Transcatheter aortic valve implantation (TAVI) currently

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1 Preoperative Assessment of Aortic Annulus Dimensions: Comparison of Noninvasive and Intraoperative Measurement Alexey Dashkevich, MD,* Philipp Blanke, MD,* Matthias Siepe, MD, PhD, Gregor Pache, MD, Mathias Langer, MD, Christian Schlensak, MD, PhD, and Friedhelm Beyersdorf, MD, PhD Departments of Cardiovascular Surgery and Diagnostic Radiology, University Medical Centre Freiburg, Freiburg, Germany ADULT CARDIAC Background. Preoperative assessment of aortic annulus diameter is crucial for valve sizing in patients scheduled for transcatheter aortic valve replacement. Computed tomographic (CT) measurements of the aortic annulus are not standardized and may yield different results depending on view due to its elliptic shape. The purpose of this study was to compare the measurement of the aortic annulus during surgery in patients undergoing conventional aortic valve replacement with noninvasive methods. Methods. In 33 patients with aortic valve stenosis (18 males, mean age ), aortic annulus diameter was measured with cardiac CT and TEE (transesophageal echocardiography) prior to open aortic valve replacement. In CT, aortic annulus diameter was assessed as the calculated average diameter of luminal area at the level of basal attachments of the leaflets by means of planimetry. Operative measurements were performed with a Hegar dilator. A Pearson analysis was applied to test for degree of correlation. Results. Calculated average diameter by CT correlated significantly with intraoperative measurements (r 0.923, p < 0.001) and with the size of implanted valve (r 0.867, p < 0.001), while correlation of TEE and intraoperative measurements was weak (r 0.523, p 0.002). The TEE tends to underestimate the dimensions of aortic annulus. Conclusions. The CT-measured aortic annulus diameter, assessed as the calculated average diameter of planimetric annulus area, seems to provide adequate dimensions similar to operative measurements with a Hegar dilator. This approach may minimize the dependency of single-view CT measurement on the elliptic shape of the aortic annulus and appears to be a feasible alternative for aortic annulus assessment in terms of candidates selection for transcatheter aortic valve replacement. (Ann Thorac Surg 2011;91:709 15) 2011 by The Society of Thoracic Surgeons Transcatheter aortic valve implantation (TAVI) currently represents a feasible alternative to conventional aortic heart surgery in very high-risk patients with severe symptomatic aortic stenosis. Precise preoperative assessment of the aortic annulus diameter is crucial for optimal valve sizing in patients scheduled for transcatheter aortic valve replacement (TAVR) and determines the procedure outcome. Different methods of preoperative annulus measurements have been used over time: transesophageal echocardiography (TEE), calibrated aortic angiography, and recently, also multislice computed tomography (MSCT) [1, 2]. In clinical practice, TEE measurements in terms of preoperative screening for TAVI have become widely expanded and are reported to be the most reliable tool to measure the diameter of the aortic root [3]. In TEE, the diameter of the aortic annulus, including all cusp calcifications, is measured on the midesophageal long-axis view of the ascending aorta and Accepted for publication Sept 17, *Both authors contributed equally to this work. Address correspondence to Dr Dashkevich, Department of Cardiovascular Surgery, University Medical Centre Freiburg, Hugstetter Str 55, Freiburg, Germany; alexey.dashkevich@uniklinik-freiburg.de. aortic valve at end-systole, according to guidelines from the American Society of Echocardiography [4, 5]. Although MSCT is able to provide detailed information about the shape of the aortic annulus and its surrounding structures [6], the use of this method in preoperative annulus sizing in TAVR patients is not standardized and is therefore not routine. Both TEE and MSCT may yield different results, depending on the view due to the elliptic shape of the aortic annulus [7], which should be regarded as a serious limitation. We have found no available studies at the moment that could provide evidence as to which of the clinically applied methods of aortic annulus measurement better refer to true annulus dimensions. Therefore, it was the purpose of this study to compare the intraoperative measurement of the aortic annulus during surgery in patients undergoing conventional aortic valve replacement with noninvasive methods by means of TEE and MSCT. Patients and Methods All procedures of this study were approved by the Ethics Committee of Freiburg University Medical Centre and followed the Declaration of Helsinki guidelines. The 2011 by The Society of Thoracic Surgeons /$36.00 Published by Elsevier Inc doi: /j.athoracsur

