Objective: Targeted temperature management (TTM) is recommended for patients suffering a cardiac arrest after restoration of spontaneous circulation (ROSC). Heart rate variability (HRV), which reflects autonomic function, has been proposed as an outcome predictor but HRV measurement is not suitable for everyday practice. RR interval variation (RRIV), which can be measured easily at the bedside using surface electrocardiography, is a parameter indicating the integrity of the autonomic nervous system. We assessed the neurologic outcomes and predictive factors involving RRIV in cardiac arrest patients who received TTM.
Materials and Methods: We performed a retrospective, single-center, observational study to describe the neurologic outcomes of cardiac arrest patients who received TTM measured by the cerebral performance categories (CPC) scale. Clinical data was collected from medical records dated from January 2010 to June 2015. RRIV was calculated by difference between the maximum RR interval and the minimum RR interval.
Results: During the study period, 46 patients were examined; 56.5% were male. The most common cause of cardiac arrest was cardiac in origin (37%). The most common initial cardiac rhythm was asystole (52.2%). RRIV was correlated with HRV parameter by standard analysis software in the first 11 patients. In our setting, 12 patients (26.1%) displayed favorable neurologic outcomes (CPC1 or 2). RRIV >40 msec was associated with favorable neurologic outcomes (p = 0.046).
Conclusion: RRIV may be used as a tool for predicting neurologic outcomes. RRIV at >40 msec was associated with favorable neurologic outcomes.

Keywords: Targeted temperature management, Cardiac arrest, Neurologic outcomes, RR interval variation