Journal of the American College of Cardiology
Underexpansion and Ad Hoc Post-Dilation in Selected Patients Undergoing Balloon-Expandable Transcatheter Aortic Valve Replacement
Author + information
- Marco Barbanti, MD∗,
- Jonathon Leipsic, MD∗,
- Ronald Binder, MD∗,
- Danny Dvir, MD∗,
- John Tan, MD∗,
- Melanie Freeman, MBBS∗,
- Bjarne Norgaard, MD†,
- Nicolaj Hansson, MD†,
- Anson Cheung, MD∗,
- Jian Ye, MD∗,
- Tae-Hyun Yang, MD∗,
- Kasia Maryniak, MD∗,
- Rekha Raju, MD∗,
- Angus Thompson, MBBS, PhD∗,
- Philipp Blanke, MD∗,
- Sandra Lauck, PhD, RN∗,
- David Wood, MD∗ and
- John Webb, MD∗∗ (webb{at}providencehealth.bc.ca)
- ∗St. Paul's Hospital, University of British Columbia, Vancouver, British Columbia, Canada
- †Aarhus University Hospital, Aarhus, Denmark
- ↵∗Reprint requests and correspondence:
Dr. John Webb, St. Paul's Hospital, 1081 Burrard Street, Vancouver, British Columbia V6Z 1Y6, Canada.
Abstract
Objectives This study sought to assess the clinical outcomes and hemodynamic performance associated with a strategy of underexpanding balloon-expandable transcatheter heart valves (THV) when excessive oversizing is a concern.
Background Transcatheter aortic valve replacement depends on the selection of an optimally sized THV. An undersized THV may lead to paravalvular regurgitation, whereas excessive oversizing may lead to annular injury.
Methods Patients (n = 47) who underwent transcatheter aortic valve replacement with an intentionally underexpanded THV (balloon-filling volume reduced ∼10%) were compared with consecutive control patients who had nominal THV balloon deployment (n = 87). Pre- and post-procedural computed tomography imaging and echocardiography were performed to assess THV stent expansion and hemodynamics.
Results Underfilling resulted in THV underexpansion that was maximal at the THV inflow (85.0 ± 7.4% vs. 102.5 ± 6.2%, p < 0.001), in study versus control groups, respectively. The study group received larger THV, although annular injury was not observed. Post-dilation was required in 10.6% and 4.6% of patients of the study and control groups, respectively (p = 0.165). Echocardiographic THV area, gradient, paravalvular regurgitation, and in-hospital outcomes were similar.
Conclusions Intentionally underexpanding balloon-expandable THV by underfilling the deployment balloon did not adversely affect procedural clinical outcomes, THV gradients, or THV areas. A strategy of underexpansion, with post-dilation as necessary, might play in role in reducing the risk of annular injury and paravalvular regurgitation in selected patients.
Transcatheter aortic valve replacement (TAVR) requires an optimally sized transcatheter heart valve (THV). Undersizing may result in paravalvular regurgitation (PVR) or device migration, whereas excessive oversizing may result in atrioventricular block, coronary obstruction, peri-aortic hematoma, mitral valve injury, septal rupture, or root rupture (1,2).
Computed tomography (CT) imaging can help optimize balloon-expandable THV size selection and reduce PVR (1,3). However, balloon-expandable valves are currently only available in a limited number of sizes. Patients with “borderline” annular dimensions, where the annular dimensions support transitioning from a smaller to a larger valve, represent a particular challenge. For example, when transitioning from a 23-mm to a 26-mm THV, the implant diameter increases by 3 mm or 13%, perimeter by 9.42 mm or 13%, and cross-sectional area by 1.15 cm2 or 28%.
Routine balloon-expandable deployment results in THV inflow diameters slightly below the stated nominal THV diameter (1,3). In vitro analysis shows that reducing balloon-fill volumes by ∼10% results in only minor hemodynamic functional changes. We hypothesized that using a strategy of underexpansion with ad hoc post-dilation as necessary when selecting a THV that would result in annular area oversizing >20% (or >10% with adverse root features) might reduce the risk of annular injury without increasing the rate of significant PVR.
Methods
Forty-seven consecutive patients with severe aortic stenosis who underwent TAVR with an intentionally underexpanded Sapien type THV (Edwards Lifesciences Inc., Irvine, California) at St. Paul's Hospital, Vancouver, Canada, and Aarhus University Hospital, Aarhus, Denmark, were included in this prospective study. For comparison, a historical cohort of 87 consecutive patients who had undergone balloon-expandable TAVR with nominally filled deployment balloons at St. Paul's Hospital (control group) was identified. All patients underwent pre- and post-procedure CT and echocardiographic imaging (Online Appendix).
