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L. McGlone, N. Patel, M. Danton.Royal Hospital for Sick Children, Glasgow, UK

Objective: Changes in heart rate variability (HRV) may be useful predictors of outcome in cardiac disease and following surgery. This is the first study to investigate changes in HRV in children in the immediate 24 h following cardiac surgery.

Methods: Twenty seven children (age one month to 15 years) undergoing cardiac surgery were recruited over a 10-month period. Complete data were obtained for 20 children, all of whom underwent surgery requiring a period of cardiac bypass. HRV was measured for one hour preoperatively and continuously for 24 h postoperatively. Time domain and frequency domain analyses of HRV were performed.

Results: Time domain analysis revealed a significant reduction in HRV measures at all time points postoperatively, compared to preoperative values. There was a significant association between one of the time domain measures (SDNNi) and duration of cardiac bypass (r = −0.486, p = 0.035). There was a trend towards a reduction in SDNNi with increasing cross clamp time (r = −0.392, p = 0.097), and reduction in SDNNi with longer PICU stay (r = −0.398, p = 0.092). Frequency domain analysis of HRV demonstrated a significant reduction postoperatively at all time points, in total power and the low and high frequency ranges. This indicates a reduction in both sympathetic and parasympathetic control of the heart. There was a correlation between postoperative total power and cardiac bypass time which approached statistical significance (r = −0.439, p = 0.053).

Conclusions: HRV can be easily measured in the immediate period post cardiac surgery. HRV is significantly reduced post cardiac surgery and reflects a reduction in autonomic cardiac control, which may contribute to low cardiac output states at this time. The mechanisms of this global reduction in autonomic control remain to be elucidated, but are related to length of bypass time. HRV may represent an objective clinical predictor …

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