Different mechanisms for persistent and residual left-to-right shunt after transcatheter sinus venosus defect closure and their management.

Transcatheter closure of superior vena cava (SVC) form of sinus venosus defects (SVDs) using covered stents is emerging as an alternative to surgery in the current decade. A covered stent placed in the cavoatrial junction creates a roof for the right upper pulmonary vein (RUPV) that stops the left-to-right shunt and redirects the vein to the left atrium. While surgical literature has clearly documented the incidence of stenosis of SVC and RUPV, sinus nodal dysfunction, and persistent residual shunts following surgical correction, it is imperative to have similar data after this new transcatheter intervention on the incidence of complications and follow-up outcomes. Since patients with pretricuspid shunts are often clinically asymptomatic, correction is primarily performed to prevent a persistent right heart volume overload and allow remodeling of the heart chambers. Any residual left-to-right shunt after a correction will result in persistent right heart dilatation. Residual flows can result from various mechanisms, including lack of apposition of the covered stent to the free edge of the SVD, fabric breach, and persistent anomalous drainage of additional right-sided pulmonary veins that drain very high in the SVC or can be due to a coexistent defect in the oval fossa. This review analyzes the different mechanisms, explains the transesophageal and angiographic images for each one, and offers solutions tailored for various reasons. Different mechanisms warrant different treatment principles. A solution for residual shunt from one mechanism may not be appropriate for residual flow through another mechanism. A thorough understanding would aid the operator in effective interventions for these SVDs.