Thanks to Li for sending out a nice summary of this subject with excerpts from the relevant UpToDate article. The bottom line is that they acknowledge the lack of prospective data on this problem, but do recommend anticoagulation for grade IV vascular injuries (complete occlusion).
The authors reference a trauma guideline that makes the same recommendation, and it turns out that the three authors of the UpToDate article are also authors, including the lead author, of the guideline. This increases our confidence that these UpToDate articles are written by knowledgeable people, but it does make it even more important to look into the source documents since the UpToDate authors are mainly referencing their own work. Following are some quotes and commentary from the guideline (emphasis added and citations removed):
Because there are no published prospective randomized clinical trials that have generated class I data, the recommendations herein are based on published observational studies and expert opinion of Western Trauma Association members . . .
. . . A few retrospective, uncontrolled case series, as well as more recent large reports from Memphis and Denver suggest that systemic heparinization and antiplatelet therapy (clopidogrel 75 mg daily or aspirin 325 mg daily) are equally efficacious in stroke prevention . . .
. . . In the absence of controlled data, systemic heparin may be preferred among patients with neurologic symptoms and in those who have no contraindications. The Memphis data demonstrate systemic heparinization’s clear efficacy in improving neurologic outcomes among symptomatic patients . .
The Memphis paper was an observational study of 87 blunt carotid (not vertebral) injuries in 67 subjects. 47 subjects received heparin, 8 had no treatment, 6 received aspirin, and 1 underwent surgical treatment. For the 47 subjects treated with heparin, outcomes were “good” in 26; “moderate” in 7; and “bad” in 14. For the 15 who did not receive heparin, outcomes were “good” in 3; “moderate” in 1; and “bad” in 11. Heparin was associated with better outcomes as compared to no heparin; p < 0.01. Because only 6 of the 15 “no heparin” subjects received aspirin, I interpret this study to show that heparin is better than no heparin, but not necessarily better than aspirin. That comparison wasn’t done (the word “aspirin” appears just once in the entire article!)
. . . Furthermore, although statistical significance was not achieved, the large series in Denver suggests that heparin may be superior to antiplatelet therapy in stroke prevention (p = 0.07) and in neurologic improvement after ischemic insult (p= 0.15).
The Denver paper was also an observational study, authored by the same group who wrote the UpToDate article and the guideline, further demonstrating the degree of self-reference with respect to this question. There were 3 strokes among 33 subjects treated with aspirin (9%) and one among the 84 treated with heparin (1%) p = 0.07. There was no statistically significant difference in neurologic outcomes in heparin-treated versus no heparin subjects (p = 0.15), which again isn’t the comparison we’re interested in anyway. They wrote that they were designing a randomized trial to answer this question, but it appears to have never taken place.
And, of course, there were significant bleeding events reported in both of the above studies.
So, it appears that the evidence for heparin being superior to aspirin for stroke prevention in the setting of blunt cerebrovascular trauma boils down to one observational study whose authors then wrote a guideline largely on the strength of their own article, followed by an UpToDate entry that references their guideline. I’m not in the trauma world, so don’t know how much weight the Western Trauma Association carries. For what it’s worth, that organization is not listed in the National Guideline Clearinghouse database.
Does any of this prove that aspirin is in fact equivalent or better than heparin in this situation? Certainly not. I just want to make the point that we don’t really know and so, as is often the case in medicine, must make individual decisions based on our best judgment.