Background: Cardiac uncoupling and reduced heart rate (HR) variability are associated with increased mortality after severe traumatic brain injury (TBI). Recent data has shown beta-blocker (betaB) exposure is associated with improved survival in this patient population. The purpose of the present study was to evaluate the effect of betaB exposure on the mortality risk of patients with severe TBI and early cardiac uncoupling.
Methods: From December 2000 to October 2005, 4,116 patients were admitted to the trauma intensive care unit. Four hundred forty-six patients (12%) had head Abbreviated Injury Scale score >/= 5 without neck injury and had continuous HR data for the first 24 hours. One hundred forty-one patients (29%) received betaB. Cardiac uncoupling was calculated as the percent of time that 5-minute HR standard deviation was between 0.3 bpm and 0.6 bpm on postinjury day 1.
Results: A relationship between betaB and survival was observed when the population was considered irrespective of length of stay or betaB start time (p < 0.001). Cardiac uncoupling appears to stratify patients into groups who might receive additional benefit from betaB, and identifies patients with increasing mortality. However, the association of betaB with survival was attenuated when analyses accounted for selection bias in betaB administration.
Conclusions: betaB exposure was associated with reduced mortality among patients with severe TBI. Though loss of HR variability has previously been associated with an increase in mortality, betaB exposure appears to be associated with increased survival across all stratifications of cardiac uncoupling.