183
Laboratory Animals (1979) 13.183-186
Electrocardiogram of the reindeer, Rangifer tarandus tarandus J. TIMISJARVI, L. HIRVONEN, P. JARVENSIVU & M. NIEMINEN Department of Physiology and Department of Zoology. University ofOulu. Kajaanintie 52A, 8F-90220 Oulu 22, Finland Summary Electrocardiograms were recorded for 50 Finnish reindeer of age 1 day to 9 years, using standard and unipolar extremity leads in the frontal plane. The range of heart rate was 40-250 beats per minute. Atrial and ventricular depolarization times were 5-10 ms shorter in newborn calves than in older reindeer, and showed only minor variance with respect to heart rate. The duration of depolarization was dependant on heart rate, and was more rapid in young calves. A-V conduction time decreased with increasing heart rate. The mode of the QRS vector was 280-290°, and the mode of the T vector 200-230° in the older animals, but 100-120° in young calves. The main deflection in the QRS complex was S in the leads 11,III and aVF. R was dominant in aVL and I. The reindeer, a semidomesticated ruminant living in the subarctic areas, has a wide range of cardiac reserves (Timisjiirvi, 1978) but it also shows great sensitivity in its circulation to various stimuli (Timisjiirvi & Hirvonen, 1978). As a physically well-trained subject with rapid reactivity, it is a useful experimental animal for studies on circulatory adaptation to a variety of environmental factors. The Finnish reindeer reaches adulthood at the age of 6 years, the males achieving a bodyweight of 100120 kg and the females 70-80 kg. The bodyweight of newborn calves, which are well developed, is 4- 7 kg. The growth of the reindeer calf is rapid during the first summer, when the daily weight gain may be as high as 400 g, but it ceases almost completely during the winter. No published information is available concerning the electrocardiogram of the reindeer. The present study describes the normal electrocardiogram of the reindeer and certain changes related to the age of the animal.
Material and methods A total of 50 reindeer (Rangifer tarandus tarandus) ranging in age from 1 day to 9 years (19 calves aged 1-30 days, 25 calves aged 5-10 months, and 6 does aged 3-9 years) and in weight from 4 to 60 kg served as the subjects of this investigation. All were in good health and free from detectable cardiovascular abnormalities. Young animals preponderated for technical and commercial reasons. Received 22 May 1978. Accepted 12 December 1978.
Electrocardiograms were recorded with a 4-channel direct-writing recorder (Mingograph EM 34; ElemaSchonander now Siemens-Elema Ab, Rontgenviigen 2, S-1 7995 Solna, Sweden) in the laboratory or with a three-channel direct-writing recorder (Mingograph Minor 3; Siemens-Elema, AB) in the open. The paper speed was 50 or 100 mm/s and the calibration setting 1 em/mY. The standard limb leads I, II and Ill, and the augmented unipolar limb leads aYR, aYL and aYF, were recorded with subcutaneous needle electrodes. Diazepam alone (1· 2-1· 5 mg per kg bodyweight) or together with pentobarbital sodium (5-20 mg/kg) was employed as a tranquilizer during the studies on the 25 calves aged 5-10 months, under laboratory conditions. The other recordings were carried out in the natural environment of the reindeer, and no sedation was used. The young calves (aged 1-30 days) were immobilized manually in the prone position, whereas the old does were immobilized with a special chute. Hypoxia was induced by means of a 10% mixture of oxygen in nitrogen, or by impairment of respiration by pentobarbital sodium under laboratory conditions. The recordings were taken according to Friedman (1971) with 3-4 complexes and intervals being measured in each lead. Function fittings were obtained by least-square solutions. The index of fitting used for the reciprocal comparisons of the equations was R. The fittings were also checked using the F test.
