The myocardium in tetralogy of Fallot: a histological and morphometric study

Patients with Tetralogy of Fallot frequently develop ventricular dysfunction in the postoperative period. The histological basis of this functional alteration has been scarcely studied.

To evaluate myocardial remodeling in anatomical specimens, comparing the subepicardial and subendocardial regions, especially because the subendocardial region is easily approached by means of endomyocardial biopsy.

Transmural sections of myocardium from the right ventricular (RV) inflow tract, anterior wall and infundibulum, and from the left ventricular (LV) free wall were evaluated regarding the degree of cardiomyocyte hypertrophy, vascularization and interstitial fibrosis were analyzed.

The mean diameter of subendocardial cardiomyocytes is similar to that of subepicardial cardiomyocytes in all regions, except for the RV infundibulum, in which subendocardial cardiomyocytes are significantly larger in relation to those of the subepicardium (p=0.007). The amount of interstitial collagen is in the upper limits of normal and was similar in the subendocardial layers in comparison with the subpericardial layer of each region; however, it was greater in the inflow tract and RV anterior wall than in the LV lateral wall. The numerical density of subendocardial capillaries was similar to that of the subepicardium and was lower than the mean minus two standard deviations of normal in all regions and layers, except for the infundibulum, in which the subepicardium showed normal values and the subendocardium showed values lower than the mean minus two standard deviations.

The postnatal myocardial changes in Tetralogy of Fallot are homogeneously distributed in the subepicardial and subendocardial halves of the ventricular walls, except for the infundibulum, which has peculiar remodeling characteristics and, therefore, is not representative of the other ventricular regions and layers for morphometric studies.