ECG: Arrhythmias in SA

Question 1

List the uses of an ECG

Answer 1

• dx of arrhythmias
• rule out arrhythmia in patients with hx of collapse
• chamber enlargement?
• electrolyte disturbances?
• dx pericardia effusion?
• monitor effectiveness of anti-arrthymic therapy
• monitor heart rhythm under GA

Question 2

What are common P wave changes?

Answer 2

• absent = pathology in atria/SAN
• wide
• tall

Question 3

What are common QRS changes?

Answer 3

• tall R = LV pathology
• deep S = RV pathology
• deep and wideS = dilated RV

Question 4

What do small QRS complexes indicate?

Answer 4

Fluid in pericardium/fat animal/barell chested

Question 5

What can a prolonged QT interval cause?

Answer 5

Excessive intracellular Ca and rapid fatal ventricular tachycardia

Question 6

What abnormalities can be seen in the ST segment?

Answer 6

• decreases below baseline = hypoxia

- slopes into T wave = LV enlargement

Question 7

How are arrhythmias classified?

Answer 7

Normal rhythm, bradyarrhythmias, tachyarrhythmias

Question 8

List common bradyarrhythmias

Answer 8

Sinus arrest, sick sinus syndrome, sinus bradycardia, atrial standstill, AV blocks

Question 9

What are the causes of sinus arrest?

Answer 9

• meds = sedatives, B blockers, Ca channel blockers, digoxin
• disease = high vagal tone, atrial disease, hypothyroidism
• metabolic = hypothermia

Question 10

Describe the pathogenesis of sick sinus syndrome

Answer 10

SAN stops for period of time. Ectopic rescue beats come from the ventricles at a rate much lower than sinus rate, >20bpm). Animal may be okay, hypotensive, faint at rest.

Question 11

What are the causes and tx of sick sinus syndrome>

Answer 11

Causes - hereditary (min Schnauzer, Westie), idiopathic disease

Tx - pacemaker, sympathomimetics, parasympatholytics

Question 12

What are the causes of sinus bradycardia?

Answer 12

Meds = sedatives, anti-tachyarrhythmics
Disease = hypothyroidism, increased ICP, dysautonomia
Metabolic = hypothermia, hyperkalaemia

Question 13

What are the causes of atrial standstill?

Answer 13

Persistent = idiopathic atrial cardiomyopathy, muscular dystrophies
Temporary = hyperkalaemia, hypoadrenocorticism, oliguric renal failure

Question 14

Describe the pathogenesis of AV blocks

Answer 14

Decreased PQ interval duration and slow conduction

Question 15

What are the causes of primary AV block?

Answer 15

Can be normal in dogs with slow HR.
Drugs = sedatives, anti-tachyarrhythmics
Disease = high vagal tone, AVN fibrosis
Metabolic = hyperkalaemia

Question 16

What are the causes of secondary AV block?

Answer 16

Can be normal in dogs with high vagal tone

Disease = vagally mediated, fibrosis/infiltration of AVN

Question 17

Describe the pathogenesis adn tx of a third degree AV block

Answer 17

Pathogenesis - P and QRS completely dissociated. Ectopic beats ~ 50bpm, P waves ~100bpm
Tx = pacemaker, sympathomimetics, prasympatholytics

Question 18

List tachyarrhythmias

Answer 18

Sinus tachycardia, supraventricular premature beat, supraventricular tachycardia, atrial fibrillation, ventricular prematire complex, VT, rapid VT

Question 19

What are the causes of tachyarrhythmias?

Answer 19

Can be normal in nervous/excitable dogs
Drugs = anti-bradyarrhythmics
Disease = anaemia, pain, shock, dehydration, septicaemia, low CO2, hyperthyroidism

Question 20

Describe the pathology of supraventricular premature beat

Answer 20

• electrical activity initiated from the atria, not SAN
• beats are premature, identical to sinus beats
• Disease = atrial dilation, atrial infiltration, atrial fibrosis, systemic disease

Question 21

What are the causes and tx of supraventricular tachycardia?

Answer 21

Causes - congenital (bypass tract), disease (atrial dilation, atrial infiltration, atrial fibrosis, systemic disease)
Tx - digoxin, diltiazem, atenolol, solatol

Question 22

Describe the pathogenesis of atrial fib

Answer 22

• associated with cardiomyopathy
• lose definitive P wave
• diff parts of atria fire at same time, AVN filters signals (300-500bpm)

Question 23

What are the causes and tx of atrial fib?

Answer 23

Causes - atrial dilation, atrial infiltration, atrial fibrosis, occult DCM
Tx - digoxin, diltiazem, atenolol (slow AVN conduction)

Question 24

What are the causes of VPC?

Answer 24

Disease = ventricular mycocardial dilation, inflammation, infiltration, fibrosis
Systemic = anaemia, septicaemia, splenic mass, GDV, pyometra
Metabolic = electrolyte imbalance
Drugs = digoxin, atropine

Question 25

What are the causes of ventricular tachycardia?

Answer 25

``` Disease = ventricular myocardial dilation, inflammation, infiltration, fibrosis Systemic = anaemia, septicaemia, splenic mass, GDV, pyometra Drugs = digoxin, atropine ```

Question 26

What are the tx options for VT?

Answer 26

Lidocaine (IV in emergency), mexilitine, sotalol, amiodarone (long time to reach steady state)

Question 27

What are the causes and tx options of rapid VT?

Answer 27

``` Causes = ventricular myocardial dilation, inflammation, infiltration, fibrosis, trauma, hypoxia Tx = lidocaine, mexilitine, sotalol, amidarone ```