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Normal electrocardiogram patterns and values in Muscovy ducks (Cairina moschata).

Abstract: To describe normal electrocardiographic parameters in conscious Muscovy ducks (Cairina moschata), standard bipolar (I, II, and III) and augmented unipolar limb (aVR, aVL, and aVF) lead electrocardiograms were recorded in 10 clinically healthy birds. Wave forms were analyzed in all leads at 50 mm/s and at 10 mm = 1 mV to determine PR, QRS, ST, QT durations; the net QRS complex; and P and T amplitudes. The polarity of each waveform was tabulated in all leads. The mean electrical axis (MEA) for the frontal plane was calculated by using leads II and III. The mean (SEM) heart rate calculated from lead II was 146.6 [+ or -] 6.8 beats/min. The P wave was predominantly positive in all leads. The dominant pattern of waveforms of the QRS complexes was rS in leads II, III, and aVF, whereas, in leads aVR, and aVL, the pattern was R. The T wave was positive in leads II, III, and aVF and was negative in leads aVR and aVL. The mean (SEM) of the heart MEA was -91.2 [+ or -] 1.8. The electrocardiographic values and patterns tabulated in these clinically normal Muscovy ducks should provide a means of comparison to aid in the diagnosis of pathologic abnormalities in this species.

Key words: electrocardiography, ECG, mean electrical axis, avian, Muscovy duck, Cairina moschata

Introduction

Even though the avian cardiovascular system is similar to that of mammals, many details are unique and specific. The avian heart is situated in the cranioventral part of the coelomic cavity, slightly to the right of midline and near sternal contact. The diaphragm is absent, and the apex is surrounded by liver tissue. The mass of the avian heart is nearly twice that of a mammalian heart of comparable size. The avian heart is designed to meet high-performance demands. (1) The stroke volume of a bird's heart is bigger and the cardiac output is higher than those of mammals, and the heart rate can increase up to 1000 beats/min based on the species, (2) which allows for high oxygen demand during flight, running, or diving. (3) Birds have a cardiac conduction system, similar to that of mammals, and consists of a sinoatrial node, an atrioventricular node, and Purkinje fibers. The sinoatrial node is the primary pacemaker, which conducts the electrical impulse to the atrioventricular node and by way of the atrioventricular bundle to the ventricles. An additional atrioventricular ring has been designed to make fast depolarization of the ventricles. In contrast to mammals, ventricular depolarization is not directed from the endocardium to the outer side of the heart but is rather diffuse. The arrival rapidity of the excitation wave on the surface of the left ventricular wall is related to the short course of the Purkinje fibers in the avian heart. The sequence of the heart depolarization is followed by the right ventricular apex, right ventricular base, left ventricular base, and then the left ventricular apex. (4,5)

The electrocardiogram (ECG) is a noninvasive, transthoracic graphic that shows electrical activity of the heart. In the clinical setting, an ECG is done subsequent to severe trauma, electrocution, or toxicoses, and in the workup of cardiac, metabolic, and/or electrolyte abnormalities. (6) Several studies have been published regarding ECGs in zoo birds. (5-11) The purpose of this study was to analyze the ECG tracings in unanesthetized Muscovy ducks (Cairina moschata) and to describe their normal ECG patterns and values. To our knowledge, the ECG parameters of the Muscovy duck have not been previously studied.

Materials and Methods

Animals

A total of 10 healthy Muscovy ducks of both sexes and weighing between 2 and 4 kg were used in this study. All the birds were physically examined before the study and determined to be healthy. The females were not reproductive at the time of the study. The birds were kept in floor pens on shaving saw dust litter and were fed a diet that consisted of corn, soybean meal, barley, salt, dicalcium phosphate, and a vitamin mineral premix. The birds were provided ad libitum access to food and water.

ECG recordings

The ECGs were recorded by an automatic recorder (Cardimax FX-2111, Fukuda, Japan) while standardized at 10 mm/mV with a chart speed of 50 mm/s. Neither sedation nor anesthesia was used during the ECG recording. The birds were placed in ventral recumbency on a wooden table covered with a plastic material. The clip electrodes were attached to the proptagium of the left and right wings, and to the skin on the left and right stifle joints. Alcohol was used to obtain good clip-to-skin contact (Fig 1). When optimal immobilization and good contact were obtained, standard bipolar (I, II, and III) and augmented unipolar limb (aVR, aVL, and aVF) leads were recorded for 20-30 seconds. All the procedures took place in an isolated room to minimize stress in the birds. (5)

ECG trace analysis

Nomenclature and ECG interpretations were based on standard methods. (5,12) In each tracing, 3 beats were selected for quality; then values of waves and intervals of P-QRS-T deflections were determined by a magnifier. The mean electrical axis (MEA) of ventricular depolarization was calculated in the frontal plane by the vector method with leads II and III. The morphologic patterns of P-QRS-T deflections were evaluated for every lead.

[FIGURE 1 OMITTED]

Statistical analysis

Descriptive statistics were analyzed by using SPSS14.0 for Windows (SPSS Inc, Chicago, IL, USA). Data are given as mean ([+ or -] standard error of mean [SEM]).

