Study on Incidence of Canine Cardiac Disorders in Jabalpur City

Heart disease in dogs is almost as common as it is in humans. Cardiac diseases in canines are an extensively studied phenomenon all over the world but meagre information has been reported in India. The recognition of canine cardiac diseases had been delayed and ignored on account of lack of awareness and knowledge by the owner and inadequate diagnostic facility in our country (Devi et al., 2009). Cardiac disorders are reported to be the second most commonly encountered disorder after cancer (Sahoo et al., 2021). Despite these numbers, many people are unaware that their dog may be at risk of heart disease. It is important that every dog considered vulnerable to cardiac diseases should be examined for cardiac function during routine examination. A delay in diagnosis and treatment could result in a grave prognosis or life-threatening condition. Many a times the condition was detected too late until pronounced signs appear (Martin et al., 2009). The substantial involvement of heart has provoked numerous investigations leading to advancements in medical and surgical management of cardiovascular disorders. Presently access to echocardiographic facility in veterinary practice has revolutionized the field of cardiology by aiding the diagnosis and management of cardiac diseases in dogs.

In a period of 06 months, starting from October, 2019 to March, 2020, 109 dogs having clinical signs related to cardiovascular disorders were screened at the Veterinary Clinical Complex, Nanaji Deshmukh Veterinary Science University, Jabalpur.

The dogs were firstly subjected to electrocardiographic examination for the assessment of the derangements in the heart conductivity. The dogs having deviation from the normal conduction activity were further subjected to echocardiographic and radiographic examination. A total of 60 dogs were confirmed to be having cardiac abnormalities.
 
Electrocardiographic examination
 
Electrocardiographic tracings were recorded with Cardiart electrocardiography machine (Cardiart 8408 View; BPL Limited) in a distraction free area. The dog was placed in right lateral recumbency with its leg perpendicular to the long axis of the body, on an insulated surface. The electrodes were attached to the dog’s skin after shaving the hair. Generous application of coupling gel was done. Each pair of limbs were not allowed to come in contact with each other. The point just proximal to the olecranon on the lateral aspect (caudal surface of elbow) was used as reference mark for the forelimbs, whereas the point proximal to the patella (over the stifle) on the lateral aspect was used as reference mark for hind limbs. The limb leads were attached to these reference marks. Three bipolar limb leads (lead I, lead II and lead III) and three augmented unipolar limb leads (aVR, aVL and aVF) were used (Fig 1).



ECG was recorded with paper speed of 50 mm/sec. Before each recording, a one millivolt standardization pulse was made. A longer rhythm strip was run on lead II and four or five beats were recorded on each lead. Tilley (1985) guidelines for measuring complexes and intervals were followed for interpretation of electrocardiograms.
 
Radiographic examination
 
Digital X rays were taken for assessment of alteration of the cardiac silhouette by using 100 mA X-ray machine and CR System. The animal was placed in the left lateral recumbency and in the dorsal recumbency to obtain right lateral and ventro-dorsal views of the thoracic region. For this view, the sternum and spine were in the same horizontal plane and the front legs were pulled as far cranially as possible. Exposure times and kilovoltage were adjusted according to the technique chart.  All radiographs were evaluated empirically.
 
Measurement of vertebral heart score (VHS)
 
The general principles followed for evaluation of cardiac radiographs were those advocated by Buchanan and Bucheler (1995). The vertebral heart score (VHS) compares the heart on the lateral view to the dog’s thoracic vertebrae. The long axis (L) of the heart was measured from the ventral border of the left main stem bronchus to the most distant ventral contour of the cardiac apex. This dimension reflects the combined size of left atrium and left ventricle and compared this to the vertebrae starting with the cranial edge of 4^th thoracic vertebra (T4) and result expressed in units of vertebral lengths.The maximum short axis (S) of the heart was measured at the widest point of the cardiac silhouette on a line perpendicular to the long axis (L) at the level of the caudal vena cava and compare this to the thoracic vertebrae, again starting from the 4^th thoracic vertebra (T4) (Fig 2). Vertebral Heart Score was calculated by using the formula:

V.H.S. = L+S = No. of vertebrae traversed.

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Measurement of cardio-thoracic ratio (CTR)
 
The Cardio-thoracic ratio (CTR) was assessed by comparing the greatest width of the heart silhouette and the distance between the thoracic walls in the same plane, according to methodology described by Mohammadyar et al., (2019) (Fig 3).

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Echocardiographic examination
 
The echocardiographic examination of the dogs was carried out to evaluate the structural and functional alterations. The animals were kept in minimal stress conditions, so that the evaluation would not be affected. The hair from the thoracic area were clipped, usually between 3^rd-5^th  inter-costal space on right side. Adequate amount of coupling gel was applied after clipping, for echocardiographic evaluation (Fig 4). Evaluation of all the dogs was performed by using sector transducer having frequency 2-4 MHz by using the ultrasonography machine. Assessment of the cardiac parameters was done by using following views:

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Long axis view
 
By placing the transducer over the palpable apex beat, on the right side with no angulation. At this position, left side of heart, ventricle and atrium was visualized, with part of right side. From the above position, the transducer was slightly rotated anticlockwise, while tilting it dorsally. This caused the sector plane to transect the aorta and permit the examination of left ventricular outflow tract and 4 chamber view.
 
Short axis view
 
Transverse or short axis image of the heart was obtained by rotating the transducer towards the sternum with reference mark turned 90 degrees from its location from long axis plane. This view permitted the examination of left ventricle with papillary muscle, mitral valve, heart-base aorta and heart base pulmonary artery. B-mode was used for the visualisation of the chambers and normal morphology of the heart and M-mode for the assessment of the diameter of various chambers of heart whereas, colour Doppler was used to check valvular leakage (valvular regurgitation).

