Work

Importance of α1‐sympathetic activity for diurnal change in ischemic threshold in patients with stable angina

Year: 1998

Type: article

Abstract: BACKGROUND: Although ischemic threshold reportedly is lower in the early morning than in the afternoon, the mechanisms that account for the diurnal change in minimal coronary vascular resistance in the potentially ischemic area are unknown. HYPOTHESIS: We hypothesized that calcium-channel blockers and alpha 1 blockers may affect the ischemic threshold in the early morning and afternoon in patients with stable angina. METHODS: Before and after the administration of the calcium antagonist amlodipine (5 mg) alone and combined with the alpha 1 blocker prazosin (1 mg), a treadmill exercise test using the Balke-Ware protocol was undertaken in the morning (8:00 A.M.) and repeated in the afternoon (1:00 P.M.) with 15 stable angina patients. The ischemic threshold was defined as a reciprocal of minimal coronary vascular resistance in the presence of comparable levels of myocardial ischemia indicated by 0.1 mV ST depression. Minimal coronary vascular resistance was calculated as mean blood pressure divided by coronary blood flow. Since the coronary blood flow is closely related to myocardial oxygen consumption, which can be replaced by the double product of heart rate and systolic blood pressure, minimal coronary vascular resistance was approximated to 1/heart rate. RESULTS: At baseline, minimal coronary vascular resistance was significantly higher in the early morning than in the afternoon (8.5 +/- 0.3 x 10(-3) min/beats vs. 7.8 +/- 0.4 x 10(-3) min/beats, p < 0.01). Although treatment with amlodipine alone did not abolish the circadian pattern of minimal coronary vascular resistance (8.0 +/- 0.6 x 10(-3) min/beats vs. 7.7 +/- 0.6 x 10(-3) min/ beats, p < 0.05), the addition of prazosin virtually eliminated the diurnal difference in minimal coronary vascular resistance (7.4 +/- 0.5 x 10(-3) min/beats vs. 7.5 +/- 0.5 x 10(-3) min/beats, p = NS). CONCLUSIONS: These findings indicate that alpha 1-sympathetic activity may play a role in the pathogenesis of the diurnal change of ischemic threshold in patients with stable angina.

Source: Clinical Cardiology

DOI: 10.1002/clc.4960210512