Results The mean heart rate of a resting reindeer of 6 months of age was 50-60 beats per minute, while various irritants such as noise, pain, arterial hypoxia, irregularities of breathing, certain phases of rumination and also immobilization led to rapid increases up to 250 b/min. The range of the heart rate of the calves in this series (aged I day to 4 weeks) was 82-250 b/min. The duration of the atrial depolarization was 57 ± 8 ms, and showed only minor decrease when the heart rate increased in the older reindeer (age 5 months or more). In the young calves the atrial depolarization was more rapid (45 ± 9 ms) and decreased more with respect to the increase in heart rate than in the former group (Fig. 1). The duration of the atrial repolarization (which could be measured in 3 cases) was about 60 ms, and the atrial electrical systole was about 150 ms at a heart rate of 177 b/min (Fig. 2), with ranges Ta 60-80 ms and electrical systole 150-200 ms, HR 136-177 b/min. The atrioventricular conduction time
Timisjiirvi, Hirvonen, Jiirvensivu & Nieminen
184 was strongly dependent on the heart rate, and was considerably shorter in the young calves than in the older animals (Fig. 1). Ventricular depolarization took 53 ± 8 ms in the older animals and decreased slightly at higher heart rates, while the young calves showed a fairly constant duration of ventricular depolarization (43 ± 7 ms) with respect to heart rate. The duration of ventricular
repolarization decreased with the increase in heart rate. The shortening of repolarization was more rapid in the young calves (Fig. 3). At heart rates of 90-230 b/min the young calves had a shorter electrical systole and longer diastole and filling period than older animals (Fig. 4). The P wave was monophasic, biphasic or bifid (Figs 2 and 5). The most common form of the QRS com-
150 u CI> OIl
E 100
•.. . ..
u
•......
100
E
...•...... •....•......
.. .-0
PQ(ol
. ......• .........
50
'
50
,
,
100
150
.
,
200 250 HEART RATE b/min
Fig. I. Duration of atrial depolarization (P wave) and of the PQ interval as a function of beart rate. Solid line reinder aged 5 months or more. DOl/ed line calves aged I day to 4 weeks. P 0 older animals; • young calves. PQ 0 older animals; • young calves. The equations for the curves are: PQ,O)= -0·28x + 165, R 0·694, F 39·9, N 45; PQ,cl = -Q·28x + 135, R 0·654, F 18·6, N 27; p,o) = -0·3x + 61. R 0·167, F 1·2, N 45; P(el = -O·lx + 60, R 0·378, F 4·2, N 27.
I
'.
~
'--
D
~-
P Ta
P
•• ••
•• ••
-.----._-~----_ -;;-;-----r-_-_.
Ta
QRSlcl
N
Z
'
50
,
,
,
,
100
150
200
250
HEART RATE b/min
Fig. 3. Duration of ventricular depolarization (QRS complex) and ventricular repolarization (T wave) as a function of heart rate. Solid line reindeer aged 5 months or more. Dol/ed line calves aged 1 day to 4 weeks. QRS 0 older animals:· • young calves. T 0 older animals: • young calves. Equations for the curves are: QRS,O) = -Q·04x + 57, R 0·227, F 2·3, N 45; QRS(C) = -0·04x + 48, R 0·188, F 0·9, N 27; TO) = 0·0009x' - 0·49x + 134, R 0·667, F 33·7, N 45; T,O)= 0.0~12x' - 0·61x + 139, R 0·584, F 10·3, N 27.
1000 u on
CI>
E
--r-
n
500
aVR ---..-aVL 1 mV
DRSl ••1
__
POCel
••••••••••
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" ,.I.e...
-:-::-:-~~...,.;..:.
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...........
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a •••••••.
'ro"",
0
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15
Fig. 2. Atrial electrocardiogram of a reindeer aged 10 months. Ventricular asystole as a result of severe arterial hypoxia. Atrial depolarization (P) is followed by atrial repolarization (Ta).
Fig. 4. Duration of the ventricular electrical systole (QT interval) as a function of heart rate. Solid line reindeer aged 5 months or more. Dolled line calves aged I day to 4 weeks. QT 0 older animals; • young calves. Equations for curves are: QTjO) = 0·OOI2x'- 1·14x + 354, R 0·936, F 298·6, N 45; QT,C)= 0·0047x'- 2·17x + 398, R 0·869, F 74·1, N 27.
