Transcatheter Aortic Valve Replacement (TAVR)

Age-related calcific aortic valve degeneration is the most common cause of aortic stenosis (AS) in adults and its prevalence steadily increases with age. Survival in patients with AS dramatically decreases with onset of symptoms (angina, syncope, congestive heart failure) with an average of 1 to 3 years and the poorest survival seen in patients with failing left ventricles. Aortic valve replacement is a proven treatment to prolong survival in patients with severe AS.

Transcatheter Valves

There are two catheter-implantable valves commercially available overseas. They are the balloon-expandable Edwards SAPIEN valve and the self-expanding Medtronic CoreValve (Fig. 17-1). The Edwards SAPIEN valve was studied in the PARTNER trial, which completed randomized enrollment in fall 2009. The Medtronic CoreValve randomized trial started enrollment in December 2010. The initial international experience and the results of PARTNER cohort A and B suggest that outcomes compare favorably with conventional valve surgery in selected patients. In November 2011, the Edwards SAPIEN valve was FDA approved and became commercially available in the United States for PARTNER cohort B (inoperable) patients.

Figure 17-1 Left, Photograph of the Edwards SAPIEN transcatheter heart valve, which consists of a stainless steel stent with bovine pericardial tissue leaflets sewn onto the balloon-expandable stent. Right, Photograph of the Medtronic CoreValve transcatheter aortic valve system, which consists of a nitinol-based frame with porcine pericardial tissue leaflets affixed to the self-expanding stent.

Transfemoral TAVR Procedure With Edwards SAPIEN valve

The procedure is typically performed in a cardiac catheterization laboratory or hybrid operating room suite. The implant procedure involves the cooperation of a multidisciplinary team, including cardiac surgery, interventional cardiology, echocardiography, and anesthesia. A surgical team and cardiopulmonary bypass machine are on stand-by in case bailout surgery is required.

Preprocedure planning includes identification of the implant side from the CTA scan and measurement of the aortic annulus to choose valve size, which will determine the size of the delivery system. Transesophageal echocardiogram (TEE) is used to size the annulus and to assist in valve positioning. Placement of the probe can be done once the patient is adequately sedated. A 23-mm valve is used for annular dimensions of 18 to 21 mm and a 26-mm valve is used for annular dimensions of 22 to 24 mm.

Femoral arterial and venous accesses are obtained on the non-implant side, and 6F sheaths are placed. These will be used for the temporary pacemaker (rapid pacing) and pigtail catheter (aortography), but they also provide rapid access in case the patient needs to be placed on emergency cardiopulmonary bypass. Pulmonary artery catheterization is done via jugular vein access. Due to the large delivery systems, surgical femoral artery cutdown and repair are best performed on the implant side. After cutdown, an 8F sheath is placed in the artery and a 6F sheath in the vein. Successful arterial closure with a Prostar XL closure device or two Perclose closure devices has been performed, making the procedure truly percutaneous. Weight-based heparin is administered intravenously once access has been obtained. Target activated clotting time (ACT) is 250 to 300 seconds.

A temporary pacemaker wire (used for rapid ventricular pacing during balloon inflations) is positioned in the right ventricle through the venous sheath on the non-implant side. A pigtail catheter is advanced to the ascending aorta and supravalvular aortography is performed in the left anterior oblique cranial and right anterior oblique caudal projections. The projection that best lays out all three aortic valve leaflets in a single plane is chosen for valve positioning.

The implant-side arterial access must be serially dilated with hydrophilic-coated dilators over a stiff 0.038-inch guidewire. From 8F, the artery is serially dilated with 10F to 24F dilators. The delivery sheaths for the 23-mm and 26-mm valves are 22F and 24F, respectively. The delivery sheath is advanced over the wire and positioned in the abdominal aorta.

