Background
Left ventricular (LV) mass is an important prognostic indicator in hypertrophic cardiomyopathy. Although LV mass can be easily calculated using conventional echocardiography, it is based on geometric assumptions and has inherent limitations in asymmetric left ventricles. Real-time three-dimensional echocardiographic (RT3DE) imaging with single-beat capture provides an opportunity for the accurate estimation of LV mass. The aim of this study was to validate this new technique for LV mass measurement in patients with hypertrophic cardiomyopathy.
Methods
Sixty-nine patients with adequate two-dimensional (2D) and three-dimensional echocardiographic image quality underwent cardiac magnetic resonance (CMR) imaging and echocardiography on the same day. Real-time three-dimensional echocardiographic images were acquired using an Acuson SC2000 system, and CMR-determined LV mass was considered the reference standard. Left ventricular mass was derived using the formula of the American Society of Echocardiography (M-mode mass), the 2D-based truncated ellipsoid method (2D mass), and the RT3DE technique (RT3DE mass).
Results
The mean time for RT3DE analysis was 5.85 ± 1.81 min. Intraclass correlation analysis showed a close relationship between RT3DE and CMR LV mass ( r = 0.86, P < .0001). However, LV mass by the M-mode or 2D technique showed a smaller intraclass correlation coefficient compared with CMR-determined mass ( r = 0.48, P = .01, and r = 0.71, P < .001, respectively). Bland-Altman analysis showed reasonable limits of agreement between LV mass by RT3DE imaging and by CMR, with a smaller positive bias (19.5 g [9.1%]) compared with that by the M-mode and 2D methods (−35.1 g [−20.2%] and 30.6 g [17.6%], respectively).
Conclusions
RT3DE measurement of LV mass using the single-beat capture technique is practical and more accurate than 2D or M-mode LV mass in patients with hypertrophic cardiomyopathy.
Left ventricular (LV) mass is an important prognostic indicator of heart failure and sudden cardiac death in patients with hypertrophic cardiomyopathy (HCM). Although cardiac magnetic resonance (CMR) imaging is the most accurate noninvasive method for assessing myocardial mass in vivo, it is relatively expensive and time consuming and is limited in patients with claustrophobia or implanted pacemakers, limiting its routine use in the daily clinical practice. Transthoracic echocardiography is a widely used modality for assessing LV morphology and function in patients with HCM and can be easily performed for longitudinal assessment. Furthermore, it provides more accurate information on hemodynamic changes. LV mass determination using M-mode or two-dimensional (2D) echocardiography has been well validated in normal or hypertensive patients with symmetrically shaped left ventricles, but LV mass calculations using M-mode and 2D techniques are based on the assumption of symmetric LV geometry. Accordingly, it can be presumed that these conventional methods have inherent limitations that might produce erroneous results in patients with HCM.
Three-dimensional (3D) assessments, which are free of geometric assumptions, might provide more accurate measures of LV mass in asymmetric left ventricles than conventional 2D methods, but the effort required to acquire and analyze 3D echocardiographic data limits clinical utility. However, the recent development of real-time 3D echocardiographic (RT3DE) imaging with single-beat capture has been shown to provide a straightforward, highly accurate means of determining LV volume and function. Additionally, this approach provides a means for calculating LV mass that is free of geometric assumptions.
We hypothesized that the accuracy of LV mass calculation in patients with HCM could be improved using RT3DE imaging with single-beat capture compared with conventional methods such as M-mode or 2D imaging. We also examined the feasibility and accuracy of this novel RT3DE technique for the determination of LV mass in patients with HCM, with CMR as the reference standard.
Methods
Study Population
Consecutive patients with HCM in normal sinus rhythm at two tertiary referral hospitals (Samsung Medical Center and Seoul National University Hospital) with established diagnoses of HCM and scheduled for CMR and echocardiography on the same day were considered for this study. Patients with poor 2D echocardiographic windows, defined as those in whom an experienced sonographer could not sufficiently discriminate the endocardial and/or epicardial borders on 2D echocardiographic images, and patients with contraindications to CMR were excluded a priori. Ultimately, 71 patients were enrolled, and these patients constituted the study cohort. The study protocol was approved by the institutional review boards of the two participating hospitals.
CMR Imaging
All patients underwent CMR studies using a 1.5-T scanner (Magnetom Avanto, syngo MR; Siemens Healthcare, Erlangen, Germany) during repeated breath holds. After localization, cine images for LV and right ventricular functional parameters were acquired using a steady-state free precession sequence (repetition time, 8–10 msec; echo time, 3–5 msec; flip angle, 20°; in-plane resolution, 1.4 to 1.6 mm × 2.2 to 2.5 mm; temporal resolution, 46 ± 8 msec) with eight to 10 contiguous short-axis slices to cover the entire left and right ventricles, with slice thickness of 6 mm and 4-mm gaps.
Image analysis was performed to determine LV mass from CMR images using commercial software (Argus version 4.02; Siemens Healthcare) by a single experienced observer blinded to all echocardiographic results. In each case, the end-diastolic frame with the largest LV cavity size was selected for LV mass measurement by retrospective image review. Endocardial and epicardial borders were manually traced in the selected image frame for the LV cavity volume and total LV volume (defined as the sum of LV cavity volume and LV myocardial volume) calculations. Papillary muscles and LV trabeculae were excluded from endocardium and included in LV cavity volume. At the base of the heart, slices were considered to be within the LV if the blood volume was surrounded by ≥50% of ventricular myocardium. Left ventricular myocardial volume was calculated by subtracting LV cavity volume from total LV volume. Finally, LV mass was calculated by multiplying LV myocardial volume by myocardial density (1.05 g/mL).
Echocardiographic Image Acquisition
After CMR acquisition, transthoracic echocardiography was performed using commercially available equipment (Acuson SC2000; Siemens Medical Solutions USA, Inc., Mountain View, CA) by a single experienced sonographer at each center, with subjects in the left lateral decubitus position. After each routine echocardiographic examination, 2D targeted M-mode echocardiographic images were acquired at the level of the mitral valve leaflet tips, in accordance with the American Society of Echocardiography (ASE) guidelines for chamber quantification. To calculate LV mass using 2D echocardiograms, short-axis view images at the mid ventricle and apical four-chamber view images were acquired. Great care was taken to avoid foreshortened acquisition of apical images.
For LV mass quantification by RT3DE imaging, a special 3D image acquisition transducer (4Z1c) was used. This transducer has a matrix array with a maximum volume angle of 90° × 90°. Volume angles and frame rates were optimized for each patient to allow visualization of both endocardial and epicardial borders.
Echocardiographic Analysis of LV Mass Measurement
Echocardiographic images were transferred to a central laboratory and analyzed by two experienced observers (E.-Y.K. and S.-H.H), who independently analyzed M-mode, 2D, and 3D echocardiographic data without knowledge of CMR data. Analyses were performed using 2D and 3D software analysis packages supplied with the echocardiographic system.
For LV mass measurement using the M-mode technique, we used the formula suggested by the ASE :
LV mass ( g ) = 0.80 [ 1.04 ( PWT + LVIDd + SWT ) 3 − LVID 3 ] + 0.6 g ,
For LV mass calculations by 2D echocardiography, we used the area-length method, as described in an ASE document on LV quantitation ; LV mass was calculated by subtracting endocardial volume from epicardial volume:
LV mass ( g ) = 1.05 × { [ 5 / 6 ( A epi × L epi ) − ( A endo × L endo ) ] } .
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