Analysis of electrocardiographic parameters in helmeted guinea fowl (Numida meleagris).
Key words: electrocardiography, ECG, cardiac, avian, helmeted guinea fowl, Numida meleagris
The avian cardiovascular system is designed to match the high metabolic demand of birds. The avian heart is comparatively large, and the heart rate, cardiac output, and blood pressure are all correspondingly high relative to mammals. These unique features of the avian heart enable birds to fly, run, or dive. (1) Birds have relatively larger hearts than mammals, and the heart size of small birds is proportionately greater than that of large birds. The avian heart is divided into 4 complete chambers. The left ventricle has a heavy wall, which is approximately 2-3 times thicker than that of the right ventricle. The left atrioventricular (AV) valve is thin, bicuspid, and membranous, whereas the right AV valve is a simple muscular flap devoid of chordae tendinae. (2) As in mammals, birds have a cardiac conduction system that consists of a sinoatrial (SA) node, an AV node, and Purkinje fibers. The SA node is the primary pacemaker from which the electrical impulse moves to the AV node then, by way of the AV bundle, to the ventricles. An additional AV ring allows for rapid depolarization of the ventricles. (3)
Techniques such as electrocardiography (ECG) and echocardiography have been used to perform repeated evaluations of cardiovascular function in birds. (4-7) Such noninvasive techniques assess cardiac function indirectly. The ECG is a graphic recording of the changes in magnitude and direction of the heart's electrical current generated by depolarization and repolarization of the atria and ventricles. Normally, each segment of the ECG arises from a specific area of the heart in sequential fashion. The P wave, QRS complex, and T wave are recognizable deflections of the ECG tracing and indicate atrial depolarization, ventricular depolarization, and ventricular repolarization, respectively. The ECG of birds is different from that of humans in that the avian QRS wave is negative. This might be explained by the fact that avian ventricular depolarization, in contrast to the process in mammals, is not directed from the endocardium to the outer aspect of the myocardium of the heart but is rather diffuse. (3) The Purkinje fibers of birds follow the coronary arteries and, therefore, take a relatively short course through the thick left myocardium. This accounts for the rapid arrival of the excitation wave at a given point on the surface of the left ventricular wall. The sequence of depolarization in the avian heart is right ventricle apex, right ventricle base, left ventricle base, and left ventricle apex. (8)
The ECG is an important tool both in the evaluation of primary cardiac disease as well as the assessment of diseases secondarily affecting the heart, such as metabolic and electrolyte abnormalities. (9) The ECG can also be part of the clinical assessment of birds in zoological collections in which cardiac, metabolic, and/or electrolyte abnormalities can result from trauma, electrocution, and poisoning. Until now, however, little information on the ECG parameters of unanesthetized avian species kept in zoological collections has been available, (10-14) although, in some cases, ECG data have been obtained from sedated or anesthetized birds. (10,12) The purpose of this study was to analyze the feasibility of obtaining ECG tracings in conscious helmeted guinea fowl (Numida meleagris) and to describe the normal ECG patterns and values for this species. To the authors' knowledge, this information has not been previously reported.
Materials and Methods
The study included 8 healthy helmeted guinea fowl, 4 males and 4 females, each weighing 1-1.5 kg and aged 6-12 months, obtained from Saei Park in Tehran, Iran. The females were not laying eggs. The birds were housed in floor pens with a sawdust substrate and were fed a diet of corn, wheat, soybean meal, barley, limestone, and salt supplemented with lysine, methionine, dicalcium phosphate, and vitamin mineral premix.
All birds received physical examinations to confirm their general health before being subjected to ECG. ECG was performed with an automatic recorder (Cardimax FX-2111, Fukuda Denshi, Tokyo, Japan), and electrocardiograms were standardized at 10 mm = 1 mV and a chart speed of 50 mm/s. Neither sedation nor anesthesia was used for ECG. Each bird was placed in ventral recumbency on a wooden table covered with plastic material. When evaluating an easily stressed bird, the bird's head was covered with a surgical cloth during handling. Four alligator clip electrodes were used, 1 each attached to the cranial aspect of the propatagium and to the skin overlying the stifle on the right and left sides. Alcohol was used to obtain adequate clip-to-skin contact. When optimal immobilization and contact were obtained, standard bipolar (I-III) and augmented unipolar (aVR, aVL, and aVF) limb leads were recorded. (15)
Analysis of ECGs
Nomenclature and ECG interpretation were performed according to standard methods. (9,15) For each tracing, 3 beats were selected for quality, then values of waves and intervals of P-QRS-T deflections were determined with the use of a magnifier. The mean electric axis (MEA) of ventricular depolarization in the frontal plane was calculated by the vector method by using leads II and III. The morphologic patterns of P-QRS-T deflections were evaluated for every lead.
