UK TAVI

“On résiste à l’invasion des armées; on ne résiste pas à l’invasion des idées” (No one can resist an idea whose time has come) – Victor Marie Hugo

Transcatheter aortic valve replacement (TAVR) has been established as an appropriate treatment option for patients with symptomatic severe aortic stenosis who are at intermediate, high, or prohibitive surgical risk. While we all are eagerly waiting for the results of large scale randomized trial evaluating “The Safety and Effectiveness of the SAPIEN 3 Transcatheter Heart Valve in Low Risk Patients With Aortic Stenosis” (PARTNER-3), Nordic Aortic Valve Intervention Trial (NOTION) results did provide an insight into potential role of TAVR in low risk populations. This small randomized trial compared TAVR (using self-expanding bioprosthesis–Corevalve) with surgical aortic valve replacement (SAVR) in an all-comers patient cohort in 3 Nordic centers¹. Among 280 patients, 81.8% of patients in this study were low risk, as assessed by Society of Thoracic Surgeons score (<4%). In the low risk cohort, at 6 years, the rates of all-cause mortality were similar for TAVR (42.5%) and SAVR (37.7%) patients (p = 0.58)¹.

These results are very encouraging and might play an important role in providing non-surgical option to low risk patient populations. However, this also raises an important question regarding the long-term durability of transcatheter bioprosthetic valve in relatively healthy and low-intermediate risk patients with longer life expectancies, especially when compared with SAVR. Interestingly, in studies reporting long-term outcomes and performance of SAVR, the definition of durability of surgical bioprosthetic valves has wide variation spanning from the need for re-operation to integration of clinical and echocardiographic outcomes. Such variations make it difficult to compare durability of SAVR and TAVR. To overcome this, standardized definitions of structural valve deterioration (SVD) and nonstructural valve deterioration (NSVD) have been proposed². In this European task force committee guidelines consensus statement, severe SVD have been defined as either mean gradient ≥40 mm Hg and/or ≥20 mm Hg increase from baseline; AND/OR  peak velocity ≥4 m/s and/or ≥2 m/s increase from baseline; AND/OR severe new or worsening intraprosthetic aortic regurgitation (AR).

Using above criteria, Blackman and colleagues have reported incidence of SVD 5 to 10 years post-procedure using U.K. TAVI (United Kingdom Transcatheter Aortic Valve Implantation) registry data³.  Among 241 patients who underwent TAVR from 2007 to 2011, severe SVD was observed in <1% patients. 91% of patients remained free of SVD on median follow up period of 5.8 years (range 5 to 10 years)³.

Thus, transcatheter bioprosthetic aortic valves are durable. But how do they fare when compared to surgical bioprosthesis?  Søndergaard and colleagues provided answer to this question using 6-year follow up data from NOTION trial¹. The effective orifice area was larger and mean gradient was lower after TAVR when compared to SAVR. Further, this significant difference was sustained on 6 years follow-up. Using standardized definitions, authors have reported higher rate of SVD for SAVR than TAVR (24.0% vs. 4.8%; p < 0.001), whereas there were no differences in NSVD (57.8% vs. 54.0%; p = 0.52); endocarditis (5.9% vs. 5.8%; p = 0.95) or bioprosthetic valve failure rates through 6 years (6.7% vs. 7.5%; p = 0.89)¹.

These results are convincing, but caution should be exercised while extrapolating them to clinical practice. In report from U.K TAVI registry, data was analyzed for only 241 patients (from >1500 patients) due to lack of echocardiographic data both at baseline and >5 years. Further, <15% patients had follow-up beyond 8 years. Later is relevant as SVD of porcine and pericardial aortic bioprostheses have been reportedly begins 8 years after implantation⁴. Similarly in report from NOTION trial, 6-year follow-up data was available only in 50 TAVR and 50 SAVR patients. Also, a core lab did not adjudicate these echocardiographic measurements.

Despite limitations, data from the UK TAVI registry and NOTION trial are very encouraging and supportive to extend indications of TAVR to a relatively younger and healthier patient population. This is especially important as global numbers of TAVR cases are projected to be double by 2025.

References:

1. Søndergaard L, Ihlemann N, Capodanno D, et al. Durability of transcatheter and surgical bioprosthetic aortic valves in patients at lower surgical risk. J Am Coll Cardiol, 73 (2019), pp. 546-553
2. Capodanno DM, Petronio AS, Prendergast B, et al. Standardised definitions of structural deterioration and valve failure in assessing long-term durability of transcatheter and surgical bioprosthetic valves. A consensus statement from the European Association of Percutaneous Cardiovascular Interventions (EAPCI) in collaboration with the European Society of Cardiology (ESC). Eur Heart J, 38 (2017), pp. 3382-3390
3. Blackman DJ, Saraf S, MacCarthy PA, et al. Long-term durability of transcatheter aortic valve prostheses. J Am Coll Cardiol, 73 (2019), pp. 537-545
4. Foroutan F, Guyatt GH, O’Brien K, et al. Prognosis after surgical replacement with a bioprosthetic aortic valve in patients with severe symptomatic aortic stenosis: systematic review of observational studies. BMJ, 354 (2016), p. i5065