Morgan et al . Acta Veterinaria Scandinavica 2011, 53:62
http://www.actavetscand.com/content/53/1/62
R E S E A R C H Open Acces s
The prevalence and nature of cardiac
arrhythmias in horses following general
anaesthesia and surgery
and Catherin e M
Ruth A Morgan1*, Alexandra G Raftery1, Peter Cripps2, Jonat han
McGowan
M Senior3
Abs tract
Backg round: The preval ence and natur e of arrhythm ias in horses follo wing gen eral ana esthes ia and surgery
is poo rly docu mented . It has been proposed that horses un dergoing emerge ncy surgery for gastroin testinal
disorde rs may be at particul ar ris k of devel oping arrhyth mias. Our primary objecti ve was to deter mine the
prevale nce and natu re of arrhyth mias in horses followin g anaesthes ia in a clinic al setting and to establ ish if
ther e was a differ ence in the prevale nce of arrhyth mias betw een horses with and witho ut gas trointestina l
disea se undergoi ng surgery. Our secon dary objecti ve was to assess selected availabl e risk factors for
associatio n with the developme nt of arrhyt hmias fol lowing ana esthes ia and surgery.
Met hods: Horses with evidence of gastroint estinal disease under going an explorato ry laparotomy and horses
with no evide nce of gastroin testinal diseas e undergoing orthopae dic sur gery betw een September 2009 and
Januar y 2011 wer e recr uited pro spective ly. A telemetric electrocard iogram (ECG) was fitte d to each hor se
followin g reco very from anae sthesia and left in place for 24 hours. Selected elec trolytes were me asured
before , during and after sur gery and data was extracted from clinical reco rds for ana lysis. Rec orded ECGs
were ana lysed and the arrhyt hmias cha racterised . Multivar iable logis tic regr ession was used to identif y risk
factors ass ociated with the devel opmen t of ar rhythmias.
Res ults: Sixty- seven hor ses with gastroint estinal disease and 37 without gastroin testinal disease wer e
recruited. Arrhyth mias wer e very common durin g the post -operative period in both gro ups of hor ses. Supr
a-ventricula r and bradya rrhyt hmias pre dominated in both groups . Th ere wer e no signi ficant diffe rences in
prevale nce of any type of arrhyt hmias betw een the hor ses with or witho ut gas trointestina l disea se. Post-o
perativ e ta chycardia and sodiu m deran gement s wer e associated wi th the developme nt of any type of ar
rhythmia.
Conc lusions : This is the firs t stud y to report the preval ence of ar rhythmias in hor ses dur ing the post
-operative perio d in a clinical settin g. This study shows that arrhythmias are very comm on in hor ses followin
g surgery. It showed no differe nces between those hor ses with or without gastroin testinal diseas e. Arrhyth
mias occur ring in hor ses durin g the post- anaesthe tic perio d req uire furth er inve stigation.
Keywor ds: equine, post-ana esthetic, elec trocardiog raphy, arrhyth mia
operative period, yet t here is very limited
literature in t hi s ar ea [ 1, 2] . A r rh yt hm i as h
Back ground
av e b e en r ep o r te d i n as so ci at i o n w it h
The prevalence of arrhythmias in horses foll owing ga s tr oi nt es ti na l di se as e [ 3] . In on e ca se
general anaesthesia is unkno wn. T exts report
s er ies of horses with ventricular tachycardia,
that horses undergoing emergency exploratory
four out o f twenty-one had undergo ne co lic
laparotomy (colic surgery) commonl y h av e a
surgery [4]. The re po rte d r isk fa ct ors as so ci
rrhythmias i n the postat ed wi th th e d eve l opm en t o f arrhyt hm ias
include hypoxia, endoto xaemia, electro lyte
imbalances and a naesthesia [5]. It seems l ogical
* Correspondence: r.a.morgan@liv.ac.u k
to assume that a h orse suffering from
1Philip Leverhulme Equine Hospital, Universi ty of Liverpool , Leahurst
Campus, Neston, Cheshire, CH64 7TE, UK Full list of author information is
gastrointestinal
availabl e at the end of the article
© 2011 Mo r ga n e t a l ; li ce ns ee B io M ed C ent ra l Lt d. Thi s is an Op en Ac ce ss ar ti cl e di s tr ib ute d un d e r th e t erm s of th e Cr eat iv e Co
mmon s At tr ib u ti on L ic e ns e ( h tt p: // c re a ti ve c om m o ns .o r g/ li ce ns e s /b y/ 2 .0 ), w hi ch p e rm i ts u nr e s tr i ct e d u s e , di s tr i bu t io n,
an d re p ro d u ct io n in a ny m e d iu m , p ro v id e d t he or ig in a l w or k i s p ro p e rl y ci te d .
Morgan et al . Acta Veterinaria Scandinavica 2011,
53:62 http://www.actavetscand.com/content/53/1/62
d i s ea se w i l l b e a t g r ea t er ri sk o f d ev el o p
i n g ar r h yt h m i a s be ca use t he y m ay be more
of te n e xposed to these f ac tors. I f the prevalence
and nature o f arrhythmias in the po st -anaes thet ic
p e riod is d e termined, t hen clinicians will b e better
a ble to identify, understand and manage those
horses developing post-operative arrhythmias.
In this study we aimed to determine t he
prevalence an d nature o f arrhy t hmias o cc urring
in the p ost-an ae sthetic per iod in a ho spital
setting and to determ ine if the r e w as a d iff ere
nce in t he preva len ce of a rrhy thmias between
horses with and without gastroin testinal disease
undergoing general anaesthesia and surgery. A
secondary a im wa s t o a ssess certai n potential
risk fact ors t ha t may be a ssociated w ith the
development o f arrhyt hmias in horses following
surgery.
We hypothesised that the prevalenc e of a rr hyt
hm ia s would b e high i n horses followi ng surgery,
and that the prevalence would be higher i n horses
w ith gastrointestinal disease.
Me thods
Study population
This study w as ap proved by the Unive rsity of L
iverpool ethics committee and informed consent was
obtained from all study participants.
Horses with evidence of gastrointestinal disease
undergoing e xploratory laparotomy and h orses
without eviden ce of ga stroin test inal dise ase unde
rgoi ng ort hopae dic surgery at t he Philip L
everhulme E quine H ospital, University o f Liverpool
betwee n September 2009 and Januar y 20 11 we r
e el i gi b l e fo r i nc l us io n i n th e st ud y . H o rs
es were included in the gastrointestinal group (GI) if
they had signs of abdomina l discomfort (colic) wh
ich required surgica l exploration and w ere found t o
ha ve a lesion of the gastrointestinal tract at surgery.
