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Toxicology Research and Application
Original Article
Comparative cardiovascular physiology
and pathology in selected lineages
of minipigs: Relation to drug
safety evaluation
Toxicology Research and Application
Volume 1: 1–8
ª The Author(s) 2017
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DOI: 10.1177/2397847317696367
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Alain Stricker-Krongrad1, Catherine Shoemake1,
Derek Brocksmith2, Jason Liu1, Robert Hamlin3,
and Guy Bouchard1
Abstract
The minipig has been increasingly recognized as a valid alternative to canines and nonhuman primates in regulatory
toxicity. This article presents the results of cardiovascular assessments in the Yucatan, Hanford, Sinclair, and Göttingen
minipigs conducted during nonclinical investigations and control toxicity testing. Cardiac electrophysiology was obtained
using clinical electrocardiogram and surgical monitor units. Peripheral vessel diameter, velocity, and flow were obtained by
Doppler ultrasonography, and cardiac vessel diameter was obtained postmortem. Anatomic parameters were obtained at
necropsy. Histopathology assessments were conducted on heart, blood vessels, and kidneys. Collected data were
compared to published cardiovascular measurements of adult humans to illustrate similarities and differences. Each lineage
of minipigs was found to have specific anatomic and physiologic characteristics that may accurately reflect response of
human cardiovascular systems in clinical investigations and toxicity testing. In conclusion, the interspecies similarities
between the cardiovascular systems make these lineages of minipigs suitable as models for the human counterpart. In
addition, these reported differences between lineages will aid investigators in selecting a relevant lineage of minipigs if
specific cardiovascular parameters are required during drug safety evaluation.
Keywords
Toxicology, cardiovascular safety, cardiovascular pathophysiology, minipig
Date received: 11 July 2016; accepted: 20 September 2016
Introduction
Miniature swine, or minipigs or miniswine, have been
increasingly recognized as a suitable nonrodent model in
place of canines and nonhuman primates in drug safety studies.1,2 They are also being used more frequently for cardiovascular safety pharmacology studies, since their anatomic
and physiologic similarities to humans favor their use.1
Although several studies have been conducted to determine
various cardiovascular characteristics of swine, including
comparing regular pig hearts to human hearts,3 comparing
electrocardiograms (ECGs) of standard pigs to minipigs,4 and
creating human disease models,4,5 the objective of this publication is specifically to create a compilation of normal and
background cardiovascular information of multiple breeds of
minipigs. The results of cardiovascular assessments in different breeds of physically normal, healthy minipigs conducted
during clinical investigations and control toxicity testing are
presented. This information will enable investigators to
1
Sinclair Research Center, Columbia, MO, USA
Sinclair BioResources, Columbia, MO, USA
3
The Ohio State University, Columbus, OH, USA
2
Corresponding author:
Alain Stricker-Krongrad, Sinclair Research Center, 562 State Road DD,
Auxvasse, MO 65231, USA.
Email: [email protected]
Creative Commons CC BY-NC: This article is distributed under the terms of the Creative Commons Attribution-Non
Commercial 4.0 License (http://www.creativecommons.org/licenses/by-nc/4.0/) which permits non-commercial use, reproduction
and distribution of the work without further permission provided the original work is attributed as specified on the SAGE and Open Access pages
(https://us.sagepub.com/en-us/nam/open-access-at-sage).
2
appropriately select the breed that exhibits cardiovascular
parameters required for individual drug safety evaluations
and also to become familiar with normal findings for the
minipig in order to adequately interpret study findings.
Materials and methods
Information was collected from control animals in various
toxicity studies and clinical investigations performed at
Sinclair Research Center, LLC (SRC) from 2005 through
2014. Certain Göttingen information, specifically heart
weight (HW), body weight (BW),6 and background histopathology, 7 was gathered from previously published
sources and incorporated into the information for completeness and comparison purposes.
