FREQUENCY, SIGNIFICANCE, AND MECHANISM OF MYOCARDIAL-ISCHEMIA DURING DAILY ACTIVITIES DETECTED BY HOLTER DYNAMIC ELECTROCARDIOGRAM

Exercise testing (EX) and Holter ECG (DCG) were performed consecutivel y in 52 patients with ischemic heart disease. A total of 100 episodes of myocardial ischemia (IE) were recorded during DCG in 30 patients, w ho constituted 94% of the patients with myocardial ischemia under 6 me tabolic equivalents (METs) during EX. A significant increase in heart rate (HR) was observed before the development of IE. The duration of t his increase in HR was longer in IE than in periods in which the HR in creased above the ischemic threshold, but without ischemia. The incide nce of IE showed two peaks at 8-10 am and 4-6 pm. The frequency of IE among all of the periods with increased HR was highest at 8-10 am (51% ). IE in the morning was associated with a lower HR than that in the a fternoon, and LF/HF, which reflects sympathetic activity, evaluated us ing power spectral analysis, increased before IE in the morning. The e arly appearance of myocardial ischemia in EX can predict its appearanc e in daily life. The increase in HR and its duration appear to be asso ciated with the development of IE. The increase in sympathetic activit y in the morning and the increase in myocardial oxygen demand accompan ied by physical activity in the afternoon most likely contributed to t he circadian variation in the incidence of ischemic episodes.