CPT S10 - Cardiac Arrhythmia Drugs

Question 1

What is an arrythmia?

Answer 1

Heart condition where disturbances in;
-Pacemaker impulse formation
-Contraction inpulse conduction
-Combination of the above
Result in rate and/or timing of myocardial contraction that generates insufficient cardiac output

Question 2

Describe Phase 0 of the action potential of a cardiac myocyte

Answer 2

Cell depolarises
Na channels open
Influx of Na

Question 3

Describe Phase 1 of the action potential of a cardiac myocyte

Answer 3

Cell slightly repolarises
Na channels close
K channels open
Efflux of K

Question 4

Describe Phase 2 of the action potential of a cardiac myocyte

Answer 4

Little change in polarisation
Ca channels open
Ca influx
Continued K efflux

Question 5

Describe Phase 3 of the action potential of a cardiac myocyte

Answer 5

Repolarisation of cell
Ca channels close
K channels remain open

Question 6

Describe Phase 4 of the action potential of a cardiac myocyte

Answer 6

Return to baseline resting potential
K channels close
Regulated by Na/K ATPase

Question 7

Describe Phase 4 of the action potential of a cardiac nodal cell

Answer 7

Very slow depolarisation
Slow influx of Na through open channels
“funny current”

Question 8

Describe Phase 0 of the action potential of a cardiac nodal cell

Answer 8

Fast depolarisation
Ca channels triggered to open at threshold
Ca influx

Question 9

Describe Phase 3 of the action potential of a cardiac nodal cell

Answer 9

Repolarisation
K channels open
Ca channels close
K influx

Question 10

How many phases are there in the action potential of a cardiac myocyte?

Answer 10

5 (0-4)

Question 11

How many phases are there in the action potential of a cardiac cell in a node?

Answer 11

3 (0, 3, 4)

Question 12

What are the effects of Na channel blockers on the heart?

Answer 12

Slows phase 0 of the cardiac myocyte
So;
-Slower conduction
-Longer action potential duration
-Slower heart rate

Question 13

What are the effects of β-blockers on the heart?

Answer 13

Reduce/prevent sympathetic stimulation via β1 receptors
Stimulation of these receptors would result in increased contractility and heart rate
So antagonism results in longer nodal refractory period and so reduced heart rate
Also reduced contractility

Question 14

What are the effects of K channel inhibitors on the heart?

Answer 14

Increased duration of phase 3 of the cardiac myocyte

Increased action potential duration

Question 15

What are the effects of drugs which inhibit Ca channels on the heart?

Answer 15

Increase duration of phase 0 of nodal cardiac cells
Slower depolarisation
So slower nodal conduction
So reduced heart rate
Also reduce likelihood of phase 4 spontaneous depolarization in cardiac myocytes