Incidence
 
Total 6245 cases were registered at Veterinary Clinical Complex (V.C.C.) during the period of six months (October, 2019 to March, 2020). Out of these 4509 (72.20%) cases were of canine, in which 109 (2.41%) were found having various symptoms of cardiac disease such as laboured breathing, exercise intolerance, distended abdomen, frequent coughing, dyspnoea, hind limb weakness, ascites, obesity and fainting or collapsing. On further examination, out of 109 cases only 60 (1.30%) cases were found to be of cardiac origin (Table 1). Badsar et al., (2018) reported that overall prevalence of cardiac abnormalities in dogs was 2.41% (40/1655) while Haritha et al., (2017) and Himalini et al., (2017) reported overall prevalence of cardiovascular diseases to be 1.77% and 1.61%, respectively which is in accordance to the present study.


 
Distribution of dogs after screening
 
The data recorded is presented in Table 2. Among the total cases (109) showing clinical signs of cardiac affections majority of dogs, 60 (55.04%) were diagnosed with various types of arrhythmias, pericardial effusion, dilated cardiomyopathy and hypertrophy. The diagnostic modalities revealed that 15 (13.76%) cases were having kidney affections, 26 (23.85%) cases showed ascites due to non-cardiac origin and 8 (7.33%) cases were having splenic and other affections. Vishnurahav et al., (2018) screened 203 suspected cases for cardiac disorders and reported the prevalence of cardiac disorders to be 28.07% (57/203) whereas Badsar et al., (2018) and Kumar et al., (2011) reported 40.81% and 55.30% prevalence of cardiac diseases amongst suspected cases. The clinical signs that are expressed by dogs having cardiac disease can be exhibited while ailments of other organ systems also. Hence, the cases having symptoms related to cardiac disease can also be caused by derangement in physiological activity of other biological tissues too.


 
Age wise incidence of dogs affected with cardiac disorders
 
Complete history of all dogs suffering with cardiac affections were recorded which included age, sex, breed, diet and duration of symptoms. Maximum incidence (48.33 per cent) of various affections diagnosed during study was related to age group of 5-10 years followed by below 5 years (36.67%) and above 10 years (15.00%) (Table 3). Haritha et al., (2017) reported highest prevalence (50.44%) in dogs between 5-10 years. Similar findings were reported by Montoya (2002), Jeyaraja et al., (2008) and Hoque et al., (2019), supporting the findings of this study. This might be due to many factors such as poor diet; lack of exercise and overweight represented the disease up to middle age as observed in the present study; the disease is not always due to senile changes. Some breeds such as Labrador and German Shepherd are predisposed to cardiac diseases, this might also be a reason to develop the disease in an early age.

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Sex wise incidence of dogs affected with cardiac disorders
 
During the study period total 4509 cases were presented at Veterinary Clinical Complex out of which 3045 were male and 1464 were female. Out of which 42 males and 18 females were suffering with various cardiac affections. Thus, the incidence was accounted to be 1.37% and 1.22%, respectively (Table 4). Whereas among 60 dogs suffering with cardiac disorders, 42 (70%) were male and 18 (30%) were female. Kumar (2019), Vishnurahav et al., (2018) and Haritha et al., (2017) also reported the similar trend regarding the gender predilection. The greater incidence (1.37%) in male dogs can be attributed to the large number of male dogs being referred to VCC or more likability of the owners for male dogs.

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Breed wise incidence of dogs affected with cardiac disorders
 
There was no breed predilection noticed, however more cases were observed in Labrador (33.33%) followed by Mongrel (25.00%), German Shepherd (13.33%) and Pomeranian (06.67 %) (Table 5). Similar findings have also been reported by Hoque et al., (2019), Badsar et al., (2018) and Reetu et al., (2017) as these authors also reported highest prevalence rate in Labradors. Labrador were affected mostly might be due to genetic predisposition of breed to the cardiac affection however no such examination was performed in the present study. Another reason was attributed to presence of obesity in Labradors with lack of exercise which can lead to significant health problems such as joint problems, metabolic and digestive disorders, back pain and heart disease. In other breeds also idiopathic cardiac affection could develop or it may be due to various predisposing factors which were beyond the capacity of present research work.

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The distribution of the 60 dogs having cardiac disorders was recorded as follows:

Arrhythmia in 42 dogs (85.71%) followed by left atrial or bi-atrial enlargement in 07 dogs (14.28%), dilated cardiomyopathy (DCM) in 06 dogs (10%), hypertrophic cardiomyopathy (HCM) in 03 dogs (05%) and pericardial effusion (PE) in 2 dogs (3.33%).

The overall incidence of cardiac disorders in a period of 6 months, from October, 2019 to march, 2020 was recorded to be 1.30%, in Jabalpur city. The incidence of cardiac disorders was recorded more to be in male dogs (1.37%) than female dogs (1.22%). The incidence was more in Labradors followed by Mongrel. The arrhythmia was encountered to be the most common cardiac disorder followed by left or bi-atrial enlargement and DCM. Hence it can be ascertained that the cardiac disorders are an important cause of suffering in dogs that are often the silent- killers. So, it’s important to develop a proper routine to diagnose cardiovascular disorders at various facilities to diagnose and treat the cardiac disorders, as early as possible. The largest portion of the favourable outcome of the treatment depends on the early and accurate diagnosis of the condition prevailing. So, echocardiography is the gold standard for the diagnosis of cardiac disorders and is definitely to be combined with electrocardiographic examination and radiographic examination for proper diagnosis of the condition.

The authors are grateful to the Dean, College of Veterinary Science and Animal Husbandry, NDVSU, Jabalpur for providing the necessary facilities to carry out the research work. This study was not possible by kind cooperation and awareness of pet lovers of Jabalpur (M.P.).

None.