METHODS
Study patients. Three different groups of patients who
underwent echocardiography at the University Hospital of Ferrara were
retrospectively examined and enrolled in the present study.
TEE group . In 53 consecutive patients referred for clinically
indicated TEE from January to April 2018, we measured the LVOTD during
both TTE and TEE. Both measurements were performed blindly one from the
other. TEE indications were: assessment of aortic and or mitral valve
disease severity (N=25), exclusion of left atrial appendage thrombi or
cardiac masses (N=13), evaluation for patent foramen ovale (N=8), and
suspected endocarditis (N=7). There was no exclusion criterion except
unmeasurable LVOTD during TTE.
Derivation group . This group was used to derive a regression
equation for predicting LVOTD using its independent determinants. It
included 340 consecutive patients with heart failure who underwent
echocardiography from January to August 2018.
Validation group . This group was used to validate the derived
regression equation and compare it with the previously published one
based on BSA (14). It included 200 consecutive patients with heart
failure who underwent echocardiography from September to December 2018.
For both the derivation and validation groups, exclusion criteria were
history of aortic valve or aortic root surgical or transcatheter
intervention (N=17, derivation group; N=14, validation group), and poor
echogenicity that could affect aortic root, LVOT, LV end-diastolic
diameter (LVEDD) and LV volume measurement (N=39, derivation group; N=18
derivation group). Aortic stenosis (aortic valve area ≤1.5
cm2) was not considered an exclusion criterion.
Demographic and clinical patients’ characteristics were collected.
TTE examination . A comprehensive two-dimensional
echocardiographic, Doppler and color Doppler examination was performed
using a GE Vivid 7 or E9 echo scanner (GE Health Care, Milwaukee, US)
equipped with a 3.5 MHz transducer. Echocardiographic images were stored
in digital format and analyzed using the EchoPAC software v. 201 (GE
Health Care, Milwaukee, US). One trained physician did all the
echocardiographic measures, according with the American Society of
Echocardiography/European Association of Cardiovascular Imaging
guidelines (17). LV end-diastolic and end-systolic volumes were
calculated from orthogonal apical views using the biplane Simpson
method. LV ejection fraction was derived from the standard equation
(17). Two-dimensional linear internal measurements of the LV were
acquired in the parasternal long-axis view carefully obtained
perpendicular to the LV long-axis, and measured at the level of the
mitral valve leaflet tips (17). Electronic calipers were positioned at
the interface between myocardial wall and cavity and the interface
between wall and pericardium (17). The diameter at the level of the
sinuses of Valsalva (SVD) was measured at end-diastole, in a strictly
perpendicular plane to that of the long-axis of the aorta using the
leading-edge-to-leading-edge convention (17). Aortic root dilatation was
defined as SVD indexed to BSA (SVDI) \(\geq\)21mm/m2,
according with previous adult normal reference studies (17-19). LVOTD
was measured using the zoom mode at the insertion of the leaflets (at
the annulus level) in midsystole with the inner-edge-to-inner-edge
approach from the parasternal long-axis view (7,17).
LVOTBSA was calculated with the equation
LVOTDBSA=12.1+5.7xBSA (14), with BSA calculated with the
Mosteller formula (14,20). For intraobserver variability, measurements
were repeated by the same physician one week later; for interobserver
variability, measurements were performed by a second physician who used
the same criteria and was blind to the results of the first observer
(17).
TEE examination . The examination was performed using a GE Vivid
E9 echo scanner equipped with a 5 MHz transducer. Echocardiographic
images were stored in digital format and analyzed using the EchoPAC
software v. 201. The LVOTD was measured using the zoom mode, as
described for TTE, on images acquired in the aortic long-axis view at
the mid-esophageal position using an image plane with about 120°
rotation (21). Measurements were performed by an independent operator
who was blind to the measurements performed on the TTE images.
Statistical analysis and study endpoints. Normal distribution
was tested with the Kolmogorov-Smirnov test. Continuous variables were
expressed as mean and standard deviation or median values with
25th and 75th percentiles if
normally or non-normally distributed, respectively. Categorical
variables were reported as counts and percentages. For continuous normal
and non-normal variables, Student’s t-test and Mann-Whitney U test were
respectively used for comparisons between two unpaired groups.
Categorical variables were compared by the chi-square test. Pearson
correlation was used for normally distributed variables, whereas
Spearman correlation was used if at least one variable had
non-parametric distribution. Comparison of LVOTD measured during both
TTE and TEE was performed using a paired Student’s t test. To assess for
error and bias, the Bland-Altman method was used. The correlation
between LVOTD, anthropometrics data (patient BSA and height), LVEDD, SVD
and age were studied with univariate linear regression analysis in the
derivation group. For the primary endpoint of the derivation study, the
covariates that were found to be statistically correlated with LVOTD
were included in the multivariate linear regression model (Model 1) in
order to derive a regression equation for predicting LVOTD
(LVOTDRE1). LVEDD and SVD were included as non-indexed
values for this analysis to facilitate the utilization of the derived
formula. The independent covariates from Model 1 were included as
indexed values in a secondary multivariate linear regression analysis
with the difference between measured LVOTD (LVOTDM) and
LVOTDBSA as endpoint, to corroborate the results of
Model 1. Secondary endpoints for the derivation group were: 1) an
analogous multivariate linear regression model (Model 2) including LV
end-diastolic volume (LVEDV) instead of LVEDD as covariate; 2) a
repeated multivariate linear regression analysis with the addition of
gender (Model 3, with LVEDD; Model 4, with LVEDV). A regression equation
was derived for each secondary multivariate model
(LVOTDRE2, LVOTDRE3,
LVOTDRE4). For the primary endpoint of the validation
study, the Student’s t-test for paired samples was used to compare
LVOTDRE1 and LVOTDBSA (14) with
LVOTDM in the validation group. As a secondary endpoint,
the other regression equations (including LVEDV and/or gender) were also
tested. Multicollinearity between the variables in all the multivariate
models was assessed by calculation of the variance inflation factor,
with a value \(\geq\)5 indicating significant collinearity. The intra-
and interobserver variability for SVD, LVEDD, LVEDV,
LVOTDM, LVOTDRE1,
LVOTDRE2 and their derived LVOT areas were assessed in a
random sample of 25 patients. Observer variability was determined as the
standard deviation of the mean error and expressed as percentage of the
first measure for each variable. Data were analyzed using the IBM SPSS
Statistics software, v. 24. Differences were considered statistically
significant for P<0.05. The study was approved by the local
Ethics Committee.