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These patients have a perimembranous VSDs, which is also called paramembranous, or conoventricular. They are located in the perimembranous septum adjacent to the septal leaflet of the tricuspid valve. They are bordered by the fibrous continuity of the AV valves and an arterial valve. They frequently extend to the outlet, or inlet septum and can also be referred to as infundibular, outlet or trabecular VSDs.
Associated lesions include â‚Ç¨¨a.aortic insufficiency which occurs because of aortic valve prolapse likely from VSD flow b. double chambered RV.
Perimembranous VSDs often close spontaneously as a result of TV valve tissue that gets â‚Ç¨?ìcaughtâ‚Ç¨¬ù in the defect creating a TV aneurysm. There is usually no effect on TV function. Generally, if none of the criteria listed below are met, time is given for the VSD to close spontaneously.
If the VSD is moderate to large (as large as 50% to 100% the dimensions of the aortic valve annulus) and the patient is symptomatic despite medical therapy or has significant LV volume overload with LV dilation or pulmonary hypertension then the defect is closed. In addition, if it hasnâ‚Ç¨‚Ñ¢t closed by some arbitrary age (elementary school age) then it is closed.
Finally, when the defect results in aortic valve prolapse and AI, the defect is usually closed regardless of the size of the VSD with the hope that further increases in AI are mitigated..
Interventional closure with a device is not yet approved. Surgical closure is usually with a patch and rarely a simple stich closure is possible with very small VSDs in young patients. Repair or replacement of the aortic valve is rarely necessary unless there is obvious abnormality of the aortic valve or the AI is severe.
A residual VSD can be quantitated by measuring the size of the defect on 2D and roughly by comparing the size of the defect on echo to the size of the aortic annulus. A moderate defect is about 50% the size of the annulus and a large one is over 75% the size. Further, if flow through the defect is restrictive it is usually small whereas unrestrictive flow suggests a large defect. This assumes there are no additional lesions that might confound calculations. Alternative non echo tests that can be used to help quantitate the size of the shunt include measuring pressures directly or performing a â‚Ç¨?ìsaturation runâ‚Ç¨¬ù (measuring mixed venous, pulmonary artery and aortic saturations with the patient preferably on as little oxygen as possible) and measuring the pulmonary to systemic blood flow ratio (Sa02-Mv02/Spv02-Spa02, assume Spa02 and Spv02 are about equal). It should be 1 but values greater than 1.5 to 1 likely need correction. In the end, the determination of what to do with a residual VSD depends on multiple factors that include the size of the shunt as well as acute and chronic hemodynamic consequences of a residual shunt and the risks of returning to bypass to repair the defect as well as the likelihood of successful repair.
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