Horses were included in the non-gastroint estinal
disease group (non-GI) if they were undergoing
orthopaedic surge ry, had shown no signs of colic in
the previous 24 hours and had normal clinical
parameters and faeces prior to surgery. Horses were
excluded from the s tudy if they were less than one
year old, m ares with foals a t foot, those t hat did
not t oler ate t he ECG, were euthanased either
during or within 24 hours of recovery from anaesthe
sia , o r w ere d iagnosed with grass s ick ness o r a
nongastrointestin al lesion a t surgery. GI group
horses were excluded as non-GI group h orses i f t
he y subsequently underwent orthopaedic surgery
and vice versa.
Data Collection
Clinical
data was
e xtracted
f rom the
case files
of those
horses
include d
in the
study to
obtain d
etai ls
prior t o
surgery,
during
surgery
and
during the
postoperative
period.
Page 2 of 8
Heparinised blood was c ollected prior to surgery,
immediately a fter recovery fr om anaesthesia (T0),
12 hours after recovery (T12) and 24 hours after
recovery ( T 24 ) . T h e b l o o d wa s a n al y se d
us i ng a b l o o d g a s a na l y zer (R adiom et er A
BL77 , Ra diom ete r) to me asu re pla sm a
concentrations of potassium, i onized calcium,
sodium an d ch lo ri de. T he A BL7 7 wa s ca li br
at ed ea ch ti me pr ior to us e i f it ha d no t be en
ca l ib ra te d i n t he p re v io us ei gh t hours.
Colloid osmotic pressure (COP) was measured usin
g a n o n co m et er (On ko m et er BM T 9 23, V i t
e c h Scientific Ltd). The onco meter underwent a
two point cal ibration ev ery we ek ag ainst w ater
and a stan dardized solution and a one point
calibration prior to every use.
An ECG Holter monitor (Televet 100, Krutech) was
fitted to each h orse on recove ry from anaesthesia,
with electrodes placed in a modified base- apex lead
co nfigu r at i o n. T h e p o s i t i v e e l ec t r o d e
w as p l a ce d 3 0 cm b el o w the w ithers on the l
eft thorax, the negative e lectrode was pla ced jus t
to t he rig ht of th e st er num . T wo fu rth er
electrodes were placed approximately 10 cm b elow
the positive electrode and o ver the left a pex of the
h eart. The recording de vice was secured to the
horse using a surcingle and ant i-cast roller.
Telemetric mode was used to ensure the quality of
trace a ft er application a nd during the recording
period.
The E CG recordings were stored on
a SD card a nd downlo aded into Tel
ev e t 100 software v e rsio n 4 .2
(KruuseA/S).Thetraceswereassessed
for diagnostic qu al ity . Dia gno st ic
tra ces wer e de fin ed as th ose al lo
wing clear identification of Q RS
depolarisations for more than 20
hours.
ECG Analysis
Televe t s of tw are was used to de te rmine R -R
intervals. An R-R inte r val d ev iation of 20% w
as chose n a s the maximum accepted deviation
as reported in previous studies [6]. Deviations of
greater than 20% were detected by the software a
nd then manually analysed by the author (RM) to
characterise the arrhythmia.
Arrhythmias were defined as follows: Sinus A
rrhythmia (SA): a rhythmical variat ion in R R i ntervals in which the heart rate slowed and then
i nc re as ed ag ai n. T h e R - R i nt e rv a l i nc r e
as e d b y l es s t h an 100%.
Supra-ventricular p rematu re de po lar i satio n
(SVPD ): The R -R i nterval de creased b y g re
ater than 20%. A P wave (usual ly of abnormal
configuration) vi si ble f ollo wed by a QRS c
omplex that was very similar t o the preceding Q
RS complexes. The P wave may not have been
visible if t he heart rate was very high (> 70 bpm)
but t he complex was judged to be
supra-ventricular i f the QRS had the sa me
configuration as those preceding it.
Morgan et al . Acta Veterinaria Scandinavica 2011,
53:62 http://www.actavetscand.com/content/53/1/62
Ve nt ri c ul ar p r em a tu r e d ep o l a ri s at i o n
( VP D ) : Th e R R int erv al d ec re ase d by grea te
r t ha n 20%. No P w av e preceding the QRS. A
QRS of abnormal configuration.
Vent ricular tachycardia (VT): four or more
VPDs occurring in succession.
Sec on d Degree A trioventricular bloc k (
2AVB): A P wave without a subsequent QRS c
omp lex and a n increase in R-R interval of 100%.
Sin us b lock (SB): An i ncrease i n R-R
interval of more than 100% with no visible P wave.
Bradyarrhythmia: Sinus arrhythmias, seco nd
degree atrioventricular block and sinus block.
Th e number o f S VPDs and V PDs o ccurring d
uring the recording period was recorded.
Statistical Analysis
Data were extracted a nd entered i nto a n
e x c e l s p r e a d s h e e t . S t a t i s t i c a l a n a l ys i s
w as ca rrie d o ut in Mi ni t ab 1 6 (Minitab
Inc) and STATA for W indows 9 (STATA Cor
p) . S tan da rd de scri pti v e st ati st ic s
wer e perf orm ed o n
thedatafollowedb yunivariable analyses
using logistic regression.
T o c o m pa r e t he b r e ed , a g e a nd se x o f t
he t w o g r o u ps an d t he pre v al en ce of d iff er en
t ar rh yt hm i as b et we en t he groups chi-squar ed a
na lys i s a nd Man n-Whitney U tests wer e pe rfo
rmed . T o co mpar e th e num be r o f SVPD s and
VPDs occurring in each group a Mann -Whitney U test
was used due to the no n-parametric nature o f the
data. Statistical significance was defined as P < 0.05.
Expl anatory variables included i n the logisti c
regression were: the presence or absence o f
gastroint estinal d is ea s e, a ge , b re e d, se x , w
ei gh t, pr e- o pe r at i v e he ar t ra t e, pre- oper
ative s core as signe d to the patient acco rding to
the A merican Society o f A naesthesiologist’ s
physical classification system ( AS A) [7], pre-ope
rative plasma co nc ent rations (mmol/L) of potas s
ium, ioni se d ca lcium , s od i u m, c hl o r i d e an d
co l l o i d os m o ti c p re ss ur e (m m H g ).
