Pathogenetic Mechanisms of Prolapsing Aortic Valve and Aortic Regurgitation Associated With Ventricular Septal Defect

The developmental mechanisms of prolapse and regurgitation of the aortic valve which complicate ventricular septal defect (VSD) were investigated from the anatomical, angiographic, and surgical viewpoints on the basis of autopsied heart specimens, preoperative thoracic aortography, and surgical records. Two major, conceptually distinct but functionally interdependent factors contribute to the aortic valve's prolapse into the VSD. The major feature of the first category is the lack of anatomical support for the valve. In subpulmonary VSD, a regional defect of the conal septal musculature which supports a section of the right coronary sinus and the annulus was observed. In infracristal VSD, a deficiency of the sinus of Valsalva was noted. The hemodynamic effects, which actually produce prolapse of the anatomically unsupported valve into the VSD, is the second contributing factor. The left-to-right shunt of blood through the VSD during the early systolic phase pulls the sagging aortic valve into the defect. The distinctive feature of the second category is that prolapse of the anatomically unsupported valve is produced by hemodynamic effects. Diastolic aortic pressure does not appear to contribute greatly to bulging of the aortic valve into the right ventricular cavity. However, in the diastolic phase, the closed valve is subject to intra-aortic pressure, causing the free margin of the prolapsed cusp to hang down, to gradually become elongated, and finally to separate from the free margin of the other two cusps, and thus be rendered incompetent.