Advance Modalities in Diagnosis and Prediction of Canine Cardiac Diseases

Cardiac diseases in dogs are widespread, with studies indicating that approximately 10-15% of the canine population are affected by some form of heart disease (MacPete, 2018). The vast majority, 95% of them are acquired and rest 5% are congenital (Hoque et al., 2019). Canine cardiac diseases encompass a broad spectrum of heart-related conditions that affect dogs, ranging from structural abnormalities to functional impairments of the heart. Congenital cardiac diseases (CHDs) include anomalies such as Patent Ductus Arteriosus (PDA), Pulmonic Stenosis (PS) and Subaortic Stenosis (SAS), Atrial septal defects (ASD), Ventricular Septal Defect (VSD), Tricuspid Dysplasia (TD) and Tetralogy of Fallot (ToF) (Buchanan, 1999; Baumgartner et al., 2003; MacDonald, 2006; Oliveira et al., 2011; Bellumori et al., 2013; Kumar and Kumar, 2024a) while acquired diseases often include valvular diseases such as dilated cardiomyopathy (DCM) and myxomatous mitral valve degeneration (MMVD) (Janus et al., 2016; Keene et al., 2019; Kumar and Kumar, 2024b). Among these, MMVD is particularly common, especially in small breed dogs and it constitutes more than 70% of the cases of heart disease in these breeds. Heart diseases are classified into stage A, B,C,D with stage C showing clinical signs of congestive heart failure by MMVD and stage D denoting patients with end stage congestive heart failure (CHF) by MMVD (Atkins et al., 2009; Keene et al., 2019). For evaluating the accuracy of radiographic diagnosis of cardiac diseases in dogs, various subjective and objective methods of calculation are used such as Vertebral heart score (VHS), thoracic depth/thoracic width, cardiothoracic ratio. VHS is the extrapolation of LA and SA of heart at the cranial 4^th thoracic vertebrae (T4). Accepted normal VHS range is 9.7±0.5  for dogs (Buchanan and Bucheler (1995); Bodh et al., 2016; Saini et al., 2023). Thoracic depth (TD): thoracic width (TW) describes the breed confirmation differences between dogs such as broad thorax and deep thorax with values ≤ 0.75 is for broad thorax and >1.25 are considered to be deep thorax. On the other hand, Two dimensional Cardiothoracic ratio (CTR) is the measure of cardiac area/ thoracic area *100. Normal CTR score is 0.42 and above 0.5 is abnormal and considered cardiomegaly (Torad and Hassan, 2014; Bodh et al., 2016).  Cardiac diseases in both human and canines are traditionally examined through physical examination, cardiac auscultation, radiography, electrocardiogram, ultrasonography and echocardiography and estimation of cardiac biomarker such as Troponin-I, C-reactive protein. Emerging methods on x-ray-based technologies (micro-CT and photon-counting CT), molecular imaging and low- and ultrahigh-field MRI, 2D speckle tracking echocardiography, ultrafast ultrasound are used now a days for better diagnosis. The goal of present research is to study prevalence of different cardiomyopathies and to access radiographic, echocardiographic and blood biochemical changes related to these diseases.