The stenotic aortic valve is crossed using standard technique. After crossing the valve with the straight wire, the catheter is advanced into the left ventricle (LV) and the straight wire is exchanged for an Amplatz super stiff (1-cm tip) guidewire with a pigtail curve. A double-lumen pigtail catheter is advanced over this wire and positioned in the LV. Baseline LV-aortic gradient is measured. The stiff wire is then advanced into the left ventricle, and the pigtail catheter is exchanged for the valvuloplasty balloon. The balloon (typically 20 × 40 mm) is positioned across the aortic valve, rapid ventricular pacing at 180 bpm is initiated, and the balloon is inflated once the systolic blood pressure has fallen below 50 mm Hg (5-sec inflation). The balloon catheter is removed with the stiff wire remaining in the LV.

Next, the RetroFlex 3 delivery prosthetic valve system with the crimped SAPIEN valve is advanced through the delivery sheath over the stiff wire. The delivery system has a flexing mechanism that assists in steering through the aortic arch and minimizes trauma on the outer curvature of the arch (Fig. 17-2). When crossing the native aortic valve, the delivery system is fully retroflexed, which gives a central and coaxial orientation of the prosthesis to the native valve. The delivery catheter also has a nose cone, which facilitates crossing of the native valve (Fig. 17-3). After the valve has been crossed, the retroflex catheter is retracted to fully expose the delivery balloon. The valve is positioned using fluoroscopy, aortography, and TEE (Fig. 17-4). Approximately 60% of the valve assembly should be on the ventricular side of the aligned sinuses. Once positioning is confirmed, rapid pacing is performed and the delivery balloon is inflated when the blood pressure falls below 50 mm Hg (Fig. 17-5). The balloon is inflated for 5 seconds, then deflated. After stent valve deployment, aortography is repeated to assess for paravalvular leak, and if significant, repeat balloon inflations may be necessary. The double-lumen pigtail catheter is again placed and final LV-aortic gradients are measured.

Figure 17-2 Diagrams of the Edwards RetroFlex 3 delivery system. A, As the delivery system approaches the transverse aortic arch, the operator retroflexes the delivery system by turning a knob on the delivery system handle. This maneuver assists in the transit across the aortic arch. B, The stent is positioned across the aortic valve. The retroflex position of the delivery system allows for a central and coaxial orientation of the prosthetic valve to the native aortic valve.

Figure 17-3 Diagram of the Edwards RetroFlex 3 delivery system. The tapered yellow nose cone facilitates crossing of the native aortic valve. The blue retroflex catheter acts as a pusher while the valve is advanced. It is important that the catheter is retracted to fully expose the delivery balloon before deployment.

Figure 17-4 Fluoroscopic view before valve deployment. Transesophageal echocardiogram (TEE) is used adjunctively for proper positioning. A pacer wire is present in the right ventricle for rapid pacing. A super stiff guidewire with a pigtail curve resides in the left ventricle. The RetroFlex catheter is retracted back to fully expose the delivery balloon. A pigtail catheter (behind the TEE probe) is also present, which was used to perform supravalvular aortography.

Figure 17-5 SAPIEN valve implantation. A, The SAPIEN valve is positioned across the native aortic valve. B, With rapid ventricular pacing, the delivery balloon is inflated to deploy the valve. C, The delivery balloon is deflated, revealing a fully expanded stent valve. D, Transesophageal echocardiogram after deployment shows two of the pericardial leaflets coapting during diastole.

Potential complications of TAVR are listed in Table 17-3.

^{Table 17-3} Complications From TAVR

TAVR, transcatheter aortic valve replacement

Percutaneous Mitral Valve Repair

The mitral valve is composed of two leaflets (anterior and posterior), the mitral annulus, the chordae, and the papillary muscles (Fig. 17-6). Dysfunction of any of these structures can cause incompetence of the valve and result in regurgitation. Mitral regurgitation (MR) is the most common form of valvular heart disease, and about half of the cases are due to myxomatous degeneration of the valve, which leads to stretching of the valve leaflets and chordae tendineae. Elongation of these structures causes prolapse of the leaflets into the left atrium and failure of the leaflets to coapt properly. If left untreated, severe MR leads to LV failure due to chronic volume overload.

