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19. Electrocardiography in Other Animals
19.1 Chelonians
Without evaluation of the heart, detailed clinical examination is not complete in any individual animal. In turtles/tortoises (chelonian), hard shell (carapace and plastron) does not allow low amplitude heart sounds to be heard through auscultation. Hence, cardiac assessment is generally omitted in chelonians’ clinical practice. Assessing heartbeat in chelonians with respiratory or cardiovascular arrest is of vital importance. Heartbeat can be determined and monitored using ultrasonic Doppler flow probe, electrocardiogram, and/or ultrasound. Electrocardiography is an invaluable technique that can be employed for monitoring cardiac function in chelonians too. As compared to canines and felines, electrocardiography in chelonians is underdeveloped, and information is scanty. It is sparingly used in clinical practice because of limited understanding regarding its interpretation. Small number of observations in most of the studies restrict usefulness of electrocardiogram in the clinical examination of chelonians. Though electrocardiography is routinely employed for evaluation of heart in canines and felines, its application in chelonians and reptiles is yet to find routine place as diagnostic technique probably because of the scarcity of electrocardiographic reference values for healthy chelonian species.
19.1.1 Positioning of Turtles/Tortoises for Electrocardiogram
The turtles/tortoises are subjected to electrocardiography by placing ventral side up. For obtaining a standard bipolar lead ECG, needle electrodes/crocodile clips are attached in a modified Einthoven lead system. Yellow and red electrodes are attached to the proximal aspects of left and right forelimbs, respectively; green and black electrodes are attached to the left and right hind limbs (Fig. 19.1), respectively. Electrocardiographic machine is standardized at the sensitivity of 1 or 2 (2 cm = 1 mV or 1 cm = 1 mV) and at a speed of 25 mm per second, and electrocardiogram is recorded in lead I, II, III, aVR, aVL, and aVF leads at room temperature (28–30 °C). The ECG tracing are analyzed for heart rate, amplitude, and duration of “P” wave, “R,” and “T” waves; QRS, QT, and R-R intervals as is done in case of dogs, cats, and ruminants.
Placement of electrode in the turtle. The animal is placed ventral side up, and yellow and red electrodes are attached to the proximal aspects of left and right forelimbs, respectively; green and black electrodes are attached to the left and right hind limbs, respectively
19.1.2 Electrocardiogram and Electrocardiographic Indices
Electrocardiogram of chelonians is having very small to imperceptible P wave, comparatively appreciable R wave, no Q or S waves, and imperceptible to small positive or negative T wave (Figs. 19.2 and 19.3). Broadly turtles’ ECG is characterized by low amplitude wave forms and lower heart rate with longer periods of repolarization (QT interval). Electrocardiographic indices of healthy conscious pet turtles are given in Table 19.1 (Varshney 2017b). Heart rate varies from 22 to 48 bpm (32.27 ± 1.14, median 32.0); P wave duration is 44.34 ± 3.63 ms (range 10–80, median 40 ms), and amplitude is 0.055 ± 0.003 mV (range 0.025–0.1, median 0.05 mV), “R” wave is comparatively conspicuous (mean 0.194 ± 0.002, range 0.025–0.7, median 0.25 mV), QRS pattern is positive and broad (mean 61.75 ± 2.75, range 20–100, median 60 ms), “T” wave is positive/negative with a mean amplitude of 0.098 ± 0.0097 mV (range 0.05–0.25, median 0.10 mV) and duration of 61.85 ± 3.66 ms (range 40–100, median 60 ms), Q-T interval is prolonged (mean 802.2 ± 51.45, range 550–1280, median 800.0 ms), and longer R-R interval (mean 1859.31 ± 59.26, range 1250–2727, median 1875 ms). P and T waves are imperceptible in many cases.
Electrocardiogram (room temperature 30 °C, lead II, sensitivity 1.0 speed 25 mm/s) of a turtle showing “P,” “R,” and “T” complexes. “P” and “T” waves are very small and negative; and R is positive and comparatively large
Electrocardiogram (lead II, sensitivity 1, speed 25 mm/s) of a tortoise showing very small to imperceptible P wave, comparatively appreciable R wave, no Q or S waves, and imperceptible to small upright T wave. Heart rate is 30 bpm
Electrocardiographic indices in conscious healthy pet turtles
ECG indices | Range | Mean ± S.E. | Median |
|---|---|---|---|
Heart rate (bpm) | 22–48 | 32.27 ± 1.14 | 32.0 |
“P” amplitude (mV) | 0.025–0.10 | 0.055 ± 0.0033 | 0.05 |
“P” duration (ms) | 10.0–80.0 | 44.34 ± 3.63 | 40.0 |
“QRS” amplitude (mV) | 0.025–0.700 | 0.194 ± 0.002 | 0.25 |
“QRS” duration (ms) | 20.0–100.0 | 61.75 ± 2.75 | 60.0 |
Q-T interval (s) | 550–1280 | 802.2 ± 51.45 | 800 |
“T” amplitudes (mV) | 0.05–0.25 | 0.098 ± 0.0097 | 0.10 |
“T” duration (ms) | 40.0–100.0 | 61.85 ± 3.66 | 60.0 |
R-R interval (ms) | 1250–2727 | 1859.31 ± 59.26 | 1875.0 |
19.1.3 Characteristics of Electrocardiogram of Chelonians
- 1.
