Pulmonary transit time measurement by contrast-enhanced ultrasound in left ventricular dyssynchrony

Abstract

Background: Pulmonary transit time (PTT) is an indirect measure of preload and left ventricular function, which can be estimated using the indicator dilution theory by contrast-enhanced ultrasound (CEUS). In this study, we first assessed the accuracy of PTT-CEUS by comparing it with dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Secondly, we tested the hypothesis that PTT-CEUS correlates with the severity of heart failure, assessed by MRI and N-terminal pro-B-type natriuretic peptide (NT-proBNP).

Methods and results: Twenty patients referred to our hospital for cardiac resynchronization therapy (CRT) were enrolled. DCE-MRI, CEUS, and NT-proBNP measurements were performed within an hour. Mean transit time (MTT) was obtained by estimating the time evolution of indicator concentration within regions of interest drawn in the right and left ventricles in video loops of DCE-MRI and CEUS. PTT was estimated as the difference of the left and right ventricular MTT. Normalized PTT (nPTT) was obtained by multiplication of PTT with the heart rate. Mean PTT-CEUS was 10.5±2.4s and PTT-DCE-MRI was 10.4±2.0s (P=0.88). The correlations of PTT and nPTT by CEUS and DCE-MRI were strong; r=0.75 (P=0.0001) and r=0.76 (P=0.0001), respectively. Bland-Altman analysis revealed a bias of 0.1s for PTT. nPTT-CEUS correlated moderately with left ventricle volumes. The correlations for PTT-CEUS and nPTT-CEUS were moderate to strong with NT-proBNP; r=0.54 (P=0.022) and r=0.68 (P=0.002), respectively.

Conclusions: (n)PTT-CEUS showed strong agreement with that by DCE-MRI. Given the good correlation with NT-proBNP level, (n)PTT-CEUS may provide a novel, clinically feasible measure to quantify the severity of heart failure.

Clinical trial registry: NCT01735838.

Keywords: B-type natriuretic peptide; cardiac magnetic resonance imaging; contrast echocardiography; heart failure; pulmonary transit time.

Figure 1

Overview of a DCE-MRI (A) and CEUS (B) in one patient. A bolus of gadolinium (A) and UCA, SonoVue 10μLmL⁻¹ (B), passed through the right and left ventricles (RV and LV). ROIs are drawn in the right (blue ROI (A) and red ROI (B)) and left ventricle (green ROI (A) and yellow ROI (B)), and signal or acoustic IDCs are estimated within the ROIs, expressed in panels C and D. The raw IDC (dotted lines) are fitted to the LDRW model (straight lines), and MTT (dashed vertical lines) of the contrast bolus in both ventricles is estimated. The difference in MTT is referred to as the pulmonary transit time. AU, arbitrary units.

Figure 2

The correlation between PTT-MRI and mean PTT-CEUS of three measurements by CEUS (A). Correlation between both techniques for nPTT (B). The dotted lines indicate the 95% CIs.

Figure 3

Bland–Altman analysis of PTT-CEUS and PTT-MRI (A). Solid line is the mean difference (bias); dashed lines are the limits of agreement (1.96 s.d.). Bland–Altman analysis of nPTT-CEUS and nPTT-MRI (B).

Figure 4

Correlations of nPTT by CEUS and left ventricular end-diastolic volume (LVEDV) index (A), left ventricular end-systolic volume (LVESV) index (B), stroke volume (SV) nonsignificant (C), ejection fraction (EF) (D), and NT-proBNP (E), and correlation of nPTT by DCE-MRI with NT-proBNP (F). Dotted lines represent 95% CI for the predicted values.