| Arrhythmogenic cardiomyopathy in Boxers is characterized by the development of ventricular arrhythmias and sudden death. Standard diagnostics, including thoracic radiographs and echocardiography are of limited use in the evaluation of Boxers with arrhythmias. Alternative diagnostics are needed to better evaluate these patients, help determine prognosis and guide therapy.; Electrophysiology testing is used in the evaluation of arrhythmias in people. The need for anesthesia, the relative expense and risks inherent to the procedure, and its limited availability preclude its use in veterinary medicine. Inexpensive, noninvasive diagnostic tests that are associated with fewer risks would significantly improve the management of patients with ventricular arrhythmias. The goal of this project was to evaluate Boxers with arrhythmias by the use of noninvasive diagnostic testing, including ambulatory electrocardiography, signal-averaged electrocardiography, QT dispersion, and heart rate variability.; The degree of arrhythmia variability evaluated by ambulatory electrocardiography can affect disease diagnosis and influence assessment of progression and efficacy of therapy. Substantial variability was identified, and suggests that an 80% reduction in arrhythmia frequency is necessary to document a drug effect, while changes of less than 80% may be within the limits of spontaneous variability.; Signal-averaged electrocardiography documented the presence of late potentials in Boxers that were most severely affected. The presence of late potentials suggests that abnormal conduction exists in these dogs, which may represent a substrate for arrhythmia formation. Identification of late potentials may therefore be a predictor for mortality.; QT dispersion from standard electrocardiographic tracings was used to identify abnormalities in repolarization. The degree of QT dispersion did not correlate with any measure of disease severity. Many severely affected dogs had no QT dispersion, and QT dispersion was identified in some less affected dogs. QT dispersion was therefore not considered to be a useful diagnostic test in these dogs.; Analysis of heart rate variability was reduced in dogs with congestive heart failure, but no reduction was identified between affected and unaffected dogs. Increased sympathetic tone is unlikely to be a discriminating feature between unaffected Boxers and those with only arrhythmias. Therefore, analysis of heart rate variability was of little value in assessing arrhythmic disease. |