The manufacturer's recommended nominal filling volume of the deployment balloons for the 20-, 23-, 26-, and 29-mm Sapien XT were 11, 17, 22, and 33 ml for the NovaFlex delivery system (Edwards Lifesciences) and (no Ascendra 20-mm system is available), 16, 20, and 30 ml for the Ascendra delivery system (Edwards Lifesciences). Our strategy was to underexpand THV when transitioning from a smaller to a larger implant by underfilling the deployment balloon ∼10%. Consequently, at the discretion of the operator, 20-, 23-, 26-, and 29-mm balloons were underfilled up to 1, 2, 3, and 4 ml, respectively (Fig. 1).
THV Balloon Volumes
Percentages of volume reduction across the different transcatheter heart valves (THV) and delivery systems according to the degree of underfilling. *Not recommended.
The study cohort then was divided in 3 subgroups (Groups A, B, and C) according to the percentage of volume reduction from the THV balloon (Fig. 1). Criteria for intentional balloon underfilling were >20% area oversizing as determined from pre-procedural CT or >10% area oversizing with adverse root features (left ventricular outflow tract calcification, shallow sinuses of Valsalva, extreme age, previous chest irradiation, female sex, relatively small body size).
Statistical analysis and definitions
Continuous variables are reported as mean ± SD and categorical variables as percentages. Continuous variables were tested for a normal distribution (QQ plot) and compared by the Student t test. For comparison of >2 continuous parametric variables, an analysis of variance was used. Categorical variables were compared by the Fisher exact or chi-square tests. Bonferroni adjustment was used when appropriate. All tests were 2-tailed and a p value of <0.05 was considered significant. Analyses were performed using SPSS statistics software (SPSS Inc., Chicago, Illinois). Outcomes are reported according to Valve Academic Research Consoritum-2 criteria (4).
Results
Clinical, echocardiographic, and CT characteristics are summarized in Table 1. Pre-operative variables were similar, although patients in the study group had a lower Society of Thoracic Surgeons) score (5.4 ± 2.6% vs. 7.0 ± 4.3%, p = 0.025). Aortic annulus CT measurements did not differ.
Baseline Clinical, Echocardiographic, and CT Characteristics
Procedural and echo outcomes
Procedural variables are listed in Table 2. In the study group, the THV balloon was underfilled by 1, 2, 3, and 4 ml in 8 (17.0%), 26 (55.3%), 11 (23.4%), and 2 (4.3%) patients, respectively. A strategy of intentional underfilling was adopted due to >20% area oversizing in 16 patients (34.0%) and due to >10% oversizing in association with adverse aortic root features in 31 patients (66.0%); 28 patients had extensive left ventricular outflow tract calcification; 7 had shallow sinuses of Valsalva; 4 had both; and 3 had small body size in relation to the nominal stent cross sectional area. The study group received larger THV; fewer 23-mm THV (14.9% vs. 24.6%, p = 0.005) and more 29-mm THV (38.3% vs. 8.0%, p < 0.001). THV embolization, multiple valve implantation, and annular injury did not occur.
Procedural Variables
Post-dilation was performed in 10.6% and 4.6% of patients of the study and control groups, respectively (p = 0.165). Among the study group, post-dilation was performed with nominal filling of the original balloon in 3 cases (in all these cases, the predicted area oversizing was ∼10%). In the remaining 2 cases, the Sapien XT 29-mm THV balloon was underfilled by 4 ml and 3 ml, respectively, and subsequently post-dilated underfilled by 2 ml, in both cases, in the presence of a tubular aortic root and predicted area oversizing >20% and severe annular calcification, respectively. In all cases, moderate paravalvular leaks were reduced to mild.
Echocardiographic THV area was 1.61 ± 0.37 cm2 versus 1.66 ± 0.41 cm2 (p = 0.463) and mean THV gradient was 11.4 ± 4 mm Hg versus 10.6 ± 3.9 mm Hg (p = 0.261) in the study and control groups, respectively. PVR was more than mild in 1 patient (2.1%) in the study group and 6 patients (6.9%) in the control group (p = 0.225). In-hospital complication rates are reported in Table 3.
