Aortic valve replacement (AVR) utilizing the open surgical techniques with the use of cardiopulmonary bypass (CPB) remains the standard of care for symptomatic patients with severe aortic stenosis (AS). Transcatheter aortic valve implantation (TAVI) has become a feasible alternative to open techniques in patients in whom open surgical treatment is contraindicated or those who are at high risk for perioperative morbidity and mortality. Many reports have shown the safety and efficacy of both transfemoral (TF) and transapical (TA) approaches to TAVI. However, a significant number of patients have poor vascular access due to either small size vessels or severe peripheral vascular disease and are only amenable to treatment with the TA approach.(1)
The currently available scoring systems for patients requiring AVR are flawed in that they are not applicable for a significant subset of those patients. They do, however, provide a framework for the complex decision making process for those who are at high risk for open surgical AVR including:
Once the patient is considered to have high surgical risk, he should undergo further workup including the following:
Cardiac catheterization to rule out significant coronary artery disease (CAD). PCI is recommended prior to TAVI if there is critical CAD that would not be better served with CABG. During cardiac catheterization also, attention should be directed at determination of the proper C-arm angles for fluoroscopic visualization of the aortic valve. This is typically a right anterior oblique and caudal view, or left anterior oblique and cranial view. It may be necessary to perform additional hemodynamic assessment of the aortic valve during this procedure as well. This is especially important in patients with left ventricular dysfunction and low gradient aortic stenosis by echocardiographic assessment. Additionally, it is important to assess the ilio-femoral vessels for tortousity and to confirm the severity of vascular occlusive disease.
Echocardiography is important to confirm the severity of aortic stenosis, rule out bicuspid aortic valve (which a relative contra-indication) and to size the aortic annulus and left ventricular outflow tract (LVOT) (Figure 1). It is also necessary to assess for concomitant Mitral valve disease. Mild to moderate mitral regurgitation (MR) is frequently associated with AS in elderly patients but does not usually require any surgical intervention and does not represent a contraindication for TAVI. However, severe MR with bulky mitral annular calcification involving the LVOT has been associated with worse midterm outcome and increased risk of para-valvular leak (2).
|Figure 1. Preoperative echocardiographic measurement of the sinotubular junction (STJ) and the aortic annulus (AA).||Figure 2. Coronal section of 3D reconstruction of Cardiac CT scan showing the dimensions of the sinotubular junction (STJ) and the aortic annulus (AA). The red arrow represents the distance between the right coronary artery (RCA) and the aortic annulus (AA).|
CT scan of the chest, abdomen and pelvis should be performed with three-dimensional reconstruction preferably with contrast if kidney function allows. The acquisition is performed with cardiac gating during the thoracic phase to assess the location of the coronary ostia in relation to the aortic annulus which is supposed to be > 10 mm to allow safe implantation of the valve (2). Additional assessment of the aorta CT scan and TEE are also important to delineate the morphology and measure the dimensions of the aortic root (Table, Figure 2).
Annulus at Hinge point
Additional assessment of the aorta and ilio-femoral vessels is performed to confirm poor access for transfemoral delivery and to prepare for a rescue cannulation in the event that conversion to cardiopulmonary bypass (CPB) becomes necessary during the TAVI procedure. Additional procedural planning performed at the time of three-dimensional CT assessment includes determination of fluoroscopic C-arm positioning and identification of left ventricular apex relationship to intercostal spaces. This assists with proper imaging and incision placement during the procedure.
Formal pulmonary function studies should also be performed to assess the severity of pulmonary disease, which so often coincides with aortic stenosis in high-risk patients. This is especially important when considering the transapical approach since these patients must be able to tolerate an anterior thoracotomy incision.
TAVI is usually performed in a hybrid operative suite designed and equipped to accommodate tools and personnel required for performing both open surgical and interventional procedures. TAVI procedures are best performed by a multi-disciplinary team including a cardiac surgeon, an interventional cardiologist and a cardiac anesthesiologist experienced in trans-esophageal echocardiogram (TEE). Other team members include a perfusionist, a surgical scrub nurse trained in transcatheter procedures, a circulating nurse, a radiology or catheterization laboratory technician and a surgical assistant. At least one member of the team must be trained in preparation and loading of the valve device, which is performed on the back table at the time of the procedure using a proprietary crimping device.
The procedural steps are as follows:
|Figure 3. Direct echocardiographic visualization of the left ventricular outflow tract during valve insertion.||Figure 4. Positioning of the transapical valve is verified using transesophageal echocardiogram with 50 % of the valve positioned above the level of the aortic annulus (red line) and 50 % below the annulus.||Figure 5. Angiographic view of the positioning of the transapical valve prior to valve deployment. It is important to ensure that 50 % of the valve is positioned above the level of the aortic annulus (red line) and 50 % below the annulus.|
|Figure 6. The valve is deployed in position during direct fluoroscopic visualization with a brief period of rapid ventricular pacing to reduce ejection.||Figure 7. Angiographic root injection is performed to confirm the position of the valve and to rule out a paravalvular or central leak.||Figure 8. Short access view of the aortic valve showing the deployed Sapien valve.|
The apex is preferable to the free wall due to greater convexity and reduced wall stress. Select an area free of epicardial fat, take full-thickness bites in the myocardium and gain access with a needle precisely at the central point within the sutures to reduce the likelihood of extending the enlarging myocardial defect beyond the control sutures. Avoid severe hypertension especially when tying the sutures. Occasionally the sutures are tied during a period of rapid ventricular pacing.
Do not hesitate to initiate temporary femoro-femoral cardiopulmonary support or to proceed for sternotomy if there is no sign of improvement with initial resuscitation. If chest compression is required during resuscitation, stent positioning and expansion of the valve must be reevaluated after resuscitation as the device may get crushed or displaced.
Routine care as for conventional AVR with special attention to the following points:
To date, the only randomized controlled trial on TAVI is the PARTNER trial. The trial has two arms; the first is comparing medical therapy to transfemoral TAVI in patients who are not candidate for open surgical intervention. The second arm is comparing TAVI (either transfemoral or transapical) to open surgical therapy in patients who are considered to have very high risk for open surgical treatment. The trial just finished enrolling patients and the results are not available yet.
There are a number of non-randomized studies that showed a 30-day mortality of 10 % with 75% survival at one year (6), which is comparable to open surgical results (7).
Publication Date: 5-Oct-2010
Last Modified: 6-Sep-2012