The normal P-R interval in infants and children.

The value of the P-R interval in the study and evaluation of treatment of rheumatic carditis, a disease predominantly of the younger ages, has prompted a re-examination of the normal P-R standards for infants and children. This study reports these data as obtained from 506 normal infants and children. The data reveal that both age and heart rate exert a significant influence on the P-R interval. The minimum, average, and maximum values are given as related to different ages and different heart rates. IN previous papers'-4 we have reported various data on the normal electrocardio-gram in infants and children. The same electrocardiographic material offered a valuable source for other analyses, such as the P-R interval. The P-R interval has been the subject of much interest for many reasons. While not specific for rheumatic carditis, changes in the P-R interval are of significant clinical value in the study of this disease. Thus a prolonged P-R has been described as the most common electrocardiographic finding5-7 in active rheumatic carditis and occasionally the only evidence of this condition.8 A marked prolonga-tion is considered by some observers as an indication of a poor prognosis.9 Shortening of the P-R interval to within normal limits is also valuable in determining subsidence of the rheumatic activity'0 and, therefore, in assessing the success of therapy." In a recent review of 66 patients given corticotropin (ACTH) or cortisone, a prolonged P-R was found to reverse to normal during therapy in 54 instances although in some the P-R pro-longation reappeared after the discontinuation of treatment.'2 A short P-R interval is a characteristic feature of nodal rhythm and of the Wolff Parkinson-White syndrome. In thyrotoxicosis the P-R may also be shortened. Physiological factors likewise play an important role in determining the P-R interval. Prolongation may be caused by vagotonia; whereas shortening is associated with sympa-thicotonia. It is obvious that the normal values of the P-R interval are important in order that the aforementioned clinical applications of P-R changes can be correctly made. Particular emphasis must be placed on the values for children because of the current interest in certain forms of treatment of rheumatic carditis, a disease predominantly of the younger ages. While there are published data on the normal P-R in children,'3-27 the need for a re-analysis of the subject seems indicated. In many reports attention is mainly directed to the average values of the P-R interval. In others, although …