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COMMENTS: CARDIOLOGY

Transcatheter aortic valve replacement in severe symptomatic aortic stenosis http://dx.doi.org/10.2174/HMJ2012010

Background

Calcific aortic stenosis (AS) is a progressive disease increasingly found in elderly patients.1 Rapid aortic valve replacement (AVR) is recommended as class I indication in symptoms development in severe AS because of the high mortality associated with lack of intervention.2 As patients age, however, comorbidities also increase and pose a barrier to conventional surgery owing to prohibitive perioperative risk. Traditionally, the surgical risk is estimated by scores such as the EuroScore or the STS (Society of Thoracic Surgery) score. Recently, the technique of percutaneous transfemoral transarterial or transapical access implantation of aortic bioprosthesis valves (TAVI) has been established, enabling even very elderly patients with high risk scores to undergo AVR. In Europe, more than 20 000 TAVI procedures have now been performed. Two types of bioprosthesis are available for clinical use at present (Figures 1 and 2), the self-expanding Medtronic CoreValve and the balloon-expandable Edwards Sapien valve. The results of the landmark PARTNER (Placement of AoRTic TraNscathetER Valve) studies of the Edwards Sapien valve were recently published and are reviewed in this paper.3,4

   

FIGURE 1 The Medtronic CoreValve consists of biological porcine tissue mounted on a self-expanding nitinol stent (Medtronic Inc.).

FIGURE 2 The Edwards Sapien valve consists of bovine tissue mounted on a balloon-expandable stainless-steel stent (Edwards Lifesciences Inc.).

Results and commentary

In the PARTNER trials, two different patient cohorts with symptomatic AS were included. Cohort A, the high-risk surgical group,3 was defined by a high STS score (> 10, predicting a perioperative mortality >15%). The second group, cohort B, comprised patients considered inoperable and at extreme perioperative risk of mortality or morbidity (> 50%).4 Inclusion criteria were aortic valve area ≤ 0.8 cm², mean gradient ≥ 40 mmHg or peak transvalvular velocity ≥ 4.0 m/s. Patients with severe aortic regurgitation, bicuspid or non-calcified AS, severe mitral regurgitation or left ventricular ejection fraction < 20% were excluded. For placement of the Edwards Sapien valve, the balloon is inflated during a brief rapid ventricular pacing at the level of the native aortic valve.

In the trial of inoperable patients (n = 358), the rate of death from any cause at 1 year was 30.7% in the TAVI group compared with 50.7% in the group receiving standard therapy including balloon aortic valvuloplasty.4 The composite endpoint of death or repeat hospitalization and cardiac symptoms was significantly reduced after TAVI, despite the higher incidence of major strokes and major vascular events.

In the recent high surgical risk cohort,4 699 patients were randomized to either transcatheter AVR (transfemoral or transapical approach in patients with inadequate femoral access) or conventional surgical replacement. The mean age was similar (83.6 and 84.5 years, respectively), as was the mean STS score (11.8 and 11.7, respectively). In both arms, about three-quarters of patients had coronary disease, with previous coronary artery bypass graft (CABG) carried out in 42.6% and 44.2%, respectively.

The rates of death from any cause at 1 year were similar: 24.2% in the TAVI arm and 26.8% in the surgical arm (P = 0.44 and P = 0.001, respectively, for non-inferiority). After TAVI, the rates of major stroke were 3.8% and 2.1% at 30 days (P = 0.20) and 5.1% and 2.4%, respectively, at 1 year (P = 0.07); major vascular complications were significantly more frequent (11.0% vs. 3.2%, respectively; P < 0.001). In the surgical group, major bleeding was more frequent (19.5% vs. 9.3%; P < 0.001), as was new-onset atrial fibrillation (16.0% vs. 8.6%; P = 0.006). Symptom reduction at 30 days was greater after TAVI; however, after 1 year there was no difference in symptom improvement between the groups. Taken together, rates of death or major stroke at 1 year were similar in both arms (TAVI 26.5% and surgery 28%). TAVI resulted in significantly more frequent paravalvular aortic regurgitation (moderate or severe) both at 30 days and at 1 year (30 days: TAVI 12.2% vs. surgery 0.9%; 1 year: 6.8% vs. 1.9%, respectively; both P < 0.001).

