INCIC cases ·
A murmur at 33: what is your diagnosis?
33-year-old man referred for a murmur. Cardiac MR with 4D Flow.
Case by Julián Vega Adauy · jvega@incic.org
4D FlowMurmur
What is your diagnosis?
Answer
Restrictive perimembranous ventricular septal defect
Perimembranous VSDShunt
In the right ventricular three-chamber view, 4D Flow shows a systolic left-to-right jet reaching the right ventricle through a small defect in the membranous septum, about 4 × 3 mm, seen en face. The shunt is not significant (Qp/Qs 1.05) and both ventricles have normal size and function.
Teaching points
- A VSD is a post-tricuspid shunt. Flow crosses the septum in systole, while the right ventricle is contracting, and goes almost straight into the pulmonary artery. The right ventricle does not hold that volume in diastole.
- The extra volume returns to the left side. It comes back through the pulmonary veins to the left atrium and ventricle. That is why a significant VSD volume-loads and dilates the left chambers, not the right ones.
- In a shunt, the chamber that receives the extra volume in diastole is the one that dilates. An ASD, pre-tricuspid, dilates the right chambers. A VSD or a ductus, post-tricuspid, dilate the left ones.
- The exception is severe tricuspid or pulmonary regurgitation, which can volume-load the right ventricle. In a VSD, a competent tricuspid valve is in a way the gatekeeper of the right heart.
- A loud murmur does not mean a large shunt. Here the defect is restrictive and the left ventricle is at the upper limit of normal (100 ml/m²). 4D Flow shows the defect and its entry into the right ventricle, and quantifies Qp/Qs in the same study.