Reindeer electrocardiogram
185
plex was qR, R or Rs in the leads I, aVR and aVL, while the forms rS, QS and Qr dominated in the leads II, III and aVF (Fig. 5A, B, D, E). In 10 out of the 50 animals studied, however, the form of the QRS was that shown in the Fig. 5C. In the newborn calves (aged 1-21 days) the SoT segment deviated by up to 0·4 mV in a direction opposed to the main deflection of the QRS complex. Fig. 6 provides a case report on reindeer precordial leads. The difficulty with unipolar precordial leads on a Wilson terminal is the lack of a standard position for the electrodes: in this study the recommendation of Sporri (I975b) for horses and cattle was adopted, but with no certainty that this was equally appropriate for reindeer.
A
I
c
B
o
II
--"'-(-_
.\...-.....1....-...-.'>:
• YL
~-_~-
E ..,-
I
---.-
, 2.
o
Fig. S. Normal electrocardiograms of reindeer aged S days to 3 years. A calf aged S days, HR 190 (note S-T deviations). B calf aged 20 days, HR 125. C calf aged 19 days, HR 115 (note different direction of QRS deflections compared with B). D calf aged 10 months, HR 60. E doe aged 3 years, HR 76.
III-.:~
Vs ~;'~;"-v-
V13-.~.~
aVR..,..J~·~
V6 ~~~
aVL -,'-v------'.'--v--
V7 '" ~;L..-
VIS--;~,'--v---
aVF -f-·.r--"--.r--....r-
V.
VI6i"-v-----l'--v---
1
I
v-:,~,~
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VI -...Jr---'r---
V. v-:~.~
V2---' ---
Vro.,..,l..----.,..,,~ VI.~
1mvlo
I
VI7--'~
2:3
sec
Fig. 6. Electrocardiogram of a standing reindeer of 4 months of age. The unipolar precordial leads were obtained by positioning needle electrodes subcutaneously around the thoracic cage within the 5th intercostal space- v, on the sternum, V 10 on the vertebral column, V ,-v. on the left side, VII-V,. on the right side (see Sparri, 1975b).
The mode of the QRS vector was 280-290° in the frontal plane in the newborn calves and in the older animals, but varied in direction in the calves aged 1721 days (Fig. 5). The P vector was 70-90°. The mode of the T vector was 200-250° in the older animals, but 100-120° in the young calves.
Discussion
The electrocardiogram is an obligatory tracing in the field of cardiovascular investigation since it provides reliable information on cardiac rhythm, heart rate, initiation of heart beat and also, to some degree, indirect evidence on the functional state of the heart muscle. A wide range of such information is readily obtainable from the conventional scalar leads, even if the records are limited to a single plane. Because of species-specific macro anatomical differences the standardization applied in one species is not suitable for another. The major determinants of the pathway by which electrical excitation spreads through a heart muscle are the geometry of the heart and the organization and position of the specialized conduction system; tous the formation of the electrocardiogram is also an anatomical problem (Scher, 1962). The reindeer heart extends from the 3rd to the 6th rib in the craniocaudal direction (Engebretsen, 1975). According to our >I-ray studies in lateral projection, the apex lies close to the diaphragm and sternum, and the base extends near to the thoracic vertebrae. The chambers of the heart have
thick walls, and the ratio between right and left ventricular wall thickness is 0·85 in the newborn calf, decreasing to 0·60 by 10 months. Heart weight is 1·2% of body weight in the newborn calf, 1·1% at 10 months, and 0·6-0·8% in older does. Cardiac hypertrophy was not observed in excised hearts, and the electrocardiograms were interpreted as representing normal animals. The anatomy of the conduction system of the reindeer heart has not been studied, but the craniallyorientated QRS vector agrees well with observations on other species made by Hamlin & Smith (1965), who categorize animal species according to their mean spatial QRS vector, one category consisting of thosesuch as primates and carnivores-whose QRS vector is caudally-orientated, and the other category of those -such as ruminants, horses and birds-in whom it is cranially-orientated. On the other hand, Sporri (1975a) also divides animals into 2 categories according to the organization of the conduction system of the heart, with horses, ruminants and birds, for example, forming one group in which the terminal branches of the Purkinje fibres reach the subepicardiac layer of the heart muscle. The present results suggest that the reindeer also belongs to this group. Growth in the reindeer is very rapid during the first
Timisjiirvi, Hirvonen, Jiirvensivu & Nieminen
186
months of life, when daily weight gain may be 300-400 g, and birth weight may double within 3-4 weeks. Thus the disappearance of the S-T segment deviations from the electrocardiogram of the calves may be a result of matUration. The development of the conduction system of the reindeer heart may be slower, however,
gIVIng rise to the variance in the QRS observed in the calves aged 16-22 days. Acknowledgement We express our gratitude for financial aid.