Further evaluation recently showed that, among inoperable patients with severe AS, TAVI resulted in significant improvements in quality of life compared with standard care maintained for at least 1 year,5 and costs for increased life expectancy were within accepted ranges for other common cardiovascular technologies.6 Long-term survival is, however, influenced by progression of the comorbidities in these highest risk elderly patients.

Previously, the aortic valve annulus diameter for the Edwards Sapien valve was limited to 18–25 mm to enable expansion into the calcified masses of the stenotic valve. For the CoreValve an annulus diameter of 20–27 mm was necessary to allow anchoring of the prosthesis below and above the annulus. Complete heart block is more common with the CoreValve owing to deeper seating in the outflow tract with proximity to the bundle of His.

Critically important is the ileofemoral diameter for catheter sheath size (7 mm for the 23-mm Edwards Sapien valve, 8 mm needed for the 26-mm valve; CoreValve minimal 6 mm). Excessive vessel tortuosity or calcification may impede sheath placement.

Further trials have been initiated to evaluate smaller access sheath sizes.7 The PARTNER 2 trial employs a newer device (Edwards Sapien XT valve) enabling a smaller diameter (minimum vessel diameter ≥ 6 mm). The Medtronic CoreValve trial is randomizing a high-risk cohort to TAVI or standard surgery and an extremely high-risk cohort with TAVI into a registry. No transapical approach is planned in the CoreValve: axillary or subclavian approaches may be applied in the case of poor femoral access.

In conclusion, in inoperable patients at highest risk, the superiority of TAVI to standard medical therapy regarding survival and functional status has been confirmed. In high-risk patients still eligible for conventional surgery, the non-inferiority and comparability of TAVI with similar results of survival at 1 year have been demonstrated. However, rates of major stroke and vascular complications remain higher in the transfemoral TAVI group. The durability of the new prosthesis devices and possible long-term effects of paravalvular aortic regurgitation after TAVI remain unclear at present. Encouraging preliminary long-term results appear to suggest that this interventional method also will be feasible in lower-risk groups in the future.

References

  1. Carabello BA, Paulus WJ. Aortic stenosis. Lancet 2009; 373:956–66. http://dx.doi.org/10.1016/S0140-6736(09)60211-7
  2. Bonow RO, Carabello BA, Kanu C, et al. ACC/AHA 2006 guidelines for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines. Circulation 2006; 114:e84–e231. http://dx.doi.org/10.1161/CIRCULATIONAHA.106.176857
  3. Smith CR, Leon MB, Mack MJ, et al. Transcatheter versus surgical aortic-valve replacement in high-risk patients. N Engl J Med 2011; 364:2187–98. http://dx.doi.org/10.1056/NEJMoa1103510
  4. Leon MB, Smith CR, Mack M, et al. Transcatheter aortic-valve implantation for aortic stenosis in patients who cannot undergo surgery. N Engl J Med 2010; 363:1597–607. http://dx.doi.org/10.1056/NEJMoa1008232
  5. Reynolds MR, Magnuson EA, Lei Y, et al.; Placement of Aortic Transcatheter Valves (PARTNER) investigators. Health-related quality of life after transcatheter aortic valve replacement in inoperable patients with severe aortic stenosis. Circulation 2011; 124:1964–72. http://dx.doi.org/10.1161/CIRCULATIONAHA.111.040022
  6. Reynolds MR, Magnuson EA, Wang K, et al. Cost effectiveness of transcatheter aortic valve replacement compared with standard care among inoperable patients with severe aortic stenosis: results from the PARTNER trial (cohort B). Circulation 2012 [Epub ahead of print].
  7. Welt FG, Davidson MJ, Leon MB, Eisenhauer AC. Transcatheter aortic valve replacement. Circulation 2011; 124:2944–8. http://dx.doi.org/10.1161/CIRCULATIONAHA.111.032243

Jutta Bergler-Klein

Department of Cardiology, Medical University of Vienna

Waehringer Guertel 18–20, 1090 Vienna, Austria

Email: jutta.bergler-klein@meduniwien.ac.at




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