Intra-operative fac tors includ ed anaesthetic agent,
administration of lidocaine, a period of
intra-operative hypoxia (PaO 2< 80 mmHg),
intra-operative plasma concentrations of potassi um,
ionised ca lcium, so di um and chloride. P ost-operat
ive factors included heart r at e a t T0, T 12 and T24,
plasma concentrations of potassium, io ni se d ca lc i
um , so diu m and ch lo rid e al l at T 0, T 12 and
T24, po st -op e ra tive fluid a nd lido caine ad minist
r a tio n and survival to discharge.
Outcomes
assessed
u sing logi
s tic
regressi
on includ
ed the
presence
ofS
VPDs or
VPDs
during the
reco rding
period an
d t he pre
s enc e of
a b ra
dyarrhyth
mia whic
h included
one or
more of
the
following:
sinus
arrhythmi
a,
sino-atrial
b lock an
d second
degree a
triovent
ricular
block. In
ord er to
take i nto
account
the wide
range o f
numbers
of prem a
ture
depolar i
satio ns
occurring
during the
recording
period
(0-40 0
SVPDs
per
Page 3 of 8
horse),
Table 1 The number of premature depolarisations
occurring in both groups of patients during the
recording period
Frequency SVPDs (n, %) VPDs (n, %) 0-1 27 (26%) 56
(54%) 2-4 27 (26%) 20 (19%) 5-20 25 (24%) 19 (18%)
20-400 25 (24%) 9 (9%)
outcom es b as ed on the num ber of prem ature
depolaris a tions o cc urring w ere also
ex am ined. The num ber o f S VPDs occ urr ing
in the po pulat ion was di vi ded into quart
iles (Tab le 1) and assess ed a s a quar tile
outco m e us ing ordinal logisti c regress ion. G
iven the d is tribution of th e f requenc y of
VPDs an outcom e of less t han or equa l to 2
or greater than 2 VPDs during the rec o rding
periodwas us edas anoutc om e and i nves tigated
u s ing binary logis tic regress ion.
Al l v ariables which wer e associat ed
wit h t he outcome
withachangeindeviance(log-likelihoodrat
io)at P < 0.25 were offered t o a f orward
multivariable logistic regression. T he
results were t hen v erified using a
backwa rd st ep wis e re gr es sio n m o
del. T he ove ra ll fit of th e model was
ascertained using the Hosmer and
Lemeshow Goodness of Fit Test [ 8].
Criterion for inclusion was a change in
deviance at P < 0.05.
Resu lts
Study Population
One hun dred and four horses were i nc luded i n the
study. Of those, 67 were horses with gastrointestinal
disease un dergoing surgery (GI group) and 37 we
re horses without gastrointes tina l disea se und e
rgoing orthopaed i c su rg er y ( no n-GI gr o up ). T
h e ty pes o f su r ger y u n de rt aken in both groups
are shown in Table 2.
T h e m e a n a g e
o f t h e G I g r o u p
w a s 1 1 . 5 y e a r s ( 1 - 3 0
y e a r s ) . T w e n t y n i n e ( 4 3 % )
w e r e m a r e s , 3 7 ( 5 5 % ) w e r e
Table 2 Distribution of surgical lesions/procedures
GI group Number (%) of horses Strangulating small intestinal 28
(42%) Non-strangulating small intestinal 7 (11%) Strangulating
large intestinal 10 (15%) Non-strangulating large intestinal 22
(33%) Non-GI group Treatment of synovial sepsis 18 (49%)
Diagnostic arthroscopy/tenoscopy 14 (38%) Annular ligament
desmotomy 2 (5%) Small tarsal joint arthrodesis 1 (3%) Splint
bone removal 1 (3%) Neurectomy and fasciotomy 1 (3%)
Morgan et al . Acta Veterinaria Scandinavica 2011,
53:62 http://www.actavetscand.com/content/53/1/62
geld ings
an d one (
2% ) was
a stall io
n. T he br
ee ds
represent
ed in this
group
were 1 6
(24%)
Cobs, 16
(24% )
Tho
roughbr
eds, 12
(18 %)
War mblo
ods, fo ur
(6% ) Wel
sh po ni
es , ei gh t
( 12 %) Ir
is h dr af t
s an d 11
(1 6% )
we r e ot
he r
breeds.
The m
ean age
for the
non-GI
group was
11 years
(4- 21
years). T
wenty-six
(70%) we
re
geldings
and 11
(30%) w
ere m ar
es. T he
breeds
represent
ed in the
non-GI
group
include d
three (8%)
Cob s, 15
(41%)
Thorough
breds,
three
(8%)
Warmb
loods, six
(16%)
Welsh
ponies an
d t w o (5
%) Iri sh
D ra fts
and eight
(2 2%) w
ere o t h
er b r e ed
s.The
gr o u p s
we r e no
t d i f fe r
en t i n ag
e(P=
0.61).
Breed
distributio
n w as
different
between
the grou
ps ( P =
0.04) with
Thorough
breds o
verrepres
ented in
the
non-GI
group.
Page 4 of 8
30 (81%)
(65%, 92%)
20 (54%)
(39%,73%)
Table 4 Prevalence of different arrhythmias during the
post-anaesthetic period in horses with and without
gastrointestinal disease
31 (84%)
(68%, 94%)
3(8%) (1.7%, 23%)
Arrhythmia GI Group N (%) (95%
Confidence Interval)
One or more SVPD 57 (85%)
(75%, 93%)
Non-GI Group N
(%) (95%
Confidence
Interval)
One or more VPD 40 (60%)
(47%, 72%)
Sinus Arrhythmia 53 (79%) (67%,
88%)
Sino-atrial Block 3 (5%) (0.9%,
13%)
SVPD- sup ravent ricula r pr emature depol
arisation VPD - Ventr icular prem ature dep
olarisati on AV - atriove ntric ular
nd2degree
block
AV
24 (36%)
(24%,
48%)
21 (57%)
(39%,
73%)
recorded in only two of t he GI group a nd none of the non -GI group. Th e p rese nce o f VT w as not assoc
iated wi t h d ea t h. Th er e we r e no st at i s ti ca ll y s i gn i f ic an t d i ff e rences between the GI group and
t he non-GI groups in th e p revalence o f S VPD s ( P = 0.60) or VPDs ( P = 0 .77) but second degree AV
block was more prevalent i n the non-GI group than in the GI group (P = 0.04).
