Vignan Yogendrakumar, MD, MSc
@VYogendrakumar

Kappelhof M, Tolhuisen ML, Treurniet KM, Dutra BG, Alves H, Zhang G, Brown S, Muir KW, Dávalos A, Roos YBWEM, et al. Endovascular Treatment Effect Diminishes With Increasing Thrombus Perviousness: Pooled Data From 7 Trials on Acute Ischemic Stroke. Stroke. 2021.

In the context of large vessel occlusion stroke, a growing number of advanced imaging studies are showing us that no two occlusions are alike. The imaging features of a thrombus can provide critical information that can inform us about the effectiveness of a given therapy. For example, the INTERRSeCT study published in 2018 showed that distal thrombus location and increased thrombus permeability were associated with increased rates of spontaneous recanalization with IV thrombolysis.

In this study, Kappelhof and colleagues utilize data from the HERMES dataset to assess thrombus permeability and determine its effect on clinical outcomes in patients who received EVT compared to those who received thrombolysis alone. The authors refer to permeability as “thrombus perviousness” and measured this by co-registering non-contrast CT (NCCT) and single-phase CTA images together and measuring the attenuation increase between NCCT and CTA images (Figure 2). The primary clinical outcome of the study was an ordinal analysis of the mRS.

Figure 2. Thrombus attenuation increase measurement.
Figure 2. Thrombus attenuation increase measurement.

Of the 443 patients included in the primary analysis, the authors found that patients in the control arm (IV thrombolysis arm) had improved functional outcomes if they exhibited higher degrees of thrombus perviousness (Figure 4). A significant interaction effect was found when thrombus perviousness was included in statistical models, indicating that the treatment effect of EVT and the control arm differ by a significant degree when stratifying by thrombus perviousness and the measured treatment effect of EVT is subsequently decreased.

Figure 4. Probability of functional independence (90-d modified Rankin Scale [mRS] score, 0–2) vs thrombus attenuation increase (TAI).
Figure 4. Probability of functional independence (90-d modified Rankin Scale [mRS] score, 0–2) vs thrombus attenuation increase (TAI).

The findings of Kappelhof and colleagues are in line with previous studies that show increased rates of recanalization when thrombi feature residual flow. Although the treatment effect did not significantly improve in the EVT arm, the findings of this study provide reassurance for patients living far from EVT centers, whose thrombi exhibit residual flow and require transfer to a comprehensive stroke center. In these patients, the thrombolysis given prior to transfer can improve the chances of favorable outcomes.

How we measure residual flow is an area of growing science in stroke with many current forms of residual flow assessment being dichotomous in nature. Kappelhof and colleagues’ concept of thrombus perviousness provides a more nuanced way of measuring residual flow, and further validation of their technique is warranted.