Prevalence Study (2017-2020) of Heart Failure among Dogs of Hyderabad, Telangana State

All the adult dogs of various breed, age and gender that were presented to the non-infectious medicine ward of Teaching Veterinary Clinical Complex, College of Veterinary Science, Rajendranagar and Veterinary Hospital  Bhoiguda, Secunderabad during 2017 -2020, were included for the present study. Further, those dogs that had a history and manifestations suggestive of heart failure were considered for detailed evaluation. All these dogs were clinically and physically evaluated in detail and later subjected for specific tests like electrocardiography, thoracic radiography and echocardiography for confirmation of cardiac disease, to access its prevalence.

Electrocardiographic evaluation of heart failure suspected dogs was carried out using smart phone based ECG (sECG), that can either be fixed onto the back of an iPhone or any android phone or can be used separately by placing the phone close to the electrodes. The left cardiac area (between 3-5 ICS) is trimmed, moistened with conduction gel or alcohol and the smart phone device was positioned on the left chest wall, just caudal to the olecranon (precordial area), with a slightly dorso-cranial / ventro-caudal orientation (Kumar et al., 2021). A single lead (L II) sECG was recorded for 30 seconds in an unsedated dog either on its right lateral recumbency or in standing position, at 25 mm/s. The recorded sECGs were automatically digitised by the device and stored as a PDF, which can subsequently be analysed on a computer and interpreted as described by Tilley (1992). Thoracic radiographs were taken on left lateral and ventro-dorsal views at the peak inspiration. Transthoracic echocardiograms were obtained with the unsedated dogs in right lateral recumbency (Allworth et al., 1995). Transducer is located parasternally between right third and sixth intercostal spaces between sternum and costochondral junction (Thomas et al., 1994). M-mode recordings were taken at the high papillary level to measure various left ventricle dimensions (AllWorth et al., 1995) and pulsed wave Doppler and colour flow Doppler was also done to confirm valvular disease (Dominique and Marc-andre, 2008).

During the study period (2017 – 2020), a total of 9369 adult dogs with the history and signs suggestive of various systemic diseases were presented and out of which, 309 were exhibiting the manifestations indicative of heart failure. All these cases when subjected for detailed analysis using ECG, thoracic radiography and echocardiography, 146/309 cases were diagnosed for heart failure. Whereas, the remaining 163/309 dogs were diagnosed with respiratory disorders (69), renal insufficiency (57), hepatic insufficiency (26), pyometra (07) and anemia (04). The overall prevalence of heart failure was observed to be 1.55 % (146) among the dogs presented with systemic diseases (9369). It was 47.25% (146) among dogs which were exhibiting clinical manifestations (309) suggestive of heart failure (Table 1 and Fig1). All these dogs that were diagnosed for heart failure were showing similar manifestations viz., exercise intolerance, dyspnoea at rest, nocturnal cough, insomnolence, anorexia etc. are associated with left main stem bronchus compression and pulmonary edema (Kumar and Kumar, 2021; Turgut et al., 2017). Coughing, which is predominant in these cases might be a result of pressure on the left mainstem bronchus caused by left atrial enlargement (Satish et al., 2011), rather than a result of pulmonary edema (Carr, 2004). Lethargy and reduced physical activity could be due to diminished oxygen delivery to the tissues associated with reduced cardiac output (Freeman, 2012). Hypostastic congestion of lungs and pulmonary edema lead to dyspnoea at rest (Ristic, 2004). Other pathophysiological events that help for the development of the clinical manifestation of the disease may include an increase in end-diastolic volume that subsequently increase myocardial stress, thinning of the myocardium and rounded left ventricle apex (Domanjko et al., 2002).