2 ADULT CARDIAC 710 DASHKEVICH ET AL Ann Thorac Surg PREOPERATIVE ASSESSMENT OF AORTIC ANNULUS 2011;91: need for individual patient consent was waived by the Institutional Review Board as the individual patient data remained not identified. Study Population The study population consisted of 33 patients (mean age , 18 male). The patients underwent conventional aortic valve replacement for severe aortic stenosis. The median European system for cardiac operative risk evaluation of the patients was and the ventricular ejection fraction was The noninvasive echocardiographic assessment of aortic valve stenosis presented the average valve opening area of cm 2. The mean transvalvular pressure gradient was mm Hg, as assessed invasively. According to the preoperative echocardiography, all patients had a tricuspid aortic valve. The following types of aortic valve prostheses were used: Carpentier-Edwards Perimount Magna (23 patients; Edwards Lifesciences, Irvine, CA), ATS Medical (7 patients; ATS Medical, Minneapolis, MN), and allograft valves (3 patients). The manufacturer s labeled valve size was used for analysis; the respective diameters of the implanted valves for each patient are listed in Table 1. All patients underwent preoperative electrocardiographic-gated dual source computed tomography (CT) of the chest and TEE as part of their preoperative assessment. In addition, patients underwent an intraoperative measurement of the aortic annulus diameter with the Hegar dilator. Computed Tomographic Protocol All CT examinations were performed using a dual source CT scanner (Somatom Definition, Siemens Medical Solutions, Forchheim, Germany). For contrast-enhanced data acquisition a bolus of 90 ml iodinated contrast agent (Imeron 350; Bracco Imaging, Konstanz, Germany) was injected at a flow rate of 4.5 ml/second through an 18-gauge needle in an antecubital vein, followed by a saline bolus chaser administered at a flow rate of 4 ml/second with a total volume of 50 ml. The scan was started with a delay of 6 seconds after the attenuation in the aortic root reached 120 Hounsfield units by means of bolus tracking. Scan parameters for cardiac CT were as follows: tube current time product, 350 mas/rotation; collimation, mm; slice acquisition, mm using the z-flying focal spot technique; pitch, 0.2 to 0.43 adapted to the heart rate; gantry rotation time, 330 ms; tube potential, 120 kv; scan direction, craniocaudal. Scan range extended from the carina to the diaphragm. The CARE Dose4D tube current modulation (Siemens Medical Solutions) and prospective electrocardiographictriggered tube current modulation [8] were employed for radiation dose reduction, the latter with a pulsing window between 30% and 80% of the RR cycle (interval between the R waves on ECG) and reduction of tube current to 20% of maximum outside the pulsing window. Given the clinical characteristics of the study population with severe symptomatic aortic stenosis, no additional beta blockade was administered to achieve slower heart rates. Computed tomographic data sets were reconstructed at 300 ms past the R-peak (end-systole) with a slice thickness of 0.6 mm and an increment of 0.4 mm using a medium soft tissue convolution kernel B20f. All data sets were transferred to a dedicated post-processing workstation equipped with Aquarius intuition (Terarecon Inc, San Mateo, CA). Preoperative Aortic Annulus Measurement by Dual Source Computed Tomography Two predefined approaches were undertaken for assessment of aortic annulus diameters. First, as reported by Tops and colleagues [6], coronal oblique and sagittal oblique views through the aortic valve were reconstructed (Fig 1A, B), the latter one with a similar orientation as the parasternal long-axis view on TTE and the midesophageal long-axis view on TEE. By reviewing the reconstructed double oblique transverse view at the level of the aortic valve (Fig 1C), the correct