Transcatheter Aortic Valve Implantation (TAVI); new technology for Heart Valve replacement

Transcatheter Aortic Valve Implantation (TAVI); new technology for Heart Valve replacement
Aortic Valve replacement in Aortic Stenosis subjects is usually carried out by highly invasive cardiac surgery; commonly known as open heart surgery. Because of operational complications and post-operative risks most of the subjects with severe Stenosis are not referred to this surgery. But a new minimally invasive technology TAVI (Transcatheter Aortic Valve Implantation) which utilizes less than 10mm catheters to replace the deteriorated valve would set a new bench mark in Cardiac Surgery, if it meets all the safety parameters. CoreValve Revalving System and Edwards SAPIEN XT Transcatheter Heart Valve are fabricated on this principle and are under clinical trials.

Aortic valve which conjuncts the left ventricle and aorta (largest artery) plays a key role in systemic blood circulation. It allows heart to pump oxygenated blood with great pressure to remaining parts of the body through aorta. Deterioration of the heart valves as age progresses and high calcium build up on them make the heart valves narrower and obstruct the normal blood supply activity. This abnormality keeps the pressure building on the heart and eventually leads to ‘Heart Failure’.

Aortic stenosis is the reduction of the orifice of the Aortic valve due to failure of its leaflets to open fully. According to survey conducted by Detroit Medical Center, this abnormality has been found to affect more than 300,000 people worldwide belonging to aged group population. Heart palpations, heart murmur and breathlessness are some of the common symptoms of Aortic stenosis. Apart from some of the surgical procedure discussed above there are not any medications to completely cure this severe disorder. There are few prescriptions commonly used by Aortic stenosis subjects to keep in check high blood pressure and other symptoms.

Replacement of the diseased valve with a healthy valve, commonly known as cardiac surgery or open heart surgery is the only lifesaver of Aortic Stenosis subjects. Different types of valves are used to replace the diseased one. Mechanical valves are more durable and last several hundred years, but they can only be utilized at the cost of life term usage of anti-coagulants which further increases the risk of bleeding. On the other hand tissue valves made of animal pericardial tissue or homograft tend not to pose the former risk but wear out faster and ask for multiple times of valve replacement surgery. So compromising with any of vales depending on the condition of the subject is mandatory. Besides, the procedure of open heart surgery itself is so complex that death on table is also unavoidable at some instances. Patients often need to be under a meticulous post-operative care and take very long time to perform normal activities. These complexities have urged for a minimally invasive valve replacement procedure to make Aortic stenosis subjects life smoother.

Transcatheter Aortic Valve Implantation is a new catheter based approach which obviates the need of open heart surgery for aortic valve replacement. Physicians can position the self-expandable prosthetic valve to the affected site using a catheter, which can be guided through a small incision made near appropriate part of the body. Medtronic’s CoreValve Revalving System and Edward Lifesciences’s Edwards SAPIEN XT Transcatheter Heart Valve are the two relatively mature candidates of this new breakthrough technology.

CoreValve Revalving system which has a valve delivery catheter of 5-6mm outer diameter and high quality porcine pericardial valve provides an explicitly significant way of Aortic Valve Implantation through subclavian arteries present below the collar bone. This approach has enabled the cardiologists to treat Aortic Stenosis subjects who are at high risk for open cardiac surgery and have their femoral arteries narrowed due to severe stenosis. This method has been granted CE mark earlier in the December and its one year follow up study has concluded reduced neurohormonal activation, regression of myocardial hypertrophy and improved quality of life in sever Aortic Stenosis subjects.[1]

Whereas the Edward Lifesciences has designed its candidate in such way that it can be precisely deployed through both transfemoral and transapical delivery systems and normal hemodynamic activities can be achieved with ease. The system has a balloon-expandable valve design which facilitates accurate vale deployment and a bovine pericardial valve treated with a high quality anti-calcification technology. The PARTNER trial results summarized by Craig R. Smith, MD, co-principal investigator of the PARTNER trial and others depicted that this new approach can improve patients’ quality of life, decrease hospitalizations for aortic stenosis at one-year.[2]

Though this new approach sound very promising and can establish a new benchmark in Aortic Valve implantation procedure but at what risks is an unanswered question yet. Hartzell V. Schaff MD a well-known cardiothoracic surgeon opined about the major complications of this approach and stated that “we are accepting TAVI at the cost of some severe risks like stroke”.[3] Larger group clinical trials which are underway are basically framed to address all these concerns. If this approach invades through all the risk barriers, it can top the list of Aortic stenosis lifesavers. Some of the European nations have already nodded their approval for TAVI but FDA is waiting for some more tangible results from the ongoing larger group clinical trials. Subjects who are currently underserved as conventional open cardiac surgery is not feasible for them can breathe a sigh of relief if this concept gets the FDA nod.

[1] American Journal of Cardiology; Vol. 107(11); 2011/06/01
[2] New England Journal of Medicine; Vol. 364 (2187-2198); 2011/06/09
[3] New England Journal of Medicine; Vol. 364 (2256-2258); 2011/06/09