Why does antihypertensive treatment prevent stroke but not myocardial infarction?

It is proposed that differences in autoregulatory reserve and blood oxygen extraction potential between the coronary and cerebral circulations explain why antihypertensive treatment effectively protects patients against stroke but has failed to reduce the increased incidence of myocardial infarction associated with hypertension. In the brain, oxygen extraction from the blood can be increased if blood pressure falls below the lower limit of autoregulation. In the coronary circulation, however, oxygen extraction is nearly maximum at rest, and lowering of blood pressure by antihypertensive therapy can lead to myocardial ischaemia.