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CVS > Drugs Affecting the Heart > Flashcards

Drugs Affecting the Heart Flashcards

1
Q

What are the criteria for classifying cardiac arrhythmias?

A

1 - Origin of the arrhythmia.

2 - Effect on heart rate.

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2
Q

What is the current classification system for antiarrhythmic drugs?

A

The Vaughan Williams classification (classes I-IV).

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3
Q

In non-pacemaker cells, which ion is responsible for the initial rising phase of action potentials?

A

Na+.

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4
Q

What is the target of class I antiarrhythmic drugs?

What is their effect on the target?

What is their effect on the profile of electrical activity of the heart?

A
  • Voltage gated Na+ channels.
  • They block the channels.
  • They alter the slope of the rising phase of cardiac action potentials.
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5
Q

List two examples of class I antiarrhythmic drugs.

A

1 - Lidocaine.

2 - Flecainide.

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6
Q

What is the target of class II antiarrhythmic drugs?

What is their effect on the target?

What is their effect on the profile of electrical activity of the heart?

A
  • Beta receptors.
  • They block the receptors.
  • They decrease sympathetic effect on cardiac action potentials and in turn decrease the slope of pacemaker potential.
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7
Q

Give an example of a class II antiarrhythmic drug.

A

Metoprolol.

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8
Q

What is the target of class III antiarrhythmic drugs?

What is their effect on the target?

What is their effect on the profile of electrical activity of the heart?

A
  • K+ channels.
  • They block the channels.
  • They prolong the repolarisation phase of the action potential.
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9
Q

List two examples of class III antiarrhythmic drugs.

A

1 - Amiodarone.

2 - Sotalol.

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10
Q

What is the target of class IV antiarrhythmic drugs?

What is their effect on the target?

What is their effect on the profile of electrical activity of the heart?

A
  • L-type Ca2+ channels.
  • They block the channels.
  • They prolong the action potential where Ca2+ influx is implicated (mostly on nodal cells but also on the plateau of contractile cells).
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11
Q

Give an example of a class IV antiarrhythmic drugs.

A

Verapamil.

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12
Q

For which area of the heart does verapamil exhibit relative cardioselectivity?

Why?

A
  • The AV node.

- Because the AV node has a particularly high concentration of L-type Ca2+ channels.

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13
Q

List 2 drugs that are not classified under the Vaughan-Williams classification system.

A

1 - Adenosine.

2 - Cardiac glycosides such as digoxin.

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14
Q

Where in the heart are adenosine receptors found?

A

In the SA and AV nodes.

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15
Q

What occurs as a result of adenosine binding to adenosine receptors?

What is the consequence of this event on the profile of electrical activity of the heart?

A
  • K+ channels open.

- This will cause hyperpolarisation, and therefore a longer refractory period.

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16
Q

What type of drug is caffeine?

A

An adenosine receptor antagonist.

17
Q

List the effects of digoxin on heart activity.

A

1 - Increased vagal activity.

2 - Decreased AV conduction rate.

3 - Decreased ventricular conduction rate.

18
Q

On which components of the body does digoxin act?

A

The CNS and on myocytes directly.

19
Q

List 4 criteria that are relevant in determining drug choice for cardiac arrhythmias.

A

1 - Type of arrhythmia.

2 - Cause of arrhythmia.

3 - Comorbidities.

4 - Drug interactions.

20
Q

List 2 conditions for which a drug that affects force of contraction might be needed.

A

1 - Heart failure.

2 - Anaphylaxis.

21
Q

In a well-functioning heart, what is the determinant of force of contraction?

A

Intracellular Ca2+.

22
Q

What are the 3 classes of inotropic drugs?

A

1 - Sympathomimetics (not covered in this lecture).

2 - Cardiac glycosides.

3 - Phosphodiesterase inhibitors.

23
Q

What is the effect of inotropic drugs on the physiological conditions of the myocyte?

A

They increase intracellular Ca2+.

*Ino = fibre, tropic = change.

24
Q

Describe the mechanism of action for cardiac glycosides such as digoxin.

A
  • Cardiac glycosides partially inhibit the Na+/K+ ATPase.
  • This diminishes the concentration gradient of Na+, which is normally abundant on the outside of the myocyte membrane.
  • This decreases the functioning of the Ca2+ / 3Na+ antiporter, which relies on the concentration gradient of Na+ to export Ca2+.
  • This results in an increased intracellular Ca2+.
25
Q

Why are there many side effects of cardiac glycosides?

List 4 side effects of cardiac glycosides.

A
  • Because Na+/K+ ATPases are ubiquitous throughout the body.

1 - Arrhythmia.

2 - Neurological disturbance.

3 - GIT problems.

4 - Gynaecomastia

26
Q

Why is gynaecomastia a side effect of digoxin?

A

Because digoxin has a similar structure to oestrogen.

27
Q

Explain the drug interaction between digoxin and diuretics.

A
  • Some diuretics can cause hypokalaemia.
  • Digoxin inhibits the Na+/K+ ATPase by binding to the same site of the ATPase as K+.
  • A decrease in K+ therefore results in an increased effect of digoxin as more binding sites become available.
28
Q

List 2 phosphodiesterase inhibitors.

A

1 - Milrinone.

2 - Enoximone.

29
Q

What is the function of phosphodiesterase?

A

Catalyse the breakdown of intracellular messengers such as cAMP and cGMP.

30
Q

What is the role of cAMP in cardiac myocytes?

A

They increase opening of the Ca2+ ion channels, causing calcium-induced calcium release (positive inotropic effect).

31
Q

Describe the mechanism of action for phosphodiesterase inhibitors in cardiac myocytes.

A
  • Inhibiting phosphodiesterase leads to an increase in intracellular cAMP.
  • An increase in intracellular cAMP leads to an increase in Ca2+ channel opening.
  • An increase in open Ca2+ channels leads to an increase in intracellular Ca2+, and therefore an increase in calcium-induced calcium release.
32
Q

Which type of phosphodiesterase is most abundant in the heart?

A

Type 3 phosphodiesterases.

33
Q

How does the half life of phosphodiesterase inhibitors compare to that of other inotropic drugs?

A

Phosphodiesterase inhibitors have a particularly short half life.

34
Q

Which section of the cardiac action potential is affected by ivabradine?

A

The pacemaker potential.

35
Q

List 3 types of drugs that affect the heart but do not act directly on the heart.

Why do these drugs have an impact on the heart?

A

1 - Diuretics (decrease blood volume).

2 - Vasodilators (increase blood volume).

3 - Angiotensin converting enzyme (ACE) inhibitors (decrease blood pressure).

CVS (18 decks)

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