Indian Journal of Animal Research

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Research Article

Indian Journal of Animal Research, volume 55 issue 8 (august 2021) : 917-923

Electrocardiographic Evaluation of Cardiac Rhythm: A Comparative Study of Apparently Healthy German Shepherd Dogs Versus Dogs with Cardiac Affections

Mamta Mishra1, Akash1,*, Sanjay Purohit2, R.P. Pandey2
1Division of Surgery, Indian Veterinary Research Institute, Izatnagar-243 122, Bareilly, Uttar Pardesh, India.
2Department of Veterinary Surgery and Radiology, U.P. Pt. Deen Dayal Upadhyay Pashu Chikitsa Vigyan Vishwavidyalaya Evam Go- Ansundhan Sansthan, Mathura-281001, Uttar Pardesh, India.
Cite article:- Mishra Mamta, Akash, Purohit Sanjay, Pandey R.P. (2021). Electrocardiographic Evaluation of Cardiac Rhythm: A Comparative Study of Apparently Healthy German Shepherd Dogs Versus Dogs with Cardiac Affections . Indian Journal of Animal Research. 55(8): 917-923. doi: 10.18805/ijar.B-4148.

ABSTRACT

Background: The objective of the present study was to define existence of age and body weight related cardiac structural and functional changes in both healthy GSD as well as those having structural or functional cardiac affections. Thus the present study was conducted to establish the reference values of various parameters of ECG based on age and body weight and further evaluation of clinical cases based on these reference values.

Methods: The present study was conducted on eight apparently healthy German shepherd dogs aged 36-72 months with body weight 22-33.2 kg free from cardio-thoracic diseases to establish the reference values of various electrocardiographic parameters (Group-I) and used to evaluate the cardiac rhythm in 3 GSD dogs having some cardiac diseases (Group-II) based on the reference values obtained from Group-I. 

Result: Heart rate showed negative correlation with age and body weight. Positive correlation of amplitude of S and T wave, QRS complex, duration of T wave, P-R interval and R-R interval with age and body weight; amplitude of Q wave, duration of P wave and Q-T interval with body weight was observed. Negative correlation of amplitude of P and R wave, S-T interval with age and body weight; amplitude of Q wave, duration of P wave and Q-T interval with age was observed.

INTRODUCTION

In recent years there has been an increase in trend and incidences of cardiac diseases in small animals, expressing itself through a wide range of signs (Oyama et al., 2013). Due to lack of awareness and subsequent knowledge by the owner and inadequate diagnostic facility in our country, diagnosis of such diseases has been either delayed or ignored (Devi et al., 2009).  Approximately about 10-15% of all dogs are affected with heart diseases (MacPete, 2018). These may be congenital (1-5%) or acquired (95%), acquired type is common among canine (Oyama and Singletary, 2010), the cause may be either valve problems (Atkins et al., 2009) accounting for 75-80% or cardiomyopathies contributing 15-20% of total acquired cardiac diseases (Chris et al., 2004). Acquired cardiac affections tend to be the most commonly encountered disorder in ageing population (Saunders, 2012). Obesity and heart diseases in dogs are encountered frequently in clinical practice (Reetu et al., 2019). Improper feeding, inadequate exercise and managemental negligence favours obesity that may leads to heart diseases (Devi et al., 2009). ECG patterns in animals can be different depending upon the body weight, age and fat deposit, causing changes in electrical activity and cardiac rhythm that can be seen in the ECG (Neto et al., 2010). Any type of disturbance or variance of a normal heart rate or rhythm in dogs is considered canine arrhythmia (Reetu et al., 2017). In dogs, cardiac arrhythmias and intra-cardiac conduction disturbances are common problems, which can be well elucidated and diagnosed using ECG (Gugjoo et al., 2014a). The QT interval measured in the ECG represents ventricular depolarization and repolarization (Tilley, 1992). Borys (1986) depicted the changing role of the electrocardiogram in the diagnosis of cardiac chamber enlargement. Fox et al., (1988) opined that ECGs obtained from dogs with DCM were usually abnormal, having widened high amplitude QRS complexes (left ventricular enlargement) and widened P wave (left atrial enlargement). Pathological arrhythmias were most commonly found in male dogs and in German Shepherds (Noszczyl Nowak, et al., 2017).

