Even though high blood pressure or hypertension has been a well-established risk factor for stroke and for deaths, it turns out that having low blood pressure is just as great a risk factor for death after stroke.

A new study suggests that stroke patients with low blood pressure and non-cardiovascular conditions, such as cancer and dementia, have a higher risk of death after stroke.

These findings appear in the journal Stroke. "Lower average blood pressure, measured in the outpatient setting, was associated with increased risk of death after a stroke event. In addition, this higher risk of death appeared to happen particularly in patients who were smokers, or had a diagnosis of cardiac disease, cancer or dementia," explained corresponding author Hugo J. Aparicio, MD, MPH, assistant professor of neurology at Boston University School of Medicine and an investigator at the Framingham Heart Study.

Current national guidelines recommend treating high blood pressure after stroke, but the timing of this treatment and whether to treat patients in a normal, low or mildly elevated range of blood pressures have been debated.

The researchers identified nearly 30,000 Veteran patients with a first ischemic stroke who had outpatient blood pressure measurements within the previous 18 months prior to the stroke. They divided this group by blood pressure categories and followed them overtime for the outcomes of all-cause and cardiovascular mortality, with the hypothesis that both very high and very low blood pressure values contribute to higher mortality risk.

They found that persons with lower blood pressure had the highest mortality, especially when they looked at a subgroup of patients with at least one comorbidity of smoking, cardiovascular disease, cancer or dementia. "Our study suggests that stroke patients with a history of low to low-normal blood pressures, some 10 per cent of stroke patients, are at high risk of mortality," said Aparicio.

The researchers hope that by investigating the factors that contribute to death after stroke, patients, families and practitioners can better understand and recognise conditions, like low blood pressure, that may predict their health outcomes. "Ideally, this information can encourage better prevention, diagnosis, and treatment of risk factors such as smoking, heart disease, and cancer, so that if a stroke does occur patients have a better chance at recovery and survival," he added.