In principle medical research is supposed to result in unequivocal guidance to doctors as to how to treat their patients. As often as not, however, the waters are muddied as much as cleared. Two papers in a recent edition of the New England Journal of Medicine about atrial fibrillation and the cause of stroke illustrate this. It has long been known that people with a clinically-detected chaotic heart rhythm called atrial fibrillation (AF) have an increased incidence of stroke by embolism; and likewise that no cause of such stroke can be found in up to 40 percent of patients who suffer from one. Their strokes are called cryptogenic. The two papers addressed the question whether, if you monitor patients with cryptogenic stroke for long enough, some or many of them will turn out to suffer from AF. This is important, because it is generally agreed that, in patients with clinically detected and symptomatic AF, anti-coagulation reduces the subsequent risk of stroke. AF, however, is not an all or none phenomenon. Some people suffer it continuously, but others only occasionally and for only a few seconds at a time. The additional risk of stroke in the latter is unknown, but is an important question because the anticoagulation designed to reduce the risk of stroke is not itself without risk, including that of another kind of stroke, the haemorrhagic kind. In other words, the risk caused by treatment could outweigh its benefits.
New studies indicate that a drug designed to reduce the risk of one kind of stroke may provoke another.