position of the intersection of both views in the center of the aortic valve, defined as the conjuncture of the three cusps, was ensured. Using the coronal and sagittal oblique views, the diameter of the aortic annulus was determined as the distance between the depicted hinge points of the aortic valve cusps ( hinge-to-hinge ; Fig 1D). Second, the dimensions of the aortic annulus were further assessed employing the concept of a virtual ring joining the basal attachments of all three aortic valve cusps, representing the inlet from the left ventricular Table 1. Summary of Intraoperative (Hegar) and Transesophageal Echocardiographic (TEE) and Computed Tomographic (CAAD) Measurements, Grouped by the Size of the Surgically Implanted Aortic Valve Prosthesis (Implanted Valve Size), Expressed as Mean Value Standard Deviation. There Was no Statistically Significant Difference in Annulus Dimension Between the Groups; Depicted p Values Are Bonferroni Corrected Implanted Valve Size (mm) Hegar (mm) CAAD (mm) TEE (mm) p Values Between Groups 19 (n 1) (n 15) (n 7) (n 6) (n 3) (n 1) All sizes (n 33)

3 Ann Thorac Surg DASHKEVICH ET AL 2011;91: PREOPERATIVE ASSESSMENT OF AORTIC ANNULUS 711 Fig 1. Hinge-to-hinge. Assessment of aortic root anatomy by reconstructing a coronal oblique view (A), a sagittal oblique view (B), and the resulting transverse image (C). Annulus dimensions were assessed using the coronal and sagittal oblique view as the distance between the depicted hinge points (D). (E) Illustrates annulus assessment by transesophageal echocardiography in the midesophageal long-axis view. ADULT CARDIAC outflow tract into the aortic root [9]. Using the coronal and sagittal oblique views, the corresponding double oblique transverse view was adjusted to transect through the basal attachments of all three cusps. In order to assess the cross-sectional area, the luminal contours were tracked on the double oblique transverse plane using automatic vessel analysis with manual correction (Fig 2C). The cross-sectional area was calculated and the maximal and minimal diameters, as displayed by the segmentation software were noted. Using the equation for the area of a disk ( r2), the average diameter of the encircled area was calculated (calculated average annulus diameter [CAAD]). Additionally, luminal diameters at the level of the virtual ring were assessed on the orthogonal coronal and sagittal oblique views (Fig 2A, B) as reported in recent literature [2, 10]. Echocardiography Multiplanar TEE was performed by an experienced cardiologist using a Philips E33 echocardiography system (Philips Healthcare, Best, Netherlands). Dimensions of the aortic annulus were assessed on the midesophageal long-axis view of the ascending aorta and aortic valve at end-systole, according to the American Society of Echocardiography guidelines [4, 5]. The aortic annulus diameter, defined as the distance between the depicted hinge points of the aortic valve leaflets, was assessed using the inner edge-to-inner edge technique (Fig 1E). Annulus calcifications were included into measurements. Intraoperative Measurements Aortic annulus size was assessed intraoperatively after resection of the aortic valve cusps and after decalcification of the aortic annulus and root in patients with aortic valve calcification and stenosis. A gauge (standard Hegar dilators, size 19 to 30 mm, unit 1 mm; Aesculap, Tuttlingen, Germany) was inserted into the annulus. Complete elastic fit of the possibly biggest dilator was defined as optimal. Statistical Analysis All continuous variables showed normal distribution as evaluated by the Kolmogorov-Smirnov tests and are reported as means 1 standard deviation. Pearson correlation analysis and Bland-Altman plots [11], with assessment of systematic bias and 95% confidence inter- Fig 2. Virtual ring and cross-sectional area assessment. In preoperative multislice computed tomography, the coronal and sagittal oblique (A) and (B), and double oblique transverse views (C) were oriented through the aortic root so that the most caudal attachment points of all three aortic cusps were depicted simultaneously on the double oblique transverse view. The contours of the cross-sectional area were tracked by means of planimetry at this very level (C). In addition, the diameters at this level were assessed on the coronal and sagittal oblique views using electronic calipers (A) and (B).

