Doppler Echocardiography in Ventricular Septal Defects

In a suprisingly short period of time, cardiac ultrasound has become accepted as an accurate and reproducible technique for the noninvasive evaluation of many aspects of both morphology and hemodynamics of ventricular septal defects. High resolution cross-sectional imaging can visualize virtually all moderate to large sized defects. Small defects (i.e. <3 mm. maximal diameter) normally lie beyond the powers of resolution of even the most modern cross-sectional imaging systems. However, such isolated small defects are virtually always associated with restrictive hemodynamics (i.e. a high trans-septal gradient with low right ventricular pressure), and although they are frequently missed by cross-sectional imaging, their high velocity trans-septal turbulent jet is easily picked up by continuous wave Doppler interrogation. From a combined complete continuous pulsed wave Doppler study both the right heart systolic pressures and the relative volume flows in the aorta and pulmonary artery can be calculated. The addition of colour flow mapping plays an important part in identifying the site (or sites) of trans-septal flow and defining the location of small restrictive defects. However, problem areas in the ultrasound evaluation of ventricular septal defects do exist: i) the presence of multiple ventricular septal defects can be missed (especialy if non-restrictive hemodynamics are present); ii) precise intra-cardiac shunt calculations in young infants are fraught with problems; iii) poor alignment with the high velocity trans-septal jet can lead to serious overestimation of right ventricular peak systolic pressure. Wrong diagnoses can occur despite the use of all three ultrasound modalities if these important pitfalls are not appreciated. In this chapter we will attempt to review the current understanding and use of cardiac ultrasound in the evaluation of the complex morphology and frequently changing hemodynamics in this important group of lesions.