American Indians at Increased Stroke Risk, Regardless of Whether They Had AFib

Gregory Marcus, MD

New research from the University of California San Francisco (UCSF) is sounding the alarm on the increased risk of stroke among people of American Indian descent, regardless of whether or not they had atrial fibrillation (AF).

Results of the study, which analyzed data from 16 million patients, indicated American Indians with AF were at a 38% greater risk of stroke compared to their non-American Indian counterparts with AF.

“The results of our study add to the growing body of evidence that race and ethnicity are important factors when assessing stroke risk,” said lead investigator Gregory M. Marcus, MD, MAS, a professor of medicine and associate chief of cardiology for research at UCSF, in a statement. “However, our findings that conventional risk factors such as AFib may not be the cause for this increased risk among American Indian individuals, suggest other influences are in play. These could possibly be related to hereditary factors, environmental exposures or disparities in access to healthcare, and this clearly warrants further attention.”

In recent years, a renewed emphasis has been placed on understanding the role of race/ethnicity plays in modifying risk of major cardiovascular events, including stroke, in various patient populations. Marcus and a team of colleagues designed the current study In an effort to further understand this risk inn American Indian individuals using data from the Healthcare Cost and Utilization Project (HCUP).

Restricting their study to residents of California, investigators performed a search of adult patients receiving emergency care from 2005-2011. In total, their search returned data related to 16,951,579 patients, including 105,822 American Indian individuals, with a median follow-up of 4.1 years. This group also included 9,618,043 White individuals, 1,367,992 Black individuals, 4,395,503 Hispanic individuals, and 1,464,219 Asian individuals.

Of note, HCUP provided investigators with information related to age, sex, income level, insurance payer, hypertension, diabetes mellitus, coronary artery disease, congestive heart failure, cardiac surgery, valvular heart disease, chronic kidney disease, smoking, obstructive sleep apnea, pulmonary disease, and alcohol use of participants. Investigators used these factors as variables in adjusted analyses.

Upon analysis, American Indian individuals had a 47% greater risk of nonhemorrhagic stroke than the rest of the study cohort (HR, 1.47; 95% CI, 1.40-1.55; P <.0001) and those with AF were at a 38% greater risk of nonhemorrhagic stroke compared to non-American Indian individuals with AF (HR, 1.38; 95% CI, 1.23-1.55; P <.0001).

Additionally, an interaction analysis suggested AF did not accentuate the risk for nonhemorrhagic stroke, with American Indian individuals without AF at a 60% increased risk versus non-American Indian individuals without AF (HR, 1.59; 95% CI, 1.51-1.67) and 40% increased risk for American Indian individuals with AF versus non-American Indian individuals (HR, 1.39; 95% CI, 1.24-1.57; P for interaction=.05).

Investigators pointed out there were multiple limitations within their study to consider. These limitations included being limited to patients in California and the observational nature of the study. Investigators also called for further research in this specific area, including randomized trials.

“While American Indian people are known to have a particularly high risk for stroke in general, the relationship between AFib and non-hemorrhagic, or non-bleeding, stroke among this group has not been thoroughly studied,” Marcus said.

This study, “Incident Strokes Among American Indian Individuals With Atrial Fibrillation,” was published in the Journal of the American Heart Association.