Wednesday, September 19, 2012

The heart rate response to adenosine: A simple predictor of adverse cardiac outcomes

BACKGROUND: the normal response to adenosine infusion typically is an increase in the heart rate of 20% or more to compensate for adenosine induced vasodilation.

METHODS: this study looked at asymptomatic diabetics undergoing stress adenosine myocardial perfusion imaging and the 5-year hard cardiac event rate. Patients were divided into two groups: 
  • Group A: Normal. Patients with an increase in heart rate of 20% or more after adenosine
  • Group B: Abnormal. Patients with an increase of less than 20% after adenosine administration.
RESULTS: During the 5-year follow-up, 3% of patients experienced a hard cardiac event. The heart rate response was independently correlated with cardiac events. Group B (blunted heart rate response) had a 9-fold increased risk of a hard cardiac event, regardless of myocardial perfusion findings. Those with a heart rate response of 40% or greater had the lowest risk, irrespective of perfusion abnormalities.

CONCLUSION: an increase in the heart rate of less 20% after adenosine infusion appears to be an independent predictor of adverse cardiac events. 

CLINICAL IMPLICATION: the heart rate response to vasodilator stress is an indirect marker of cardiac autonomic neuropathy. Advanced cardiac disease is likely to have more cardiac neuropathy and as a result a blunted heart rate response to vasodilator stress with adenosine, and presumably also the other vasodilator agents dipyridamole and regadenoson. I-123 MIBG imaging directly measures sympathetic innervation of the heart, and a fast washout of the tracer is predictive of hard cardiac events in patients with heart failure. This agent has potential to also be a useful prognostic tool in diabetics.

REFERENCE: The heart rate response to adenosine: A simple predictor of adverse cardiac outcomes in asymptomatic patients with type 2 diabetes.: Int J Cardiol. 2012 Sep 12;