Natural history of tetralogy of Fallot in infancy. Clinical classification and therapeutic implications.

We employ a classification system for tetralogy (TF) that correlates clinical findings with the nature and severity of right ventricular (RV) outflow obstruction. Group 0 infants are acyanotic, Group 1 and 2 infants have intermittent or mild cyanosis with hypoxic spells, Group 3 infants have severe cyanosis without spells, and Group 4 infants have severe cyanosis and pulmonary artery (PA) hypoplasia without spells. Since 1964, 59 infants were identified as having TF, documented by catheterization. Contrary to previous reports, the majarity (40 of 59) were acyanotic (Group 0) at birth. Cyanosis and hypoxic spells subsequently developed at mean ages of 6.1 and 13.4 mo respectively, due to increasing muscular infundibular hypertrophy, as well as fibrosis and growth failure of the RV outflow tract, due to diminished pulmonary blood flow. At catheterization (mean age 12.7 mo) only two were still in Group 0. An understanding of the progressive nature of TF suggests that infants in groups 1-3 can have total correction before significant undergrowth of the RV outflow tract occurs. Shunts are performed only in Group 4 infants. Twenty-eight infants from ten weeks to two years old had total correction. Five were under six months. There were two operative deaths (7%) and no late deaths. Heart block did not occur. Late hemodynamic studies in 17 patients reveal good relief of RV obstruction (mean RV-PA gradient 19 mm Hg) and no significant shunts. The natural history of TF in infancy can be successfully interrupted in most cases by early correction.