Antiarrhythmics - Class IV (Ca2+ channel blockers)

Question 1

The cardiac electrophysiology in a pacemaker cell has only 3 phases, which ultimately lead to an action potential (as seen in the image). What is occurring at stage 4?

1 - pacemaker potential phase
2 - depolarisation phase
3 - Leaky K+ phase
4 - Ca2+ leaking into cell phase

Answer 1

1 - pacemaker potential phase

• similar to resting membrane potential
• around -65 mV

Question 2

The cardiac electrophysiology in a pacemaker cell has only 3 phases, which ultimately lead to an action potential (as seen in the image).To move between phase 4 and 0, there is a special type of channel located on the pacemaker cells that allows Na+ to flow into the pacemaker cells, raising the action potential to -50 mV. What is the channel called?

1 - Na+ channel
2 - Na+/K+ ATPase channel
3 - hyperpolarization-activated cyclic nucleotide-gated channels (HCN)
4 - Na+/Ca2+ co-transport

Answer 2

3 - hyperpolarization-activated cyclic nucleotide-gated channels (HCN)

• important when cells hyperpolarise following an action potential, these channels help the pacemaker cell get close to action potential and fir again
• called the funny current

Question 3

The cardiac electrophysiology in a pacemaker cell has only 3 phases, which ultimately lead to an action potential (as seen in the image). The funny current (Na+ entering the pacemaker cells) then enters phase 0. What is this phase called?

1 - pacemaker potential phase
2 - depolarisation phase
3 - Leaky K+ phase
4 - Ca2+ leaking into cell phase

Answer 3

2 - depolarisation phase

• Na+ enters cell through HCN
• Ca2+ enters the cell through Ca2+ channels
• pacemaker cells membrane potential becomes + (around 10mV

Question 4

The cardiac electrophysiology in a pacemaker cell has only 3 phases, which ultimately lead to an action potential (as seen in the image). In phase 0 Na+ and Ca2+ enter pacemaker cells causing depolarisation (aprox 10 mV). The pacemaker cell then enters phase 3. What of the following then happens here?

1 - Ca2+ channels close
2 - Na+ channels remain open
3 - K+ channels open and K+ leaves the cell
4 - all of the above

Answer 4

4 - all of the above

• lots of K+ channels
• overall this causes the membrane potential to drop called repolarisation
• phase 4 begins again

Question 5

In a myocyte cell the cardiac electrophysiology has 5 phases (0-4), which ultimately lead to an action potential (as seen in the image). Phase 0 is the resting phase (-90mV). What then enters the myocyte through gap junctions that raises the resting membrane potential (-90mV) to the threshold potential (-70mV)?

1 - Na+
2 - K+
3 - Ca2+
4 - Mg+

Answer 5

3 - Ca2+

Question 6

In a myocyte cell the cardiac electrophysiology has 5 phases (0-4), which ultimately lead to an action potential (as seen in the image). Phase 0 occurs when the the membrane potential reaches -70mV. Which channels then open causing depolarisation, reaching around 20mV?

1 - Na+
2 - K+
3 - Ca2+
4 - Mg+

Answer 6

1 - Na+

Question 7

In a myocyte cell the cardiac electrophysiology has 5 phases (0-4), which ultimately lead to an action potential (as seen in the image). Following depolarisation, we reach phase 1, called initial repolarisation. Which 2 of the following occurs here?

1 - Na+ channels close
2 - K+ channels open and K+ leaves the cell
3 - Ca2+
4 - Mg+

Answer 7

1 - Na+ channels close
2 - K+ channels open and K+ leaves the cell

• causes a drop in membrane potential

Question 8

In a myocyte cell the cardiac electrophysiology has 5 phases (0-4), which ultimately lead to an action potential (as seen in the image). Following initial repolarisation (phase 1), to stop the myocyte going into full repolarisation, another channel opens and the membrane potential plateaus, called the plateau phase. Which channel opens to maintain this plateau phase (phase 2)?

1 - Na+ channels
2 - K+ channels
3 - Ca2+ channels
4 - Mg+ channels

Answer 8

3 - Ca2+

• Ca2+ flows into the cell
• membrane charge is maintained
• responsible for heart contraction

Question 9

In a myocyte cell the cardiac electrophysiology has 5 phases (0-4), which ultimately lead to an action potential (as seen in the image). Following the plateau phase (phase 2) which is when the heart contracts, which of the following occurs in phase 3, called repolarisation?

