Cardiac septation in atrioventricular canal defect.

To determine the relative contributions of the atrial and ventricular septa to total cardiac septation in patients with atrioventricular (AV) canal defect, two-dimensional echocardiography was used to measure the length of each portion of the septum in 14 patients with partial AV canal and 13 patients with the complete form of this lesion. Results were compared with similar data from 30 normal children, 10 patients with dilated cardiomyopathy and 11 patients with ostium secundum atrial septal defect. In patients with partial AV canal, the portion of total cardiac length occupied by the atrial septum did not differ from normal (24.8 +/- 9.9% versus 28.7 +/- 7.9%, p greater than 0.05), but there was a deficiency of both AV and ventricular septal tissue, the latter occupying only 48.2 +/- 7.0% of total cardiac length (versus 57.9 +/- 4.1% in normal subjects, p less than 0.05). Similarly, patients with complete AV canal had a normal amount of atrial septal tissue, a deficiency of AV septal tissue and a deficiency of ventricular septal tissue which was even greater than that of patients with a partial defect (39.4 +/- 5.0% versus 48.2 +/- 7.0%, p less than 0.05). Thus, although partial AV canal defect is often called ostium primum atrial septal defect, the amount of atrial tissue is usually normal, the defect being formed by a deficiency of AV and ventricular septal tissue. In the complete form of the lesion, the deficiency of ventricular septal tissue is greater.