Animals
Sinclair, Hanford, and Yucatan minipigs were obtained from
Sinclair BioResources, LLC. Göttingen minipigs were purchased from Marshall BioResources (Clyde, NY). Anywhere
from 5 to 119 animals of each breed were used to collect each
parameter. All procedures and animal care conformed to the
Guide for the Care and Use of Laboratory Animals published
by the US National Institutes of Health and were approved
by the SRC Animal Care and Use Committee.
Housing
All minipigs were individually housed, with the exception
of four females that were group-housed two to an enclosure. All pens were stainless steel with a minimum of
3 5.5 ft floor space. Pen walls were either completely
solid or had solid lower walls with upper vertical bars; all
front gates were made of vertical bars. Flooring was made
of raised polyvinyl chloride-coated self-spanned metal. A
metal chain was suspended in each pen for enrichment.
Harlan® Teklad #7037C (Madison, WI), Purina® Sinclair
S9 (Montgomery City, MO), or other equivalent miniswine
diet was fed at maintenance once a day. Deep well water
was provided ad libitum. Ambient temperature was maintained at 15 C–30 C (59 F–86 F). Humidity ranged from
12.8% to 100%. Lighting was maintained at a 12-h light/
dark cycle and lights were turned on at 6:00 a.m.
Cardiovascular parameters
HW and kidney weights (KW) were recorded at SRC.
Göttingen HW and BW were obtained from Bollen et al.6
and incorporated for comparison purposes.
External iliac and femoral artery measurements were
assessed in vivo using Siemens G60 ultrasound (Washington,
DC) and OEC Medical C-arm fluoroscope (Salt Lake City,
UT) series 9600. Left anterior descending artery internal
diameter (LAD ID), left circumflex artery internal diameter
(LCX ID), right coronary ID, aorta outer diameter (OD)
and ID, and carotid ID were measured postmortem with
Toxicology Research and Application
electronic calipers. Heart height and circumference were
also measured postmortem.
ECGs were obtained from 3- to 9-month-old minipigs
using Schiller AT-2 or AT-2 plus multichannel ECG (Baar,
CH) units. Animals were placed in sternal recumbency in a
sling or in lateral recumbency on a nonconducting surface.
Hair was clipped prior to attaching electrodes. Leads I, II, and
III were the minimum recording requirement; leads aVR,
aVL, and aVF were generally included as well. ECGs were
recorded at a paper speed of 25 mm/s for 20–60 s and then
briefly recorded at 50 mm/s. Results were read by a veterinary
cardiologist, and the electrographic parameters heart rate
(HR), RR, PQ, QRS, and QT intervals were calculated from
the ECG wave. For interbreed and interspecies comparisons,
allometric body mass corrections were applied to the HR using
a geometric ratio, HR/BW0.25, and conventional human geometric ratio was considered to be 240.8 The following QT
interval corrections (QTc) were applied: QT/RR, Fredericia
(QTc[F]), and Bazett (QTc[B]). In addition, a hyperbolic formula was used to estimate the correction parameters for the
QT interval based on the present set of individual data in the
different breeds: QTc ¼ a [(RR)e], where a is the correction
factor and e is the power factor of the hyperbolic function.
Chemistry
Serum chemistries were run in one of two qualitycontrolled laboratories: either at Antech Diagnostics ®
Laboratory (Antech, Chesterfield. MO) or on a Beckman
Coulter AU480 Chemistry Analyzer at SRC. Samples were
obtained from 2- to 4-month-old Sinclair, 3- to 6-month-old
Hanford, 3- to 6-month-old Yucatan, and 3- to 14-monthold Göttingen minipigs. Hanford and Sinclair serum chemistry testing was performed at Antech, Yucatan serum chemistries were run at either Antech or SRC, and Göttingen
serum chemistries were performed at SRC.
Pathology
Gross and microscopic cardiovascular and renal pathology
were performed by anatomic pathologists. Additional
Göttingen histopathology was obtained from Gad et al.7
and included for comparison purposes.
