CHARACTERIZATION OF ANEURYSMAL TRANSFORMATION IN PERIMEMBRANOUS VENTRICULAR SEPTAL-DEFECTS - AN ADHERED ANTERIOR LEAFLET OF TRICUSPID-VALVEPREDISPOSES TO THE DEVELOPMENT OF LEFT-VENTRICULAR TO RIGHT ATRIAL SHUNT

Background: The most common type of left ventricular-to-right atrial s hunts are those associated with perimembranous ventricular septal defe ct when the defects diminish in size via aneurysmal transformation. Th is study is to characterize the echocardiographic features and to dete rmine the possible mechanisms. Methods and results. From January 1986 to December 1992, of 930 consecutive patients with isolated perimembra nous ventricular septal defect, 692 showed evidence of aneurysmal tran sformation. Excluding those with subaortic ridge, echocardiographic an alysis was based on 664 of them. Of these, 94 patients had left ventri cular-to-right atrial shunts, 115 had their defects spontaneously clos ed and in 455 only interventricular shunt persisted. Four types of ech ocardiographic findings featured in the aneurysmal transformation proc ess: type A, both the anterior and septal leaflets of tricuspid valve contributed to the process; type B was similar to type A, but the are- like structure from the anterior leaflet is much less evident; in type C, only the septal leaflet, and in type D, other adjacent tissues, co ntribute to the aneurysmal transformation. Type A morphology was close ly associated with the development of left ventricular-to-right atrial shunt while types C and D were most commonly seen in those spontaneou sly closed defects and those with only interventricular shunt. The veg etations 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 inte rventricular shunt. Conclusion: The morphology of the aneurysmal trans formation in perimembranous ventricular septal defect can be character ized 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 ventr icular-to-right atrial shunts.