ANATOMIC AND PHYSIOLOGICAL HETEROGENEITY IN PATIENTS WITH SYNDROME-X - AN INTRAVASCULAR ULTRASOUND STUDY

Objectives. We used intravascular ultrasound imaging of the epicardial vessels to assess coronary morphology, vasomotor response to exercise and exercise-vasomotion after beta-adrenoceptor blockade in patients with syndrome X. Background. Syndrome X is defined as chest pain, abno rmal exercise test results and normal coronary angiographic findings. Because of the limitations of coronary angiography, intravascular ultr asound was used to define coronary pathophysiology. Methods. Thirty pa tients with syndrome X were studied with intravascular ultrasound imag ing (30 MHz, 4.3F catheter) of all three major epicardial vessels. Sup ine arm exercise was performed during coronary imaging. Lumen area was assessed at rest and during peak exercise. The exercise-imaging proto col was repeated after loading with 0.1 mg/kg body weight of intraveno us propranolol. Results. Three morphologic groups were identified usin g intravascular ultrasound: normal coronary arteries (no plaque, intim al thickness <0.25 mm, n = 12), atheromatous disease (mean [+/-SD] are a stenosis 37.9 +/- 7.2%, n = 10) and marked intimal thickening (0.73 +/- 0.11 mm, n = 8). Patients with normal coronary arteries displayed a vasodilatory response to exercise (+16.9% area increase); patients w ith abnormal coronary arteries displayed a vasoconstrictive response t o exercise (-17.4% in the group with plaque; -17.6% in the group with intimal thickening). Propranolol loading attenuated the vasodilatory r esponse in the group with normal coronary arteries (+6.4% area increas e) and attenuated the vasoconstrictive response in the two groups with abnormal coronary arteries (-8.0% in the group with plaque; -8.8% in the group with intimal thickening). Conclusions. Most patients with sy ndrome X have abnormal coronary arteries by intravascular ultrasound. Intravascular ultrasound identifies three distinct morphologic groups: normal coronary arteries, atheromatous plaque and intimal thickening. Exercise-vasomotion is normal in patients with syndrome X who have no rmal coronary arteries by ultrasound; patients with abnormal arteries (plaque or intimal thickening) have an abnormal (constrictive) respons e to exercise. Propranolol loading attenuates vasoreactivity in all su bgroups, suggesting divergent therapeutic utility.