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Cardiac Imaging |
1 From the Institute of Diagnostic Radiology (H.A., S.W., B.B., S.L., L.M.D., B.M., T.B.), Clinic for Cardiovascular Surgery (A.P.), and Institute of Anesthesia (D.B.), Division of Cardiovascular Anesthesia, University Hospital Zurich, Raemistrasse 100, CH-8091 Zurich, Switzerland. Received March 17, 2005; revision requested May 10; revision received May 19; accepted June 20; final version accepted August 25. Supported by the National Center of Competence in Research, Computer Aided and Image Guided Medical Interventions of the Swiss National Science Foundation. Address correspondence to H.A. (e-mail: hatem.alkadhi{at}usz.ch).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEReferences |
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Materials and Methods: The study had institutional review board approval; patients gave informed consent. Twenty patients (11 men, nine women; mean age, 63 years) with AS and 20 patients (10 men, 10 women; mean age, 65 years) without underwent transthoracic echocardiography (TTE), transesophageal echocardiography (TEE), and retrospectively electrocardiographically gated 16–detector row CT. Twenty CT data sets were reconstructed in 5% steps of R-R interval; data analysis was performed with four-dimensional software. Maximum AVA in systole planimetrically measured with CT (AVACT) was compared with AVA planimetrically measured with TEE (AVATEE), AVA calculated with the continuity equation and TTE (AVATTE), and transvalvular pressure gradients determined with the Bernoulli equation and TTE. Correlations among AVACT, AVATTE, AVATEE, and transvalvular pressure gradients were tested with bivariate regression analysis; agreement between methods was assessed with the Bland-Altman method.
Results: In patients without AS, mean AVACT was 3.56 cm2 ± 0.66 and mean AVATEE was 3.43 cm2 ± 0.69. In patients with AS, mean AVACT was 0.89 cm2 ± 0.35; mean AVATEE, 0.86 cm2 ± 0.35; and mean AVATTE, 0.83 cm2 ± 0.33. Mean transvalvular pressure gradient was 51 mm Hg ± 22. Significant correlations were present between AVACT and AVATEE (r = 0.99, P < .001), AVACT and AVATTE (r = 0.95, P < .001), and AVACT and transvalvular pressure gradients (r = –0.74, P < .01). Mean differences were –0.08 cm2 (limits of agreement: –0.32, 0.16) for AVACT versus AVATEE and 0.06 cm2 (limits of agreement: –0.15, 0.26) for AVACT versus AVATTE.
Conclusion: Planimetric measurements of AVA with retrospectively electrocardiographically gated 16–detector row CT allow classification of AS that is similar to that achieved with measurements by using echocardiographic methods.
© RSNA, 2006
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEReferences |
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The most common clinical application of cardiac multi–detector row computed tomography (CT) includes the evaluation of coronary artery stenosis. Coronary artery disease and aortic stenosis often manifest simultaneously because both entities share a common pathophysiologic pathway (14). Researchers in preliminary studies (15–18) with multi–detector row CT have suggested a certain correlation between the degree of aortic valve calcification and the severity of aortic stenosis. Some investigators have shown this correlation to be curvilinear (19), and a direct estimation of the severity of aortic stenosis through the assignment of a score to aortic valve calcification should therefore be undertaken with caution. The purpose of our study was to prospectively evaluate whether planimetric measurements of the AVA with 16–detector row CT allow the classification of aortic stenosis.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEReferences |
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Between May 2003 and June 2004, we prospectively enrolled 95 patients with known coronary artery disease who were referred for multi–detector row CT of the coronary arteries as part of another study, which also had local ethics committee approval and for which informed consent was obtained. Exclusion criteria included renal insufficiency (creatinine level, >120 µmol/L), a history of an adverse reaction to iodinated contrast medium, and arrhythmia. Fifteen patients were excluded because of an increased serum creatinine level (n = 10), a previous allergic reaction to iodine-based contrast medium (n = 3), and arrhythmia (n = 2). From the remaining 80 patients, all 20 patients who had aortic stenosis (11 men, nine women; mean age, 63 years ± 10 [standard deviation]; range, 40–85 years) were included in our study. For comparison, 20 patients without aortic stenosis (10 men, 10 women; mean age, 65 years ± 9; range, 43–82 years) were randomly selected from our computer database from the same group of 80 patients and were assigned to be a control group. No significant difference was present between the group of patients with aortic stenosis and those without aortic stenosis in regard to age (P = .44, Wilcoxon rank sum test) and sex (P = .53, 
2 test). Presence or absence of aortic stenosis was suggested by findings at clinical examination and chest radiography, was confirmed with results of coronary angiography that included those of ventriculography, and was quantified by using echocardiography in all patients.
