Sequence of mechanical and electrical changes during myocardial ischemia: assessment by an ambulatory left ventricular function monitor.

To investigate the relationship between left ventricular function and electrical changes during myocardial ischemia, ambulatory left ventricular function monitoring and ECG recording were made during the ergometer exercise test in 14 patients with coronary artery disease. An ambulatory ventricular function monitor consists of a small cadmium telluride (CdTe) radionuclide probe (250 g) affixed to the patient's chest wall, a preamplifer (10 g), and a portable data acquisition unit (600 g). Left ventricular time-activity curves were recorded continuously using this monitor, and the end-systolic count (volume), end-diastolic count (volume) and ejection fraction were calculated after background subtraction. Twenty-eight exercise tests were performed in the supine and upright positions. In 15 tests, left ventricular dysfunction, i.e., an increase in the end-systolic count (greater than or equal to 10%) and a decrease in ejection fraction (greater than or equal to 5%), and ST depression (greater than or equal to 0.1 mV) were observed. In these 15 tests, exercise duration was 362 +/- 27 sec. Left ventricular dysfunction occurred earlier than ST depression and the time difference was 97 +/- 19 sec. Left ventricular function recovered 33 +/- 8.5 sec after discontinuation of exercise, while ST depression continued for the additional 85 +/- 18.5 sec after recovery of left ventricular function. In conclusion, 1) left ventricular dysfunction occurs earlier than electrical changes during exercise-induced ischemia; 2) left ventricular dysfunction improves earlier than electrical changes after exercise; and 3) the same temporal sequence exists in the restoration from myocardial ischemia.