Elevated Flow Velocity in Transcranial Doppler: Discrepancies Between Actual Vasospasm Locations and Flow Measurements.

BACKGROUND

Transcranial Doppler (TCD) is widely used to predict cerebral vasospasm in patients with subarachnoid hemorrhage by monitoring mean flow velocity (MFV) in major cerebral arteries. However, its accuracy in identifying specific arteries affected by vasospasm remains unclear. This study investigates the correlation between elevated MFV and the actual location of vasospasm, considering the influence of adjacent artery vasospasms.

METHODS

We conducted a retrospective observational study of patients with subarachnoid hemorrhage who underwent transcranial Doppler monitoring and subsequent angiography between March 2017 and December 2020. The primary exposure was the maximum MFV recorded in the middle cerebral artery (MCA), anterior cerebral artery (ACA), and intracranial internal carotid artery (ICA). The primary outcome was the presence and location of vasospasm, confirmed by angiography. The Kruskal-Wallis test compared MFV distributions among vasospasm groups, and logistic regression evaluated associations between MFV values and vasospasm presence in each artery.

RESULTS

Among 367 hemispheres, vasospasm was present in 16%, with 7% involving a single artery and 8% involving multiple arteries. MFV increased not only in arteries directly affected by vasospasm but also in adjacent arteries (P<0.001, Kruskal-Wallis test). MCA vasospasm was associated with increased MCA MFV (odds ratio [OR], 1.036 [95% CI, 1.019-1.053], P<0.001). ICA vasospasm was associated with increased ICA MFV (OR, 1.023 [95% CI, 1.006-1.040], P = 0.007). ACA vasospasm, however, was not associated with ACA MFV (OR, 1.011 [95% CI, 0.996-1.025], P = 0.142) but instead correlated with MCA MFV (OR, 1.040 [95% CI, 1.024-1.056], P<0.001).

CONCLUSION

MFV elevations occur in both affected and adjacent arteries, suggesting the interconnected response of cerebral arteries to vasospasm. Unlike MCA and ICA, ACA vasospasm does not correlate with ACA MFV but instead with MCA MFV. These findings challenge conventional assumptions about transcranial Doppler interpretation and suggest that MFV increases should be viewed as a general marker of vasospasm rather than an artery-specific indicator.