All 40 patients (20 patients with aortic stenosis and 20 control patients) had coronary artery disease, four patients had mitral regurgitation (two patients with aortic stenosis and two patients without aortic stenosis), two patients with aortic stenosis had mitral stenosis, and no patient had aortic regurgitation. Twenty-eight patients had a recent history of myocardial infarction (19 patients with aortic stenosis and nine patients without aortic stenosis). The cause of aortic stenosis was degenerative in all 20 patients. All multi–detector row CT and echocardiographic examinations were performed within 5 days. All patients underwent cardiac bypass graft surgery, and, in addition, 16 patients underwent aortic valve replacement (biologic prostheses in six and mechanical prostheses in 10). Four patients did not undergo aortic valve replacement because the degree of stenosis was classified as only mild, and their symptoms did not warrant surgical replacement of the valve.
Echocardiography
In all 40 patients, preoperative TTE was performed by using a multiplanar 2.5-MHz transducer (Sequoia 512; Acuson, Mountain View, Wash), and results were interpreted by an echocardiographer with 7 years of experience. In all 40 patients, intraoperative TEE was performed by using a multiplanar 5-MHz probe (Sonos 5500; Philips Medical Systems, Andover, Mass), and results were interpreted by another echocardiographer (D.B., with 7 years of experience). The examinations included M-mode, two-dimensional, continuous-wave, and color Doppler echocardiography and were performed according to international guidelines (20,21). The two echocardiographers were blinded to the results with the other modalities. Mean heart rates were 74 beats per minute ± 8 (range, 46–83 beats per minute) during TTE and 73 beats per minute ± 14 (range, 40–93 beats per minute) during TEE.
Multi–Detector Row CT
All 40 patients had a sinus rhythm with a mean heart rate of 76 beats per minute ± 11 (range, 42–92 beats per minute). No significant difference was present between the heart rate of patients with aortic stenosis and those without (P = .25, Wilcoxon rank sum test). Similarly, no significant difference was present between heart rates of patients with and those without aortic stenosis during CT, TTE, and TEE (P > .05). No beta-receptor–blocking medication was administered prior to the examination. CT was performed with a 16–detector row scanner (Somatom Sensation 16; Siemens Medical Solutions, Forchheim, Germany) with a gantry rotation time of 0.375 second. One hundred milliliters of iodixanol (Visipaque 320; Amersham Health, Buckinghamshire, England), 320 mg of iodine per millileter, was injected into a superficial vein in the antecubital fossa with a 20–22-gauge needle via a power injector (CT Injector; Ulrich Medical, Ulm-Jungingen, Germany) at a rate of 4 mL/sec. For optimal intraluminal contrast enhancement, the delay time between the start of contrast medium administration and the start of imaging was determined for each patient by using a bolus-tracking technique (CARE-Bolus; Siemens Medical Solutions). The region of measurement was placed in the ascending aorta, and the threshold level was set at 150 HU. Administration of the bolus of contrast medium was followed by a 30-mL saline chaser bolus administered at the same flow rate.
Repetitive low-dose monitoring examinations (120 kV, 10 mA, 0.5-second scanning time, 1-second interscan delay) were performed 10 seconds after contrast medium injection began. After the preset contrast enhancement threshold level of 150 HU was reached, the multi–detector row CT examination was automatically initiated. Data acquisition was performed in a craniocaudal direction with 16 detector rows and a section thickness of 0.75 mm (16 x 0.75 mm), a table feed of 3 mm per rotation, a gantry rotation of 0.375 second, and pitch of 0.25. The x-ray tube potential was 120 kV, and the effective tube current was 550 mA. The CT protocol was well tolerated by all patients, and all were able to hold their breath during data acquisition (mean data acquisition time, 25 seconds ± 2; range, 23–29 seconds).