Statistical analyses were performed by using descriptive statistics with SPSS 14.0 for Windows (SPSS Inc, Chicago, IL, USA). Data were recorded as mean (SD).
An example of the standard ECG leads taken sequentially is shown in Figure 1. Morphologic patterns of the P-QRS-T deflections and their values are presented in Tables 1 and 2, respectively. Heart rates of the birds studied were 316-375 beats/ min with a mean (SD) of 338.4 [+ or -] 18.99 beats/min. Amplitudes were highest in lead III and were so low as to be virtually immeasurable in lead I. A normal sinus rhythm was recorded in all the birds.
The P wave was predominantly positive in leads I (100%), II (100%), III (87.5%), aVL (75%), and aVF (100%), and was positive in 50% of the birds in lead aVR. In all leads except lead I, the ranges of the P wave amplitude and PR interval were 0.05-0.2 mV and 0.03-0.06 seconds, respectively. The predominant pattern of wave forms in the QRS complexes was RS in leads II (100%), III (87.5%), and aVF (75%); Rs in lead I (50%); QR in lead aVR (87.5%); and qR (100%) in lead aVL. Values for the net QRS amplitude, which demonstrates the positive minus negative deflection voltages of the QRS complexes are included in Table 2. The ranges of net QRS amplitudes and QRS segments in all leads except lead I were -0.60 to 0.35 mV and 0.03-0.04 seconds, respectively. The T wave was predominantly positive in leads I (75%), II (100%), III (100%), and aVF (100%), and negative in leads aVR (100%) and aVL (100%). The range of T-wave amplitudes in all leads except lead I was 0.10-0.45 mV. The ranges of QT intervals and ST segments in all leads except lead I were 0.10-0.14 seconds and 0-0.05 seconds, respectively. The mean (SD) of the MEA was -60.2[degrees] [+ or -] 24.0[degrees] with a range of -98[degrees] to -10[degrees].
[FIGURE 1 OMITTED]
The present study provides clinically useful ECG data for conscious helmeted guinea fowl. Electrocardiograms were easily obtainable in unsedated birds. These findings will, it is hoped, facilitate understanding of ECG changes in cardiovascular diseases of helmeted guinea fowl. Many studies of avian ECG have used anesthesia to facilitate collection of data. (10,16-18) However, anesthesia may influence ECG waves and intervals. (10,18) In a comparative study of African grey (Psittacus erithacus) and Amazon (Amazona species) parrots that were unanesthetized and anesthetized with isoflurane, QT intervals were significantly different between anesthetized birds and unanesthetized birds (0.048-0.095 seconds and 0.038-0.070 seconds, respectively). (18,19) Arrhythmias (including second- and third-degree AV-block), sinus arrest, T-wave depression, and atrial premature contraction, have been described in bald eagles (Haliaeetus leucocephalus) anesthetized with isoflurane. (20) A negative P wave in lead II, reported in 1 red-tailed hawk, was likely the result of anesthesia. (10) These findings suggest that ECG data are more reliable when recorded in the conscious animal. (9,21) However, body motion and the stress of handling can create alterations in the ECG recordings of unanesthetized animals. To minimize such disadvantages in the present study, birds were transferred to a quiet place, and the head was covered during ECG. After attaching the electrodes and before recording, the birds were rested for several minutes. Each ECG was recorded for at least 2 minutes to help override the influence of transient arrhythmias.
Positioning of birds during ECG can significantly alter ventilation. Birds positioned in dorsal and right lateral recumbency reportedly have lower lung and air-sac volumes and greater lung density compared with those positioned in sternal recumbency. (22,23) Sternal positioning, as was used for the birds in this study, helps maintain normal cardiopulmonary anatomic and physiologic orientation, which in turn may affect blood pressure, perfusion, cardiac outflow, and function.