The present research study was carried out at the Department of Veterinary Surgery and Radiology and Veterinary Clinical Complex (VCC), College of Veterinary Science and Animal Husbandry, Bhubaneswar, between January 2024 to November 2024. Preliminary patient data such as age, sex, breed, body weight, general physical examination (including auscultation, arrythmia), clinical symptoms, radiographic and echocardiographic positioning were recorded in Table 1. The study population were divided into three groups; Group I are clinically healthy animals with normal heart size and echocardiographic findings; Group II with preclinical and clinical cardiac diseases with echocardiographic findings; Group-III animals are clinical cardiac diseases with confirmed cardiomyopathies requiring chronic medical management. Thoracic radiography with two orthogonal views (right lateral/ left lateral and ventrodorsal/ dorsoventral) was taken in animals for calculation of VHS, CTR and TD/TW in three groups. Electrocar- diographic recordings were conducted on all dogs following the methodology outlined by Tilley (1992), employing the Magic Rx maestros four lead ECG machine. Preparatory phase of ECG involves removal of any metallic items worn by dog and its handler, dog to be in relaxed, calm state without panting. Electrodes were then affixed to the right foreleg, left foreleg, left hind leg and right hind leg following application of electroconductive gel at all these sites. Parameters from the ECG were documented using a strip from lead II, with wave widths recorded in milliseconds and amplitudes in millivolts. Echocardiographic procedure was performed with Wipro GE Logiq F8 Expert ultrasound machine, equipped with a multifrequency (3-4 MHz) cardiac probe. Preparatory phase involves, thorough shaving and positioning the dogs in right lateral recumbency or left lateral recumbency on a specialised table with V”-shaped cutout in the tabletop, allowing heart to drop below the lungs and suitable for clear imaging. Some of the standard view recorded in this procedure are a) right parasternal long axis 4- chamber views, b) right parasternal long axis 5- chamber views/ left ventricle outflow view c) right parasternal short axis views d) left apical views. Two dimensional M- mode echocardiographic measurement placed at the Left ventricle (LV) level and mitral valve (MV) level records values for  interventricular septal thickness at end diastole (IVSd), left ventricular internal diameter at end diastole  (LVIDd), left ventricular posterior wall thickness in diastole (LVPWd), interventricular septal thickness at systole (IVSs), left ventricular internal diameter at systole  (LVIDs), left ventricular posterior wall thickness in systole (LVPWs),  Ejection fraction (EF%), fractional shortening (FS%), E-point septal separation (EPSS) in all the three groups.


 
Statistical analysis
 
The quantitative data in this study were expressed as Mean ± Standard Error (SE), while the qualitative data were represented in terms of frequency or percentage. The One-Way Analysis of Variance (ANOVA) with the Games-Howell post hoc test was utilized from the IBM SPSS software package, specifically version 20 of the Statistical Package for Social Sciences. Pearson’s correlation coefficient was applied for variables with a normal distribution, whereas Spearman’s correlation coefficient was used for variables that did not follow a normal distribution.

The present study population comprises of 40 animals; Group I consists of 18 healthy dogs, Group II consists of 14 animals under preclinical group and Group III consists of 8 animals with clinical manifestations of confirmed cardiomyopathies. The general body condition parameters, breed distribution across the groups are presented in Table 2. Overweight animals are risk of developing heart diseases or cardiomyopathies. VHS are greater in dogs showing cardiomyopathies in Group III (n=8) with values 10.8±0.48 (Fig 1a and 1c) > Group II (n=14) 10.6±0.62> Group I (n=18) 9.58±0.5 (Chart 1). There was a significant (P<0.05) difference between VHS values of clinical group with respect to values of normal heart sized group. CTR values for three groups are, Group I (n=18) 0.42±0.5 < Group II (n=14) 0.49±0.62 < Group III (n=8) (Fig 1b) 0.54± 0.48 (Chart 2). There was a significant (P<0.05) difference between CTR values of clinical group with respect to values of normal heart sized group. Normal right parasternal long axis 4- chamber echocardiographic views (Fig 2a), right parasternal short axis views with LA:Ao ratio 1.01 (Fig 2b) and colour doppler view of images at mitral valve (Fig 2c) are shown for reference guide. Two dimensional (2-D) right parasternal short axis view images had been recorded starting from the apex then papillary muscles and chordae tendon, mitral valve aorta-left atria and finally pulmonary artery. Left atrium: Aorta (LA:Ao) ratio greater than 1.6 (Fig 2d) is generally considered indicative of left atrial enlargement in dogs (Salguero et al., 2018). LA:Ao ratio for three groups are, Group I (n=18) 1.20±0.06< Group II (n=14) 1.34±1.50< Group III (n=8) 1.66±0.09 (Chart 3). Values of LA and LA/Ao belonging to clinical group showed significant difference (P<0.05) with respect to values of normal heart sized group and preclinical group. M-mode measurement of different parameters (IVSd, IVSs, LVIDd, LVIDs, LVPWd, LVPWs, EF%, FS% and EPSS) were compared between normal(G-I), preclinical and clinical cardiac diseases (G-II) and confirmed cardiomyopathies (G-III) in (Chart 4). A normal recording of M-mode reading in a labrador at LV level and power doppler reading at mitral valve level is shown in Fig 3a and  3b. ECG recording in Fig 4a described reduced P wave in a boxer with irregular PP intervals resulting in dilated cardiomy-opathy. Tachycardia and Arrythmia can be easily identified in large breed dog such as labrador, bull mastiff (Fig 4b,c,and d) through 4 lead or 6 lead ECG machine (MR 900) which were again subjected to B-mode 2D-echocardio graphy or M- mode echocardiography for describing the animal as DCM and CHF as in the present case.   


















