Background Differentiating occlusion of the circumflex branch of the left coronary artery (also called the circumflex artery) from occlusion of the right coronary artery is often difficult because either may be associated with a pattern of acute inferior myocardial infarction on the electrocardiogram.

Objectives To determine if an inexpensive 18-lead electrocardiogram can provide useful information in differentiating sites of coronary occlusion.

Methods Continuous 18-lead electrocardiograms, including standard 12-lead, right ventricular, and posterior leads, were recorded in 38 and 50 subjects undergoing percutaneous coronary interventions in the right coronary artery and the circumflex artery, respectively.

ResultsST-segment elevation in the posterior leads was twice as frequent during occlusion of the circumflex artery as during right coronary occlusion (P < .001). ST-segment elevation in the right ventricular leads and inferior leads occurred more often during occlusion of the right coronary artery than during occlusion of the circumflex artery. ST-segment depression in lead aVL is highly suggestive of right coronary occlusion, whereas ST-segment elevation in posterior leads without depression of the ST segment in lead aVL is highly sensitive and specific for occlusion of the circumflex artery.

Conclusions ST-segment changes in the 18-lead electrocardiogram can be used to differentiate between occlusions of the circumflex artery and occlusions of the right coronary artery. Knowing which vessel is occluded before percutaneous coronary intervention can help in planning the procedure and recognizing when patients are at high risk for disturbances in conduction at the atrioventricular node.

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