Characterization of Cardiac Diseases in Dogs Prevalent in Indian Conditions

Cardiac diseases are commonly encountered in general veterinary practice and it is estimated that approximately 10% of all dogs presented for primary care to veterinary hospitals have cardiac diseases in North America (Atkins et al., 1991). Whereas Haritha et al., (2018) conducted a study in India on dogs brought to PVNRUVAFS, Rajendranagar, Hyderabad and found overall prevalence of cardiac disorders to be 1.77%. Another researcher Thirunavukkarasu, (2019) conducted study in Chennai during study period 2018- 2019 and reported incidence of acquired heart diseases (AHD) to be 0.37 per cent. AHD occurs most often secondary to degenerative mitral valve disease, dilated cardiomyopathy (DCM) and pericardial diseases. Hypertrophic cardiomyopathy (HCM) is another acquired heart disease which is a rare form of heart muscle disease in dogs (Thirunavukkarasu, 2019). Auscultation, radiography, electrocardiography, echocardiography and biochemical tests are most useful diagnostic procedures employed in recognizing the cardiac diseases in dogs (Hoque et al., 2019).

Thoracic radiography is the most commonly applied method for the diagnosis of congestive heart failure and considered as clinical gold standard (Balbarini et al., 1991). Electrocardiography is another non-invasive diagnostic tool for monitoring heart rate, cardiac rhythm, conduction integrity and electrical axis (Mukherjee et al., 2015). Echocardiography has emerged as the most versatile imaging technique for the study of cardiac diseases (Bodh et  al., 2016). Circulating cardiac biomarkers also continue to generate lot of interest in research (Schober et al., 2010] and need to be studied in detail.                  

Canine cardiac diseases are being studied around the globe but research in this part of country is lacking. Therefore, present study was planned with the objective to diagnose and characterize different canine cardiac affections reported in referral hospital setups of northern part of India and also to identify sensitivity of biochemical and cardiac bio-markers for these cardiac diseases. Assessment of different echocardiographic indices was undertaken for further characterization of cardiac affections.

Approval from Institutional Animal Ethics Committee was taken. Present study was carried out on dogs presented to Veterinary Clinical Complex, Lala Lajpat Rai University of Veterinary and Animal Sciences (LUVAS), Hisar for a period of 8 months i.e. from August’ 2019 to March’ 2020. Out of total 2582 screened dogs, 41 dogs were suspected for cardiac affections based on preliminary screening and were included in the study. Six healthy dogs were included as control group.
 
a) Haemato-biochemical examination
 
Haematological estimation was done using Automated hematology cell counter MS4s, MeletSchlosing Lab and for biochemical and electrolytes estimation (EM Destiny 180, Erba Diagnostics Mannheim GmbH and EasyLyte EXPAND analyzer was used.
 
b) Radiographic measurements
 
 
Thoracic radiography was performed with an X-ray unit (Siemens X- Ray machine) and images processed through Computed radiography system (Konica Minolta PVT, LTD).  Heart size in the lateral view was evaluated using vertebral heart scale (Buchanan and Bucheler, 1995).
 
c) Electrocardiography
 
Electrocardiogram was recorded using ECG 300G- VET CONTEC Electrocardiograph machine and Bailey’s hexaxial limb lead as described by Tilley and Smith, (2008).
 
d) Echocardiography
 
Siemens Acuson S2000 ultrasound machine (Siemens Healthcare Pvt. Ltd.) with multifrequency (2-4MHz) cardiac phased array probe was used. All the dogs were clipped on the right and left thoracic wall from 2^nd to 7^th intercostal spaces as described by (Boon, 2011) and placed in lateral recumbency on a specially designed table having “V”- shaped cut on the table top. .
 
e) Cardiac biomarker estimation
 
Serum samples collected on first day was stored at -20°C for Cardiac Troponin I estimation using commercially available Canine Cardiac Troponin 1 ELISA kit (Bioassay Technology Laboratory).
 
f) Statistical analysis
 
Statistical analysis performed using SPSS 23. Duncan test and two-way ANOVA with repeated measures was applied on the data obtained. The results were presented as Mean±S.E. at 5 per cent level of significance (p=0.05).