CT Data Postprocessing
For image reconstruction, a segmented adaptive cardiac reconstruction algorithm was used (22). With this algorithm, one uses raw data from one subsegment of consecutive multisection spiral CT data from the same cardiac phase at heart rates lower than 65 beats per minute. At higher heart rates, two subsegments from adjacent cardiac cycles contribute to the partial scan data segment. Transverse CT images were reconstructed with a section thickness of 1.00 mm and an increment of 0.5 mm. Depending on the individual anatomy, the reconstructed field of view was individually fitted to the actual cardiac size in each patient (mean field of view, 203 mm ± 15; range, 172–232 mm; image matrix, 512 x 512 pixels). Twenty data sets of transverse images obtained at every 5% step of the R-R interval were reconstructed by using a Bf30 medium soft-tissue kernel. These data sets were then loaded into interactive image-processing software (Syngo InSpace4D; Siemens Medical Solutions), which enables three-dimensional processing in real time and thus displays the beating heart in any desired plane. The velocity of video presentation could be individually determined, and the readers were allowed to pause the cine-mode videos and scroll through the volume and phases until they found the best image for visualization of a particular structure or abnormality. The readers also were allowed to individually adjust window center and window level settings for image analysis. The mean time for postprocessing, which included data reconstruction and analysis by using the four-dimensional software, was 29 minutes ± 6 (range, 22–36 minutes).
CT Image Quality
For the purpose of analysis of image quality, the aortic valve (cusps and their free edges) was assessed in parallel and perpendicular planes during midsystole (ie, open valve), middiastole (ie, closed valve), and in the phases between midsystole and middiastole. The two phases between midsystole and middiastole were analyzed together and were termed transitional phases, defined as the phases of rapid valve motion between midsystole and middiastole and vice versa. Two readers (S.W., T.B.), each with 5 years of experience in cardiac CT, independently assessed the image quality for each anatomic component (ie, the aortic cusps, free edges, and commissures) in all three phases with a four-point Likert scale: score 1, bad (nondiagnostic and delineation of anatomic details of the valve not possible); score 2, poor (diagnostic with poor visibility of the anatomic details of the aortic valve cusps and free cusp edges); score 3, good (good visibility of the anatomic details of the aortic valve); and score 4, excellent (excellent visibility and differentiation of the anatomic details of the aortic valve).
Aortic Valve Morphologic Characteristics and Calcification at TEE and CT
All readers of multi–detector row CT and TEE images were asked to classify the valve as bicuspid or tricuspid, according to morphologic characteristics. A bicuspid aortic valve was defined as a valve with complete fusion of two cusps without a central raphe; as a result, complete absence of a commissure between the fused cusps was observed (6). Assignment of a quantitative score for aortic valve calcification on CT images was not possible because all patients underwent contrast material–enhanced CT. Instead, the degree of calcification of each cusp (ie, right coronary, left coronary, and noncoronary cusp) was semiquantitatively assigned a grade by all readers of multi–detector row CT and TEE images independently according to the classification system of Rosenhek et al (23): grade 1, no calcification; grade 2, mild with small isolated spots of calcification; grade 3, moderate with multiple larger spots of calcification; and grade 4, severe with extensive calcification of the entire cusp.
Artifacts from Valve Calcification with CT
Artifacts related to valve calcification with multi–detector row CT were independently classified by both readers as follows: grade 1, severe artifacts, which prevented valve assessment; grade 2, moderate artifacts, which severely compromised assessment; grade 3, few artifacts, which slightly compromised assessment; and grade 4, no artifacts with no compromise in valve assessment.
Movement Restriction of Aortic Cusps with TEE and CT
Restriction of movements was classified with both TEE and multi–detector row CT separately for each cusp by both readers independently as follows: grade 1, no movement restriction; grade 2, mild movement restriction that affected less than one-third of the cusp; grade 3, moderate movement restriction that affected between one-third and two-thirds of the cusp; and grade 4, severe movement restriction that affected more than two-thirds of the cusp.