Data
Data are expressed as mean + standard deviation, unless
indicated otherwise. Parametric linear, logarithmic, and
hyperbolic regression analyses were conducted using
Microsoft Excel (MS Office 2013).
Results
Cardiovascular parameters
There was great variation in both HW and BW across breeds
(Table 1). Overall, at 3–9 months of age, both Hanford males
HW: heart weight; BW: birth weight.
54.9 + 8.5
262.9 + 32
0.48 + 0.05
85.6 + 20.0
282.7 + 53.4
0.34 + 0.04
Body weight (kg)
Heart weight (g)
HW:BW ratio
88.4 + 26.1
261.0 + 40.5
0.31 + 0.04
Yucatan (1–2 years)
Hanford (1–4.5 years)
Sinclair (2–4.7 years)
Adult males
14.4 + 2.5
62.5 + 10.9
0.44 + 0.027
14.8 + 1.7
63.6 + 13.2
0.43 + 0.079
Body weight (kg)
Heart weight (g)
HW:BW ratio
Female
37.6 + 1.9
153.2 + 8.7
0.41 + 0.021
34.7 + 2.0
138.7 + 6.7
0.40 + 0.024
25.5 + 5.8
118.4 + 25.2
0.47 + 0.063
24.9 + 5.3
108.4 + 24.4
0.44 + 0.083
17.2 + 0.14
85.3 + 13.3
0.50 + 0.081
27.6 + 0.99
88.7 + 1.0
0.32 + 0.0078
3
Male
3–9 months
Sinclair
Table 1. Organs weights in control minipigs.
Male
Hanford
Female
Male
Yucatan
Female
Male
Göttingen
Female
Stricker-Krongrad et al.
and females have larger HW and BW than the other breeds.
On the other hand, Göttingen males had the highest heart
weight to body weight ratio (HW:BW), yet females had the
smallest. Other than the Göttingen females, the Hanford breed
as a whole had the smallest HW:BW. When the data from the
3- to 9-month-old minipigs are compared to the findings in the
older population of minipigs, it is clear that HWs and BWs
increased with age, while HW:BW decreased with age. Of the
breed information available at the older ages, the Hanford
breed persisted in having the largest HW, but the Sinclair
breed was the one with the largest BW and the smallest
HW:BW. The Yucatan minipigs had the smallest BW and
largest HW:BW; the age range of the Yucatan population was
also younger than that of the other two breeds.
In comparison, KWs also demonstrated variation across
the different breeds. Again, Hanford males and females had
larger KWs, 148.1 + 26.1 g and 121.9 + 16.0 g, respectively, than the other breeds. Yucatan male and female
KWs were 140.93 + 7.55 g and 94.22 + 9.36 g, respectively. Sinclair male and female KWs were the smallest at
58.9 + 6.92 g and 53.2 + 4.10 g, respectively. Likewise,
kidney weight to body weight ratio (KW:BW) decreased
with age as well. Sinclair males and females had KW:BW
of 0.47 + 0.10 and 0.43 + 0.05, Yucatan males and
females had KW:BW of 0.51 + 0.08 and 0.36 + 0.01,
and Hanford males and females had KW:BW of 0.39 +
0.05 and 0.36 + 0.05, respectively.
In vivo vascular measurements of external iliac and
femoral arteries of 15- to 19-month-old Yucatan minipigs
were as follows: left external iliac: velocity of 14.82 +
3.32 cm/s, diameter of 4.89 + 0.34 mm, flow of 138.80
+ 32.39 ml/min; right external iliac: velocity of 16.56 +
3.53 cm/s, diameter of 4.80 + 0.30 mm, flow of 151.14 +
38.82 ml/min; left femoral: velocity of 15.88 + 3.69,
diameter of 3.84 + 0.24 mm, flow of 93.30 + 26.92 ml/
min; right femoral: velocity of 14.33 + 2.64 cm/s, diameter of 3.93 + 0.35 mm, flow of 87.64 + 21.54 ml/min.
