Introduction

Histological studies of third degree atrioventricular block (AVB) in dogs have shown fibrotic and degenerative changes in the atrioventricular conduction system and suggested these might be secondary to an undiagnosed inflammatory process.

The acute phase response is an immediate to early non specific reaction to tissue injury (inflammation, infection, trauma), which serves to restore the body homeostasis. The four main positive acute phase proteins (APPs) in canine medicine are C-reactive protein (CRP), serum amyloid A (SAA), haptoglobin (Hp), and α1-acid glycoprotein (AGP), with CRP and SAA considered to be the major APPs.

The aim of this study was to determine whether dogs with third degree AVB exhibited higher values of APPs (especially CRP and SAA), compared to other forms of arrhythmia, supporting an inflammatory aetiology. Myocardial inflammation is likely to lead to cell damage and leakage of Troponin I (cTnI) from the myocyte, thus the serum concentrations of individual APPs were also compared to those of cTnI.

Methods

Dogs diagnosed with arrhythmias from 2008 to 2010 by the Cardiopulmonary Service, Hospital for Small Animals, Royal (Dick) School of Veterinary Studies, University of Edinburgh were enrolled in the study. Arrhythmias were identified on electrocardiography or 24 hour Holter monitoring.

Twenty-seven dogs with different arrhythmias were included in the study. APPs and cTnI were analysed from residual serum from clinical cases that had been stored frozen at -80°C. Dogs were divided in the following 4 groups according to their arrhythmia: third degree AVB (n = 8), supraventricular tachycardia (SVT) secondary to an accessory pathway (n = 7), atrial fibrillation (n = 6) and ventricular arrhythmia (n = 6). Normal reference ranges provided by the laboratory were used as control values.

Results

Median values of CRP and SAA were higher in dogs affected with third degree AVB (13.78 and 7.89 mg/l respectively) compared to other arrhythmias (of which highest median values were 10.73 and 1.80 mg/l respectively); however overlap with normal values and among groups was present, with no significant difference between arrhythmia groups (p = 0.521). The SVT group had the lowest values of APPs and cTnI.

Conclusion

The results of this study might suggest that the aetiology of third degree AVB has an active inflammatory component, however the serum APPs values showed marked overlap with other arrhythmias. Further studies are needed to determine the role of inflammation in cardiac arrhythmias.