Quantification of Aortic Stenosis
The AVA calculated with the continuity equation (1,2) and TTE (AVATTE) was determined in all 20 patients who had aortic stenosis. Continuous-wave Doppler spectra of aortic stenosis were traced from multiple transducer positions to obtain the maximum velocity. To minimize sampling artifacts, the three highest velocity beats were averaged to assess the peak and mean gradients. Furthermore, in all 20 patients who had aortic stenosis, mean systolic pressure gradients across the stenotic valve were calculated with TTE from the peak velocity across the obstruction and the velocity in the left ventricular outflow tract by using the Bernoulli equation (6). Calculations of the AVATTE and transvalvular pressure gradients in patients who did not have aortic stenosis were not performed.
The planimetrically measured AVA with TEE (AVATEE) was determined with an electronic caliper on a short-axis view of the aortic valve (24) in all 40 patients; three consecutive measurements were obtained and averaged. The smallest orifice during maximum opening in systole at the cusp tips was identified, and the view on which the aorta had a circular shape and all cusps were visualized simultaneously was considered adequate.
With multi–detector row CT, the plane that demonstrated the orifice with the smallest opening during the phase of maximum valve opening was chosen on images obtained in double-oblique parallel planes through the aortic valve. The plane was perpendicularly oriented to the left ventricular outflow tract across the aortic valve. The maximum AVA in systole planimetrically measured with CT (AVACT) was determined; three measurements were obtained and averaged. Measurements were performed in consensus by both readers who were blinded to the results of TTE and TEE.
Statistical Analysis
All statistical analyses were performed by using commercially available software (SSPS 11.5 for Windows, SPSS, Chicago, Ill). Quantitative variables are expressed as the mean ± standard deviation. Interobserver agreement for image quality, valve morphologic characteristics, valve calcification, calcification-related artifacts, and movement restriction of the aortic cusps with multi–detector row CT was expressed in terms of Cohen 
statistics (25). The values for interobserver agreement in regard to the five qualities noted were interpreted according to the classification of Landis and Koch (26) as follows: poor, 0.20 or less; fair, 0.21–0.40; moderate, 0.41–0.60; good, 0.61–0.80; or excellent, 0.81–1.00. The Wilcoxon rank sum test with exact sample methods was used to compare the intermodality scores of valve calcification and movement restriction between multi–detector row CT and TEE and to compare the AVACT and AVATEE values between patients with aortic stenosis and patients without aortic stenosis. The relationships between continuous variables from AVACT, AVATTE, AVATEE, and the mean systolic transvalvular pressure gradient were tested by using bivariate regression analysis along with 95% confidence intervals. The agreement between different methods was assessed with the method of Bland and Altman (27). P values less than .05 were considered to indicate statistically significant differences.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEReferences |
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= 0.629) to excellent ( = 0.925) (Table). For perpendicular planes, mean image quality scores ranged from 2.85 to 3.62, whereas for parallel planes, mean scores ranged from 3.04 to 3.85. No reader rated image quality of the aortic cusps in any cardiac phase and plane as bad (grade 1).
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= 0.712); that of the right coronary cusp, as 1.20 ± 0.28 and 1.28 ± 0.23 ( = 0.812); and that of the left coronary cusp, as 1.44 ± 0.15 and 1.35 ± 0.16 ( = 0.742), respectively. Calcification assessment with multi–detector row CT did not differ significantly from that with TEE in regard to the noncoronary (P = .581), right coronary (P = .712), and left coronary (P = .698) cusps.
In the patients with aortic stenosis at both TEE and multi–detector row CT, 18 (90%) of the valves were classified as tricuspid and two (10%) were classified as bicuspid. The mean degree of calcification of the noncoronary cusp, as assessed with CT, was rated by readers 1 and 2, respectively, as 2.68 ± 1.16 and 2.72 ± 1.22 ( = 0.735); that of the right coronary cusp, as 2.72 ± 1.18 and 2.80 ± 1.23 ( = 0.863); and that of the left coronary cusp, as 2.64 ± 1.05 and 2.64 ± 1.13 ( = 0.884). Calcification assessment with multi–detector row CT did not differ significantly from that with TEE in regard to the noncoronary (P = .839), right coronary (P = .768), and left coronary (P = .882) cusps.
Artifacts from Valve Calcification with CT
In patients without aortic stenosis, artifacts related to valve calcification were rated by both readers as few (grade 3) in the same three (15%) patients and as not present (grade 4) in 17 (85%) patients.
