Decreased heart rate variability in significant cardiac events

The heart rate variability (HRV) of 82 patients exhibiting sinus rhythm and admitted for possible myocardial infarction (MI) was evaluated. Using a simple information entropy measure to quantify the HRV, patients subsequently diagnosed with MI or experiencing significant dysrhythmia (n = 35) exhibited less entropy (0.28 +/- 0.15) within the first 24 h after admission than those patients (n = 45) with no MI (0.36 +/- 0.14; p less than .01). Although correlations between entropy and age and heart rate (HR) were significant (p less than .01), the additional explained variance was minimal. The groups were compared for sex, age, mean HR, past medical history and medications taken and were found to be statistically similar. In our patients without significant dysrhythmias on admission, HRV appeared to be an index for significant cardiac events, and thus may prove to be a useful tool in clinical situations where other objective decision criteria are lacking.