Artificial Heart Valves
Historical
Valve replacement surgery owes its origin to Charles Hufnagel (1952). He implanted a
prosthetic cardiac valve in the descending thoracic aorta of a patient who had a leaky aortic
valve (aortic regurgitation).
Albert Starr was a cardiothoracic surgeon who collaborated with Lowell Edwards, an engineer,
and developed a caged aortic valve (1957).
Nina Braunwald designed and implanted a polyurethane prosthesis in the mitral position
(1960). In the same year, Harken and Soroff put in a double cage ball valve in the position of the
aortic annulus.
Types of Heart Valves
Until about a decade ago, most of the heart valves were implanted by open heart surgery.
Catheter implanted valves have become increasingly popular thereafter; these are deployed by
means of special catheters which are inserted in the groin and advanced to the heart.
The prosthetic valves that are implanted by means of open heart surgery belong to two broad
categories, namely, mechanical prostheses, and bioprostheses. Mechanical prosthetic
cardiac valves have either one, or two leaflets. These leaflets are like the movable wooden
parts of the doors in our homes. The valve leaflets allow easy flow of blood when they are open,
but very little flow when they are closed. The insignificant leakage of blood in the closed position
of the valve is more by design than by accident. These washing jets allow blood to clean the
valve leaflets and prevent the formation of blood clots on their surfaces to an extent.
Bioprosthetic cardiac valves are made from the tissues of living beings such as cows, pigs, or
even humans. Cadaveric tissue valves are sometimes harvested from brain-dead subjects
within 24 hours.
Which Valve is the Best for You?
Transcatheter Aortic Valve Replacement (TAVR) is as good as Surgical Aortic Valve
Replacement (SAVR) for most patients. However, the former is many times more expensive.
Transcatheter replacement of the mitral, tricuspid, and pulmonary valves are in the final stages
of clinical trials and are expected to hit the road within the next few years.
Mechanical Prosthesis, or Bioprosthesis?
Implantation of a mechanical prosthetic cardiac valve implies that the patient will require life-
long anticoagulation with warfarin. The use of Direct Acting Oral Anticoagulants (DOAC) such as
dabigatran, rivaroxaban, and apixaban is not recommended for these patients. Mechanical
prosthetic valves are robust, and are expected to last longer.
Patients with bioprosthetic valves generally do not require anticoagulation beyond the first few
months. However, they are relatively fragile and require re-do surgery after a few years.
In general, mechanical prosthetic cardiac valves are recommended for patients who are
younger than 65 years; and bioprosthesis for those who are older than 65.
Complications
Denton Cooley , the pioneer cardiothoracic surgeon, was never tired of saying, "Apply, Simplify,
Modify". His adage has been exemplified by the succesful development and deployment of
artifical heart valves upward of six decades. Complications are now much less frequent,
although they continue to occur, as outlined in the foregoing discussion. Many of these
complications call for another operation. Sadly, some are fatal.
1. Immediate Complications
There may be bleeding from the groin or chest wound as a result of the operation.
Tiny bits of calcium from the aorta, or blood clots, may migrate to the brain. They may cause
cognitive impairment, paralysis, visual loss, and other complications.
Varying degrees of heart block may appear after the operation. Some of the higher grades of
block may mandate the implantataion of a permanent pacemaker.
2. Delayed complications
All prosthetic valves have the potential to undergo degeneration. The bioprosthetic valves
usually degenerate earlier than the mechanical prostheses.
There can be growth of fibrous tissue called pannus on the surface of the valve leaflets. This
may result in narrowing, or leakage of the artificial valve.
There may be thromboembolic complications. This means that the patient's blood can clot on
the surface of the valve leaflets. If they are large enough, they may impair the opening and
closing of the valve leaflets leading to dysfunction of the prosthesis.
Bacteria and fungi can settle on the surface of the prosthetic cardiac valve and give rise to
infective endocarditis. This is a dreaded complications and can be life-threatening. These
patients have high rise of temperature and require several weeks of intravenous antimicrobial
injections. Sometimes, the valve leaflets are eaten away by the bacteria to such an extent that
the valve has got to be replaced.
The siutures at the periphery of the implanted valve can sometimes give away and cause
paravalvular leakage. While some of these leaky valves can be fixed with devices inserted
from the groin, others may call for fresh open heart surgery.
Follow-up of Patients
The patients or their relatives should not take it for granted that the disease is cured after a
successful heart valve operation. Follow-up with a cardiologist should be regular, and life-long.
The time interval between two succesive consultations depends on the clinical profile of the
patient.
For patients who require warfarin, there should be fine tuning of the dose once in every month.
Some of these patients need to be seen more frequently. It is important to realise that too little of
warfarin may cause formation of blood clots in the heart, while too much warfarin cause
alarming bleeding. Sadly, the dose of warfarin required to cause optimum anticoagulation varies
from patient to patient, and even in the same patient from time to time.
Quite a few of these patients require other classes of medicines such as antiplatelet agents,
angiotensin converting enzyme inhibitors, angiotensin receptor blockers, mineralocorticoid
receptor antagonists, beta blockers, and so on. Many of them need clinical examination and
investigations to rule out the potential side effects of useful medicines.
Ther tests such as ECG, and echo Doppler study at required from time to time to detect and
treat the various complications pertaining to prosthetic cardiac valves.
Patients who are planning to have prosthetic cardiac valves need to follow a disciplined lives.
Disclaimer
This article has been written for creating awareness among the members of the public. It is not intended to be a
substitute for medical advice. The author accepts no responsibility of errors of coomission and omission. Please
refer to the standard textbooks and guidelines as applicable.
