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Counter-clockwise vortical blood flow in the main pulmonary artery in a patient with patent ductus arteriosus with pulmonary arterial hypertension: a cardiac magnetic resonance imaging case report
© The Author(s). 2016
Received: 14 January 2016
Accepted: 3 August 2016
Published: 8 August 2016
In patients with pulmonary hypertension (PH), duration of vortical blood flow along the main pulmonary artery enables estimation of the mean pulmonary arterial pressure (mPAP) non-invasively. It remains to date not known, if this method is applicable in patients with pulmonary arterial hypertension (PAH) and abnormal aortic-to-pulmonary shunting.
The present case analyzes the effect of a patent ductus arteriosus (PDA) on pulmonary artery flow patterns in PAH (mPAP from right heart catheterization, 75 mmHg). PH-associated vortical blood flow, which is typically observed rotating in a clockwise direction when viewed in right ventricular outflow tract orientation, was found nested in PDA left-to-right shunting. Even though rotating counter-clockwise, duration of vortical flow translated into correct non-invasive mPAP estimate.
This case indicates that PH-associated vortex rotation is not restricted to clockwise direction, and that vortex-based estimation of elevated mPAP might also be feasible in patients with PAH and PDA.
In patients with pulmonary hypertension (PH) without abnormal aortic-to-pulmonary shunting, PH is associated with vortical blood flow along the main pulmonary artery, whose duration is linearly related to elevated mean pulmonary arterial pressure (mPAP) [1, 2]. Typically, vortex formation takes place at the posterior wall of the main pulmonary artery, and the vortex rotates in a clockwise direction when viewed in the right ventricular outflow tract (RVOT) orientation [1, 3–5].
Pulmonary arterial hypertension (PAH) is a complication in patients with patent ductus arteriosus (PDA), and the retrograde blood flow in the main pulmonary artery caused by left-to-right shunting via the PDA might modify flow patterns typically observed in PH . Potentially, it might affect the presence of a vortex per se, the vortex location, the rotational direction, and also the relationship between vortex duration and mPAP. To approach these issues, pulmonary arterial blood flow patterns were analyzed in a patient with PDA and PAH.
Preterm birth (35th week of pregnancy); bronchopulmonary dysplasia; severe obstructive pulmonary disease
Echocardiography: enlarged RV and RA; normal LV and LA; small PDA with left-to-right shunt
Aortic angiography: PDA diameter, 3.5 mm
Right heart catheterization and PDA trial occlusion: mPAP, 70 mmHg; RV pressures did not significantly decrease after trial occlusion
Echocardiography: RV/LV/PV diameter, 24/55/34 mm; maximal pressure gradient across PDA, 16 mmHg
2006 – 2014:
Bosentan therapy and close meshed therapy monitoring
Echocardiography: RV/LV/PV diameter, 28/54/35 mm; maximal pressure gradient across PDA, 16 mmHg
Right heart catheterization and PDA trial occlusion: PAP, 94/53/70 mmHg; RAP, 4 mmHg. RV pressures did not significantly decrease after trial occlusion
Echocardiography: RV/LV/PV diameter, 24/59/39 mm
Right heart catheterization: see case presentation. Clinical classification: PAH associated with congenital heart disease (PDA) according to positive treatment effect of Bosentan
Cardiac MR: see case presentation
MR 4D flow data were acquired in free breathing, covering the heart, pulmonary artery and aorta with gapless slices of a retrospectively ECG-gated, segmented, two-dimensional spoiled gradient-echo-based cine phase-contrast sequence with three-directional velocity encoding in RVOT orientation. Velocity fields were calculated, visualized and analyzed by dedicated prototype software (4D Flow V2.4, Siemens Healthcare, Erlangen, Germany) .
Irrespectively of the underlying etiology of PH, vortical blood flow along the main pulmonary artery has been identified as a marker of elevated mPAP [1–3]. The formation of this vortical flow has been attributed to the appearance of a thickened boundary layer in the main pulmonary artery caused by increased pulmonary vascular resistance, reduced compliance and altered pulse wave reflection [1, 3]. Owing to the curvature of the vessel this thickened boundary layer is located at the posterior wall of the main pulmonary, which leads to the formation of a clockwise rotating vortex.
In the present case of PDA and PAH, vortex formation is observed at the anterior wall of the main pulmonary artery and its rotational direction is counter-clockwise. This flow topology has not been described neither in PH in general, nor in PAH in particular [1–5, 9]. It could be speculated that the PDA jet which is pressing the pulmonary arterial forward flow against the posterior vessel wall impedes vortex formation in this region. Jet stream boundaries on the other hand give generally rise to zones of turbulent mixing ; PDA jet could therefore favor vortex formation at the anterior wall of the main pulmonary artery.
In PH patients without PDA, duration of vortical blood flow in the main pulmonary artery was found to be closely related to mPAP . Notably, mPAP calculated from the duration of vortical blood flow in the present case revealed good agreement with the mPAP measured by RHC. It could therefore be conjectured that the observed counter-clockwise rotating vortex is similarly related to inadequate release of blood from the main pulmonary artery into the pulmonary vasculature as the clockwise rotating vortex in patients with elevated mPAP without PDA. This would mean that the vortex – irrespectively of its rotational direction – represents a mechanism of “kinetic energy storage”, counteracting the increased vascular resistance and the reduced compliance in PH. Clinical studies including patients with PDA with/without PAH and with/without Eisenmenger’s syndrome are needed to gain better insights into the complex hemodynamics of PDA with PAH.
The current case indicates that vortex-based estimation of elevated mPAP might be feasible in patients with PDA. However, this case also shows that in a patient with PDA, the location and direction of vortical blood flow may differ from those typically seen in patients with PH without PDA.
mPAP, mean pulmonary arterial pressure; MR, magnetic resonance; PAH, pulmonary arterial hypertension; PDA, patent ductus arteriosus; PH, pulmonary hypertension; RHC, right heart catheterization; RVOT, right ventricular outflow tract; tvortex, period of existence of vortical blood flow
The authors thank Ada Muellner, MSc for reviewing the manuscript.
The study has received funding from the Styrian government, Department 8 for Science and Research (grant number A3-16.R-8/2012-8). G.A. was supported by the Oesterreichische Nationalbank, Anniversary Fund (grant number 141223).
Availability of data and materials
All data are available from the corresponding author.
UR and GR drafted the manuscript and acquired and analyzed 4D flow data. GA and MF performed and reported the cardiac MRT investigation; GK and HO performed and evaluated RHC. AG and AFS provided 4D Flow software for image analysis and visualization. All authors read and approved the final manuscript.
G.R., A.G., and A.F.S. are employed by Siemens Healthcare. All authors declare that they have no conflicts of interest relevant to this manuscript.
Ethics approval and consent for publication
Patients presented in this report were investigated within a prospective study approved by the local ethical review board (ClinicalTrials.gov Identifier NCT01725763). Written informed consent was obtained. A copy of the written consent is available for review by the Editor-in-Chief of this journal.
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