Abnormal Throughput Coronary Flow in Syndrome X
To elucidate the mechanism of ST segment depression in patients with syndrome X, myocardial blood flow and myocardial O2 and lactate uptake were evaluated in 25 patients who had exhibited chest pain but had normal coronary arteriograms. Fourteen of the patients had chest pain and ST segment depression in an exercise stress test (SX), while the remaining 11 did not exhibit either of these symptoms (control). Atrial pacing induced significant ST segment depression in all patients with SX and did not do so in controls. There was no evidence of coronary artery spasm produced by intravenous administration of ergometrine maleate in any patients. Myocardial blood flow was measured with a Webster’s thermodilution catheter. Coronary flow reserve was defined as the increase occurring in coronary flow after the administration of intravenous dipyridamole (0.56 mg/kg), divided by coronary flow at rest. After the administration of dipyridamole, the coronary flow reserve was 2.70 in the SX group and 2.90 in the controls; this difference was not significant. During atrial pacing, there was a reduction of myocardial lactate uptake and a rise in left ventricular end-diastolic pressure in the SX group, but not in the controls. Oxygen saturation in coronary sinus blood did not change significantly in the controls, while it rose significantly in SX patients.