Myocardial bridging and milking effect of the left anterior descending coronary artery: Normal variant or obstruction?

Abstract

Of 5,250 patients undergoing coronary arteriography over a 5 year period, 27 (0.51 percent) had an intramyocardial segment of the left anterior descending coronary artery producing a milking effect or constriction of the artery during systole. Of these, 11 patients with otherwise normal coronary arteries were studied. Hemodynamic data, coronary sinus blood flow and myocardial lactate extraction were measured during atrial pacing at rates of 120 and 150 beats/min and during a 60 watt supine ergocycle exercise test. The degree of narrowing of the left anterior descending coronary artery during systole was graded 3 (greater than 75 percent), 5 patients; 2 (50 to 75 percent), 4 patients; and 1 (less than 50 percent), 2 patients. Four patients with a grade 3 milking effect had S-T depression in the electrocardiogram indicating anterior wall ischemia and lactate production during pacing at 149 ± 2 (mean ± standard error of the mean) beats/min. Three patients had severe angina during pacing. Two patients with a grade 2 milking effect had angina-like chest pain and electrocardiographic changes during pacing at 150 beats/min. However, lactate extraction was unchanged during pacing. Two patients with a grade 1 milking effect had no angina and no electrocardiographic or metabolic abnormalities. Coronary sinus blood flow increased significantly with pacing and ergocycle exercise in all patients (rest 118 ± 8 ml/min; pacing at 150 beats/min 219 ± 27 ml/min; ergocycle exercise 251 ± 17 ml/min) (P < 0.001). We conclude that a grade 3 milking effect observed at coronary arteriography can result in significant obstruction of the left anterior descending coronary artery with typical angina and anterior wall ischemia during tachycardia. Surgical periarterial muscle resection or bypass of the left anterior descending coronary artery might be considered in symptomatic patients with this rare anomaly.