Transcranial Doppler Velocities and Angiographic Vasospasm after SAH: A Diagnostic Accuracy Study

Abstract

Background and purpose: After aneurysmal SAH, transcranial Doppler is commonly used to monitor cerebral vasospasm. The diagnostic accuracy of transcranial Doppler flow velocity values in detecting angiographic vasospasm in patients requiring urgent endovascular intervention has not been established.

Materials and methods: We performed a retrospective analysis of a consecutive series of patients with aneurysmal SAH who underwent transcranial Doppler (index test) within 24 hours of conventional angiography (reference test). The judgment of 33%, 50%, and 66% degree of vessel narrowing on angiography was independently established by multiple neuroendovascular clinicians. Vessel-specific per-segment and per-patient transcranial Doppler velocities were studied using receiver operating characteristic curves, the Youden index, and minimal acceptable sensitivity models. Optimal mean flow-velocity thresholds were explored to calculate sensitivity and specificity using a per-patient judgment of vasospasm of at least 50% angiographic narrowing in any large arterial segment except A1.

Results: In 221 patients, vasospasm was found in 15%, 8%, and 4% of arteries when the degree of reference angiographic luminal narrowing was 33%, 50%, and 66%, respectively. Mean flow velocities were significantly higher in vasospastic segments (P = . 001), but per-segment exploratory analyses yielded unsound mean flow velocity thresholds. The Youden and minimal acceptable sensitivity models proposed mean flow velocity thresholds of approximately 160 cm/s for the anterior circulation and 80 cm/s for the posterior circulation in the per-patient diagnosis of angiographic vasospasm (≥50%), yielding a sensitivity of 80%-90% (95% CI, 0.77-0.96), but with a corresponding specificity of 50% (95% CI, 0.40-0.56).

Conclusions: In this study, a threshold transcranial Doppler mean flow-velocity value that would accurately diagnose ≥50% angiographic vasospasm remained elusive.

FIG 1.

Flow chart of patients included in the diagnostic accuracy study.

FIG 2.

Mean flow velocities for patients with and without vasospasm, defined as 33% (A), 50% (B), and 66% (C) vessel narrowing. MFV thresholds for anterior and posterior circulation vessels are shown (dashed lines). Note that for all individual arterial segments, MFVs were significantly higher for spastic vessels. Four asterisks indicate P < .0001; 2 asterisks, P < .01; 1 asterisk, P < .05. Error bars represent 95% confidence intervals.

FIG 3.

Sensitivity, specificity, and the Youden number at various possible mean flow velocity cutoffs for anterior circulation arterial segments. This data-driven method of analysis shows that the best MFV cutoff is close to 160 cm/s. Data for posterior circulation segments are not shown.

FIG 4.

Per-patient analysis of the diagnostic accuracy of TCD. Distributions of the maximal mean flow velocity found in any segment of the anterior circulation with or without vasospasm according to thresholds of 33% (A), 50% (B), and C) 66%. The 80% sensitivity line is labeled. Corresponding ROC curves are presented in A’, B’, and C’. Note the large amount of overlap of the curves despite acceptable areas under the curve (AUCs).