Can Balloon Aortic Valvuloplasty Help Determine Appropriate Transcatheter Aortic Valve Size?
Vasilis C. Babaliaros, MD*,*,
David Liff, MD*,
Edward P. Chen, MD*,
Jason H. Rogers, MD ,
Ryan A. Brown, MD,
Vinod H. Thourani, MD*,
Robert A. Guyton, MD*,
Stamatios Lerakis, MD, FACC*,
Arthur E. Stillman, MD, PhD*,
Paolo Raggi, MD, FACC*,
Jennifer E. Cheesborough, BS*,
Emir Veladar, PhD*,
Jacob T. Green, MD*,
Peter C. Block, MD, FACC*
* Andreas Gruentzig Cardiovascular Center, Emory University Hospital, Atlanta, Georgia
University of California, Davis Medical Center, Sacramento, California
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Abstract
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Objectives: We sought to study the potential role of balloon aortic valvuloplasty (BAV) in sizing the aortic annulus in patients before transcatheter heart valve (THV) implantation.
Background: Despite clinicians' growing experience with THV procedures, the best method of annulus sizing remains unclear.
Methods: Twenty-three patients with aortic stenosis (<1.0 cm2) who were undergoing surgical valve replacement were enrolled. Pre-operative echocardiographic measurements of the annulus and computed tomography measurements of valve calcium were made. Intraoperatively, a valvuloplasty balloon of known size and inflatable pressure was inserted into the aortic valve and inflated. The development of intraballoon pressure in addition to the nominal inflation pressure (AIBP) reflected the apposition of balloon and valve. Surgical annulus was measured by cylindrical sizers.
Results: In patients with tricuspid valves, AIBP was generated in 11 of 12 patients when the balloon diameter was greater than the surgically measured annulus, regardless of leaflet calcification (2 of 10 patients when balloon  surgical annulus). In bicuspid valves, high AIBP ( 1 atm) was encountered with balloons that were within 1 mm of annulus size, and leaflet dehiscence occurred with larger balloons (n = 2 patients). Annulus size was underestimated by transthoracic echocardiogram and transesophageal echocardiogram compared with surgery (p < 0.001): transthoracic echocardiogram = 21.5 ± 1.8 mm, transesophageal echocardiogram = 22.0 ± 1.6 mm and surgical = 23.2 ± 1.9 mm (range 20 to 27 mm, mode 22 mm).
Conclusions: These data suggest that measuring AIBP during balloon aortic valvuloplasty in tricuspid valves is an important adjunctive measurement of the aortic annulus and may help in determining the appropriate THV size.
Key Words: percutaneous • transcatheter • aortic valve • aortic stenosis • balloon aortic valvuloplasty
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Abbreviations and Acronyms
| | AIBP = additional intraballoon pressure | | BAV = balloon aortic valvuloplasty | | CT = computed tomography | | TEE = transesophageal echocardiogram | | THV = transcatheter heart valve | | TTE = transthoracic echocardiogram |
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Transcatheter heart valve (THV) replacement is an emerging technology used to treat high-risk patients with aortic stenosis. It is conceptually different than surgical aortic valve replacement in that the native valve is not excised but instead serves as the anchor for implanted devices. In addition, an exact method for determining correct THV size is challenging because of the clinician's inability to visualize the valve directly or use valve sizers. Consequently, adverse events related to undersizing and oversizing have occurred: para-valvular leak (1–3), valve embolization (1–6), coronary obstruction (5,6), and injury to the aorta.
In this pilot study, we report a unique method of sizing the aortic annulus by using balloon aortic valvuloplasty (BAV). To verify the accuracy of our method, we performed balloon sizing of the annulus during surgical valve replacement and compared these results with the surgically measured annulus. We also assessed the role of leaflet calcification and compared echocardiographic measurements of the annulus with those measured at surgery. These data may have implications for valve sizing before THV implantation.
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Methods
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Twenty-three patients that gave informed and signed consent were recruited from Emory University Hospital (Atlanta, Georgia), Emory-Crawford Long Hospital (Atlanta, Georgia) (n = 21), and University of California, Davis (Sacramento, California) (n = 2) from September 2006 to August 2007. Patients who were referred for elective, surgical aortic valve replacement to treat severe and symptomatic stenosis (valve area <1.0 cm2) of the native aortic valve were eligible to participate. The study was approved and performed in accordance with the regulations of the hospital institutional ethic committees (Emory University and University of California Davis).
Echocardiographic measurements.
Pre-operative transthoracic echocardiograms (TTEs) and intraoperative transesophageal echocardiograms (TEEs) were read by an experienced echocardiographer. The aortic annulus (internal distance between the lowest insertion of the noncoronary and right coronary aortic cusp), sinus of Valsalva, and the sinotubular junction were measured in the 3-chamber, long-axis view (with TEE) and parasternal long-axis view (with TTE). Three measurements were made to confirm the annulus dimension. In cases of discordant measurement, the largest annular dimension was used.
