Author: Kevin Spellman, MD and Michael A. Evans, MD; Ann & Robert H. Lurie Children’s Hospital of Chicago, Northwestern Feinberg School of Medicine
A 3-year-old male toddler with a history of balanced, complete atrioventricular septal defect who is status post a two-patch repair presents to the operating room for resection of a subaortic membrane. Pre- and post-repair intraoperative transesophageal echocardiogram (TEE) images are illustrated below.
Based on the TEE findings, which of the following is the MOST appropriate course of clinical management?
Top: Clip 1 Preoperative: Mid Esophageal Aortic Valve Long Axis
Bottom: Clip 2 Post-Repair: Mid Esophageal Aortic Valve Long Axis
EXPLANATION
A subaortic membrane may occur alone or in combination with other congenital heart defects - such as Shone’s complex, Tetralogy of Fallot, or ventricular septal defect. Discrete membranous subaortic stenosis (DMSS) is the most common type of congenital subvalvar aortic stenosis, which can occur alone or in association with other cardiac anomalies of the aortic and mitral valves. Mitral valve anomalies are present in 48% of patients with DMSS due to the close relationship between the mitral valve and the aortic valve.
Patients with complete atrioventricular septal defects (AVSDs) are at risk for developing a subaortic membrane throughout life due to turbulent flow that occurs secondary to an elongated and narrowed left ventricular outflow tract (LVOT). Common complications that may occur after surgical resection of a subaortic membrane include residual or recurrent subaortic stenosis, heart block, septal perforation, mitral valve perforation, and mitral valve regurgitation. Often, a septal myotomy or myectomy is performed along with a subaortic membrane resection, which is associated with a decreased risk of subaortic membrane recurrence in patients who have had previous cardiac surgery. This benefit has not been reproduced in patients with an isolated subaortic membrane.
TEE Clip 2, obtained after surgical resection of the subaortic membrane, demonstrates moderate to severe left atrioventricular valve (LAVV) regurgitation. Thus, the correct answer choice is B - resume cardiopulmonary bypass and repair the LAVV.
The close association of the subaortic membrane with the anterior leaflet of the LAVV creates a potential hazard for anterior leaflet perforation or injury when resecting a subaortic membrane. Acute LAVV regurgitation is not tolerated well hemodynamically due to a sudden development of left atrial hypertension, diminished stroke volume due to regurgitant blood flow, and a subsequent reduction in cardiac output. Recognition of acute LAVV regurgitation on a TEE can be delayed when the severity is underestimated due to a low flow state across the valve secondary to acute heart failure.
Answer A (to resect additional subaortic membrane) is incorrect, as the post-repair TEE demonstrates more laminar flow in the LVOT. Answer C (perform aortic valve replacement) is incorrect, as the post-repair echo demonstrates only trivial aortic insufficiency. Aortic insufficiency is commonly seen in patients with a subaortic membrane and typically improves after resection of the membrane. Answer D (administer protamine) is incorrect because the acute LAVV regurgitation should be repaired as it may not be well tolerated hemodynamically and may worsen over time.
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