Postmortem cardiac vessel measurements were taken
from Sinclair minipigs that were 2–4.7 years old, as well
as 1- to 4.5-year-old Hanfords; slightly different measurements were taken from 1- to 2-year and 6- to 9-month-old
Yucatans. Sinclair and Hanford minipigs had similar heart
circumference and height; Sinclair had a circumference of
22.1 + 1.85 cm and height of 13.6 + 1.02 cm, while
Hanford had a circumference of 23.1 + 1.95 cm and height
of 12.8 + 1.30 cm. Sinclair and Hanford minipigs also had
similar aorta ID and OD; Sinclair had an aorta ID of 16.43
+ 1.66 mm and an OD of 20.52 + 1.84 mm, and Hanford
had an aorta ID of 16.87 + 3.69 mm and an OD of 21.06 +
4.02 mm. All three breeds had LAD ID, LCX ID, and right
coronary ID measured; in that order, the results were as
follows: Sinclair: 1.87 + 0.27 mm, 2.49 + 0.82 mm,
1.47 + 0.25 mm; Hanford: 1.70 + 0.35 mm, 2.31 +
0.38 mm, 1.52 + 0.44 mm; 1- to 2-year Yucatan:
1.54 + 0.52 mm, 1.93 + 0.71 mm, 1.51 + 0.42 mm;
6- to 9-month Yucatan: 1.65 + 0.30 mm, 1.83 + 0.45
4
Toxicology Research and Application
Table 2. Mean ECG results in control minipigs, 3–9 months of age.
Sinclair
BW (kg)
HR (beats/min)
HR:BW (geometric ratio)
RR (ms)
PR (ms)
QRS (ms)
QT (ms)
QT/RR
QTc[F] (ms) [Fridericia’s]
QTc[B] (ms) [Bazett’s]
Hanford
Male
Female
Male
7.9–30.1
133 + 41
259
488 + 136
91 + 15
41 + 8
257 + 45
0.526
327 + 34
370 + 30
6.5–29.1
126 + 43
246
527 + 166
87 + 14
44 + 8
262 + 46
0.497
326 + 28
365 + 24
11.2–46.2
113 + 24
248
555 + 126
108 + 17
36 + 4
277 + 39
0.499
338 + 27
375 + 37
Female
Yucatan
Male
Female
Göttingen
Male
9.1–44.3 15.06–31.65 14.89–29.06 17.2–21.3
115 + 23
96 + 13 104 + 31
100 + 7
248
211
223
208
540 + 108 636 + 86 637 + 212 602 + 40
106 + 14
103 + 10 113 + 14
106 + 8
36 + 4
40 + 7
39 + 6
52 + 5
270 + 32
275 + 29 270 + 39
291 + 21
0.501
0.432
0.424
0.483
333 + 24
320 + 24 317 + 20
345 + 19
372 + 40
345 + 22 344 + 22
375 + 18
Female
15.7–21.1
92 + 7
193
655 + 51
119 + 3
54 + 2
302 + 10
0.461
348 + 8
373 + 10
ECG: electrocardiogram; BW: birth weight; HR: heart rate.
Figure 1. (a) Lead II configuration QRS complexes electrocardiograms in pigs and dogs with comparison of the different segments (QT,
QLVPend, and QS2) in relation to the electromechanical window (EMw). (b) Individual hyperbolic relationship between the RR interval
and the QT interval in all breeds of minipigs.
mm, 1.91 + 0.24 mm. The Yucatan minipigs carotid
IDs are 2.48 + 0.45 mm for the 1- to 2-year-olds and
1.62 + 0.42 mm for the 6- to 9-month-olds.
The distribution of HR across the breeds is shown in Table
2. HR at rest ranged from 96 to 133 beats/min in the males and
from 92 to 126 beats/min in the females. Some differences
could be noticed between the breeds, and for comparison
purposes, an allometric geometric body mass correction was
applied to the HR. The mean geometric ratio was 236 with a
standard deviation of 51. Interbreed comparisons indicated
that the smallest ratio was found in the Göttingen male and
female and the highest ratio was found in the Hanford male
and female. This is in line with the observation that Göttingen
minipigs had the highest HW:BW ratio.
