ELECTROCARDIOGRAPHIC STUDIES IN DOGS WITH CHRONIC MITRAL VALVE DISEASE

K. Revathi1, N. Madhavan Unny2, Usha Narayana Pillai3, S. Ajithkumar4 and R. Uma
1MVSc Student, 2Assistant Professor, 3Professor and Head, Department of Veterinary Clinical Medicine, Ethics and
Jurisprudence, 4Professor and Head, University Veterinary Hospital and Teaching Veterinary Clinical Complex,
College of Veterinary and Animal Sciences, Mannuthy, Thrissur (Kerala).
[Received: 06.8.2018; Accepted: 18.2.2019]
{DOI 10.29005/IJCP.2019.11.1.011-014}

Twenty dogs with chronic mitral valve disease were evaluated for the evidence of electrocardiographic
variations. The changes recorded were atrial fibrillation, first degree atrioventricular block, second degree
atrioventricular block, ventricular premature complex, sinus tachycardia, ‘P’ mitrale, ST coving, increased amplitude of
R wave and low amplitude of QRS complex. Normal sinus rhythm was also recorded.
Keywords: Atrial fibrillation, Chronic mitral valve disease, Electrocardiography, Ventricular
premature complex.

Chronic mitral valve disease is the most common acquired heart disease in dogs. It is estimated to account for 75 per cent of all cardiac diseases in dogs (Atkins et al., 2009). Electrocardiography (ECG) is widely used as
a diagnostic tool for cardiac disorders.Though ECG cannot be considered as diagnostic in most of the cardiac ailments, it is of utmost importance in recording life threatening arrhythmias. The present study describes
electrocardiographic changes in dogs with chronic mitral valve disease.

Materials and Methods
Twenty dogs with chronic mitral valve disease were selected for the study. Definitive diagnosis of the disease was done by echocardiographic examination. Electrocardiograms were recorded using BPL-CARDIART-6108T ECG machine at a paper speed of 25mm/second and sensitivity of 1mv = 10 mm (Martin, 2002). Standard bipolar limb lead II was studied. Animal was placed in right lateral recumbency in an isolated environment for 5 to 10 minutes in
presence of owner before attempting ECG.

Results and Discussion
Arrhythmias were recorded in fourteen animals. Six animals showed normal sinus rhythm. Types of cardiac arrhythmias recorded were atrial fibrillation, first degree atrioventricular (AV) block, second degree
AV block, ventricular premature complex (VPC), sinus tachycardia, ‘P’ mitrale, increased amplitude of R wave,ST coving and low amplitude QRS complexes. Atrial fibrillation was recorded in two Labrador retrievers (Fig. 1). Borgarelli et al. (2004) and Jung et al. (2016) also made similar observations in dogs with mitral valve disease. Structural changes that result associated with mitral valve disease affecting left atrium can increase the atrial wall stress.

Electrical changes associated with remodeling of the left atrium can also result. These changes can produce atrial  fibrillation as also reported by Van den Berg et al. (2002) and Hunter et al. (2012). Loss of atrial contraction
and shortened diastolic filling time in atrial fibrillation reduce cardiac output and increase atrial filling pressure. Quality of life of the patient is compromised in such situations as also mentioned by Burashnikov and
Antzelevitch (2010).

Ventricular premature complex (VPC) was recorded in two ECGs (Fig. 2). In VPCs, electrical impulses are initiated within the ventricles instead of sinoatrial node causing  ventricles to contract too early. These cases require urgent therapeutic interventions. First degree AV block and second degree AV

block were present in two cases each (Fig. 3, 4). Second degree AV block results from degenerative lesions caused by endocardiosis, fibrosis and physical disruption from cardiomayopathy or from inflammatory conditions as also reported by Ettinger and Feldman (2005). Similarly Rasmussen et al. (2012) reported, ventricular premature
complexes and second degree AV block were the common findings in dogs with myxomatous mitral valve disease and the frequency did not affect the severity of disease.

One dog had sinus tachycardia without any other morphological change (Fig. 5). Sinus tachycardia is an early sign of cardiac compensation. Early neuro-hormonal activation causes higher heart rate in the beginning stage of mitral valve disease.

P mitrale and increased amplitude of R wave was recorded in one case which was suggestive of left atrial and ventricular enlargement (Fig. 6). These changes occur because of the chronic hemodynamic changes secondary to mitral regurgitation. Left atrium is the first chamber subjected to the increase in internal pressure created by the regurgitant jet while size of the left ventricle deteriorates progressively with the cardiac overload as also mentioned by Baison et al. (2016). Echocardiographic examination confirmed the left atrial and ventricular enlargement in
this case.

Electrocardiograms of three animals showed ST coving (Fig. 2). Similarly Suh et al. (2006) reported, ECG signs indicating myocardial hypoxia can be seen in advanced stages of heart failure. Low amplitude QRS complexes were observed in one non-descript dog with pleural effusion (Fig.7). This was in accordance with the findings of Smith et al. (2015). Low amplitude QRS complexs are associated with hindrance in the transmission of cardiac electrical impulses due to the presence of fluid in the thoracic cavity. Normal sinus rhythm was noticed in six cases
(Fig. 8). Similarly Baison et al. (2016) recorded sinus rhythm in seventeen out of eighteen dogs with chronic mitral valve disease. Variations in ECG in such cases may occur as haemodynamic changes and neurohormonal
activation results through the course of the disease.

Different variations in ECG were recorded in the present study. Interpretation of electrocardiograms will be of benefit in cases that require immediate treatment for the variations in addition to the treatment instituted for chronic mitral valve disease.

References
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