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Transcatheter aortic valve replacement: History and current indications

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ABSTRACTTranscatheter aortic valve replacement is an effective way to treat patients with symptomatic severe aortic valve stenosis who are deemed high risk or inoperable. Current data suggest that the mortality and stroke rates are acceptable compared to surgical aortic valve replacement. There is a possible utility in moderate-risk patients as more data become available.

KEY POINTS

  • In randomized trials, transcatheter aortic valve replacement (TAVR) has produced results that are comparable to surgical aortic valve replacement in high-risk patients. TAVR is superior to medical management in patients who cannot undergo surgery, although it is associated with higher rates of stroke.
  • Risk assessment and suitability for TAVR is determined by a heart team composed of interventional cardiologists and cardiac surgeons. Society of Thoracic Surgeons Score and a number of other criteria mentioned below are considered during this process.
  • The transfemoral arterial approach is the most common approach used by most institutions, but other approaches such as transaortic, transapical, transaxillary, and transcarotid are utilized if suitable in patients who have difficult femoral access.


 

References

Transcatheter aortic valve replacement (TAVR) has established itself as an effective way of treating high-risk patients with severe aortic valve stenosis. With new generations of existing valves and newer alternative devices, the procedure promises to become increasingly safer. The field is evolving rapidly and it will be important for interventional cardiologists and cardiac surgeons alike to stay abreast of developments. This article reviews the history of this promising procedure and examines its use in current practice.

HISTORICAL PERSPECTIVE

In 1980, Danish researcher H. R. Anderson reported developing and testing a balloon-expandable valve in animals.1 The technology was eventually acquired and further developed by Edwards Life Sciences (Irvine, California).

Alain Cribier started early work in humans in 2002 in France.2 He used a transfemoral arterial access to approach the aortic valve transseptally, but this procedure was associated with high rates of mortality and stroke.3 At the same time, in the United States, animal studies were being carried out by Lars G. Svensson, Todd Dewey, and Michael Mack to develop a transapical method of implantation,4,5 while John Webb and colleagues were also developing a transapical aortic valve implantation technique,6,7 and later went on to develop a retrograde transfemoral technique. This latter technique became feasible once Edwards developed a catheter that could be flexed to get around the aortic arch and across the aortic valve.

As the Edwards balloon-expandable valve (Sapien) was being developed, a nitinol-based self-expandable valve system was introduced by Medtronic: the CoreValve. Following feasibility studies,5,8 the safety and efficacy of these valves were established thorough the Placement of Aortic Transcatheter Valves (PARTNER) trial and the US Core Valve Pivotal Trial. These valves are currently approved by the US Food and Drug Administration (FDA) for patients for whom conventional surgery would pose an extreme or high risk.9–11

CLINICAL TRIALS OF TAVR

The two landmark prospective randomized trials of TAVR were the PARTNER trial and CoreValve Pivotal Trial.

The PARTNER trial consisted of two parts: PARTNER A, which compared the Sapien balloon-expandable transcatheter valve with surgical aortic valve replacement in patients at high surgical risk (Society of Thoracic Surgeons [STS] score > 10%), and PARTNER B, which compared TAVR with medical therapy in patients who could not undergo surgery (combined risk of serious morbidity or death of 50% or more, and two surgeons agreeing that the patient was inoperable).

Similarly, the CoreValve Pivotal Trial compared the self-expandable transcatheter valve with conventional medical and surgical treatment.

TAVR is comparable to surgery in outcomes, with caveats

In the PARTNER A trial, mortality rates were similar between patients who underwent Sapien TAVR and those who underwent surgical valve replacement at 30 days (3.4% and 6.5%, P = .07), 1 year (24.2% and 26.8%), and 2 years (33.9% and 35.0%). The patients in this group were randomized to either Sapien TAVR or surgery (Table 1).10,12

The combined rate of stroke and transient ischemic attack was higher in the patients assigned to TAVR at 30 days (5.5% with TAVR vs 2.4% with surgery, P = .04) and at 1 year (8.3% with TAVR vs 4.3% with surgery, P = .04). The difference was of small significance at 2 years (11.2% vs 6.5%, P = .05). At 30 days, the rate of major vascular complications was higher with TAVR (11.0% vs 3.2%), while surgery was associated with more frequent major bleeding episodes (19.5% vs 9.3%) and new-onset atrial fibrillation (16.0% vs 8.6%). The rate of new pacemaker requirement at 30 days was similar between the TAVR and surgical groups (3.8% vs 3.6%). Moderate or severe paravalvular aortic regurgitation was more common after TAVR at 30 days, 1 year, and 2 years. This aortic insufficiency was associated with increased late mortality.10,12

In the US CoreValve High Risk Study, no difference was found in the 30-day mortality rate in patients at high surgical risk randomized to CoreValve TAVR or surgery (3.3% and 4.5%) (Table 1). Surprisingly, the 1-year mortality rate was lower in the TAVR group than in the surgical group (14.1% vs 18.9%, respectively), a finding sustained at 2 years in data presented at the American College of Cardiology conference in March 2015.13–16

TAVR is superior to medical management, but the risk of stroke is higher

In the PARTNER B trial, inoperable patients were randomly assigned to undergo TAVR with a Sapien valve or medical management. TAVR resulted in lower mortality rates at 1 year (30.7% vs 50.7%) and 2 years (43.4% vs 68.0%) compared with medical management (Table 1).17 Of note, medical management included balloon valvuloplasty. The rate of the composite end point of death or repeat hospitalization was also lower with TAVR compared with medical therapy (44.1% vs 71.6%, respectively, at 1 year and 56.7% and 87.9%, respectively, at 2 years).17 The TAVR group had a higher stroke rate than the medical therapy group at 30 days (11.2% vs 5.5%, respectively) and at 2 years (13.8% vs 5.5%).17 Survival improved with TAVR in patients with an STS score of less than 15% but not in those with an STS score of 15% or higher.9

The very favorable results from the PARTNER trial rendered a randomized trial comparing self-expanding (CoreValve) TAVR and medical therapy unethical. Instead, a prospective single-arm study, the CoreValve Extreme Risk US Pivotal Trial, was used to compare the 12-month rate of death or major stroke with CoreValve TAVR vs a prespecified estimate of this rate with medical therapy.14 In about 500 patients who had a CoreValve attempt, the rate of all-cause mortality or major stroke at 1 year was significantly lower than the prespecified expected rate (26% vs 43%), reinforcing the results from the PARTNER Trial.14

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