MATERIALS AND METHODS

Place and span of study
 
The  study was carried out in the Teaching Veterinary Clinical Complex, Kothari Veterinary Hospital, College of Veterinary Science and Animal Husbandry, U.P. Pandit Deen Dayal Upadhyaya Pashu-Chikitsa Vigyan Vishwavidyalaya Evam Go-Anusandhan Sansthan, Mathura-281001 (U.P). Present study was undertaken within a span of 2 years and the animals in the study were presented to the TVCC within this period.
 
Subjects of study
 
Cardiac diseases tend to be age dependent as the prevalence increase dramatically in 4-5 yrs. and above (Buchanan, 1977; Thrusfield et al., 1985; Borgarelli et al., 2004). Thus the present study was conducted on GSD dogs with an average age of 4 yrs (2 - 6 yrs) and average body weight of 20 kg (15-35 kg) in 2 groups that were presented during study period at Teaching Veterinary Clinical Complex of Institute.
 
Group I: Eight apparently healthy medium size German shepherd dogs (GSD) free from cardiothoracic diseases.
 
Group II: Three GSD having cardiothoracic affections.
 
Selection of animals
 
In the present study, dogs having normal physiological parameters were considered as healthy and were included within Group-I while those having any deviation of vital indices from normal were categorized into Group-II. Temperature (°F), respiratory rate (breaths/min), heart rate (beats/min), pulse (beats/min) were recorded using digital thermometer, observing thoracic excursions, stethoscope, auscultation using a clinical stethoscope and palpation of femoral artery, respectively (Table 1).
 

Table 1: Mean ± S.E. values of various clinico-physiological parameters in dogs of group-I and ÉÉ.


 
Site preparation and method
 
The dogs were placed in right lateral recumbency on a table with an insulating mattress over it. Both of the humerii and femora were kept in perpendicular position to the long axis of the body. Legs were kept well apart from each other. Metallic object were kept away from the body. Area of interest was shaved and normal saline was applied on it for better contact of the electrodes with skin thus enhancing the electrical conductivity.
       
The Right Arm (RA) and Left Arm (LA) clips were placed just proximal to the olecranon process on the caudal aspect of the appropriate foreleg. Right Leg (RL) and Left Leg (LL) clips were attached over the patellar ligament on the anterior aspect of the appropriate hind leg using electrocardiographic lead II measurements (Fig 2).
 

Fig 2: Electrocardiogram of Dog of group-II, taken at 50mm/s and calibration of 10mm=1mV showing abnormal amplitude and duration.


 
Electrocardiographic machine
 
ECGs were obtained in a single channel electrocardiographic machine (Vesta 301i, RMS India) with paper speed of 50 mm/sec and calibration of 10 mm equal to 1 mV (Fig 1).
 

Fig 1: Electrocardiogram of Dog of group-I, taken at 50mm/s and calibration of 10mm=1mV showing normal amplitude and duration.


 
Parameters
 
The following parameters were measured from the ECG recordings as described by Pourjafar et al., (2011a).
 
Amplitude (mV)
 
The amplitude of P, Q, R and T wave were measured on vertical axis from the baseline to the highest or lowest point of the wave on ECG. It measured in millivolts (mV). Each small block represents 1 mm or 0.1 mV; each large block, 5 mm or 0.5 mV.
       
The amplitude of P-wave represents the magnitude of atrial depolarization and spreads from the sinoatrial node to the atrioventricular node. Variation in P-wave amplitude may be explained due to stress exhibited during ECG recording (Avizeh et al., 2010; Ferasin et al., 2012). The amplitude of R-wave is most commonly used to evaluate the left ventricular function and considered a good indicator for ventricular contractibility (Gugjoo et al., 2014). Increase in P wave amplitude is an indicator of right atrial enlargement. Tall P waves are seen in Right atrial hypertrophy and/or dilatation. Increase in the later portion of the P wave in lead II indicates left atrial enlargement (Tilley et al., 1992).
 
Duration (Second)
 
The duration of P, QRS complex, T wave forms and P-R, R-R, Q-T and S-T intervals were measured on horizontal axis on the baseline on ECG. It is measured in second. The rate of paper (i.e. of recording of the EKG) is 25 mV/s which results in: 
 
        1 mm = 0.04 sec (or each individual block).
        5 mm = 0.2 sec (or between 2 dark vertical lines).
 
