Efficacy and Safety of Postdilation for a Self-Expanding Transcatheter Heart Valve

Abstract

Background. Data are lacking regarding the outcomes of balloon postdilation (BPD) for the Acurate neo and neo2 devices. The aim of this study was to assess the impact of BPD in a large, single-center cohort of patients treated with the Acurate platform. Methods. For this retrospective analysis, we included all patients with severe aortic stenosis who underwent transfemoral transcatheter aortic valve replacement (TAVR) with the Acurate neo or neo2 prosthesis at our institution. Results. Among 1417 Acurate recipients, BPD was required in 521 cases (36.8%) for relevant paravalvular regurgitation (PVR) (n = 418) and incomplete prosthesis expansion or increased transprosthetic gradients (n = 103). Overall, BPD was successful in 87.9% and led to a significant reduction of more-than-mild PVR from 32.0% to 7.5% (P<.001). In the BPD group, prosthesis-patient mismatch (PPM) was less common. Prosthetic leaflet damage or valve dislodgment due to BPD occurred in 6 cases (1.2%). All other outcomes were similar between groups with and without BPD, including rates of aortic root injury, stroke, acute kidney injury, permanent pacemaker implantation, and all-cause 30-day mortality. Independent predictors of the need for BPD were higher mean transaortic gradients, severe aortic valve calcification, less prosthesis oversizing, and the use of larger prosthesis sizes. Conclusion. For transfemoral TAVR using the Acurate neo/neo2, BPD effectively reduces relevant PVR and decreases the risk of PPM without increasing adverse events. Transcatheter heart valve damage associated with BPD is rare, commonly avoidable, and does not jeopardize the net benefit of BPD.

Keywords: Acurate, balloon valvuloplasty, postdilation, self-expanding prosthesis

Balloon postdilation (BPD) is a common procedural step during transcatheter aortic valve replacement (TAVR) that may be considered in the event of paravalvular regurgitation (PVR), incomplete prosthesis expansion, or residual transprosthetic gradients.^1-6 The beneficial effects of BPD regarding reduction of PVR and improved hemodynamics have been demonstrated previously for balloon-expandable and self-expanding transcatheter heart valves (THVs).^2,4 However, to date, there are no data on the efficacy and safety of BPD for the Acurate neo system. This could be particularly relevant, as the lower radial force of the Acurate platform might be more prone to stent recoil following BPD.⁷ In this context, further open issues relate to the optimal type and size of balloon valvuloplasty catheters that are used for BPD.

The present study aimed to assess the impact of BPD in a large, single-center cohort of patients treated with the Acurate platform.

Methods

Study design. The study cohort comprised all patients who underwent transfemoral TAVR for native aortic stenosis using the Acurate neo or neo2 THV at our institution. Severity of aortic stenosis was determined according to existing guidelines.⁸ All patients were discussed within a heart team consisting of a cardiac surgeon, an interventional cardiologist, and a cardiac anesthetist. Baseline characteristics were prospectively documented in a database that included demographics, comorbidities, risk scores, and echocardiography data. Preprocedural multidetector computed tomography (MDCT) of the entire aorta and iliofemoral arteries was performed as clinical routine using a 64-slice or 192-slice dual-source scanner (Somatom Definition or Force; Siemens Healthcare), as previously described.⁹ MDCT datasets were analyzed in a standard fashion using dedicated software (3mensio; Pie Medical). The cover index was calculated to determine the degree of valve oversizing [cover index = 100 × (THV size – perimeter-derived annulus)/THV size]. The aortic valve calcium score (AVCS), presented in Agatston units (AUs), was measured according to the Agatston method using noncontrast-enhanced MDCT scans.¹⁰ The presence of eccentric periannular calcification was determined by visual estimation of the aortic valve in short-axis views and maximum intensity projections, as previously described.¹¹

Due to the retrospective character of the study, ethical approval was waived by the institutional ethics committee. The study adhered to the principles of the Declaration of Helsinki.

