TAVR: An Advance in Both the Equipment and the Practice of Medicine

No survey of trends in medical equipment would be complete in the year 2013 without mention of the remarkable emerging technology of transcutaneous aortic valve replacement, or TAVR. Aortic stenosis is a disease that results from obstruction to the valve that regulates blood flow coming from the left ventricle of the heart, the major pumping chamber of oxygenated blood to the body, to the aorta, or major arterial conduit that delivers that blood. From its strategic location, it is not difficult to see that obstruction of this valve can have a major impact on patient well-being and survival. In fact, untreated, aortic stenosis is progressive and lethal. Although most commonly found in the elderly, as a result of valvular degeneration and calcification, it can occur much earlier in life (even in infants) from congenital causes or infections (rheumatic). Because the disease appears to share certain risk factors with atherosclerotic coronary artery disease—diabetes, smoking, hyperlipidemia—it was at one time thought the processes were related, and that statins might prove effective in halting or slowing the progression of the disease. The scientific evidence has not well supported the former belief, while, unfortunately, the latter treatment has proven therapeutically ineffective. Since the problem is essentially a mechanical one, the only proven therapy is replacement of the aortic valve. Traditionally this requires heart surgery during which the valve is replaced with either a mechanical or biologic prosthesis. Because the severe stages of the disease are most commonly present in the elderly, physicians have been reluctant to refer patients for surgical correction, despite the fact the results of this surgery in the very elderly have improved dramatically over the past two decades. As a result, it is currently estimated that nearly one third of people suffering from symptomatic aortic stenosis receive no therapy at all.

 

It was to respond to this unmet need that innovative physicians sought an alternative to surgery. Bolstered by the success of percutaneous interventions for the treatment of obstructive coronary artery disease, the first approach was to apply an expanding balloon across the stenotic valve in an effort to open the valve orifice—an “aortoplasty”—similar to initial approach to coronary obstructions with balloon angioplasty (prior to the introduction of stents). Although occasionally successful in relieving obstructions, results tended to be transient, due to severe fixed calcific nature of the lesion. With the success of various stents in keeping obstructed coronary arteries open, an innovative cardiologist in France hypothesized that a stent mounted with a bioprosthetic valve could potentially keep the aortic orifice open and functioning—leading to the first successful percutaneous aortic valve implantation. Because the native diseased valve is not removed, but merely pushed aside up against the wall of the aorta, because of the proximity of the orifices of the coronary arteries, because of the residual calcium, because of the need to position the valve exactly in the right location (too low and it will move in the ventricle and embolize, too high and it will obstruct the coronary ostia), because of the need for large bore catheters in order to deliver the device, and because of the need to deploy while the heart is beating rather than while on cardiopulmonary bypass, the first generation of devices has not been without its potential problems. There is a 2-6% incidence of stroke, approximately one fifth of patients are left with some degree of back-leakage around the valve, some 10% experience serious vascular complications, there is an occasional need for a pacemaker, and, depending upon the risk profile of the patients being treated, there is a potential mortality.

 

Interestingly and encouragingly enough, unlike the case of percutaneous coronary interventions, when devices were introduced and used with little clinical evidence to support their introduction, in this country, these devices are being very carefully studied and regulated. Rather than viewing this as a “turf” war between surgeons and cardiologists, both groups have come together to embrace this potential technical advance and to study its most appropriate application. It is this new paradigm of evidence-based progress and professional collaboration which is potentially even more remarkable than the technological advances of the catheter itself. It is just these areas of providing the medical profession with the research-based evidence that is needed for real progress, as well as the facilitation of collaboration, that characterizes the efforts of the Florida Heart Research Institute in its mission to stop heart disease through research, education and prevention.