**3.8 Tetralogy of fallot**

Tetralogy of Fallot (TOF) consists of VSD, overriding aorta, RVOT obstruction, and RV hypertrophy. It can be associated with right aortic arch, additional VSDs, absence of the pulmonic valve, coronary artery anomalies, systemic venous anomalies, AP window, and LVOT obstruction. Surgery involves VSD closure and repair or reconstruction of RVOT (Shinebourne et al., 2006).

The pathophysiological changes in patients with TOF are related to the shunt flow across a large VSD and the degree of RVOT obstruction. RV pressure is increased due to large VSD flow and RVOT obstruction. When the RV pressure is greater than systemic pressure, a right-to-left shunt and arterial desaturation will ensue. There may be little or no right-to-left shunt if the RVOT obstruction is not severe. The common associated cardiac anomalies include right-sided aortic arch in 25%, ASD in 10%, and coronary anomalies in 10% of patients with TOF.

Preoperative TEE exam can evaluate the degree of RV hypertrophy and aortic overriding, the site and severity of RVOT obstruction, size and location of VSD, direction and magnitude of shunt flow, ventricular and valvular function, morphology of pulmonary arteries, and associated cardiac lesions such as ASD. Overriding aorta and anterior malalignment of outlet septum can be best seen in mid-esophageal aortic valve long-axis view (Figure 14). RVOT obstruction and shunt across VSD can be evaluated in mid-esophageal RV inflow-outflow view (Figure 15). Valvular and supravalvular pulmonary stenosis can be demonstrated in upper-esophageal aortic short-axis view. Post-repair TEE evaluation should include the presence and degree of residual RVOT obstruction, residual intracardiac shunt, peripheral pulmonary stenosis, aortic and pulmonary regurgitation, and ventricular function.

Fig. 14. Tetralogy of Fallot. The mid-esophageal aortic valve long-axis view demonstrates the overriding of aorta. LA, left atrium; LV, left ventricle; RV, right ventricle; Ao, aorta.

Fig. 15. Tetralogy of Fallot. The right ventricle (RV) inflow-outflow view shows a ventricular septal defect (D) and infundibular pulmonary stenosis (arrow). Ao, aorta.