Procedural aspects and types of balloons. Details of the design of the prosthesis and the implantation technique have been described previously.⁷ The decision to perform predilation or postdilation as well as the balloon type and size were at the operator’s discretion. After valve deployment, prosthesis function was examined by means of simultaneous invasive hemodynamic measurement and aortography via a pigtail catheter that was placed slightly above the commissural posts using 20-25 mL of contrast agent with a flow of 20 mL/s. Inconsistent findings were verified on the table by transthoracic echocardiography. Indications for BPD were relevant PVR, incomplete expansion of the prosthesis, and increased transprosthetic gradients. Supplemental Table S1 provides the types and specifications of the balloons that were used for BPD.

Outcomes of interest and definitions. The primary outcome of interest was the rate of ad hoc BPD use during the index TAVR procedure and its success rate. Success of BPD was defined as reduction of PVR to < moderate as measured intraprocedurally, mean transprosthetic gradient <20 mm Hg, absence of severe prosthesis-patient mismatch (PPM) according to Valve Academic Research Consortium (VARC)-2 criteria at discharge echocardiography,¹² and absence of damage to or embolization of the prosthesis leading to functional impairment as a consequence of BPD.

Secondary outcomes of interest were the incidences of complications potentially related to BPD, including annular rupture, aortic dissection, ventricular septal defect, stroke, acute kidney injury (AKI), and permanent pacemaker implantation (PPI). Further secondary outcomes of interest were 30-day all-cause mortality and significant PVR, which was defined as PVR ≥ moderate at discharge echocardiography, or bail-out measures for relevant PVR during the index hospital stay, including the implantation of a second valve or conversion to surgical valve replacement.

Statistical analysis. Continuous variables are presented as median and interquartile range (IQR); categorical data are presented as number (percentage). Continuous data were compared using the Wilcoxon rank-sum test; categorical data were compared using the Fisher’s exact test or Chi-square test, as appropriate. To determine independent predictors of the need for BPD and success of BPD, binary logistic regression analysis was computed by entering all covariates that in the univariate analysis had P≤.10 into the multivariable analysis. A 2-sided P<.05 was considered significant. All analyses were performed using STATA IC, version 16.1 (StataCorp LLC).

Results

Study cohort. Between May 2012 and March 2021, a total of 1417 patients, median age, 81.9 years (IQR, 78.6-85.0), 65.1% female, underwent transfemoral TAVR using either the neo or neo2 valve. Baseline characteristics, MDCT measurements, procedural data, and ­outcomes stratified into BPD group (n = 521; 36.8%) vs no BPD group (n = 896; 63.2%) are provided in Table 1 and Table 2. Predilation was more frequent in the BPD group than in the no-BPD group (78.3% vs 58.5%, respectively; P<.001). Patients who underwent predilation had higher AVCS than those without predilation (2498 AU [IQR, 1908-3198] vs 1254 AU [IQR, 925-1631]; P<.001). Repeated BPD was required in 58/521 cases (11.1%; n = 2 in 57 cases, n = 3 in 1 case). Indications for BPD were relevant PVR (n = 418) and incomplete prosthesis expansion or increased transprosthetic gradients (n = 103). In 87/521 cases (16.7%), the balloon size was numerically larger than the native perimeter-derived annulus diameter, but in only 7/521 cases (1.3%) did the balloon size exceed the annulus diameter by ≥1 mm (Figure 1). In 10/521 cases (1.9%), the balloon size was equal to or larger than the prosthesis diameter. Procedure duration, fluoroscopy time, and use of contrast agent were higher in the BPD group than in the no-BPD group.

Efficacy of postdilation. BPD was successful in 458/521 cases  overall (87.9%). When comparing BPD vs no-BPD patients, relevant PVR was more common in the BPD group, but BPD led to a significant reduction in more-than-mild PVR from 32.0% to 7.5% (P<.001). Figure 2 shows the distribution of PVR degree before and after BPD among patients undergoing BPD. In the BPD group, the indexed aortic valve area was larger and PPM was less common (Table 2).

Among the 58 patients requiring multiple BPDs, the success rate of BPD was numerically, but not significantly, higher when using balloon sizes that were larger than the perimeter-derived annulus diameter (balloon size > annulus in 22/26 [84.6%] vs balloon size ≤ annulus in 23/32 [71.9%]; P=.25). Details of the 26 patients requiring multiple BPDs in whom balloon sizes exceeded the native annulus diameter are listed in Supplemental Table S2. In almost half of these patients (13/26; 46.2%), BPD was successful only after stepping up to a balloon size that distinctly exceeded the annulus size.