Low heart rate.
- 2.
Low amplitude waves.
- 3.
Many times P and T waves imperceptible.
- 4.
No Q and S waves.
19.1.4 Abnormal Electrocardiograms (Figs. 19.4, 19.5, 19.6, 19.7, 19.8 and 19.9)
(a) Electrocardiogram (lead II, sensitivity 1, speed 25 mm/s, at room temperature of 30 °C) of an adult male conscious pet turtle weighing 900 g, showing sinus rhythm with heart rate as of 40 bpm; very low amplitude (0.05 mV) but broad (60 ms) “P”; P-R interval of 240 ms; “QRS” (0.7 mV, 80 ms); prolonged S-T interval (440 ms); +ve, small and broad “T” (0.2 mV. 120 ms); prolonged Q-T interval (640 ms); and R-R interval as 1480 ms suggesting cardiomyopathy. (b) Dorso-ventral radiograph of a healthy turtle showing lungs and no radio-opacity of the heart as heart is poorly observed structure situated in the cranial part of coelomic cavity in healthy turtles/tortoises. (c) Dorso-ventral radiograph of the turtle showing enlarged shadow of the heart and fluid in whole of the coelomic cavity. The visible shadow (marked with arrows) is of heart due to heart enlargement or cardiac effusion (Varshney and Monapara 2019). Heart enlargement in this turtle is also reflected in electrocardiogram in Fig. 19.4a
(a) Electrocardiogram (lead II, sensitivity 1, speed 25 mm/s, at room temperature of 30 °C) of a 5-year-old turtle with pneumonia showing sinus tachycardia (heart rate 120 bpm, R-R interval 0.56 s), R wave 0.15 mV, QRS 0.04 s, “P” and “T” waves are not appreciable. (b) Dorso-ventral radiograph of the same turtle showing increased radio-opacity of both lungs suggesting lung congestion/pneumonia
Electrocardiogram (lead II, sensitivity 2, speed 25 mm/s, at room temperature of 30 °C) of a 30 g tortoise showing ventricular premature complex (4th). Other complexes 1, 2, 3, and 5 are normal
Electrocardiogram (lead II, sensitivity 2, speed 25 mm/s, at room temperature of 30 °C) of 1.6 kg star tortoise showing sinus tachycardia (heart rate 90 bpm with almost constant R-R interval). “P” and “T” complexes are very very small
Electrocardiogram (lead II, sensitivity 2, speed 25 mm/s, at room temperature of 30 °C) of a 200 g star tortoise with almost no activity showing ventricular escape rhythm
Electrocardiogram (lead II, sensitivity 2, speed 25 mm/s at room temperature of 30 °C) of a female 4-year-old turtle with anasarca showing sinus rhythm with a heart rate of 60 bpm; imperceptible “P” wave; broad (0.06 s) and small (0.05–0.1 mV) “R” wave; imperceptible “T” wave; and almost regular R-R interval of 1.0 s suggesting sinus tachycardia (Varshney 2016)
19.2 Snakes
Reptile cardiology is in infancy. The heart of snakes and chelonians is three-chambered organ. Some workers consider sinus venosus as a separate chamber. Ventricular septum or ridge is incomplete. Blood flow pattern is little different in reptiles owing to three-chambered organ. Reptile heart needs to be examined during routine clinical examination as many signs of cardiac disease are nonspecific. Auscultation may help in evaluating heart to some extent. By putting a wet cloth over heart region, friction is reduced, and auscultation is facilitated. Detection and differentiation of arrhythmias and heart enlargement in snakes can be diagnosed by electrocardiography. It is very sparingly used in the clinical examination of reptiles as knowledge about reptile electrocardiogram is very limited. Since heart rate of reptiles is related to environmental temperature, it is mandatory to maintain reptile within its preferred optimum temperature zone during electrocardiographic examination.
19.2.1 Signs of Heart Disease
Dullness.
Peripheral edema.
