24 hour ambulatory blood pressure variability and cardiac parasympathetic function 2 and 6 weeks after acute myocardial infarction

The aim of the study was to assess non-invasively circadian blood pressure rhythm as well as the influence of parasympathetic function 2 and 6 weeks after acute myocardial infarction treated with beta-blocking agents. Twenty-four patients with uncomplicated first myocardial infarction, and aged less than 60 years, underwent ambulatory blood pressure recordings every 15 min during the day (0900-2100 h) and every 30 min during the night (2100-0900 h), 2 and 6 weeks after infarction. The deep breathing test (6 breaths/min) was performed on each occasion. Normal circadian blood pressure rhythm was maintained with a nocturnal decline of 10 to 15%. Both for systolic and diastolic blood pressure a moderate increase was obtained after 6 weeks (107.8 ± 9.2 mmHg vs. 111.8 ± 10.3 mmHg; NS and 64.9 ± 4.5 mmHg vs. 68.8 ± 6.5 mmHg;p < 0.05). The respective blood pressure variations were significantly higher at that time (10.0 ± 2.4 mmHg vs. 13.6 ± 4.2 mmHg;p < 0.001 and 7.9 ± 1.7 mmHg vs. 11.7 ± 3.5 mmHg, p < 0.001). There was a close correlation (r=0.60, p < 0.005) between 24-h diastolic blood pressure variability and the results of the parasympathetic function test (deep breathing) 2 weeks after infarction. We conclude that the circadian blood pressure rhythm persists after acute myocardial infarction. The correlation between blood pressure variability and parasympathetic function early after infarction suggests a role for vagal control in post-infarction blood pressure variability.