Background
Long-axis images of the inferior vena cava (IVC) have limitations as surrogates for IVC morphology in grading central venous pressure (CVP) by two-dimensional echocardiography (2DE), because of the various cross-sectional morphologies and the translational motion of the IVC induced by sniffing. On the basis of the relationship between venous pressure and compliance, it was hypothesized that the cross-sectional morphology of the IVC, which was obtained using three-dimensional echocardiography, might estimate CVP more accurately compared with standard grading by 2DE.
Methods
Sixty consecutive patients who underwent right-heart catheterization studies were prospectively enrolled. Echocardiography was performed <24 hours before catheterization. From three-dimensional data sets, a cross-section of the IVC was determined that was perpendicular to the long-axis reference of the IVC. Short diameter (SD), long diameter (LD), the ratio of SD to LD (S/L) as the sphericity index, and area were measured on this cross-sectional IVC image.
Results
CVP correlated moderately with SD ( r = 0.69, P < .001), strongly with S/L ( r = 0.75, P < .001), and modestly with area ( r = 0.47, P < .001) but not with LD ( r = 0.24, P = .17). The largest areas under the curve by receiver operating characteristic analyses to detect CVP ≥ 10 mm Hg were 0.98 (95% CI, 0.97–1.0; P < .001) for S/L, 0.83 for SD (95% CI, 0.74–0.94; P < .001), and 0.70 for area (95% CI, 0.56–0.84; P = .02). If a cutoff value of 0.69 for S/L was used, the sensitivity, specificity, and accuracy to detect CVP ≥ 10 mm Hg were 0.94, 0.95, and 0.95 and for CVP grading by 2DE were 0.59, 0.98, and 0.85, respectively. Estimations of CVP were more accurately reclassified using S/L rather than grading by 2DE (net reclassification improvement, 0.38; 95% CI, 0.31–0.44; P < .001).
Conclusions
S/L of an IVC cross-section measured using three-dimensional echocardiography may be a reliable parameter to estimate CVP compared with standard grading by 2DE.
Interest in right-sided heart failure (HF) has been increasing in the management of left-sided HF. Because volume overload of the venous vascular bed is the cause of systemic congestion in right-sided HF, central venous pressure (CVP) is used as a surrogate for intravascular volume status. In addition, CVP is an indicator of filling pressure. CVP is not only a simple hemodynamic parameter to measure, but it is also known as a determinant of clinical outcomes in patients with various cardiac diseases. Peripheral congestion, in particular renal congestion caused by increased CVP, also has been investigated as having a central role in cardiorenal syndrome in HF. Thus, as the significance of CVP assessment increases, echocardiography is being widely used to estimate CVP levels in the clinical setting because of its noninvasiveness. The current guidelines recommend estimation of CVP by using a combination of inferior vena cava (IVC) diameter and the collapse rate of the IVC with the sniff maneuver. However, findings from major studies evaluating the correlation between the IVC and CVP are controversial. Thus, we hypothesized that long-axis images of the IVC might have limitations as surrogates for IVC morphology, because the IVC is often elliptical, curved, and flat in cross-section. In addition, translational motion of the IVC caused by sniffing might be a limitation in assessing the collapse rate accurately. On the basis of the relationship between venous pressure and venous compliance, the cross-sectional morphology of the IVC might be useful to estimate CVP. In addition, three-dimensional (3D) echocardiography (3DE) might be helpful in assessing the correct cross-sectional morphology of the IVC because of limitations of two-dimensional (2D) echocardiography (2DE). Therefore, we aimed to investigate the accuracy of CVP estimation by using cross-sectional morphology parameters of the IVC obtained using 3DE compared with the general grading of CVP on 2DE.
Methods
Study Design
To assess the associations between IVC parameters and CVP, we prospectively enrolled 60 consecutive patients who underwent right-heart catheterization studies for the assessment of cardiovascular diseases at the University of Tsukuba Hospital from April 2014 to May 2016. The indications for right-heart catheterization studies were as follows: hemodynamic evaluation for decision making regarding intervention in valvular diseases or congenital heart diseases, to diagnose a cause of HF with or without right ventricular biopsy, to assess the therapeutic effects in HF or pulmonary hypertension, and to diagnose the cause of pulmonary hypertension with or without pulmonary artery angiography.
