With this procedure, high-frequency alternating current is used to coagulate and desiccate tissue. Radiofrequency ablation (RFA) has become a favored modality for treatment of twin-reversed arterial peusion (TAP) sequence, also known as acardiac twin (Chap. 45, p. 880). Without treatment, the mortality rate for the normal or pump twin in severe TRAP sequence exceeds 50 percent. he procedure is also used for selective termination with other monochorionic twin complications (Bebbington, 2012).
Under sonographic guidance, a 17-to 19-9auge RF A needle is directed into the base of the umbilical cord of the acardiac twin and inserted into its abdomen. After a 2-cm area of coagulation is achieved, color Doppler sonography is applied to veriy absent low into the acardius. In several centers, survival rates for the normal twin following RF A have signiicantly improved (Lee, 2007; Livingston, 2007). RF A was performed at approximately 20 weeks' gestation in 98 pregnancies with TRAP sequence reported by the North American Fetal Therapy Network (NAFTNet). The median gestational age at delivery was 37 weeks, and the neonatal survival rate was 80 percent. The major complication was prematurely ruptured membranes and pre term birth. Twelve percent were delivered at approximately 26 weeks (Lee, 2013).
RFA has generally been ofered for TRAP sequence when the volume of the acardiac twin is large. In the NFTNet series cited above, the median size of the acardius relative to the pump twin was 90 percent (Lee, 2013). Considering procedure-related risks, expectant management with close fetal surveillance is instead considered if the estimated weight of the acardius is below 50 percent of the pump twin Jelin, 2010). Finally, acardiac twins are more likely to complicate monoamnionic gestations. In one recent series, pump twin survival following RFA was 88 percent in monochorionic diamnionic pregnancies but only 67 percent in monoamnionic pregnancies (Sugibayashi, 2016).
Selected fetal cardiac lesions may worsen during gestation, further complicating or even obviating options for postnatal repair. Severe narrowing of a cardiac outflow tract may result in progressive myocardial damage in utero, and a goal of fetal intervention is to permit muscle growth and preserve ventricular function (Walsh, 2011). These innovative procedures include aortic valvuloplasy for critical aortic stenosis; atrial septostomy for hypoplastic left heart syndrome with intact interatrial septum; and pulmonary valvuloplasy for pulmonary atresia with intact interventricular septum.