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People with atrial fibrillation (Afib) account for a growing proportion of ischemic strokes and have worse outcomes when it does occur, according to a nationwide analysis of more than 900,000 stroke patients.

About 20% of ischemic stroke patients had Afib in 2014, up from about 16% in 2003, reported Mohamad Alkhouli, MD, of West Virginia University in Morgantown, and co-authors online in JACC: Clinical Electrophysiology.

Despite overall improvements in stroke prevention and outcomes, the negative effect of Afib was steady over the 12-year period: Afib stroke patients had nearly 10% mortality, compared with about 6% for patients without Afib.

"Stroke prevention is the cornerstone of the management of atrial fibrillation," Alkhouli said. "Yet the prevalence of Afib among patients admitted with acute ischemic stroke is rising, especially among white and elderly patients."

These are important findings, but they don't necessarily mean Afib is more widespread, noted Oussama Wazni, MD, of the Cleveland Clinic, who was not involved in the study. A combination of factors, including an aging population, could account for the increase. "It also most likely means we are detecting atrial fibrillation more frequently," he said.

But more importantly, it could mean that many patients with Afib are undertreated, Wazni observed. "This is one of the main issues with atrial fibrillation right now. Patients continue to be undertreated with oral anticoagulation," he told 乌鸦传媒.

Afib patients, historically, have had worse stroke outcomes than those without Afib, but whether that trend persisted was unknown. "This study is the largest contemporary study assessing the burden of Afib-associated stroke at a national level," Alkhouli told 乌鸦传媒.

In this analysis, Alkhouli and colleagues identified 930,010 patients with acute ischemic stroke from 2003 to 2014 in the National Inpatient Sample. Of those stroke patients, 168,806 (18.2%) had Afib, with the prevalence rising from 16.4% in 2003 to 20.4% in 2014.

Stroke patients with Afib were older (82 versus 70 years) and more likely to be female (59.3% versus 51.8%) and Caucasian (80.6% versus 67.3%) than patients without the arrhythmia (P<0.001). The Afib subgroup also had more major comorbidities, with the exception of diabetes and smoking.

Afib patients were more likely to receive thrombolytic therapy and mechanical thrombectomy for their stroke (5.1% versus 3.5%, and 0.9% versus 0.4%, respectively, P<0.001).

Even so, propensity-score matching of 125,203 stroke patients with Afib and without -- matched for those treatments -- showed worse outcomes in the Afib group, with 9.9% versus 6.1% dying in-hospital (P<0.001).

Stroke in Afib patients also was associated with higher incidences of acute kidney injury, bleeding and infectious complications, and severe disability. Afib stroke patients were more likely to have longer hospital stays, higher cost of care, and more non-home discharges.

"We need more efforts and research to identify effective prevention and management strategies that can address the persistent substantial burden of ischemic stroke in Afib patients," Alkhouli told 乌鸦传媒.

Wazni added that these poorer stroke outcomes "emphasize why, when patients are diagnosed with atrial fibrillation, it's very, very important to manage them appropriately, and most importantly, to treat them with oral anticoagulation as indicated."

The study also raised the question of routine surveillance for Afib in patients with risk factors like hypertension, Wazni added. "Should we be monitoring those patients and doing more surveillance to detect Afib? That's a bigger question."

Future research should examine whether the racial disparity in Afib-related stroke is genetic or stems from potentially modifiable factors, and whether the negative effect of Afib in stroke persists among patients being treated with adequate anticoagulation, the authors noted.

Limitations included use of an administrative database that collected data for billing purposes, such that miscoding may have occurred, and lack of data on stroke severity, anticoagulation, and implantable Afib devices.

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