The mean number of SVPDs occurring in both groups during the r eco rding period was
2 7 (0-400) and the mean number of VPDs occur ring in both groups was 7.5 (0 -161). The
mean number of SVPDs i n the GI group wa s 30 (0 -4 00) and i n t he n on -GI group was
21 (0-400), with no difference between groups (P =0.09). The
meannumberofVPDsintheGI groupwas7(0100) and i n t he non -GI group was 9 (0-161),
w ith no diff er en c e be twee n g r oups ( P = 0.57) . T he dis tr i bu tion of arr h ythm ia
frequency is shown in Table 5.
Identification of risk factors associated with development of arrhythmias following surgery
The variables which were significant after univariable analysis are given in the a dditional fi les f or each
of the
equiremen
s following
received
ts as d
surgery. O f
lidocaine
etermined
t hese all
during
by the
but one r
the
ecei v ed
peri-ope
Th e p re - o p er at i v e ma na ge m en t o f t he c anaestheti
supplemen
rative
as e s d ep en de d on clin ical presen tation and the st.
tary pot ass
period;
type of surge ry undertake n a nd w as d etermine d Forty-five
ium and
40 (
b y t he c lin icia n a nd an aesthetist in charge of the (67%) o f
calc ium .
62%)
case. All horses in the non-GI group were deprived of colic
Ove rall 42
during
food for at least 10 hours p rior to surgery b ut the y patients
(6 3%) of th
surgery
were a llow ed free a ccess t o wa te r. A ll of th e ho received in
e colic
and 20
rs es i n t he s tu dy re ce i v ed i nt r ave no us cr ys travenous
crystalloid
patients
(30%) d
talloids d uring surgery titrated according t o r
Ventricular
uring the post-operative period.
Tachycardi
Hypokalaemia and h ypocalcaemia we re co
a
mmon i n both gr oups in the post-operative perio d
( Table 3). In the n on-GI group the preva le nc e o f
h y p ok al ae mia w as significantly lower at T12 (P
= 0.002) and the prevalence of hypoca lcaemia was
significantly l ower at T12 (P < 0.001) and T24 ( P <
0.001).
2(3%)
(0.36%,
10.4%)
0 (0%)
(0%,
13%)
Prevalence of Arrhythmias
The use of the T ele metric E CG w as well t ole
rated by the study po pul a tion and produce d ECG t
rac es o f diagnostic quality.
Arrhythmias were common following surg ery in
both groups (Table 4) , with SVPDs and b radyar
rhythmias most commonly detec ted. Ve ntricular
t achycardia was
Table 3 The prevalence of hypokalaemia and hypocalcaemia in patients with and without gastrointestinal disease during the
post-anaesthetic period
aTime
post surgery 0 hours 12 hours 24 hours n (%) of horses with GI disease with hypokalaemia (< 3.5 mmol/l) b38 (58%) 55 (85%) 47
(71%) n (%) of horses without GI disease with hypokalaemia 19 (53%) 21(58%) 21(62%) n (%) of horses with GI disease with
hypocalcaemia (< 1.45 mmol/l)60 (92%) 42 (66%) 28 (48%) n (%) of horses without GI disease with hypocalcaemia 35 (97%) 9 (25%) 2
(6%)
Bor er and Cor ley 2006 [31]
Van de r Kolk et al 2002
b[32]
a
Morgan et al . Acta Veterinaria Scandinavica 2011,
53:62 http://www.actavetscand.com/content/53/1/62
factors for the development of VPDs during the
post-anaesthetic period
Predictor OR 95% CI P-value HR T12 (bpm) 1.03 1.00-1.07
0.042* Post-operative Na T24 (mmol/l) 1.19 1.03-1.38 0.021*
Table 5 Multivariable ordinal logistic regression model of risk
factors for developing SVPDs during the postanaesthetic
period
Predictor OR 95% CI P-value Post-operative Na T12 (mmol/l)
0.81 0.71-0.92 0.001* ASA score
Reference 1 1.0 2 0.53 0.17-1.65 0.273 3 0.20 0.07-0.60 0.004*
4 0.23 0.08-0.65 0.006* 5 1.60 0.10-26.95 0.743
Log-Lik eli hood = -1 25.765 Test that all slopes are zero: G = 20.
063, DF = 5, P-Va lue = 0.001
fi v e ou tc o me s ; 1 o r m or e S VP D ( A dd i t i on
al fi l e 1 A dd i tional File 2), SVPDs in quartiles
(Additional File 3 Add it io n al File 4) , 1 or mo re
VPD ( Ad ditio n al F ile 5 Additional File 6) , greater
than 2 VPDs (Additional File 7 Add i tion al F ile 8) ,
bra dya rrh ythm i as ( Add iti on al Fil e 9 Additional
File 10).
Multivariable a nalysis s howed an association
between higher sodium c o nc en trati o n a t T 12 an
d t he lik eli hood of developing SVPDs). O rdinal
regression was used to inve stigate risk facto rs
which may be associated with th e number of SVPDs
devel oping. In the final model a higher sodium
concentration a t T12 and a higher AS A s co r e r es
ul t e d i n an o v er al l de cr ea se d l i ke l i h o o d
of h av ing a higher number of SVPDs ( Table 5).
The p resence or absence of gastrointes tinal disea
se wa s s igni fi ca nt in the model but was not
retained due to t he high c ollinearity of this factor
with ASA score ( P < 0.001).
The risk of more than one VP D in the
rec ording period w as in crea sed b y hi
gh h ea rt rate at T12 an d higher sodium
at T24 (Table 6). When the outcome of
more th an 2 VPD s wa s in ves t iga te d
in a mu l ti -v ar ia bl e mo de l, n o r i s k
f a ct o r s w e r e i d en t i fi e d . I n co
nt r as t , h i g h e r h ea r t
ratesatT0decreasedthelikelihood
ofdeveloping bradyarrhythm ias.
Disc ussion
T hi s i s th e f i rs t st u dy to r ep o r t t h e p re v al
en ce o f di f fe r ent ar rhythmias in ho rses during the
post-anaesthetic pe r i od an d h as sh o wn th at ca
rdi ac ar rh yt hm i as o cc ur i n a very high proportion
of horses following anaesthes ia.
