UCSF

Autonomic nervous system (ANS) dysfunction has been associated with cardiac arrhythmias and death. The aim of this research was to determine whether electrocardiographic (ECG) measures of ANS function, heart rate variability (HRV) and heart rate turbulence (HRT), have prognostic value in patients with acute coronary syndrome (ACS). A secondary analysis was performed using 24-hour ECG recordings from patients enrolled in the IMMEDIATE AIM Trial, a prospective NIH-funded study conducted from 2002 - 2005. The ECG recordings were begun within minutes (median, 45 minutes) from patients' presentation to the UCSF Emergency Department with ACS symptoms. HRV and HRT were computed using research software (HRV Laboratory, St. Louis, MO). A total of 193 patients had recordings with sufficient data for analysis.

Multivariate analyses demonstrated that 5 HRV measurements were significantly associated with all-cause 1-year rehospitalization (p-values<.05). HRT was associated with cardiac-related 30-day and 1-year ED readmission and/or death. Patients with disrupted HRT markers had greater risk of adverse 30-day outcomes compared to patients with healthy markers (hazard ratio=3.6, p=.01), and greater risk of adverse 1-year outcomes (hazard ratio=3.2, p<.001). Comparison of HRT and routinely-measured TIMI risk scores showed similar sensitivity and specificity for 30-day (areas under the curve: HRT=0.647; TIMI=0.687) and 1-year outcomes (HRT=0.657; TIMI=0.605).

In conclusion, HRT provides a viable alternative to TIMI scores for risk assessment in patients with ACS. With appropriate software, HRT and HRV could be obtained from the ECG monitoring nurses routinely perform. Future studies are needed to determine whether ANS ECG markers identify patients who warrant closer follow-up.