Left ventricular distensibility and passive elastic stiffness in atrial septal defect

Diminished left ventricular distensibility has been postulated as a cause of left ventricular failure in atrial septal defect. To evaluate this hypothesis the indexes of left ventricular compliance and stiffness were estimated in 15 patients with atrial septal defect and the results compared with those in 10 normal subjects. Age, peak left ventricular systolic pressure, end-diastolic pressure, ejection fraction and cardiac index did not differ significantly between groups. Left ventricular end-diastolic volume for the atrial septal defect group was significantly less than that for the control group (mean ± SD, 61 ± 9 ml/m² versus 73 ± 13, p < 0.05) in keeping with previous studies. The slope of the log pressure-volume relation was significantly greater in the group with atrial septal defect than in the normal group (0.056 ± 0.010 versus 0.044 ± 0.008, p < 0.01), consistent with increased chamber stiffness. For a group of six patients with atrial septal defect and elevated left ventricular end-diastolic pressure, normalized compliance was significantly less than that in the control group (0.017 ± 0.001 versus 0.036 ± 0.007, p < 0.02). The slope k of the elastic stiffness-stress relation for the total group with atrial septal defect was significantly greater than that of the normal group (21.0 ± 2.3 versus 18.1 ± 2.3, p < 0.01). An index of muscle fiber stretch (dV/VdP × end-diastolic stress × 100) was significantly less in the atrial septal defect group than in the control group (74 ± 24 versus 106 ± 22, p < 0.01). Thus, left ventricular compliance and muscle stiffness may be adversely affected in atrial septal defect. Abnormal distensibility may exist in the presence of elevated left ventricular diastolic pressure and may have a rote in the genesis of left ventricular failure in this setting.