Table 6 Multivariable binary logistic regression model of risk
Log-Lik eli
hood = -6 2.88
Test that all
slopes are
zero: G = 9.2
03, DF = 2,
P-Va lue = 0.01
Page 5 of 8
h orses u ndergoin g c olic surgery d eveloped
more tha n one V PD per hour; four developed VT
and 11 had more than one SVPD per ho ur d uring
th e p ost -o perative p e riod . H owever , no ne of
the ho rses unde rgoing ortho paedic surg ery
Few o f the risk factors i nv estigated were f ound
developed a tachyarrhythmia [2]. In contrast, in
to be associated with the prese nce of absence or the study present ed here, the majority of ho rses
SVPDs and VPDs.
had a n arrh ythmi a and most had on e or mor e
It is known t hat p hysiolog ic al a rrhythm ias SVPD during th e post-ope rative period. F ewer
are common i n healthy horses at rest. S
horses developed V PDs and o nly t wo had
tudies have shown t ha t sinus a rrhythm ia, s
periods of VT, b oth of t hese latter horses bei n g
econd degree atrioventricular block
i n the GI group. It is, h owev er, difficult to comp
andisolatedpremature
ar e t he two st u dies as the c r iter ia fo r defining
depolarisationsoccuratrestin th e no r ma l ho
rs e [9, 10 ]. In ho r se s, si nu s ar rh yt hm i a
ha s b ee n m o st c om m o nl y de te ct ed d
ur i ng t h e r ec ov er y p er i o d fo l l o wi ng
ex er ci s e an d i s co ns i de re d a ma ni fe
st at i o n of th e switch from dominance of the
s ym path etic drive to paras y m pat hetic drive
[11]. Sinus ar rhyt hm ia was noted in 8 1% of
horses in this study popul ati on; it is p l au s i
b l e t ha t du ri n g t h e p o st - o pe ra ti v e
p er i o d a si m i l ar chan ge in autonom ic
balan ce occurs. As expected, the development
of b radyarrhythm ias (SA, 2 AVB a nd SB) w as
l ess likel y i n the presence of a higher heart
rate i n this population. No other risk factors
were identified.
SV PD s and VPDs we r e m or e c om m on in
the pop ula tion in t his s tud y t han p r evi ous l y
r eporte d i n hea lth y ho r s es at r es t and at
ex erc is e. Sup r a or v en tr ic ular dep ol ar i s a ti
o ns m a y b e a s s oc i at ed w i t h un de r l yi
n g c ar d i ac or n on c ar diac dis eas e, but t
he y h av e als o b een d em ons tr at e d in n orm a
l an im als . In f r eq u en t SV PDs ha ve b ee n
s hown to oc c ur at r es t, dur ing w a r m - up,
ex erc is e a nd r ec ove r y in 22.4% t o 76 . 2% o f
c lini c a ll y h e alth y h or s es [6,1 2,13 ]. VP D s
oc c u r l es s f r equentl y in t he r es tin g hors e,
with pre val enc e r epor t s o f betwee n 0% [6]
and 3. 7% [ 13 ] . Do g s , c a ts an d h um an s
al l h av e a h i gh p r e v al e nc e ( 3 2 - 78% ) o f
VPD s du r in g 2 4 ho u r E CG r e c o r di ng s o f
apparent l y hea lth y s u bj e c ts [14 - 17]. In th is
s tud y S VP Ds wer em or ec om m onthanVPDs bu t
both oc c u rred in a lar ge pr o po r t ion of h
ors es w ith a nd wi th o ut gas tr oint es tina l
dis eas e.
There were no statistically significant differences
in the prevalence of S VPDs or VPDs in horses
with or without g astr ointestinal disease in t his
study. The prese nc e o f g astro in t e st in al d i s
ea se (re f le ct ed in a h i g her ASA score) was
associated with a reduction in the likelihood of
developing a high numb er of SVPDs and was not
a risk factor for developin g VPDs. These findings
differ from previous literature [2]. In one study of
horses under going sur ger y [2], eight out o f 3 5
Morgan et al . Acta Veterinaria Scandinavica 2011,
53:62 http://www.actavetscand.com/content/53/1/62
arrhythm ias a nd the methods of r ec ording
them were differ ent. Fur therm or e, bas ed on
the prevalenc e repor ted inthat s tudy[2],our
s tudyonl yhadapower of0.6f or 95% c onf id
enc e o f d e te cting a diff er e n c e b e tw een
th e groups de s pi t e a c hie vin g tw ic e t he
num bers in e ac h g r o u p . I t wo ul d a p p e
ar f r o m o u r d a t a t ha t t h e p r e s en c e
or absenc e of gas tr ointes tinal dis eas e is not
as im portant as the ac t of gener al anae
s thes ia a nd s ur ger y in the developm ent o f
arrhythm ias. H owever , based on the da ta c o
ll ect ed i n th is st udy , a r e tr o s p ec tiv e
pow er c al c ulat io n shows that in or der to
detec t a d iffer enc e in, f or ex am pl e th e pre
s e nce o f VPD s , be tw een t he pop ula ti o ns
over 200 0 hor ses would b e r equired. W e
would s uggest a f ur ther m ulti -c entr ed s tudy
m ay be requir ed to dem onstr ate s uc h a
differenc e.
There is little p ublishe d d ata o n t he prevalenc e
of pos t-ope rativ e ar rhyt hmia s in human medi ci
ne, but routine elect rocar dio graphic m onitor ing is
carr ied out in most recovery roo ms. T h e American
Society of Anaesthesiol ogists (AS A) guidelines [
18] for post-operativ e monitoring state t hat ‘ The
lite rature i s i nsufficient to eva luate the impact of c
ardiovascular assessment and m on i t o ri ng on pe
r i - op er at i v e c om pl i ca t i o ns , an d th e l i
terature i s s ilent regarding r ou tine electroca
rdiographic monitor ing.’ A recent review of the
human literature [19] found an overall prevalence
rate for post-operative ar r hy th m ia s o f 7% b ut
no te d t he la ck of l ar g e s cal e pr ospectiv e
studies using continuous monitoring. Cardiac
arrhythmias i n dog s f ollo wing surgery a re co
mmon; Bu h l e t al . [ 20 ] sh o we d th at 93 % o f
do g s ha d a p at ho l o g i ca l ar r h yt hm i a ei t h
er d ur i n g th e fi r s t 24 ho u rs f o l l o wing s
urgery or during a 2 4 hour p eriod 5 days after
surgery.