Statistical analysis
 
The mean and standard error for each set of radiographic, electrographic and echocardiographic parameters were calculated. These parameters were compared in group-I and group-II. Bivariate Pearson’s correlation test was used to establish the correlation of various radiographic, electrographic and echocardiographic parameters with body weight and age of animals (Snedecor and Cochran, 1994). The level of statistical significance was set at P>0.05 or p>0.01.

RESULTS AND DISCUSSION

ECG was performed in all dogs in right lateral recumbency using lead-ΙΙ. Amplitude and duration of various segments were measured.
 
Amplitude
 
The amplitude of P, Q, R, S and T waves were measured on vertical axis from the base line to the highest and lowest point of the wave on electrocardiogram (Fig 1 and 2, Table 2). The amplitude of P, R, S and T wave were positive and Q was negative in both the groups. Mean ± S.E. values of amplitude of P, Q, R, S and T were 0.29 ± 0.04 (range 0.2 - 0.4) mV, 0.33 ± 0.07 (range 0.1 - 0.6) mV, 1.35 ± 0.12 (range 1 - 1.8) mV, 0.05 ± 0.02 (range 0 - 0.1) mV and 0.23 ± 0.05 (range 0.1 - 0.5) mV, respectively in animals of the group-Ι. Non-significant (p³0.05) negative correlation of P and R wave while non-significant (p³0.05) positive correlation of S and T wave were found with age and body weight were found. Non-significant (p³0.05) negative correlation of Q wave with age and positive correlation with body weight was found. These measured 0.18 ± 0.07 (range 0.05 - 0.3) mV, 0.06 ± 0.05 (Range 0 - 0.15) mV, 0.47 ± 0.03 (range 0.4 - 0.5) mV, amplitude of S wave were lacking and 0.38 ± 0.11 (range 0.25 - 0.6) mV, respectively in animals of the group- ΙΙ.
 

Table 2: Mean ± S.E. values of amplitude in millivolts of P, Q, R, S and T wave in base - apex lead- II of electrocardiography in dogs of group-I and II.


 
Duration
 
The duration of P, QRS complex, T wave forms and P-R, R-R, Q-T and S-T intervals were measured on horizontal axis on the baseline on electrocardiogram (Fig 1 and 2, Table 3 ). Mean ± S.E. values of duration of P wave, QRS complex, T wave forms and P-R, R-R, Q-T and S-T intervals were 0.06 ± 0.01 (range 0.03 - 0.1) seconds, 0.03 ± 0.01 (range 0.02 - 0.06) seconds,  0.05 ± 0.01 (range 0.02 - 0.1) seconds, 0.11 ± 0.01 (range 0.08 - 0.14) seconds, 0.48 ± 0.05 (range 0.36 - 0.7) seconds, 0.16 ± 0.01 (range 0.1 - 0.2) seconds and 0.14 ± 0.01 (range 0.1 - 0.18) seconds, respectively in animals of the group-I.  While these measured 0.04 ± 0.01 (range 0.01 - 0.06) seconds, 0.03 ± 0.01 (range 0.02 - 0.06) seconds, 0.03 ± 0.01 (range 0.02 - 0.04) seconds, 0.11 ± 0.01 (range 0.1 - 0.12) seconds, 0.53 ± 0.02 (range 0.5 - 0.56) seconds, 0.17 ± 0.02 (range 0.14 - 0.2) seconds and 0.19 ± 0.02 (range 0.16 - 0.22) seconds, respectively in animals of the group-ΙΙ.
 

Table 3: Mean ± S.E. values of various parameters in base - apex lead- II of electrocardiography in dogs of group-É and ÉÉ.


 
Significant (p³0.01) negative correlation of heart rate with age and body weight was found.
       
The heart rate was calculated by multiplying the speed of the electrocardiogram with 60 and then dividing it with R-R interval. Mean ± S.E. values of 134.75 ± 12.36 (range 86 - 166) bpm and 112.67 ± 3.85 (range 107 - 120) bpm in the dogs of group-I and ΙΙ, respectively.
       
