VETERINARSKI ARHIV 69 (4), 211-219, 1999

ISSN 1331-8055 Published in Croatia

Contribution to standardisation of heart rate and electrocardiographic values in Doberman pinschers

Alan Kovacevic*, Martina Duras, and Tomislav Gomercic

Faculty of Veterinary Medicine, University of Zagreb, Zagreb, Croatia

* Contact address:
Dr. Alan Kovacevic,
Ambulatory Clinic, Faculty of Veterinary Medicine, University of Zagreb, Heinzelova 55, 10000 Zagreb, Croatia,
Phone: 385 1 23 90 260; Fax: 385 1 214 697; E-mail: alan.kovacevic@kkh.unibe.ch

Kovacevic, A., M. Duras, T. Gomercic: Contribution to standardisation of heart rate and electrocardiographic values in Doberman pinschers. Vet. arhiv 69, 211-219, 1999.

ABSTRACT

In this study electrocardiographic values of 44 Doberman pinscher dogs (11 months to 8.5 years old and with body masses of 34.4±4.9 kg) were measured. After clinical examination no signs of any disease were found, and anamnestic data indicated no cardiac disorders. After data analysis values of heart rate (127.9±23.6 beats per minute, with a range of 70 to 176 min^-1), P wave amplitude (0.211±0.072 mV, with a range of 0.1 to 0.35 mV), P wave duration (0.04±0.003 s, with a range of 0.03 to 0.05 s), QRS complex duration (0.053±0.01 seconds, with a range of 0.02 to 0.07 s), R wave amplitude (1.66±0.56 mV, with a range of 0.6 to 3 mV), Q wave amplitude (0.65±0.4 mV, with a range of 0.05 to 1.8 mV), Q-T interval duration (0.187±0.024 s, with a range of 0.14 to 0.26 s) and S-T segment level (-0.049±0.068 mV, with a range of -0.2 to 0.1 mV) were similar to published standard values, but values of mean electrical axis (50.9°±26°, with a range of -42° to 101°) were considerably aberrant.

Key words: Doberman pinschers, electrocardiogram, mean electrical axis, heart rate, P wave, QRS complex, Q wave, R wave, S-T segment, Q-T interval

Introduction

Approximately 10% of patients presented to veterinary clinics are dogs and cats with cardiovascular disorders (Allen and Kruth, 1988). The clinical examination of these patients includes electrocardiography, as the method most frequently used. Electrocardiography is an examination method that graphically shows electric actions of the heart, recorded over a given period from the body surface of an animal or human. The graphic presentation of these actions is known as an electrocardiogram (ECG). ECG is simple to obtain from cats and dogs and is also easy to analyse following the recommended methods (Tilley, 1985).

The greatest value of the ECG lies in recognizing arrhythmias. Today, electrocardiography is the most precise method in diagnosing arrhythmias. A special method of electrocardiography is Holter monitoring. Holter monitoring provides ambulatory recording in everyday stress conditions (Ware, 1998; Miller et al., 1999). A very important value of the ECG is showing changes in heart size. These changes can be concealed on an ECG, and so ultrasonic and radiographic examinations have to be made in order to confirm any suspicion (Smith and Hadlock, 1995).

Significant differences have been established in ECGs of different dog breeds. ECG values of dogs of mixed breed are mentioned in literature earlier than ECG values of purebred dogs (Rezakhani et al., 1990). In most professional publications, values of ailing dogs are presented; therefore more is known today about pathologic than about physiologic ECG values (Tilley, 1985; Tilley et al., 1993).

Using published ECG values, as well as values from his own studies, Tilley (1985) proposed standard ECG values of dogs. Today, these standards are those most often used to distinguish pathologic from physiologic values during ECG analysis.

One important factor to have a great influence on amplitudes of ECG waves is chest depth. Dogs with a deep chest show waves with higher amplitudes than fat dogs or dogs with a wide chest (Tilley, 1985)

Studies made on German shepherds (Rezakhani et al., 1990), Mastin Espanol   (Bernal et al., 1995) and beagles (Strasser et al., 1997) contributed to breed standardisation of ECG values. Standard ECG values of Doberman pinschers have yet to be published in literature.