Abnormalities associated with P, QRS and T that were detected among these heart failure dogs include, wide and / or elevated P, R and QRS waves, atrial fibrillation and ventricular premature complexes. Auscultation of cardiac area revealed murmur of varied intensity (G I to IV). The systolic murmur on auscultation is a hallmark of the valvular disease, where the intensity varies with severity of disease and can be a significant among aged dogs (Kumar and Kumar, 2021). Presence of S3 sound with an increased intensity of S1 and decreased S2 sound on left cardiac area are significant physical findings of MMVD (Hagstrom et al., 1995). Bulge of left atrium, elevation of trachea, pulmonary congestion and vertebral heart score ranging from 11.8 to 13.2, were the significant radiographic abnormalities of the present heart disease cases. Radiographic assessment of cardiac size is another important guide to diagnose cardiac disease which also be used to monitor the severity of disease (Thrall, 2007), though it is difficult to make accurate subjective assessment whether the cardiac silhouette is enlarged or misshapen (Nakayama et al., 2001). However, thoracic radiography is considered the clinical ‘‘gold standard’’ method for the diagnosis of heart failure (Balbarini et al., 1991). Radiographically estimated vertebral heart score of more than 12 dogs along with plasma NT pro-BNP (>1500 pmol/L) are the significant aspects of threatened heart failure among chronic mitral valve diseased dogs (Bonagura and Schober, 2009). The common echocardiographic abnormalities noticed among these 146 heart failure dogs include hypokinesis of interventricular septum, dilated atria, ventricles, degeneration of mitral valve leaflets, kinking, prolapse and flail nature of mitral valve leaflets and pericardial effusion. Based on these findings dilated cardiomyopathy, valvular disease and pericardial effusion were diagnosed as the causes of heart failure. Though, clinical and physical examination, thoracic radiography, electrocardiography, echocardiography and cardiac biomarkers are available diagnostic tools (Nakayama et al., 2001), non invasive techniques like radiography and echocardiography are the most common diagnostic procedures used in confirming the heart disease in dogs (Kumar et al., 2021). The degree of prevalence of heart failure in dogs noted in the current study is in agreement with that of Satish et al., (2011) who reported an overall occurrence of cardiac disease in dogs as 1.65 % and it was 48.6% among dogs exhibiting clinical manifestations suggestive of heart disease. Haritha et al., (2017) reported overall prevalence of cardiac disease in dogs as 1.77% and the prevalence among the dogs exhibiting clinical signs suggestive of heart disease was 56.21%. The prevalence of DCM in dogs was reported to be between 0.45% and 1.1% by the COVE study group (1995). However, higher prevalence rate was also reported by other workers as 11.3% (Detweiler and Patterson, 1965), 10% (Atkins et al., 2009) and 5% (Ettinger and Suture, 1970). Baumgartner and Glaus, (2004) reported prevalence rates of 49.40% (valvular disease), 21.10% (DCM), 12.4% (pericardial effusion) and 0.60% (hypertrophic cardiomyopathy). Low prevalence of 0.68% was reported by Kumar et al., (2021) and 0.5% by Sisson et al., (2000). Deepti et al., (2016) reported the occurrence of CHF in dogs as 0.45%, MVD as 0.11% and DCM as 0.34%, respectively. The difference in the prevalence rates of the heart disease in dogs could be due to the diverse populations being screened in each study with respect to age, breed, gender and geographical location.

The various cardiac diseases viz., dilated cardiomyopathy, valvular diseases and pericardial diseases that are responsible for heart failure in the present study are more predominantly recorded (51.37%) in dogs between 10 to 14 year. This was followed by 32.87% among 5 to 10 year old dogs and 10.27%  among those aged more than 14 years and less prevalence rate of 05.48% was recorded in dogs of less than 5 years (Fig 2). These findings are near agreement to the findings of Satish et al., (2011) who reported that age wise occurrence of cardiac disease in dogs was 61.24% in 10 to 14 years of age, 21.12% in 5-9 years, 12.18% in more than 14 years and 5.46% in less than 5 years of age. Haritha et al., (2017) reported the highest prevalence of DCM in dogs between 05 to 10 years of age (50.44%), whereas Deepti et al., (2016) reported the age wise highest prevalence in 5-10 years of age (54%), Jeyaraja et al., (2008) reported the average age as 8.5±0.5 yrs and whereas, Tidholm et al., (2001) stated that age at onset of clinical signs varies considerably, although most dogs are initially presented at the age of five to seven years. The current findings are in agreement with Kumar et al., (2021) who reported higher prevalence of cardiovascular diseases in aged dogs, stating that the ageing process affects the heart and the blood vessels by depleting cardiovascular reserve and altering the responses to various diseases and medications. Ageing has selective effects on peripheral vascular function, including a reduced arterial dilating response to catecholamines.



With respect to breed wise prevalence study, the highest number of various cardiac diseases were detected among Labrador retriever (39.72%) followed by Pomeranian (26.71%), Spitz (13.01%), Doberman (06.16%), Boxer (04.11%), Cross breed (04.11%), Cocker spaniel (02.74%), Pug (2.05%) and lowest number of cases (01.37%) that were diagnosed for for heart failure was recorded in Dachshund (Fig 3). This pattern of variation in prevalence could be attributed to the predominance of a larger number of dogs of Labrador retriever and Pomeranian breeds in the geographic place where the present study was carried out. It is also evident that higher prevalence of heart failure in certain breeds that could be possibly related to inherited transmission of heart disease in these breeds. Dukes (2000) detected the familial predisposition to DCM in certain breeds like Doberman pinscher and Boxers. Dilated Cardiomyopathy occurs with significantly greater frequency in pure bred dogs than cross breed dogs (Mc Ewan et al., 2003). Clinical forms of DCM have been described in giant breed dogs (Tidholm, 2001), Doberman pinscher (Domanjko et al., 2002) and Boxers (Valentina et al., 2011). Further, canine DCM has been documented in many breeds, although uncommon in dogs weighing less than 15 kg (Fox, 1998).



The prevalence of heart failure was relatively higher in male dogs (66.44%) when compared to that of females (33.56%) and these findings are in accordance with that of Deepti et al., (2016), Haritha et al., (2017) and Satish et al., (2011), who documented greater prevalence of cardiac disease in males than in females. Sisson et al., (2000) also observed that the males were nearly twice as often affected than females with respect to the development of heart failure or sudden death with dilated cardiomyopathy and Martin et al., (2009) reported males are nearly four times more affected than female dogs (Fig 4).

Dogs presented with the history and signs like dyspnoea at rest, exercise intolerance and low physical activity should be considered for cardiac evaluation by ECG, thoracic radiography and echocardiography. Even though, the heart failure is common among all the breed and gender of adult dogs, more emphasis in evaluation should be given among Labrador retriever and also among those dogs that are more than 10 years.