Electrocardiographic segment values are shown in
Table 2 as well and also exhibited some variability across
breeds. As expected, the largest RR intervals were found in
the breeds with the lowest HR. The lengths of the different
segments PR, QRS, and QT were found to be in keeping
with the length of the RR interval across all breeds. The
average uncorrected QT interval length was 273 + 39 ms.
The HR dependency of the QT interval was evaluated by
plotting the uncorrected QT against RR (Figure 1(b)). A
hyperbolic formula was the best fit (Pearson’s R ¼ 0.75),
and the estimated parameters were a ¼ 358 and e ¼ 0.46.
This is in keeping with the QT corrections established by
Bazett and Fridericia, which are e ¼ 0.5 and 0.3, respectively. It also indicates that Bazett’s correction might be a
better fit for QT adjustment to RR in the minipigs.
Clinical pathology
Figure 2 demonstrates serum chemistry values commonly
measured in evaluation of cardiovascular safety. The
Stricker-Krongrad et al.
Figure 2. Serum chemistry values (in mmol/L) of the four discussed breeds of minipigs; results are mean + standard deviation.
Göttingen breed exhibited slightly lower mean electrolyte
values than the others but had some of the highest total
cholesterol and triglyceride values as well. The Sinclair
breed had a noticeably higher phosphate level than the
others; otherwise, Sinclair, Hanford, and Yucatan minipigs
had very similar electrolyte values.
Anatomic pathology
Among the multiple studies conducted at Sinclair and utilized as resources for anatomic pathology information, there
were no recorded macroscopic pathologic findings in the
hearts or kidneys. Overall, the incidence of cardiovascular
background histopathologic findings was rather low as well
(Table 3). One finding consistent across the breeds was renal
mononuclear infiltrates of mild to moderate severity. The
Göttingen breed had the lowest incidence of findings relative
to the number of animals (143 males and 143 females). The
Hanford breed (59 males and 60 females) had the most
findings; most were various forms of inflammation, including chronic interstitial inflammation, lymphohistiocytic
inflammation, and arteritis/periarteritis in the kidneys and
endocarditis, myocarditis, and epicarditis of the heart. Yucatan minipigs (18 males and 21 females) had a relatively high
occurrence of mononuclear infiltrates in the kidneys (33.3%
of males and 52.4% of females) and a lower incidence in the
heart (5.2% of males). Myriad other findings varied widely
across the breeds, as listed in Table 3.
Discussion
The use of minipigs in biomedical research has been increasing over the past decades,9 and understanding of swine
5
physiology and pathophysiology, including cardiophysiology, is increasing as well.10,11 For an example, a comparison
of human and swine similarities and differences focusing on
the cardiovascular system and related functions is displayed
in Table 4. The differences do not imply that the information
on anatomical and physiological processes between swine
and man may not be applied to humans. In fact, we can profit
from these differences by learning more about the cardiovascular pathophysiological processes observed in humans
and can extrapolate the information gleaned from minipig to
man as well as to other minipigs.
It is widely recognized that there are hematologic, pathologic, age, and size-related background differences between
the breeds of minipigs, and these background differences
need to be recognizable and kept in consideration when interpreting study data.4,12 The task of determining normal minipig cardiovascular information is well underway by many;
some of these past findings were compared to corresponding
results of the current study and were found to be equivalent.
For example, the current Göttingen ECG findings are comparable to those in a study by Schuleri et al.4 comparing adult
Göttingen minipigs to juvenile Yorkshire pigs, as well as to
those reported by Eckenfels and Schuler.13 Additionally,
Smith et al.12 have compared cardiac function and morphology among 4-month-old Yucatan and Hanford minipigs; the
Hanford breeds of their study had a smaller HW:BW than the
Yucatan breeds, which is similar to the 3- to 9-month findings of the present study. Although the present study is not
exhaustive by any means, these reported differences between
breeds will aid investigators in selecting a relevant lineage of
minipigs for specific cardiovascular parameters that may be
required during drug safety evaluation.
