Valve Repair and Replacement for Aortic Stenosis

Dateline: 06/08/97

In last week's introduction, I just touched upon the different options of treating Aortic Stenosis. In this article, I will discuss the two major surgical methods used - Valve Repair and Valve Replacement.

VALVE REPAIR

Valve repair (or Valvuloplasty) is one of the earliest operations for aortic stenosis. In it's crudest form, it was performed first as early as 1913, when a surgeon named Tuffier used his finger as a dilator, and invaginated the wall of the aorta into the orifice of the aortic valve, thus widening it and relieving stenosis.

In later years, minor modifications were included. Smithy, in 1947, used a tubular metal dilator passed into a small opening in the left ventricle to dilate the orifice of the aortic valve. Bailey used the same dilator in a retrograde direction, by introducing it from the carotid artery in the neck and guiding it into the aortic valve orifice.

In infants and children with aortic stenosis due to birth defects of the valve, similar techniques are still employed sometimes. Closed surgical valvotomy using a metal Hegar dilator, or more recently using a balloon catheter, have been useful methods. The balloon catheter is positioned across the aortic valve where it is inflated. The inflated balloon tears open the aortic valve at the points of fusion, and relieves stenosis.

Today, most such balloon dilatation procedures are performed non-surgically using cardiac catheterization methods. Through a small needle stick in the groin or forearm, a long thin tube called a catheter (with an inflatable balloon) is inserted into the arterial stream. As it is observed using x-ray imaging techniques, the catheter is guided across the aortic valve, and the balloon inflated. The extent and duration of inflation is determined by the severity of stenosis of the aortic valve, and the procedure can be repeated until adequate relief is obtained.

It was however only after the invention of the heart-lung machine, and the advent of open heart surgery, that aortic valve repair really came of age. The heart could now be stopped for a long period, and the aorta safely opened. The aortic valve is inspected directly, its disease evaluated, and the appropriate reparative procedure carried out.

In most cases, all that is required is to split open the commissures (junction between two adjacent leaflets) which are stuck together due to disease, causing the narrowing. In some patients, the valve leaflet itself may become thick and stiff, and may need to be "shaved" or sculpted to become thinner and pliable. In older adults, calcium may get deposited on the valve producing stenosis. Recently, methods have become available to treat this condition using ultrasonic waves (CUSA device) to fragment and remove the calcium plaques rendering the valve translucent and pliable.

Some complications are inevitable with these methods. A small risk of death (around 2%), and a chance of late sudden death has been noted in children who undergo the balloon dilatation procedure. Excessive dilatation of the valve may make it leaky - a condition called Aortic Regurgitation. Injury to the blood vessels, perforation of the heart chambers by the dilator, rhythm disturbances, infection and cardiac arrest are other complications that may occur during or after the procedure. Most often, these operations are only palliative - that is, they temporarily relieve the obstruction, but do not preclude recurrence. In fact, repeat operation for aortic re-stenosis is rather common after some years.

VALVE REPLACEMENT

While repairing a diseased aortic valve has many advantages (including the non-requirement of anti-coagulant medication, and absence of valve related morbidity), some valves are so badly diseased that a reparative procedure is simply not possible. The surgeon is left with no alternative but to remove it, and replace it with an alternative valve. The most widely used replacement device is the prosthetic heart valve. Others like the homograft and pulmonary autograft have become popular in recent times, and I will discuss them in the following weeks.

The first successful prosthetic aortic valve replacement was performed by Starr and Edwards in 1961, and this opened up a new era in heart surgery. Mechanical valves have evolved over time, with advances in engineering and bio-material technology helping to design very efficient devices. However, no man-made valve yet has equalled the efficiency and resilience of the natural valve.

Aortic replacement devices are one of three categories - ball and cage valve, single tilting disc valve and double leaflet valve. The ball and cage device (e.g. Starr-Edward model) was the fore-runner of all devices, and is still used widely. It has a silicon ball that moves like a poppet inside a metal cage. The single tilting disc valve (e.g. Medtronic-Hall model) has a disc that tilts to allow blood to flow across the valve, and then closes to prevent back-leak. The bi-leaflet valve (e.g.St.Jude Medical model) has two leaflets that move apart to permit blood flow and swing shut again.

The operation to replace an aortic valve is an open-heart procedure, performed with the aid of a heart-lung machine. The native diseased valve is excised and the replacement device is sutured in its place using various techniques.

The efficiency of a replacement valve is judged by a number of factors. Hemodynamic performance, resistance to infection, hemolysis, thromboembolic complications and durability are but some of the concerns while choosing the most appropriate device.

By its very nature, prosthetic heart valves necessitate medication to prevent blood clots forming on the foreign surfaces. These medications, called anticoagulants or "blood thinners", must be taken life-long, and have their own side effects, and cause some morbidity.

Complications may occur after valve replacements too. A small risk of operative mortality still remains. In the long term too, patients with an artificial valve have a lesser life expectancy than healthy individuals, though the course is much better than the natural history of the disease. Thrombo-embolism (clot formation with bits breaking off and entering the blood stream into the brain), infective endocarditis, bleeding related to anticoagulant overdose, hemolysis (damage to blood cells due to contact with the artificial surface of the valve) and prosthetic dehiscence with para-valvular leak are some of the major complications.

In the next article on this section, I will discuss the role of the aortic homograft as a replacement device for aortic stenosis.