In the present study, cardiac dynamics and functional differences were found between healthy (Group-I) and diseased (Group-II) German Shepherd dogs. The amplitude of P, R waves were found to be higher, T wave amplitude was lesser in animals of the group-I while in animals of the group-II P, R waves were lesser and T wave was higher as compared to values fetched from previous studies. Duration of P wave was higher in animals of group-I while it was almost equal to the previous studies in animals of group-II. PR interval and QRS complex were within the normal limit in animals of both the groups compared to the values reported earlier for PR interval and the QRS complex (Mukherjee et al., 2015). The QT interval, which is a dynamic physiological variable that can be affected by the velocities of both the ventricular conduction and repolarization, was in accordance with the earlier reports (Gugjoo et al., 2014) in animals of both group-I and II. In the present investigation, T-wave duration, which is directly related to the repolarization of the ventricular myocardial cells, were found to be within the normal range as reported by earlier observation in animals of group-II while it was slightly higher in animals of group-I (Gugjoo et al., 2014).
        
Rezakhani et al., (1990) in a study on 48 GSD dogs recorded and analysed age dependent values of various electrocardiographic parameters. On comparing those values with the present study it was found that, all the values were in the established reference range, the values for amplitude and duration of P waves were higher; Q, S wave were less and that of R and T wave were almost equal as compared to the values obtained in the previous study (Rezakhani et al., 1990). Similar study was also conducted by Spasojević Kosić et al., (2017) on 20 German shepherd dogs, where he compared the values of ECG between young and old GSD dogs with no apparent signs of cardiovascular and respiratory illness. Results in this study were slightly different from the previously published ECG values of German Shepherd dogs (Rezakhani et al., 1990) and higher values of P wave amplitude, PR duration and R wave amplitude were measured. Mean ± SE Value for amplitude and duration of P wave in young GSD dogs was less, while that of PR interval, R wave amplitude, QRS duration, QT interval and amplitude, Duration of T wave were equal as compared to old dogs. However, values of both groups were within the reference range.  The values of R wave amplitude and QRS complex duration were significantly different between dogs of different age. The values extracted through the study were very close to the reference values of Group-I animals that were established in present study.
       
On analysing and comparing these reports with our data, some reasons causing changes in ECG values were identified these can be positioning of the animals, breed and size. Positioning of the dogs should be considered at the time of ECG recording and different foreleg positions, in particular, can have a marked effect on the ECG. Further altered polarity if present in T-wave in Lead II can be due to an elevation of the diaphragm during respiration (Tilley, 1992). Other reasons reported to cause deviation in these values include different levels of sex hormones such as estradiol and dihydrotestosterone (Drici et al., 1996). Heart rate is higher in cats aged 11-36 months due to increased estrogen levels and this is in agreement with an experiment on dogs where heart rate decreased in the absence of sex hormones (Fulop et al., 2006). Kannan et al., (2018) also measured P duration (sec), PR interval (sec) and RS interval (sec). These measured 0.02 ± 0.00, 0.10 ± 0.01 and 0.03 ± 0.00 in young animals while 0.03 ± 0.00, 0.10 ± 0.01 and 0.04 ± 0.00 in adults. He also measured heart rate in young animals, 177 ± 6.15 bpm while it was 147 ± 6.67 in adults. HR was found to be highest in Labrador (110.6 ± 5.1 beats/min) followed by Golden Retriever (105.6 ± 5.2 beats/min) and German shepherd (104.6 ± 5.6 beats/min) (Mukherjee et al., 2015). HR is highly variable due to stress and excitation in dogs (Hanton and Rabemampianina, 2002). In the present study, heart rate was higher in animals of both group-I and II.
       
According to the results of our study, aging with high body weight leads to changes of cardiac electrical characteristics in German shepherd dogs. Both parameters of ventricles depolarization, QRS duration and R wave amplitude were significantly different between dogs of different age, while QRS Complex and P wave values shows major difference in animals of group-II.

CONCLUSION

There are potentials as well as limitations of canine electrocardiography since it provides information based only on the spread of depolarization and repolarisation through the heart muscle. The above study was done to establish breed specific age and body weight dependent reference values for German shepherd dogs and it may be helpful in evaluation of cardiac rhythms in any age and body weight groups of German shepherd dogs not only in disease condition but also under various physiological conditions.

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