Interventional procedures seem to have widespread appeal, even in situations unsupported by proven results; this seems mostly driven by the emotive acceptance of patients influenced by their physicians.
In valve replacement, re-entry after previous operations is a well known risk factor and this is particularly so for congenital cases requiring re-replacement of biological conduits previously implanted for right ventricular outflow tract (RVOT) reconstruction. The enlarged right heart in these cases closely adheres to the sternum, and, at times, this poses an unaffordable risk of heart injuries at the time of sternal re-entry.
The pioneering work of Philippe Bonhoeffer has led to the use of percutaneous insertion of biological valves in the structurally deteriorated conduits previously used for RVOT reconstruction. Despite the few anecdotal reports of intraprocedural complications, this technique has gained worldwide acceptance, supported by robust results. Nevertheless, transcatheter aortic valve replacement needs to prove its effectiveness in comparison to surgical valve replacement, which remains the gold standard, even in high-risk patients.
Currently available bioprostheses have proven results - with freedom from structural failure - for up to 15-20 years in selected age groups of patients. The predicted and observed mortality in low-risk patients is as low as one per cent. The challenge comes when cardiac surgeons are facing those patients with clear contraindications to surgery, such as anatomical difficulties (eg, porcelain aorta) or co-morbidities (eg, extreme old age associated with renal failure). In these cases, alternative less invasive procedures are a must.
Left, Core-Valve implanted in aortic position - first Italian implant performed in Padova by Dr A. Ramondo in July 2007. Right, aortography showing no residual perivalvular leak.
The ability to insert devices not only through the femoral artery but also with a trans-apical approach (through the apex of the left ventricle) appears to be extremely appealing, providing a unique opportunity to select the tailored solution for each patient according to the anatomy of left ventricular outflow tract. Experience in percutaneous aortic valve insertion is progressing rapidly. The proof of concept has been made, the technique is out there, it is feasible and reproducible.
One of the driving forces is that there are many patients who are not candidates for cardiac surgery because of the risk, but who can benefit from endovascular procedures. Identifying the patients who will benefit from the procedure is crucial and worthwhile in terms of resource allocation. The life expectancy of these patients will be a major factor in deciding whether or not to implant.
Patient life expectancy also raises concerns about the ability of the devices to remain intact over the long term. None of the percutaneous aortic valves currently available has provided any provisional data regarding durability.
This raises ethical issues over their use in other patients where long-durability will be an important requisite. Nevertheless, if percutaneous valves can provide a reasonable durability of more than eight to ten years, it seems appropriate to link together the expertise of cardiac surgeons and interventional cardiologists to offer patients the best of both practices.
This can be argued as the “valve in a valve” concept. Quality of life after aortic valve replacement plays a major role in terms of patients’ satisfaction. Biological prostheses implanted with surgical techniques do not require anticoagulant treatment and therefore appear to be the valve of choice, but for younger patients their durability is less than satisfactory (eight to ten years).
The potential to implant percutaneous valves once or twice inside the stent of a previously implanted bioprosthesis will extend the valves’ durability for a total of at least 25-30 years before both the bioprostheses and valves have to be removed in a repeat operation. The risk of the repeat operation is similar to that of the first operation, but it should provide patients with bioprostheses that will last the rest of their lives.