Background
Increased left ventricular (LV) mass is associated with adverse cardiovascular outcomes, and its accurate assessment is important. The aim of this study was to analyze the degree of difference among various methods of LV mass calculation based on transthoracic echocardiographic (TTE) measurements and cardiovascular magnetic resonance (CMR) measurements, especially in patients with aortic stenosis with varying degrees of LV hypertrophy (LVH). The mechanism underlying this disagreement was also investigated.
Methods
Ninety-nine patients with moderate to severe aortic stenosis and 33 control subjects matched for age, sex, body weight, and height were enrolled in this prospective observational cohort study. All patients underwent TTE and CMR imaging. LV mass index (LVMI) was calculated using three formulas on the basis of TTE measurements (the Penn-cube, American Society of Echocardiography [ASE], and Teichholz methods) and compared with measurements obtained using CMR, the reference method.
Results
Although all methods calculated using TTE measurements showed good correlations with CMR measurements, LVMI measured using the Penn-cube and ASE methods tended to be larger than LVMI measured using CMR (difference in LVMI by the Penn-cube and ASE methods, 59.3 ± 29.7 and 30.6 ± 22.3 g/m 2 , respectively). This tendency decreased with the Teichholz method (difference in LVMI by the Teichholz method, 22.9 ± 19.1 g/m 2 ). The degree of LVMI overestimation was significantly different among the three methods ( P < .001 by one-way analysis of variance), which was more significant in patients with LVH, especially with the Penn-cube method (differences between CMR and TTE measurements in patients with aortic stenosis and LVH, 66.3 ± 34.8 vs 31.2 ± 26.6 vs 15.5 ± 20.9 g/m 2 for the Penn-cube, ASE, and Teichholz methods, respectively; P < .001 with post hoc Tukey analysis). There was a good correlation between LVMI and LV diameter-to-length ratio ( r = 0.468, P < .001), which suggested that the left ventricle takes on a more globular shape with the increase of LVMI, resulting in a significant deviation from the basic assumptions on which the Penn-cube and ASE methods were built.
Conclusions
Current methods of calculating LVMI from echocardiographic measurements carry a tendency to measure LVMI larger than methods based on CMR measurements, which was more significant in patients with LVH. The change of the left ventricle’s shape with LVH may be a plausible explanation for this, and a correction method may be needed when calculating LVMI from echocardiographic measurements, especially in patients with LVH and smaller body size.
Highlights
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The Penn-cube, ASE, and Teichholz methods tend to measure LVMI larger than CMR in Asians.
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The degree of LVMI overestimation is greater in patients with LVH than in those without LVH.
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The degree of overestimation is greater with the Penn-cube and ASE methods than with the Teichholz method.
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This discrepancy between CMR and TTE imaging may be due to the deviation from the basic geometric assumptions on which the Penn-cube and ASE methods were built.
In patients with aortic stenosis (AS), left ventricular (LV) hypertrophy (LVH) develops as a compensatory response to normalize the wall stress and the oxygen demand of the left ventricle. However, this cascade of compensatory responses alters the myocardium, which leads to adverse clinical consequence such as diastolic dysfunction, impairment of systolic function, and heart failure in the long term. Accordingly, accurate assessment of LVH plays an important role in the prediction of prognosis in patients with AS.
Calculating LV mass index (LVMI) using transthoracic echocardiographic (TTE) imaging is a common way to assess the presence or absence of LVH in current clinical practice. The American Society of Echocardiography (ASE) method and the Penn-cube method, two common formulas for calculating LVMI from TTE measurements, were derived from the basic geometric assumption that the left ventricle has a prolate ellipsoid shape. On the other hand, the Teichholz method has a different basis from the other two methods. This method accepts the concept that LV long-axis diameter may decrease as LV short-axis diameter increases and, accordingly, corrects the mass calculation according to LV volume.
Previous studies have demonstrated that the calculation of LVMI using TTE measurements tends to overestimate LVMI in comparison with LVMI measured using cardiovascular magnetic resonance (CMR), the reference method for in vivo LVMI assessment to date. However, those studies were limited in sample size and provided only simple correlations between these two modalities. In addition, the previous studies did not examine the reasons why the calculation of LVMI using TTE measurements tends to overestimate LV mass. Especially given that LVMI is a critical prognostic factor in patients with AS undergoing surgical correction, whether the current status of calculating LVMI using echocardiographic measurements matches that of other modalities requires more validation. Moreover, whether this holds true for only patients with LVH or patients across the spectrum of LVMI has not been assessed in depth.
In the present study, we attempted to analyze the discrepancies among various LV mass calculation methods on echocardiographic measurement in comparison with CMR measurement in patients with moderate to severe AS. In addition, we investigated the underlying mechanism of the differences in LVMI calculated using TTE measurements and using CMR measurements.
Methods
Patient Population
A total of 99 patients with moderate to severe AS (i.e., maximal transaortic velocity > 3 m/sec or mean transaortic pressure gradient > 30 mm Hg and aortic valve area (AVA) ≤ 1.5 cm 2 with normal LV systolic function [LV ejection fraction ≥ 50%]) were enrolled in this prospective study. In addition, 33 control subjects matched for age, sex, and anthropometric measurements, devoid of any cardiovascular risk factors or diseases, were also enrolled prospectively for comparison. Patients with decreased LV systolic function, prior myocardial infarction, or significant valvular heart disease other than AS were excluded. All patients were studied with TTE and CMR imaging, within 1 month, at Seoul National University Hospital and Samsung Medical Center, and no patients experienced any changes in functional status or hemodynamics during this period. All patients gave informed consent to participate in the study, the protocol of which was approved by the institutional review boards of the two institutions. All anthropometric data were acquired on the day of enrollment.
Echocardiography
All patients underwent comprehensive echocardiographic examinations with adequate equipment (Vivid 7; GE Vingmed Ultrasound AS, Horten, Norway) according to current ASE recommendations.
LV mass was calculated from the TTE measurements using the following equations:
ASE method 1 : 0.8 × { 1.04 × [ ( IVSTd + LVIDd + PWTd ) 3 − LVIDd 3 ] } + 0.6.
Penn – cube method 5 : 1.04 × [ ( IVSTd + LVIDd + PWTd ) 3 − LVIDd 3 ] − 13.6.
Teichholz method 6 : 1.04 × { [ 7 .0 / ( 2.4 + IVSTd + LVIDd + PWTd ) ] × ( IVSTd + LVIDd + PWTd ) 3 − [ 7 .0 / ( 2.4 + LVIDd ) ] × LVIDd 3 } .
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