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Transcatheter Aortic Valve Implantation (TAVI)

A new gentle method of therapy in aortic stenosis

To reduce the chances of undergoing major heart surgery, heart valve prostheses have been developed that can be positioned on the beating heart through a catheter. The access to the heart is, in the majority of cases, gained through an arterial blood vessel in the groin or under the clavicle (collarbone); if these arteries are unsuitable for this method, the new heart valve can be implanted through the tip of the left ventricle – and regardless of the method, without the need to connect the patient to the heart-lung machine. In many cases, a general anesthetic can be dispensed with. Such a procedure is, therefore, referred to as a minimally invasive or keyhole surgical procedure.
 

The TAVI procedure

The fundamental principle: There is no longer a need for the thorax (chest cavity) to be completely opened for the operation. The new heart valve can be placed in the correct position either through a small incision at the apex of the heart (transapical) or entirely via a catheter (transfemoral).

Due to the development of powerful new materials, today’s very stable and durable heart valves are constructed so that they can be folded together into a very small form before the implantation. By using either an adapter or simply sending it through a cardiac catheter the new heart valve can be brought up to the heart. A wire serves as a guide rail taking it up to the main artery. For older models which utilize flaps, a small incision is made in the chest wall and then also in the apex of the heart, whereby most recent foldable-types are now so flexible and small that they can be completely transported via a catheter. 
 
Regardless of the procedure, a comprehensive and accurate preoperative diagnosis is important. With modern imaging techniques the optimal size of the prosthesis and access path can be selected in advance. The various prostheses cannot be inserted via any access (i.e. the apex of the heart, aorta or subclavian artery).

Left: transapical (through the apex of the heart) Access for the implantation of the new valve. The thorax is opened for this access path with a small incision.
 
Right: transfemoral (via the groin artery) access for valve implantation. From the femoral artery to the heart, a catheter provides access to a new valve.

The basic principle is the same for all procedures: 

 First, a wire is inserted and laid across the narrowed valve. Then, the valve is "blown" by means of a balloon catheter that has been guided over the wire into the valve. After the balloon has been inflated, the valve flaps are pushed to the edge of the main artery so that the new valve can be inserted. Then comes the crucial step – first, a guide sleeve is inserted to the intended position of the valve, then, the valve can be deployed. 
Depending on the particular type of valve, the flaps unfold automatically or it is deployed by means of another balloon. After this procedure is completed, the new valve is positioned in the passageway between the chambers and begins to function immediately after removal of the catheter implant material.
 

The transapical route

For this access path a small skin incision and an opening to the ventricle are required.

 
First, an incision is made in the chest area located at the apex of the pericardium (the tip of the heart).  Then, using a special insertion utensil, the heart muscle itself, more specifically, the apex of the heart is punctured. The guide wire (see above) passes through the heart valve and, by means of this wire, the new valve may be placed in position. The advantages of this method are that the access path is direct, and the valve does not need to be significantly deformed. Possible disadvantages can be considered to be the necessary opening of the heart muscle and also the need for general anesthesia.
 

A B C D
Figure 1: Sequential steps of transapical TAVI procedure. A: after opening the thorax and the pericardium, a delivery system is introduced through the heart muscle. Then, the narrowed aortic valve is "blown up" with a balloon and made passable for the new valve. B: The valve prosthesis is advanced over a wire through the ventricle and C: unfolded in the valve plane. 
D: The new valve is now located in place of the former, calcified valve.
 

 

Transfemoral valve implantation ( without opening the chest)

Minimally invasive procedures allow the gentle replacement of heart valves through a blood vessel in the groin

Unlike the transapical TAVI procedure, in this case the access is gained via an artery in the groin. For this purpose, the prosthesis must be significantly thinner as well as foldable and flexible enough to be introduced through a catheter system. The obvious advantage of this method is that no operation is necessary in the strictest sense of the word. 
 
As with the other cardiac catheterization procedure, a small incision and incision point in the artery suffices insert the installation sheath. 
A sealing system seals off the resulting hole in the artery. This elegant approach is not possible in all patients. Strong calcifications or bends in the pelvic vessels may impede the procedure. To what extent the reduction of the valve for insertion affects the durability of the prosthesis has so far not been investigated.

Minimal invasive Implantation einer Aortenklappe: TAVI

A B C D
Figure 1: Sequential steps of the TAVI procedure.
A: Through a blood vessel in the groin, the old, narrowed aortic valve is "blown up" with a balloon and made accessible for the prosthesis.
B: The valve prosthesis is advanced over a wire through the main artery (aorta) and C: unfolded in the valve position. 
D: The new valve is now located in place of the former, calcified valve.

 

TAVI - An intervention for critically ill and very old patients?
The surgical treatment of aortic valve stenosis (AS) has a long history, so that there are meaningful numbers as to the success and complication rates of such surgical interventions. However, even if a relevant portion of all patients with AS, in principle, requires an operation, they do not receive it: if the risk of surgery is relatively high, an operation is rejected by the surgical team, or, the patient is not even considered for an operation, since even the family doctor considers the risk of an operation to be too high. Currently, the risk of dying from a surgery or serious damage can be estimated by a point system. If the risk score is too high, the operation is no longer considered an option.
 
The TAVI prostheses were specifically designed to close this type of gap. There are estimates that 20 to 30 % of all treatable AS patients are not even presented as candidates for surgery. The first control-group studies were therefore carried out with patients who had previously been found to be too ill for conventional surgery. Recent data demonstrates, however, that even "healthier" patients can benefit from the TAVI treatment. The discussion of how far the limit for age and severity of comorbidities may be lowered hat yet to be completed. New valve systems are currently being tested specifically for this issue in clinical trials. At the Isar Heart Center in Munich transfemoral implantation system is a preferred treatment.
 
If you want to know more about this procedure or discuss a possible intervention, or are in need of a second opinion, Assoc. Prof. Dr. Klaus Tiemann and Assoc. Prof. Dr. Alexander Leber are  at your disposal . To make an appointment concerning heart valve surgery at Isar Heart Center, click here.

Deployment process material of original catheter 

A complete representation of the procedure in English can be found here
 
Images courtesy of Edwards Lifesciences Services GmbH, Medtronic, Inc., and Jena Valve Company.

 

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