Arrythmias presentation by Prof Celia Marr

Cardiac dysrhythmias in horses
Celia M Marr
celia.marr@rossdales.com
Control of heart rate at rest
• Equine resting heart rate is low: 25 - 42 bpm
• Horses have very little or no sympathetic tone at
rest
• Parasympathetic tone is high
• The vagus innervates both the sinoatrial and the
atrioventricular nodes
• The horse can reduce its heart rate by delaying
conduction at the atrioventricular node
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SECOND DEGREE ATRIOVENTRICULAR BLOCK
•
•
•
First:
•
closure of the atrioventricular
valves
•
opening of the semilunar valves
Second:
•
closure of the semilunar valves
•
opening of the atrioventricular
valves
Fourth:
•
atrial systole
Le-lub-dub
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Le-lub-dub
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Le
Le-lub-dub
ECG Interpretation
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SECOND DEGREE ATRIOVENTRICULAR BLOCK
P QRST P
QRST
P
P
P
P
Sinus rhythm restored during
exercise
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QRST
P QRST
Pathogenesis of atrial fibrillation
RE-ENTRY
Requires an area of Unidirectional block
UNIFORM
REFRACTORY
PERIODS
CRITICAL ATRIAL MASS
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VARIABLE REFRACTORY
PERIODS
Pathogenesis of atrial fibrillation
Normal heart:
high vagal
tone maintains
low heart rate
Intermittent conduction
through atrioventricular
node
Irregular R-R interval with f waves
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Significant
underlying
heart disease:
increased
sympathetic
tone: high
ventricular rate
Pathogenesis of atrial fibrillation
CRITICAL ATRIAL MASS
VARIABLE REFRACTORY
PERIODS
• High vagal tone
• normal horses
• Myocardial pathology
• Electrolyte disturbances
disease
• Normal horses
• Atrial enlargement
• Mitral or tricuspid
regurgitation
• Congenital heart
disease
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ATRIAL FIBRILLATION:
PRESENTING SIGNS
• Atria contribution to
ventricular filling = 15%
• With no other cardiac disease,
AF will only cause exercise
intolerance if in vigorous
exercise
• Racehorses, Eventers, some
hunters
• Can be an incidental finding
• Breeding stock, hacks, some
show jumpers
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ATRIAL FIBRILLATION
•
Exercise intolerance/poor performance
•
Reluctance to participate in exercise
•
Irregularly-irregular cardiac rhythm
•
intermittent long pauses interspersed
with rapid runs
•
no fourth heart sound
•
loud third heart sound
•
Variable pulse quality
•
Variable intensity of heart sounds
•
Exercise-induced pulmonary
haemorrhage
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PAROXYSMAL ATRIAL FIBRILLATION
Ohmura H et al, JAVMA, 2003, 223, 84-88
•
gastrointestinal disease (ventricular arrhythmias more common)
•
exercise-induced
•
minimum frequency = 0.03% (no. of episodes/no.of starts)
minimum prevalence = 0.29%(no. of horses with AF/no. of
horses)
•
prevalence in slow/non-finishing horses = 1.39%
•
recurrence rate = 6.1% (10 year study, 115 horses, 108 single
episode, 6 two episodes, 1 three episodes
•
92% resolved spontaneously within 24 hours without treatment,
•
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2 with 15-20g QS at 24 hours, 2 spontaneously within 48
hours, 4 with 15-20g QS within 48-120 hours
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Sustained Atrial Fibrillation
Diagnostic Approach
Goal
•
identify and characterise any
underlying cardiac disease
• clinical exam
• echocardiography
• clinical pathology
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• Atrial fibrillation is an
effect and not a cause of
congestive heart failure
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Clinical Findings that might
indicate underlying heart disease:
• tachycardia
• heart rate > 50 bpm
• cardiac murmurs
• particularly murmurs of AV
regurgitation
• venous distension and pulsation
• peripheral oedema
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CLINICAL DECISION-MAKING
Incidental
Finding
Athlete with
exercise
intolerance
Heart failure
Cardioversion
Palliative
furosemide
digoxin
ACE inhibitors
No treatment
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Quinidine
• Class 1A sodium channel blocker
• Prolongs the effective refractory period
• Decreases myocardial conduction velocity
& prolongs QRS and QT intervals
•
•
•
•
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Vagolytic
Alpha-adrenergic antagonist
Proarrhythmic
Gastrointestinal ulceration
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Quinidine Sulphate
6
4
2
0
0
2
4
6
8
10
12
14
16
18
20
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• Administer by nasogastric tube until either
normal sinus rhythm restored or serious
side-effects occur
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Extra-cardiac side effects
•
•
•
•
•
•
•
respiratory stridor
penile protrusion
neurological deficits
flatulence
diarrhoea
colic
tend to be seen in horses that
require prolonged treatment
• GI effects are the main cause
of treatment failure
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Cardiovascular side-effects
• hypotension
• rapid supraventricular tachycardia
• ventricular arrhythmias
• both potentially fatal
arrhythmias
• independent of plasma
concentrations
• monitor the ECG
continuously
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Hypotension
ALPHA ADRENERGIC ANTAGONIST
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•
•
keep the horse calm
•
iv fluids (or phenylephrine) may be
necessary
do not allow any form of exercise during
treatment
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Ventricular Arrhythmias
PROARRHYTHMIC EFFECT
• Magnesium sulphate
• Propanolol
• Lignocaine
• NOT Procainamide (same class as quinidine)
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Atrial fibrillation: Pre-treatment
Supraventricular tachycardia: ventricular rate around 200
Supraventricular tachycardia with variable conduction following digoxin
Normal sinus rhythm
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RAPID SUPRAVENTRICULAR TACHYCARDIA
VAGOLYTIC EFFECT
•
Emergency treatment required if ventricular
rate > 120 /min and rising
•
•
•
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Digoxin
Propanolol
Diltiazem
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Can we predict which horses
will develop major problems
during quinidine treatment?
