Case Studies

Question 1

Which would produce a louder heart sound - an increased or decreased pressure gradient between the atria and ventricles?

Answer 1

Increased pressure gradient - heart sound is valve snapping closed

Question 2

What could be two features of the ECG trace in a horse in atrial fibrillation?

Answer 2

There are too many P waves

The R-R intervals are irregular (heart rate)

Question 3

What are the possible sources of electrical impulses in atrial fibrillation (3)?

Answer 3

The SA node
The ectopic pacemaker tissue in the atrium
The AV node

Question 4

What are the two major ways that atrial fibrillation impacts upon ventricular filling? (EDV)

Answer 4

1. Increased and irregular frequency of impulses means ventricular diastole is sometimes cut short, leading to an irregular EDV and thence irregular stroke volume from beat to beat
2. The atria are not contracting which, at rest, contribute 20% of ventricular filling prior to ventricular systole. As HR climbs, this contribution rises, and the lack of coherent atrial electrical activity becomes more clinically significant for the animal

Question 5

What two factors contribute to pulse pressure? Which of these has to be smaller to make the palpable pulse weaker?

Answer 5

PP = systolic pulse - diastolic pulse
Systolic pulse must be smaller to reduce this value
* if diastolic pressure were larger, the value would also be reduced

Question 6

What are three factors that could have potentially contributed to the development of atrial fibrillation in a horse?

Answer 6

1. Myocardial disease
2. Large heart size
3. ++ vagal tone

Question 7

What is the dose and admin scheme for quinidine?

Answer 7

20mg/kg (usually about 10g) every 2h until effect is seen or animal starts to show clinical signs of toxicity

Question 8

What are the expected clinical signs of quinidine toxicity in the horse? (4)

Answer 8

Anorexia, depression, in-coordination and colic

Question 9

What kind of continuous monitoring should be performed on a horse starting a quinidine trial?

Answer 9

ECG

Question 10

What are three drugs that are used in the management of atrial fibrillation in dogs? Which is used most commonly?

Answer 10

Digoxin - first line therapy
Ca2+ channel blockers
Beta blockers (propanolol?)

Question 11

What contributes to the variable P wave in the ECG trace of an animal with a fib?

Answer 11

Variable direction of impulses travelling around the atrial muscle
Variable size of atrial mass depolarising at any given time

Question 12

Which part of the ECG reflects LV mass?

Answer 12

R wave amplitude

Question 13

Can AV valve incompetence explain a pulse defecit?

Answer 13

No - would get regular SV , despite reduced CO

Question 14

How does quinidine work?

Answer 14

Reduces Na+ entry to cardiomyocytes through the voltage gated Na+ channels (slows upswing). In so doing, it increases the electrical threshold of membrane excitability in cardiomyocytes

Question 15

With what event does the threshold for APs in pacemaker cells of the heart correspond?

Answer 15

Threshold for opening of voltage gated Ca2+ channels

Question 16

What are three things that could increase the intensity of heart sounds ?

Answer 16

Increased contractility
Increased cardiac filling
Increased EDV

Question 17

Which part of the ECG represents conduction of the impulse through the AV node?

Answer 17

The P-R interval