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Lee and Sung: The Lower, The Better? Think Beyond the Gradient after Transcatheter Aortic Valve Replacement for Small Annulus
Patient with severe aortic stenosis and small aortic annulus poses a clinical challenge when dealing with either surgical or transcatheter aortic valve replacement (TAVR). The main concern of the small anatomy is the increasing risk of suboptimal prosthetic valvular hemodynamics and the subsequent prosthesis-patient mismatch (PPM). From the surgical perspective, several special designs, including supra-annular position, stentless valve, sutureless valve, and streamlined sewing ring with external mounting valve were attempted to get larger effective orifice area (EOA) of prosthetic valve.1) Aortic root enlargement is also an attractive surgical technique to put a larger prosthetic valve when encountering small anatomy. On the other hand, the transcatheter heart valve (THV) carries important features, such as the absence of sewing ring and oversizing deployment, which facilitate larger EOA as compare to traditional surgical valves. The superior hemodynamic performance of THV over surgical valves has been observed in the randomized controlled trials.2)3)
As compared to the Western countries, small anatomy is more prevalent in the Asian. Lee et al.4) have reported a single-center study of 70 patients with severe aortic stenosis and small annulus (mean diameter of ≤23 mm or minimal diameter of ≤21 mm) underwent TAVR with either a self-expanding valve (SE-THV) or a balloon-expandable valve (BE-THV). While SE-THV was associated with larger EOA, better hemodynamic performance, and less PPM, the procedural safety and clinical outcome at 1-year were comparable between the different valve platforms. In addition, the pacemaker implantation rate and the presence of para-valvular leakage (SE-THV vs. BE-THV: 46.7% vs. 32.0%, p=0.347) were also similar between BE-THV and SE-THV.
However, the result of this study should be interpreted cautiously. Although the valvular hemodynamic is superior with SE-THV, the Doppler-derived trans-prosthetic gradients are usually higher and the estimated EOA is smaller, as compare with the catheter-derived measures due to pressure recovery phenomenon.5) In general, the difference is negligible in the absence of a small aortic root. Furthermore, the discordance of trans-valvular gradients between Doppler-derived measurements and invasive measurements is described among different type of THV. Aalaei-Andabili et al.6) have demonstrated a significant difference between invasive measurement and Doppler-derived gradients (7.5±3 mmHg vs. 11.4±4.5 mmHg, p<0.001) after BE-THV implantation. In contrast, there was no significant difference by either measurement for SE-THV (invasive vs. Doppler-derived gradient: 10.3±3.4 mmHg vs. 8.5±4.6 mmHg, p=0.18). Theoretically, only catheter can directly measure the pressure gradient across the prosthesis. By echocardiogram, the pressure gradient and EOA are calculated by Bernoulli's equation according to the difference of flow velocity along with Doppler alignment. Therefore, we need invasive data to conclude the true hemodynamic performance between SE-THV and BE-THV.
Recently, Hase et al.7) have demonstrated SE-THV has superior hemodynamic performance over BE-THV for patients with small annulus in Optimized CathEter Valvular iNtervention-Transcatheter Aortic Valve Implantation registry. Among patients with extremely small annulus (mean diameter of ≤21 mm), 1-year survival rate was slightly higher with BE-THV than SE-THV (91.3% vs. 82.2%, p=0.09). In another randomized controlled study, Portico THV (Abbott Structural Heart, St. Paul, MN, USA) has exerted larger EOA and less gradient than BE-THV at 24 months. However, the all-cause mortality at 24 months is significantly higher with Portico valve than BE-THV (22.7% vs. 15.6%, p=0.03).8) Regarding surgical prosthetic aortic valve, Kim et al.9) reported superior valvular hemodynamics, and better regression of left ventricular mass index in patients with supra-annular implantation rather than intra-annulus prothesis. But, the mortality rate, and major adverse events, including stroke, infective endocarditis and re-operation were similar between surgical approaches.
As expanding indications of TAVR, for those with younger age and longer life-expectancy, it is reasonable to choose a proper aortic prosthesis which can exert lowest complications as well as better efficacy and durability. Even though we know that pursuing lower trans-valvular pressure gradient and higher EOA of prosthetic valve is an ideal goal, we should also judge every patient by clinical characteristics and take other factors into consideration, including coronary accessibility and risk of permanent pacemaker. For the particular patients, the ongoing study—The Small Annuli Randomized To Evolut or Sapien trial will compare valve safety and performance in randomized head-to-head fashion. We hope future studies will explore the net clinical impacts, the left ventricular remodeling, and many unanswered questions in patients with small anatomy.

Notes

Funding: The authors received no financial support for the research, authorship, and/or publication of this article.

Conflict of Interest: The authors have no financial conflicts of interest.

Data Sharing Statement: The data generated in this study is available from the corresponding author upon reasonable request.

Author Contributions:

  • Conceptualization: Lee CW, Sung SH.

  • Investigation: Lee CW.

  • Supervision: Sung SH.

  • Writing - original draft: Lee CW.

  • Writing - review & editing: Sung SH.

The contents of the report are the author's own views and do not necessarily reflect the views of the Korean Circulation Journal.

References

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