Detection, frequency and clinical significance of silent myocardial ischaemia in patients with chronic stable angina.

Forty-two patients (mean age 50 years) with chronic stable angina pectoris were subjected to exercise treadmill testing, coronary arteriography and left ventricular cineangiography. Twenty-one of these patients also underwent Holter monitoring for 24 hours. On exercise treadmill testing, angina was the endpoint in 24 (57%), while 18 (43%) developed significant ST segment depression without symptoms. Holter monitoring in 27 patients revealed a total of 248 episodes of myocardial ischaemia of which 210 (84%) were asymptomatic. ST segment depression at 80 mS from J point varied from 1 to 4 mm, and the average duration of ischaemic episodes during Holter monitoring was 9 minutes (range 30 seconds to 1 hour). Heart rate during the ischaemic episodes varied between 65-85 beats/minute. Coronary angiography revealed triple vessel disease in 22 (52%) and double vessel and single vessel involvement in 10 (24%) each. Left ventricular ejection fraction was less than 50% in only 3 (7%) patients. Thus silent myocardial ischaemia is detected frequently in patients with angina pectoris. It occurs during routine daily activity, and on exercise. Heart rate at which silent myocardial ischaemia occurs is much less during daily activity as compared to exercise induced ischaemia. All patients who were detected to have silent myocardial ischaemia had significant coronary artery disease. These findings are of prognostic and therapeutic value.