The CoreValve ReValving System™ (Medtronic Inc., Irvine, USA) consists of porcine pericardial leaflets mounted within a self-expanding nitinol frame (Fig. 4.5). The current-generation device is compressed within its Accutrak™ delivery catheter and introduced through an 18 French sheath. It is manufactured in 26, 29, and 31 mm outer diameters, as measured at the ventricular part of the frame, recommended for use in patients with annulus diameters of 20–23, 23–27, and 26–29 mm, respectively. The frame has an overall length of up to 55 mm, and in addition to anchoring at the level of the annulus and valve leaflets, the CoreValve extends superiorly to anchor in the ascending aorta.

Careful evaluation of the aortic root and ascending aorta, in addition to that of the aortic annulus, is required to avoid compromise of the coronary artery ostia and avoid valve embolization (Fig. 4.6). It is recommended that a coronary ostial height of 15 mm is required to ovoid coronary obstruction if the 12 mm skirt is deployed too aortic. Additionally, the sinus of Valsalva width needs to be greater than 27 mm for the 26 mm device and greater than 29 mm for the larger devices, to ensure a space surrounding the central waist of the device, to house the displaced native valve leaflets. The recommended maximum diameter of the ascending aorta is 40, 43, and 43 mm for the 26, 29, and 31 mm devices, respectively, to allow for satisfactory anchoring of the device at its upper portion (Table 4.2). Care must be taken in those patients with bypass grafts to ensure the device does not interfere with graft ostia.

Since the CoreValve is self-expanding, it has the potential benefit of partial retrieval if positioned incorrectly (Fig. 4.7). Disadvantages when compared with the SAPIEN valves include a higher rate of atrioventricular block, pacemaker insertion, paravalvular regurgitation, and the potential late consequences of covering the coronary ostia.

Several newer transcatheter heart valves are under evaluation, including the Lotus™ valve (Boston Scientific Inc., USA), Portico™ (St Jude Medical Inc., USA), Engager™ (Medtronic Inc., USA) [15], JenaClip™ (JenaValve Inc., DE) [16, 17], Acurate (Symetis Inc., CH), and Direct Flow™ valves (Direct Flow Medical Inc., USA) (Fig. 4.8) [18, 19]. Generally, these next-generation valves are self-expanding and include features that may facilitate valve positioning and improve annular sealing, with lower-profile delivery systems to accommodate smaller vessel diameters. These valves are currently under clinical evaluation and it remains unclear whether outcomes will be inferior, comparable, or superior to current-generation THVs.

Although feasible in most patients with severe aortic stenosis, TAVR is generally utilized in patients not suitable for surgical AVR, who are likely to derive functional and survival benefit. The evaluation of potential TAVR patients is a complex process involving a multidisciplinary team approach; key members of the team include the primary cardiologist, interventional cardiologist, cardiothoracic surgeon, vascular surgeon, cardiac anesthesiologist and perfusionist, echocardiographers, and cardiac imaging specialists, as well as specialized nursing. This multidisciplinary approach is also applied during performance of the procedure and postoperative care of the patient [20].

“High-risk” surgical patients are often defined as having a Society of Thoracic Surgeons Predicted Risk of Mortality (STS-PROM) at 30 days of greater than 10 % or logistic EuroSCORE of greater than 20 % (Box 4.1). These risk calculators are often limited, however, and do not account for several pertinent clinical risk factors, such as previous coronary artery bypass grafting with patent grafts, porcelain aorta, previous chest radiotherapy, severe lung disease, and liver cirrhosis.

A comprehensive evaluation involving transthoracic echocardiography, coronary angiography, aortic angiography, and CT is required prior to TAVR to assess the aortic annulus dimensions and geometry, access site, and approach. Transthoracic echocardiography is used to assess valve morphology, transaortic gradient, valvular regurgitation, calcification, orifice area, and other concomitant cardiac pathologies. It is also used as a screening tool to evaluate aortic annulus dimensions prior to device selection. Final valve sizing, however, is usually dependant on intraoperative two-dimensional long-axis TEE measurements. Three-dimensional annular sizing with 3-D echocardiography and CT is emerging as a potentially more accurate way of sizing the aortic annulus, the latter of which is utilized by many operators including our own. Generally, the implanted valve should be slightly larger than the annulus size to minimize the risk of malapposition, paravalvular leak, and valve embolization associated with undersizing. Excessive oversizing, however, may result in incomplete stent expansion potentially affecting valve hemodynamics or aortic root injury or rupture.

Arterial access is assessed with the combination of invasive angiography and contrast-enhanced CT (Fig. 4.9). As discussed above, the evaluation of arterial dimensions and the presence or absence of atheroma, calcification, and tortuosity is fundamental in the assessment of the TAVR patient in minimizing potential major vascular complications.

The aortic root is assessed using invasive angiography and contrast MDCT to evaluate root and valvular calcification, left main height from the left coronary cusp insertion (due to risk of coronary obstruction), and technical issues related to each valve type and delivery system. Left and right heart catheterizations are also performed to assess the presence of pulmonary hypertension and coronary ischemia and the need for revascularization prior to TAVR. Percutaneous revascularization may be considered as a staged procedure in the presence of a large ischemic burden; however, in the majority of cases, this is not required. Measurement of the aortic transvalvular pressure gradient and calculation of aortic valve orifice area may be useful in cases of aortic stenosis of uncertain severity on transthoracic echocardiography.

Ideally, TAVR should be performed in regional centers of excellence with a dedicated heart valve program and high procedural volumes [20]. The procedure may be undertaken in a cardiac catheterization laboratory with modifications or in a hybrid operating room equipped with high-quality fluoroscopic imaging; the facilities need to be large enough to accommodate sophisticated X-ray imaging integrated with echocardiography, cardiopulmonary bypass and intra-aortic balloon pump machines, and anesthesia equipment, with surgical sterility standards mandatory.