Atrioventricular conduction and cardiovascular mortality: Assessment of recovery PR interval is superior to pre-exercise measurement

BackgroundA prolonged electrocardiographic PR interval at rest has been considered a benign phenomenon until recently.ObjectiveWe hypothesized that measurement of the PR interval during recovery from physical exertion could improve cardiovascular mortality risk stratification because it would track the dynamic influences of homeostatic mechanisms controlling atrioventricular (AV) conduction.MethodsA total of 1,979 consecutive patients (1,244 men and 735 women) with clinically indicated bicycle ergometer tests enrolled in FINCAVAS (the Finnish Cardiovascular Study) were included in the study. The PR interval was measured at 1 min before and at 2 min after exercise.ResultsDuring the mean follow-up period of 47 months (interquartile range: 37 to 59 months), 50 cardiovascular deaths (end point) were registered. The unadjusted hazard ratios (HR) in Cox regression analyses were significant for both continuous PR interval and first-degree atrioventricular (AV) block for pre- and post-exercise phases. After adjustment for standard markers, the PR interval for 20-ms increments (HR: 1.17, P = .117) and first-degree AV block (HR: 1.85, P = .138) during the pre-exercise phase were not prognostic. However, during recovery from exercise, prolonged AV conduction achieved significance both in continuous (HR: 1.29, P = .006) and dichotomized analyses (HR: 2.41, P = .045).ConclusionThe PR interval before exercise is not a robust risk stratifier for cardiovascular death during 4-year follow-up. Post-exercise assessment of AV conduction may offer improved prediction because of functional abnormalities that become manifest only during this physiologic challenge to the heart.