Figure 17-6 Mitral valve apparatus is a composite anatomical structure that requires integral preservation for its proper function and is dependent on the intricate interplay between the annulus, the commissures, the mitral leaflets, the chordae tendineae, and the subvalvular apparatus, including the papillary muscles and the left ventricular wall.

Surgical mortality is significantly better when the mitral valve is repaired rather than replaced. With mitral valve replacement, the mitral valve apparatus is disrupted, which causes adverse effects on LV geometry, volume, and function. Therefore, whenever possible, all efforts should be made to repair the valve and preserve the subvalvular apparatus. In the Euro Heart Survey, almost half of the patients with severe MR were denied surgery. Impaired LV function, older age, and comorbidity were associated with surgery denial.

Percutaneous transcatheter mitral valve therapies have evolved less rapidly when compared to the aortic and pulmonary valves. Endovascular access is more difficult with transcatheter mitral valve therapies since a transseptal puncture is required to have access to the mitral valve. More importantly, the inherent complexity of the mitral valve apparatus poses a challenge to catheter-based techniques. Any derangement of one or more of its components may result in significant valvular dysfunction. A clear understanding of these anatomical and functional properties becomes essential when distinguishing the pathophysiologic mechanisms that differentiate primary from secondary valvular disease as well as in the development of surgical and new alternative percutaneous transcatheter therapies.

There are numerous transcatheter mitral valve repair strategies that have been developed over the recent years. These include leaflet repair, direct and indirect annuloplasty, and ventricular and annular remodeling devices (see Table 17-1).

The MitraClip (Fig. 17-7) currently represents the most widely used percutaneous repair technique. In 1991, Dr. Alfieri performed a mitral valve repair without annuloplasty using a stitch “edge-to-edge” technique to create a double-orifice valve. The durability of this procedure (>1500 patients) led to the development of a percutaneous technique using a clip to approximate the valve leaflets instead of a suture. The MitraClip system has been evaluated in the EVEREST I and EVEREST II studies.

Figure 17-7 MitraClip mitral valve repair system. A, The device is covered with polyester fabric to facilitate tissue in-growth. The distal gripping elements help with leaflet fixation. B, The clip is delivered via a transseptal guiding catheter. The MitraClip is steered until axially aligned and centered over the origin of the regurgitant jet. C, The clip mechanically coapts the anterior and posterior leaflets in a similar fashion to the Alfieri stitch technique, creating a double orifice valve. D, The clip is deployed and mitral regurgitation is reduced.

Mitral Valve Anatomy

The mitral valve anatomy must have sufficient leaflet tissue amenable for mechanical coaptation with the MitraClip. A key anatomical inclusion criterion includes a regurgitant jet origin associated with the A2 to P2 segments of the mitral valve (Fig. 17-8). For patients with functional MR, a coaptation length of at least 2 mm and a coaptation depth of no more than 11 mm are required. For patients with leaflet flail, a flail gap less than 10 mm and a flail width less than 15 mm are required (Fig. 17-9).

Figure 17-8 Nomenclature of the anterior and posterior leaflets of the mitral valve. A key anatomical inclusion criterion in the EVEREST trials was a regurgitant jet origin associated with the A2 to P2 segments.

Figure 17-9 Key anatomical eligibility criteria. The coaptation length must be ≥ 2 mm. Coaptation depth must be <11 mm. If a flail leaflet exists, the flail gap must be <10 mm, and the flail width must be <15 mm. These anatomical characteristics are necessary for sufficient leaflet tissue for mechanical coaptation when the MitraClip device is used.

Conclusion

As with the initial phases of coronary intervention, rapid technological advances in parallel with good clinical results will ultimately permit routine use of these novel methods in a broader population. Too many patients with significant valvular dysfunction are not being offered potentially life-preserving therapy. Transcatheter valve procedures thus far appear to be durable alternative treatments for valvular heart disease in select patients.