In patients with aortic stenosis, calcification-related artifacts were detected in the same 13 (65%) patients by both readers and were rated as moderate (grade 2) in five (reader 1) and four (reader 2) patients and as few (grade 3) in eight (reader 1) and nine (reader 2) patients (Fig 1). Severe artifacts from calcification, which prevented valve assessment (grade 1), were not observed.
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= 0.709); that of the right coronary cusp, as 1.10 ± 0.13 and 1.13 ± 0.17 ( = 0.854); and that of the left coronary cusp, as 1.03 ± 0.05 and 1.06 ± 0.08 ( = 0.837). Results from CT did not differ significantly from those from TEE in regard to the noncoronary (P = .651), right coronary (P = .324), and left coronary (P = .451) cusps.
In patients with aortic stenosis, the mean degree of movement restriction of the noncoronary cusp on CT images was rated by readers 1 and 2, respectively, as 2.48 ± 1.03 and 2.37 ± 1.02 ( = 0.843); that of the right coronary cusp, as 2.56 ± 1.00 and 2.44 ± 1.07 ( = 0.777); and that of the left coronary cusp, as 2.33 ± 0.98 and 2.44 ± 0.87 ( = 0.773). Results from multi–detector row CT did not differ significantly from those with TEE in regard to the noncoronary (P = .332), right coronary (P = .290), and left coronary (P = .207) cusps.
Quantification of Aortic Stenosis
The mean AVACT in patients without aortic stenosis was 3.56 cm2 ± 0.66 (range, 2.49–4.76 cm2) and that in patients with aortic stenosis was 0.89 cm2 ± 0.35 (range, 0.44–1.53 cm2), with a significant difference between the two groups (P < .001).
The mean planimetric AVATEE in patients without aortic stenosis was 3.43 cm2 ± 0.69 (range, 2.30–4.90 cm2), and that in patients with aortic stenosis was 0.86 cm2 ± 0.35 (range, 0.40–1.60 cm2), with a significant difference between groups (P < .001).
The mean AVATTE in patients with aortic stenosis was 0.83 cm2 ± 0.33 (range, 0.40–1.60 cm2), and the mean transvalvular pressure gradient with TTE was 51 mm Hg ± 22 (range, 13–87 mm Hg).
A significant correlation was present between planimetric AVACT and AVATEE measurements (r = 0.99, P < .001, n = 40) (Fig 2a), between planimetric AVACT measurements and AVATTE calculations (r = 0.95, P < .001, n = 20) (Fig 3a), and between planimetric AVACT measurements and mean transvalvular pressure gradients (r = –0.74, P < .01, n = 20) (Fig 4).
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Figure 5 demonstrates three examples of calcified and stenotic aortic valves as demonstrated with multi–detector row CT and TEE.
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DISCUSSION |
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Structural Valve Abnormalities and Surgical Valve Replacement
Preoperative knowledge about aortic valve morphologic characteristics and extent of aortic valve calcification is desirable when one is planning surgical valve replacement (19). For example, the presence or absence of a bicuspid aortic valve poses a risk factor for postoperative complications after aortic valve and aortic root replacement (29). Similarly, extensive valve calcification is associated with a higher prevalence of surgical difficulties; placement and fixation of the valve prosthesis into the annulus, as well as insertion of the coronary arteries, after aortic root replacement are complicated by severe calcification (30). Furthermore, preoperative quantification of valve calcification in patients who are undergoing aortic valve replacement allows prediction of postoperative conduction defects (31). Our results were similar to the results of a previous study (18) with four–detector row CT, for we were able to accurately depict morphologic abnormalities of the aortic valve with similar results when we compared results achieved with CT and echocardiography. In addition, the use of 20 reformations in 5% steps of the R-R interval enabled dynamic aortic valve imaging throughout the cardiac cycle and allowed a correct estimation of cusp motion restriction, which represents the major pathophysiologic contributor to aortic stenosis (32).
Classification of Aortic Stenosis
Determination of severity of aortic stenosis is crucial, and many laboratory tests are available; however, exact classification remains difficult because all methods have limitations peculiar to the techniques (1,5,6,11–13,33,34).
