Blood pressure elevation after phenylephrine infusion may adversely affect myocardial perfusion in patients with coronary artery disease

Abstract

Background: Although blood pressure is a major determinant of myocardial oxygen-demand, little information is currently available regarding the changes in blood pressure (BP) during myocardial ischemia. Since BP elevation may cause left ventricular (LV) wall stress and an increase in oxygen demand, infusion of an α-adrenergic agonist, such as phenylephrine (PH), may provoke changes in myocardial perfusion in coronary artery disease (CAD) patients. As the effects of BP changes alone on myocardial perfusion have never been assessed by thallium-201 (Tl) scintigraphy, we investigated the effects of BP elevation after PH infusion, in order to study the hypothesis that pressure loading alone without increases in heart rate, may provoke transient impairment of regional myocardial perfusion, in CAD patients. Patients and methods: Forty-one (41) patients with angiographically documented CAD, aged 54±8 years, were included in our study. Each patient was given, without any complications, a PH (0.1 mg/ml) dose infused at a rate of 0.8 ml/mm, determined by a standardisation procedure and producing a mean blood pressure elevation of approximately 30% above baseline levels and a heart rate response to levels of no less than 50 bpm. One minute after the desired blood pressure and heart rate responses were reached, 2 mCi of Tl were injected and the PH infusion continued until the termination of the test. Tl scintigraphy was performed both 2 min after Tl injection and 4 h later, while the results were correlated to coronary angiography findings. Results: PH scintigraphy produced 152 total defects. The mean perfusion defect size (%) was 14±12 and was directly related to the number of diseased vessels, i.e., 2% for one-vessel disease, 15% for two-vessel disease and 25% for three-vessel disease ( P<0.05). The lowest percentage Tl activity values were 56±14 and were inversely related to the number of diseased vessels ( P<0.01). The mean Tl lung counts/pixel values were 25±8 while it increased as the number of diseased vessels increased ( P<0.01). The mean lung/heart ratio values were 0.31±0.08 while it increased as the number of diseased vessels increased ( P<0.01). Conclusion: BP elevation after PH loading, produces a significant impairment of myocardial perfusion, that correlates well with the extend of angiographic findings.