Echocardiographic study was done using the Sonoscape SI-8000 Machine in the LUTH cardiovascular laboratory using 3.5 MHz transducer probe. The subjects laid in the left
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decubitus position and the researcher performed a 2 Dimensional (2D), 2D directed M-mode and Doppler transthoracic echocardiography in parasternal, apical and subcostal views on all 240 participants in the study.
2D-directed M-mode measurements were done in accordance with the recommendations of the American Society of Echocardiography.113 M-mode measurements at aortic valve level from the parasternal long axis view (PLAX) were: left atrial diameter (LAD), aortic root diameter (AO), right ventricular outflow tract (RVOT) diameter. M-mode measurements at mitral valve tip level were: left ventricular end systolic and diastolic diameters (LVESD, LVEDD), right ventricular end diastolic diameter (RVDD), right ventricular free wall thickness, left ventricular wall thickness consisting of interventricular septal thickness (IVS) and posterior wall thickness (PWTd) at end diastole and E point septal separation (EPSS).
LV ejection fraction (LVEF) and fractional shortening were also derived by the menu already preset.
ECHOCARDIOGRAPHY DIAGNOSTIC VIEWS AND MEASUREMENTS
PAH affects right heart function/parameters/variables and its diagnosis requires exclusion of left heart dysfunction as a cause of Pulmonary Hypertension. This study was essentially a study of selected right heart variables with measurement of left heart variables to exclude left heart dysfunction. Selected right heart variables include ERV, RVOT, TAPSE, RAA, FAC, TR Vmax, RVOT-AT, RAP and MPI. These variables assess right heart function. TR Vmax is a diagnostic marker of PAH while TAPSE and RVOT-AT are surrogate markers of PAH. RAP is utilised in calculation of Pulmonary Hypertension. FAC has been shown to correlate with right ventricular ejection fraction. MPI is an assessment of ventricular function which utilises systolic and diastolic parameters in its measurement.
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(1) Peak tricuspid regurgitant velocity (TR Vmax): This is a reflection of the pressure difference between the right ventricle (RV) and right atrium (RA). It was obtained by performing a colour doppler guided continuous wave (CW) doppler on the regurgitant jet of the tricuspid valve in the apical 4 chamber (A4CH) view, right ventricular inflow tract view and parasternal short axis view of the tricuspid valve. The highest velocity obtained from any of these views was selected. TR Vmax cut off for this study was ≥ 2.9 m/s.62
(2) Tricuspid regurgitant pressure gradient (TR PG): Also a reflection of pressure difference between the RV and RA was derived from the formula: 4 x (TR Vmax)2 = TR PG.62 This calculation was pre-set in the machine.
(3) Right atrial pressure (RAP): This was derived from the inferior vena cava (IVC) diameter and its variation with respiration. The long axis of the IVC was visualized in the subcostal view. IVC diameter was measured by 2D-guided M-mode measurement just distal to the junction of the hepatic veins which lie approximately 0.5-3.0cm to the ostium of the right atrium.155 Two IVC measurements were obtained. IVC max at end expiration and IVC min after the patient was asked to sniff. See Appendix IV for the guide that was used in calculating the RAP.32,113
NB: PASP ≈ RVSP = 4(TR Vmax)2 + RAP (in the absence of pulmonary stenosis). [PASP:
pulmonary artery systolic pressure; RVSP: right ventricular systolic pressure; TR Vmax:
tricuspid regurgitant maximal velocity]
A cut off value of PASP > 36mmHg suggesting PH was employed in this study based on ESC 2009158 and ASE2010159 recommendations. These were the prevailing guidelines during the planning and execution of this study. However, the recently published 2015 ESC guideline has de-emphasized the use of PASP and suggests simply quoting the maximum TR-jet velocity.62
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This method of using TTE derived PASP was used by Chillo et al,70 ferrand et al,72 Owusu et al32 and Byer et al68 in their studies on PAH in HIV positive subjects.
Median values of PASP and TR Vmax of the controls were also obtained and can be used as our local values.
(4) Right ventricular outflow tract acceleration time (RVOT AT): This is a surrogate measure of pulmonary artery pressure (PAP) measured from onset of flow to peak velocity. This measurement was done in the parasternal short axis (PSAX) view with the pulse wave (PW) Doppler sample volume placed in the (RVOT). Normal RVOT AT for this study was >110ms. Values lower than 105ms are highly suggestive of PH.113,118,156
(5) Left ventricular mitral E and A157 (LV M E/A): Transmitral pulse wave Doppler velocity measurements were obtained with a 2mm sample volume placed at the tips of the mitral valve leaflets to assess peak E (early diastolic), A (late diastolic) velocities and E wave deceleration time (DT).