In cardiovascular studies, since utilizing anatomy comparable to that of humans is crucial, minipig selections are
often based more on size than on age or breed. According to
Swindle et al.,2 the only minipig breed to develop organs
completely comparable to those of humans in size are the
Hanford minipigs, and they achieve this at 6–8 months of
age. It is valuable, though, to have normal cardiovascular
information for all breeds, detailing not only weights and
organ size but also physiologic functions, background histopathology, and drug safety responses. To this extent, a
comparison of cardiac function and size is shown in Table
1. As demonstrated, some variations in cardiovascular
function relative to body size occur among these lineages.
For example, the Hanford males had a slightly smaller
HW:BW at 3–9 months of age than the other groups
(Hanford: 0.41; Sinclair: 0.43; Yucatan: 0.47; Göttingen:
0.50). HW:BW along with HW and BW separately can be
utilized to find a breed and an age that most closely resembles humans. The interspecies similarities between the
cardiovascular systems make these lineages of minipigs
suitable as models for the human counterpart. The in vitro
vascular dynamics and vessel diameters, as well as the
postmortem cardiac vessel measurements described earlier,
are also of value, since minipigs are the ideal size for
6
Toxicology Research and Application
Table 3. Percentage incidence of background histopathologic features in control minipigs (%).
Sinclair
Aorta
Proliferation, intimal
Heart
Epicardial adhesion
Epicarditis
Endocarditis
Myocarditis
Other inflammation
Purkinje fiber vacuolation
Arteritis/periarteritis
Cartilaginous metaplasia
Myocardial necrosis
Perivascular infiltrates
Mononuclear infiltrates
Kidney
Glomerulosclerosis
Glomerulonephritis
Fibrosis, glomerular, focal
Fibrosis, interstitial
Mononuclear infiltrate
Eosinophils, pelvic
Lymphohistiocytic infiltrate
Lymphohistiocytic inflammation
Chronic interstitial inflammation
Arteritis/periarteritis
Tubular basophilia
Tubular epithelium regeneration
Hyperplasia, intimal, segmental
Mineralization
Casts, tubular
Cyst
Hanford
Göttingen
Male
(N ¼ 11)
Female
(N ¼ 11)
Male
(N ¼ 60)
Female
(N ¼ 59)
Male
(N ¼ 18)
Female
(N ¼ 21)
Male
(N ¼ 143)
Female
(N ¼ 143)
–
–
1.7
–
–
–
–
–
–
–
–
–
9.1
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
1.7
–
6.7
15.0
1.7
–
–
–
–
–
–
–
3.4
3.4
6.7
–
1.7
1.7
–
–
–
–
–
5.6
–
–
–
–
–
5.1
–
5.1
5.1
–
–
–
–
4.8
–
–
–
4.8
–
–
–
–
–
–
–
–
–
–
–
–
0.7
–
–
–
–
–
–
–
–
–
–
0.7
9.1
–
–
–
18.2
–
–
36.4
–
–
27.3
–
–
–
–
–
–
–
–
–
27.3
–
–
27.3
–
–
27.3
–
–
–
–
–
1.7
–
1.7
1.7
10
–
6.7
15
43.3
5
–
3.3
1.7
3.3
–
–
–
–
–
–
10.2
–
5.1
11.9
44.1
3.4
1.7
–
–
1.7
–
1.7
–
–
–
–
33.3
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
52.4
–
–
–
–
–
–
–
–
–
–
–
–
0.7
–
–
12.6
–
–
–
–
–
4.2
–
–
8.4
0.7
–
–
–
–
–
15.4
0.7
–
–
–
–
6.3
–
–
4.9
–
0.7
Table 4. A comparison of human and swine cardiovascular
system and function.