Proposed
risk factors
fo r the d
ev
elopment
of ar
rhythm i as
i nc l ud e
en d o to x
ae m i a,
el ec tr o l
yt e d i so
rd er s, a
ci do si s,
hy po xi a
o r se v er
e p ul mo
na ry di se
as e, ad
mi ni st ra
ti o n of dr
ugs and
anaesthes
ia [4]. In t
his study,
a limited
nu m b er
o f t h es e
fa ct o r s
w er e i n
v es t i g a
te d a nd ,
o f t he s
e, very
few w ere
a sso
ciated with
the de
velopment
of the di ff
er en t ty
pe s o f ar
rh yt hm ia
. S od ium
ap p ear
ed to i nfl
uenc e the
d
evelopme
nt of
SVPDs a
nd VPDs;
this m ay
reflect th e
hydra tion
status of
the horses
following
surgery
and would
require f
urther inve
stigation.
A higher
ASA s core
in this
study was
found t o r
educe t he
likeliho o d
of ha vi ng
a hi gh er
nu mbe r o
f S VP Ds .
T he re as
o ns for t
his a re
unc l ear
but one
could s
pecu late
that horses
assessed
pre-operati
vel y to be
i n a worse
phy
siological
condition
ma y re
ceive dif
fer ent
post-opera
tive care
and may
have a
ltered
autonomic
activity c
ompared
to their
healthier
counterpar
ts. The
horse ’ s
pre and p
ost-operat
iv e r eq ui
re m en t s
fo r an a lg
es i a an d
ot he r dr
ug s, su ch
as alpha 2
agonists,
also
require co
nsideration
. Further i
nve st ig at
i on of fa ct
o rs wh ic
h ha v e no
t be en in
cl ud ed i
n the
current
study,
such as
packed
cell
volume,
total
Page 6 of 8
protei n, a ci d -base b al an ce a nd p ost-opera t
ive m a na g ement that ma y be associated with the
development o f arrhythmias is warranted.
Abnorm al itie s of plas ma elect rol yte con cent ra
tions ar e frequently ci ted a s a cause of cardiac
arrhythmias. Horses with gastrointestinal disease
often have sign ificant elec t rolyte imbalan ces the m
ost common of which ar e hy po kal aem i a, hyp o
ma gn esa em i a an d hy po cal cae mi a [21,22].
Hypocalcaemia and hypokalaemia were common i n
ho r s es b o t h wi t h an d wi t h o ut g a st r o i n te
s ti na l di se as e following surgery in t his study an
d ye t plasma e lectrolyte concentrations we re not
associ ated with the developme nt of either SVPDs o
r V PDs. In common with other e quine hospitals, our
patients receive intensive monitoring and, if
necessary, i ntravenous supplemen tation of elec
trolyt es. C onsequent ly none of the horses in this
study had profound electrolyte abnormalities. It is
unknown w hether mor e pronounced electrolyte
abnormalities may have induced further arrhythmias.
Stu die s have sho wn t hat th e ma jor ity of ho rs
es und er going c olic surger y have a degree of
hypomagnesaemia [ 2 2] . I t i s u nf o r t un at e t h at
d ue t o t h e c o ns t r ai nt s o f t h e cl inic facili ties
we were unable to measure m agnesium in this study.
The d irect association between low magnesium
levels and arrhythmias is unclear [23] and further
work in this area is warranted.
Endotoxaemia has been a ssociated with t he
developmen t of arrh ythm ias in ho rses with ga
stro-i nt esti nal dis ease. Possible mechanisms for
this i nclude ischaemic injury to the myocardium,
electrolyte imbalances and al tera tion s in memb ra
ne pe rmea bilit y. R epor te d mark ers of e ndotoxa
emia in cl ude p y rexia , t a chy ca rdia, t ac
hypnoea, alterations i n mucous m embrane colour,
neutropaenia and e levation in packed cell v olume a
nd total protein [24]. In this study s pecific markers
of endotoxaemia were not inve stigated. It ca n be
assume d that horses with gastrointes tinal disea se,
increased pre- operative heart r at e, post-operative
heart rate and those requiring p ost-operative i
ntravenous fluid t herapy may be more likely to be
suffering from end otoxaemia than others. Of t hese
only an increased heart rate at T 12 increased the
risk o f devel opment of VPDs. Further investigation
of endotoxaemia markers for an association wi t h ar
rh yt hm i a s i s wa rr an t ed , b ut gi v en t he si mi
l ar i t ie s in arrhythmia prevalence between the
non-GI a nd GI groups it is unlikely t hat t he
presence of endotoxaemia ha d a p r of ou nd effe ct
on th e de velopment of arrhythmias in this
population. T he measurement of cardiac troponin 1
m ay have been a useful addition t o d etermine if
there was extensive myocardial damage in any of
the horses following anaesthesia and surgery [25].
The findings o f this study indicate that rather
than a primary disease predispo sing ho rses t o
po st-o perative arrhy thmias, it may be g eneral a
naesthesia, surgery and
Morgan et al . Acta Veterinaria Scandinavica 2011,
53:62 http://www.actavetscand.com/content/53/1/62
group. Further work i s r equired to ascertain the
prevalence and na ture of a rrhythmias i n th ose
horses that fail to survive the immediate
post-operative period.
recove ry. If t his i s t he case then changes in
Conc lusions
autonomic balanc e driven by stress and gene ral a
naesthesia may play the l arger r ole i n
development of cardiac arrhythmi as th an dis eas e
fa ct o rs su ch as h yp oxi a o r en dot oxa emia. In
people, mental and physical stress can increase
cardiac electrical instability and a recognised link ex
ists between e mo tional and physical stressors a nd
spontaneous ventricular arrhythmias [26]. The role
of the autonomic n ervo us system in the
development of arrhythmias i s an a rea of i nc
reasing interest in h uman m ed i ci ne [ 27 , 28 ] . Gi
v en t he i m po rt an c e of v ag a l t o ne i n
physiological arrhythmias i n the horse, it is certainly
worth considering an autonomic basis fo r a
rrhythmias f o llow ing s u rge r y. As se ss men t of
h ea rt r ate va ri abil ity ma y be a u sefu l t ool i n i
dentifying an d qu antify in g the degree to which
autonomic inf l uen ces aff ect the likelihood of a h
orse develo ping a post-o per at ive ar r hy thmia
[29] . S ur gery i ts el f al so in curs an i nfla mma tor
y re sp on se which may be responsib le f or the
developm ent o f arrhythmias. Further investigation
and assessment of hospitalised horses not
undergoin g surgery is required to ascertain the role
of the autonomic nervous system in the development
of arrhythmias.