Trends of cardiac diseases in dogs of this northern part of country revealed that 0.77% of the reported patients were having cardiac diseases. Almost similar prevalence was reported by Thirunavukkarasu, (2019) in Chennai. Out of 41 suspected dogs, 11 dogs were ruled out on the basis of electrocardiographic and radiographic findings. These ruled out 11 dogs were later confirmed to be affected with respiratory affections. Remaining thirty dogs were screened with echocardiography and 20 cases turned out to have confirmed cardiac diseases. Echocardiographic findings categorised these affected dogs into five categories. Most common cardiac disease diagnosed was DCM (8 dogs; 40%) followed by PE (4 dogs; 20%), HCM (3 dogs; 15%), R- CHF (3 dogs; 15%) and systolic dysfunction (2 dogs; 10%). Similar reports on the predominance of DCM among acquired cardiac diseases were reported by Satish Kumar et al., (2016) and Jan et al., (2018) in different parts of India in different breeds. DCM predominance seems to be because it has long been suspected to have a genetic basis and autosomal dominant mode of transmission had been reported in Newfoundland (McEwan, 1998). Predominance of Labrador retriever in this part of country makes DCM to be predominantly occurred cardiac diseases. Maximum occurrence of cardiac diseases was observed in 4-9 years age group i.e. adult dogs (60%) followed by 0-4 year age group (25%) and 9-14 years age group (15%). Male dogs dominated females in overall occurrence of cardiac diseases with 60% (12/20) and 40% (8/20) respectively. Higher occurrence in male dogs may be because of preference of pet owners for keeping male dogs in comparison to female dogs. Although with this amount of sample size true sex predisposition cannot be predicted.

Breed wise distribution revealed  Labrador retriever to be most predisposed (45%) followed by Pug (20%), Rottweiler (15%), German shepherd (10%), Golden Retriever (5%) and Mongrel (5%). Labrador retriever predominance suggesting higher ownership of this breed in our locality as well as because of inbreeding of poor breed lines (Vishnurahav et al., 2018).

Haematological parameters revealed significant increase in neutrophil count in affected dogs as compared to control. This increase attributed to inflammatory reaction associated with increased level of TNF and IL^-1 (Singh et al., 2014) or due to concurrent secondary bacterial infection of respiratory tract (Venkatesakumar et al., 2018). Significant increment in Lactate dehydrogenase (LDH) with mean value (291.65- 586.47 IU/l) was recorded (except systolic dysfunction), in contrast to control group animals as shown in Fig 1. Elevated LDH may be due to limited skeletal muscle blood flow in patients with cardiac diseases leading to low cardiac output and increased peripheral resistance and muscle degeneration (Indhu et al., 2018). So, elevated serum-LDH might be considered as a risk factor for cardiac diseases in dogs and can be a routine biochemical indicator for cardiac affections.



Electrocardiographic and radiographic findings of affected dogs are presented in Table 1 and 2 respectively. Radiographic findings like globoid cardiac silhouette, increased sternal contact, cardiomegaly, tracheal elevation, left atrial, left ventricular and right ventricular enlargement are suggestive of cardiac diseases. Left ventricular enlargement (72.7%) gave indication about myocardial diseases i.e. DCM and HCM. Globoid cardiac silhouette (75%) found to be characteristic for PE. In the present study VHS (11.8- 13.5) was found to be sensitive in diagnosing cardiac cases but lack further characterization. Moreover, VHS had unspecified sensitivity and can suffer from considerable observer variation (Ferasin et al., 2013).