Similarities
Differences
Body size
Heart size
Coronary collaterals and
dominance
Diet (omnivorous)
“M1-maneuver”
Clotting profile
Skin physiology
Clotting (fibrinolytic pathway)
Purkinje fibers distribution
EM “window”
Predilection to arrhythmia
Eye
Gastric system
Yucatan
Sensitivity to anesthesia
Vascular inaccessibility
Subgross lung morphology
Atrial activation sequence
Clotting (rotation
thromboelastometry)
Ventricular activation
Hepatic “bridges”
EM: electromechanical.
testing intra- and extravascular devices designed for
humans.5 Additionally, drug safety pharmacology as a specialized area focusing on the negative effects of drugs on
key physiological systems conducts many testing
procedures in vitro (ligands, isolated heart, isolated
organs); however, in vivo tests are also an integral part
of these assessments. Frequently, minipigs are used for
these live animal studies, and the evaluation of the functional cardiovascular system, in addition to the anatomical
characteristics, is a high priority.
Figure 1(a) shows a “typical” QRS complex in lead II
from a pig (top) and from a dog (bottom). The pig represents a category II complex (most mammals except primates and carnivores) and the dog represents category I
(primates and carnivores).14 The differences in configurations of these QRS complexes arise principally from differences in pathways of ventricular activation; those in
turn arise from differences in distribution of Purkinje
fibers within the ventricular-free walls and from anastamotic branches between the left and right main bundles
observed in animals of category II 15 (Figure 3). The
“electromechanical window” (EMw) describes the temporal difference between these events (cf Figure 1). The
EMw is calculated as the difference between the QT interval and the QVLPend interval. The EM coupling is the
Stricker-Krongrad et al.
Figure 3. Comparative distribution of Purkinje fibers within the
ventricular walls in category I animals (dog and primates) and
category II animals (pig and noncarnivore mammals) with underlining differences in the electromechanical window (EMw).
relationship between the duration of electrical systole
(measured indirectly by the time between the Q wave and
the end of the T wave; QT interval) and that of the
mechanical systole (measured indirectly by the time
between the Q wave and the second heart sound; QS2).
In healthy animals, the duration of the QT interval is
shorter than but closely parallels the duration of the
QS2. Changes in autonomic tone are associated with an
inversion of this normal EM coupling ratio; this ratio has
been singled out as a useful indicator of several cardiovascular diseases, such as “the QT>QS2 Syndrome.”16
Notice that the highly different configurations of the QRS
complexes stem from differences in ventricular activation
that stem from differences in distribution of Purkinje
fibers and are underlined by differences in the EMw, leading to shorter QT and longer EMw in swine (Figure 3).
Variations in cardiovascular parameters, such as the QRS
complexes, do also occur among the different lineages of
minipigs and should be considered when constructing
experimental designs (cf Figure 1(a) and Table 2). For example, the electrophysiological heart segments duration (e.g.
mean RR ranging from 488 to 655 ms and mean QT interval
ranging from 262 to 302 ms) and their ratio (QT/RR) varied
among the three lineages (Table 2). The same applies to the
QTc, either by QTc[F] or QTc[B]. In addition, the power
function analysis of the present data set of individual QT and
RR intervals indicates that QTc[B] might be better fitted for
the minipig than the other methods of correction (Figure
1(b)). This indicates that minipigs (and pigs) tend to be
characterized by shorter QT interval when compared to the
EMw but are characterized by longer relative QT when
compared to human (QT: 375 ms and QT/RR: 0.45217).