Clinical In-Hospital Outcomes
CT outcomes
THV expansion at the inflow was 85.0 ± 7.4% versus 102.5 ± 6.2% (p < 0.001), at the mid-portion, 88.0 ± 7.0% versus 102.4 ± 6.3% (p < 0.001), and at the outflow, 91.5 ± 6.9% versus 102.8 ± 6.0% (p < 0.001) in study versus control groups, respectively (Fig. 2, Table 4). THV eccentricity at the inflow was 3.6 ± 3.5 versus 2.5 ± 2.4 (p = 0.039), at the mid-portion, 4.0 ± 4.2 versus 2.7 ± 2.7 (p = 0.027), and at the outflow, 2.8 ± 3.5 versus 2.7 ± 2.7 (p = 0.759) in study versus control groups, respectively. An underexpansion strategy was associated with a lower frequency of excess oversizing (Figs. 3 and 4).
THV Frame Expansion
The ratio of actual transcatheter heart valve (THV) stent area measured with computed tomography to nominal THV area according to THV size in the control group and in the study group according to the percentage of volume reduction. UF = underfilling.
Predicted and Actual Annular Area Oversizing
Rate of predicted computed tomography–based >20% annular area oversizing and actual oversizing >20% in patients with normal and underfilled transcatheter heart valve balloons.
Predicted Reduction in Area Oversizing
Actual annular area oversizing with balloon underfilling (UF) as compared to predicted with nominal balloon filling.
Ratio of Actual THV Stent Area Measured With CT to Nominal THV Area According to THV Size and Degree of Underfilling
Discussion
In the context of TAVR, aortic annular dimensions are established on the basis of noninvasive imaging. Modest CT annular area oversizing facilitates minimal PVR with a low risk of annular injury (1,3). However, prosthesis area oversizing >20% is associated with a higher risk of aortic root rupture; a risk that may be amplified by various factors, particularly subannular calcification (2).
THV function
Echocardiographic transvalvular gradients, effective orifice areas, the absence of valvular regurgitation, and procedural success were comparable in both groups. Post-dilation due to PVR was more frequent in the underfilled group than in the control group. PVR that was more than mild was less frequent in the study group, although this was not statistically significant. Importantly, an oversized, but underexpanded, THV may allow for greater flexibility in terms of post-dilation than an undersized but fully expanded THV would.
Post-TAVR CT analysis
Nominally filled deployment balloons resulted in a prosthesis cross-sectional CT area that correlated well with the nominal THV area indicated by the manufacturer. Underfilling by 3% to 6% resulted in a 15.4% reduction in actual THV area; underfilling by 9% to 10% resulted in an 18.4% reduction; and underfilling by 11% to 15% resulted in a 20% reduction. Underfilling resulted in underexpansion that was most marked in the inflow segment, likely due to the constraint of the annulus.
Study limitations
In vitro studies have demonstrated that marked underexpansion of valve stent frames can result in frame eccentricity, suboptimal leaflet coaptation, and contact between the leaflets and the frame, potentially reducing leaflet durability. Consequently, routine underexpansion cannot be advocated in patients for whom specific concerns do not exist and long-term durability is important. Among the study group, we included 3 patients who received an underexpanded Sapien 3 THV.
Conclusions
Intentionally underexpanding balloon-expandable THV by modestly underfilling the deployment balloon led to predictable reduction of THV expansion. This did not adversely affect short-term clinical or echocardiographic outcomes. A strategy of underexpansion with post-dilation as necessary may offer the opportunity for a more individualized approach to TAVR allowing for the reduction of the risk of both annular injury and paravalvular regurgitation in patients with borderline annular geometry. The impact of underexpansion on durability and late outcomes remains to be determined.
Appendix
Appendix
For supplemental computed tomography and echocardiographic methods, please see the online version of this article.
Footnotes
Drs. Leipsic, Binder, Cheung, Ye, Wood, and Webb have received consulting fees from Edwards Lifesciences. Dr. Norgaard has received a research grant from Edwards Lifesciences. Dr. Hansson has received grant support from Edwards Lifesciences. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose.
- Abbreviations and Acronyms
- CT
- computed tomography
- PVR
- paravalvular regurgitation
- TAVR
- transcatheter aortic valve replacement
- THV
- transcatheter heart valve
- Received July 2, 2013.
- Revision received October 4, 2013.
- Accepted October 8, 2013.
- American College of Cardiology Foundation
