ABSTRACT
The objectives of this study were to explore the mechanisms of cardiac autonomic system (CAS) impairment and to assess whether warm blood cardioplegia can prevent the decrease of heart rate variability (HRV) after CPB. Twelve adult mongrel dogs were divided into two groups. One group received warm blood cardioplegia and maintained at a systemic temperature of 38 degrees C throughout the experiment (WB group). The other received cold crystalloid cardioplegia at 31 degrees C and topical hypothermia (CC group). Anesthesia was induced and maintained with sodium pentobarbital and isoflurane. The heart was exposed through a right thorectomy. CPB was established using a single right atrial cannula. The arterial cannula was placed in the right femoral artery. The crossclamp time for both groups was 30 minutes. Serum potassium levels were normalized throughout the study. Each animal's ECG was continuously recorded for 24 hours before surgery and for the first five postoperative days (POD) using a two-channel Holter monitor. The data were analyzed for heart rate variability (TP = total power, 0.01-1.00; LF = low frequency, 0.04-0.15; HF = high frequency, 0.15-0.40; LF/HF). There were no differences in the preoperative values. In both groups the TP, LF, and HF decreased, compared to control (P < 0.05), with CC group having significantly lower TP, LF and HF than the WB group (P < 0.05). The LF/HF did not change both between groups and between before- and after-CPB in each group (P > 0.05). The mean heart rate at 24 hours (MHR) increased in both groups, compared to control (P < 0.05), with CC group having a significantly higher MHR than WB group (P < 0.05). The data suggest that CPB, with warm blood or cold crystalloid cardioplegia does not disturb the balance of CAS, but it causes the decrease of HRV, and warm blood cardioplegia can not prevent the impairment of HRV.
