Cow Hearts: Beefy Benefits for Humans

By May 14, 2020 Uncategorised

heart2According to the CDC, heart disease is the leading cause of death in the U.S., killing more than 600,000 Americans each year.

  • More than five million Americans are diagnosed with heart valve disease annually.
  • Heart valve disease can occur in any single valve or a combination of the four valves, but diseases of the aortic and mitral valves are the most common.
  • Calcific aortic stenosis is the most common form of aortic stenosis (AS).
  • While up to 1.5 million people in the U.S. suffer from AS, approximately 500,000 within this group of patients suffer from severe AS. An estimated 250,000 patients with severe AS are symptomatic.
  • Without an aortic valve replacement (AVR), as many as 50 percent of patients with severe AS will not survive more than two years after the onset of symptoms.

Aortic valve stenosis — or aortic stenosis — occurs when the heart’s aortic valve narrows. This narrowing prevents the valve from opening fully, which reduces or blocks blood flow from your heart into the aorta and onward to the rest of your body.

heart picRecent advances in the treatments for aortic valve stenosis[1] seem to be tipping doctors and patients increasingly towards xenografts for treatment.  Traditional treatment regimes have involved open heart surgery, focused on the replacement of the damaged aortic valve with a mechanical replacement.  The move away from these highly invasive operations has been prompted largely by a single, increasingly attractive development: Transcatheter Aortic Valve Replacement, or TAVR.

The new method of TAVR was only approved as recently as August 2019 for low-risk patients, as new research began to overturn the idea that mechanical heart valves were superior for patients with significant post-operative life expectancy.  The old thinking went like this: since mechanical heart valves do last longer, these valves could provide patients with a lower risk of failure, complications or repeat surgery.  The problem is that some of these assumptions are no longer true, and in many cases, “biologic valves are better even in the young patient.”[2]

The only true representation of the above claims is the fact that mechanical heart valves last longer.  That’s absolutely true; a valve made from titanium or other high-strength, highly impervious material can last for decades.  Unfortunately, these materials increase the risks of blood-clots since platelets have an affinity for collecting on non-biogenic surfaces.  These blood clots can result in thromboses, heart attacks and strokes.

The current treatment regimen is at best an uneasy compromise, because patients are assigned a life-long regimen of anti-coagulants that must balance the risks of clots against the risks of fatal bleeding, hemorrhagic stroke and other complications from the anti-coagulants.  The mortality and morbidity due to surgical complications and failure of the mechanical valves are complicating factors as well.

TAVR addresses some of these problems with short-term mortality by significantly reducing the risks of open heart surgery.  The minimally-invasive procedure begins by inserting a catheter into the femoral artery (or another blood vessel) and threading it up into the aorta.  Once there, in the increasingly common valve-in-valve (VIV) procedure, a collapsible replacement valve can be delivered right inside the aortic valve and then expanded.  Once it’s inside the valve, the new valve holds everything open during systole, meaning output resistance drops and the heart doesn’t have to work as hard.  The new valve will also close more effectively, so blood doesn’t continually wash back and forth, which further eases stress on the heart.

TAVR heart valves are typically made from cow pericardium[3], which also eliminates the platelet adhesion problems seen with mechanical valves.  Some people can go off of blood thinners, and not have to worry about their potential side effects.  The primary disadvantage of TAVR valves is their limited lifespan of 10 to 12 years.  New refinements are addressing this problem: recent studies have shown the chances of having problems with repeat surgeries and TAVR for failed bio-prosthesis valves are either the same, or slightly better for redo TAVR[4].  In another study of approximately 50 patients who had redo TAVR due to failing bio-prosthetic valves, every patient survived to discharge, with only one serious bleed and one minor, non-disabling stroke[5].  In fact, the lower risk of early- and mid-term morbidity associated with TAVR means that for many people, the procedure offers the best chance to live their best lives – living with the highest quality and lowest risk of disability.

[1] Source for stenosis diagram: Michigan Medicine, Frankel Cardiovascular Center.  https://www.umcvc.org/conditions-treatments/aortic-stenosis.

[2] Expert Analysis. 2015 Surgical Aortic Valve Replacement: Biologic Valves Are Better Even in the Young Patient. American College of Cardiology.

[3] Source for TAVR diagram: TCTMD.com

[4] Maxwell, Y.R. 2018.  Valve-in-Valve TAVR: Mortality, Adverse Events Similar to Redo Surgery at 30 Days. TCTMD/the heart beat.  < https://www.tctmd.com/news/valve-valve-tavr-mortality-adverse-events-similar-redo-surgery-30-days>.

[5] Barbanti, et al. 2016. Circ. Cardiovasc. Interv. (9):e003930.  Outcomes of Redo Transcatheter Aortic Valve Replacement for the Treatment of Postprocedural and Late Occurrence of Paravalvular Regurgitation and Transcatheter Valve Failure.  < https://pubmed.ncbi.nlm.nih.gov/27578840/>. DOI: 10.1161/CIRCINTERVENTIONS.116.003930

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