Ascites.
Cyanosis.
Anorexia.
Weight loss.
Sudden death.
19.2.2 Placement of Electrodes for Electrocardiogram
The heartbeat is located visually in dorsal recumbency and right arm (red) and left arm (yellow) electrodes (needle) are placed two heart length cranial to heart on right and left side, respectively; right limb (black) and left limb (green) electrodes are placed two heart length caudal to the heart on right and left side, respectively (Fig. 19.10). Electrocardiographic machine is standardized at 10 mm = 1 mV and at a speed of 25 mm per second, and electrocardiogram is recorded in lead I, II, III, aVR, aVL, and aVF leads at 28–30 °C room temperature.
Placement of electrode in a snake. Right arm (RA red), left arm (LA yellow) electrodes are placed two heart length cranial to heart on right and left side, respectively; right limb (RL black) and left limb (LL green) electrodes are placed two heart length caudal to the heart on right and left side, respectively
19.2.3 Electrocardiogram and Electrocardiographic Indices in Snakes
Electrocardiogram of snakes (Fig. 19.11) is comprised of three main complexes (“P,” “QRS,” and “T”) as seen in canines, felines, humans, and ruminants. In snakes, depolarization begins with SV, and the “P” wave is created by atrial contraction. It is followed by ventricular contraction resulting into “R” wave. Repolarization of ventricle is represented by “T” wave. Low amplitudes of the complexes are the characteristic of snake electrocardiogram as is the case with chelonians.
Electrocardiogram (lead II, sensitivity 1, speed 25 mm/s at room temperature of 30 °C) of a rattle snake showing “P,” “QRS,” and “T” complexes
19.2.4 Factors Influencing Electrocardiogram of the Snakes
- 1.
Heart rate is dependent on body temperature.
- 2.
Body temperature is dependent on environmental temperature.
- 3.
Intervals such as “P-R” and “Q-T” are dependent on heart rate.
19.2.5 Uniqueness of Reptile Electrocardiogram
- 1.
Low heart rate.
- 2.
Very low electrical amplitude of the waves.
- 3.
Many times P and T waves imperceptible.
- 4.
P may be negative.
- 5.
No Q and S waves.
19.2.6 Cardiovascular Diseases in Snakes
- 1.
Primary heart diseases in snakes are not common.
- 2.
Mostly heart ailment is secondary to systemic diseases.
- 3.
Congenital defects of atrioventricular valves and stenosis of vessels may cause primary heart disease.
- 4.
Endocarditis and congestive heart failure have been reported in python.
- 5.
Cardiomyopathy has been reported in snakes.
- 6.
Increased repolarization time on calcium-deficient diet leading to secondary nutritional hyperparathyroidism has also been reported.
19.2.7 Abnormal Electrocardiogram in a Cobra Snake (Fig. 19.12)
Electrocardiogram (lead II, sensitivity 1, speed 25 mm/s at room temperature of 30 °C) of the cobra snake (weighing 1.0 kg) showing negative “P” wave, increased amplitude of the “R” wave (3.0 mV), broad “QRS” (280–320 ms), and negative “T” wave suggesting heart enlargement (Varshney and Chaudhary 2014)
19.3 Avian Species
Avian cardiology is a developing area in veterinary medicine. Despite a great magnitude of cardiac diseases in avian species, its diagnosis poses a great challenge to veterinarians. Cardiovascular diseases often remain undiagnosed in avian species until the heart decompensate because of nonspecific clinical signs and limited diagnostic techniques. For evaluation of the heart in birds, auscultation is unrewarding owing to fast heart rate. Though electrocardiography is routinely employed for evaluation of heart in canines and felines, its application in avian patients is yet to find routine place as diagnostic technique probably because of the scarcity of electrocardiographic reference values for healthy avian species. Though pigeons are high-endurance birds having an elevated cardiopulmonary capacity, they are also prone to cardiac problems. For detecting cardiac arrhythmias and heart enlargement in pigeons, electrocardiography is an important noninvasive cost-effective potential tool. It is all the more important that reference values for each species/breeds of birds are worked out because of the differences in the electrocardiographic parameters between different breeds.
19.3.1 Placement of Electrodes for Electrocardiogram in Pigeons
The pigeons are manually restrained in dorsal recumbency without any anesthetic or tranquilizer. Leads are attached on the right wing (RA), left wing (LA) and left leg (LL), and right leg(RL) at gastrocnemius muscle as shown in Fig. 19.13. Feathers are clipped on the proximal part of the rachis of the feathers, and gel is applied liberally between skin and clips. The standard bipolar limb leads (lead I, II, III) and augmented leads (aVR, aVL and aVF) are recorded in a quiet place, after comfortably settling of the pigeons for 5–10 min, on a multichannel electrocardiographic machine with a paper speed of 25 or 50 mm/s and calibration of 10 or 20 mm equal to 1 mV. A frequency filter may be used to avoid muscular tremor artifacts. ECG recordings are analyzed for amplitude and duration of “P,” “QRS,” and “T” waves; P-R, Q-T, and R-R intervals in lead II.
