Discussion
The role of echocardiography in detecting cardiovascular abnormalities is increasing worldwide (4, 13). Considering the cost effectiveness of non-invasive echocardiography modality , it could be an alternative screening tool in detecting or excluding PHTN if it is proven to have acceptable adequacy (4). The aim of this study was to assess the properties of the hepatic vein Doppler signal as an echocardiographic parameter in detecting PHTN. Because hepatic vein is affected by RV function besides PHT; we divided our PHTN patients into two groups based on RV dysfunction, including PHTN with significant RV dysfunction and PHTN without significant RV dysfunction
The normal flow-pattern in the middle HV is phasic, in which the most predominant velocities are antegrade. Pulsed-wave Doppler assessment describes 3–4 distinct waveforms after atrial contraction: (1) large systolic antegrade wave (negative velocity) (S-wave); (2) small retrograde late systolic wave (positive velocity) (V-wave), (3) early to mid-diastolic antegrade wave (D-wave), (4) late diastolic retrograde wave (A-wave) (14).
In our study 13 cases in normal group, 16 cases in PHTN without significant RV dysfunction and 11 cases in PHT with significant RV dysfunction had all 4 distinct waveforms and 12 cases in normal group, 11 cases in PHT without significant RV dysfunction and 11 cases in PHT with significant RV dysfunction had 3 distinct waveforms (absent V wave). The findings of the current study revealed that A velocity , A/S were significantly higher in PHT group with and without significant RV dysfunction compared to normal group, while S/S+D and S/D were significantly higher just in PHT with significant RV dysfunction compared to normal group. It was previously reported that the systolic wave is diminished in PHT and therefore S is reduced. A/S, A/(S+D), AVTI/(SVTI+DVTI) were positively correlated with mPAP (3). It was previously shown that PHT group had higher A velocity ;VTI A ;VTI A/VTI S+VTI D were higher in PHTN patients compared to healthy controls (14). Inclusion of patients with PHTN with and without significant RV dysfunction in this study enabled us to evaluate the effect of RV dysfunction on PHTN.
The differences between the findings of our study and previous studies is may be due to dividing the PHT patients based on RV function and also exclude patients with severe TR(table2). Based on the findings of our study, it can be hypothesized that increase in SPAP increased RV afterload, which may lead in chamber remodeling and increased in muscle mass. Increased RV end diastolic pressure (RVEDP) is the hemodynamic consequence of RV hypertrophy. As RA pressure is not reduced at this point, the duration of backflow in IVC and the HV persists will be longer compared to the backflow across the Tricuspid valve. Therefore, a large A-wave in terms of duration and velocity is observed in HV Doppler assessment. Therefore, A/S also increases to values higher than 1 in PHTN even at early stages. This pattern was the main finding on HV Doppler assessment in PHT with and without significant RV dysfunction(table2). When RV longitudinal motion is significantly reduced, the S wave is blunted or reduced in HV Doppler with consequent re-emergence or increase in D velocity .Therefore, S/S+D and S/D could only differentiate normal PAP from PHT with significant RV dysfunction and thus may not be useful in differentiating normal SPAP from PHT without RV dysfunction that is not an issue in previous echo study. Furthermore, as evidenced by the findings of the current study, increased D and decreased S values in PHT patients with RV dysfunction magnifies the changes due to RV function and the S/D might detect significant RV dysfunction earlier compared to other echocardiographic parameters(table2).
The findings of this study revealed that A wave velocity and duration could be a predictor for PHT patients regardless of RV dysfunction although the result for the A wave duration was not statistically significant in PHT patients. It was previously reported that in PHTN patients, the peak A wave velocity significantly increases compared to healthy individuals, which was in line with the findings of the current study (7). As A velocity is a determinant of RV filling function, combination of RV dysfunction and PHTN will result in significant change in A velocity that may make it a better marker for determining RV function in PHTN patients compared to other echocardiographic parameters in the current study (table2) (15). It was previously shown that the use of parameters that are calculated based on dividing A, S, and D including A/S, A/(S+D) and AVTI/(SVTI+DVTI) could be more sensitive in detecting PHTN compared to A, S, and D alone (6, 16, 17). This finding was in line with the finding of the current study.
The findings of this study also revealed that hepatic venous systolic filling fraction had an acceptable sensitivity in detecting normal SPAP patients from PHT patients (80%), while its specificity was low (64%). Similar sensitivity and specificity were found hepatic venous systolic filling fraction in detecting normal RV function in PHT patients (table2). It was previously reported that hepatic venous systolic filling fraction less than 55% had 86% sensitivity and 90% specificity in detecting PHTN (7). The difference between the findings of this study and the finding of latter studies may be due to the effect of RV function and TR severity on echocardiographic parameters(table2). The high sensitivity of hepatic venous systolic filling fraction in detecting normal PAP indicates that this marker can be appropriate in ruling out PHTN but due to its low specificity, this marker could not be used as a diagnostic marker for PHT. There is a need for further studies to confirm these findings.