Table 4.16 - Characteristics of Ventricular Septal Defects (the most common heart defect).

Small/restrictive VSD:

Tiny crevice size to 50 - 60% of aortic diameter; orifice of defect limits maximal flow such that RV pressure doesn't reach systemic.
Blood shunted across defect proportional to defect size; flow from LV to RV occurs throughout systole giving a pansystolic murmur.
O₂ step-up seen in RV relative to RA; increase proportional to extent of shunt flow.
Pulmonary blood flow increases; increase in lung vascularity is seen on X-ray.
X-ray, ECG & echocardiography determine degree of enlargement.

Altered pressures and saturation -
Normal small VSD

RA 2 5

RV 20 25

PA 20/5 (12) 25/10 (17)

PA 70% 85%