Previously, direct planimetry of the AVA by using magnetic resonance (MR) imaging was demonstrated to be feasible, and results with that technique and results with echocardiography and ventriculography with a catheter (7,8) showed a good correlation. The results of our study are similar to those reported with MR imaging and demonstrate that there is a significant correlation between planimetric AVA measurements with multi–detector row CT and the results obtained with TEE and TTE. Furthermore, the association between planimetry with CT and transvalvular pressure gradients was moderate and indicated a reduction of the AVA with increasing transvalvular pressure gradients.
When we assessed the planimetrically measured orifice area, a potential flaw might have occurred in that with poor left ventricular systolic function and low stroke volume, the pressure necessary to open the cusps to the full extent may not have been generated and, hence, may have led to an underestimation of the AVA (7). On the other hand, researchers in a study (35) with TEE simultaneously compared the planimetric measurement of the AVA with the calculated AVA in patients with aortic stenosis and demonstrated that changes of transvalvular blood flow did not result in significant alterations of planimetric AVA measurements.
Another limitation of planimetric AVA measurements could arise from the fact that the continuity equation is used to determine the effective area, whereas planimetry is used to measure the anatomic area; the latter is supposed to be larger than the former (12). This could explain the slight overestimation in regard to AVA measurements with CT and TEE compared with measurements with TTE, as also has been observed in our study; however, these differences were not significant.
Aortic Valve Calcification and Stenosis
Recently, investigators in a large comprehensive study (19) examined the hemodynamic correlates, the diagnostic value, and the outcome implications of quantitative aortic valve calcification measurements in 100 patients with aortic stenosis and found this correlation to be curvilinear. These investigators concluded that the grade of aortic valve calcification and that of stenosis provide complementary information. Moreover, the valve calcification score was an independent predictor of survival and, thus, provided important outcome information (19). This finding supports the idea that valve calcification is associated with a 50% increase in the risk of death from cardiovascular disease, even in the absence of left ventricular outflow tract obstruction (36). One of the implications of our investigation for application in further imaging studies in patients with aortic stenosis is that the extent of aortic valve calcification should not be taken as a direct marker of the severity of aortic stenosis, as has been previously suggested (15–18), but that aortic valve calcification should be separately quantified in addition to severity of aortic stenosis.
Study Limitations
The following study limitations have to be acknowledged. Only patients who had both coronary artery disease and aortic stenosis were included in our study, which potentially could have led to an inclusion bias. Furthermore, only two patients had a bicuspid aortic valve; therefore, the applicability of the data for nondegenerative causes of aortic stenosis remains to be elucidated. Clearly, more data from a larger patient population that includes patients without coronary artery stenosis and patients with nondegenerative aortic stenosis are needed. Another drawback of our study is the lack of AVA data (with use of the continuity equation) and transvalvular pressure gradients for patients without aortic stenosis for comparison with data from CT. Finally, a limitation is the irradiation inherent in the CT technique. For the purpose of dose reduction, we restricted our protocol to a single contrast-enhanced CT scan at the expense of performing quantitative assignment of scores to aortic valve calcification. The data set in our study was used not only for aortic valve imaging but also, primarily, for assessment of coronary arteries (as part of another study), and the same data also may be used to quantify parameters for ventricular function.
Conclusions
Planimetric measurements of the AVA by using 16–detector row CT allow a classification of aortic stenosis that is similar to that achieved with measurements by using clinically established echocardiographic methods. Multi–detector row CT also demonstrates morphologic valve abnormalities and, thus, yields important structural information before aortic valve replacement surgery.
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ADVANCES IN KNOWLEDGE |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONADVANCES IN KNOWLEDGEReferences |
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FOOTNOTES |
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Abbreviations: AVA = aortic valve area • AVACT = maximum AVA in systole planimetrically measured with CT • AVATEE = AVA planimetrically measured with TEE • AVATTE = AVA calculated with the continuity equation and TTE • TEE = transesophageal echocardiography • TTE = transthoracic echocardiography
Authors stated no financial relationship to disclose.
Author contributions: Guarantors of integrity of entire study, H.A., S.W., L.M.D., B.M., T.B.; study concepts/study design or data acquisition or data analysis/interpretation, all authors; manuscript drafting or manuscript revision for important intellectual content, all authors; manuscript final version approval, all authors; literature research, H.A., S.L., L.M.D.; clinical studies, all authors; statistical analysis, H.A., L.M.D.; and manuscript editing, H.A., S.W., A.P., D.B., B.B., L.M.D., B.M., T.B.
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