Equine Dysrhythmias: Detection, Diagnosis, Management

Question 1

What are the heart sounds

Answer 1

S1: lub

S2: dup

S3: de

S4: lu

S4-S1-S2-S3

Question 2

what is the cause of S4

Answer 2

atrial contraction

active ventricular filling with increase in atrial pressure

semilunar valve closed

this phase (S4) is followed by closure of mitral and tricuspid valve S1

Question 3

what causes S1

Answer 3

AV valve closure occurs after rapid ventricular filling

ventricular contraction with increase in ventricular pressure is then followed by raised arterial pressure and reduced ventricular volume

semilunar valve closes directly after this contraction (S2)

Question 4

what causes S2

Answer 4

semilunar valves close after ventricular contraction

deceleration of blood in the great vessels, and retrogradal flow against the valves creates the second heart sound

Question 5

what causes S3

Answer 5

ventricular filling sound

there is passive filling of the ventricles as atrial pressure exceeds ventricular pressure, and deceleration of this blood results in S3

ventricle volume increases in this phase

Question 6

what are the most common non pathological dysrhythmias (5)

Answer 6

1. second degree AV block
2. sinus block
3. sinus arrhythmia
4. atrial premature contractions
5. ventricular premature contractions

Question 7

which dysrhythmias should disappear with exercise or adrenaline

Answer 7

1. second degree AV block
2. sinus block
3. sinus arrhythmia

Question 8

what are bradyarrhythmias that are pathological

Answer 8

1. third degree AV block
2. sinus bradycardia

Question 9

what are pathological dysrhythmias that occur with normal heart rate (3)

Answer 9

1. atrial fibrillation
2. atrial premature contractions
3. ventricular premature contractions

Question 10

what are tachyarhythmias

Answer 10

1. AF, APCs or VPCs
2. ventricular tachycardia

Question 11

what should you observe on an ECG

Answer 11

1. R-R interval: is it regular?
2. paper speed to calculate HR
3. look at P waves and QRS complexes, are they matched? is there a P wave for every QRS? is there a QRS complex for every P wave?
4. are the P waves and T waves similar morphology?

Question 12

what sounds occur during the P wave

Answer 12

S4

Question 13

what sounds occur during the R wave

Answer 13

S1

Question 14

what sounds occur during the T wave

Answer 14

S2

Question 15

what is second degree atrioventricular block (mobitz type 2)

Answer 15

AV node blocks the impulses from progressing through the purkinje fibres and depolarizing the ventricles

it is normal for fit horses with high vagal tone

Question 16

what rhythm is this

Answer 16

second degree AV block – mobitz type 2

AV node blocks the impulses from progressing through the purkinje fibres and depolarizing the ventricles

Question 17

what rhythm is this

Answer 17

sinoatrial block

heard in horses with slow resting HR

complete pause where the isn’t SA node depolarization

Question 18

what causes advanced second degree AVB or 3rd degree AVB

Answer 18

1. electrolyte imbalances
2. digitalis toxicity
3. AV nodal disease (inflammatory, degenerative)

Question 19

how is adavanced second degree AVB/3rd degree AVB treated

Answer 19

correct underlying cause

pacemaker

Question 20

what is shown here

20 yo pony, showing collapse after competition over 3 month period

after atropine shown an AV block and abnormal QRS-T complex

Answer 20

sick sinus sydrome

Question 21

what is shown here

Answer 21

3rd degree atrioventricular block

not a normal contraction between atrium and ventricles

massive reduction in CO and will be susceptible to low BP and collapse

Question 22

what are ventricular premature contractions/depolarizations

Answer 22

are extra, abnormal heartbeats that begin in the ventricles, or lower pumping chambers, and disrupt regular heart rhythm

Question 23

what rhythm is shown here

Answer 23

normal rate, abnormal rhythm

ventricular premature contractions/depolarizations (ectopic beats)

normal QRS with inverted morphology arising from a ventricular focus

Question 24

how do you investigate isolated ectopic beats

Answer 24

1. serum electrolytes: Ca, Mg, Na, K, Cl
2. markers of cardiac inflammation (cTnl)
3. acute phase protein markers, white cell differential count
4. 24h ECG monitoring to determine frequency

Question 25

how do you treat isolated ectopic beats

Answer 25

1. correct electrolyte disturbances & investigate underlying cause 2. ? corticosteroids if evidence of inflammatory focus 3. pheytoin for treatment of VPCs 4. rest

Question 26

what are tachydysrhythmias

Answer 26

1. atrial fibrillation 2. APCs/VPCs 3. ventricular tachycardia

Question 27

what is atrial fibrillation

Answer 27

irregularly irregular pulse, which may be low, normal or high in rate no detectable S4 in prolonged pauses