Calcium measurements.
To assess whether the degree of valve calcification plays a role in balloon sizing, assessment of valve calcification was made by fluoroscopic (7) and noncontrast, gated, computed tomography (CT) imaging of the aorta before intraoperative BAV. Fluoroscopy was used for qualitative evaluation of valvular calcification (classified as mild, moderate, or severe) from the anteroposterior, left anterior, and right anterior oblique projections. Calcium confined to leaflet tips was defined as mild, calcium extending from the leaflet tips to the leaflet bases was considered moderate, and bulky calcification that extended from tip to base in all 3 leaflets was considered severe.
Computed tomography imaging of the aortic valve was performed with 1 of 2 64-slice multidetector CT scanners (Lightspeed VCT, GE, Milwaukee, Wisconsin, or Definition, Siemens, Malvern, New Jersey). Calcium scoring was limited to the aortic valve leaflets from the sinotubular junction to the leaflet bases (coronary, mitral valvular, and annular calcification were excluded). Calcium scores were calculated according to the Agatston method and divided into 3 categories (mild, moderate, or severe) to approximate the classification of patients by fluoroscopy.
Balloon aortic valvuloplasty.
Intraoperative BAV was performed from the anterolateral aortotomy in the ascending aorta, after establishment of cardiopulmonary bypass and before resection of the native leaflets. Z-MED balloons (NuMED, Inc., Hopkinton, New York) were used and connected in parallel to a 30-ml inflation syringe and an indeflator device (Fig. 1A). The balloon size was selected so the diameter was within 2 mm of the annulus measured by TEE. Before intraoperative BAV, balloons were inflated with saline on a sterile table to a pressure of 2 atms measured by an indeflator. The volume injected and balloon diameters were recorded.
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Figure 1 Intraoperative Balloon Aortic Valvuloplasty: Schema of Set-Up and Forces Exerted
(A) Balloon catheter is attached to inflation syringe (Sy) and indeflator (In) in parallel via a 4-way stop cock to measure pressure in the balloon during inflation. (B) At maximal inflation, radial force (quantified by AIBP) is exerted by the native valve on the balloon (arrows) and by the balloon on the valve. AIBP = intra-balloon pressure in addition to the nominal inflation pressure of 2 atms.
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After exposure of the native valve, the deflated balloon was inserted directly into the valve orifice and inflated with the same volume of saline used during preparation on the sterile table. At full inflation, the intraballoon pressure was measured by the indeflator and the additional intraballoon pressure (AIBP) was calculated by subtracting the nominal inflation pressure of 2 atms. We postulated that the presence of AIBP would indicate the native aortic valve was exerting radial force on the balloon (Fig. 1B) and thus result in a snug fit of the balloon within the valve. The lack of AIBP would indicate the balloon was too small for the valve.
Two inflations were performed to verify the intraballoon pressure. Visual inspection by the primary surgeon confirmed full expansion of the balloon and whether there was complete apposition of the balloon within the native valve. After BAV, the balloon was removed, reinflated with the same volume on a sterile table, and remeasured. The larger diameter was used for discrepancies between the measurements taken before and after the procedure.
Other measurements.
After intraoperative BAV, the valve and aorta were examined carefully for signs of trauma. Subsequently, the valve leaflets were excised, weighed and photographed. Surgical aortic annulus size was measured to the nearest millimeter by the surgeon using a stentless valve sizer.
Statistical analysis.
Differences in leaflet weights were evaluated in mild, moderate, and severe calcified valves with the use of a 1-way analysis of variance. Comparison of annulus size by echocardiographic variables with surgical findings was performed using a corresponding t test. Additionally, a Bland-Altman analysis was used to assess the level of agreement between measurement of the annulus at surgery and by echocardiography. Also, a 1-way repeated-measures analysis of variance with Dunnett test was performed and annulus means were calculated with a Bonferroni adjustment. An analysis of covariance was done to evaluate the differences in the slope of balloon diameter—surgical annulus against AIBP for different levels of calcification. A Pearson correlation coefficient was performed to check the relation of body surface area, height, sinotubular dimension, and sinus of Valsalva dimension with surgical annulus measurements. Differences were considered statistically significant at p <0.05. All values were expressed as mean ± SD.
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Results
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Patient characteristics.
Patient (n = 23) characteristics are listed in Table 1. The majority were elderly (age >70 years), with tricuspid aortic valve degeneration, and isolated surgical aortic valve replacement. One-third of patients had renal failure, although only 1 patient was receiving hemodialysis pre-operatively. Overall comorbidity is reflected by the surgical risk scores (8–10).
Evaluation of aortic valve calcium.
