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.
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[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