The anatomic correlate of ventricular dysfunction in tetralogy of fallot.

Using a quantitative microscopic technique, we quantitated right and left ventricular interstitial tissue space vs. myocardial fiber space in 4 groups of autopsied hearts: 1) 5 normal hearts; 2) 5 hearts from infants _??_ 2 years old with tetralogy of Fallot; 3) 10 hearts from children 21/2-13 years old with tetralogy of Fallot, and 4) 5 hearts from adult patients _??_20 years old with tetralogy of Fallot. The proportions of interstitial tissue and myocardial fiber were quantitated using planimetry of the projected photomicrographs. The proportion of interstitial tissue in Group II was similar to that in Group I, except for a mild increase of interstitial tissue in left ventricular apex of Group II. The proportion of interstitial tissue was significantly increased in Groups III and IV when compared with normal controls (p<0.001). When Groups II and III were compared, a significant increase of interstitial tissue in right ventricle (p<0.05) and left ventricular body (p<0.01) was noted in the latter group. And finally a comparison of Groups III and IV showed that although there was no difference between their right ventricles, and left ventricular apices, however the left ventricular body of Group III contained significantly more interstitial tissue and less myocardial fiber (p<0.001). It is thus demonstrated that up to 2 years of age both right and left ventricles of patients with tetralogy of Fallot were comparable to normals as far the proportion of myocardial fiber and interstitial tissue space were concerned. After this age the proportion of interstitial tissue increases dramatically up to 13 years of age, In patients older than 13 years, the left ventricular myocardial fiber is further reduced with increasing interstitial tissue. Thus the anatomic correlate of myocardial dysfunction documented in older subjects with tetralogy of Fallot before and following total correction, consists of ever increasing interstitial tissue and loss of myocardial fiber, most probably due to persistent and chronic hypoxia. Total correction of tetralogy of Fallot prior to the age of 2, may prevent or halt the progression of such irreversible myocardial damage.