Alterations in dispersion of cardiac repolarization and autonomic balance in the splenectomized dog

Abstract

Ventricular premature contraction (VPC) in the splenectomized dogs remains a major concern during post-operative period since it may progress to fatal arrhythmia, ventricular fibrillation (VF). Twelve splenectomized dogs were recruited in the present study and further divided into 2 groups according to the number of VPC/24 hours, low VPC (n=6) and high VPC groups (n=6). None of the dogs received antiarrhythmic drug or digoxin prior to the study. Holter device was attached for 30 minutes in pre-operative period and 9 days after surgery while during the post-operative period, ECG signals were continuously recorded throughout 72 hours. Blood samples were collected at both pre-operative and post-operative (day 2 and 9) for complete blood count (RBC, Hct, platelet, WBC), blood chemical profiles (ALT, ALP, BUN, creatinine, total protein, Na+, K+) and concentrations of norepinephrine (NE) and epinephrine (E). The results revealed that the number of VPC was highest at day 3 (p<0.05) then declined at day 9. The HR in all dogs and low VPC group were decreased (p<0.05) compared with pre-operative period whereas SBP was unchanged. The Tp-Te was significantly increased on day 2 and day 1 (p<0.05) in low and high VPC groups, respectively. For time domain analysis of HRV, SDANN, SDNN index, SDNN, pNN50 and RMSSD tended to enhance after surgery compared with pre-operative period. In frequency domain analysis, HF and TP in all dogs increased having the decreased LF/HF after operation when comparing with pre-operative period. Nonetheless, lower HF and higher LF/HF were observed in high VPC group on day 2 (p<0.05) compared with low VPC group. NE and E increased significantly on day 2 after surgery in all dogs with the statistical significance of NE in high VPC group (p<0.05) compared with pre-operation. Additionally, concentrations of NE and E obtained from pre-operative, day 2 and day 9 after surgery were related to the number of VPC in all dogs and high VPC group (p<0.05). This study demonstrated that the splenectomized dogs had VPC after surgery. The catecholamine and Tp-Te were enhanced postoperatively along with enhanced cardiac ANS activity, particularly parasympathetic modulation. However, parasympathetic modulation in low VPC group was more dominant than high VPC group.