At the end of 2014, the American Heart Association reported that stroke had dropped from the nation’s fourth-leading cause of death to number five, according to new federal statistics. It is the second time since 2011 that stroke has dropped a spot in the mortality rankings.
This is good news.
“But, the cause is unknown in about 30 to 40 percent of those stroke cases,” said Scott Kasner, MD, MSCE, professor of Neurology and director of Penn’s Comprehensive Stroke Center. “We can’t make much more progress in prevention until we can better understand the cause.”
Kasner and colleagues recently embarked on a study to determine whether atrial fibrillation (AF), an irregular heartbeat known to put patients at risk for stroke -- five million new cases of the condition are diagnosed each year in the United States -- was the cause in 250 patients who had a stroke between April 2010 and November 2012. The researchers first needed to see which patients were at risk for or had AF. After discharge, the patients were placed on 28-day mobile cardiac outpatient telemetry, an at-home cardiac monitoring technology that continually monitors cardiac activity via three electrodes placed on the chest. When the system detects an arrhythmia, the monitor automatically transmits the data to a central monitoring station for further analysis. Any symptoms recorded by the patient are also transmitted.
“We thought we would be able to predict which patients would be at highest risk for atrial fibrillation based on two things—what the acute stroke looks like on an MRI or CT scan, and a common risk rating tool which predicts AF risk in stroke patients,” Kasner said. That tool takes into account the patient’s age, whether the patient has a history of congestive heart failure, hypertension, diabetes, vascular disease or previous stroke or blood clot, and sex, as women are known to be at greater risk for stroke due to AF.
The team was surprised to find that this was not the case.
In fact, the single biggest predictor of AF was evidence of prior brain infarction, injury due to low blood flow, even though that prior injury never caused any symptoms. Age was also found to be a predictor. AF was found in 33 percent of subjects over age 60 and with some prior brain injury as seen on MRI. Among younger patients without prior brain infarction, AF was found in onlyfour percent of cases. The findings were reported in the journal Stroke.
People can have subtle strokes or stroke-like damage to the brain that is able to be seen on an MRI, but the effects are what physicians refer to as clinically silent. Sometimes the damage does not affect the key areas of the brain that control speech, movement, sensation, or vision, and is therefore are not readily recognized by the patient or family members, Kasner explained. Sometimes the symptoms are felt by the patient, but are subtle and are not diagnosed at the time as stroke symptoms.
“This study shows the value of outpatient cardiac monitoring in helping us understand who is at greatest risk for an AF diagnosis,” Kasner said. “And as importantly, it gives us greater insight into which patients we should diagnose and treat most aggressively for AF and potential stroke recurrence.”