1 - Ca2+ channels close
2 - K+ channels remain open
3 - Ca2+ is pumped out of the cell
4 - all of the above

Answer 9

4 - all of the above

• myocyte returns to resting membrane potential of around -90mV

Question 10

When looking at an ECG, what does the P wave represent in relation to an an action potential?

1 - sum of depolarisation in all atrial myocytes
2 - sum of depolarisation in all ventricle myocytes
3 - sum of repolarisation in all atrial myocytes
4 - sum of repolarisation in all ventricle myocytes

Answer 10

1 - sum of depolarisation in all atrial myocytes

Question 11

When looking at an ECG, what does the QRS wave represent in relation to an an action potential?

1 - sum of depolarisation in all atrial myocytes
2 - sum of depolarisation in all ventricle myocytes
3 - sum of repolarisation in all atrial myocytes
4 - sum of repolarisation in all ventricle myocytes

Answer 11

2 - sum of depolarisation in all ventricle myocytes

• atrial myocytes also repolarise here as well, but this is masked by the QRS

Question 12

When looking at an ECG, what does the ST segment represent in relation to an an action potential?

1 - sum of depolarisation in all atrial myocytes
2 - sum of depolarisation in all ventricle myocytes
3 - sum of repolarisation in all atrial myocytes
4 - plateau phase

Answer 12

4 - plateau phase

• this is when the ventricle contract and pump blood

Question 13

When looking at an ECG, what does the T wave represent in relation to an an action potential?

1 - sum of depolarisation in all atrial myocytes
2 - sum of depolarisation in all ventricle myocytes
3 - sum of repolarisation in all ventricle myocytes
4 - plateau phase

Answer 13

3 - sum of repolarisation in all ventricle myocytes

Question 14

When looking at an action potential, which 2 phases would Ca2+ channel blockers be effective?

1 - phase 2 in myocytes
2 - phase 0 in myocytes
3 - phase 3 in pacemaker cells
4 - phase 0 in pacemaker cells

Answer 14

1 - phase 2 in myocytes
3 - phase 3 in pacemaker cells

Question 15

Calcium is released into the smooth muscle of the blood vessels and cardio myocytes which contribute to vasoconstriction. What is the mechanism of action of Ca+ channel blockers?

1 - binds and inhibits angiotensin II receptors
2 - inhibits ACE
3 - inhibit beta receptors
4 - binds and inhibits L-type Ca2+ channels

Answer 15

4 - binds and inhibits L-type Ca2+ channels

• non competitive antagonist
• ⬇️ Ca2+ in vascular and cardiac cells and inhibit vasoconstriction so good for blood pressure
• reduces Ca2+ released into myocytes lowering force of contraction

Question 16

In addition to acting in smooth muscle arterioles (cause vasodilation) and, cardiac myocytes (reduce contraction force) where else can Ca2+ affect?

1 - AV node
2 - SA node
3 - accessory pathways
4 - all of the above

Answer 16

1 - AV node

• reduce AV conduction

Question 17

Which of the following are calcium channel blocker medications that we need to know from our core drug list?

1 - Ramipril, Diltiazem, Verapamil
2 - Amlodipine, Ramipril, Verapamil
3 - Amlodipine, Bisoprolol, Verapamil
4 - Amlodipine, Diltiazem, Verapamil

Answer 17

4 - Amlodipine, Diltiazem, Verapamil

• remember DAV

Question 18

Which of the following drugs is the first line drug for hypertension, using the cuts offs below in a patient aged >55 y/o and black ethnicity?

• Stage 3: SBP >180 mmHg Treat immediately
• Stage 2: BP >160/100 mmHg Treat once confirmed on 24hr BP
• Stage 1: BP > 140/90 mmHg Treat if end-organ damage or if diabetic

1 - ace inhibitors (ACE-I)
2 - calcium channel blockers
3 - alpha blockers
4 - angiotensin receptor2 blockers

Answer 18

2 - calcium channel blockers

• Amlodipine would be the first choice for hypertension
• Verapamil is 1st choice for arrhythmias
• Diltiazem is bit of cardiac and vascular
• remember DAV
• essentially when an ACE-I or ARB-II are unsuitable

Question 19

Calcium channel blockers (CCB) are indicated in patients with ischaemic heart disease. There are 2 types of CCB:

• dihydropyridines
• nondihydropyridines

Which of these acts predominantly on vascular cells and which acts predominantly on cardiac cells?

