Materials and Methods
Study design: A prospective cross-sectional study carried out
at the University of Alabama At Birmingham from June 2016 to December
2016 and approved by the Institutional Review Board of the University of
Alabama At Birmingham (RB-170119002) and written informed consent was
obtained from all subjects.
Study population: Patients were enrolled sequentially as they
met study inclusion criteria identified by the Obstetric Anesthesiology
fellow at the time of daily patient board check out. A total of 46
patients with singleton pregnancies were enrolled into four groups:
early and late PEC with early and late gestational age-matched
normotensive pregnant controls. The incidence of PEC was defined and
classified according to the American College of Obstetricians and
Gynecologists (ACOG) (2013) revised criteria[2]. Early PEC was
defined as PEC diagnosed at or before 34 weeks of gestation and late PEC
was defined as PEC ≥ 34 weeks of gestation. Blood pressure at the time
of enrollment was measured manually according to the guidelines of the
National High Blood Pressure Education Program Working Group on High
Blood Pressure in pregnancy. All of the measurements were performed in
the left arm, in the sitting position, with the arm at the level of the
heart. Patients underwent physical exams to rule out signs of severe PEC
in the form of visual disturbances, headaches or right upper quadrant
abdominal pain. Patients with severe preeclampsia, with history of heart
failure or ejection fraction (EF) <40%, valvular heart
disease, chronic hypertension, PA stenosis, congenital heart disease,
and those who were in eclampsia, were excluded from the study. None of
the patients had chronic kidney disease.
Echocardiography: TTE was performed on all participants upon
the diagnosis of PEC and admission to the ward before delivery. All TTE
exams were performed by a board-certified single provider (AZ) with a
10-year experience in echocardiography and ultrasonography, using the
same device (SPARQ (Philips Vingmed Ultrasound, Horten, Norway) and
transducer (S5-1, MHz phased-array). A second board certified observer
(BJM) who was blinded to the patients’ group designation and who had not
attended the initial examination analyzed the echocardiographic exams
post hoc. The values entered by the initial examiner were concealed
prior to the examinations entered by the second observer.
Electrocardiography was recorded continuously during echocardiographic
studies. Two-dimensional, M-mode, and tissue Doppler TTE imaging were
performed according to American Society of Echocardiography
guidelines[9].
A conventional, focused, and modified apical four-chamber view (mA4CW),
parasternal long axis (PLAX), parasternal short axis (PSAX), left
parasternal RV outflow, and the left parasternal RV inflow (RV) views
were obtained. RV basal diameter (RV-Bd) was measured from mA4CW,
focusing on RV at end-diastole. The right atrium (RA) long and short
axis diameters (RAd-lax/RAd-sax) and right atrial area (RAA) were
measured from mA4CW at end-systole. The RVOT outflow tract (RVOT)
diameter was measured from left PSAX at end-diastole. RV free wall
thickness (RV-FWT) was measured from left PLAX at end-diastole using
M-mode. Pulsed wave Doppler was performed at the mitral, tricuspid,
pulmonary, and aortic valves. RV systolic function was evaluated using
the fractional area of change (FAC), tricuspid annular plane systolic
excursion (TAPSE) and tissue Doppler imaging of the peak systolic
velocity of the lateral tricuspid annulus. TAPSE was measured using M
mode from the apical 4 chamber view. RV diastolic function was estimated
using early and late diastolic waves across the tricuspid valve and
across the tricuspid annulus. RV myocardial performance index (RV MPI),
a representation of the global systolic and diastolic function of the RV
was calculated as described before using pulsed wave Doppler velocity
and the formula RV MPI = (RV isovolumic contraction time (IVCT)) + RV
isovolumic relaxation time (IVRT)/ RV ejection time (ET) [10]. RV
ejection time was measured from the pulsed wave Doppler across the right
ventricular outflow tract in the left parasternal RV outflow view. RV
MPI reference range RV MPI < 0.4. RV cardiac output and stroke
volume were calculated in accordance of guidelines[9]..
Apical 4 chamber views were specifically optimized to visualize the RV
to obtain echocardiographic cine loops by recording 3 consecutive heart
cycles with a frame rate > 60 frames/sec. Offline analyses
were performed using a dedicated software (Qlab 10.3, Philips
Healthcare). To assess tissue-tracking tricuspid annular displacement
(TTAD) user defined 3 points were selected in RV focused view as
follows: at the point of insertion of the lateral (TTAD L), and septal
(TTAD S) leaflets and at midpoint (TTAD MP) of the tricuspid valve to
the tricuspid annulus and the RV apex. The software automatically
tracked tissue-tracking tricuspid annular displacement (TTAD) and
calculated the TTAD at the RV free wall, the TTAD at the
interventricular septal wall and the TTAD at the midpoint of TV annulus,
as well as the percent displacement of midpoint (TTAD MP%). In some
patients (n=1 in Early C, n=2 in early PEC, n=3 in late C and n=2 in
late PEC) the image quality was inadequate to reliably assess TTAD and
in the case of one patient there was no agreement between the two
observers, resulting in exclusion from the analysis. The resulting
number for TTAD measurements are listed in Table 3. The apical 4 chamber
and the parasternal SAX views were used to measure left ventricular (LV)
EF by the area-length technique[9]. LV endocardial fractional
shortening measured by M mode, fractional area of change, and lateral
mitral annular peak tissue velocity measured by tissue Doppler imaging,
were all measured from the parasternal long axis, parasternal SAX, and
apical 4 chamber views, respectively, according to guidelines[9].
