Longer Bouts of Atrial Arrhythmia Have Worse Outcomes

LOS ANGELES – The Registry of Atrial Tachycardia and Atrial Fibrillation Episodes in the Cardiac Rhythm Management Device Population (RATE) shows that long episodes of atrial tachycardia or atrial fibrillation (AT/AF) are linked to a higher risk of adverse events in patients with cardiac rhythm management devices.

Results from RATE, presented by Dr Steven Swiryn (Northwestern University, Chicago, IL) at last week's American Heart Association 2012 Scientific Sessions, showed that patients with cardiac rhythm control devices who only experience short episodes of AT/AF are at about the same risk for adverse events as otherwise-similar patients who never experience an episode of AT/AF. However, the data Swiryn presented showed that any long episode of AT/AF is associated with a higher risk of hospitalization for clinical AT/AF in implantable cardioverter defibrillator (ICD) and pacemaker patients. Also, greater frequency of AT/AF episodes is associated with higher risk of any adverse events and higher risk of AF hospitalization in ICD patients.

The assigned respondent on the RATE presentation, Dr Bernard Gersh (Mayo Clinic, Rochester, MN), pointed out that the RATE results appear to confirm the finding of ASSERT--that subclinical atrial arrhythmias in pacemaker patients are common and significantly predictive of stroke or systemic embolism.

"This is a fundamental contribution that may really change our clinical practice," Gersh said. Citing long-term data from the Mayo Clinic showing that stroke is often the first clinical manifestation of atrial fibrillation, he suggested that patients at risk for AF may need to be treated to prevent stroke even before showing symptoms of atrial arrhythmia.

Longer Episodes, More Episodes Increases Risk

RATE enrolled and followed 5379 patients with cardiac rhythm control devices from 2007 through 2012, including 3141 patients with pacemakers and 2238 with ICDs. The average follow-up was about two years, during which the registry collected data from 20 153 adjudicated ECGs. During the study, there were 2232 hospitalizations--about half of the study population--and 11 in-hospital cardiac deaths, plus another 350 out-of-hospital deaths have not yet been fully adjudicated. All event ECGs were evaluated in 600 randomly selected patients--300 with pacemakers and 300 with ICDs--by teams of two adjudicators, and the interobserver agreement was very high.

Short episodes were defined as an AT/AF episode that began and ended within one electrocardiogram tracing, while long episodes lasted more than one tracing.

Multivariate logistic regression for pacemaker patients showed that, compared with patients with no AT/AF episodes, patients experiencing long episodes of AT/AF were at greater risk (odds ratio 1.84) for all adverse events–-including hospitalization for AF, heart failure, ventricular tachycardia, stroke or transient ischemic attack, syncope, or in-hospital cardiac death. The association of long AT/AF episodes with either AF hospitalization or heart-failure hospitalization alone did not reach statistical significance. Patients with only short episodes of AT/AF were not at increased risk for adverse events compared with patients with no episodes.

Among ICD patients, patients experiencing long episodes of AT/AF were at greater risk of all adverse events than patients with no episodes (odds ratio of 1.56). Long episodes of AT/AF were also strongly associated with a greater risk of AF hospitalization (odds ratio 5.86) in the ICD patients. Short episodes of AT/AF were not associated with increased risk in the ICD patients.

Also, ICD patients experiencing more than the median number of separate AT/AF episodes were at higher risk for all adverse events than patients at or below the median, especially for AF hospitalization, but more frequent AT/AF episodes were not associated with a statistically significant greater risk of heart-failure hospitalization.

Gersh suggested that more specific measurements of the duration of AT/AF episodes would provide a better understanding of "atrial-fibrillation burden."

"If you have one episode lasting 50 hours, does that mean as much as 50 episodes of one-hour duration each? These are figures that we're going to need to try to understand, because there's no question that we're going to be seeing more and more silent atrial fibrillation as we use these devices," he said. He added that further studies may show that there is a significant incidence of clinically silent atrial fibrillation in patients with risk factors for AF, but not an ICD or pacemaker, who should be considered for anticoagulation therapy to prevent stroke.

Disclosures for Swiryn were not available. Gersh has consulted for Medtronic, Bristol-Myers Squibb, and Ortho-McNeil-Janssen Pharmaceuticals.