(6) LV Isovolumetric relaxation time157 (LV IVRT): Time between closure of the aortic valve and opening of the mitral valve. IVRT was also measured from an apical 5 chamber view with the sample volume placed midway between the aortic and mitral valves.
See Appendix V for the diastolic pattern used in this study.
(7) Myocardial performance index (MPI): Myocardial Performance Index, also known as Tei Index,160 is a combination of systolic and diastolic measurements of IVCT + IVRT /RVOT ET. Two different views were obtained for the determination of MPI - the apical four-chamber view for the tricuspid inflow pattern and the parasternal short axis right ventricular outflow tract view for the determination of ejection time.
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The normal range for RV MPI is 0.28-0.33.113, 160-161 It is relatively unaffected by heart rate, loading conditions or the presence and the severity of tricuspid regurgitation. In patients with idiopathic pulmonary arterial hypertension, the index correlates with symptoms.
(8) RV tissue Doppler investigation (RV TDI): This is a measure of RV longitudinal diastolic function. Measured in the A4CH view using PW tissue Doppler investigation (TDI). The sample volume was placed at the basal lateral RV myocardium and measurement taken at diastole. Values <10 cm·s−1 was diagnostic of right ventricular diastolic dysfunction.42
(9) Left Ventricular tissue Doppler investigation (LV TDI): This is a measure of LV diastolic function. Measured in the A4CH view using PW tissue Doppler investigation (TDI). The sample volume was placed at the basal lateral wall of LV myocardium and measurements taken. Values <10 cm·s−1 were diagnostic of left ventricular diastolic dysfunction.42
(10) Right atrial area (RAA): RAA was obtained by tracing the right atrial endocardium in systole from the annulus, along the free wall to the apex, and then back to the annulus, along the interventricular septum in the A4CH view. Normal is < 20cm2.42
(11) Left atrial area (LAA): LAA was also obtained by tracing the left atrial endocardium in systole from the annulus, along the free wall to the apex, and then back to the annulus, along the interventricular septum in the A4CH view. Normal is < 20cm2.42 (12) Right ventricular fractional area change (RV FAC): Right ventricular fractional area
change (FAC) was calculated as follows:
RV FAC (%) = (AED – AES) / AED X 100
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Where AED is end-diastolic area and AES is end-systolic area, measured from the apical four chamber view. FAC was obtained by tracing the RV endocardium both in systole and diastole from the annulus, along the free wall to the apex, and then back to the annulus, along the interventricular septum. Normal: 32 – 60. Values < 32 indicate reduced RV systolic function.113,164,165
(13) Left ventricular end-diastolic dimension (LVeDD) (cm): vertical distance from the left side of the interventricular septum to the endocardium of the left ventricular posterior wall at end of diastole measured in the PLAX.113
(14) Septal wall thickness (IVS): vertical distance between right and left septal surfaces at end diastole and was measured in the PLAX.113
(15) Left ventricular end-systolic dimension (LVeSD) (cm): vertical distance measured from the left side of the interventricular septum to the endocardium of the left ventricular posterior wall at end of systole (peak downwards motion).113
(16) Tricuspid annular plane systolic excursion (TAPSE): This is a measure of RV longitudinal systolic function. The measurement was taken in the A4CH view with the M mode cursor placed across the lateral tricuspid annulus and the total excursion measured. Normal TAPSE was taken as >1.5mm.113
(17) RV free wall thickness: Vertical distance between right and left surfaces of the anterior free wall was measured at end diastole in the PLAX. Values > 0.5 cm was diagnostic of RV hypertrophy.160
42 3.8 DATA ANALYSIS
Data was analysed with the statistical package for social sciences (SPSS) version 16.0.
Normally distributed numerical data were presented as means and standard deviations, while the skewed data were expressed as medians and ranges. Categorical variables were presented as proportions. Means were compared using Students T test or the analysis of variance (ANOVA) or Kruskal Wallis test when not normally distributed. Categorical variables were compared using the chi-square test or the Fisher’s exact test when cell counts were less than 5.
Correlation analyses were done to demonstrate relationship between PASP and specific clinical and echocardiograhic variables. Pearson’s correlation was performed for normally distributed variables. Spearman’s rank correlation was employed for variables not normally distributed.
Multiple linear regression analyses were performed in order to determine the clinical and echocardiographic parameters that were independently associated with PASP amongst the study population. A P value ≤ 0.05 was taken as statistically significant.
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CHAPTER FOUR RESULTS