Results

An example of a tracing of the standard limb leads (6 leads) in a Muscovy duck is shown in Figure 2. The morphologic patterns of P-QRS-T deflections and their values are offered in Tables 1 and 2, respectively. The heart rate of the ducks ranged from 111 to 187 beats/min, with a mean ([+ or -] SEM) of 146.6 [+ or -] 6.8 beats/min. There was a normal sinus rhythm in all the ducks. The ECG values in lead I were determined to be too small to evaluate. The P wave dominantly was positive in leads II (100%), III (100%), aVR (100%), aVL (80%), and aVF (100%). The range of P-wave amplitudes in all leads was 0.02-0.61 mV. The range of the PR intervals in all leads was 0.04-0.10 seconds. The dominant pattern of waveforms was rS in leads II (100%), III (100%), and aVF (100%), whereas in leads aVR and aVL, the pattern was R (100% and 60% respectively). The range of net QRS amplitudes (net amplitude = positive minus negative deflection voltages of QRS complex) and QRS durations were -6.6 to 5.8 mV and 0.03-0.17 seconds in all leads. The T wave was positive in leads II (100%), III (100%), and aVF (100%), and was negative in leads aVR (100%) and aVL (100%). The range of T wave amplitudes was 0.03-0.48 mV in all leads. The range of QT intervals and ST segments were 0.06-0.18 seconds and 0.02-0.09 seconds in all leads, respectively. The mean (SEM) value of the heart MEA was -91.2 [+ or -] 1.8 (-97 to -80).

[FIGURE 2 OMITTED]

Discussion

ECG is a noninvasive technique that is widely used to evaluate cardiac function during infectious and noninfectious diseases. (13-17) As has been reported in mammals, (18) ECG parameters differ significantly among species of birds. (6,7,12,18-22) These variations in ECG parameters among species support the need to determine specific ECG patterns and reference values for each species of exotic birds. The aim of this study was to determine normal values of ECG parameters in Muscovy ducks that can be used in cardiac evaluations in a clinical setting. In contrast to the methods of many previous studies, (7,17,22-24) we did not anesthetize the study birds to record ECGs. It is clear that ECG parameters (waves and intervals) change in anesthetized birds. (7,22) Ideally, ECG measurements may be best when the animal is conscious but quiet. (5,6,11,21)

The P-wave morphology has been found to vary in the different leads, probably due to physiologic variations. Uzun et al (25) reported that the P wave was negative in aVR and aVL, whereas it was positive in all the remaining leads in partridges (Alectoris species). Talavera et al (12) found that the P wave was mainly positive in leads I, II, III, aVL, and aVF and was negative in lead aVR in unanesthetized raptors. Hassanpour et al (5,6,11) observed that the P wave was mainly positive in all measured leads in helmeted guinea fowl (Numida meleagris) and green peafowl (Pavo muticus), whereas, in golden eagles (Aquila chrysaetos), the P wave was mainly negative in leads III and aVR. Moreover, 7 normal morphologies of P waves were described in healthy domestic fowl. (26)

The range of the mean P-wave amplitudes in all leads was 0.09-0.21 mV, which was fairly similar to the value described by Uzun et al (25) in partridge and by Hassanpour et al (5,6,11) in helmeted guinea fowl, green peafowl, and golden eagles. A smaller P wave was reported in anesthetized raptors, (8,27) which was probably due to the effect of anesthesia on heart function. The atrial depolarization and atrioventricular conduction time did not exist in the PR interval and segment in the study of raptors. Atrial repolarization was not present as Ta wave in the PR segment. The presence of Ta in the ECG of birds is normal, but, in some animals, such as dogs, it is considered as evidence of right atrial hypertrophy. (28-30)

In this study, the mean QRS polarity was always negative in leads II, III, and aVF. None of the ducks showed an R pattern in these leads. These results agree with studies in other avian species. (5,6,8,10-12,23) The ST segment shows the early phase of ventricular repolarization, and it is normally isoelectric. The ST segment is very short or absent, and the S wave rises directly into the T wave (ST slurring). (31) In mammals, this change can be attributed to myocardial ischemia. (18) In healthy birds, however, ST slurring is frequently described with an undetermined cause. (31,32) In our study, the ST segment was identifiable in most of the tracings, but ST slurring was not found. The T wave represents the ventricular repolarization, being that its polarity is mainly opposed to the main vector of QRS complex and always positive in leads II, III, and aVF. (5,8,10,11,19,20)

The QT interval in an ECG represents the total time needed for the ventricles to depolarize and repolarize. The duration of the QT interval in our study was nearly in agreement with the values reported previously in partridge, helmeted guinea fowl, and green peafowl. (5,11,25) The QT interval may change in electrolyte disturbances, drug toxicity, anesthesia, hypothermia, and central nervous system disease in dogs and cats, but changes in the QT interval alone should not be used as the basis to make a diagnosis. (18) We have calculated the MEA from the vectors of ventricular depolarization in leads H and III by using the Bailey hexaxial system. (4) The negative polarity of the QRS complex in II, III, and aVF leads is characteristic of the avian ECG and causes the MEA to be negative (approximately -90[degrees], cranial). (5,7,11) This negative polarity of the QRS complex is the major difference in birds compared with the dog, cat, or man. (18,31) The depolarization wave of the ventricles in birds begins subepicardially and spreads through the myocardium to the endocardium, whereas in the dog, depolarization of the ventricles starts subendocardially. It is perhaps this difference that causes the MEA to be negative in birds. (31) Determining the MEA could be important in the diagnosis of disease in avian species. Major deviations from a normal MEA are known to occur in cardiac disease in turkeys and chickens. (13-16,33) Therefore, establishing the normal value of the MEA in individual species is necessary to compare MEA values of birds with pathologic conditions.

