A morphometrical study of myocardial disarray associated with right ventricular outflow tract obstruction.

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Abstract
To define quantitatively the histological characteristics of the hypertrophied myocardium of the right ventricular outflow tract in patients with congential heart disease, a light-microscopic study of biopsy specimens obtained from 20 cases with tetralogy of Fallot (TOF) and 14 cases with muscular obstruction of the right ventricular outflow tract (RVOTO) was performed using a semi-automatic sampling counter. As the controls, the crista suprasventricularis of 11 autopsied cases without cardiac diseasewere used. The TOF patients were divided into 2 groups: those with (9 cases) or without (11) a history of hypoxic spells. The myocyte diameter was calculated according to Chalkley''s27 and Arai''s method28. The areas of myocardial fibrosis and myocyte disarray were determined quantitatively by the point count method. Myocaridal fibrosis was classified into 5 types: focal, mild perimysial, severe perimysial, perivascular and plexiform. In the control group, the myocyte diameter and area of fibrosis and disarray tended to increase with age. In the obstructive groups, the myocyte diameter and area of disarray were greater than those of the control in any age group. Myocyte diameter tended to increase with age in all groups, except for the TOF cases with a history of hypoxic spells. The latter also had the largest area of myocardial disarray (25.3%) (P < 0.01), and a largest area of fibrosis (20.5%) than the TOF cases without spell (14.4%), but severe perimysial fibrosis was observed in only 5 of the 9 patients with spell. The lack of a relation between the pressure and the presence of an increased area of the myocardial disarray in TOF with spells implies that this myocardial change is brought about by myocardial abnormality accompanied by cardiac malformation.