Dec. 05, 2018
Hypoplastic left heart syndrome (HLHS) with an intact or severely restrictive atrial septum carries the highest risk of mortality within the first few hours of life, and constitutes about 10 percent of all patients with HLHS. Having a decompressing vein (that diverts blood flow from the hypertensive left atrium and pulmonary veins into a systemic vein) or antegrade flow through patent mitral and aortic valves may allow for a limited time of hemodynamic stability after birth. However, emergent relief of obstruction at the atrial level is needed for survival.
The best strategy to obtain this relief is not yet established. "Fetal interventions, postnatal transcatheter interventions and postnatal surgical resection have all been used, but the mortality risk continues to be high in this subgroup of patients," says M. Yasir Qureshi, M.B.B.S., a pediatric cardiologist at Mayo Clinic in Rochester, Minnesota. Dr. Qureshi led a team of pediatric cardiologists, pediatric cardiac surgeons and maternal-fetal specialists in a novel, sequential approach to managing this pathology in a fetus with HLHS with intact atrial septum (HLHS-IAS) that was developing hydrops. This approach consisted of percutaneous in utero fetal atrial septostomy followed by ex utero intrapartum treatment (EXIT) to surgical atrial septectomy.
A 28-year-old mother who was gravida 4 para 2 was referred to Mayo Clinic for further management of prenatally diagnosed fetal HLHS. Fetal echocardiogram performed at 28 weeks gestation demonstrated HLHS-IAS with mitral valve hypoplasia, aortic valve atresia, hypoplastic left ventricle and hypoplastic ascending aorta. The atrial septum was thick and muscular.
Pulmonary venous Doppler showed to-and-fro flow with prominent flow reversal during atrial systole consistent with severe restriction at the atrial level resulting in hypertensive left atrium. There was no decompressing vein or any antegrade flow through the left heart. Follow-up fetal echocardiogram performed the following week showed the new development of a small right-sided pleural effusion and pericardial effusion (fetal hydrops). Due to the development of these early signs of fetal hydrops, percutaneous fetal intervention was recommended.
Ultrasound-guided percutaneous fetal atrial septostomy
The fetal atrial septostomy was performed under local maternal anesthesia and sedation. The fetus was gently positioned in order to have the correct needle access. A combination of anesthetic medications was injected percutaneously into the left arm of the fetus under ultrasound guidance. Again, under ultrasound guidance, a trocar needle was advanced percutaneously into the amniotic space and was directed through the fetal chest wall and into the right atrium. The atrial septum was punctured with the needle trocar, and the trocar was removed. A coronary wire was advanced through the needle into a pulmonary vein. A coronary angioplasty balloon was advanced over the wire and inflated multiple times to dilate the atrial septum.
Once flow across the atrial septum was demonstrated by color Doppler, the balloon was withdrawn into the needle and the needle, balloon and wire were removed. A small pericardial effusion was observed but did not progress or require drainage. Fetal heart rate remained stable between 120 to 140 beats per minute, and ventricular function remained normal during the entire procedure.
"Follow-up fetal echocardiogram performed one week after the intervention demonstrated resolution of pericardial and plural effusions," says Nathaniel W. Taggart, M.D., a pediatric cardiologist at Mayo Clinic in Rochester, Minnesota. The atrial septum was still restrictive, but with blood flow across the septum. The patient was closely followed by a maternal fetal medicine specialist and a pediatric cardiologist weekly. Fetal echocardiogram performed at 33 weeks of gestation showed reappearance of a right-sided plural effusion. Percutaneous re-intervention was not deemed appropriate in this setting due to thick and muscular atrial septum.
Due to evolving hydrops fetalis, EXIT to surgical atrial septectomy with possible need of extracorporeal membrane oxygenation (ECMO) was recommended. The likelihood of a poor outcome and the added risks of EXIT procedure were discussed in detail with the patient. Alternative management options were discussed. After an extensive multidisciplinary discussion, the patient elected to proceed with EXIT procedure and open septostomy. Ethical approval was obtained from the Pediatric Ethics Board.
EXIT to surgical atrial septectomy
An EXIT delivery was performed at 34 weeks of gestation under maternal general anesthesia. The fetus was partially delivered and the fetal-placental circulation was maintained. After transthoracic echocardiographic confirmation of the diagnosis, a median sternotomy was performed. The external inspection of the heart likewise confirmed the fetal diagnosis of HLHS with severely hypoplastic ascending aorta, large main pulmonary artery and a large ductus arteriosus that supplied the descending aorta.
A central line was placed in the right atrium and secured to the chest wall to enable medication administration and fluid resuscitation. A long purse-string suture was placed in the right atrial free wall. The superior and inferior venae cavae were temporary clamped with vascular clamps, and the heart was allowed to empty. Entry into the right atrium was made through an incision within the purse-string suture. The septum primum was resected, and the heart was de-aired by removing the temporary clamps on the venae cavae. Finally, the purse string was pulled to control the bleeding.
Acidosis and anemia were corrected. Epicardial echocardiography confirmed adequate communication between the right and left atria and no restriction at the interatrial septum. The fetus was then intubated and ventilated. ECMO was on standby, but since the fetus responded well to ventilation, ECMO was not needed. The fetus was then completely delivered by clamping the umbilical cord. The neonate was then transferred to a separate operating room for completion of the procedure, where umbilical arterial and venous catheters were placed. The chest was then temporarily closed after placing the standard surgical drains, and the neonate was transferred to the cardiac surgical intensive care unit (ICU). No intraoperative complications for either the mother or the neonate were encountered.
"Intact or severely restrictive atrial septum poses a high risk of mortality in patients with HLHS," according to Rodrigo Ruano, M.D., Ph.D., chair of Maternal and Fetal Medicine. Development of hydrops commonly portends in utero fetal demise. Many of the in utero or postnatal interventions, including ECMO support, can be futile due to abnormal pulmonary vasculature (diffuse hypoplasia of pulmonary arteries, "arterialization" of pulmonary veins with muscular media and severe pulmonary hypertension).
Initial percutaneous intervention in this case allowed resolution of developing hydrops early on, avoiding fetal demise. The atrial septum had some flow but continued to be restrictive due to its muscular nature. Recurrence of hydrops required more definitive management. Waiting until term would have likely led to in utero fetal demise; as a neonate starts breathing and the lungs expand, there is an increase in pulmonary blood flow that results in severe pulmonary congestion and pulmonary edema if the obstruction is not relieved.
EXIT to surgical septectomy allowed for the relief of atrial level obstruction prior to the neonate's first breath, avoiding need for ECMO. This is the first reported case where an EXIT procedure has been used without cardiopulmonary bypass for an open-heart operation in humans and provides a promising alternative strategy for management of HLHS-IAS.