Acknowledgments: This work had been supported by the funds granted by the Vice Chancellor for Research of Shahrekord University.

References

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Hossein Hassanpour, DVM, PhD, and Pooria Khadem, DVM

From the Department of Physiology, Faculty of Veterinary Medicine, Shahrekord University, Shahrekord, Iran (Hassanpour); and the Department of Basic Sciences, Faculty of Veterinary Medicine, Garmsar Branch, Islamic Azad University, Garmsar, Iran (Khadem).
Table 1. The morphologic patterns of P-QRS-T deflections in
electrocardiograms recorded in Muscovy ducks (n = 10)  under
manual restraint.

                P wave, %         QRS, %             T wave,

Lead    Positive   Negative   rS    qR    R    Positive   Negative

II        100         0       100    0     0      100         0
III       100         0       100    0     0      100         0
aVR       100         0         0    0   100        0       100
aVL        80        20         0   40    60        0       100
aVF       100         0       100    0     0      100         0

Table 2. Electrocardiographic values listed as mean ([+ or -]
SE) (range) of standard leads recorded in Muscovy ducks (n
= 10) under manual restraint.

                                         ECG lead

Parameter                     II                    III

P amplitude, mV       0.21 [+ or -] 0.05    0.14 [+ or -] 0.02
                          (0.10-0.61)           (0.06-0.22)
Net QRS amplitude,    -4.23 [+ or -] 0.77   -2.54 [+ or -] 1.36
  mV (a)                (-6.30 to 2.30)       (-5.70 to 5.80)

T amplitude, mV       0.29 [+ or -] 0.03    0.22 [+ or -] 0.04
                          (0.18-0.48)           (0.05-0.40)

QRS segment, s        0.05 [+ or -] 0.002   0.07 [+ or -] 0.01
                          (0.04-0.06)           (0.04-0.17)

PR interval, s        0.06 [+ or -] 0.003   0.06 [+ or -] 0.004
                          (0.04-0.08)           (0.04-0.07)

ST segment, s         0.06 [+ or -] 0.004   0.05 [+ or -] 0.003
                          (0.04-0.09)           (0.04-0.07)

QT interval, s        0.15 [+ or -] 0.006   0.14 [+ or -] 0.01
                          (0.11-0.18)           (0.06-0.17)

                                         ECG lead

Parameter                     aVR                   aVL

P amplitude, mV       0.12 [+ or -] 0.02    0.09 [+ or -] 0.004
                          (0.02-0.20)           (0.08-0.10)
Net QRS amplitude,    2.69 [+ or -] 0.17    2.10 [+ or -] 0.90
  mV (a)                  (1.80-3.60)           (0.00-5.30)

T amplitude, mV       0.15 [+ or -] 0.02    0.13 [+ or -] 0.02
                          (0.03-0.26)           (0.05-0.18)

QRS segment, s        0.04 [+ or -] 0.002   0.04 [+ or -] 0.003
                          (0.03-0.05)           (0.03-0.05)

PR interval, s        0.08 [+ or -] 0.004   0.07 [+ or -] 0.01
                          (0.06-0.10)           (0.06-0.09)

ST segment, s         0.05 [+ or -] 0.003   0.06 [+ or -] 0.01
                          (0.04-0.06)           (0.04-0.07)

QT interval, s        0.14 [+ or -] 0.01    0.14 [+ or -] 0.01
                          (0.11-0.15)           (0.12-0.15)

                           ECG lead

Parameter                     aVF

P amplitude, mV       0.15 [+ or -] 0.02
                          (0.07-0.25)
Net QRS amplitude,    -5.05 [+ or -] 0.33
  mV (a)               (-6.60 to -3.60)

T amplitude, mV       0.30 [+ or -] 0.03
                          (0.13-0.45)

QRS segment, s        0.05 [+ or -] 0.025
                          (0.03-0.06)

PR interval, s        0.07 [+ or -] 0.003
                          (0.05-0.08)

ST segment, s         0.05 [+ or -] 0.004
                          (0.02-0.08)

QT interval, s        0.14 [+ or -] 0.01
                          (0.11-0.17)

(a) Net QRS amplitude indicates positive minus negative
deflection voltages of the QRS complex.
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Author:Hassanpour, Hossein; Khadem, Pooria
Publication:Journal of Avian Medicine and Surgery
Article Type:Report
Date:Dec 1, 2013
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