to the Academy
vector
as
of Finland
References Engebretsen, R. H. (1975). Topography of internal organs of reindeer (Rangifer larandus). ACla velerinaria scandinavica 16,suppl. 57,1-18.
Friedman, H. H. (1971). Diagnostic electrocardiography
and vectorcardiography. New York: McGraw-Hill. Hamlin, R. L. & Smith, G. R. (1965). Categorization of common domestic mammals based upon their ventricular activation process. Annals of the New York Academy of Sciences 127,195-203. Scher, A. M. (1962). Excitation of the heart. In Handbook of physiology (ed. W.F. Hamilton), section 2. vol. I. Washington: American Physiological Society.
Das Elektrokardiogramm J. TIMISJARVI,
Sporri, H. (1975a). Elektrokardiographie. Grundlagen der Elektrokardiographie (I). Tierarzlliche Praxis 3, 1-6. Spiirri, H. (I 975b). Elektrokardiographie. Grundlagen der Elektrokardiographie (3). Tiercirzlliche Praxis 3,263-269. Timisjiirvi, J. (1978). Left ventricular volumes and functioning of the reindeer heart. Basic Research in Cardiology 73,355-364. Timisjiirvi, J. & Hirvonen, L. (1978). Pulmonary circulation in the reindeer. Basic Research in Cardiology 73, 497505.
des Rentiers Rangifer tarandus tarandus
L. HIRVONEN,
P. JARVENSIVU
Zuzammenfassung Von 50 tinnischen Rentieren im Alter von 1 Tag bis zu 9 Jahren wurden EKG's aufgenommen. Dazu wurden Standard- und unipolare Extremitiiten-Ableitungen in einer frontalen Projektionsebene verwendet. Die Herzfrequenzen lagen in einem Bereich von 40-250 Schliigen/Minute. Vorhof- und Kammer-Depolarisationszeiten waren bei neugeborenen Kiilbern 5-10 mS kiirzer als bei iilteren Rentieren. 1m Zusammenhang mit der Herzfrequenz zeigten sie nur geringe Veriinderungen. Die Dauer der
& P. NIEMINEN Depolarisation war von der Herzfrequenz abhiingig, sie war bei jungen Kiilbern verkiirzt. Die A(trio)-V(entrikuliir)Ueberleitungszeit war bei erhohter Herzfrequenz vermindert. Die Mehrzahl der QRS-Vektoren lag im Bereich von 280290°, die meisten T-Vektoren iilterer Tiere bei 200-230°, bei jungen Kiilbern jedoch im Bereich von 100-120°. In den Ableitungen Il, 1lI und aVF zeigte die S-Zacke den grossten Ausschlag innerhalb des QRS-Komplexes, in den Ableitungen aVL und I wies die R-Zacke die grosste Amplitude auf.
