Atrial septal defect MRI


 * Associate Editor(s)-In-Chief: Priyamvada Singh, M.B.B.S. mailto:psingh@perfuse.org; ; Assistant Editor(s)-In-Chief: Kristin Feeney, B.S. mailto:kfeeney@perfuse.org

Overview
Magneic resonance imaging (MRI) can be used as a diagnostic tool in identifying an atrial septal defect. It also helps in visualization of the pulmonary veins, quantifying right ventricular volume and shunt size. Velocity-encoded, phase difference MRI can assess the magnitude of left-to-right shunting as reliably as is done by cardiac catheterization. Also, it has the advantage of being a non-invasive tool compared to the invasive cardiac catheterization. Additionally, phase-contrast cine MRI is more reliable than spin-echo images in determining the size of defect that in turn helps to make a better therapeutics decision i.e. trans-cutaneous or the surgical closure .However, its current utility is limited for smaller defects and in inconclusive echocardiography findings.

Indications
MRI can successfully diagnose atrial septal defect. However, due to the availability of other non-invasive, cheap and sensitive methods like echocardiography its utility is limited for smaller defects.

Advantages

 * Phase velocity MRI mapping can measure the ratio of pulmonary to systemic blood flow (Qp:Qs), ventricular volume, shunt size and pressure gradient across the heart chambers. It is as sensitive as cardiac catheterization that is considered a gold standard.
 * Effective tool when echocardiographic results are inconclusive (small defects).
 * Can provide morphologic image of the heart in neonates
 * Provides multiple images of the heart per cardiac cycle.
 * Non-invasive imaging method

Disadvantages

 * Requires general anesthesia
 * Can misdiagnose certain anatomical structures for e.g. thin fossa ovalis can be mistaken for an ostium secundum defect.
 * Static images can provide a skewed perception of the thickness of the septum.

==ACC / AHA Guidelines - Evaluation of the Unoperated Patient (DO NOT EDIT) == {{cquote|

Class I
1) ASD should be diagnosed by imaging techniques with demonstration of shunting across the defect and evidence of RV volume overload and any associated anomalies. (Level of Evidence: C) }}

Supportive trial data

 * In a study done by Hundley et al. velocity-encoded, phase difference MRI have been found to assess the magnitude of left-to-right shunting as reliably as was done by cardiac catheterization. Also, it has the additional advantage of being a non-invasive tool compared to the invasive cardiac catheterization.


 * In another study done by Holmvang et al. Phase-contrast cine MRI has been found to be more reliable than Spin-echo images. The phase contrast MRI defines the defect shape by the cross section of the shunt flow. Due to the accurate diagnosis of the defect size it helps in making a decision on the therapeutics aspect of the patient i.e. transcutaneous catheter or surgical closure. On the other hand, spin-echo images, are not very accurate in finding ASD size and septal thinning adjacent to a secundum ASD may be falsely considered a part of the defect