[Value of negative U waves in coronary artery spasm]

The significance of U-wave inversion during coronary arterial spasm was investigated in 188 consecutive ergometric tests performed in 69 patients. All patients had previously undergone coronary arteriography which had clearly shown coronary spasm either at rest or after a single 0.4 mg injection of ergometrine. The ergometrine tests were then performed at the patient's bedside using a standard protocol with injection of incremental doses of ergometrine: 0.05, 0.1, 0.2 and 0.4 mg every 5 minutes with 12-lead ECG recordings every minute. Fifty of the 59 patients with positive tests had classical signs of spasms: ST elevation or depression and/or T wave inversion; the other 9 patients had inversion of the U wave alone (2 cases) or associated with classical ST segment changes in the remaining cases. The 10 other patients had no ECG changes although 2 of them suffered typical anginal pain. Negative U waves were observed in 4 of the 12 patients with spasm of the left anterior descending artery, accompanied by ST elevation in the anterior wall leads. A negative U wave would appear to be a sign of less ischaemia than the classical ECG changes because anginal pain is less common: 4 out of 9 cases in which U wave inversion was a very early change, 8 out of 9 cases in which it was the first or only abnormality. The recognition of a negative U wave increases the sensitivity of the electrocardiogram during resting angina and allows earlier treatment of coronary spasm with nitrate derivatives after an ergometrine test.