Fluoroscopic evaluation (n = 23) showed that 6 patients had mild (26%), 12 moderate (52%), and 5 had severe (22%) valvular calcification. In accordance with the fluoroscopic assessment, the corresponding valvular calcium score on CT was <1,500 AU for mild, 1,500 to 5,000 AU for moderate, and >5,000 AU for severely calcified valves. Calcium score and corresponding leaflet weights of the aortic valve are shown in Table 2. The majority of patients had moderate aortic valve calcification; bicuspid valve calcification was not significantly different than tricuspid valves (Agatston calcium scores 4,943 ± 4,772 vs. 2,940 ± 2,074, p = NS). There was a trend toward a difference in leaflet weight among the 3 groups of patients by calcium scores: mild versus moderate, p = 0.09; moderate versus severe, p = 0.05. A significant difference in leaflet weight was observed between patients with mild and severe calcium score: mild versus severe, p = 0.04.
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Table 2 Categorization of Calcium Scores (Computed Tomography) of the Stenotic Aortic Valve With Corresponding Leaflet Weights
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Evaluation of aortic valve annulus.
In 23 patients, the aortic annulus was measured intraoperatively with the use of surgical sizers (Table 3, Fig. 2
). Annulus size ranged from 20 to 27 mm diameter; the most common size was 22 mm. On average, the TTE results underestimated the surgical annulus by 1.7 mm (p < 0.001, adjusted p value with Bonferroni correction = 0.01), and the TEE results underestimated the surgical annulus by 1.2 mm (p < 0.001, adjusted p value with Bonferroni correction = 0.08). The surgical annulus measurement did not correlate with the body surface area (BSA) (r = 0.27, p = 0.1) but did correlate with height (all valves: r = 0.48, p = 0.01; tricuspid aortic valves: r = 0.60 and p < 0.01). The surgical annulus measurement correlated with sinotubular (r = 0.49, p < 0.01) and sinus of Valsalva (r = 0.7, p < 0.001) TEE measurements. In 7 patients, the TEE annulus was  2 mm smaller than the surgical annulus measurement; in 11 patients, the TTE annulus was 2 mm smaller than the surgical annulus. The degree of calcification and bicuspid morphology did not impact the accuracy of the measurement by TTE or TEE.
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Table 3 Aortic Annulus Size measured by Transthoracic, Transesophageal Echocardiography, and Surgical Sizing Cylinders
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Figure 2 Bland-Altman Plot of Annulus Measurement at Surgery and by Echocardiography
(A) Bland-Altman plot comparing annulus measurement at surgery with TTE. (B) Bland-Altman plot comparing annulus measurement at surgery with TEE. TEE = transesophageal echocardiogram; TTE = transthoracic echocardiogram. Filled diamonds = difference; black lines = mean difference; blue lines = mean difference ± SD.
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Intraoperative BAV.
Intraoperative BAV was performed with balloons ranging from 18 to 29 mm in diameter. Seven patients had inflations performed with 2 balloons of increasing sizes. When inflation of the balloon generated AIBP, direct visualization confirmed balloon–valve apposition and a snug fit in all cases; similarly, lack of AIBP reflected incomplete apposition of the balloon and valve. To determine the role of the annulus dimension on balloon–valve apposition, the balloon and aortic annulus size were plotted against the AIBP during BAV. In patients with tricuspid aortic valves (Fig. 3A), AIBP was generated in 11 of 12 patients when the balloon diameter was larger than the surgical annulus, regardless of the extent of leaflet calcification. When the balloon diameter was equal to or less than the surgically measured annulus, AIBP was generated in only 2 of 10 patients.
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Figure 3 Effect of Balloon Oversizing the Annulus in Tricuspid Aortic Valves
(A) Comparison of difference between balloon diameter and surgically measured annulus versus additional intraballoon pressure (AIBP) in mild (blue diamonds), moderate (red squares), and severely (yellow triangles) calcified tricuspid aortic valves (B) Comparison of difference between balloon diameter and transesophageal echocardiogram (TEE)-measured annulus versus AIBP in mild, moderate, and severely calcified tricuspid aortic valves.
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Currently, when THV implantation is performed, THV size is selected to be >2 mm larger than the annulus measured by TEE (3,4,6). To test the accuracy of this strategy, we reanalyzed our data in relation to TEE annulus measurements in the same patients (Fig. 3B). When the balloon diameter was greater than the TEE annulus + 2 mm, AIBP was generated in 8 of 9 patients. When the balloon diameter was smaller than TEE annulus + 2 mm, 5 of 13 valves generated AIBP.