4 ADULT CARDIAC 712 DASHKEVICH ET AL Ann Thorac Surg PREOPERATIVE ASSESSMENT OF AORTIC ANNULUS 2011;91: vals (limits of agreement, calculated as mean difference 1.96 standard deviation of the difference), were used to assess agreement for anatomic measurements by the different measurement techniques. We performed an analysis of variance for repeated measurements and the F test. The Student t test with Bonferroni correction for multiple comparisons was used for post hoc comparisons. All statistical analyses were performed using SPSS software (SPSS 17.0; SPSS Inc, Chicago, IL). A p value less than 0.05 was considered statistically significant. Results Preoperative assessment of aortic annulus diameter by means of MSCT and TEE and intraoperative measurement with Hegar dilators were applied to all 33 patients undergoing conventional aortic valve replacement. Summaries of patient-based results for different annulus measurements are grouped by the size of the surgically implanted valve prosthesis and are listed in Table 1. Selected Bland-Altman plots are shown in Figure 3. The diameter of the aortic annulus by hinge-tohinge measurements in CT was mm on the coronal oblique view and mm on the sagittal oblique view. The CAAD at the level of the most basal attachment points of the aortic cusps (virtual ring), as assessed by means of planimetry was mm. Mean maximal and mean minimal diameters were mm and mm, respectively. At the level of the most basal attachment points of the aortic cusps, coronal and sagittal diameters were mm and mm, respectively. The mean difference between the coronal and the sagittal diameter at this level was mm, indicating an oval shape of the aortic annulus. The diameter of the aortic annulus assessed by TEE on the midesophageal long-axis view was mm and the intraoperatively assessed aortic annulus diameter by means of the Hegar dilator was mm. The comparison of the results of aortic annulus assessments by different methods (TEE, CT, and intraoperative assessment) did not demonstrate any significant difference between the groups; neither if grouped by the size of surgically implanted valve nor if compared en bloc (Table 1). According to Bland-Altman analysis, TEE tended to underestimate the aortic annulus diameter as assessed intraoperatively by Hegar dilator measurements with a mean difference of mm (limits of agreement 5.5 mm; 4.1 mm). No systematic difference was observed between CAAD assessment by MSCT and Hegar dilator measurements (mean difference mm), and limits of agreement were found to be tighter ( 1.6 mm; 2.4 mm). The mean difference between the CAAD and TEE measurements was mm (limits of agreement 3.9 mm; 6.0 mm). The CAAD and intraoperative Hegar dilator measurements showed a strong and significant correlation (r 0.923, p 0.001), whereas TEE and Hegar measurement only showed weak correlation (r 0.523, p 0.002); the related scatter plots with regression are demonstrated in Figure 4. Compared with CAAD, correlation was weaker for CT-based coronal and sagittal hinge-to-hinge measurements and intraoperative Hegar assessment (r and r 0.623, p 0.01, respectively). Similarly, single coronal and sagittal caliper measurements at the level of the basal attachment sites of all three aortic cups (virtual ring) showed a weaker correlation with intraoperative Hegar dilator measurements (r and r 0.802, p 0.01, respectively), when compared with CAAD. The correlation between CAAD and TEE measurements was weak (r 0.517, p 0.002). The CAAD and the size of the surgically implanted valve prosthesis showed a strong and significant correlation (r 0.867, p 0.001). Comment In the present study, the anatomy of the aortic root was assessed with MSCT, TEE, and intraoperative measurements in 33 patients with aortic valve stenosis, who underwent conventional surgery. The precise preoperative assessment of aortic annulus diameter [12] is crucial for optimal valve sizing in patients scheduled for transcatheter aortic valve replacement and is one of the determinates for the procedure outcome. At present, there is no gold standard for noninvasive assessment of aortic annulus dimensions. In clinical practice, echocardiography and angiography have been widely used in terms of annulus sizing before TAVI. The first clinical experience, based on valve sizing with TEE and angiography, delivered good results with low early Fig 3. Agreement of preoperative and intraoperative measurements. Bland Altman analysis comparing annular measurements using (A) transesophageal echocardiography (TEE) and intraoperative Hegar measurements, and (B) CAAD (calculated average annulus diameter) and intraoperative Hegar measurements. Thick solid line depicts the mean of difference of TEE or CAAD and intraoperative Hegar measurements; dotted lines depict the limits of agreement (mean difference 1.96 standard deviation of the difference).