The horse s we re c lin i cal cases and as s uch
rec eived a number of drugs that m ay ha ve been
anti or proa rrhyt hmo g en ic . The most obv io us
of the s e, l idoc a in e, was a dmini stered to 62%
of patients with GI disease as is common practice in
many referral hospitals. Lidocaine is of te n us ed as
an ant i -arrh yt hmoge nic fo r tre atme nt of VT in
horses [30 ]. Lidocaine administration, howeve r, did
not have a significant influence on the multi-variable
models for a ny of the a rrhythmias. The
administration of lidocaine may have influenced the
results o f t his study in that it may ha ve reduced
the prevalence of arrh ythmias w ithin the GI group.
This influence would require f urther investigation
but this study gives useful information for clini cal ca
ses where lidocaine is used frequently.
The h orses u ndergoing s urger y included in
this study h ad survived for at l east 24 hours
post-operatively. Given these c rit e ria, it is po
ssib le that t he prevalence o f a rrhythmi as in
those h orses t hat d o not survive may be
different and potentially more clinically significant
because these may represent the most critically ill
This study
has
shown
that
arrhythmia
s are
common
in this
clinical
population
of horses
following
surgery.
SVPDs a
nd
bradyarrh
ythmias
such a s
sinus
arrhythmia
, AV b
lock and
sin us b
lock pre
domi nat
e. T he
pre senc e
of
Page 7 of 8
gastrointestinal disease, in these c linical
cases w hich recei ved i nt e nsiv e sup portiv
e therapy, did not a ffec t the prevalen ce of
an y type o f arrhythm ia. Post -operative ta ch
yc ar d ia an d sod ium d er an ge me nt s we r
e fo un d to b e associ ated with the
developm ent of arrhythmias following surgery,
the b iological significance of which i s un cl
ea r . It i s p o ss i bl e , t h er e fo re , t h at
ot he r f ac t o rs , su c h as aut on om i c b al
an ce, al so pl ay a r ol e i n ar rh yt hm oge
nesis in the post-operativ e p eriod. Further,
more exte nsive, investigation of possible risk
factors is required t o understand the
pathogenesis of po st -operative ar rhythm ias.
None o f t he arrhythm ias identified in t his
study required specific t reatment and none
was directly associated wi th the death o r e
uthanasia of a case. It is
im portanttobeawareofsuchahighprevalenceof
arrhythm ias d uring t his pe riod a nd, if t
achycardia persists or an a bno rmal rhyt h m
is iden tified, further i nv es tigation is
required.
Com peting inte rest State ment
The a uthors declare that they h ave n o c
ompeting interests.
Additio nal material
Additi onal file 1: Outcome Binary SVPD Univari able Categorical
Analyse s.docx.
Additi onal file 2: Outcome Binary SVPD Univari able Continuous
Analyse s.docx.
Additi onal file 3: Outcome Ordinal SVPD Univari able Categorical
Analyse s.docx.
Additi onal file 4: Outcome Ordinal SVPD Univari able Continuou s
Analyse s.docx.
Additi onal file 5: Outcome Binary VPD Univariable Categorical
Analyse s.docx.
Additi onal file 6: Outcome Binary VPD Univariable Continuous
Analyse s.docx.
Additi onal file 7: Outcome 2 VPDs Univariable Catego rical Analyse s.
docx.
Additi onal file 8: Outcome 2 VPDs Univariable Continuo us Analyses .
docx.
Additi onal file 9: Outcome bradyarrhyth mias Univariable
Catego rical Analyse s .docx.
Additi onal file 10: Outcome bradyarrhyth mias Univariable
Continuo us Analyses.docx .
Acknowledge ments The authors thank The Horse Trust for the ir generou s
funding of this research and the author ’ s (R.A.M) Clinical Scholarship. We
would also like to thank all of the inter ns at the Philip Leverhulme Equin e
Hospital for the ir help with data collection.
Author deta ils
12Philip Leverhulme Equine Hospital, Universi ty of Liverpool , Leahurst
Campus, Neston, Cheshire, CH64 7TE, UK.Institute of Infection and Global
Health, Universi ty of Liverpool , Leahurst Campus, Neston, Cheshire, CH64
Morgan et al . Acta Veterinaria Scandinavica 2011,
53:62 http://www.actavetscand.com/content/53/1/62
3
7
T
E
,
U
K
.
Page 8 of
8
Anesthesiologists Task Force on Post anaesthetic Care.
Anesthesiology 2002, 96 :742-752.
20. Buhl K, Kersten U, Kramer S, Mischke R, Fedrowitz M, Nolte I: Incidence
of post-anaesthetic arrhythmias in dogs. J Small Anim Pract 2005, 46
:131-138.
21. Dart AJ, Snyder JR, Spier SJ, Sullivan KE: Ionized calcium concentration
in horses with surgically managed gastrointestinal disease: 147 cases
(1988-1990). J Am Vet Med Assoc 1992, 201 :1244-1248.
22. Garcia-Lopez JM, Provost PJ, Rush JE, Zicker SC, Burmaster H,
Freeman LM: Prevalence and prognostic importance of hypomagnesemia
and hypocalcemia in horses that have colic surgery. Am J Vet Res 2001,
62:7-12.
23. Millane TA, Ward DE, Camm AJ: Is hypomagnesemia arrhythmogenic?
Clin Cardiol 1992, 15:103-108.
24. Lohman KL, Barton MH: Endotoxaemia. In Equine Internal Medicine
Edited by: Reed SM, Bayly WM, Sellon DC , 3 2010, 816-817.
25. Kraus MS, Jesty SA, Gelzer AR, Ducharme NG, Mohammed HO, Mitchell
LM, Soderholm LV, Divers TJ: Measurement of plasma cardiac troponin 1
concentrations by use of a point of care analyzer in clinically normal horses
and horses with experimentally induced cardiac disease. Am J Vet Res 2010,
71 :55-59.
26. Lampert R, Joska T, Burg MM, Batsford WP, McPherson CA, Jain D:
Emotional and physical precipitants of ventricular arrhythmia. Circulation
2002, 106 :1800-1805.
