The cardiac transit time measured from dynamic lung perfusion scan correlates with right heart hemodynamics: comparison with invasive catheterization and doppler echocardiography

Objectives: Lung ventilation-perfusion (V/Q) scan plays an important role in the management of pulmonary hypertension (PH) patients. It reliably excludes a potentially curable disease, the chronic thromboembolic pulmonary hypertension (CTEPH). The imaging of tracer transit through the heart during lung perfusion scan may provide valuable information on right heart hemodynamics. The aim of this study is to calculate the cardiac transit time during the flow phase of lung perfusion scan and to correlate the result with echocardiography and invasive catheterization.

Methods: We identified 62 consecutive patients who received doppler echocardiography (DE) to rule in PH, V/Q scan to exclude CTEPH, and right heart catheterization (RHC) to confirm the diagnosis. The dynamic flow images were acquired by a dual-head gamma camera during Tc-99m macroaggregated albumin injection. Three regions of interest were manually drawn on superior vena cava (SVC), pulmonary artery (PA), and lung; and three time-activity curves were generated by using the geometric mean of anterior and posterior projections. We applied the continuous-time Markov chain to model the tracer transit from SVC to PA. The lung activity was used for background correction. Iterative deconvolution was performed to estimate right heart transit function. The resulting cardiac mean transit time (CMTT) was compared with tricuspid / pulmonary regurgitation severity from DE, and was correlated with mean pulmonary artery pressure (mPAP) / pulmonary vascular resistance (PVR) from RHC.

Results: Our algorithm successfully modeled the right heart transit function for all of the scans. The CMTT was 2346±1214 ms (ranged from 661 ms to 6528 ms) in this group of patient. The CMTT was significantly higher for patients with moderate to severe tricuspid regurgitation (2732 ms vs. 1593 ms, p<0.001) or moderate to severe pulmonary regurgitation (2568 ms vs. 1508 ms, p<0.001). The CMTT correlated moderately with mPAP (r=0.570, p<0.001). A strong correlation was observed between CMTT and PVR (r=0.765, p<0.001).

Conclusions: The right heart transit time can be calculated from the flow phase of lung perfusion scan, and it correlates well with right heart hemodynamics measured by DE and invasive RHC. The dynamic flow V/Q scan may allow one-stop-shop evaluation of both pulmonary thromboembolic disease and right heart hemodynamics.

• Download figure
• Open in new tab
• Download powerpoint