Syndrome X is characterized by an abnormal vasomotility of coronary microvessels. It is unknown whether the presence of an ischemic-like pattern in the electrocardiogram at rest (T-wave inversion) reflects a more severe vasomotion disturbance. Changes in coronary sinus flow (thermodilution) and epicardial vessel diameter (quantitative angiography) during adrenergic activation were measured with a standard cold pressor test in patients with syndrome X whose electrocardiogram at rest was normal (group 1:17 patients) or showed stable, symmetrically inverted T waves (group 2:22 patients). Cold pressor test increased mean blood pressure and rate-pressure product to a similar extent in both groups, increased coronary sinus flow in group 1 (88 ± 29 to 119 ± 36 ml/min; p <0.05) and not in group 2 (109 ± 37 vs 104 ± 36 ml/min; p = not significant), and decreased coronary resistance in group 1 (1.38 ± 0.42 to 1.19 ± 0.38 mm Hg/ml/min; p <0.05) and augmented it in group 2 (1.06 ± 0.32 to 1.28 ± 0.43 mm Hg/ml/min; p <0.02). During cold stimulus, the proximal and middle segments of epicardial arteries showed negligible changes in their lumen, whereas the distal segment dilated in group 1 (1.81 ± 0.27 to 2.01 ± 0.32 mm; p <0.05) and constricted in group 2 (1.82 ± 0.12 to 1.62 ± 0.20 mm; p <0.05). Differences in coronary hemodynamic and angiographic responses between the groups were statistically significant (p <0.05). The adrenergic test was repeated after administration of intravenous propranolol (0.1 mg/kg) for the following reasons: β blockers are currently used in syndrome X; β blockade may worsen vasoconstriction, leaving α-adrenergic activity unopposed; and consequently, cases like these may worsen with β blockade. After propranolol, cold pressor test maintained the same effects on coronary flow and diameter in group 1, and elicited a weaker vasoconstrictor response in group 2. Thus, negative T waves in syndrome X identity a subgroup of patients with a vasoconstrictor response to adrenergic activation that involves the microcirculation as well as the distal part of the epicardial branches. In these cases β blockade with propranolol is not detrimental, but appears to be even beneficial.
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine