THE ECG CURVE IN DOGS SUFFERING FROM SELECTED RESPIRATORY SYSTEM DISORDERS

Urszula Pasławska, Agnieszka Noszczyk-Nowak

ABSTRACT

The aim of the present research is to state if there are statistically important differences between ECG curves dogs suffering from chosen pulmonary diseases and healthy dogs.

Key words: dog, respiratory diseases, ECG curve.

INTRODUCTION

Electrocardiography is one of the most valuable methods of cardiological examination because it not only helps in specifying disorders of the heart rhythm, but it can also give many suggestions about different non-heart diseases as well, for example lung diseases.

Numerous authors e.g. Allen, Kruth, Garvey communicate that there are characteristic changes caused by lung diseases, which can be evidenced by enlargement of the right heart: increased amplitude of P wave without prolongation of its period (P- pulmonale), right axis deviation, present S wave, and low amplitude of R wave in lead I and a high amplitude of R wave in lead III. This diagnosis requires confirmation by different diagnostic methods that are suitable for this kind of illnesses, e.g. X-ray, ultrasound.

The aim of the present research is to state if there are statistical vital differences between the picture of ECG curve among dogs suffering from chosen pulmonary diseases and healthy dogs.

MATERIAL AND METHODS

Our research was based on 104 dogs of different breeds with pulmonary diseases.

Diagnosis was based on a complete examination including interview, physical examination, hematologic and biochemical analysis, X-ray, ultrasound, endoscopic and electrocardiographic examination.

Radiographs of each dogs were taken in right or left lateral recumbency and dorso-ventral views. Radiographs were assessed without knowledge of the clinical status of the patient. Radiographs from dogs with evidence of interstitial pattern were subjectively categorized as being normal, mild, moderate or severe, depending on the degree of increased opacity within the lungs and the loss of contrast within the lungs between the pulmonary tissue and other structures. Bronchoscopy was performed in all dogs from group 4, and some dogs from other groups. Bronchoscopic examination of the trachea and the lower airways was performed in anaesthetised dogs using a flexible 100 cm length, 9 mm outer diameter videoendoskope (Olimpus CLE-10 ). A video recording of each bronchoscopic examination was made.

The dogs were divided into 4 groups: 1- dogs with lung cancer (25 dogs), 2- dogs with acute bronchitis (23 dogs), 3- dogs with chronic respiratory diseases (27 dogs), 4- dogs with tracheocollaps (29 dogs).

EKG examinations were made without using any means of physical or pharmacological restraint as their usage could influence the recording. The electrodes were attached at points specified by the Standards for Canine Electrocardiography, The Academy of Veterinary Cardiology Committee Report 1977. Nine leads were used: I, II, III, aVR, aVL, aVF, CV1, CV2 and CV4. The diagnosis was prepared on the basis of recordings from all leads. Electrocardiograph data was collected in a computer database by writing down the results received from lead II. It is considered to be the basic lead because of very good legibility of all waves, and it is consistent with anatomical and electric heart axis. The ECG recordings were analysed according to common procedures such as measuring heart rate, leading rhythm and (eventually) arrhythmias, amplitude and time of waves: P, Q, R, S and T; appearance of additional waves, duration of intervals and complexes: PQ, QRS, ST, QT, value of mean electrical axis, as well as other visible features of recording.

The collected data was submitted to a statistical study. The average and standard deviations were calculated. The results were examined comparing results in pairs by means of Walda-Wolfowitz test, U Mann-Whitney test and Kołmogorow-Smirnow test. T-student test and analysis of correlations were used in cases of regular distribution. The tests were made at level p < 0.05

Proper ECG values among dogs are as follows: heart rate 60-150/min, sinus rhythm (respiratory arrhythmia), P wave maximum 0.04 s/ 0.4 mV, PQ interval 0.06 – 0.13 s, QRS complex maximum 0.06 s, R wave maximum 3.0 mV, T wave maximum not exceeding 25% of R wave amplitude, mean electrical axis – nomogram 40-100°.

RESULTS

Tabel 1 shows average age, sex and dominant factors of pulmonary illness. ECG changes observed in the dogs with pulmonary diseases are collected in table 2.

Statistically relevant differences in the time of QRS complex duration were visible between the group of dogs with inflammation and the group of dogs suffering from trachea cartilage degeneration p = 0.0085 (Mann’s –Whitney’s test).

The correlation between the following were shown:

• clinic group and QRS p = 0.004, negative correlation

• clinic group and the dogs’ weight p = 0.000001

• HR and QT time p = 0.0000001, negative correlation

• P time and P amplitude p = 0.003 positive correlation

Dogs being the subject of cardiological examinations also had pulmonary disease and were middle age or elderly (Table 1). Cough was the dominating symptom and it was the only clinical symptom observed in all the groups. Specification of other clinical symptoms reported by the owners is presented in Table 1. In all the groups that were examined, big and medium-sized dogs were most prevalent, which reflects the preferences of dog owners from the vicinity of Wroclaw. Among the patients of our clinic, male dogs of average size prevail.

