What is required for TAVI to become the new gold standard?

Since its introduction into clinical practice, transcatheter aortic valve implantation (TAVI) has revolutionised the treatment of aortic stenosis and has entered international guideline recommendations.^1,2 However when we talk about “gold standard treatment” in patients with aortic stenosis, we need to be aware that the spectrum of patients who suffer from this condition is much larger than that of patients currently enrolled in TAVI trials. Patient cohorts currently referred for surgery include a large variety of patients including those with congenital aortic stenosis, younger patients who are currently recommended for mechanical surgical aortic valve replacement, patients with bicuspid aortic valve disease, patients with endocarditis and those with concomitant coronary artery or additional heart valve disease. In all of these patients TAVI is not recommended and therefore it is impossible to include them into thoughts about the future gold standard.

While we are certainly not at the stage where we could consider TAVI as a gold standard therapy for all patients, it is remarkable that the procedure has already become the gold standard treatment for patients unsuitable for surgical aortic valve replacement.  The impressive outcomes from TAVI trials and registries that included high-risk, and now even intermediate-risk, patients have resulted in a massive rise in TAVI procedures worldwide. High-risk and intermediate risk patients are now discussed by heart teams around the world and considered for TAVI, particularly if they have favourable anatomy.

Trials on intermediate risk do not only show a high degree of procedural safety for TAVI, but also faster postoperative recovery and superior long-term mortality in patients suitable for transfemoral TAVI.^3,4,5 However, we should remember that, so far, the mean age in most TAVI trials is still around 80 years and, mostly, patients >75 years have been enrolled. Given that only 30% of patients who undergo surgical intervention for aortic stenosis in the UK are aged >75 years, we do not know how TAVI compares with surgery for the majority of patients we see in clinical practice.

Also, when we try to find an answer on what one needs for TAVI to become the gold standard, it is important to keep the strengths of surgical aortic valve replacement in mind. Most important may be the fact that we have accurate risk scores, such as the Society of Thoracic Surgeons risk score, for surgery, which not only predict mortality but also morbidity. Surgical prosthetic valve implantation can be individualised to each patient, with even mechanical prostheses being available in younger patients and long-term outcome data for certain valve prostheses extending beyond 25 years. These strengths play a particular role when it comes to the aortic valve treatment in younger low-risk patients.

Potential barriers to using TAVI in lower risk patients

While the risk of significant paravalvular leakage has decreased with the latest generations of transcatheter heart valves, the rate of pacemaker implantations and the uncertainty about durability of transcatheter heart valves remain a concern when one considers TAVI in younger low-risk patients. In this respect, the recently identified issue of subclinical valve thrombosis found in transcatheter valves⁶ and the surprisingly high degeneration of TAVI devices in octogenarian patients reported by Dvir et al at EuroPCR (17–20 May, Paris, France) are a particular concern. The incidence of stroke is reported to be lower in intermediate-risk patients (compared with higher risk cohorts) but given that the mechanism of stroke post TAVI remains the same in low risk patients as it does in high-risk patients, it may not decrease further while the risk of stroke after surgical aortic valve replacement in this group is particularly low—which may result in a disadvantage for TAVI in this cohort.

Given these various concerns, heart teams should be careful about extrapolating the results of intermediate-risk patients to all low-risk patients with aortic stenosis, particularly younger patient cohorts. Therefore, we wonder if the first next step should be to establish TAVI in the low-risk group of elderly patients >75 years of age before exposing younger patients to potential risks? This patient group will particularly benefit from early mobilisation and will be less at risk of long-term issues after pacemaker implantation, paravalvular leakage and impaired durability of transcatheter heart valves.
Given the excellent experience TAVI teams across the world have made with treatment selection by the heart team, these patients should be seen and their treatment options discussed by teams of cardiologists and surgeons to optimise their outcome in the future. Additionally, the results from previous and future trials, as well as large TAVI registries, should be used to get more information on transcatheter heart valve durability at 10 years and also to build a risk score for TAVI which can be used to assess strength of TAVI and surgery for individual patients.

References

1. Nishimura et al. J Thorac Cardiovasc Surg 2014; 148(1): e1–e132.
2. Vahanian et al. Eur J Cardiothorac Surg 2012; 42(4): S1–44.
3. Walther et al. J Am Coll Cardiol 2015; 65(20): 2173–80.
4. Leon et al. N Engl J Med 2016; 374(17): 1609–20.
5. Arnold et al. Cardiovasc Interv 2015; 8(9): 1207–17.
6. Makkar et al. N Engl J Med 2015; 373(21): 2015–24.

Miriam Silaschi is at Department of Cardiac Surgery, Mid-German Heart Center, University Hospital Halle (Saale), Germany and Olaf Wendler is at Department of Cardiac Surgery, Mid-German Heart Center, University Hospital Halle (Saale), Germany

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