Tissue or Mechanical Heart Valve?
Mechanical and Tissue Heart Valves
Background:
When heart valve disease progresses to the point that
treatment by medicines does not provide relief from a
patient’s symptoms, surgery to repair or replace the valves
becomes the best alternative. If the surgery is not a repair,
homograft or autograft, the choice is most likely between
carbon-based mechanical valves and biological tissue
valves.
The physician and patient will choose the type of valve,
taking into account the patients’ overall condition and
preference. Some of the patient factors considered are:
Age and life expectancy: Although age is not a rigid
indicator, the American College of Cardiology and
American Medical Association guidelines indicate that
mechanical valves are generally appropriate for a
majority of patients 65 years old and younger, or
patients already on coumadin.
Other diseases: Lung, liver and kidney disease,
diabetes, cancer and other chronic conditions can affect
life expectancy and alter the age criterion.
Heart and vascular system condition: Coronary, carotid
and peripheral artery diseases and heart rhythm
disturbances can affect valve selection.
Patient lifestyle and preference: Life situations or
intangible factors often influence valve selection.
Tissue Heart Valves:
Tissue valves are harvested from pig heart valves (porcine)
or cow heart sac (bovine). These tissues are treated and
neutralized so that the body will not reject them. Some are
mounted on a frame or stent; others are used directly
(stentless).
The lifetime of a tissue valve is typically 10 to 15 years,
often less in younger patients. Over this time the valve will
likely be degenerating to the point of requiring replacement.
Because valve replacement surgery carries a significant
risk of death, patient life expectancy is a major criterion in
considering a tissue valve.
With relatively high pressure gradients, stented tissue
valves do not perform as well as the native valve in terms of
blood flow. Tissue valves without frames (stentless)
improve blood flow, although they are more difficult to put
in place and are not usable in all cases.
The primary advantage of tissue valves is their lower
requirement for anticoagulation therapy, which reduces the
incidence of bleeding. For the majority of tissue valve
patients, taking an aspirin a day is sufficient
anticoagulation therapy. Many patients with tissue valves,
however, do not enjoy this benefit due to anticoagulation
requirements for other heart or vascular conditions.
Mechanical Heart Valves:
The most widely used mechanical valves are made from
pyrolytic carbon, which has been used for over 30 years.
Most are bileaflet designs, meaning that they employ two
carbon “leaflets” to regulate flow to a single direction.
The primary advantage of mechanical valves is that they
will last a patient’s lifetime. Mechanical valves are
preferred for patients with life expectancies beyond 10-15
years because they eliminate the mortality risk inherent in
the replacement of a worn out tissue valve. The best
mechanical valves, such as the On-X valve, have excellent
flow performance, rivaling that of the native valve even in
the small sizes.
The main drawback of mechanical valves has been their
requirement for warfarin anticoagulation therapy, with its
accompanying risk of bleeding. Bleeding events are rare but
are potentially fatal. With properly managed anticoagulation
therapy, rates are low for both bleeding and clotting.
Mechanical valves can sometimes be audible when opening
and closing. The sound level varies with the patient, but
among those noticing it, a small number of patients find the
sound disturbing, while others find it reassuring.
The Choice:
Valve selection is a balancing act between the major
positives and negatives of both valve types:
The limited durability of tissue valves (performance
degradation and the stress or mortality of reoperation).
The requirement for lifelong anticoagulation therapy of
mechanical valves.
The decision is reached differently for each patient as many
factors are considered and weighed but the goal is always
to improve quality of life while minimizing risk.

Medical News Today reported that an Italian surgeon is to announce updated plans to conduct the world's first human head transplant within the next 2 years. Now, a 30-year-old Russian man is set to become the first person to undergo the procedure.

The HEAVEN-GEMINI procedure - which is estimated to take 100 surgeons around 36 hours to complete - will involve spinal cord fusion.

Dr. Sergio Canavero, of the Turin Advanced Neuromodulation Group (TANG) in Italy, first spoke of his plans to carry out the first human head transplantation in July 2013 - a project named HEAVEN-GEMINI.

At the American Academy of Neurological and Orthopedic Surgeons' 39th Annual Conference in Annapolis, MD, in June, Dr. Canavero will present updated plans for the project, addressing some of the previously identified challenges that come with it.