       
Measurements for the left ventricular study were taken from the papillary muscles level in the right parasternal short-axis image. EPSS for the mitral valve study was measured as the distance between the lowest part of the interventricular septum and the maximum excursion of the mitral valve. E- point septal separation (EPSS) is a measure of visual estimation of LVEF left ventricular ejection fraction, a healthy cardiac function. This is one of the visual estimations of LVEF without quantitative measurement. EPSS is measured in the parasternal long axis view (PLAX) of the heart, which gives a view of the left ventricle and is often used to assess its function. EPSS is obtained by placing the M-mode tracer over the distal tip of the anterior leaflet of the mitral valve, as in the Fig 5. The E-point Septal Separation (EPSS) is the very small space that exists between the E-point and the interventricular septum in a healthy heart. Consequently, there is a negative correlation between LVEF and EPSS. Reduced LVEF is indicated by an EPSS > 7 mm. In case, EPSS ≥ 13 mm correlates with severely decreased function, with an estimated LVEF of ≤ 35%. An abnormal EPSS of 0.816 cm is shown in Fig 5a and Fig 5b.


       
In the current study, the distribution across these groups was relatively balanced, with 45% of the dogs classified as having normal heart sizes, 35% falling into the preclinical category and 20% being in the clinical stage. These findings underline the critical need for early detection, regular monitoring and timely intervention in veterinary practice to manage and potentially prevent the progression of heart disease in dogs. The clinical group, comprising 8 animals with confirmed cardiomyopathies, had the highest mean age at 8.90±0.72 years. This trend highlights a clear progression, where advanced cardiac conditions are more commonly observed in older animals. Labrader retrievers, Rottweilers, Dobermans, Spitz and pugs are the common breed showing increased predisposition to age related cardiac conditions. In some cases, Doberman are found with associted symptoms like cyanosis and jaundice suggesting a susceptibility to specific diseases.  Pugs, showing signs such as heart murmurs, ascites and limb swelling, may point to their predisposition to heart issues in middle to older age. Breeds like German Shepherds, Golden Retrievers and Dachshunds also featured, though in smaller numbers.
       
In this study, VHS values were measured and compared across three groups of dogs to evaluate potential cardiac abnormalities. Groups 2 and 3 demonstrated mean VHS values of 10.6±0.62 and 10.8±0.48, respectively which are at the upper limit of the accepted range, suggesting a tendency toward cardiomegaly with underlying cardiac conditions, such as dilated cardiomyopathy (DCM). The increased VHS in Groups 2 and 3 highlights the potential of this method as a reliable diagnostic tool for early detection of cardiac abnormalities. The study also utilises cardiothoracic ratio (CTR) to assess heart size relative to the chest cavity, providing valuable insight into heart health and its potential compromise. Group 3 with mean CTR 0.54±0.48, exceeding the normal range indicated  presence of cardiomegaly, consistent with the likelihood of underlying cardiac issues such as dilated cardiomyopathy (DCM) or other heart conditions. The elevated CTR in this group highlights a clear association with cardiac enlargement and the need for further diagnostic and therapeutic intervention.
       