Severe left atrial dilatation in DCM affected dogs causes atrial fibrillation (Jeyaraja et al., 2015). Electrocardiographic findings for DCM and HCM recorded in present study were left atrial (54.54%) and left ventricular enlargement (45.45%) respectively, low voltage QRS and electrical alterans (75% each) in Pericardial effusion (PE) and right atrial enlargement (66.67.%) in R-CHF. Changes in electrical alterans may be because of alternating configuration of the ventricular action potential or alternating changes in intra ventricular conduction or due to exaggerated anatomical or swinging motion of the heart within distended pericardial sac (Bodh et al., 2016). Low voltage QRS complex in PE might be because of internal short circuiting of the electrical currents by the accumulated fluid within the pericardial space (Wray, 2014).

Increased mean values (151.72 ng/l - 586.47 ng/l) of canine cTnI were observed in cardiac affected dogs on day 0 before the start of therapy as compared to the control group (91.33ng/l), with HCM (586.47ng/l) having highest mean value (Fig 1). Similar findings were reported by Chun et al., (2010) in PE affected dogs and by Falk et al., (2013) in CHF affected dogs.

Mean ± SE of M mode echocardiographic parameters are presented in Table 3. In DCM affected dogs, B-mode examination revealed left atrial enlargement, left ventricle enlargement and thinning of inter-ventricular septum. M-mode echocardiographic findings showed significant increase in mean values of LVIDs (53.49±2.97mm), LVIDd (61.83±3.44mm) with significant decrease in mean values of IVSd (7.18±0.64mm), IVSs (7.16±0.89mm), LVPWs (10.54±1.24) and LVPWd (7.58±0.78) in DCM affected dogs. There was reduced contractility of chambers manifested by low EF% (30.11±3.23%) and FS% (13.43 ±1.62%). Present findings were in agreement with earlier studies Karlapudi et al. (2012) and Sidhu et al., (2018). Right parasternal short axis view at the level of mitral valve showed increased EPSS ranging from 9-16mm. LA/Ao was significantly increased indicating left atrial enlargement (Fig 2). Significant increase in mean values of end diastolic volume (EDV) (150.99±22.70ml) and end systolic volume (ESV) (106.39±16.67ml) was also observed. Dogs having pericardial effusion showed presence of hypoechoic to anechoic free space between epicardium and pericardial sac and swinging motion of heart (Fig 3). In HCM concentric LV hypertrophy indicated by increased IVSd/LVIDd was the most important echocardiographic finding as. There was significant decrease in mean values of LVIDs (14.40±2.85mm), LVIDd (24.23±1.98mm) with significant increase in mean values of LVPWd (13.20±2.06mm), IVSd (10.83±1.10mm). Papillary muscle hypertrophy with increased echogenicity of left ventricular posterior wall was also observed on B-mode image in HCM affected dogs. In R- CHF, prominent echocardiographic findings were right sided chambers enlargement i.e. right heart dilatation, bowing of interventricular septum towards left ventricle due to pressure or volume overload and increased right ventricle chamber size compared to left ventricle chamber size. Echocardiographic finding in systolic dysfunction revealed significant decrease in mean values of EF (17.82±6.55%) and FS (10.84±6.06%) and significant increase in ESVI (end systolic volume index). 





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Echocardiography serves as the most sensitive non-invasive diagnostic tool for cardiac diseases diagnosis and categorisation. Prevalence of cardiac disease was found to be 0.77% (20/2582) with dilated cardiomyopathy to be most prevalent cardiac disease. Labrador retriever reported to be most predisposed breed for DCM in this Northern part of India followed by Rottweiler as most affected with pericardial effusion. Adult dogs (4-9 years age group) were found to be more commonly affected and should be screened routinely for cardiac affections. Cardiac troponin-I with cut off value above 92 ng/l detect all forms of cardiac affections and serve as reliable sensitive biomarker, while Lactate dehydrogenase serve as good screening biochemical marker with significant increase in all the cardiac cases ranging from 291 IU/l to 586.4 IU/l. Further work needs to be undertaken in different breeds of India and for longer duration to better understand cardiac diseases in relation to breed, area and lifestyle of pet parents.