Though researchers have seriously questioned the feasibility of Dr. Canavero's plans, it seems the first human head transplantation is a step closer to becoming a reality; Valery Spiridonov, a 30-year-old computer scientist from Vladimir, Russia, is the first person to volunteer for the procedure.

Spiridonov has Werdnig-Hoffman disease - a rare genetic muscle wasting condition, also referred to as type 1 spinal muscular atrophy (SMA). The condition is caused by the loss of motor neurons in the spinal cord and the brain region connected to the spinal cord. Individuals with the disease are unable to walk and are often unable to sit unaided.

Spiridonov was diagnosed with Werdnig-Hoffman disease at the age of 1 and told MailOnline that he volunteered for HEAVEN-GEMINI because he wants the chance of a new body before he dies.

'"I can hardly control my body now," he said. "I need help every day, every minute. I am now 30 years old, although people rarely live to more than 20 with this disease."

Donor body will be attached to recipient's head through spinal cord fusion

Dr. Canavero told CNN he has received an array of emails and letters from people asking to be considered for the procedure, many of which have been from transgender individuals seeking a new body. However, the surgeon says the first people to undergo the procedure will be those with muscle wasting conditions like Spiridonov.

The procedure - which is estimated to take 100 surgeons around 36 hours to complete - will involve spinal cord fusion (SCF). The head from a donor body will be removed using an "ultra-sharp blade" in order to limit the amount of damage the spinal cord sustains.

"The key to SCF is a sharp severance of the cords themselves," Dr. Canavero explains in a paper published earlier this year, "with its attendant minimal damage to both the axons in the white matter and the neurons in the gray laminae. This is a key point."

The spinal cord of the donor body will then be fused with the spinal cord of the recipient's head. Chemicals called polyethylene glycol or chitosan can be used to encourage SCF, according to Dr. Canavero. The muscles and blood supply will then be sutured.

The recipient will be kept in a coma for around 3-4 weeks, says Dr. Canavero, during which time the spinal cord will be subject to electrical stimulation via implanted electrodes in order to boost the new nerve connections.

The surgeon estimates that - with the help of physical therapy - the patient would be able to walk within 1 year.

Spiridonov admits he is worried about undergoing the procedure. "Am I afraid? Yes, of course I am," he toldMailOnline. "But it is not just very scary, but also very interesting."

"You have to understand that I don't really have many choices," he added. "If I don't try this chance my fate will be very sad. With every year my state is getting worse."

Spiridonov talks more about his decision to participate in HEAVEN-GEMINI in the video below:

Dr. Canavero branded 'nuts'

Dr. Canavero has previously admitted there are two major challenges with HEAVEN-GEMINI: reconnecting the severed spinal cord, and stopping the immune system from rejecting the head. But he claims that recent animal studies have shown the procedure is "feasible."

Unsurprisingly, however, researchers worldwide are highly skeptical of the proposal. Talking to CNN, Arthur Caplan, PhD, director of medical ethics and NYU Langone Medical Center in New York, NY, even called Dr. Canavero "nuts."

Caplan said the procedure needs to be conducted many more times on animals before it is applied to humans, adding that if the technique is feasible then Dr. Canavero should be trying to help paralyzed patients before attempting whole body transplants.

And talking to New Scientist earlier this year, Harry Goldsmith, a clinical professor of neurosurgery at the University of California-Davis, said the project is so "overwhelming" that it is the chances of it going ahead are unlikely.

"I don't believe it will ever work," he added, "there are too many problems with the procedure. Trying to keep someone healthy in a coma for 4 weeks - it's not going to happen."

Spiridonov says he is well aware of the risks, though he is still willing to take a chance on Dr. Canavero.

"He's a very experienced neurosurgeon and has conducted many serious operations. Of course he has never done anything like this and we have to think carefully through all the possible risks," he told MailOnline, but adds that "if you want something to be done, you need to participate in it."

Though it not been confirmed when the procedure will be performed, Spiridonov says it could be as early as next year. Watch this space.

Latest update

In October 2015 we interviewed Dr. Sergio Canavero about his plan to perform the first human head transplant in December 2017 - a procedure he claims will take around 150 surgeons and nurses approximately 36 hours to complete and will cost around $11 million. You can read the full interview here.