COPENHAGEN, DENMARK. There are two major types of stroke – ischemic stroke is caused by an obstruction in a small artery resulting in stoppage of the blood supply to an area of the brain (infarction). A hemorrhagic stroke does not involve an obstruction but rather a rupture of a blood vessel, which results in interrupting the blood supply to the affected area of the brain. Ischemic stroke can be further divided into two types – thrombotic and embolic. Both involve the obstruction and subsequent stoppage of the blood supply to an area of the brain (infarction). However, the mechanism by which the obstruction occurs differs.

A thrombotic stroke involves the formation of atherosclerotic plaque and subsequent narrowing and clot (thrombus) formation at the point of obstruction. In an embolic stroke, on the other hand, the obstruction is caused by the lodging of an embolus (blood clot or atherosclerotic plaque) formed in the heart or in an artery outside the brain. Cardiogenic emboli (blood clots originating in the heart) can form on heart valves, particularly prosthetic ones, or as a result of mitral stenosis. Cardiogenic emboli can also originate from the walls of the heart as a result of a heart attack (myocardial infarction), atrial fibrillation or congestive heart failure or from a benign atrial tumour (myxoma).

A group of Danish medical doctors and statisticians have just completed a major study to determine the risk factors, severity and incidence of ischemic and hemorrhagic stroke in Denmark. Their study involved almost 40,000 patients who had suffered a stroke in the period from March 2001 to February 2007. Of these patients 25,123 had complete data including CT or MRI scans, admission stroke severity as measured by the Scandinavian Stroke Scale (SSS), risk factors, and ultimate outcome (survival or death). The highlights of the study are:

• Ten percent of the strokes recorded were hemorrhagic and these tended to be considerably more severe than the ischemic strokes.
• The risk of dying from a hemorrhagic stroke was 13% during the first 7 days, 20% during the 30 days following the stroke, and 25% during the 90 days following. Corresponding mortality rates for ischemic strokes were 1.8%, 4.8%, and 11%. All told, 49% of hemorrhagic stroke victims died during the follow-up as compared to 26% in the ischemic stroke group.
• The major risk factors favoring ischemic stroke over hemorrhagic stroke were intermittent arterial claudication, a previous stroke or heart attack, diabetes, and atrial fibrillation.
• The major risk factors favoring hemorrhagic stroke were smoking and heavy alcohol consumption.
• There was no difference in gender, age and prevalence of hypertension between patients with ischemic stroke and those with hemorrhagic stroke.

The researchers conclude that hemorrhagic strokes are generally more severe and have a poorer outcome than do ischemic strokes.

Andersen, KK, et al. Hemorrhagic and ischemic strokes compared: stroke severity, mortality, and risk factors. Stroke, Vol. 40, June 2009, pp. 2068-72

Editor's comment: It is unfortunate that the researchers did not include an evaluation of the relative risk of ischemic versus hemorrhagic stroke in patients taking warfarin or aspirin. Both drugs are acknowledged as important risk factors for hemorrhagic stroke. Nevertheless, it is of considerable interest to establish that the risk factors favoring one type of stroke over the other are different. In considering the above results, it should be kept in mind that AF on its own is not a risk factor for ischemic stroke. It only becomes one when accompanied by other risk factors such as hypertension and heart disease.