Safety of postdilation. THV damage following BPD occurred in 6/521 cases (1.2%) and included device embolization (n = 3) and prosthetic leaflet damage (n = 3) (further details in Supplemental Table S3). In the BPD group, there were no cases of annular rupture or ventricular septal defect and 2 cases with aortic dissection that were not directly related to BPD. The combined safety endpoint as defined above and all other VARC-2 outcome measures were similar between BPD and no-BPD patients.

Among BPD cases in which the balloon size exceeded the perimeter-derived annulus diameter, no incremental damage was noted (Figure 1). All-cause 30-day mortality rates were similar between the groups.

Predictors of postdilation and its success. In the univariate analysis, female sex, prior atrial fibrillation, a higher mean transaortic gradient, a higher AVCS, the presence of eccentric aortic valve calcification, less THV oversizing (smaller cover index), predilation, the use of neo, and the use of medium and large THV sizes were associated with BPD. In the multivariable analysis, a higher mean transaortic gradient, a higher AVCS, a smaller cover index, and the use of larger THV sizes independently predicted the need for BPD (Supplemental Table S4).

Successful BPD was univariately associated with a lower mean transaortic gradient, a lower AVCS, aggressive predilation (balloon size ≥ [perimeter-derived annulus – 1 mm]), the use of neo2, the use of size small THVs, a higher cover index, and the use of larger balloon sizes for BPD (greater balloon-annulus ratio). In the multivariable analysis, only aggressive predilation, the use of neo2, and a higher cover index independently predicted success of BPD (Supplemental Table S5).

Discussion

The present study analyzed the efficacy and safety of BPD in a large population treated with the Acurate neo or neo2 THV. The main findings show that: (1) BPD for Acurate THV is successful in the majority of cases with efficient reduction of relevant PVR and PPM rates; and (2) BPD for Acurate THV is safe and does not increase rates of stroke, PPI, AKI, and early mortality. The occurrence of THV damage in rare cases should be noted, but this risk may be minimized with precautionary measures.

The use of a balloon size slightly larger than the perimeter-­derived native annulus diameter for selected cases may increase the success rate of BPD, and in the present cohort this procedure was found to be safe. Additionally, independent predictors of the need for BPD were higher mean transaortic gradients, higher AVCS, smaller cover index, and the use of larger (medium and large) THVs.

Frequency and predictors of postdilation. Rates of BPD differ primarily according to the type and generation of THV. The lowest rates have been reported for balloon-expandable devices (Sapien/Sapien XT, 12.4%-41%; Sapien 3, 12.5%),^2-4,6 whereas self-expanding THVs commonly have higher rates of BPD (CoreValve, 20%; Evolut R, 33%-36%; Portico, 43%).^1,2,13-15

The BPD frequency of 36.8% in the present analysis is ­slightly lower than previously reported for the Acurate neo THV (45%-52%),^16,17 even when taking into account the Acurate generation (neo, 37.8%; neo2, 29.8%). This may be attributed to a different patient selection with avoidance of severely calcified anatomies and a different sizing approach that was employed in our center based on greater experience over time.^9,18 In addition, the propensity of the operator to perform BPD may vary individually and across centers; thus, the willingness to accept residual PVR might be greater in older patients or when the risk of performing BPD appears high, eg, in cases of uncertainty regarding capture of the temporary pacing leads or in the presence of severe annular calcification.

Predictors of BPD include higher transaortic gradients and more severe aortic valve calcification as nonmodifiable patient-related factors, whereas employing more oversizing may help to prevent BPD. The lower rate of BPD when using small-sized THVs may be explained by the relatively higher radial force than medium or large sizes. The higher rate of BPD among patients who underwent predilation most likely is related to the higher AVCS in this group than in those without predilation.

