The role of echocardiographically assessed dynamic right ventricular functions in determination of functional capacity of heart failure

Aim: The exact mechanisms of exercise intolerance in heart failure (HF) patients are still unknown. Although HF is known as a hemodynamic syndrome, many of studies could not delineate a strong relationship between cardiac performance and symptoms. There are limited studies in literature regarding the effect of right ventricular functions on functional capacity of heart failure patients. Some previous studies had shown the effect of right ventricular functions on functional capacity. 2D speckle tracking echocardiography technique is a Doppler independent tool which enables the assessment of myocardial strain and strain rate with the help of a special software. The plasma concentration of natriuretic peptides are helpfull markers in diagnosis and treatment of heart failure. Previous studies have shown the correlation between levels of natriuretic peptides and functional capacity of heart failure patients. The 6-minute walk test (6MWT), has become a popular method of evaluation of functional capacity in the last 10 years. This test is easily performed and a reliable method. Previous studies have shown the correlation between the walking distance and peak oxygen consumption. This study was designed to investigate the correlation between 6MWT distance and right ventricular functions in class I-III heart failure patitents with ejection fraction lower than 40%. Also we investigated the correlation between echocardiographic parameters and 6MWT distance and NT-pro-BNP levels. Method: Heart failure patients with ischemic and non-ischemic etiology and with a left ventricular ejection fraction lower than 40% were included in the study. 6MWT were performed to all patients. NT-pro-BNP levels were determined. Standard two dimensional echocardiography, M-mode, Doppler and tissue Doppler echocardiographic analysis were performed for each patient. Global left ventricular longitudinal peak systolic strain (LTGS), circumferential peak systolic strain (SGS), radial peak systolic strain and right ventricular free wall longitudinal peak systolic strain parameters were calculated with the 2D speckle tracking echocardiography for each patient. Results: 50 patients with mean ejection fraction of 28,78 ± 6,0% were included in the study. 6MWT distance, 6MWT test duration and work achieved in this test were found to be well correlated with the NT-pro-BNP levels (r = -0,595, p<0,01; r = -0,699, p<0,01; r = -0,673, p<0,01 respectively). The RGS was not correlated with the NT-pro-BNP levels, however, the SGS was weakly correlated with NT-pro-BNP (r = 0,319, p<0,05), and the correlation between LTGS and NT-pro-BNP was modest (r = 0,461, p<0,01). NT-pro-BNP levels were correlated with the RV-STR (r = -0,372, p<0,01). Among all echocardiographic variables, the best correlation with NT-pro-BNP was in E/(mean-S X mean-E') and LAVI parameters (r = 0,715, p<0,01 ve r = 0,688, p<0,01, respectively). The area under curve was the highest for E/(mean-S X mean-E?) to estimate a NT-pro-BNP level greater than 900 pg/ml (AUC = 0,898, p<0,0001). In multivariate analysis which are modelled with parameters of left ventricular deformation (LTGS, RGS, SGS), left atrial volume index (LAVI) and parameters for pulmonary capillary wedge pressure estimates - the E/mean E' and E/(mean -S X mean -E?)-, the LAVI was found an independent variable in determination of NT-pro-BNP levels in two distinct models (respectively for LAVI ß =0,548, p<0,01 ; Adj-r2 = 0,448, p<0,001 and for LAVI ß = 0,569, p<0,01; Adj- r2 = 0,450, p<0,001). The best independent parameter was SGS (ß = -0,263, p = 0,028), and the second best independent parameter was RV-STR (ß = -0,271, p=0,035) in multivariate analysis to determine 6MWT distance. The independent variables for determination of RV-STR were E/(mean S X mean E?) and M-PAB respectively (for E/(mean S X mean E?) ß = 0,392, p = 0,018 and for M-PAB ß = 0,299, p = 0,027; Adj-R2: 0,357, p<0,001 respectively). NT-pro-BNP levels were found higher in patients with RV-STR lower than -18,5 %, and the difference was statistically significant. The 6MWT distance (488,2 ± 130,9 meters vs 327,9 ± 146,2 meters, p<0,01) and the work achieved in 6MWT (386,8 ± 129,9 joules vs 236,5 ± 125,7 joules, p<0,01) were higher in patients with higher RV-STR. The parameters to estimate left ventricular filling pressures, the E/ mean -E' (16,64 ± 7,91 vs 22,76 ± 7,46, p<0,01) and the E/(mean -S X mean -E?) (374,0 ± 208,4 vs 650,3 ± 267,5, p<0,01) were found lower in patients with higher RV-STR. There were no difference in RGS and SGS among groups, however the LTGS was found to be higher in patients with higher RV-STR, and the difference was statistically significant (-8,45 ± 2,59% vs -6,16 ± 2,78%, p<0,01). Discussion and conclusion: The right ventricular free wall systolic strain was found to be correlated with functional capacity and even it is found to be an independent predictor of functional capacity. In left heart failure, the left ventricular filling pressure estimates and mean pulmonary artery pressure estimates, were found independent determinants of right ventricular function. The irreversible pulmonary vascular remodelling and increase in pulmonary vascular resistance which developed secondary to chronic left ventricular pressure load may be the reason for this result