Ventricular Septal Defect

The most common ventricular septal defects (VSDs) are of the membranous type—located just underneath the aortic valve.There are currently no FDA-approved devices to close membranous VSDs. There is one membranous VSD occluder that is available elsewhere in the world. This device is eccentric with a recessed aortic margin to avoid interference with this valve.This device is much more technically demanding to implant than the ASD or PDA devices. Reports of late complete heart block are worrisome and thought to be due to the constant radial force of the nitinol against the bundle of His, which is intimately associated with the posterior margin of the membranous VSD. Because the surgical results for membranous VSDs are generally excellent, any transcatheter device will need to meet or exceed this high standard to become an acceptable alternative.

Muscular VSDs are found elsewhere in the ventricular septum. While situated away from the conduction system, they are often multiple or associated with a membranous VSD. Unlike membranous VSDs,muscular VSDs, especially when multiple or located at the apex of the heart, are surgically challenging. The only transcatheter device that is FDA-approved to close these defects is the CardioSeal. This device is a doubleumbrella device with four ‘arms’ of nitinol wire on each umbrella supporting a square Dacron patch. Although this device was originally designed to close atrial communications, the lack of surgical or transcatheter alternatives to address complex muscular VSDs allowed FDA approval of the CardioSeal device for muscular VSD closure. However, the large delivery system (11 French) and poor retrievability characteristics limit the utility of the CardioSeal device for this indication. There is a muscular VSD occluder based on the same nitinol frame design as their ASD device, but with a thicker connecting waist and smaller retention disks to conform to the muscular septum. This device is much easier to retrieve and reposition, and has a smaller delivery system than the CardioSeal. It is in the final phases of FDA approval.

A VSD occluder specifically designed to treat postmyocardial infarction (MI) ventricular septal defects is, at present, limited to investigational use in the US.

Stenotic and Regurgitant Lesions

A mainstay of interventional congenital cardiology is the use of transcatheter balloon dilation and stenting to relieve vascular stenoses. Areas that frequently require dilation and/or stenting in the congenital population are the pulmonary arteries, aorta, and various conduits and venous baffles. Most of the balloons and stents used by congenital cardiologists were designed and approved for use in the peripheral vascular and biliary systems. In the past few years, several balloons have been specifically manufactured for congenital cardiology applications. One example is the ‘Balloon-in-Balloon’ (BiB), which is an innovative design with a smaller inner balloon and larger outer balloon. This design facilitates the delivery of large stents in structures, such as the pulmonary artery or aorta, limiting the risk of balloon rupture during stent placement.

The stents used by congenital cardiologists in the US are all adapted from other approved indications such as biliary and peripheral vascular stenting. Though designed for other applications, the availability of premounted stent-balloon combinations has greatly facilitated the delivery of medium-sized stents in small children (see Figure 5).

Early clinical trials are under way to evaluate the use of transcatheter delivery of stent-mounted valves. Many congenital heart patients have had reconstruction of the pathway from the right ventricle to the pulmonary artery with surgically placed, valved homografts. As the valve function of these homografts deteriorates over time, these patients can be left with significant pulmonary regurgitation—the deleterious consequences of which are increasingly being appreciated.Transcatheter placement of a new valve is desirable to avoid repeat surgery. The current technology is based on a bovine interval jugular valve mounted inside a balloon-expandable stent. Early work conducted in Europe developing this system appears promising^.6 The long-term durability of these implanted valves remains to be seen.

Summary

Many tools to treat children and adults with congenital heart disease are devices adapted from other applications. Recently, devices specifically for use in congenital heart disease have been FDA-approved and have dramatically advanced the non-surgical care of patients with congenital heart disease. Further development of tools specifically designed for congenital heart applications are forthcoming and will continue to advance the field.