During the study, arterial BP and ECG leads (II) were continuously monitored on an oscilloscope with polygraphy. In this study, coronary arteriograms were analyzed separately by two independent observers. Coronary spasm was defined as total or subtotal obstruction (ie, > 99%) associated with an attack of chest pain, ischemic ST-segment changes on the ECG, or both. Focal spasm was defined as a discrete transient vessel narrowing of ≥ 99% that was localized in the major coronary artery, whereas diffuse spasm was diagnosed when transient vessel narrowing of ≥ 99%, compared with baseline coronary angiography, was observed from the proximal to distal segment in the three major coronary arteries. Proximal spasm was defined according to the American Heart Association (AHA) classification8 of segments 1, 2, 5, 6, and 11, and distal spasm also was defined according to AHA classification of segments 3, 4, 7, 8, 9, 12, 13, and 14. Patients with catheter-induced spasms were excluded from this study. Significant organic stenosis was defined as a ≥ 75% luminal narrowing. Coronary arteries were measured after the intracoronary administration of isosorbide dinitrate (2.5 to 5.0 mg) to evaluate coronary atherosclerosis according to the AHA classification system.