Congenital defects of the heart and great vessels, among the most common congenital malformations, affect about 1 percent of live births. There are a few recognized causes of these defects, such as German measles (rubella), which affects the developing fetus, but, for the most part, the causes are not known.
More than half of congenital cardiovascular defects involve abnormal blood flow or obstruction of blood flow through the heart. Pulmonary outlet obstructions and defects in the pulmonary valve are among the most common of all congenital heart defects. Remember that deoxygenated blood returns from the body to the right atrium, flows into the right ventricle, and is pumped into the lungs to become oxygenated. There are valves between the atrium and the ventricle and between the ventricle and the lungs. The area between the right ventricle and the lungs is the right ventricular outlet or pulmonary outlet.
Treatment of pulmonary outlet defects often involves the implantation of a valved conduit to re-establish normal hemodynamics. The concept of a conduit was introduced in 1966 and resulted in immediate hope for many parents of children with congenital heart disease. A conduit is basically a preserved valve from another human (homograft) or from a cow’s neck vein.
Both the homograft and the bovine alternative have a relatively high likelihood of becoming calcified or damaged because they are foreign to the host. The damage can result in:
- Stenosis, which reduces the diameter and hence blood flow to the lungs
- Damage to the valve mechanism, which results in backward flow of blood
- A combination of both stenosis and regurgitation
Any of these endpoints can cause a tremendous increase in the workload of the right ventricle. As the damage worsens, it creates enough disruption of normal hemodynamics that an intervention is required to repair the conduit.
For some patients, dilation with a balloon or the insertion of a stent is all that is required. But for many, surgery involving a sternotomy (a type of incision in the center of the chest that separates the sternum to allow access to the heart) and cardiopulmonary bypass is required. Unfortunately, for children born with these defects, the need for revision surgery occurs every few years because of their rapid growth.
Physicians have been looking for a less invasive and less damaging approach to revise failed conduits for several decades.
In late July, the FDA’s Circulatory System Devices Panel unanimously recommended a Humanitarian Device Exemptions approval of a new device that can be implanted without opening the chest. It is the Melody Transcatheter Pulmonary Valve and the accompanying Ensemble Transcatheter Delivery System, manufactured by Medtronic. It uses a catheter to deliver the heart valve into the conduit.
The device is created by sewing a cow’s jugular vein into the hollow core of a metal stent. Since it is effectively a tissue valve, there is typically no need for long-term anticoagulation therapy.
The Melody valve has been approved in Europe since October 2006 and in Canada since December 2006. Nearly 1,000 patients have received this device worldwide.
The proposed indications are for patients with the following conditions:
- Regurgitant prosthetic right ventricular outflow tract (RVOT) conduits with a clinical indication for invasive or surgical intervention
- Stenotic prosthetic RVOT conduits where the risk of worsening regurgitation is a relative contraindication to balloon dilation or stenting
- Existence of a full circumferential RVOT conduit that was equal to or greater than 16mm in diameter when originally implanted
This device reduces the total number of open chest surgical procedures that these people may undergo. It also allows for intervention at an earlier point as cardiac dysfunction progresses.
This procedure is likely to avoid the prolonged hospitalization that usually accompanies an open thoracotomy and cardiovascular surgery in these fragile patients.
In addition to a long list of potential complications associated with any cardiac catheterization procedure, this intervention can cause hemorrhaging, residual or increasing valvular disease, pressure gradients, progressive thickening and peeling of the intima of the device, infection of the graft, endocarditis, regurgitation, hemolysis, deterioration of the implant, thrombus formation, and pulmonary embolism.
The lifetime of the Melody device is not known. It is expected that the same procedure can be repeated one or more times until the entire conduit will need to be replaced.
The FDA panel’s recommended approval was based on a trial with 99 patients. Ninety-seven percent of attempts resulted in successful implantation. Of those with a successful immediate result, 88 percent had acceptable hemodynamics at 6 months. The stent fractured in 18 percent of patients, of whom one third required intervention. The median time to intervention was 11 months. The panel’s approval was accompanied by several conditions: a five-year post-approval study, revision of the submitted patient brochures and instructions for use, and implementation of a physician training and education program.
In a typical child, the implantation takes about 1.5 hours and requires only a single night in the hospital, compared to a 7–14 day stay for an open chest surgical procedure.
Managed care implications
This device is considerably less invasive to patients than an open chest/open heart surgical procedure. It also results in a significantly shortened hospital stay. Although Medtronic has not announced the price of the device, it is likely that the total cost will be less than the surgical alternative. But the biggest advantage will be to the small hearts — hearts that will avoid a scalpel.