Effect of age and heart rate on the conduction of the sinus node impulse to the ventricle.

The PR interval of the electrocardiogram is made up of the conduction intervals through the atrial muscle, the atrioventricular node, the bundle of His, and the bundle-branch and Purkinje fibers. Knowledge of normal conduction intervals and their relationship to age and sinus cycle length is important for the purpose of defining conduction delays at various sites. We analyzed intracardiac conduction intervals in 70 children with normal hearts, or with insignificant congenital heart lesions, who had been studied over the last 7 years. Linear and multilinear regressions were made, with age and sinus cycle length as the independent variable and the conduction interval as the dependent variable. The PR interval and intraatrial and AV node conduction times had a small but statistically significant positive correlation with age and were independent of sinus cycle length. The conduction time in the His-Purkinje system was not dependent upon either age or sinus cycle length. (The sinus cycle length increases with age.) By using mean values and two standard deviations, the normal range for intraatrial conduction was 2 to 38 msec; for AV node conduction, the range was 44 to 112 msec; and for the His-Purkinje conduction, the range was 23 to 55 msec.