Determination of left to right shunt by thermodilution in patients with ventricular septal defect.

A modified thermodilution technique was used to determine the quantity of shunt in patients suffering from congenital heart disease with a left to right shunt. In our modification, the thermistor was placed within the pulmonary artery and an indicator was injected into both sides of the heart. In a series of 33 cardiac catheterizations in children (1-17 years) with ventricular septal defect (VSD), pulmonary blood flow (Qp), systemic blood flow (Qs) and the ratio of Qp to Qs (Qp/Qs) were determined by this and ordinary oximetry (Fick) methods. Correlation coefficients between indexes obtained by these methods were 0.54 (Qp), 0.78 (Qs), and 0.75 (Qp/Qs). The estimates of Qp and Qp/Qs obtained by thermodilution were smaller than those obtained by the Fick method. This modification of thermodilution is simple, rapid, and useful in clinical practice.