Normal Rhythms, Enlargement Patterns And Conduction Disturbances

Question 1

Sinus arrhythmias

Answer 1

Dogs only

Question 2

Wondering pacemaker

Answer 2

Vagally mediated
Changes in P wave height
Taller P waves with faster heart rates and higher sympathetic tone
Shorter P waves with slower heart rates and higher vagal tone

Question 3

RA enlargement

Answer 3

Tall, peaked P waves in leads II III and avF

Question 4

LA enlargment

Answer 4

Wide, sometimes notched P waves

Question 5

LV enlargement

Answer 5

Tall R waves in lads I II III and avF
Or
Wide QRS

Question 6

Sinus rhythm

Answer 6

Upright P in I II III and avF

Question 7

RV enlargement

Answer 7

Deep S waves in leads I II III and avF

Dogs with tricuspid valve dysplasia can also have ‘splintered’ QRS complexes (also referred to a Rr pattern)

Question 8

Hyperkalemia

Answer 8

Mild - spiked tall T wave
Moderate - small P wave, tall T waves, bradycardia
Severe - less of P waves, bradycardia, wide QRS complexes, right bundle branch block

Question 9

Hypokalemia and hypocalcemia

Answer 9

Could cause QT interval prolongation

Question 10

Pericardial effusion

Answer 10

Complex size reduced due to attenuation by the fluid or because of reduced intra cardiac blood volume
Electrical alternans = beat to beat QRS variation
Due to swinging of the heart within the pericardium

Question 11

Right bundle branch block (RBBB) ECG hallmark

Answer 11

Widened QRS (>80 ms dog)

Question 12

RBBB

Answer 12

+/- underlying cardiac disease

Question 13

1st degree AV block

Answer 13

Slow AV node conduction
But all impulse get through
Prolonged PR interval

Question 14

Etiologies for 1st degree AV block

Answer 14

Structural AV node disease
Elevated vagal tone
Drugs
Hyperkalemia
Hypothermia

Question 15

2nd degree AV block

Answer 15

Some sinus depolarizations get through others don’t

Can also be due to elevated vagal tone

Question 16

Diseases that increase vagal tone can cause

Answer 16

GI disease, ocular disease, respiratory disease, urinary tract disease

Question 17

Types of 2nd degree AV block

Answer 17

Mobitz type I (Wenkeback phenomenon)
Mobitz type II
High grade

Question 18

Mobitz type I

Answer 18

Wenkeback phenomenon
Progressive PR prolongation prior to block
May be due to elevated vagal tone or drugs can be normal in athletic horses and very young puppies

Question 19

Treatment for Mobitz type I

Answer 19

Vagalytics
Sympathomimetics
Discontinue drugs

Question 20

Mobitz type II

Answer 20

No PR prolongation prior to block
Usually indicates structural cardiac disease
Less common than Mobitz type I
Monitor

Question 21

High grade

Answer 21

Cannot determine if Mobitz type I or II because there are no 2 consecutively conducted beats
Describes by the ratio of. P waves. To QRS complexes
Usually associated with structural AV node disease (no or minimal response to atropine)
If non atropine can responsive and clinical signs present, pacemaker implantation is indicative

Question 22

3rd degree AV block

Answer 22

No sinus depolarizations get through
SA node continues to depolarize fast
Escape rhythms take over to “rescue” the ventricles
No relationship between P and QRS (no constant PR)
Slow ventricular rate (depends on level of escape)

Question 23

Escape rhythms for 3rd degree AV block

Answer 23

Junctions escape rhythm

Ventricular escape rhythm

Question 24

Junction all escape rhythm

Answer 24

40 - 60 bpm

Complexes look “supraventricular”

Question 25

Ventricular escape rhythm

Answer 25

20-40 bpm

Complexes look “ventricular”

Question 26

Etiologies from 3rd degree AV block

Answer 26

Idiopathic (probably degenerative)
Infectious/inflammatory
rarely congenital
Rarely neoplastic
Associated with hyperthyroidism and cardiomyopathy in cats

Question 27

Treatment for 3rd degree AV block

Answer 27

Pacemaker implantation

Question 28

Low voltage complexes

Answer 28

Normal variations
Obesity
Pleural effusion
Pericardial effusion
Hypothyroidism
Pneumothorax
Pulmonary thromboembolism
Hypoproteinemia