Transcatheter Aortic Valve Implantation (TAVI) for the Treatment of Aortic Valve Stenosis: a Systematic Review

Introduction: Aortic stenosis (AS) is the most common form of heart valve disease in the western world. As the population ages, this disease is becoming an increasing burden on patients and on the health care system. Current drug therapies (medical management (MM)) cannot reverse the course of AS. For most individuals with severe AS, surgical aortic valve replacement (SAVR), which requires open heart surgery and cardiopulmonary bypass, remains the standard therapy. However, a sub-group of patients with aortic stenosis are unsuitable for or at high risk to undergo SAVR due to their frailty or other comorbidities. Transcatheter aortic valve implantation (TAVI) - a novel, less invasive treatment option – was developed as an alternative for patients who are not suitable or at high risk for undergoing surgery. Objective: This study is intended to assess the feasibility, safety, efficacy and clinical effectiveness of TAVI, using the transfemoral (TF) and transapical (TA) approaches, in comparison to medical management or SAVR in patients with severe symptomatic AS; and to compare the outcomes associated with the two different approaches for valve implantation (TF and TA). Methods: A comprehensive literature search was conducted using eight electronic databases to identify studies of TAVI (TF and/or TA) for the treatment of AS. Data from the selected studies were extracted by two reviewers. Outcomes considered were feasibility, safety, efficacy and effectiveness of TAVI. Study quality was assessed and information was tabulated to identify trends or patterns. Results were pooled across studies for each outcome. Results: Fifty six relevant studies were identified: 37 studies (including seven comparative studies) assessed clinical outcomes, 14 studies discussed health-related quality of life, and five studies examined the impact of the learning curve on feasibility and safety of TAVI on patient outcomes. The overall procedural success rate was 96% (88% - 100%). Studies that examined the learning curve for TAVI demonstrated it had a significant impact - increasing the procedural success rate and decreasing 30-day mortality. The mean combined periprocedural and cumulative all-cause mortality rate at 30 days for TAVI compared to the control groups (MM and/or SAVR) in the same or different studies was: 9.0%, n = 10,500 vs 2.8%, n = 179, and 6.7%, n = 302, respectively. Permanent pacemaker implantation was three times more common with the Medtronic CoreValve compared to the Edwards SAPIEN prosthesis (26.5% vs 8.2%), but when both TAVI valves were compared with SAVR, there was no statistically significant difference. Major vascular complications occurred more frequently in the TF group (11.6%) than in the MM, SAVR or the TA groups. The rate of acute kidney injury requiring renal replacement therapy did not differ significantly between the TAVI and control groups, but was three times higher with the TA compared to the TF approach (7.3% vs 2.5%). TAVI achieved significant hemodynamic improvement as measured by echocardiography. The pooled estimate for moderate or severe paravalvular aortic regurgitation after TAVI was 7.2% (with no significant difference between TAVI approaches). Paravalvular aortic regurgitation occurred more frequently with TAVI than with SAVR. One year survival rates ranged from 68% to 77% for TAVI patients in the comparative studies and 72% to 85.3% in the case series studies. For MM and SAVR, the one year survival rate was 45% to 49.7% and 73.4% to 83%, respectively. Studies that compared patients’ quality of life before and after TAVI found significant improvement at one-year follow-up. Conclusions: TAVI offers a safe and effective treatment for severe aortic stenosis in patients who are not suitable for or are at high risk to undergo SAVR. Unfortunately, current shortcomings in the evidence on long term outcomes make it difficult to determine the effectiveness of TAVI in high risk patients who may be candidates for surgery.