Answer 19

• dihydropyridines =
  vascular cells
• nondihydropyridines = cardiac cells

Question 20

There are 3 key calcium channel blockers that we need to be aware of: Amlodipine, Diltiazem, Verapamil. Which of these 3 drugs is a dihydropyridines, and preferrentially targets the vasculature cells?

1 - Amlodipine
2 - Diltiazem and Verapamil
3 - Amlodipine and Diltiazem
4 - all 3 drugs

Answer 20

1 - Amlodipine

Question 21

There are 3 key calcium channel blockers that we need to be aware of: Amlodipine, Diltiazem, Verapamil. Which of these 3 drugs is a non-dihydropyridines, and preferentially targets the cardiac cells?

1 - Amlodipine
2 - Diltiazem and Verapamil
3 - Amlodipine and Diltiazem
4 - all 3 drugs

Answer 21

2 - Diltiazem and Verapamil

• varapamil is the most cardioselective
• diltiazem has good anti-arrhythmic qualities

Question 22

There are 3 key calcium channel blockers that we need to be aware of: Amlodipine, Diltiazem, Verapamil. Which of these 3 drugs is indicated in controlling heart rate in patients with supraventricular arrhythmias, including atrial fibrillation, atrial flutter and supraventricular tachycardia?

1 - Amlodipine
2 - Diltiazem and Verapamil
3 - Amlodipine and Diltiazem
4 - all 3 drugs

Answer 22

2 - Diltiazem and Verapamil

• non-dihydropyridines which are the most cardiac cell specific
• varapamil is the most cardioselective

Question 23

Verapamil and Diltiazem are indicated in which of the following?

1 - Atrial fibrillation - slows ventricular rate
2 - Supraventricular tachycardia
3 - IHD
4 - all of the above

Answer 23

1 - Atrial fibrillation - slows ventricular rate
2 - Supraventricular tachycardia

• Ca2+ channel blocker can inhibit phase 2 in myocytes and phase 3 in pacemaker cells, so reducing AV firing

Question 24

Verapamil and Diltiazem are the two most cardiac selective calcium channel blockers. Which of the following is NOT an affect they have on the heart?

1 - suppress cardiac conduction, particularly across the AV node
2 - reduce ventricular rate
3 - increase contractility
4 - reduce afterload and therefore myocardial oxygen demand

Answer 24

3 - increase contractility

• they actually reduce contractility

Question 25

There are 3 key calcium channel blockers that we need to be aware of: Amlodipine, Diltiazem, Verapamil. Verapamil is a non-dihydropyridines, and preferentially targets the cardiac cells. Which of the following is NOT a common adverse effect of Verapamil?

1 - constipation
2 - heart block
3 - cardiac failure
4 - ankle swelling
5 - bradycardia

Answer 25

4 - ankle swelling
- not common with verapamil

• Diltiazem can affect cardiac and vascular cells, so can cause these effects

Question 26

Verapamil and diltazem should be used with caution in patients with impaired left ventricular function. Why is this?

1 - precipitate or worsen heart failure
2 - vasodilatory affects increase pressure on heart
3 - increase SVR and therefore the pressure on the heart
4 - damage the aortic valve

Answer 26

1 - precipitate or worsen heart failure

Question 27

Verapamil and diltazem should be avoided in patients with AV nodal block. Why is this?

1 - can cause flushing
2 - can cause headaches and increase heart rate
3 - can cause heart block
4 - increase SVR and therefore the pressure on the heart

Answer 27

3 - can cause heart block

• if AV node conduction is slow already, Verapamil and diltazem could make it worse

Question 28

There are 3 key calcium channel blockers that we need to be aware of: Amlodipine, Diltiazem, Verapamil. Verapamil and Diltiazem are non-dihydropyridines, and preferentially targets the cardiac cells. These drugs should not be used in conjunction with which other class of anti-hypertensives?

1 - ACE inhibitors
2 - Angiotensin-II receptor blockers
3 - α-blockers
4 - β-blockers

Answer 28

4 - β-blockers

• non-dihydropyridines and B-blockers are negatively inotropic and chronotropic
• inotropic affects contractility of the heart
• chronotropic affects the rate of the heart
• together both could cause heart failure, bradycardia or asytole and should only be used under close supervision

Question 29

What is the standard dose patients are prescribed verapamil for supreventrivcular tachycardia?

1 - 4-20mg 8/h
2 - 30-50mg 8/h
3 - 50-90mg 8/h
4 - 40-120mg 8/h

Answer 29

4 - 40-120mg 8/h