Laboratory Animals (1979) 13.183-186
Electrocardiogram of the reindeer, Rangifer tarandus tarandus J. TIMISJARVI, L. HIRVONEN, P. JARVENSIVU & M. NIEMINEN Department of Physiology and Department of Zoology. University ofOulu. Kajaanintie 52A, 8F-90220 Oulu 22, Finland Summary Electrocardiograms were recorded for 50 Finnish reindeer of age 1 day to 9 years, using standard and unipolar extremity leads in the frontal plane. The range of heart rate was 40-250 beats per minute. Atrial and ventricular depolarization times were 5-10 ms shorter in newborn calves than in older reindeer, and showed only minor variance with respect to heart rate. The duration of depolarization was dependant on heart rate, and was more rapid in young calves. A-V conduction time decreased with increasing heart rate. The mode of the QRS vector was 280-290°, and the mode of the T vector 200-230° in the older animals, but 100-120° in young calves. The main deflection in the QRS complex was S in the leads 11,III and aVF. R was dominant in aVL and I. The reindeer, a semidomesticated ruminant living in the subarctic areas, has a wide range of cardiac reserves (Timisjiirvi, 1978) but it also shows great sensitivity in its circulation to various stimuli (Timisjiirvi & Hirvonen, 1978). As a physically well-trained subject with rapid reactivity, it is a useful experimental animal for studies on circulatory adaptation to a variety of environmental factors. The Finnish reindeer reaches adulthood at the age of 6 years, the males achieving a bodyweight of 100120 kg and the females 70-80 kg. The bodyweight of newborn calves, which are well developed, is 4- 7 kg. The growth of the reindeer calf is rapid during the first summer, when the daily weight gain may be as high as 400 g, but it ceases almost completely during the winter. No published information is available concerning the electrocardiogram of the reindeer. The present study describes the normal electrocardiogram of the reindeer and certain changes related to the age of the animal.
Material and methods A total of 50 reindeer (Rangifer tarandus tarandus) ranging in age from 1 day to 9 years (19 calves aged 1-30 days, 25 calves aged 5-10 months, and 6 does aged 3-9 years) and in weight from 4 to 60 kg served as the subjects of this investigation. All were in good health and free from detectable cardiovascular abnormalities. Young animals preponderated for technical and commercial reasons. Received 22 May 1978. Accepted 12 December 1978.
Electrocardiograms were recorded with a 4-channel direct-writing recorder (Mingograph EM 34; ElemaSchonander now Siemens-Elema Ab, Rontgenviigen 2, S-1 7995 Solna, Sweden) in the laboratory or with a three-channel direct-writing recorder (Mingograph Minor 3; Siemens-Elema, AB) in the open. The paper speed was 50 or 100 mm/s and the calibration setting 1 em/mY. The standard limb leads I, II and Ill, and the augmented unipolar limb leads aYR, aYL and aYF, were recorded with subcutaneous needle electrodes. Diazepam alone (1· 2-1· 5 mg per kg bodyweight) or together with pentobarbital sodium (5-20 mg/kg) was employed as a tranquilizer during the studies on the 25 calves aged 5-10 months, under laboratory conditions. The other recordings were carried out in the natural environment of the reindeer, and no sedation was used. The young calves (aged 1-30 days) were immobilized manually in the prone position, whereas the old does were immobilized with a special chute. Hypoxia was induced by means of a 10% mixture of oxygen in nitrogen, or by impairment of respiration by pentobarbital sodium under laboratory conditions. The recordings were taken according to Friedman (1971) with 3-4 complexes and intervals being measured in each lead. Function fittings were obtained by least-square solutions. The index of fitting used for the reciprocal comparisons of the equations was R. The fittings were also checked using the F test.
