Double-tap: Doubling-down on optimal THV expansion

Transcatheter aortic valve implantation (TAVI), since its introduction into clinical practice two decades ago, had a remarkable impact on the management and treatment of patients with symptomatic severe aortic stenosis.1 Initially envisioned as an option for patients deemed inoperable or at high surgical risk, the apparent success in terms of procedural safety, technical feasibility, and clinical outcomes soon transformed TAVI into an appealing strategy also for lower-risk as well as younger patients, who might even outlive their implanted bioprosthesis.2 However, the adoption of TAVI also in such patient cohorts, while bearing the promise of a minimally invasive procedure with a shortened hospital stay and a rapid recovery, brings the responsibility to not only perform a safe procedure, as it was the case in elderly high-risk cohorts, but to set the basis for extended optimal transcatheter heart valve (THV) performance and, wherever possible, consider factors that may impact on or prolong durability. Along with the data on clinical outcomes across all risk profiles came several learnings on device choice, THV positioning, and procedural techniques that may serve in this regard of improved efficacy, performance, and lastly, potential longevity. A particular aspect that, recently, has attracted increasing attention is the achieved frame expansion of placed THVs after implantation.3 There is an inherent sense to the argument that, similar to coronary stents, THV stent frames should be as uniformly expanded as possible, to enable the most ideal flow-through. This holds especially true since there seems to be a link between circular stent-frame expansion and coaptation of the bioprosthetic leaflets sutured to the stent frame, which, if the THV stent remains non-circular, seem to exhibit a higher degree of pin-wheeling.4 While many different factors of the baseline anatomy, in combination with the device choice and the actual implant position, may influence THV expansion after first device release, the only one available option to then improve circularity of the stent frame is a potential post-dilatation. In the case of balloon-expandable (BEV) THVs, performing a second dilatation with the delivery balloon at unchanged volume, a technique referred to as ‘double-tap’, will enable a straightforward attempt at optimizing frame expansion without adding much complexity to the procedural workflow. Given the increased awareness of frame expansion and the convenience to implement such a double-tap during BEV implantation, it has been implemented with low threshold in recent practice. However, while the mere fluoroscopic effect following double-tap may be easily appreciable and apparent, actual evidence on its real geometric effect as well as on its impact on technical and clinical outcomes remains scarce. It is against this background that Maznyczka et al., in this issue of EHJ-Valvular and Structural Heart Disease, provide an important piece of evidence regarding the effect of double-tap on THV expansion and on short-term 30-day clinical safety outcomes.5 Assessing 113 patients who received a BEV TAVI by means of the SAPIEN-3 Ultra RESILIA (Edwards Lifesciences) device, implanted using double-tap technique, they could identify a significant fluoroscopic increase of THV expansion after repeated dilatation at the inflow (88.6% to 96.4%), mid-portion (80.1% to 90.8%) and outflow (90.1% to 97.6%) levels of the prostheses. The effect of double-tap was more pronounced in patients with bicuspid anatomy and in those with a calcium volume >385 mm3. The reported rates of stroke (3.5%) and new permanent pacemaker implantation (6.2%) compare favourably with the local single-centre experience of historical outcomes in patients who have received the same device without the double-tap technique being applied, thus suggesting no signal of impaired procedural safety. This is further reflected in the 30-day safety outcomes reported. These findings strengthen the evidence base regarding the actual geometric benefits of the double-tap technique, enabling improved circular expansion of BEV THVs. The remaining question for clinical practice comes down to the, in parts yet unknown, longer-term effects of such improved stent frame geometry. The effects of a less distorted THV frame and, thus, less contorted and pin-wheeled THV leaflets may be threefold in terms of timing: Initially, improved stent expansion may reduce paravalvular leakage and better immediate haemodynamics. Immediate pressure-wire measurements pre- and post-double-tap could, indeed, show a further reduction of trans-THV gradients in a small series assessed using a pressure-sensing guidewire.6 Then, in mid-term alterations in stent conformation and leaflet symmetry may contribute to the formation of hypoattenuated leaflet thickening and leaflet thrombosis.3 While larger studies are needed to finally clarify