Even so, information obtained from the pig, with a congenitally relatively long QT interval, may be extrapolated
to man. Those who study both pigs and dogs are well aware
that the pig develops arrhythmias, including ventricular
7
fibrillation, with little provocation, whereas the dog
requires, at times, monumental interventions. Thus, in the
evaluation of the cardiovascular effects of drugs, studies
conducted on pigs might be expected to possess relatively
high sensitivity compared with studies on dogs. The effects
of known antiarrhythmic drugs have indeed been tested in
minipigs and have demonstrated that minipigs can be used
for prediction of drug-induced QT interval prolongation.18
The similarities between their cardiovascular systems make
these four lineages of minipigs suitable animals to model
the human counterpart. The fundamental cardiac conduction differences lie in the nerve fiber content of the swine
heart, which has a bundle richer in nerve trunks, supporting
the role of a neurogenic component to conduction in swine.
As indicated, EMw predicts the susceptibility to arrhythmia
(EMw lengthening results in Torsade de Pointes (TdP) and
EMw shortening results in absence of TdP). Therefore,
swine are more prone to develop TdPs than any other species. In addition, because their diastole is relatively brief,
swine are prone to coronary insufficiency. This results in
increased sensitivity and decreased specificity when evaluating the effects of drugs (e.g. dofetilide, omecamtiv,
mecarbil) or exercise on cardiac electrophysiology. In addition, these QRS intervals and their underlying EMw differences will aid investigators in selecting a relevant lineage
of minipigs if specific cardiovascular parameters are
required.
Serum chemistry results (Figure 2) are frequently used
as indicators of cardiac health. Since cardiovascular health
and renal health are frequently inextricably linked, renal
findings are included alongside cardiovascular findings in
the present study. To develop a model of hypercholesterolemia, hypercholesterolemia and hypertriglyceridemia
can be induced in swine through diet. Hypercholesterolemic swine, like humans, can then develop atherosclerosis
and decreased cardiac function. Heart failure results in
decreased renal blood flow, which leads to renal ischemia.
Subsequent damage to the glomerular epithelium leads to
decreased glomerular filtration. When this decreased filtration is severe enough, phosphate is retained which causes a
secondary hypocalcemia. Additionally, serum potassium
levels can vary; if hyperkalemia occurs, it can in turn have
serious effects on cardiac rhythm. Finally, as tubular
resorption decreases with decreased renal function, sodium
and chloride are lost as well eventually resulting in hyponatremia and hypochloremia.19
Being able to use this background information to select a
breed of minipigs most relevant to studies requiring similarities to humans also requires knowledge of normal
human data; this can be drawn from establishmentspecific references, or it can be determined based on published information. For example, according to one of the
Center for Disease Control’s National Health Statistics
Reports, the mean resting pulse rates in adults over 20 years
of age from 1999 to 2008 were 74 beats/min for females
and 71 beats/min for males.20 Standard published human
8
ECG results consist of an HR of 60–100 beats/min, a mean
PR interval of 120–200 ms, a mean QRS interval of
<120 ms, and a mean QT interval of 420 ms.21,22 In an
earlier National Health Statistics Report, the mean weight
of female adults over 20 years of age in the United States
from 2003 to 2006 was 74.7 kg and that of males was
88.3 kg.23 Additionally, a study evaluating the diseasefree aging heart reported BW from adults over 20 years
of age ranging from 51 to 99 kg and HW of 123 to 306 g.24
Conclusions
Enormous amounts of valuable information on cardiovascular physiology and pathophysiology have resulted from
experiments conducted on minipigs. Minipigs have many
anatomical and physiological differences in cardiovascular
and related functions from man, but they have many similarities as well (Table 4). Because of features of pathophysiology and safety pharmacology, minipigs will remain useful
for anticipating findings in man and, where differences exist,
they may be exploited to understand physiology and pathophysiology in other species. Further assessments comparing
the translational values of data from swine, dog, nonhuman
primate, and small rodents to man may be performed from
existing databases or from species to species comparisons
made in retrospective studies, such as this one, or in prospective trials. Continuing to contribute background and
translational data will further the value of minipigs as a
continuously increasing participant of the drug safety and
cardiovascular pharmacology industry.
Declaration of conflicting interests
The author(s) declared no potential conflicts of interest with respect
to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research,
authorship, and/or publication of this article.
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