Echocardiographic studies were performed <24 hours before catheterization. The hospital ethics committee approved the research protocol, and informed consent was obtained from each subject. This study complied with the Declaration of Helsinki.
Echocardiography
Comprehensive transthoracic echocardiographic examinations were performed using a Vivid E9 system (GE Vingmed Ultrasound AS, Horten, Norway) with a variable-frequency 2.5- to 5-MHz sector transducer, and each echocardiographic parameter was measured and evaluated according to American Society of Echocardiography guidelines. Left ventricular volume, left ventricular ejection fraction, pulsed Doppler transmitral flow profiles, and tissue Doppler studies using the spectral Doppler method on the mitral annulus were assessed. Right ventricular function was assessed using tricuspid annular plane systolic excursion and fractional area change ratio. In patients with tricuspid regurgitation (TR), peak pressure gradients between the right ventricle and right atrium were measured, and the degree of TR was assessed as the ratio of the maximal TR jet area to the corresponding right atrial area; <20% was defined as mild TR, 20% to 40% as moderate TR, and ≥40% as severe TR. The velocity of flow in the hepatic veins was recorded from the subcostal window, and the hepatic systolic (S) and diastolic flow (D) velocities and S/D ratio were measured. With the patient in the supine position, IVC diameters were measured in the subcostal view at 1.0 to 2.0 cm from the junction with the right atrium. IVC diameters were measured as the inner-to-inner dimension of the IVC. The maximum diameter of the IVC and the percentage decrease in diameter during inspiration were measured. Per American Society of Echocardiography guidelines, CVP was estimated using three grades: 3, 8, and 15 mm Hg.
Three-Dimensional Echocardiography
Three-dimensional echocardiographic data sets consisting of four consecutive cardiac cycles at end-expiration were obtained using a subxiphoid approach with the patient in the supine position. In patients with atrial fibrillation, a single-beat full-volume three-dimensional echocardiographic data set was acquired. From these 3D data sets, a cross-section of the IVC was determined that was perpendicular to the long-axis reference of the IVC at 0.5 to 3 cm from the right atrium by offline analysis using commercially available software (EchoPAC PC version 104.3.0; GE Vingmed Ultrasound AS) ( Figure 1 ). On the cross-sectional image of the IVC, the short diameter (SD), long diameter (LD), cross-sectional area (CSA), and indexed CSA, calculated as IVC area divided by body surface area, were measured. The line for the LD measurement was determined by visual evaluation and corrected manually to obtain the maximum length. In addition, SD was measured on the longest line perpendicular to the direction of the line used to measure LD. The ratio of SD to LD (S/L) was calculated.
Cardiac Catheterization
Right-heart catheterization was performed via a femoral or jugular vein approach. A 7-Fr balloon-tipped Swan-Ganz pulmonary artery catheter (Baxter Healthcare, Irvine, CA) was used to measure right atrial pressure, right ventricular pressure, pulmonary artery pressure, and pulmonary capillary wedge pressure. All pressure data were measured at end-expiration, and the reported values represent the average of five to 10 cardiac cycles. The cardiac index was measured using the Fick method.
Reproducibility
Two observers independently assessed the 3D IVC parameters in 20 patients. To test intraobserver variability, a single observer analyzed the data twice on occasions separated by 1 month. To test interobserver variability, a second observer analyzed the data without knowledge of the first observer’s measurements. Reproducibility was assessed as the mean percentage error (absolute difference divided by the mean of the two observations).
Statistical Analysis
Results are expressed as number (percentage) or as mean ± standard deviation. Correlations between CVP and 3D IVC parameters were evaluated using Pearson correlation coefficients. Correlations between CVP and CVP grading by 2DE were assessed using Spearman rank correlation. We assessed the performance of the 3D IVC parameters to predict CVP ≥ 10 mm Hg using the area under the curve of the receiver operating characteristic curve.
Agreement on the diagnosis of CVP ≥ 10 mm Hg between the catheterization data and the S/L ratio and American Society of Echocardiography guideline–based CVP of 15 mm Hg was assessed using the Cohen κ coefficient.
The incremental effects of the S/L ratio to predict CVP ≥ 10 mm Hg were assessed using net reclassification improvement (NRI), which was calculated as follows:
NRI = [ P ( up | D = 1 ) − P ( down | D = 1 ) ] − [ P ( up | D = 0 ) − P ( down | D = 0 ) ] ,
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