Studies made in the USA and Canada showed that Doberman pinschers have a high tendency to dilatative cardiomyopathy (Ettinger et al., 1992; Sisson and Thomas, 1995). James and Darke (1968) described specific pathohistologic findings in Doberman pinschers that died suddenly. Tidholm and Jönsson (1997) emphasized that Doberman pinschers with dilatative cardiomyopathy very often have ventricular tachycardia in electrocardiographic findings. Everett et al. (1999) described specific histomorphologic changes in the heart muscle of Doberman pinschers with dilatative cardiomyopathy, which is frequently the cause of electrocardiographic changes. Associated with ultrasonic and radiographic examination, electrocardiography plays an important role in diagnosing dilatative cardiomyopathy (Calvert et al., 1997). From our investigation we wish to contribute to the standardization of ECG values in Doberman pinschers and to make the distinguishing of pathologic and physiologic findings in these breeds easier.

Materials and methods

The examination of animals took place in the period from 18^th April to 4^th October 1997, at the Clinic for Internal Diseases, Faculty of Veterinary Medicine, University of Zagreb, Zagreb, Croatia, and at the "Veterinarska stanica Varazdin" veterinary practice in Varazdin, Croatia. Owners brought their dogs for examination following a mailed invitation to all owners of Doberman pinschers who are members of the Doberman Pinscher's Club registered at the Croatian Cinologic Association, and to all owners of Doberman pinschers registered with the "Veterinarska stanica Varazdin" veterinary practice.

Owners of 45 Doberman pinschers responded to the invitation. In this study, values were taken from those dogs showing no signs of illness after clinical examination, and whose anamnestic data did not indicate cardiac disorders. These conditions were not found in one animal, whose rectal temperature was 40 °C. This study comprises values of 44 Doberman pinschers from 11 months to 8.5 years of age (average age 42.3±25.2 months). The group included 25 male dogs (average body mass 36.3±4.2 kg) and 19 bitches (average body mass 31.6±4.6 kg).

Details of owners were recorded at the commencement of the examination, as well as sex, age and name of the dog. Owners were requested to list all health disorders, if any, suffered by their dogs. Rectal temperature was then measured; heart and respiratory rates were counted, and body mass was noted. Shape and attitude were also described. Mucous membranes of eyes, nose and mouth were checked and submandibular, prescapular and popliteal lymphatic nodes were palpated. By palpating both femoral arteries, femoral pulses were examined for rate, rhythm and amplitude. Capillary refill time was determined on the mouth mucous membrane. By neck inspection the filling of jugular veins and presence of the jugular pulse were observed. The presence, site and force of the heartbeat (ictus cordis) were checked. The abdomen was evaluated for size and site of liver and spleen and presence of ascites by palpation. The presence and quality of heart sounds, the point of maximal intensity of heartbeat (puncta maxima) and, if present, murmurs, especially heart murmurs were auscultated.

At this point, the examination was continued with electro- cardiography. The patient was laid on a table in a right lateral position. An assistant held his right forearm over the animal's neck so that the animal was unable to raise its head. With his right hand, the assistant held the animal's forelegs slightly spread so that they did not touch but parallel to each other and perpendicular to the spinal column. In the same position, the assistant held animal's hind legs with his left hand. The owner stood by the animal's head and kept the animal calm, as no restraining drugs were used during the recording.

Alligator clip electrodes for attachment to the skin were used for the recording. On forelegs, the electrodes were attached proximal to the olecranon, and on hind legs over the patellar ligament on the caudal aspect of the appropriate leg. The electrode for recording the precordial lead was placed at the left sixth intercostal space, at the costochondral junction.

The recording was performed on a single-channel electrocardiograph  (Simpliscriptor EK 31, Hellige, Germany) on heat sensitive paper.

Every recording started with a sensitivity check: 1 cm of stylus movement corresponding to 1 mV. At paper speed 25 mm/s, three or four heart actions in each lead were recorded in the following order: lead I, II, III, aVR, aVL, aVF, V₄. Afterwards, lead II was recorded for 10 seconds at paper speed 50 mm/s. The standard analysis of recorded ECG values was performed with the help of a calliper on the lead II recording made at paper speed 50 mm/s. The mean electrical axis was determined by measuring the net amplitude of QRS complex in lead I and III, and the value was read from standard tables (Tilley, 1985). The Q-T interval varies inversely with the heart rate. We did not correct the Q-T interval as no standard formulas and tables exist for dogs (Tilley, 1985).