5 Ann Thorac Surg DASHKEVICH ET AL 2011;91: PREOPERATIVE ASSESSMENT OF AORTIC ANNULUS 713 Fig 4. Preoperative and intraoperative assessment. Scatter plots with regression line (continuous line) and 95% confidence interval (dotted lines): (A) CAAD (calculated average annulus diameter in multislice computed tomography) and intraoperative Hegar dilator measurements showed a stronger correlation (r 0.923, p 0.001) than (B) transesophageal echocardiography (TEE) measurements and intraoperative Hegar dilator measurements (r 0.523; p 0.002). ADULT CARDIAC complication rates, whereas long-term results and late complications rates will have to be observed further [13]. However, the lack of congruence between prosthesis and annulus size is a strong determinant of paravalvular aortic regurgitation or valve migration, and one of its most likely causes is (besides incorrect positioning) the undersizing of the valve prosthesis [12, 14]. Therefore, optimal preoperative sizing seems to be prudent to avoid significant complications after the implantation. Computed tomography recently demonstrated that the aortic annulus is more oval than circular [6]. Furthermore, although commonly applied, the term aortic annulus is not used uniformly, mainly due to the complex anatomy of the semilunar hinges of the aortic leaflets, which tend to take the form of a three-pronged coronet rather than a circle and or a true ring [9]. The aortic annulus measurement by means of twodimensional (2D) methods (TEE, angiogram, single oblique view in CT) appears to be restricted to a single plane or a limited field of view. A single plane measurement of oval aortic annulus can lead to significant differences in assessment results while using these imaging modalities [2]. The approach of three-dimensional (3D) imaging, as known for CT, magnetic resonance imaging, or 3D echocardiography [15 18], allows complete morphologic analysis of aortic valve structures and seems to be preferable for preoperative valve sizing. Compared with 2D TEE, 3D TEE was demonstrated to achieve the best agreement with annulus measurement by means of MSCT [19]. In our study, we attempted to compare the results of the two modalities of aortic annulus measurement, TEE and CT, with true aortic annulus dimension, assessed intraoperatively. Similar study approaches have already been published in the past. Willmann and colleagues [20] demonstrated good agreement aortic annulus assessment in CT and measurement during aortic valve replacement. In their study only a plane view of aortic annulus in CT, formally equal to measurements with TEE, was compared to intraoperative data. In our study we did not limit CT measurements to a single plane. Instead, we applied several different measurements to the CT data sets, as published in recent literature [2, 6]. First, we used hinge-to-hinge measurements in the coronal and sagittal oblique views. Second, we adopted a virtual ring model, as described by Tops and colleagues [6], joining the basal attachments of all three aortic valve cusps, representing the inlet from the left ventricular outflow tract into the aortic root [9]. Within this model, we assessed the CAAD by means of planimetry, as well as the coronal, sagittal, minimal, and maximal diameters at this level. The CAAD was compared with TEE and intraoperative measurements as well as to the size of the surgically implanted valve. Among all measurement techniques, CAAD showed the strongest correlation with intraoperative Hegar dilator measurements. Furthermore, CAAD showed a strong correlation with the size of the surgically implanted aortic valve prosthesis. The correlation of TEE assessed diameter and intraoperative measurements was weaker. Moreover, TEE tended to underestimate aortic annulus dimensions when compared with intraoperative measurements. In contrast to 2D TEE and single caliper measurements in CT, the planimetry-based CAAD appears to allow for a more comprehensive assessment of the ovoid shape and minimizes