Occasional erratic heart rhythms appear to cause about one-fifth of strokes for which a cause is not readily established, according to research presented at the American Stroke Association’s International Stroke Conference 2012.
About one-third of survivors leave the hospital with the cause of their stroke still undetermined.
“Identifying and treating these patients for irregular rhythm could reduce the recurrence of stroke by 40% compared to reducing the risk by treating them with aspirin,” said Daniel J Miller, the study’s first author and a senior staff neurologist at Henry Ford Hospital in Detroit, USA. “The cause does not make a difference if there is not a treatment, and recently two new medications – dabigatran and rivaroxaban – have been approved by the FDA to treat this problem.”
The study confirmed a 2008 report that found 13 of 56 patients (23%) whose heart rhythms were measured by automated monitors for 21 days had paroxysmal atrial fibrillation. Such episodes can last for a few seconds up to several days.
The 2008 study suggested that erratic beats of less than 30 seconds might indicate more prolonged episodes of paroxysmal atrial fibrillation that lead to small blood clot formation in the hearts of patients with otherwise unidentified causes for their strokes. Since the study, stroke specialists have debated the importance of paroxysmal atrial fibrillation to patients.
Some stroke centres, including Henry Ford Hospital, adopted the Mobile Cardiac Outpatient Monitoring (MCOT) system as a method of identifying paroxysmal atrial fibrillation.
Miller and his colleagues examined the medical records of 156 patients (half women) who had undergone monitoring no more than six months after a stroke or transient ischaemic attack (TIA), most of them for 21 days. Ninety-seven per cent were not taking prescription anticoagulation drugs.
Of the total, 27 patients (17.3%) had one or more paroxysmal atrial fibrillation episodes during monitoring and the number increased significantly over time. In the first two days, 3.9% of the patients experienced an episode of paroxysmal atrial fibrillation. The percentage rose to 9.2% after one week, 15.1% at two weeks and 19.5% by three weeks, after accounting for those that had stopped monitoring early.
Patients identified at study entry with premature atrial contractions – the most common type of erratic heartbeats – were 13.7 times more likely to have paroxysmal atrial fibrillation than those without the rhythm problems. “That is a very high risk,” Miller said.
Excluding TIA patients, the presence of premature atrial contractions in stroke survivors increased their risk of paroxysmal atrial fibrillation to 17 times. Each one level increase in a patient’s National Institutes of Health Stroke Scale increased the risk of atrial fibrillation by 20%. The 42 point scale provides physicians a standardised method to assess a patient’s stroke-induced impairment.
The other risk factors applicable to stroke and TIA patients were:
- Being female. Women in the study had 6.2 times a man’s risk of paroxysmal atrial fibrillation. In stroke patients alone, the risk was 4.6 times.
- Having a left atrium enlarged by 1 centimetre in diameter. This finding increased the atrial fibrillation risk 2.3 times.
- A reduction in blood pumped by the heart. People whose left ventricle expelled 10% less blood than a healthy heart had a 1.8 times risk.
“Patients with stroke of unknown origin should have at least 21 days of MCOT monitoring to reliably detect paroxysmal atrial fibrillation in order to reduce their risk of future stroke,” Miller said.