Results

Of all values received from the measurements during the examinations performed on Doberman pinschers in this study, we analysed age, body mass, heart rate, amplitude and duration of P wave, amplitude of R and Q waves, duration of the QRS complex, duration of QT interval, S-T segment in comparison with the level of the baseline and mean electrical axis. The data are statistically edited and for every parameter the average value, standard deviation, the lowest and the highest values (Table 1) are determined. The body mass of three dogs could were unable to be measured because they were too aggressive. The average heart rate of bitches was 118,9±25,7 beats per minute (with a range of 70 to 176) and for male dogs 134.6±19.9 (with a range of 95 to 176).

Table 1. Values of 44 Doberman pinschers obtained during clinical and electrocardiographic examination

*P<0.005; **P<0.05 - significantly different between sexes

Discussion

The average heart rate determined in Doberman pinschers included in this investigation was 127.9±23.6 beats per minute with a range of 70 to 176. The lowest value was 70, the highest 176. The lowest value corresponds to published standard dog heart rate values (Tilley, 1985; Forenbacher et al., 1966; GomerCiC and GomerCiC, 1996). The highest heart rate was higher in 27 dogs (61%) than published by Forenbacher et al. (1966) and it also did not correspond in 4 dogs (10%) with the values published by Ettinger et al. (1992), GomerCiC and GomerCiC (1996) and Tilley (1985).

A significant difference (P<0.05) was found in heart rate values in male and female dogs. The average heart rate in bitches was 118.9±25.7 beats per minute, while in male dogs it was 134.6±19.9. This is contrary to the statement that the heart rate in females is more frequent than in male dogs (Forenbacher et al., 1966). Our opinion is that bitches become calmer with sexual maturity in contrast to male dogs.

The average amplitude of the P wave was 0.211± 0.072 mV with a range of 0.1 to 0.35 mV, which corresponds to standard values (Tilley, 1985). The duration of P wave was from 0.03 to 0.05 s (average 0.040±0.003). Three dogs had a prolonged duration of the P wave that lasted over 0.040 seconds. This could be due to left atrial dilatation as a result of a pathologic process, or to an individual characteristic. Ultrasonic doppler examination is necessary to determine the cause of prolonged P wave duration.

In one dog the wandering pacemaker was present and the characteristics of the P wave and P-R interval could not have been determined. The presence of the wandering pacemaker is a physiologic finding in dogs (Tilley, 1985).

The duration of the P-R interval in one dog was 0.14 seconds. Compared to standard values this is a value of a dog with first-degree atrioventricular block (Tilley, 1985).

The amplitude of R waves varied in the examined Doberman pinschers from 0.6 to 3 mV (average 1.66±0.56 mV). This is in agreement with standard values (Tilley, 1985). An investigation on German Shepherds showed similar values (1.65±0.55 mV) (Rezakhani et al., 1990). Another study on endurance-trained Alaskan sled dogs showed a much higher amplitude of R waves, being 3.02 mV average with a range of 1.49 to 4.4 mV (Hinchcliff et al., 1997). The opinion of the authors is that high values are the result of a cardiac hyperthrophy following strenuous training.

The average duration of QRS complex was 0.053±0.01 seconds, with a range of 0.02 to 0.07 seconds. Following the standard values published by Tilley (1985) the longest duration of QRS complex in large dog breeds should be 0.06 seconds. Tilley's opinion is that a longer QRS complex duration is a result of a heart block, or enlargement of the left, right or both ventricles. In our study, we measured QRS complex for a duration of 0.07 seconds in two Doberman pinschers. We did not perform any further examination, so it is not known if these values are the result of a pathologic process or if they are individual characteristics.

The Q wave was present on 43 ECGs. The ECG of one dog did not show a Q wave. The average amplitude of the Q waves was 0.65±0.4 mV (from 0.05 to 1.8 mV). According to Tilley (1985) a high voltage of the Q wave is a physiologic finding in dogs with a deep chest. The presence of the Q wave in 43 of 44 dogs (98%) serves to confirm Tilley's statement.

The average duration of the Q-T interval was 0.187±0.024 seconds (from 0.14 to 0.26 s). The lowest value is 0.001 s shorter, and the highest value is 0.001 s longer, than the standard value (Tilley, 1985). The Q-T interval varies with heart rate. The faster the heart rate, the shorter the Q-T interval. There are tables that show the physiologic change of the Q-T interval compared to the heart rate for humans, but not for dogs. This is why the Q-T interval is not particularly helpful in veterinary medicine (Tilley, 1985).

The average level of the S-T segment compared to the baseline was -0.049±0.068 mV (from -0.2 mV to 0.1 mV). These values correspond to standard values (Tilley, 1985).

