1. Among patients with suspected pulmonary artery hypertension, vortical blood flow measurement by magnetic resonance (MR) imaging agreed closely with direct pressure measurement by during right heart catheterization.
2. The duration of vortical blood flow corresponded linearly with the degree of pulmonary artery hypertension and served as a specific and non-invasive method for its detection.
Evidence rating: 3 (Average)
Study Rundown: Patients with suspected pulmonary arterial hypertension (PAH) often undergo right heart catheterization (RHC) to directly evaluate pulmonary artery (PA) pressure, the current gold standard in diagnosis. Given the risks and invasive nature of RHC, non-invasive techniques such as echocardiography are often used as surrogates for the evaluation of right heart pressure but are limited by significant variability in interpretation and performance. Cardiac MR imaging represents a diagnostic alternative to echocardiography in the evaluation and diagnosis of PAH, and is associated with a high sensitivity and specificity in the evaluation of other cardiac conditions. Patients with PAH have altered flow through their PA as a result of the increased pressure, which can be characterized by vortical blood flow. In this study, patients who had or were suspected of having PAH and had undergone RHC were evaluated with cardiac MR imaging to evaluate vortical flow parameters. Two radiologists characterized both the presence and duration of this flow while blinded to the results of the catheterizations. Flow parameters were then compared against the known RHC values, specifically the mean pulmonary artery pressure (mPAP). The results suggested a strong linear correlation between the duration of the vortical flow and an increase of mPAP, suggesting that PA vortical flow may be a useful, noninvasive diagnostic surrogate among patients with suspected PAH. This study was limited by its relatively small size and the heterogeneity of PAH causes in the study population, which may have affected the type of blood flow observed in the PA and possibly increased the variability in characterization of blood flow in patients with different PAH etiologies. Future studies with a larger cohort of these types of patients should be conducted to verify the independent relationship between vortical flow and PAH, regardless of its underlying etiology.
In-Depth [prospective cohort]: This study prospectively enrolled a total of 145 patients (mean age 60 years ± 12) with suspected PAH to undergo cardiac MR imaging for the characterization of vortical blood flow within the main pulmonary artery. All imaging was conducted after technically successful right heart catheterization for direct measurement of pulmonary artery pressure, which served as the reference standard for PAH diagnosis. Velocity fields were computationally derived from the cardiac MRI imaging and analyzed by two radiologists who were blinded to the RHC results. In each patient, the presence or absence of vortical blood flow on cardiac MR imaging was noted; when present, the duration of vortical flow was also determined. There was no bias between readers and an interobserver variability of 3%.
A strong, positive correlation was found between the linear model of mPAP and vortical flow duration, with a threshold mPAP value for the appearance of vortical flow of 16.0 mmHg (95% CI: 14.9, 17.1) and a linear increase in the vortical flow time with increasing mPAP. Vortical flow that lasted longer than 14.3% of the cardiac cycle positively identified PAH with a sensitivity of 97% and a specificity of 96%; a value below 14.3% indicated the presence of borderline elevated mPAP. The linear model of mPAP versus flow time could not be validated for extremely high values of mPAP given the low the number of available cases and increased complexity in flow patterns at higher pressures.
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