Assessment of systolic and diastolic function via Tissue Doppler echocardiography in Boxers affected with ARVC compared to normal Boxers and non-Boxer control dogs

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Orr, Jeremy
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University of Guelph

This thesis is an investigation of cardiac function in Boxer dogs affected by Arrhythmogenic Right Ventricular Cardiomyopathy (ARVC). ARVC is the most common acquired cardiac disease reported in the Boxer breed. It is characterized by ventricular arrhythmia of right ventricular origin, resulting in clinical signs of syncope, exercise intolerance, congestive heart failure and sudden death. Structurally, ARVC in the Boxer is characterized by infiltration of the right ventricular myocardium with fibrofatty tissue, which is believed to the arrhythmogenic substrate. Diagnosis of the disease currently relies on the use of Holter monitors, however given the inherent variability associated with Holters, false negatives can occur. Therefore, adjunctive diagnostic modalities are needed to aid in the diagnosis of ARVC-suspected dogs that have inconclusive Holter recordings. Our objectives were to assess both systolic and diastolic function using Tissue Doppler echocardiography (TDI) measured at the medial and lateral mitral valve annulus and the lateral tricuspid valve annulus in Boxers affected with ARVC compared to non-affected normal Boxers and non-Boxer control dogs. Signal averaged ECG (SAECG) was also performed in all dogs, and troponin I concentrations were measured. Dogs were classified into five groups using Holter monitors and measurement of frequency of ventricular arrhythmia (VPCs/hr). Seventy dogs in total were evaluated for the study, with 15 Boxer dogs in group 1 (>= 1000 VPCs/24 hrs), 10 Boxer dogs in group 2 (200-999 VPCs/24 hrs), 15 Boxer dogs in group 3 (25-199 VPCs/24 hrs), 15 Boxer dogs in group 4 (<= 24 VPCs/24 hrs) and 15 non-Boxer control dogs in group 5 (5 24 VPCs/24 hrs). Two-dimensional echocardiography, TDI, SAECG and troponin I concentrations were measured in all dogs. When comparing all groups, there were no significant differences in the TDI parameters measured between groups. This finding suggests that ventricular dysfunction may be uncommon in affected Boxer dogs. Furthermore, no significant correlations between TDI and SAECG variables were found. Significant differences in troponin I concentrations were found between groups of dogs, namely Boxers and the non-Boxer control dogs. However, a correlation between VPCs/hr and troponin I concentration was not found.

Boxer dogs, systolic, diastolic, Tissue Doppler echocardiography, Arrhythmogenic Right Ventricular Cardiomyopathy