title: Quantification of Retrograde Blood Flow in the Descending Aorta Using Transesophageal Echocardiography in Comparison to 4D Flow MRI.
abstract: BACKGROUND
  Retrograde diastolic blood flow in the proximal descending aorta (DAo), which connects plaques ≥4 mm thickness with brain-supplying arteries, has previously been identified as a possible source of brain embolism. Currently, only 4D flow MRI is able to visualize and quantify potential retrograde embolization pathways in the DAo in-vivo. Hence, it was our aim to test if the extent of retrograde flow could be estimated by routine 2D transesophageal echocardiography (TEE).
  
  
  METHODS
  Forty-eight acute stroke patients were prospectively included and they underwent Doppler examinations of the transition zone between the aortic arch and the DAo using a 20 mm 2D sample volume in longitudinal section at 90-140° Doppler angle during routine TEE. Velocity-time-integrals (VTI) were studied for antegrade and retrograde velocities and the ratio (VTIratio) was calculated and correlated with the length of retrograde pathlines at that site, which were visualized using 4D flow MRI at 3-Tesla. A receiver operating characteristic (ROC) curve was used to evaluate a threshold value of VTIratio in differentiating large (≥3 cm) from small (<3 cm) retrograde flow extent.
  
  
  RESULTS
  At the TEE measurement site, the mean VTIratio was 0.53 ± 0.16 and the mean length of retrograde pathlines reaching back into the aortic arch was 3.1 ± 1.4 cm. VTIratio was an independent predictor of retrograde pathline length (r = 0.44; p = 0.002). ROC analysis identified a VTIratio threshold value of 0.6012 with a sensitivity of 0.5, a specificity of 0.92, and positive and negative predictive values of 0.84 and 0.68, respectively. Accordingly, 11 (22.91%) patients had a VTIratio cutoff value ≥0.6012 and corresponding retrograde pathline length ≥3 cm in 4D flow MRI.
  
  
  CONCLUSIONS
  TEE allows predicting the length of retrograde pathlines. Hence, it may offer a cost-effective way to investigate independent predictors of DAo flow reversal in large-scale studies. However, TEE is only of limited value as a screening tool for high retrograde flow in a clinical setting, as only ∼23% of patients can be spared 4D flow MRI, which remains indispensable for the exact assessment of individual embolization pathways from plaques of the DAo in-vivo.
authors.affiliation: Department of Neurology, University Medical Center Freiburg, Freiburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Wehrum
authors.forename: Miriam
authors.initials: M
authors.lastname: Kams
authors.forename: Felix
authors.initials: F
authors.lastname: Günther
authors.forename: Primrose
authors.initials: P
authors.lastname: Beryl
authors.forename: Werner
authors.initials: W
authors.lastname: Vach
authors.forename: Iulius
authors.initials: I
authors.lastname: Dragonu
authors.forename: Andreas
authors.initials: A
authors.lastname: Harloff
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001013:Aorta, Thoracic / Q000473:pathology / Q000503:physiopathology*; D001018:Aortic Diseases / Q000175:diagnosis / Q000503:physiopathology*; D017548:Echocardiography, Transesophageal / Q000379:methods; D005260:Female; D006439:Hemodynamics / Q000502:physiology*; D006801:Humans; D020766:Intracranial Embolism / Q000000981:diagnostic imaging*; D018810:Magnetic Resonance Angiography / Q000379:methods; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020521:Stroke / Q000503:physiopathology*