Results The mean heart rate of a resting reindeer of 6 months of age was 50-60 beats per minute, while various irritants such as noise, pain, arterial hypoxia, irregularities of breathing, certain phases of rumination and also immobilization led to rapid increases up to 250 b/min. The range of the heart rate of the calves in this series (aged I day to 4 weeks) was 82-250 b/min. The duration of the atrial depolarization was 57 ± 8 ms, and showed only minor decrease when the heart rate increased in the older reindeer (age 5 months or more). In the young calves the atrial depolarization was more rapid (45 ± 9 ms) and decreased more with respect to the increase in heart rate than in the former group (Fig. 1). The duration of the atrial repolarization (which could be measured in 3 cases) was about 60 ms, and the atrial electrical systole was about 150 ms at a heart rate of 177 b/min (Fig. 2), with ranges Ta 60-80 ms and electrical systole 150-200 ms, HR 136-177 b/min. The atrioventricular conduction time
Timisjiirvi, Hirvonen, Jiirvensivu & Nieminen
184 was strongly dependent on the heart rate, and was considerably shorter in the young calves than in the older animals (Fig. 1). Ventricular depolarization took 53 ± 8 ms in the older animals and decreased slightly at higher heart rates, while the young calves showed a fairly constant duration of ventricular depolarization (43 ± 7 ms) with respect to heart rate. The duration of ventricular
repolarization decreased with the increase in heart rate. The shortening of repolarization was more rapid in the young calves (Fig. 3). At heart rates of 90-230 b/min the young calves had a shorter electrical systole and longer diastole and filling period than older animals (Fig. 4). The P wave was monophasic, biphasic or bifid (Figs 2 and 5). The most common form of the QRS com-
150 u CI> OIl
E 100
•.. . ..
u
•......
100
E
...•...... •....•......
.. .-0
PQ(ol
. ......• .........
50
'
50
,
,
100
150
.
,
200 250 HEART RATE b/min
Fig. I. Duration of atrial depolarization (P wave) and of the PQ interval as a function of beart rate. Solid line reinder aged 5 months or more. DOl/ed line calves aged I day to 4 weeks. P 0 older animals; • young calves. PQ 0 older animals; • young calves. The equations for the curves are: PQ,O)= -0·28x + 165, R 0·694, F 39·9, N 45; PQ,cl = -Q·28x + 135, R 0·654, F 18·6, N 27; p,o) = -0·3x + 61. R 0·167, F 1·2, N 45; P(el = -O·lx + 60, R 0·378, F 4·2, N 27.
I
'.
~
'--
D
~-
P Ta
P
•• ••
•• ••
-.----._-~----_ -;;-;-----r-_-_.
Ta
QRSlcl
N
Z
'
50
,
,
,
,
100
150
200
250
HEART RATE b/min
Fig. 3. Duration of ventricular depolarization (QRS complex) and ventricular repolarization (T wave) as a function of heart rate. Solid line reindeer aged 5 months or more. Dol/ed line calves aged 1 day to 4 weeks. QRS 0 older animals:· • young calves. T 0 older animals: • young calves. Equations for the curves are: QRS,O) = -Q·04x + 57, R 0·227, F 2·3, N 45; QRS(C) = -0·04x + 48, R 0·188, F 0·9, N 27; TO) = 0·0009x' - 0·49x + 134, R 0·667, F 33·7, N 45; T,O)= 0.0~12x' - 0·61x + 139, R 0·584, F 10·3, N 27.
1000 u on
CI>
E
--r-
n
500
aVR ---..-aVL 1 mV
DRSl ••1
__
POCel
••••••••••
P(a)
N:s:
" ,.I.e...
-:-::-:-~~...,.;..:.
50
...........
co..
III Dill
a •••••••.
'ro"",
0
1:1 0 ' •••••.••••
CI> OIl
"
a •••••.• "
RR OTCol OTic)
[--0
Os-50 .•. · ---'00 •.... · -----'15~0---2..• 0-0---2.•. S0HEART RATE b/min
15
Fig. 2. Atrial electrocardiogram of a reindeer aged 10 months. Ventricular asystole as a result of severe arterial hypoxia. Atrial depolarization (P) is followed by atrial repolarization (Ta).
