Abnormal regional myocardial flow in myocardial bridging of the left anterior descending coronary artery.

A patient with angina pectoris, myocardial bridging of the left anterior descending coronary artery and otherwise normal coronary arteries is presented. Regional myocardial blood flow was studied with the thermodilution technique. Atrial pacing of the heart at a rate of over 140/min reproduced the anginal syndrome, with S-T segment depression in the electrocardiogram. There was a transient decrease in great cardiac vein flow during rapid pacing with a simultaneous increase in total coronary sinus flow. The study demonstrates that in this patient, a myocardial bridge was associated with decreased blood flow to the area perfused by the bridged artery with a concomitant increase in coronary sinus flow as the pacing rate was increased from 96 to 150 and 180/min. After administration of nitroglycerin, the bridging effect was more accentuated on angiography; pacing-induced tachycardia was associated with similar changes in great cardiac vein and coronary sinus flows with less S-T segment depression in the electrocardiogram and chest pain of milder intensity.