Efficacy of postdilation. The successful reduction of PVR by BPD in the present cohort is consistent with results of previous reports.^5,6 Additional beneficial effects observed as a consequence of BPD were lower transprosthetic gradients and less frequent moderate or severe PPM.⁴ Importantly, the higher frequency of relevant PVR in the BPD group is a common finding that is related to the greater need for BPD and may not be considered a consequence or failure of BPD.^1-5

When the neo2 device was used, success rates of BPD and the cover index (eg, more oversizing) were higher. Success rates were also higher following more aggressive predilation. The additional sealing skirt of the neo2 generation may contribute to reducing the rate of relevant PVR. Likewise, increased oversizing has been shown to decrease PVR.¹⁸ The improved success rate of BPD following aggressive predilation is a novel finding in the setting of TAVR and may be analogous to lesion preparation using high-pressure, noncompliant balloons for percutaneous coronary intervention.¹⁹

Safety of postdilation. Typical safety concerns regarding BPD include injury of the native anatomy (annular rupture, aortic dissection, ventricular septal defect), damage of the prosthesis (leaflet rupture, device embolization), stroke, AKI, and PPI. Our results show that with respect to the Acurate platform, BPD is safe and is not associated with higher risk of damage to the native anatomy, stroke, AKI, PPI, and 30-day all-cause mortality. Similarly, most previous studies demonstrated that BPD is safe for various THV types.^1,4 However, there are reports of increased stroke rates associated with the use of balloon-expandable ­devices,^2,4,6 although not regarding self-expanding THVs.^1,5 This may be related to different degrees of device landing-zone calcification, which is commonly more severe in cases applying balloon-expandable THVs.²⁰ Another reason could be the frequent practice of using the balloon of the delivery system for BPD, which may increase the risk of stroke during repassage of the aortic arch and when the reinserted delivery system has not been prepared and flushed thoroughly.

A single report by Harrison et al showed that AKI was more frequent among BPD patients who were implanted with the CoreValve device, which was related to a greater use of contrast agent.⁵ In the present cohort, the use of contrast agent was significantly increased in the BPD group, but the absolute difference was small, which may explain why AKI did not occur more frequently following BPD.

Prosthesis damage and embolization associated with BPD. Damage to the THV associated with BPD was rare overall and involved direct injury to the prosthetic leaflets (n = 3) and device embolization (n = 3) (Supplemental Table S3). Factors that may increase the risk of prosthetic leaflet damage during BPD include the ratio between balloon and THV size, the position of the balloon, and balloon movement due to residual output stemming from ineffective rapid ventricular pacing. In 1 of these cases, the balloon size was 25 mm for Acurate neo size medium, which may have been the main reason for the damage to the leaflets. Therefore, as the manufacturer recommends, the balloon size should not be larger than the prosthesis diameter minus 1 mm. However, balloon size alone may not be the only causative factor, as in the 2 other cases of prosthetic leaflet injury, the balloon size was far smaller than the prosthesis size. Moreover, in 9 other cases, the balloon size for BPD equaled or even exceeded the prosthesis size without any occurrence of THV damage.

The 3 cases of device embolization that were associated with BPD occurred for various reasons, including capture failure during rapid ventricular pacing, retrieval of the preshaped stiff wire over the balloon catheter, and recrossing of the prosthesis with the balloon catheter via one of the stabilization arches, which caused dislodgment during retrieval of the deflated balloon (Figures 3A-3D). Even though capture failure during rapid ventricular pacing ultimately must be considered a fateful event,²¹ greatest care should be employed to achieve a stable position of the temporary pacing wire with reliable pacing thresholds. The risk of device embolization during retrieval of the preshaped stiff wire may be eliminated by exchanging the stiff wire over a pigtail catheter instead of using the balloon catheter.

Finally, to avoid unnecessary recrossing of the prosthesis, it is recommended to maintain transprosthetic access to the left ventricle unless the decision has been made regarding BPD.⁷ In the situation where the Acurate valve has to be recrossed (either due to inadvertent withdrawal of the wire or in staged procedures), a pigtail catheter should be used and placed at the top of the commissural posts for crossing. Thereafter, it is mandatory to confirm the correct wire position via fluoroscopy (Figures 3E, 3F). Any resistance when advancing the balloon should raise the suspicion of false recrossing and prompt verification of the wire position. A detailed review of cases revealed that THV damage associated with BPD may be commonly avoided with some precautionary measures.  

