Cardiac dysrhythmias in horses

Transcription

1 Cardiac dysrhythmias in horses Celia M Marr celia.marr@rossdales.com

2 Control of heart rate at rest Equine resting heart rate is low: 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 3

3 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 Le-lub-dub Le Le-lub-dub 4

4 ECG Interpretation 5

5 SECOND DEGREE ATRIOVENTRICULAR BLOCK P QRST P P P QRST QRST P P P QRST Sinus rhythm restored during exercise cmarr,

6 Pathogenesis of atrial fibrillation RE-ENTRY Requires an area of Unidirectional block UNIFORM REFRACTORY PERIODS VARIABLE REFRACTORY PERIODS CRITICAL ATRIAL MASS cmarr, 2013

7 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 Significant underlying heart disease: increased sympathetic tone: high ventricular rate cmarr,

8 Pathogenesis of atrial fibrillation CRITICAL ATRIAL MASS Normal horses Atrial enlargement Mitral or tricuspid regurgitation Congenital heart disease VARIABLE REFRACTORY PERIODS High vagal tone normal horses Myocardial pathology Electrolyte disturbances disease 9

9 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 10

10 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 11

11 PAROXYSMAL ATRIAL FIBRILLATION Ohmura H et al, JAVMA, 2003, 223, 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, 2 with 15-20g QS at 24 hours, 2 spontaneously within 48 hours, 4 with 15-20g QS within hours 12

12 Sustained Atrial Fibrillation Goal Diagnostic Approach identify and characterise any underlying cardiac disease clinical exam echocardiography clinical pathology 13

13 Atrial fibrillation is an effect and not a cause of congestive heart failure 14

14 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 15

15 CLINICAL DECISION-MAKING Incidental Finding Athlete with exercise intolerance Heart failure No treatment 16 Cardioversion Palliative furosemide digoxin ACE inhibitors

16 Quinidine Class 1A sodium channel blocker Prolongs the effective refractory period Decreases myocardial conduction velocity & prolongs QRS and QT intervals Vagolytic Alpha-adrenergic antagonist Proarrhythmic Gastrointestinal ulceration 17

17 18

18 Quinidine Sulphate Administer by nasogastric tube until either normal sinus rhythm restored or serious side-effects occur

19 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 20

20 Cardiovascular side-effects hypotension rapid supraventricular tachycardia ventricular arrhythmias both potentially fatal arrhythmias independent of plasma concentrations monitor the ECG continuously 21

21 Hypotension ALPHA ADRENERGIC ANTAGONIST keep the horse calm do not allow any form of exercise during treatment iv fluids (or phenylephrine) may be necessary 22

22 Ventricular Arrhythmias PROARRHYTHMIC EFFECT Magnesium sulphate Propanolol Lignocaine NOT Procainamide (same class as quinidine) 23

23 Atrial fibrillation: Pre-treatment Supraventricular tachycardia: ventricular rate around 200 Supraventricular tachycardia with variable conduction following digoxin Normal sinus rhythm 24

24 RAPID SUPRAVENTRICULAR TACHYCARDIA VAGOLYTIC EFFECT Emergency treatment required if ventricular rate > 120 /min and rising Digoxin Propanolol Diltiazem 25

25 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 26

26 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 27

27 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: % 28

28 Electrical Cardioversion RA RPA LA LPA Frye et al, 2002, J. Am Vet Med Assoc, 2002; 220: McGurrin MK, Physick-Sheard PW, Kenney DG.J Vet Intern Med 2008;22: McGurrin MK, Physick-Sheard PW, Kenney DG, et al. J Vet Intern Med 2005;19: McGurrin MK, Physick-Sheard PW, Kenney DG, et al. J Vet Intern Med 2003;17: De Clercq D, van Loon G, Schauvliege S, et al. Vet J 2008;177:

29 McGurrin, KJ, Physick-Sheard, PW, Kenney, DG (2005) How to perform transvenous electrical cardioversion in horses with atrial fibrillation J. Vet. Cardiol. 7, RPA LPA 30

30 31

31 Side-effects: fatal arrhythmias Ventricular fibrillation Third degree AV block 32

32 Atrial Fibrillation and poor performance Onset within last 48 hours Onset >48 hours, < 3-4 months normal echocardiogram Uncertain or prolonged duration, mild heart disease Quinidine failure 33 Monitor Quinidine sulphate 1. DC conversion, 2. alternative anti-dysrhythmics

33 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 34

34 Does sustained atrial fibrillation cause collapse or death during exercise? 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 35

35 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 cmarr,

36 PATHOGENESIS OF TACHYARRHYTHMIAS Primary Myocardial disease Viral Bacterial Parasitic Toxic Nutritional Cardiomyopathy Neoplasia Immune-mediated Secondary to other factors Hypoxia Endotoxaemia Electrolyte disturbances Acid-base disturbances Catecholamine-induced Vagally-induced Idiopathic

37 Hypocalcaemia, hypomagnesaemia, hypokalaemia and metabolic acidosis

38 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 39

39 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 40

40

41 DVD includes 70 cases contributed by 17 authors 42 If you buy this book - also buy a stethoscope speaker pad: