31. Mymin, D., Mathewson, F.A.L., Tate, R.B., Manfreda, J.: The natural history of primary first degree atrioventricular heart block. N Eng J Med 315: 1183-1187, 1986.
Findings in a 30 year longitudinal study of 3983 men with respect to 1st degree heart block (PR interval > .22 sec) occurring in the absence of other evidence of heart disease (P1 HB) were analyzed. There were 176 cases of P1 degree HB with incident cases numbering 124. The incidence rose steadily after age 40 and averaged 1.13/1000 person years over the entire exposure period. The following characteristics in the P1 HB cases were compared to those of 176 age-matched controls: histories of scarlet fever, rheumatic fever, diphtheria, smoking habit, blood pressure, body build. There were no significant differences (P>0.5). Prognosis in cases was compared with that of controls by survival analysis. There were 25 cases of ischemic heart disease, 4 of other organic heart disease, 28 total deaths and 11 ischemic heart disease deaths. Corresponding figures in the controls were 25, 2, 19 and 7 respectively (P>. 0.5). Ischemic heart disease morbidity was not increased in cases attaining longer PR intervals. Progression to higher grades of block occurred in only 2 cases of P1 HB. The high prevalence at entry and increasing incidence after 40 suggest 2 peak periods of incidence, one in youth and another in middle age whose respective etiologies remain speculative. In view of the prognostic findings and the rare occurrence of advanced degrees of atrioventricular block it is concluded that P1 HB is a benign condition.
Key words: Atrioventricular block, PR interval, Conduction, 1st degree Heart block