Fig. 4. Duration of the ventricular electrical systole (QT interval) as a function of heart rate. Solid line reindeer aged 5 months or more. Dolled line calves aged I day to 4 weeks. QT 0 older animals; • young calves. Equations for curves are: QTjO) = 0·OOI2x'- 1·14x + 354, R 0·936, F 298·6, N 45; QT,C)= 0·0047x'- 2·17x + 398, R 0·869, F 74·1, N 27.
Reindeer electrocardiogram
185
plex was qR, R or Rs in the leads I, aVR and aVL, while the forms rS, QS and Qr dominated in the leads II, III and aVF (Fig. 5A, B, D, E). In 10 out of the 50 animals studied, however, the form of the QRS was that shown in the Fig. 5C. In the newborn calves (aged 1-21 days) the SoT segment deviated by up to 0·4 mV in a direction opposed to the main deflection of the QRS complex. Fig. 6 provides a case report on reindeer precordial leads. The difficulty with unipolar precordial leads on a Wilson terminal is the lack of a standard position for the electrodes: in this study the recommendation of Sporri (I975b) for horses and cattle was adopted, but with no certainty that this was equally appropriate for reindeer.
A
I
c
B
o
II
--"'-(-_
.\...-.....1....-...-.'>:
• YL
~-_~-
E ..,-
I
---.-
, 2.
o
Fig. S. Normal electrocardiograms of reindeer aged S days to 3 years. A calf aged S days, HR 190 (note S-T deviations). B calf aged 20 days, HR 125. C calf aged 19 days, HR 115 (note different direction of QRS deflections compared with B). D calf aged 10 months, HR 60. E doe aged 3 years, HR 76.
III-.:~
Vs ~;'~;"-v-
V13-.~.~
aVR..,..J~·~
V6 ~~~
aVL -,'-v------'.'--v--
V7 '" ~;L..-
VIS--;~,'--v---
aVF -f-·.r--"--.r--....r-
V.
VI6i"-v-----l'--v---
1
I
v-:,~,~
V14~'--y---,"-v-,
VI -...Jr---'r---
V. v-:~.~
V2---' ---
Vro.,..,l..----.,..,,~ VI.~
1mvlo
I
VI7--'~
2:3
sec
Fig. 6. Electrocardiogram of a standing reindeer of 4 months of age. The unipolar precordial leads were obtained by positioning needle electrodes subcutaneously around the thoracic cage within the 5th intercostal space- v, on the sternum, V 10 on the vertebral column, V ,-v. on the left side, VII-V,. on the right side (see Sparri, 1975b).
The mode of the QRS vector was 280-290° in the frontal plane in the newborn calves and in the older animals, but varied in direction in the calves aged 1721 days (Fig. 5). The P vector was 70-90°. The mode of the T vector was 200-250° in the older animals, but 100-120° in the young calves.
Discussion
The electrocardiogram is an obligatory tracing in the field of cardiovascular investigation since it provides reliable information on cardiac rhythm, heart rate, initiation of heart beat and also, to some degree, indirect evidence on the functional state of the heart muscle. A wide range of such information is readily obtainable from the conventional scalar leads, even if the records are limited to a single plane. Because of species-specific macro anatomical differences the standardization applied in one species is not suitable for another. The major determinants of the pathway by which electrical excitation spreads through a heart muscle are the geometry of the heart and the organization and position of the specialized conduction system; tous the formation of the electrocardiogram is also an anatomical problem (Scher, 1962). The reindeer heart extends from the 3rd to the 6th rib in the craniocaudal direction (Engebretsen, 1975). According to our >I-ray studies in lateral projection, the apex lies close to the diaphragm and sternum, and the base extends near to the thoracic vertebrae. The chambers of the heart have
thick walls, and the ratio between right and left ventricular wall thickness is 0·85 in the newborn calf, decreasing to 0·60 by 10 months. Heart weight is 1·2% of body weight in the newborn calf, 1·1% at 10 months, and 0·6-0·8% in older does. Cardiac hypertrophy was not observed in excised hearts, and the electrocardiograms were interpreted as representing normal animals. The anatomy of the conduction system of the reindeer heart has not been studied, but the craniallyorientated QRS vector agrees well with observations on other species made by Hamlin & Smith (1965), who categorize animal species according to their mean spatial QRS vector, one category consisting of thosesuch as primates and carnivores-whose QRS vector is caudally-orientated, and the other category of those -such as ruminants, horses and birds-in whom it is cranially-orientated. On the other hand, Sporri (1975a) also divides animals into 2 categories according to the organization of the conduction system of the heart, with horses, ruminants and birds, for example, forming one group in which the terminal branches of the Purkinje fibres reach the subepicardiac layer of the heart muscle. The present results suggest that the reindeer also belongs to this group. Growth in the reindeer is very rapid during the first
Timisjiirvi, Hirvonen, Jiirvensivu & Nieminen
186
months of life, when daily weight gain may be 300-400 g, and birth weight may double within 3-4 weeks. Thus the disappearance of the S-T segment deviations from the electrocardiogram of the calves may be a result of matUration. The development of the conduction system of the reindeer heart may be slower, however,
gIVIng rise to the variance in the QRS observed in the calves aged 16-22 days. Acknowledgement We express our gratitude for financial aid.
