Ambulatory electrocardiographic evaluation of overt cardiomyopathies in dogs

Holter monitoring has emerged as a reliable diagnostic tool in veterinary cardiology for identifying and analysing cardiac diseases associated with varying stages of abnormal electrophysiological activity. In conjunction with echocardiography, it is currently considered as the gold standard for diagnosing dilated cardiomyopathy (DCM) in dogs. This study aimed to evaluate heart rate, electrocardiographic pauses, heart rate variability and arrhythmias associated with overt phase of DCM in dogs. A total of eight dogs diagnosed with overt DCM underwent 24-hour Holter monitoring, following established protocols. The collected Holter data were analysed statistically, and ECG waveforms were manually reviewed to assess different arrhythmias. Ventricular premature complexes were the most common arrhythmia observed (87.50 per cent), followed by atrial fibrillation which may indicate advanced stages of cardiovascular compromise. Significantly elevated minimum and average heart rates, along with reduced electrocardiographic pause beats and pause times suggested cardiac compensation and sympathetic overstimulation. Among heart rate variability (HRV) parameters, time-domain measures such as SDNN, SDANN, and pNN50, indicative of sympathetic activity and compromised cardiovascular health were notably altered. Furthermore, frequency-domain HRV parameters, including VLF and LF, which reflect baroreceptor-mediated sympathetic stimulation, were significantly reduced in dogs with overt DCM. In conclusion, Holter monitoring serves as both a vital diagnostic tool for identifying predominant arrhythmias and assessing autonomic imbalances, and as a prognostic test to determine the severity and stage of overt DCM in dogs.