In pulmonary arterial hypertension (PAH), increased vascular resistance causes functional and structural changes in the right ventricle (RV), ultimately leading to right heart failure and death. Predictors of patient survival include RV cardiac index (RVCI) and pulmonary vascular resistance (PVR). First-pass contrast bolus hemodynamics, such as cardiopulmonary transit time (PTT), full-width-half-maximum (FWHM), and time-to-peak, have been associated with left ventricular (LV) function; however, their relation to RV function and pulmonary hemodynamics as well as their significance in PAH have not been investigated.
To evaluate first-pass contrast bolus hemodynamic parameters in relation to biventricular function and pulmonary hemodynamics in patients undergoing right heart catheterization (RHC) for known or suspected PAH.
43 patients (36 females, 58.7 years) underwent RHC and 3T cardiac MRI on the same day. 32 were confirmed to have PAH (mPAP 40 [29-49] mmHg), 11 did not have PAH (mPAP 17 [15-20] mmHg). 18 age- and gender-matched healthy volunteers were included.
For evaluation of bolus hemodynamics, a 1:10 diluted contrast bolus (0.0025ml/min/kg) of gadopentetate dimeglumine was administered intravenously, and a short-axis saturation-recovery GRE slice was acquired in the proximal third of both ventricles over 40 heartbeats with one image per beat. For analysis, two regions of interest were drawn in the right and left ventricular cavities, and time-intensity curves were generated. From these curves, PTT, FWHM, and time-to-peak were calculated (Figure 1).
Figure 1. ROI Placement and Time-Intensity Curves. Short-axis saturation-recovery GRE image (A) demonstrates regions of interest placed in the right (red) and left (green) ventricular cavities. Time-intensity curves (B) illustrate the passage of the contrast bolus through the regions of interest and signify the calculated parameters; peak-to-peak cardiopulmonary transit time, full-width-half-maximum (FWHM), and time-to-peak (TTP)
Right-to-left-ventricular PTT, LV FWHM, and LV time-to-peak for PAH patients (8.2s, 8.2s, 4.8s) were significantly longer than for non-PAH (6.5s, p=0.006; 5.0s, p=0.01; 3.6s, p=0.01) and control subjects (6.4s, p=0.0003; 5.2s, p=0.0004; 3.2s, p<0.0001) (Table 1). There were significant correlations of all three parameters with pulmonary hemodynamics and biventricular function and structure (Table 2). In linear regression analysis, including PVRI, ventricular mass index (VMI), and CI as covariates, PTT was predicted by RVCI and VMI, while FWHM and time-to-peak were predicted by PVRI. In receiver operator characteristics (ROC) analysis for transit time to distinguish between PAH patients with and without right heart failure (RVCI <2.2L/min/m2) the area under the ROC curve was 0.82 with a sensitivity of 100% and specificity of 63.6% for a threshold of 8.1s.
While right-to-left-ventricular PTT in PAH patients is mainly predicted by right ventricular cardiac function and biventricular remodeling, time-to-peak and FWHM are associated with pulmonary vascular resistance. Their predictive value regarding patient prognosis warrants further investigation.