Question 28

what is typically present with atrial fibrillation

Answer 28

variable systolic murmur frequently present variable jugular pulse wave-form

Question 29

what is the etiology of atrial fibrillation

Answer 29

1. large atria 2. high vagal tone

Question 30

how does a large atria cause atrial fibrillation

Answer 30

circadian movement of impulses wave of depolarization meets atrial myocytes that have already repolarized allowing continuation of contraction activity blocked at the AV node, resulting in atrial fibrillation without ventricular response **loss of coordination between AV and SA node**

Question 31

how does high vagal tone cause atrial fibrillation

Answer 31

different duration of refractory period in different cells

Question 32

what are the cardiovascular effects of atrial fibrillation (4)

Answer 32

usually no clinical signs at rest 1. decreased ventricular filling at exercise (atrial contraction contributes to last 1/3 of ventricular filling) 2. decreased force of ventricular contraction 3. increased heart rate at exercise compared to horse without AF to compensate for decreased stroke volume 4. owner may report horse to be lethargic or to have prolonged recovery after exercise. Depending on work of horse, AF may be noted incidentally on clincal exam

Question 33

what rhythm is shown here

Answer 33

atrial fibrillation irregular RR intervals long pauses before there is QRS complexes fibrillation waves, no normal P waves

Question 34

what rhythm is shown

Answer 34

atrial fibrillation variable pauses between heart beats (up to 6-7s pauses before QRS comes in) fibrillation wave irregular RR interval

Question 35

how do you determine whether or not an AF is a candidate for cardioversion (9)

Answer 35

1. is there underlying heart disease 2. duration of dysrhythmia (more likely to convert if \<6 weeks in AF) 3. type of work required? is maximal CO required? 4. cost 5. side-effects 6. poor prognosis if pathological murmur (esp MR) with volume overload 7. prev unsuccessful treatment 8. heart rate \> 55 bpm 9. more likely to revert to AF if there is chamber enlargement

Question 36

what is used during cardioversion therapy

Answer 36

quinidine sulphate 22 mg/kg per os at 2h intervals

Question 37

how is atrial fibrillation treated

Answer 37

titrated quinidine sulphate

Question 38

what are the side effects of quinidine sulphate (3)

Answer 38

**1. vagolytic agent:** supraventricular tachycardia may result from loss of AV node blockade of atrial impulses **2. prolongs action potential:** ventricular tachycardia is more serious side effect, which can be fatal if not addressed **3. alpha adrenoceptor antagonist:** vasodilation, hypotension --\> can cause collapse if already in congestive heart failure

Question 39

what are common signs of quinidine sulphate toxicity

Answer 39

1. depression, colic, diarrhea 2. muzzle swelling

Question 40

what are serious side effects of quinidine sulphate

Answer 40

1. marked supraventricular tachycardia (100-120 bpm) 2. severe colic 3. weakness 4. laminitis 5. hypotension and collapse 6. sudden death --\> most likely due to severe ventricular tachycardia

Question 41

how is quinidine sulphate toxicity managed

Answer 41

1. stop dosing 2. mineral oil given via NG tube to decrease absorption 3. sodium bicarbonate protein binding and reduce availability of QS

Question 42

how do you manage serious cardiac side effects from quinidine sulphate (5)

Answer 42

1. lignocaine infusion to reduce ventricular response rate if \>100 bpm 2. digoxin IV to decrease tachycardia 3. MgSO4 infusion if torsades de pointes develops 4. shock fluids 5. absolute rest

Question 43

what is torsades de pointes

Answer 43

prolonged QT and ventricular tachycardia treated by magnesium sulphate bolus injections of 4 mg/kg every 2 minutes --\> blocks calcium channels

Question 44

what rhythm is shown

Answer 44

torsades de pointes

Question 45

what is transvenous electrical cardioversion

Answer 45

catheters placed in RA and left PA synchronous electrical shock delivered, timed to QRS complex

Question 46

when do ventricular ectopic beats become a problem

Answer 46

if the HR is above 100 bpm if R-on-T phenomenon is present

Question 47

what is shown here

Answer 47

ventricular ectopic beats

Question 48

what rhythm is shown here

Answer 48

ventricular tachycardia ventricular ectopic beats with HR over 100

Question 49

how is ventricular tachydysrhythmias treated

Answer 49

procainamide infusion at 1 mg/kg/min avoid quinidine gluconate if concurrent hypotensive cardiac output failure lignocaine infusion (20-50 mcg/kg/min IV) consider MgSO4 infusion if VT refractory to treatment

Question 50

what can cause ventricular tachydysrhythmias (4)

Answer 50

1. myocardial hypoxia 2. electrolyte derangement 3. myocardial inflammation 4. secondary to endotoxemia

Question 51

how is equine myocarditis diagnosed

Answer 51

1. clinical pathology 2. echocardiography 3. assay for cardiac troponin I myocardial polypeptide may follow viral finection such as equine influenza

Question 52

how is equine myocarditis treated

Answer 52

1. acute anti-dysrhythmic theray 2. dexamethasone if non life-threatening ventricular tachycardia 3. pasture rest dependent on HR and clinical picture