Pathophysiology of silent myocardial ischemia during daily life. Hemodynamic evaluation by simultaneous electrocardiographic and blood pressure monitoring.

The role of myocardial oxygen demand in the genesis of silent myocardial ischemia was evaluated by measuring the heart rate and blood pressure changes preceding the silent ischemic events during daily life in 25 men with proven coronary artery disease. Simultaneous 24-48-hour ambulatory electrocardiographic and blood pressure monitoring were performed during unrestricted daily activities. Of the 92 transient ischemic events recorded during monitoring, 85 (92%) were silent. Sixty-one percent of the silent events were preceded by an increase in the heart rate of 5 beats/min or more. Seventy-three percent of the silent ischemic events showed an average increase of 10 mm Hg in systolic blood pressure within 6 minutes preceding the onset of ST segment depression. The silent ischemic events showed a circadian pattern with a high density (34% of total events) between 6:00 AM and noon. The increase in heart rate and blood pressure paralleled the increase in silent ischemic events during these hours. These results showing significant (p less than 0.001 for both) increases in heart rate and blood pressure preceding a majority of silent ischemic events suggest that increase in myocardial oxygen demand plays a significant role in the genesis of silent ischemia. This pathophysiological mechanism has important therapeutic implications.