Contributors: Laura Downey, MD and Rajesh Punn, MD
Lucile Packard Children’s Hospital at Stanford University
After the bicuspid aortic valve, a ventricular septal defect (VSD) is the most common congenital cardiac lesion, comprising almost 50% of all congenital heart disease (1,2). The reported prevalence is between 1,667-6,616 per 1 million live births depending on the study. However the actual incidence is unclear since many VSDs close spontaneously (1,2). VSDs may occur in isolation or in conjunction with other complex cardiac lesions (i.e. Tetralogy of Fallot, Transposition of the great arteries (TGA), or AV canal defect), which will be discussed elsewhere.
Simply, a VSD is a defect of the ventricular septum that allows communication between the right and left ventricle. Physiologically, a VSD is a simple shunt. The size of the defect is the primary determinant of the shunting. If the VSD is small, the flow through the defect will be limited and there is a large pressure gradient across the defect – restrictive shunt. In a large defect, the pressure gradient across the VSD is low and direction of the shunt is more dependent on the systemic and pulmonary vascular resistances – unrestrictive shunt.
The intraventricular septum is formed by the growth and fusion of 1) the muscular septum, 2) inferior endocardial cushion, and 3) the conal septum. A defect in the development of any portion of the septum will result in a VSD. There are four categories of VSDs named based on the anatomical position. We will describe the main types of VSDs and focus on imaging for membranous VSDs.
Types of VSDs
Membranous (perimembranous, subaortic, conoventricular): Membranous VSDs are the most common type of VSD, comprising 75-80% of all defects (2). Membranous VSDs lie just below the aortic valve and the septal leaflet of the tricuspid valve. These VSDs can have extensions into the inlet or muscular septum, which may undergo closure either by tricuspid septal leaflet tissue or prolapse of an aortic cusp. On echo, this may look like an aneurysm of the ventricular septum or result in LV outflow obstruction respectively (3). The Bundle of His and AV node lie close to these defects; post-operative heart block is a known surgical complication (4). Many of these VSDs will close spontaneously.
Subpulmonic (outlet, supracristal, infundibular, conal septal, doubly committed subarterial defects): These VSDs lie superior and anterior in the ventricular septum. These occur in about 5-7% of VSDs and are located immediately beneath the aortic and pulmonary valves (1,2). These rarely close spontaneously.
AV canal (inlet): AV Canal VSDs, which make up about 5% of VSDs, occur posterior and superior between the annulus of the tricuspid valve and the attachments of the tricuspid valve to the ventricular septum (1,2). These defects are rarely isolated, but rather associated with endocardial cushion defects and AV canal defects.
Muscular Defects: Muscular VSDs, between 10-15% of defects, may be found anywhere in the muscular intraventricular septum. – apical, anterior, midmuscular, or posterior. Often the heavy trabeculation of the RV septum make these defects difficult to identify and may underestimate the actual size (1,2,3). These VSDs often close spontaneously. Multiple defects may be referred to as a “Swiss Cheese” septum, but often function like a large VSD (3).
Goals of echocardiography:
The goals of ECHO in assessing VSDs preoperatively
- Determine the location and size of the defect
- Determine relationships with nearby structures (ie. Aortic and pulmonary valves)
- Measurement of defect margins
- Hemodynamic assessment including flow direction (by color and spectral Doppler)
- Estimation of RV systolic pressure (TR jet velocities)
- Mean transseptal pressure gradient
- Evidence of hemodynamic load (LV enlargement, systolic septal flattening associated with RV pressure load, increased pulmonary blood flow)
- Biventricular function
- Associated lesions
The goals of ECHO in assessing VSD repair:
- Biventricular function
- Residual VSD
- LVOT obstruction
- Volume status and need for inotropic support
Preoperative Evaluation and Associated ECHO views:
TTE Imaging of VSDs
Parasternal long-axis of membranous VSD
Parasternal long-axis of membranous VSD with Doppler
Parasternal long-axis of multiple muscular VSDs with and without color
Apical four chamber view of muscular VSD
TEE Imaging of Membranous VSD
4 Chamber View Mid Esophageal View (TEE, 0 Degrees)
4 Chamber View Mid Esophageal View showing left to right shunt (TEE, 0 Degrees, with Doppler)
Mid Esophageal Long Axis View (TEE, 121 degrees)
Mid Esophageal Short Axis View (TEE, 55 degrees)
Mid Esophageal Short Axis View (TEE, 55 degrees, with Doppler)
References:
1. Hoffman, JIE. Epidemiology of congenital heart disease: Etiology, pathogenesis, and incidence. In: Yagel S, Silverman NH, Gembruch U, eds. Fetal cardiology. London: Martin Dunitz, 2003.
2. Kussman, B and DiNardo, J. The Cardiovascular System. A Pratical Approach to Pediatric Anesthesia. Editors: Robert S. Holzman, Thomas J Mancuso and David M Polaner. Lippincott Williams & Wilkins. Philadelphia. 2008. Pg 306-374.
3. Forbus, GA and Shirali, GS. Anomalies of the Ventricular Septum. Echocardiography in Pediatric and Congenital Heart Disease: From Fetus to Adult. Edited by Wyman W. Lai, Luc L. Mertens, Meryl S. Cohen and Tal Geva. 2009 Blackwell Publishing Ltd. Pg 176-187.
4. Jonas, R. Ventricular Septal Defect. Comprehensive Surgical Management of congenital heart disease. Editor: Richard Jonas. Macmillan Publishing Solutions. 2004. Pg 242-255.
