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Fig. 3. Amplatzer Muscular Ventricular Septal Occluder. (A) Photograph of the device; the waist is wider than that of the Amplatzer Septal Occluder to allow for the thicker muscular ventricular septum. (B) Left ventricular angiogram 3 mo after device placement showing complete occlusion of a midmuscular ventricular septal defect.

Fig. 3. Amplatzer Muscular Ventricular Septal Occluder. (A) Photograph of the device; the waist is wider than that of the Amplatzer Septal Occluder to allow for the thicker muscular ventricular septum. (B) Left ventricular angiogram 3 mo after device placement showing complete occlusion of a midmuscular ventricular septal defect.

Surgical closure of muscular ventricular septal defects is often difficult because the right ventricular aspect of the defect can be hidden from the surgeon's eyes by trabeculations within the right ventricular cavity. This results in a high incidence of residual leaks with a right ventricular approach. Directly incising the left ventricle allows clearer visualization of the defect margins, but left ventricular aneurysms or diminished left ventricular function sometimes result (18). The potential for such complications has made transcatheter closure an attractive alternative.

The Amplatzer Muscular Ventricular Septal Occluder is very similar to the Amplatzer Septal Occluder. Fortunately, like a secundum atrial septal defect, muscular ventricular sep-tal defects are separated from cardiac valves by myocardium. Yet, the obvious difference between the two malformations is the thickness of the ventricular myocardium. Hence, these devices were designed with a greater distance between the disks to accommodate such differences in myocardial thicknesses (Fig. 3). In addition, greater stability can be produced by radial force applied against the thicker muscular ventricular septum, and thus the retention disk diameters were decreased to 6-8 mm larger than the waist.

Attempts at transcatheter closure of muscular ventricular septal defects using the Clamshell/CardioSEAL device were reported to produce a 40% incidence of residual leaks (19). It should be noted that these devices have a central post instead of a waist that is the size of the defect. Thus, the "retention" disks designed had to be at least twice the diameter of the defect; residual leaks likely result from migration of the central post within the defect. In contrast, the self-centering Amplatzer Muscular Ventricular Septal Occluder is fixed within the defect by its waist. Another advantage of the Amplatzer device is the smaller maximum device diameter required to close a muscular ventricular septal defect compared with central post devices.

Successful animal trials to close surgically created muscular ventricular septal defects have supported application for human use (20). To date, the Amplatzer Muscular Ventricular Septal Occluder has been deployed in eight patients at the University of Minnesota; it should be noted that three devices were implanted in the operating room directly through the right ventricular wall without cardiopulmonary bypass. Complete defect closure was detected in all eight study subjects, and there were no serious or major adverse events. FDA trials are in progress. This device should significantly improve the care of children who need closure of a muscular ventricular septal defect.

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