The pathophysiology of ventricular septal defect (VSD) is determined by the size of the defect and the state of the pulmonary vascular resistance. We assessed the morphology of VSD using 3D transthoracic echocardiography (3D-TTE) and the ability to estimate the pathophysiology.

Forty-eight children with isolated unique muscular (77%) and membranous VSD (23%) were included. Severity of the VSD was rated according to their pathophysiology. (Type 1: minor left-to-right (L-R) shunt; 2a: significant L-R shunt (left ventricular end diastolic diameter (LVEDD) Z-score>2); 2b: VSD associated with pulmonary hypertension). 3D VSD measurements were obtained after a multi-planar reconstruction of a TTE 3D full volume (X5-1 or X7-2 matrix probes, ie33, Philips). Diagnosis properties of the ratio of 3D VSD area to aortic annulus area (3DA/AAA), 3D VSD area to body surface area (3DA/BSA) and 2Dmax diameter to BSA (2DD/BSA) were compared.

Median age was 8.5 month-old (min 1 max 123). LVEDD Z-score was>2 in 19 children (40%), (12 (25%) had pulmonary hypertension). 3D-VSD systolic area, 3D and 2D max. diameters were correlated with LVEDD. (r=0.71, r=0.52, r=0.55, P<0.05). Systolo-diastolic variation of 3D VSD area was higher in muscular than in membranous VSD (Median 54%vs27%, P=0.0001). VSD were asymmetric with a mean ratio of maximal to minimal 3D diameters of 2.1±1.3 in membranous VSD and 3.2±1.5 in muscular VSD (P=0.01). VSD severity was correlated with LVEDD Z-score, 3DA/AAA and 3DA/BSA ratio (r=0.52, r=0.63, r=0.60, P<0.05), but not with the 2DD/BSA ratio. Ability to diagnose type 2b VSD was higher with the 3DA/AAA or 3DA/BSA ratio than the 2D/BSA ratio (ROC area 0.97 and 0.96 vs 0.85). A 3DA/AAA ratio>0.39 has a sensitivity of 92% and a specificity of 97% to diagnose a 2b-VSD.

3D-TTE allows a morphological and a quantitative assessment of muscular and membranous VSD. The 3DA/AAA ratio is an accurate diagnostic tool to assess the pathophysiology of the VSD.