Abstract
First-degree atrioventricular block (AVB) is a common electrocardiogram finding in clinical practice. Vascular dysfunction is associated with cardiovascular disease and events. There is no information on the association of AVB with vascular function. The purpose of this study was to evaluate the associations of PR interval with vascular function assessed in well-characterized subjects. A total of 2220 subjects were enrolled in this study. We evaluated endothelium-dependent vasodilatation assessed by flow-mediated vasodilation (FMD) and endothelium-independent vasodilatation assessed by nitroglycerine-induced vasodilation (NID) in 106 subjects with first-degree AVB (70 men; mean age, 64.3 ± 12.9 years) and 1241 subjects with normal PR interval (531 men; mean age, 56.1 ± 13.9 years). Subjects with first-degree AVB had a lower FMD value than that in subjects with normal PR interval (3.5 ± 2.4% vs. 4.9 ± 3.3%, P < 0.001). FMD was significantly lower in subjects with first-degree AVB than in subjects with normal PR interval even after adjustment of confounding factors for assessment of endothelium-dependent vasodilatation (OR: 1.73, 95% CI: 1.11-2.70; P = 0.015). Although NID was significantly lower in subjects with first-degree AVB than in subjects with normal PR interval (11.1 ± 6.0% vs. 13.6 ± 6.1%, P < 0.001), there was no significant difference in NID between the two groups in multivariate analysis (OR: 1.48, 95% CI: 0.91-2.41; P = 0.117). Both endothelium-dependent and endothelium-independent vasodilation in the brachial artery are impaired in parallel with the prolongation of atrioventricular conduction. After adjustments of confounding factors for vascular function, first-degree AVB is associated with impaired endothelium-dependent vasodilatation but not with impaired endothelium-independent vasodilatation. From the aspect of vascular function, it is unlikely that first-degree AVB is an electrocardiography abnormality with a good prognosis.