Idiopathic infantile hyperplastic and hypertrophic cardiomegaly (congenital cardiac hypertrophy)

Abstract

The cause of “congenital idiopathic hypertrophy” of the infantile heart remains an enigma in those cases in which all factors known to produce cardiac hypertrophy have been ruled out. 1 The two mechanisms of idiopathic enlargement which have been suggested are hypertrophy and hyperplasia. Among the studies supporting the thesis of hypertrophy are those of Dammin and Moore, 2 who demonstrated in their case an increase in the width and total number of fibers without a concomitant increase in the total number of nuclei. The protagonist of hyperplasia as a cause of cardiac enlargement is MacMahon, 3 who observed many mitotic figures in the myocardium of a 6-month-old infant whose heart was twice normal weight. The purpose of this article is to present further evidence that idiopathic cardiac enlargement in infants may be the result of myocardial hyperplasia as well as of hypertrophy. In the hypertrophied adult heart, Karsner, Saphir, and Todd 4 demonstrated that, while the myocytes and nuclei are not increased in number, the individual fibers are enlarged. Thus, for a given unit of tissue there is a decrease in the number of nuclei because of the increased volume of sarcoplasm, the total number of nuclei in the heart remaining essentially unchanged. Dammin and Moore concluded from a study of their single case of infantile idiopathic myocardial enlargement and a control that, while the total number of nuclei in the heart remains constant, the number and width of the fibers are increased. They felt that their case should be regarded as one of cardiac hypertrophy. Inherent in the previously mentioned criteria for myocardial hypertrophy is a definition of hyperplasia, namely, the demonstration of a significant increase in the total number of myocytes within a given heart.