Right Atrial Surgery without Caval Snaring

Background During tricuspid valve replacement in a patient with previous mitral valve surgery, we made an incidental observation that the right atrium can be opened without caval snaring and without air entering the venous reservoir. We tested this hypothesis on an animal model. Methods Two patients underwent right atrial surgery using percutaneous cannulation, and no air was entrained without caval snaring. This principle was tested in an animal model using 2 pigs weighing 80 kg each. Percutaneous cannulae were placed under epicardial echo guidance with their tips 4 cm from the right atrium. A “collapsible bag with air drainage system” was introduced into the venous return system to quantify air return from the superior vena cava (SVC) and inferior vena cava (IVC). Two types of percutaneous cannulae with (Cardiovations Quick Draw) and without (Biomedicus) proximal side holes were tested. Results In the animal model using Biomedicus cannulae, upon opening the right atrium, air was entrained from the SVC cannula at 60 mL/minute with no air in the IVC. There was no difference in the amount of air between the two cannulae. Pressures measured were 5 cm of water in the IVC and −20 cm water in the SVC. Epicardial ultrasound demonstrated complete collapse of both vena cavae. Partial clamping of the SVC cannula reduced the amount of air to 60 cc/min, and placing a small straight clamp at the SVC atrial junction eliminated the air. No air was noted in IVC cannula. Conclusions Inferior vena caval drainage by percutaneous cannula does not entrain air with either type of cannula and without snaring (both in clinical cases and animal model). This might be explained by the presence of a competent Eustachian valve. However, the SVC is not immune to air. Minimal air (approximately 60 mL/minute) could be managed by partial clamping or completely be avoided by placing a small straight clamp without snaring.