Houman Khosravani, MD, PhD
“We hold these truths to be self-evident” is stated in the Declaration of Independence, and some say that with the passage of time, all becomes self-evident. Thus, what is the impact of time, and what is the truth behind the function and abundance of collateral circulation? These answers are critical to the late-window management of acute stroke. The topic will be one that keeps on giving, and an important contribution to this topic comes from a recent paper by Vagal et al.
In both early and extended time-windows brought about by DAWN and DEFUSE 3, the presence and functional capacity of robust collaterals has become uniquely important. The ischemic penumbra can persist for prolonged periods of time (up to 48 hrs), and its survival rests in part with the collateral circulation. The ability to assess this important aspect of tissue health is key in the evolution of thinking that is taking place: a move from time-window to tissue-health window. At the forefront of this assessment is perfusion imaging — in the case of this research, using CT perfusion. Understanding how time affects the natural history of the penumbra stands to inform assessment and decision-making in the era of EVT for patients within 24 hrs of symptom onset. Vagal et al. explore time from stroke onset and infarct growth in untreated acute ischemic stroke patients within this time window with the purpose of understanding how collaterals affect this evolution. However, it is important to note that data in this study were collected in the era of TPA first up to 3 hrs, then up to 4.5 hrs, and IA-TPA up to six hours (spanning 2003-2011) — thus, prior to the current EVT era. Nonetheless, patients who met inclusion criteria did not receive any therapy allowing for assessment of the penumbra’s natural history.