ECG changes observed in the dogs with pulmonary diseases were small and different from ones expected (Table 2). All the dogs had a relatively high heart rate 144-148/min. The highest heart rate was observed in dogs having acute bronchitis. In the analysed cases unexpected changes of P wave were observed. Typical features indicating the right atrial enlargement caused by pulmonary hypertension is the increase of P wave amplitude above 0.4 mV without prolongation of the time duration, which gives the P wave a peaked shape as reported by many autors: Allen D. G. & Kruth S. A. & Garvey M. S, Kittleson M.D & Kienle R.D., Lewczuk J. & Piszko P. & Sobkowicz-Woźniak B. & Jagas J. & Sawa W. & Wrabec K., Swift S . No such statistically important change were observed in the examined dogs. In all the groups the P wave amplitudes were at the top of physiological range as was the time duration . A positive correlation was observed between the ampli tude of P wave and P wave time (Fig. 1).

Another frequently mentioned by many authors feature characteristic of right ventricle enlargement as a consequence of pulmonary hypertension is right axis deviation (Allen D. G. & Kruth S. A. & Garvey M. S, Brandenburg R.O. & Fuster V. & Giuliani E.R. & McGoon D.C., Niemand N.G. & Suter P.F., Lewczuk J. & Piszko P. & Sobkowicz-Woźniak B. & Jagas J. & Sawa W. & Wrabec K., Swift S.). This was not observed in the examined dogs. The value of the mean electrical axis was in the middle range of the norms. These changes suggest that pulmonary diseases lead to total heart failure not only as a result of right heart overload. Even sever and chronic pulmonary diseases are compensated by the cardiovascular system. Based on electocardiographic changes such as heart rate, amplitude of P and R wave, time of QRS complexes, it can be stated that acute infections of pulmonary system are the biggest burden for the heart. Although the values of HR and QRS compl exes were the highest in these dogs, they did not exceed the norm. Chronic illnesses give smaller deviations in ECG picture, which were disproportionally small in relation to the degree and nature of pulmonary tissue changes. Significant differences in the size of animals were noticed between the groups that were examined: dogs with tracheocollapse had a statistically significant smaller body weight than those with tumors and acute infection of pulmonary diseases. Dogs with tracheocollapse had mean body weight of 10 kg (Fig. 2).

A negative correlation between duration of QRS complexes and the examined group was noticed. The longest durations of QRS compleses were detected in groups of dogs with the highest body weight, and resultant biggest hearts (Fig. 3).

Prolongation of depolarisation can be a consequence of a longer pathway for electrical impulses and cannot be related to intravetricular block. It cannot be univocally assumed, however, that prolongation of QRS complexes results from pathological cardiac hypertrophy.

Based on the above analysis it is possible to say that even very severe and long-term pulmonary diseases are compensated by the cardiovascular system and give only small changes in the ECG picture. Neither very severe processes nor the length of illness influence the changes of the ECG curve.

REFERENCES

1. Allen D. G., Kruth S. A., Garvey M. S., 1994: Small Animal Medicine. J.B. Lippicott Company, Philadelphia., 223, 225.

2. Edwards J.N.,1987: Bolton’s Handbook of Canine and Feline Elektrocardiography. sec. ed. W.B. Saunders Company, Philadelphia., 23-24, 45.

3. Kittelson M.D., Kienle R.D., 1998: Small animal cardiovascular medicine. Mosby, St. Louis., 87

4. Lewczuk J., Pliszko P., Sobkowicz-Woźniak B., Jagas J., Sawa W., Wrabec K., 1996: Hemodynamiczne, echokardiograficzne i elektrokardiograficzne studium prawego przedsionka w sercu płucnym.[Hemodynamic, ultrasound and electrocardiographic study of right atrium in cor pulmonale] Kardiologia Polska 44, 106-109 [in Polish].

5. Niemand H.G., Suter P.F.,1994: Praktikum der Hundeklinik. Blackwell Wissenschafts – Verlag, Berlin, 409.

6. Schmidt K., Kurzbein U., 1995: Anleitung zur EKG- Auswertung bei Hund und Katze . Schlütersche , Hannover., 21-22

7. Swift S., 1996: Manual of cardiorespiratory medicine and surgery. Virginia Luis Fuentes and Simon Swift Columbia., 62, 64.

8. Tilley L.P., 1989: EKG bei Hund und Katze. Schlütersche, Hannover., 60.

Responses to this article, comments are invited and should be submitted within three months of the publication of the article. If accepted for publication, they will be published in the chapter headed ‘Discussions’ in each series and hyperlinked to the article.