to the Academy
vector
as
of Finland
References Engebretsen, R. H. (1975). Topography of internal organs of reindeer (Rangifer larandus). ACla velerinaria scandinavica 16,suppl. 57,1-18.
Friedman, H. H. (1971). Diagnostic electrocardiography
and vectorcardiography. New York: McGraw-Hill. Hamlin, R. L. & Smith, G. R. (1965). Categorization of common domestic mammals based upon their ventricular activation process. Annals of the New York Academy of Sciences 127,195-203. Scher, A. M. (1962). Excitation of the heart. In Handbook of physiology (ed. W.F. Hamilton), section 2. vol. I. Washington: American Physiological Society.
Das Elektrokardiogramm J. TIMISJARVI,
Sporri, H. (1975a). Elektrokardiographie. Grundlagen der Elektrokardiographie (I). Tierarzlliche Praxis 3, 1-6. Spiirri, H. (I 975b). Elektrokardiographie. Grundlagen der Elektrokardiographie (3). Tiercirzlliche Praxis 3,263-269. Timisjiirvi, J. (1978). Left ventricular volumes and functioning of the reindeer heart. Basic Research in Cardiology 73,355-364. Timisjiirvi, J. & Hirvonen, L. (1978). Pulmonary circulation in the reindeer. Basic Research in Cardiology 73, 497505.
des Rentiers Rangifer tarandus tarandus
L. HIRVONEN,
P. JARVENSIVU
Zuzammenfassung Von 50 tinnischen Rentieren im Alter von 1 Tag bis zu 9 Jahren wurden EKG's aufgenommen. Dazu wurden Standard- und unipolare Extremitiiten-Ableitungen in einer frontalen Projektionsebene verwendet. Die Herzfrequenzen lagen in einem Bereich von 40-250 Schliigen/Minute. Vorhof- und Kammer-Depolarisationszeiten waren bei neugeborenen Kiilbern 5-10 mS kiirzer als bei iilteren Rentieren. 1m Zusammenhang mit der Herzfrequenz zeigten sie nur geringe Veriinderungen. Die Dauer der
& P. NIEMINEN Depolarisation war von der Herzfrequenz abhiingig, sie war bei jungen Kiilbern verkiirzt. Die A(trio)-V(entrikuliir)Ueberleitungszeit war bei erhohter Herzfrequenz vermindert. Die Mehrzahl der QRS-Vektoren lag im Bereich von 280290°, die meisten T-Vektoren iilterer Tiere bei 200-230°, bei jungen Kiilbern jedoch im Bereich von 100-120°. In den Ableitungen Il, 1lI und aVF zeigte die S-Zacke den grossten Ausschlag innerhalb des QRS-Komplexes, in den Ableitungen aVL und I wies die R-Zacke die grosste Amplitude auf.
