Victor J. Del Brutto, MD
Early recanalization with mechanical thrombectomy gives stroke patients with large vessel occlusion the best chance to achieve a good functional outcome. Successful angiographic reperfusion as determined by a good TICI score implies restoration of cerebral blood flow to ischemic tissue, thus preventing neuronal death, which result in a better functional recovery after stroke. However, this happy ending story could be distorted in the post interventional course by abnormal cerebral hemodynamics including no-reflow phenomena, vessel reocclusion, focal vessel stenosis, or hyperperfusion with high risk of hemorrhagic conversion.
It is appealing to have a diagnostic tool that could be routinely used to detect early hemodynamic changes after thrombectomy in order to predict the aforementioned complications. Bedside Transcranial Doppler (TCD) is a fast, non-invasive and reliable way of evaluating cerebral hemodynamics after ischemic stroke. In the present article, Kneihsl and colleagues showed that 36% of patients with initial successful endovascular recanalization had abnormal blood flow in the recanalized artery, and, as expected, abnormal cerebral flow was associated with poor 90-day outcome. As explained by the authors, abnormal TCDs could be classified into those with increased and decreased mean velocities in the vessel of interest. Increased velocities could be explained by failure of cerebral autoregulation with consequent hyperperfusion phenomena and high risk of hemorrhagic complications. Alternatively, high velocities could be found with residual vessel stenosis in patients with underlying atherosclerosis that developed occlusion due to in situ thrombosis. On the other hand, decreased velocities with dampened or absent flow could be secondary to vessel reocclusion, proximal high-grade stenosis, or distal occlusion of smaller caliber vessels. The later is usually associated with high pulsatility index (PI) and resistance index (RI) as indicators of increased distal resistance such as in no-reflow phenomena.
In a separate study, Ng and colleagues1 used TCD after successful thrombectomy in patients with M1 occlusion to detect microvascular changes in the ischemic territory. They found that almost half of the patients have abnormally elevated PIs and RIs. These elevated indices of microvascular resistance were associated with less hemorrhagic complications but worse clinical outcomes, likely due to poor tissue reperfusion. The authors concluded that TCDs could provide clinical relevant biomarkers of no-reflow phenomena post-revascularization.
In summary, TCD provides useful information to understand the pathophysiological changes after restoration of cerebral blood flow in patients with large vessel occlusion that undergo mechanical thrombectomy. In addition, TCD may help identify therapeutic targets in order to prevent complications and improve functional outcomes. More research is needed in this field to validate these findings.
- Felix C. Ng , Bronwyn Coulton , Brian Chambers , Vincent Thijs. Persistently Elevated Microvascular Resistance Postrecanalization: A Clinical Marker of No-Reflow Phenomenon. Stroke. 2018; 49:2512–2515.