whether such leaflet alterations are only subclinical, a growing body of evidence is providing conclusive hints that these imaging findings are, indeed, linked to poorer clinical outcomes and increased rates of clinical events such as late stroke following TAVI.7,8 Finally, there might be a correlation between stent frame underexpansion with associated leaflet alterations and mid- to late-term THV performance, especially in terms of leaflet degeneration and, lastly, bioprosthetic valve failure.9 Taking together all those potential critical aspects that are associated with THV frame underexpansion, which, following the data at hand by Maznyczka et al., can successfully be alleviated by means of double-tap of BEV THV, standardized implementation of this technique in the procedural workflow seems reasonable (Figure 1). Although this technique carries a supposedly good safety profile according to the present study, some additional considerations before performing the second inflation seem appropriate: While inflation with the same volume may not mean an additional risk for annular rupture since the initial inflation was without injury, still, some hemodynamic risk of a repeated pacing run is not negligible. Thus, in patients who are unstable throughout the procedure or become unstable during the initial pacing run, a routine double-tap should be considered carefully. In patients who present hemodynamically unstable already during initiation of the procedure and before the first pacing run for initial THV implantation, instead of a double-tap technique, a prolonged single balloon-inflation might be considered to still improve expansion of the stent frame without confronting the already unstable patient with the additional burden of repeated pacing runs. Another potential risk associated with repeated balloon inflation might be a higher rate of new pacemaker dependency due to repeated pressure on the conduction system during double-tap. On the other hand, in BEV THV, additional ventricular foreshortening after double-tap may even be protective for the conduction system as the inflow-struts of the stent frame are moved further upwards, away from the conduction system. One final potential risk of double-tap, which will need more pre-clinical investigation, are possible micro-lesions of the THV leaflets caused by repeated imprint of the stent frame, when the leaflets are pushed outwards during balloon-inflation, which could, in the end, counteract potential beneficial effects on leaflet durability.10 Overview of rationale and considerations around routine double-tap in balloon-expandable transcatheter aortic valve implantation. Abbreviations: BEV = balloon-expandable valve, HALT = hypoattenuated leaflet thickening, PVL = paravalvular leakage, TAVI = transcatheter aortic valve implantation Weighing the study findings, it also needs to be noted that such a technique can only be applied for BEV THV, and the risk-benefit profile for post-dilatation in self-expandable prosthesis might be different. Furthermore, a reason to perform a second balloon-inflation may not only be mere stent geometry as addressed by double tap, but also other reasons, such as peri-valvular leakage, can play an additional important role when considering repeated inflation (in 12.4% of the study’s patients, re-inflation with added volume was performed). Finally, it needs to be noted that stent frame circularity in the present study, similar to current practice, was assessed in only one angulation—especially, in asymmetric calcium distribution, it might be necessary to identify a ‘maximum constriction’ projection along the narrowest plane for THV expansion in that given anatomy to really understand the present stent frame geometry. In conclusion, the discussed data are of great importance as they confirm the technical and geometric success of the double-tap technique. Given the context of continuously aggregating evidence on the significance of circular frame expansion, correlated with THV performance as well as longevity, it seems appropriate and advisable to integrate the performance of double-tap into contemporary BEV practice (wherever haemodynamics and acute procedural safety allow) to achieve as good immediate and also longer-term outcomes as possible. Continuous follow-up of BEV patients treated with double-tap will be essential to further confirm that doubling down on frame expansion will also translate into doubling down on optimal THV performance and clinical outcomes throughout the whole lifespan of the implanted prostheses. Jonathan Curio (Writing—original draft, Writing—review & editing [lead]), and Victor Mauri (Writing—original draft, Writing—review & editing [equal]) Dr. Curio has received research grant support from Boston Scientific; has served on an advisory board for Medtronic; and has received travel support from Laralab, Cardiovalve, and JenaValve Technology. Dr. Mauri has nothing to declare. Nothing to disclose.