IN ADVANCE
• Tachyarrhythmias
• not really - appears to be an individual horse,
idiosyncratic response
• GI and other extra-cardiac side effects
• prolonged treatment duration, usually horses
with under-lying heart disease and/or longstanding AF
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Can we predict which horses will develop major
problems during treatment?
DURING TREATMENT
• Prolonged QRS duration
• Ventricular premature depolarisation
• Long QT and ST segment changes
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How many horses develop major problems
during quinidine treatment?
• Depends on case type
• dose and duration of treatment are
influenced by AF duration and
underlying heart disease
• Variable population including
older animals around 40% have
side-effects
• Young, racing STD/TBs have
problems less commonly
• Life threatening arrhythmias: 4 - 8%
• Diarrhoea: 15 - 25 %
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Electrical Cardioversion
RA
RPA
LA
LPA
Frye et al, 2002, J. Am Vet Med Assoc, 2002; 220: 1039-1045.
McGurrin MK, Physick-Sheard PW, Kenney DG.J Vet Intern Med 2008;22:609-615.
McGurrin MK, Physick-Sheard PW, Kenney DG, et al. J Vet Intern Med 2005;19:695-702.
McGurrin MK, Physick-Sheard PW, Kenney DG, et al. J Vet Intern Med 2003;17:715-718.
De Clercq D, van Loon G, Schauvliege S, et al. Vet J 2008;177:198-204.
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McGurrin, KJ, Physick-Sheard, PW,
Kenney, DG (2005) How to perform
transvenous electrical cardioversion in
horses with atrial fibrillation
J. Vet. Cardiol. 7, 109-119
RPA
LPA
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Side-effects: fatal arrhythmias
• Ventricular fibrillation
• Third degree AV block
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Atrial Fibrillation and poor performance
Onset within last
48 hours
Monitor
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Onset >48 hours,
< 3 - 4 months
normal
echocardiogram
Quinidine
sulphate
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Uncertain or
prolonged duration,
mild heart disease
Quinidine failure
1. DC
conversion,
2. alternative
anti-dysrhythmics
Long-term Prognosis
Depends on
• degree of underlying cardiac disease
• duration prior to treatment
• less than 3 months
• recurrence rate 15%
• greater than three months
• recurrence rate 60%
• higher prevalence of side-effects associated with
prolonged duration of treatment
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Does sustained atrial fibrillation cause collapse
or death during exercise?
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•
Typically, horses with sustained atrial
fibrillation do NOT collapse
•
Sudden onset (paroxysmal) AF can be
associated with collapse or severe distress
•
Some horses with sustained AF have exerciseinduced ventricular tachycardia or
inappropriately high ventricular rates
•
Some horses will have EIPH at relatively low
intensity exercise
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ORIGIN OF PREMATURE DEPOLARISATIONS
Base-apex lead
Sinus:
bifid P
negative QRS
Supraventricular:
premature
abnormal P with
normal QRS-T
Ventricular
No P
premature
abnormal QRS-T
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PATHOGENESIS OF TACHYARRHYTHMIAS
Primary Myocardial disease
•
Viral
•
•
Bacterial
•
Toxic
•
•
Nutritional
•
•
Neoplasia
•
Idiopathic
Parasitic
Cardiomyopathy
Secondary to other factors
• Hypoxia
• Endotoxaemia
• Electrolyte disturbances
• Acid-base disturbances
• Catecholamine-induced
• Vagally-induced
Immune-mediated
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• Hypocalcaemia,
hypomagnesaemia,
hypokalaemia and
metabolic acidosis
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Clinical management of
tachydysrhythmias
• High index of suspicion required
• Judge arrhythmias by the company
they keep
• Aim treatment at underlying cause
• Reserve specific anti-arrhythmic
therapy for life-saving situations
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Summary
• Many normal horses have bradydysrhythmias at rest that
are of no clinical significance
• Atrial fibrillation is the most important clinically
significant arrhythmia
• Atrial fibrillation requires treatment if it is affecting the
horse's role as a performance animal
• Other tachydysrhythmias are seen occasionally, usually
secondary to physiological/pathophysiological states
associated with exercise or systemic illness
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DVD includes 70 cases contributed by 17 authors
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If you buy this book also buy a
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