Showing attachment of electrodes in pigeon. Electrodes are attached on the right wing (RA), left wing (LA) and left leg (LL), and right leg (RL) at gastrocnemius muscle
19.3.2 Electrocardiogram and Electrocardiographic Indices in Pigeons
Electrocardiogram of the pigeon is comprised of “P,” “QRS,” and “T” complexes (Figs. 19.14 and 19.15) as seen in other animals. “P” wave is small, peaked, or slightly isoelectric, positive, and monophasic. PR segment is either depressed or isoelectric owing to fast heart rate. “Q” wave is absent. “R” wave is very small (r), but “S” (negative deflection) is quite appreciable. In most of the pigeons the “QRS” is of rS pattern in lead II. The polarity of “QRS” is negative in lead II, III, and aVF and positive in avR and aVL (Fig. 19.15). The “QRS” complex in lead I is very small or isoelectric. “ST” segment is slurring. “T” wave is generally positive in lead I, II, III, and aVF and negative in lead aVR and aVL leads.
Electrocardiogram of clinically healthy pigeon (lead II, sensitivity 2, speed 50 mm/s) showing “P,” “QRS,” and “T” complexes
Electrocardiogram of clinically healthy pigeon in limb leads (lead I, II, III) and augmented leads (aVR, aVL, and aVF) on a multichannel electrocardiographic machine with a paper speed of 50 mm/s and calibration of 20 mm equal to 1 mV
Electrocardiographic indices of healthy pigeons are given in Table 19.2 (Varshney 2017a). The heart rate in pigeons varies from 200 to 400 bpm with a mean of 315.40 ± 26.72 and a median of 300. “P” waves amplitude ranges from 0.05 to 0.35 mV with a mean of 0.156 ± 0.0056 and a median of 0.15 mV. Its duration varies from 0.02 to 0.06 s with a mean duration of 0.032 ± 0.0006 s (median 0.03 s). The mean “P-R” interval is 0.036 ± 0.0005 s (range 0.02–0.06 s; median 0.04 s). “QRS” complex is predominantly negative in the form of rS. The “S” amplitude ranges from 0.10 to 0.80 mV with a mean of 0.445 ± 0.0027 mV and a median of 0.40 mV. Its duration varies from 0.02 to 0.08 s with a mean of 0.033 ± 0.0005 s and a median of 0.03 s. The “T” wave is generally positive with an amplitude of 0.370 ± 0.0139 mV (range 0.10–1.3 mV and median as 0.35 mV) and duration of 0.051 ± 0.0006 s (range of 0.02–0.12 s and median of 0.05 s). The “QT” interval varies from 0.02 to 0.12 s (0.0417 ± 0.0005 s and median of 0.04 s). “R-R” interval varies from 0.0.30 to 0.15 s (mean 0.194 ± 0.0041 s; median 0.20 s) depending upon heart rate. High heart rate has shorter R-R interval.
Electrocardiographic indices in conscious healthy domestic pigeons (lead II)
ECG indices (n = 180) | Range | Mean ± S.E. | Median |
|---|---|---|---|
Heart rate (bpm) | 200–400 | 315.40 ± 26.72 | 300.0 |
“P” amplitude (mV) | 0.05–0.35 | 0.156 ± 0.0056 | 0.15 |
“P” duration (s) | 0.02–0.06 | 0.032 ± 0.0006 | 0.03 |
P-R interval (s) | 0.02–0.06 | 0.036 ± 0.0005 | 0.04 |
“S” amplitude (mV) | 0.10–0.80 | 0.445 ± 0.0027 | 0.40 |
“S” duration (s) | 0.02–0.08 | 0.033 ± 0.0005 | 0.03 |
S-T segment (s) | 0.00–0.03 | 0.0083 ± 0.0011 | 0 |
Q-T interval (s) | 0.02–0.10 | 0.0417 ± 0.0005 | 0.04 |
“T” amplitudes (mV) | 0.10–1.30 | 0.370 ± 0.0139 | 0.35 |
“T” duration (s) | 0.02–0.12 | 0.051 ± 0.0006 | 0.05 |
R-R interval (s) | 0.11–0.42 | 0.206 ± 0.0041 | 0.20 |
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