CORRELATION OF PULMONARY CAPILLARY WEDGE PRESSURE CALCULATED BY ECHO-DOPPLER WITH INVASIVE MEASUREMENT BY SWAN GANZ CATHETER IN POST CORONARY ARTERY BYPASS GRAFT PATIENTS

The present study was conducted to correlate PCWP estimated by Doppler Echocardiography with that obtained by Swan-Ganz catheter in patients with post coronary artery bypass graft surgery and to evaluate the feasibility and accuracy of Doppler Echocardiographic data. The present study provides evidence that in patients with coronary artery disease who underwent elective CABG surgery, PCWP can be reliably and accurately estimated by combining Doppler Echocardiographic variables of mitral flow and Tissue Doppler imaging and the relationship between E/Ea ratio and measured PCWP by Swan Ganz catheter was the strongest of all Doppler variables determined. 0.311, p = 0.069). The E/FPV ratio > 2 for predicting an elevated PCWP (> 15mmHg ) in post CABG patients had good sensitivity (96%) and specificity (89%) . It should be determined in conjugation with E/Ea ratio for the assessment of both diastolic function and filling pressure. It was found that PCWP determined by different Echocardiographic equations had significant positive correlation with PCWP measured by Swan-Ganz Catheter, but additional studies are required to identify the accuracy and physibility of Echocardiographic technique in other category of patients. This simple, repeatable, readily available noninvasive tool may reduce the need for right heart catheterization in acutely ill patients and may provide us with easy bedside method of estimating and monitoring PCWP.

The Swan-Ganz catheter can be placed at the bedside within few minutes even in critically ill patients. Although placement of these catheters is not difficult, some training and experience are required to avoid complications and for proper interpretation of the haemodynamic data.
In non-sedated, spontaneously breathing cardiac patients, doppler indices derived from mitral and pulmonary venous flows obtained using transthoracic Echocardiography have been shown to be acceptable estimation of pulmonary capillary wedge pressure. More recently, the flow propagation velocity of early mitral inflow measured by Color Mmode Doppler and the ratio between the early mitral inflow measured by conventional doppler and the displacement of the mitral annulus measured by Tissue Doppler imaging have been shown to accurately reflect PCWP in cardiac patients. Therefore, a non-invasive technique that could simply and reliably predict filling pressures would be invaluable not only in the diagnosis, but more importantly in tailoring therapy.
The present study therefore is aimed to assess, whether pulmonary capillary wedge pressure measured from a pulmonary artery catheter (Swan-Ganz) could be accurately predicted using Echocardiographic indices derived from transthoracic conventional Doppler and Tissue Doppler imaging in a series of post coronary artery bypass graft surgery patients.
A Colour M-Mode Doppler image of the left ventricular filling inflow in early diastole was obtained with an aliasing velocity set between 50 and 75% of velocity of early mitral (E) filling. The mitral inflow was recorded 4cm into the left ventricular cavity from the plane of the mitral valve (annulus). The flow propagation velocity of mitral flow in early diastole was calculated by using a slope caliber. Doppler tissue imaging (DTI) longitudinal velocities of mitral annulus were recorded with 5mm sample volume placed at the junction of septal and mitral annulus, utilizing the technique described by Brun et al. Doppler derived pulmonary artery systolic pressure (PASP) was estimated from tricuspid regurgitation velocity according to modified Bernoulli's equation and cut of value of 35mmHg was set to identify patients with pulmonary hypertension. All Echocardiographic measurements were averaged over three consecutive beats. The ultrasound beam was placed as parallel as possible to the mitral annulus. All pulse and

Statistical Analysis
The numerical data obtained from this study was analyzed and significance of differences was estimated by using statistical methods. Results are reported as frequencies, percentages, means and standard deviations (SD) as applicable. Pearson correlation co-efficient was used to measure the relationship between catheter derived PCWP and Echocardiographic variables. Stepwise multiple linear regression analysis was used to estimate the relation between parameters obtained by Doppler Echocardiography examination and PCWP. The graphical representations, correlation tests and Pearson correlation coefficient were employed to establish the relationship between catheters derived PCWP.