In this study, the left atrium (LA) measurements showed a progressive increase across the groups. Group 3 demonstrated a marked rise in LA measurements indicating significant left atrial enlargement, likely associated with underlying cardiac conditions such as mitral valve disease or dilated cardiomyopathy. The LA/Ao ratio, an important diagnostic marker, also showed a clear trend of increase across the groups. In Group 3, the LA/Ao ratio was significantly higher at 1.66±0.09, clearly indicative of left atrial enlargement and a strong likelihood of underlying cardiac pathology.
       
End-point septal separation (EPSS) is a key echocar-diographic measure used to assess the function of the left ventricle, particularly in relation to mitral valve motion. EPSS is measured as the distance between the interventricular septum and the mitral valve during early diastole. An increase in EPSS typically indicates left ventricular dysfunction and poor myocardial contractility, often associated with dilated cardiomyopathy (DCM) or other forms of heart failure. EPSS values in Group I and  II are consistent with what is expected in healthy dogs or those with no significant cardiac dysfunction. Low EPSS values generally imply that the left ventricle is functioning efficiently and the mitral valve is properly positioned with minimal separation during contraction, a hallmark of a healthy heart. However, Group 3 exhibited a markedly higher EPSS value of 1.40±0.30. This significant increase in EPSS is a clear indication of left ventricular dysfunction, likely due to myocardial dilation or reduced contractility. In dogs with conditions such as dilated cardiomyopathy (DCM), the left ventricle becomes dilated, leading to an increased distance between the interventricular septum and the mitral valve during diastole. This is consistent with the observed findings in Group 3, where the enlarged left ventricle is struggling to contract efficiently, resulting in a poor mitral valve closure and greater separation. The elevated EPSS value in Group 3 is therefore suggestive of more advanced cardiac pathology, likely indicative of congestive heart failure or other severe forms of cardiac dysfunction.
       
M-mode echocardiography provides critical insights into the structural and functional aspects of the heart, allowing for precise measurement of parameters such as interventricular septal thickness (IVSd, IVSs), left ventricular internal diameter (LVIDd, LVIDs), left ventricular posterior wall thickness (LVPWd, LVPWs), ejection fraction (EF%), fractional shortening (FS%) and the early diastolic mitral septal separation (EPSS). These parameters are crucial in evaluating the health of the heart and detecting various cardiac conditions, such as dilated cardiomyopathy (DCM) or heart failure, in dogs.

This study provides valuable insights into the progression of cardiomyopathies in dogs and highlights the importance of various diagnostic tools such as thoracic radiographs, electrocardiography and echocardiography in identifying and monitoring heart diseases. The data demonstrates that both preclinical and clinical signs of heart disease are associated with increased heart size and reduced heart function, with significant changes in echocardiographic parameters like EF%, FS% and EPSS in more advanced stages of the disease.  The findings underscore the utility of these diagnostic tools for early detection, which is essential for better management of cardiac diseases in dogs. The increased prevalence of cardiomyopathies in older dogs, particularly male dogs and certain breeds, should be considered when assessing risk factors. Regular monitoring and early intervention are crucial in managing heart disease, improving the quality of life and extending the lifespan of affected dogs. Future studies with larger sample sizes and more diverse populations may provide additional insights into the specific breed and environ- mental factors contributing to cardiomyopathy in dogs.

The present study was supported by Département of Veterinary Surgery and Radiology, Odisha University of Agriculture and Technology (OUAT).
 
Ethical statement
 
The diagnostic modalities in these cases were performed in Veterinary Clinical Complex, College of Veterinary Science and AH, OUAT. The study does not need an Ethical approval, as all the procedure are part of routine clinical examinations.
 
Disclaimers
 
The views and conclusions expressed in this article are solely those of the authors and do not necessarily represent the views of their affiliated institutions. The authors are responsible for the accuracy and completeness of the information provided, but do not accept any liability for any direct or indirect losses resulting from the use of this content.
 
Informed consent
 
As the present study involves only diagnostic modalities, no invasive procedures were involved during the handling of animal for clinical examinations. As and when required appropriate ethical measures have been adopted by the authors.