the dependency of single-view measurement (TEE) on elliptic shape of the aortic annulus. We assume that CAAD seems to provide adequate dimensions of the aortic annulus, similar to operative measurements with the Hegar dilator, and appears to be more precise than TEE measurement. The strong correlation of CAAD with the size of the implanted valve prosthesis enhances the credibility of CT measurements. It is unclear whether the systematic, but small, difference between annulus measurements by means of TEE and CAAD in CT ( mm) may have any clinical relevance. The routinely practiced oversizing of the prosthesis by up to 20% [12] might probably make the small differences in measured aortic annular diameters using TEE or CT clinically negligible. Further studies will be needed to prove the clinical relevance of depicted differences between TEE and CT for the clinical outcome. Still, CAAD assessment by CT should be considered in preoperative valve sizing because of its good agreement with the true dimensions of the aortic annulus. This is supported by recent findings, that compared with 2D TEE and other CT-based measurement techniques, CAAD most strongly correlates with the area of the unfolded stent in patients with balloon-expandable TAVI [21]. Devices for TAVI are circular and not ovoid when viewed axially, and as recently demonstrated, the Edwards Sapien transapical valve prosthesis (Edwards Life-

6 ADULT CARDIAC 714 DASHKEVICH ET AL Ann Thorac Surg PREOPERATIVE ASSESSMENT OF AORTIC ANNULUS 2011;91: sciences Inc) expands to an almost circular shape in most patients [2]. Thus, it may be assumed that balloonexpandable TAVI alters the configuration of the native annulus, analogous to introducing the Hegar dilator into the ovoid annulus. Some limitations of the present study need to be addressed. The intraoperative measurements were done after decalcification of aortic valve and resection of the valve leaflets. The deviation from the noninvasive measurements with TEE and CT on the intact valve structure should still remain minimal, while annulus calcifications were included into the measurements. While we could demonstrate solid statistical significance within our sample size of 33 patients, further studies in a larger patient cohort may be reasonable for more clinical evidence. In summary, CT-based aortic annulus measurement employing calculated average diameter assessment by means of planimetry seems to provide adequate dimensions similar to operative measurements with the Hegar dilator. The strong correlation of CAAD with the size of an implanted valve prosthesis enhances the credibility of CT measurements. The TEE tends to underestimate the aortic annulus diameter compared with intraoperative measurements. The CAAD approach may minimize the dependency of single-view CT measurement on the elliptic shape of the aortic annulus and appears to be a feasible alternative for aortic annulus assessment in terms of candidates selection for transcatheter aortic valve replacement. References 1. Moss RR, Ivens E, Pasupati S, et al. Role of echocardiography in percutaneous aortic valve implantation. JACC Cardiovasc Imaging 2008;1: Wood DA, Tops LF, Mayo JR, et al. Role of multislice computed tomography in transcatheter aortic valve replacement. 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Assessment of aortic annulus dimensions for Edwards SAPIEN Transapical Heart Valve implantation by computed tomography: calculating average diameter using a virtual ring method. Eur J Cardiothorac Surg 2010 [Epub ahead of print]. INVITED COMMENTARY Accurate measurement of the diameter of the aortic annulus is critical for the correct placement of stented valves in transcatheter aortic valve implantation. Overestimation of the size of the aortic annulus leads to undersizing of the valve prosthesis and an increase in paravalvular leak and, possibly, prosthesis migration by The Society of Thoracic Surgeons /$36.00 Published by Elsevier Inc doi: /j.athoracsur