Discussion:-
Insertion of pulmonary artery catheter (Swan-Ganz) is invasive procedure and has multiple known complications. Thus if Echocardiographic estimation of PCWP is accurate and comparable, it would be very useful in managing post CABG patients in ICU. In the present study, the relationship between E/Ea ratio and PCWP was the strongest of all Doppler variables measured. A statistically significant positive correlation of E/Ea ratio (r = 0.954) was observed with catheter derived PCWP (P<0.001). Also, the pulmonary capillary wedge pressure calculated from equation1 by using E/Ea ratio (PCWP Ea ) had significant positive correlation with measured PCWP (r = 0.918, P < 0.001). But the relationship between peak early diastolic wave velocities (E) and measured PCWP by Swan-Ganz was not statistically significant (r = 0.311, p = 0.069) in our study.
Firstenbers M. S. et. al. (2000) found in their study that in healthy volunteers, the peak velocity of early mitral flow (E) is the best predictor of an elevated PCWP. But the peak E velocity increases with preload and decreases with impaired relaxation and tachycardia.
In spontaneously breathing cardiac patients, tachycardia and impaired left ventricular relaxation are frequently observed acting as confounding factors on E, which is no longer an accurate predictor of elevated left ventricular filling pressure. These were the findings of the study conducted by Ommen S. R. et. al. (2000) and similar findings were observed in the present study.
Several investigators have shown that the E/Ea (E/E') relationship is valid for determining filling pressures in various patients population with underlying cardiac disease similar to the present study group. Nagueh (1997) and colleagues have validated the relationship between E/E' and measured PCWP in patients with either impaired or pseudonormal relaxation or with sinus tachycardia.
Sundereswaran et. al. (1998) studied the post heart transplant patients for estimation of left and right ventricular filling pressures by echocardiography and correlated with measured PCWP. He concluded that E/E' ratio was best correlated with invasive measurement for PCWP.
The E/Ea ratio correlation with PCWP was also validated in coronary artery disease with normal LV systolic function and valvular heart disease. Diwan A et. al. (2005) studied the patients with mitral valve disease and found the positive correlation between TE -Ea (interval between onset of mitral E and annular early diastic velocity (Ea) by Tissue Doppler) and E/E' ratio for calculation of PCWP.
Thus the present study findings of strongest correlation of measured PCWP with E/Ea ratio are consistent with various previous studies.
In the present study, an attempt was also made to determine the sensitivity and specificity of E/Ea ratio below 8 and above 15 for predicting the pulmonary capillary wedge pressure.

Conclusion:-
The present study provides evidence that in patients with coronary artery disease who underwent elective CABG surgery, Pulmonary Capillary Wedge pressure can be reliably and accurately estimated by combining Doppler Echocardiographic variables of mitral flow and Tissue Doppler imaging. In the present study, the relationship between E/Ea ratio and measured PCWP by Swan Ganz catheter was the strongest of all Doppler variables determined. E/Ea ratio < 8 indicates normal PCWP and E/Ea ratio > 15 indicates elevated PCWP. There was no statistically significant correlation between peak E wave velocities and measured PCWP by Swan-Ganz catheter (r = 0.311, p = 0.069). The E/FPV ratio > 2 for predicting an elevated PCWP (> 15mmHg ) in post CABG patients had good sensitivity (96%) and specificity (89%) . It should be determined in conjugation with E/Ea ratio for the assessment of both diastolic function and filling pressure. It was found that PCWP determined by different Echocardiographic equations had significant positive correlation with PCWP measured by Swan-Ganz Catheter, but additional studies are required to identify the accuracy and physibility of Echocardiographic technique in other category of patients. This simple, repeatable, readily available noninvasive tool may reduce the need for right heart catheterization in acutely ill patients and may provide us with easy bedside method of estimating and monitoring PCWP.