Transcatheter aortic valve replacement: History and current indications

Five-year outcomes

The 5-year PARTNER clinical and valve performance outcomes were published recently¹⁸ and continued to demonstrate equivalent outcomes for high-risk patients who underwent surgical aortic valve replacement or TAVR; there were no significant differences in all-cause mortality, cardiovascular mortality, stroke, or need for readmission to the hospital. The functional outcomes were similar as well, and no differences were demonstrated between surgical and TAVR valve performance.

Of note, moderate or severe aortic regurgitation occurred in 14% of patients in the TAVR group compared with 1% in the surgical aortic valve replacement group (P < .0001). This was associated with increased 5-year risk of death in the TAVR group (72.4% in those with moderate or severe aortic regurgitation vs 56.6% in those with mild aortic regurgitation or less; P = .003).

If the available randomized data are combined with observational reports, overall mortality and stroke rates are comparable between surgical aortic valve replacement and balloon-expandable or self-expandable TAVR in high-risk surgical candidates. Vascular complications, aortic regurgitation and permanent pacemaker insertion occur more frequently after TAVR, while major bleeding is more likely to occur after surgery.¹⁹ As newer generations of valves are developed, it is expected that aortic regurgitation and pacemaker rates will decrease over time. Indeed, trial data presented at the American College of Cardiology meeting in March 2015 for the third-generation Sapien valve (Sapien S3) showed only a 3.0% to 4.2% rate of significant paravalvular leak.

Contemporary valve comparison data

The valve used in the original PARTNER data was the first-generation Sapien valve. Since then, the second generation of this valve, the Sapien XT, has been introduced and is the model currently used in the United States (with the third-generation valve mentioned above, the Sapien S3, still available only through clinical trials). Thus, the two contemporary valves available for commercial use in the United States are the Edwards Sapien XT and Medtronic CoreValve. There are limited data comparing these valves head-to-head, but one recent trial attempted to do just that.

The Comparison of Transcatheter Heart Valves in High Risk Patients with Severe Aortic Stenosis: Medtronic CoreValve vs Edwards Sapien XT (CHOICE) trial compared the Edwards Sapien XT and CoreValve devices. Two hundred and forty-one patients were randomized. The primary end point of this trial was “device success” (a composite end point of four components: successful vascular access and deployment of the device with retrieval of the delivery system, correct position of the device, intended performance of the valve without moderate or severe insufficiency, and only one valve implanted in the correct anatomical location).

In this trial, the balloon-expandable Sapien XT valve showed a significantly higher device success rate than the self-expanding CoreValve, due to a significantly lower rate of aortic regurgitation (4.1% vs 18.3%, P < .001) and the less frequent need for implantation of more than one valve (0.8% vs 5.8%, P = .03). Placement of a permanent pacemaker was considerably less frequent in the balloon-expandable valve group (17.3% vs 37.6%, P = .001).²⁰

PREOPERATIVE CONSIDERATIONS AND EVALUATION CRITERIA

Currently, TAVR is indicated for patients with symptomatic severe native aortic valve stenosis who are deemed at high risk or inoperable by a heart team including interventional cardiologists and cardiac surgeons. The CoreValve was also recently approved for valve-in-valve insertion in high-risk or inoperable patients with a prosthetic aortic valve in place.

The STS risk score is a reasonable preliminary risk assessment tool and is applicable to most patients being evaluated for aortic valve replacement. The STS risk score represents the percentage risk of unfavorable outcomes based on certain clinical variables. A calculator is available at riskcalc.sts.org. Patients considered at high risk are those with an STS operative risk score of 8% or higher or a postoperative 30-day risk of death of 15% or higher.

It is important to remember, though, that the STS score does not account for certain severe surgical risk factors. These include the presence of a "porcelain aorta" (heavy circumferential calcification of the ascending aorta precluding cross-clamping), history of mediastinal radiation, “hostile chest” (kyphoscoliosis, other deformities, previous coronary artery bypass grafting with adhesion of internal mammary artery to the back of sternum), severely compromised respiratory function (forced expiratory volume in 1 second < 1 L or < 40% predicted, diffusing capacity for carbon monoxide < 30%), severe pulmonary hypertension, severe liver disease (Model for End-stage Liver Disease score 8–20), severe dementia, severe cerebrovascular disease, and frailty.

With regard to this last risk factor, frailty is not simply old age but rather a measurable characteristic akin to weakness or disability. Several tests exist to measure frailty, including the “eyeball test” (the physician’s subjective assessment), Mini-Mental State Examination, gait speed/15-foot walk test, hand grip strength, serum albumin, and assessment of activities of daily living. Formal frailty testing is recommended during the course of a TAVR workup.

Risk assessment and patient suitability for TAVR is ultimately determined by the combined judgment of the heart valve team using both the STS score and consideration of these other factors.

Implantation approaches

Today, TAVR could be performed by several approaches: transfemoral arterial, transapical, transaortic via partial sternotomy or right anterior thoracotomy,^21,22 transcarotid,^23–25 and transaxillary or subclavian.^26,27 Less commonly, transfemoral-venous routes have been performed utilizing either transseptal²⁸ or caval-aortic puncture.²⁹

The transfemoral approach is used most commonly by most institutions, including Cleveland Clinic. It allows for a completely percutaneous insertion and, in select cases, without endotracheal intubation and general anesthesia (Figure 1).

In patients with difficult femoral access due to severe calcification, extreme tortuosity, or small diameter, alternative access routes become a consideration. In this situation, at our institution, we favor the transaortic approach in patients who have not undergone cardiac surgery in the past, while the transapical approach is used in patients who had previous cardiac surgery. With the transapical approach, we have found the outcomes similar to those of transfemoral TAVR after propensity matching.^30,31 Although there is a learning curve,³² transapical TAVR can be performed with very limited mortality and morbidity. In a recent series at Cleveland Clinic, the mortality rate with the transapical approach was 1.2%, renal failure occurred in 4.7%, and a pacemaker was placed in 5.9% of patients; there were no strokes.³³ This approach can be utilized for simultaneous additional procedures like transcatheter mitral valve reimplantation and percutaneous coronary interventions.^34–36