A possible model of the anginal syndrome with normal coronary arteriograms: microembolization of canine coronary arteries.

To investigate whether disseminative coronary embolization with microspheres brings about a pathophysiological mimicking of the syndrome of exertional angina with a normal coronary arteriogram, 25 dogs were studied immediately and 2 weeks after the coronary embolization with microspheres 15 micron [2.5 X 10(5) or 5.0 X 10(5)/regional flow (ml/min)] and 25 micron [2.0 X 10(5)/regional flow (ml/min)] in diameter. Two weeks after embolization with the 15-micron microspheres, the resting coronary blood flow recovered to the control (preembolization) level with the absence of myocardial necrosis, but the coronary flow reserve was significantly lower. In ten dogs receiving the larger dose embolization (5 X 10(5)/regional flow (ml/min], lactate production or a marked decrease in lactate extraction was observed during rapid atrial pacing. In five dogs subject to 25-micron microsphere embolization, however, disseminative patchy myocardial necrosis was observed and the coronary flow reserve remained normal. These results indicate that the chronic state after microembolization with a large dose of 15-micron microspheres mimics the syndrome of exertional angina with a normal coronary arteriogram, whereas 25-micron microsphere embolization does not. Thus, the condition of some patients with a normal coronary arteriogram but with reduced coronary flow reserve may be attributable to microcirculatory disturbances in the coronary arterioles or smaller vessels. Moreover, we observed that the coronary flow at the induction of myocardial ischemia by pacing was much less than the reactive hyperemic flow. This discrepancy may be a characteristic feature in this syndrome.