A significant difference from the published standard values (Tilley, 1985) and a wide range of measured values was found during determination of the mean electrical axis (MEA). The examined Doberman pinschers showed a MEA with a range of -42° to 101° (average 50.9°±26°). For the interpretation of our results it is important to emphasize that MEA direction depends on the site, size and the conduction system of the heart, so it is an individual or a breed characteristic (Tilley, 1985) or a result of pathologic process in the heart, i.e., heart block or heart enlargement (KovaCeviC, 1998.). The wide range of our measurements of MEA and the significant deviation from the standard value in 11 of 44 examined dogs (25%) does not agree with the statement that MEA in deep-chested dogs is usually vertical, and that the range of measured values is narrow (Tilley, 1985). Our opinion is that the left MEA deviation in 10 of 11 dogs, whose values of MEA are not in accordance with standard values, is not a breed characteristic but a result of pathologic process in hearts of these dogs. According to the literature the Doberman pinscher breed tends to have dilatative cardiomyopathy (Keene, 1989; Bonagura and Lehmkuhl, 1994; Calvert et al., 1997a). The characteristic of dilatative cardiomyopathy in Doberman pinschers is a progressive loss of heart muscle contractility, which results in ventricular enlargement, especially left ventricular enlargement (Keene, 1989; Calvert et al., 1997a). Left MEA deviation is a sign of left ventricular enlargement or left bundle branch block (Tilley, 1985) but a final diagnosis of these two diseases can only be made through ultrasonic or radiographic examination (Allen and Kruth, 1988). In our investigation these two examinations were not applied, so we do not know if in 10 Doberman pinschers with left MEA deviation a pathologic process is present, although we cannot exclude this possibility.

The limitations (i.e. no ultrasonic and radiographic examination) in this study showed the importance of adding these methods to the examination of all cardiac illnesses, excluding arrhythmias, which can be diagnosed only by electrocardiography. Our study also established that without these methods, physiologic electrocardiographic values can sometimes not be distinguished from pathologic. The reason for this can also be found in the big difference in standard values in different breeds. For veterinary practitioners, standard breed values based on electrocardiographic, ultrasonic and radiographic examinations performed on big groups of animals of the same breed obtained over a longer period, would be very helpful in distinguishing physiologic from pathologic findings.

Acknowledgements
We would like to thank "Veterinarska stanica Varazdin" and Mr. Marijan Sabolic, DVM for their kind assistance in the organisation of the practical part of this study.

References

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Received: 13 August 1999
Accepted: 18 October 1999

Kovacevic, A., M. Duras, T. Gomercic: Prilog standardizaciji vrijednosti frekvencije rada srca i elektrokardiografskih vrijednosti u dobermana. Vet. arhiv 69, 211-219, 1999.

SAZETAK

U ovom radu izmjerene su elektrokardiografske vrijednosti 44 pasa pasmine doberman u dobi od 11 mjeseci do 8,5 godina, prosjecne mase 34,4±4,9 kg. Njima nakon klinicke pretrage nisu utvrdeni znakovi bolesti, a anamnesticki podaci nisu upucivali na poremecaje rada srca. Obradom podataka utvrdeno je neznatno odstupanje vrijednosti frekvencije rada srca (127,9±23,6 otkucaja u minuti u rasponu od 70 do 176 min^-1), visine P vala (0,211±0,072 mV, u rasponu od 0,1 do 0,35 mV), trajanja P vala (0,040±0,003 s, u rasponu od 0,03 do 0,05 s), trajanja QRS kompleksa (0,053±0,01 s, u rasponu od 0,02 do 0,07 s), visine R zupca (1,66±0,56 mV, u rasponu od 0,6 do 3 mV), visine Q vala (0,65±0,4 mV, u rasponu od 0,05 do 1,8 mV), trajanja Q-T intervala (0,187±0,024 s, u rasponu od 0,14 do 0,26 s) i razina S-T spojnice (-0,049±0,069 mV, u rasponu od -0,2 do 0,1 mV) od objavljenih standardnih vrijednosti pasa, dok je odstupanje smjera glavne elektricne osi (50,9°±26° u rasponu od -42° do 101°) znatno.

Kljucne rijeci: doberman, elektrokardiogram, glavna elektricna os, frekvencija rada srca, P val, QRS kompleks, Q val, R zubac, S-T spojnica, Q-T interval