Balloon size and type. The balloon size exceeding the annulus size intuitively raises concerns, particularly in annular rupture. In the CoreValve US clinical trials, among the 782 patients who required BPD, there were 3 cases reported to be fatal annular ruptures following BPD that were likely due to oversized balloons (all 28 mm) in relation to the native anatomy.⁵ The authors suggest choosing a conservative balloon size for BPD, particularly in the presence of annular or left ventricular outflow tract (LVOT) calcification. However, a detailed review of the narratives reveals that there was massive oversizing of the balloon in 2 cases with confirmed annular rupture (case 1: perimeter-derived annulus 26.4 mm, LVOT size 21 mm; case 2: perimeter-derived annulus 23.8 mm, LVOT size 18 mm), whereas in the third case (­perimeter-derived annulus 29 mm, LVOT size 20 mm), annular rupture in a strict sense was not confirmed but was assumed due to pericardial effusion and table death.

Indeed, in using balloon-expandable devices, it is common that the diameter of the balloon and prosthesis are larger than the native annulus diameter. In the present cohort, the extent of balloon oversizing was minimal and commonly did not exceed 1 mm, which may not relevantly increase the risk of annular rupture unless there is heavy annular or subannular calcification. On the other hand, among patients with oversizing, there were 13 cases with successful BPD only after stepping up to a balloon size that distinctly exceeded the annulus size (Supplemental Table S2).

Importantly, the selection of a balloon size that is larger than the native annulus diameter should only be considered after unsuccessful BPD with a balloon size that is slightly smaller or equals the native perimeter-derived annulus diameter. The decision to step up to a balloon diameter that exceeds the native annulus size must be made after a careful risk-benefit assessment in consideration of the effectiveness of the previous BPD, the balloon type and size that was used, the mechanism of PVR, the individual impact and tolerance of residual PVR, and device landing-zone calcification and distribution.  

Study limitations. The present study is a retrospective, nonrandomized analysis from a single center without core laboratory adjudication of aortography and echocardiography results. Given the heterogeneity of balloon types used and the fact that predilation and postdilation were commonly performed by hand inflation without pressure manometer control, the actual balloon diameter that was achieved may diverge from the nominal values reported by the manufacturers.

Conclusion

For transfemoral TAVR using the Acurate neo/neo2 THV, BPD effectively reduces relevant PVR and decreases the risk of PPM without increasing adverse events. THV damage associated with BPD is rare, is commonly avoidable, and does not impair the net benefit of BPD.

Acknowledgment. We thank Elizabeth Martinson, PhD, from the KHFI Editorial Office for her editorial assistance.

Affiliations and Disclosures

From the ¹Kerckhoff Heart Center, Department of Cardiology, Bad Nauheim, Germany and DZHK (German Center for Cardiovascular Research), partner site Rhein-Main, Frankfurt am Main, Germany; ²Kerckhoff Heart Center, Department of Cardiac Surgery, Bad Nauheim, Germany, DZHK (German Center for Cardiovascular Research), partner site Rhein-Main, Frankfurt am Main, Germany; ³Justus-Liebig University of Giessen and Marburg, Department of Cardiology, Giessen, Germany; and ⁴St Johannes Hospital, Department of Cardiology, Dortmund, Germany; ⁵Johann-Wolfgang-Goethe University, Department of Cardiac Surgery, Frankfurt, Germany.

Disclosure: The authors have completed and returned the ICMJE Form for Disclosure of Potential Conflicts of Interest. Dr Kim has received proctor/speaker honoraria from Abbott, Boston Scientific, Edwards Lifesciences, and Medtronic. Dr Möllmann has received proctor/speaker honoraria from Abbott, Boston Scientific, Biotronik, and Edwards Lifesciences. Dr Nef has received proctor/speaker honoraria from Boston Scientific. Dr Hamm has served on the advisory board for Medtronic. Dr Choi has served on the advisory board for Edwards LifeSciences; has received proctor/speaker honoraria from Cytosorbents, CryoLife, and Getinge. The remaining authors report no conflicts of interest regarding the content herein.

Manuscript accepted September 1, 2021.

The authors report that patient consent was provided for publication of the images used herein.

Address for correspondence: Christian W. Hamm, MD, PhD, Kerckhoff Heart Center, Department of Cardiology, 61231 Bad Nauheim, Germany. Email: c.hamm@kerckhoff-klinik.de

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