Estimation of PA pressure by echocardiography: We first
attempted to estimate PA systolic pressure using the Bernoulli equation
(PAP = 4 x TRvel2) from the tricuspid regurgitation
jet velocity, in case a tricuspid regurgitant jet was discerned[11].
Since we only had three patients with reliably detectable tricuspid
regurgitation jet, these data are not reported.
Since in most cases the tricuspid regurgitant jet was not discerned, the
mean pulmonary artery pressure (MPAP) was estimated from the PAAT
measured across the pulmonary valve using pulsed Doppler waveform. We
were unable to use the most commonly used formulas that rely on linear
equations to estimate MPAP (if PAAT is ≥ 120ms, estimated MPAP = 79 -
(0.45x PAAT), if PAAT is < 120 ms, estimated MPAP = 90 -
(0.62xPAAT), because several (5/11) control pregnant patients had PPAT
beyond the cut-off limit of these equations (170 ms). Instead we used a
logarithmic equation according to the formula validated by Kitabatake et
al[12] and Yared et al [13], which is not limited by the
extremes:
estimated MPAP=10-0.0068*(PAAT)+2.1
PAAT-based analysis was also analyzed by categorical assessment using
cutoff value of PAAT =100 ms. It was shown that in non-pregnant
individuals, PAAT<100ms predicts PAH and increased pulmonary
vascular resistance with a sensitivity of 84% and specificity of 90%
[14].
Pulmonary vascular resistance was estimated from estimated MPAP and RV
cardiac output (RV CO) using the following formula[15]:
‘Estimated PVR=estimated MPAP/RV CO’
Estimation of left atrial pressure by echocardiography: We
utilized a noninvasive method to assess the filling pressure for the
left ventricle, which is based in measuring the E and A waves of mitral
valve flow velocity and by measuring the velocity of the mitral annulus
(e’). Mitral E/A >2 and E/e’ >14 show good
correlation with elevated LV filling pressures [16].
Statistical analyses: Statistical analyses were performed using
Prism (GraphPad Software, La Jolla, CA), unless noted otherwise. The
primary variables for assessing differences was estimated mean pulmonary
artery pressure and PAAT. Since estimated pulmonary artery pressure is
directly calculated from PAAT, we considered these as a single primary
variable. All other variables reported are secondary variables.
Continuous variables were presented as mean ± standard deviation.
Normality test was calculated by four different methods automatically by
Prism: Anderson-Darling (A2*) (AD), D’Agostino-Pearson omnibus (K2)
(DP), Shapiro-Wilk (W) (SW) and Kolmogorov-Smirnov (distance) (KS).
PAAT, RVMPI, maternal age, GA at admission, diastolic BP, Heart rate, RV
FAC, RV COi and TAPSE passed normality tests by all four methods,
estimated pulmonary artery pressure, RV SVi, Systolic BP passed three,
BMI, estimated PVR, TTAD S and TTAD MP % passed two, MV E/e’, TTAD L
and TTAD MP only passed DP, MV E/A only passed KS, mean BP and GA at
delivery did not pass any. For variables that failed at least two
normality tests we used Kruskal-Wallis test with Dunn’s post-hoc
analysis. Variables that tested at least three normality tests were
considered to be continuous variables and ANOVA was used with
Bonferroni’s post-hoc analysis. Categorical variables were analyzed
using first by Fisher’s exact test for 2x4 tables (VassarStats free
online calculator developed by Richard Lowry, PhD;http://vassarstats.net/fisher2x4.html)
followed by pairwise Fisher’s exact test with Bonferroni’s correction. A
P value <0.05, after applying correction for multiple
comparisons, was considered to be statistically significant.
Inter-observer reliability was determined using Bland– Altman
methodology and expressed as bias (mean difference) and 95% limits of
agreement (2 X SD mean difference). The correlation between estimated
MPAP and mean AP was analyzed using linear regression analysis. Since
this is an exploratory study with the main purpose to determine whether
a larger study is warranted, the sample sizes were not based on power
calculation.