As is the case among mammalian species, significant differences in most ECG parameters have been described among avian species. (9,10,15,18,21,24,25) These findings support the need to ascertain reference values and specific ECG patterns for each exotic bird species. In our study, P wave morphology varied among ECG leads. Upon review of other studies, this may be an example of an interspecific physiological variation. In a study of 4 species of conscious raptors (the Eurasian kestrel [Falco tinnunculus], Griffon vulture [Gyps fulvus], little owl [Athene noctua], and Eurasian eagle owl [Bubo bubo]), the P wave deflection was predominantly positive in leads I, II, III, aVL, and aVF and was negative in lead aVR. (15) Another study in partridges (Alectoris chukar and Alectoris graeca) reported a negative P wave deflection in leads aVR and aVL, and a positive deflection in all remaining leads. (26) A study in healthy domestic fowl described different normal morphologies of P waves with a range of mean P wave amplitudes in all leads except lead I of 0.08-0.13 mV. (27) These findings approximated those recorded in partridge (A chukar) (0.1 mV in lead II). (26)
Atrial depolarization and AV conduction time did not exist in the PR interval and segment in this study. There was no Ta wave, representing atrial repolarization, in the PR segment. The Ta wave is considered to be indicative of right atrial hypertrophy in some animals such as the dog; however, it has been described in healthy birds without general abnormalities in atrial size. (25,28) A Ta wave has been reported in the ECG of pigeons (Columba livia gutturosa) and Eurasian kestrels but not in the Griffon vulture, little owl, or Eurasian eagle owl. (15)
In the present study, QRS polarity was always negative in leads II, III, and aVF. None of the helmeted guinea fowl showed an R deflection in these leads. These results are corroborated by previous ECG studies in other avian species. (8,12,14,15,17,18) The ST segment represents the early phase of ventricular repolarization and is normally isoelectric. In birds, the ST segment is very short or absent, and the S wave rises directly into the T wave (ST slurring). (19) This change in mammals can be attributed to myocardial ischemia (9); however, in healthy birds, ST slurring of undetermined etiology is frequently described. (19,28) In our study, the ST segment was identifiable in most tracings, and ST slurring was found in some of them. In agreement with other ECG studies in birds, the ST segment was generally above baseline. (14,18,19)
In birds, the T wave, which represents ventricular repolarization with a polarity primarily opposed to the main vector of the QRS complex, is predominantly positive in leads I, II, III, and aVF. (12,14,24,25) The QT interval represents the total time needed for the ventricles to depolarize and repolarize. The QT interval's duration in our study (0.12 seconds) approximated that reported previously in partridges (A graeca and A chukar). (26) Changes in QT interval may be seen with electrolyte disturbances, drug toxicity, anesthesia, hypothermia, and central venous system disease in most mammals, although alterations in the QT interval alone are usually not sufficient to make a diagnosis. (9) In birds, prolongation of the QT interval may be associated with electrolyte disturbances (eg, hypokalemia or hypocalcemia) or may occur during anesthesia. (18,19)
In this study, we calculated the MEA from the vectors of ventricular depolarization in leads II and III by using the Bailey hexaxial system. (8,29) The avian ECG characteristically has a negative MEA (cranial), which implies the negative polarity of the QRS complex in leads II, III, and aVF. (10,19,30) This constitutes the major difference in the normal ECG of the bird compared with that of the dog, cat, or man. (9) The likely reason for this disparity is that in birds, the depolarization wave in the ventricles begins subepicardially and spreads through the myocardium to the endocardium, whereas in the dog, ventricular depolarization starts subendocardially. (19) The MEA in the present study was -98[degrees] to -10[degrees]. The MEA can have significant interspecific variability in birds, but the values are always negative. Major deviations from a normal MEA can be useful in identifying different cardiac diseases in turkeys and chickens. (10,16,17,31)
To ensure that any deviations from normal ECG parameters are truly associated with pathology, comparisons must be made with reference to data for a particular species. This study described interpretative ECG tracings in conscious helmeted guinea fowl. Data obtained regarding rhythm, heart rate, morphologic patterns, and magnitude of component deflections provides clinically useful information for this species.
Acknowledgments: This work was supported by funds granted by the Vice Chancellor for Research of Shahrekord University.
