients with TVP than in patients without evidence of TVP. Moreover, flow-mediated vasodilation in response to papaverine was almost abolished in patients with TVP. Vasodilation in response to nitroglycerin and maximal increase in flow velocity in response to papaverine was similar in both groups. These results suggest that TVP is associated with endothelial dysfunction, which may contribute to the pathogenesis of TVP and its vascular complications.