EXPLANATION


Pulmonary atresia with intact ventricular septum (PA/IVS) is a rare right-sided obstructive lesion, with an incidence of 1-3% in the congenital heart disease population. It is characterized by an imperforate pulmonary valve, absence of antegrade blood flow from the right ventricle (RV) to the pulmonary arteries (PA), an intact ventricular septum and a variable degree of RV hypoplasia. Disease severity and management options are determined primarily by the size of the RV and the tricuspid valve annulus. Embryologically, flow across the tricuspid valve into the RV and through the PAs is critical for adequate development of the RV. With an atretic pulmonary valve, RV growth will be limited, and the ventricle will remain small and hypertensive. RV hypertension allows ventricular sinusoids to remain open, and to potentially create ventriculo-coronary fistulas, which are present in 50% of children with PA/IVS.


Coronary fistulas can increase the risk of coronary ischemia from RV steal during RV decompression. In the presence of proximal coronary stenosis or atresia, perfusion of the distal myocardium will be dependent on the deoxygenated blood coming retrogradely from the RV sinusoids. This phenomenon is referred to RV-dependent-coronary-circulation (RVDCC). The definition of RVDCC varies somewhat, but it is commonly described as the presence of ventriculo-coronary connections with angiographically severe obstruction of at least two major coronary arteries, complete aorto-coronary atresia, or situations in which a significant portion of the left ventricular myocardium is supplied directly by the RV. Other centers use the presence of any coronary-cameral fistula with proximal obstruction and angiographic evidence of RV myocardial perfusion through those fistulous connections. Spigel et al analyzed the outcomes of 103 patients with PA/IVS, 28 of whom had RVDCC. RVDCC was further classified based on location of coronary obstruction. Eighteen (64%) of the RVDCC patients had proximal obstruction, and the left anterior descending artery was involved in 23 (82%) patients. Mortality rate was 36%. Transplant-free survival was 54% at 6 months, and 46% at 1 and 10 years. Patients with proximal obstruction had decreased transplant-free survival compared to those with distal obstruction (44% vs 70% at 6 months). The authors inferred that proximal stenosis places a higher mass of myocardium at risk for ischemia. Interestingly, patients with distal obstruction did not have a statistically significant difference in transplant-free survival from patients without RVDCC. In 2023, Cheung et al published a retrospective, multicenter study of 295 neonates with PA/IVS that described major adverse cardiac events after the patients’ first intervention. In the 279 patients that did undergo a first procedure, major adverse cardiac events occurred in 20% and the mortality rate was 8%. After a multivariate analysis, risk factors for major cardiac events included lower weight at the time of the first procedure as well as the presence of stenosis in two major coronary artery branches. Of note, patients with an aortopulmonary shunt or a ductal stent were more likely to require CPR, even when patients with RVDCC were removed from the statistical analysis. This highlights the fact that children with single-ventricle parallel physiology remain at high risk for myocardial ischemia.


Identifying RVDCC is thus one of the crucial first steps in managing children with PA/IVS, as it will determine the safety of proceeding with RV decompression through opening the RVOT in the catheterization laboratory or with the use of cardiopulmonary bypass (CPB). In the setting of RVDCC, RV decompression leads to increased diastolic runoff from the coronaries into the RV, resulting in myocardial ischemia or infarction. At present, the gold-standard for diagnosing RVDCC is coronary angiography, with injection of the aorta and the RV, although echocardiography could potentially identify proximal stenosis or atresia. If RVDCC is ruled out, RV decompression is feasible with minimal risk of RV ischemia. Definitive management and prognosis of PA/IVS will then depend on the size and function of the right-sided structures. More recently, several centers have been moving towards catheter-based interventions in the cardiac catheterization lab along with diagnostic angiogram versus traditional surgery, thereby avoiding CPB. Radiofrequency ablation and balloon dilation of the pulmonary valve may be attempted in patients with adequate RV size and function, as well as in those with less favorable anatomy with the goal of growing the right-sided structures. Patients with RVDCC and/or those directed towards a single-ventricle palliation may undergo ductal stenting at the same time or soon after coronary angiography.


Perioperative management of patients with RVDCC requires extra vigilance. Close monitoring of the ECG for signs of ischemia is essential, well as avoiding excessive vasodilation and hypovolemia. Vasodilation may be precipitated by fever, the use of anesthetic medications or vasodilators, such as nitroprusside or milrinone. Hypovolemia from excessive diuresis or gastrointestinal losses should be managed appropriately. Maintenance of RV preload and aggressive treatment of tachycardia and hypotension is critical to preventing myocardial ischemia and cardiac arrest.


The most appropriate initial step in the management of the patient in the stem is to define coronary anatomy and determine the presence of RVDCC. If RVDCC is confirmed, then any procedures that decompress the RV, such as radiofrequency perforation and ballooning of the pulmonary valve, are contraindicated. If the ductal anatomy is amenable to stent placement, this is appropriate to maintain pulmonary blood flow until the next stage of palliation. If ductal stenting is unsuccessful or not possible, an aorto-pulmonary shunt may be required or treatment with a continuous prostaglandin infusion.


REFERENCES


Gleich S, Latham GJ, Joffe D, Ross FJ. Perioperative and Anesthetic Considerations in Pulmonary Atresia with Intact Ventricular Septum. Semin Cardiothorac Vasc Anesth. 2018;22(3):256-264. doi:10.1177/1089253217737180


Spigel ZA, Qureshi AM, Morris SA, et al. Right Ventricle-Dependent Coronary Circulation: Location of Obstruction Is Associated with Survival. Ann Thorac Surg. 2020;109(5):1480-1487. doi:10.1016/j.athoracsur.2019.08.066


Cheung EW, Mastropietro CW, Flores S, et al. Procedural Outcomes of Pulmonary Atresia with Intact Ventricular Septum in Neonates: A Multicenter Study. Ann Thorac Surg. 2023;115(6):1470-1477. doi:10.1016/j.athoracsur.2022.07.055