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Hossein Hassanpour, DVM, PhD, Hamed Zarei, DVM, PhD, and Peyman Hojjati, DVM, PhD
From the Department of Basic Sciences, Faculty of Veterinary Medicine, Shahrekord University, Saman St, Shahrekord, Iran (Hassanpour); and the Departments of Basic Sciences (Zarei) and Clinical Sciences (Hojjati), Faculty of Veterinary Medicine, Islamic Azad University, Garmsar Branch, Garmsar, Iran.
Table 1. Morphologic patterns of P-QRS-T deflections and their relative frequencies in electrocardiograms of 8 helmeted guinea fowl. All values indicate percentages. P wave QRS complex Positive Negative rS QR qR RS Rs R I 100 0 0 0 0 0 50 50 II 100 0 0 0 0 100 0 0 III 87.5 12.5 12.5 0 0 87.5 0 0 aVR 50 50 0 87.5 12.5 0 0 0 aVL 75 25 0 0 100 0 0 0 aVF 100 0 25 0 0 75 0 0 T wave Positive Negative I 75 25 II 100 0 III 100 0 aVR 0 100 aVL 0 100 aVF 100 0 Table 2. Electrocardiographic values of 5 standard limb leads in 8 helmeted guinea fowl. Each parameter is represented by the mean (SD) with ranges in parentheses. Amplitudes were virtually immeasurable in lead 1. II III P wave amplitude 0.12 [+ or -] 0.026 0.13 [+ or -] 0.038 (mV) (0.10-0.15) (0.10-0.20) Net QRS -0.11 [+ or -] 0.141 -0.21 [+ or -] 0.176 amplitude (MV) (a) (-0.35 to 0.05) (-0.60 to -0.05) T wave amplitude 0.28 [+ or -] 0.065 0.29 [+ or -] 0.078 (mV) (0.20-0.40) (0.20-0.45) QRS segment (s) 0.04 [+ or -] 0.005 0.04 [+ or -] 0.005 (0.03-0.04) (0.03-0.04) PR interval (s) 0.04 [+ or -] 0.008 0.04 [+ or -] 0.005 (0.03-0.05) (0.04-0.05) ST segment (s) 0.03 [+ or -] 0.006 0.04 [+ or -] 0.011 (0.02-0.04) (0.02-0.05) QT interval (s) 0.12 [+ or -] 0.007 0.12 [+ or -] 0.010 (0.10-011) (0.11-014) aVR aVL P wave amplitude 0.09 [+ or -] 0.018 0.08 [+ or -] 0.021 (mV) (0.05-0.10) (0.05-0.10) Net QRS 0.05 [+ or -] 0.107 0.17 [+ or -] 0.092 amplitude (MV) (a) (-0.05 to 0.30) (0.05-0.35) T wave amplitude 0.18 [+ or -] 0.037 0.14 [+ or -] 0.032 (mV) (0.10-0.20) (0.10-0.20) QRS segment (s) 0.03 [+ or -] 0.005 0.04 [+ or -] 0.005 (0.03-0.04) (0.03-0.04) PR interval (s) 0.05 [+ or -] 0.013 0.05 [+ or -] 0.011 (0.03-0.06) (0.03-0.06) ST segment (s) 0 [+ or -] 0 0.01 [+ or -] 0.008 (0-0) (0-0.04) QT interval (s) 0.11 [+ or -] 0.009 0.12 [+ or -] 0.012 (0.10-0.12) (0.10-0.12) aVF P wave amplitude 0.11 [+ or -] 0.017 (mV) (0.10-0.15) Net QRS -0.18 [+ or -] 0.162 amplitude (MV) (a) (-0.50 to 0) T wave amplitude 0.29 [+ or -] 0.064 (mV) (0.20-0.40) QRS segment (s) 0.04 [+ or -] 0.004 (0.03-0.04) PR interval (s) 0.04 [+ or -] 0.009 (0.03-0.06) ST segment (s) 0.03 [+ or -] 0.007 (0.02-0.04) QT interval (s) 0.12 [+ or -] 0.012 (0.10-0.11) (a) Net QRS amplitude indicates positive minus negative deflection voltages of the QRS complex.
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|Title Annotation:||Original Studies|
|Author:||Hassanpour, Hossein; Zarei, Hamed; Hojjati, Peyman|
|Publication:||Journal of Avian Medicine and Surgery|
|Date:||Mar 1, 2011|
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