Valve Surgery
Aortic Valve Replacement
The indications of aortic valve replacement are aortic valve stenosis (tightness) or incompetence (impaired closure). Basically speaking, there are two types of aortic valves used as a replacement; mechanical and biological.
The mechanical valves are composed of a sewing ring and housing containing either one or two leaflets. The leaflets of mechanical valves, whether one or two, are constituted of extremely hard carbon-based material, with a durability exceeding the life span of the patient.
Although the life-long durability is a big advantage, these valves have the disadvantage of being thrombogenic. Because of the foreign nature of these valves, the blood tends to form clots on their surfaces. As a consequence, these clots could prevent the normal opening and closure of the valve. In addition, these clots could detach and embolize into the brain arteries leading to stroke. They can also embolize into other arteries such as those in the legs leading to ischemia.
Clot formation on the mechanical valves can only be avoided by life life-long treatment with anticoagulants such as Marcumar. Marcumar tablets should be taken daily and the effect on coagulation should be controlled at least once every 14 days or preferably once weekly. The effect on anticoagulation is assessed by measuring the INR (International Normalized Ratio). This can be done by the family doctor or by the patient himself using a small device for INR-self-measurement. The INR-self-measurement is as simple as measuring the blood glucose level in diabetic patients using self-measurement devices. The INR level should be kept within a certain predetermined range. Too much Marcumar (high INR) leads to tendency to bleeding, while too little Marcumar (low INR) leads to tendency to thrombosis. Both complications have a yearly incidence of about 1 to 2 % of patients treated with Marcumar. This roughly means that the patient has a risk of about 10 to 20 % to suffer from a complication within 10 years of treatment with Marcumar.
Therefore nowadays a tendency to use biological valves is recognised world-wide.
The conventional biological valves are constituted of a metal stent, to which a valve from a pig or from the pericardium of a cow is fixed.
The advantage of these valves is that Marcumar is needed for only 3 months after the operation. The disadvantage of these valves is the early degeneration leading to re-operation within 10 to 20 years after implantation of the valve.
Subsequently, a new kind of biological valves, the so called Freestyle stentless valves was introduced in the 90s of the last century. In this kind of valves, all components of the pig's valve including the aortic wall are kept together as one unit without mounting the valve to a metal stent.
The blood flow through these valves is, to a great extent, similar to the flow through a normal human valve and is clearly better than the flow through the conventional biological valves with stents.
Because of that and because the patient doesn't need any Marcumar even during the first 3 postoperative months, we consider these valves as the first choice in patients older than 60 years.
There're two techniques to implant these valves; the subcoronary implantation and the total root replacement. In the subcoronary technique, the aortic wall of the patient is kept intact. The diseased valve is carefully excised and the tailored stentless valve is sutured in the position of the excised valve.
In the total root replacement, not only the diseased aortic valve is replaced, but the whole aortic root of the patient. The left and right coronary arteries of the patients are implanted in the freestyle valve in the total root technique. This technique is technically demanding, but the hemodynamic results are even better than the subcoronary technique, so that no difference could be noticed by Echocardiography between the valve implanted using this technique and the normal human valves.
Because of the advantageous hemodynamic characteristics, these valves are less exposed to the unnatural forces that lead to early degeneration of the conventional biological valves. Accordingly, the long-term results are expected to be better than the conventional biological valves. With excellent results, more than 1200 stentless valves were implanted in Heart Center Lahr / Baden by 2007.
The implants used for aortic replacement are either non-metalic or contain iron-free metals. There's no evidence that any of these valves has any interaction with the magnetic fields. That was also confirmed by the studies of Dr. Emanuel Kanal, who studied all Medtronic valves and annuloplasty products. He proved that all these products have no interaction with the magnetic field during the application of 3.0 Tesla.
MRI Safe Heart Valve Products http://www.heart-lahr.com/arzt/herz/therapie/Medtronic.pdf
For more information about heart & vessels, please click here http://www.medtronic.de/germany/patienten/herz.html
Please also take notice of the Therapy Practices
For more details please visite the Guidebook for Patients
"Operationen am Herzen - Herzklappenchirurgie".
