Posts Tagged ‘implantable defibrillator’

Journal Club 22 February 2012


Subclinical Atrial Fibrillation and the Risk of Stroke




An observational study of patients with recent pacemaker of defibrillator implantation


65 years of age or older, with hypertension and no history
of atrial fibrillation, in whom a pacemaker or defibrillator had recently been implanted


Longitudinal observation of sublcinical atrial arrhtyhmias and risk of stroke or systemic embolism.
Subclinical atrial arrhythmia was defined as atrial arrhythmia with rate greater than 190 beats per minute for greater than 6 minutes at 3 month device assessment. Mean follow was for 2.5 years.


An observational studies. The outcomes of patients with and without subclinical atrial arrhythmias was assessed.
Patients with pacemakers were randomly assigned to receive or not
to receive continuous atrial overdrive pacing


Risk of ischemic stroke or systemic embolism.



By 3 months, subclinical atrial tachyarrhythmias detected by implanted devices had
occurred in 261 patients (10.1%). Subclinical atrial tachyarrhythmias were associated
with an increased risk of clinical atrial fibrillation (hazard ratio, 5.56; 95% confidence
interval [CI], 3.78 to 8.17; P (hazard ratio, 2.49; 95% CI, 1.28 to 4.85; P = 0.007).

Of 51 patients who had a primary outcome event, 11 had had subclinical atrial tachyarrhythmias detected by 3 months,
and none had had clinical atrial fibrillation by 3 months. The population attributable
risk of stroke or systemic embolism associated with subclinical atrial tachyarrhythmias
was 13%. Subclinical atrial tachyarrhythmias remained predictive of the primary
outcome after adjustment for predictors of stroke (hazard ratio, 2.50; 95% CI, 1.28 to
4.89; P = 0.008).

Continuous atrial overdrive pacing did not prevent atrial fibrillation.


Subclinical atrial tachyarrhythmias, without clinical atrial fibrillation, occurred frequently
in patients with pacemakers and were associated with a significantly increased
risk of ischemic stroke or systemic embolism.

Discussion Summary 

  • Although the risk of ischemic stroke and systemic embolism was higher in patients with subclinical atrial arrhtyhmias this is based on 11 patients. The majority of events occurred in patients without subclinical atrial arrhythmias
  • CHADS2 point estimates of risk were consistent with gradient of risk. However, small event numbers limit conclusions
  • There was greater prevalence of anticoagulant use in follow up in the subclinical atrial arrhythmia group. This, therefore, may lead to underestimation of the risk,
  • There is limited information regarding the burden of arrhythmia and risk. The highest quartile of duration of arrhythmia (hours) had approximately four fold increase in event rate compared with the lowest quartile. Again this is based on 11 patients.
  • Continuous atrial overdrive pacing did not reduce frequency of follow up atrial fibrillation. This was low frequency event.