Natural course of a prolonged PR interval and the relation between PR and incidence of coronary heart disease. A 7-year follow-up study of 1832 apparently healthy men aged 40-59 years.

During a baseline cardiovascular survey PR was measured in a strictly standardized way in 1832 men aged 40-59 years, free from coronary heart disease (CHD). Of 1758 men still alive, 1585 underwent an identical follow-up study 7 years later. A total of 1570 were in sinus rhythm. The following findings were made: (1) Baseline and follow-up prevalence of a prolonged PR (greater than or equal to 0.22 s) was identical (5.3 vs. 5.4%). (2) Only 60% of restudied men with a prolonged PR also had prolonged PR at follow-up. (3) Only 1 of 98 with a prolonged baseline PR had a more advanced AV block at follow-up, whereas an additional 4 had conditions which might influence the AV node (1 Bechterew's disease and 3 mild aortic valve stenosis). (4) The incidence of all CHD events found during the follow-up study (CHD deaths, myocardial infarction, angina pectoris, and pathologic exercise ECGs) was moderately but significantly lower in men with a prolonged PR than among men with a PR less than or equal to 0.21 s. Thus a prolonged PR is rarely an indicator of impending, more severe conduction disturbances; it is mostly a benign, functional finding in middle-aged men free from overt heart disease and is not positively associated with CHD. Rather PR may be moderately and inversely associated with latent CHD.