Background: The most common type of left ventricular-to-right atrial shunts are those associated with perimembranous ventricular septal defect when the defects diminish in size via aneurysmal transformation. This study is to characterize the echocardiographic features and to determine the possible mechanisms.
Methods and results: From January 1986 to December 1992, of 930 consecutive patients with isolated perimembranous ventricular septal defect, 692 showed evidence of aneurysmal transformation. Excluding those with subaortic ridge, echocardiographic analysis was based on 664 of them. Of these, 94 patients had left ventricular-to-right atrial shunts, 115 had their defects spontaneously closed and in 455 only interventricular shunt persisted. Four types of echocardiographic findings featured in the aneurysmal transformation process: type A, both the anterior and septal leaflets of tricuspid valve contributed to the process; type B was similar to type A, but the arc-like structure from the anterior leaflet is much less evident; in type C, only the septal leaflet, and in type D, other adjacent tissues, contribute to the aneurysmal transformation. Type A morphology was closely associated with the development of left ventricular-to-right atrial shunt while types C and D were most commonly seen in those spontaneously closed defects and those with only interventricular shunt. The vegetations of infective endocarditis were located at the atrial side of the tricuspid valve in patients with left ventricular-to-right atrial shunts, while they were in the right ventricle in those with only interventricular shunt.
Conclusion: The morphology of the aneurysmal transformation in perimembranous ventricular septal defect can be characterized by echocardiograms. Although the septal leaflet of the tricuspid valve is usually involved in this process, it is the incorporation of the anterior leaflet that predisposes to the development of left ventricular-to-right atrial shunts.