27. Verrier RL, Antzelevitch : Autonomic aspects of arrhythmogenesis: The
enduring and the new. Curr Opin Cardiol 2004, 19:2-11.
28. Kapa S, Venkatachalam KL, Asirvatham SJ: The autonomic nervous
system in cardiac electrophysiology: An elegant interaction and emerging
concepts. Cardiol Rev 2010, 18 :275-284.
29. Bowen IM: Ambulatory electrocardiography and heart rate variability. In
Cardiology of the Horse.. 2 edition. Edited by: Marr CM. Saunders Elsevier;
2010:127-137.
30. Reef VB, Marr CM: Dysrhythmias: assessment and medical management.
In Cardiology of the Horse.. 2 edition. Edited by: Marr CM. Saunders Elsevier;
2010:159-178.
31. Borer KE, Corley KTT: Electrolyte disorders in horses with colic. Part
1: Potassium and magnesium. Equine Vet Educ 2006, 18:266-271.
32. Van Der Kolk JH, Nachreiner RF, Refsal KR, Brouillet D, Wensing T:
Heparinised blood ionised calcium concentrations in horses with colic or
diarrhoea compared to normal subjects. Equine Vet J 2002, 34:528-531.
doi:10.1186 /1751-0147-53- 62 Cite this article as: M organ et al .: The
prevalence and nature of cardiac arrhythmias in horses followin g ge neral
anaesth esia and surge ry. Acta Veterinaria Scan dinavica 20 11 53 :62.
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Institute of Ageing and Chronic Disea se, University of Liverpool ,
Leahurst Campus, Neston, Cheshi re, CH64 7TE, UK.
tistical analysis. RM, JMS and CM draft ed the manus cript. All author s read
and approved the final manuscript.
Authors ’ contributions RM, AR and JMS initiated and designed the stud y and
collected the data. RM analysed the data. RM and PC performed the sta
Authors ’ Information RM MA VetMB CertAVP (EM) MRCVS Horse Trust
Senior Clinical Scholar in Equine Intern al Medicine, Universi ty of Liverpool
AR MA VetMB MRCVS Ass istant Veterinary Surg eon JMS PhD BVSc
CertVA DipECVAA MRCVS Lecture r in Veterinary Anaesth esia, Head of
Veterinary Anesthesia, Universi ty of Liverpool PC BVSc BSc, MSc, PhD
MRCVS Senior Lecturer in Epidemiology , University of Liverpool CM BVSc
Dip VetClinStud MACVS c PhD DEIM DipECE IM FHEA MRCVS Senior
Lecturer in Equine Internal Medicine , University of Liverpool
Received: 11 August 2011 Accepted: 23 Nove mber 2011
Published: 23 November 2011
References
1. Marr CM, Reef VB: Cardiovascular complications in the intensive care
patient. In Cardiology of the Horse.. 2 edition. Edited by: Marr CM. Saunders
Elsevier; 2010:267-276.
2. Protopapas K: Studies on Metabolic Disturbances and Other
Postoperative Complications Following Equine Colic Surgery. PhD
Thesis University of London, Department of Clinical Veterinary Science;
2000.
3. Cornick JL, Seahorn TL: Cardiac arrhythmias identified in horses with
duodenitis/proximal jejunitis: six cases (1985-1988). J Am Vet Med Assoc
1990, 197 :1054-1059.
4. Reimer JM, Reef VB, Sweeney RW: Ventricular arrhythmias in horses:
21 cases (1984-1989). J Am Vet Med Assoc 1992, 201 :1237-1243.
5. Bonagura JD, Miller MS: Junctional and ventricular arrhythmias. J Equine
Vet Sci 1985, 5 :347-350.
6. Buhl R, Meldgaard C, Barbesgaard L: Cardiac arrhythmias in clinically
healthy showjumping horses. Equine Vet J 2010, 42 :196-201.
7. American Society of Anesthesiologists website: ASA Physical status
classification system. [http://www.asahq.org/clinical/physicalstatus.htm].
8. Hosmer DW, Lemeshow S: Applied Logistic Regression New York: Wiley;
1989. 9. Raekallio M: Long term ECG recording with Holter monitoring in
clinically
healthy horses. Acta Vet Scand 1992, 33:71-75. 10. Scheffer CW,
Robben JH, Sloet van Oldruitenborgh-Oosterbaan MM:
Continuous monitoring of ECG in horses at rest and during exercise. Vet
Rec 1995, 137:371-374.
11. Van Loon G, Patteson M: Electrophysiology and arrhythmogenesis. In
Cardiology of the Horse.. 2 edition. Edited by: Marr CM. Saunders Elsevier;
2010:51-69.
12. Ryan N, Marr CM, McGladdery AJ: Survey of cardiac arrhythmias during
submaximal and maximal exercise in Thoroughbred racehorses. Equine Vet
J 2005, 37 :265-268.
13. Barbesgaard L, Buhl R, Meldgaard C: Prevalence of
exercise-associated arrhythmias in normal performing dressage horses.
Equine Vet J 2010, 42:202-207.
14. Dickinson DF, Scott O: Ambulatory electrocardiographic monitoring in
100 healthy teenage boys. Brit Heart J 1984, 51 :179-183.
15. Takada H, Mikawa T, Murayama M, Sugai J, Yamamura Y: Range of
ventricular ectopic complexes in healthy subjects studied with repeated
ambulatory electrocardiographic recordings. Am J Cardiol 1989, 63:184-186.
16. Meurs KM, Spier AW, Wright NA, Hamlin RL: Use of ambulatory
electrocardiography for detection of ventricular premature complexes in
healthy dogs. J Am Vet Med Assoc 2001, 218:1291-1292.
17. Hanås S, Tidholm A, Egenvall A, Holst BS: Twenty-four hour Holter
monitoring of unsedated healthy cats in the home environment. J Vet
Cardiol 2009, 11:17-22.
18. Silverstein JH, Apfelbaum JL, Barlow JC, Chung FF, Connis RT,
Fillmore RB, Alabama D, Hunt SE, Joas TA, Nickinovich DG, Schreiner
MS: Practice guidelines for postanesthetic care: A report by the American
Society of
19. Walsh SR, Tang T, Wijewardena C, Yarham SA, Boyle JR, Gaunt ME:
Postoperative arrhythmias in general surgical patients. Ann Roy Coll Surg
Eng 2007, 89 :91-95.