In patients with bicuspid valves, the generation of AIBP with balloons that were larger than the surgically measured annulus was noted in 4 of 4 patients (Fig. 4A). But in addition, AIBP was generated in 2 of 7 patients with balloons equal to or less than the surgically measured annulus. High AIBP (1 atm) was generated with balloons that were within 1 mm of the surgical annulus. In 2 patients in whom larger balloon sizes were used (>3 mm above the surgically measured annulus), partial leaflet avulsion occurred, and initial high AIBP decreased to 0.4 and 0.5 atm (Fig. 4A). The data for bicuspid valve sizing guided by the TEE annulus are shown in Figure 4B: 3 of 3 patients developed AIBP when the balloon size was greater than the TEE annulus + 2 mm versus 3 of 7 patients when dilated with smaller balloons.
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Figure 4 Effect of Balloon Oversizing the Annulus in Bicuspid Aortic Valves
(A) Comparison of difference between balloon diameter and surgically measured annulus versus additional intraballoon pressure (AIBP) in mild (blue diamonds), moderate (red squares), and severely (yellow triangles) calcified bicuspid aortic valves. (B) Comparison of difference between balloon diameter and transesophageal echocardiogram (TEE)-measured annulus versus AIBP in mild, moderate, and severely calcified bicuspid aortic valves. *Leaflet avulsion.
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Discussion
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In current practice, TEE measurement of the aortic annulus is used for THV sizing (3–6,11). In our study, the TEE underestimated the surgical annulus size by >1 mm (p < 0.001), with differences up to 3 mm. We do not believe that these differences are caused by inaccurate measurement; rather, these differences probably occur because the aortic annulus is not circular but elliptical (12). Therefore, measurement of the annulus diameter in a single 2-dimensional view has limitations. We propose that in addition to ultrasound measurement, BAV can be used as a surrogate valve sizer, much as a surgeon measures the annulus directly. This strategy can be performed by connecting an indeflator and inflation syringe in parallel to the balloon catheter, as described in this study, or by using a large-volume indeflator for inflation.
The generation of AIBP occurs when the balloon oversizes the surgical annulus (>2 mm than TEE annulus). The native leaflets in a tricuspid valve provide little resistance because they are displaced to the open position during balloon inflation. From our data, the smallest balloon diameter that produces AIBP is equivalent to the surgically measured annulus. Thus, if BAV is used in THV size selection, the THV size must be larger than this minimal balloon diameter.
Balloon sizing of the aortic annulus does not appear to be helpful in bicuspid valves. In our experiments, balloons smaller than the surgically measured annulus produced AIBP; thus, the leaflets, rather than the annulus, must have resisted balloon inflation. This observation is not surprising because the bicuspid aortic valve, by its geometry, will not conform to a circular shape (13–15). In 2 patients with bicuspid valves, the leaflets were partially torn from the annulus, and AIBP was then generated by apposition of balloon and annulus. Because of the unpredictable nature of the bicuspid valve during BAV (13,14,16–20), such valves have been excluded from THV protocols. Additional research is needed before THV implantation can be extended to patients with echocardiographic evidence of a bicuspid valve.
Study limitations.
This protocol was a pilot study, and the number of patients was small. The most important limitation in this study was that a THV was not deployed into the native valve after measurement of AIBP. Although balloon sizing may be appropriate to determine the minimal THV size to generate radial anchoring force, the optimal size to prevent embolization and paravalvular leak based on the AIBP produced during BAV will require more study.
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Conclusions
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Exact annular measurements are critical for selection of appropriate THV sizes and successful anchoring. The use of TEE often causes one to underestimate the dimensions of the aortic annulus measured at surgery, which emphasizes the need for an adjunctive measuring technique. We conclude that BAV can be used to help size the annulus in patients with tricuspid aortic valves. We are currently using this strategy in patients before THV implantation. In one of our first patients, the TEE annulus measured 22 mm, AIBP was 0.5 atm with the use of a 23-mm balloon valvuloplasty catheter, and a 26-mm balloon-expandable THV was implanted with no paravalvular leak. More patients are needed to validate these findings with balloon and nonballoon-expandable THV devices. Additionally, patients with bicuspid aortic valves will require more study to understand adjunctive methods for measuring the annulus and the role the leaflets and annulus play in BAV and THV implantation.
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Footnotes
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Dr. Babaliaros is a consultant for Medtronic. Dr. Chen is a consultant for Medtronic and St. Jude Medical. Dr. Rogers is a consultant for Boston Scientific, Medtronic, and Ample Medical. Dr. Block is an E-Valve consultant and stock holder, Direct Flow stock holder, Medtronic consultant, and Ample Medical consultant. NuMED (Hopkinton, New York) contributed Z-MED balloons to support this research.
* Reprint requests and correspondence: Dr. Vasilis C. Babaliaros, Department of Cardiology, Emory University Hospital, 1364 Clifton Road, Suite F606, Atlanta, Georgia 30322 (Email: Vasilis.babaliaros{at}emoryhealthcare.org).
Manuscript received November 3, 2007;
revised manuscript received June 3, 2008,
accepted June 27, 2008.
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Abstract
Methods