L05: Drugs And The Heart Flashcards
How can drugs act to affect the heart function
Directly
Indirectly
What does the direct action of drugs affect
Rate
Force of contraction in myocytes
What does indirect action of drugs do to affect the heart function
Affect the vasculature
Affect blood volume
Why do we need drugs that affect the rate of the heart
To treat arrhythmia
What is arrhythmia
A disorder where the area is disturbed
Why is the rate disturbed in arrhythmia
Generation and conduction being abnormal
What do anti arrhythmic drugs affect
The ion current which affect the AP
How many classes of drugs does anti arrhythmic drugs have
4
What are the classes of anti arrhythmic drugs dependent on
Which channels they work on
Which channels does class 1 anti arrhythmic drugs work on
Voltage gated sodium channels
What are class 1 anti arrhythmic drugs
Voltage gated sodium channel blockers
Give an example of a class 1 anti arrhythmic drug
Lidocaine
What is the role of class 2 anti arrhythmic drugs by blocking voltage gated sodium channels
Slows depolarisation and increases the refractory period
What channels do class 2 anti arrhythmic drugs work on
Beta 1 adrenoceptors
What are class 2 anti arrhythmic drugs
Beta blockers
What is the role of class 2 anti arrhythmic drugs
Reduce the effect of the sympathetic ns on the SAN
Give an example of a class 2 anti arrhythmic drug
Metropol
Which channels do class 3 anti arrhythmic drugs work on
Potassium channels
What are class 2 anti arrhythmic drugs
Potassium channel blockers
What is the effect of the class 2 anti arrhythmic drugs
Prolong action potential
Give an example of a class 3 anti arrhythmic drug
Amiodarone
Solalol
Which channels do class 4 anti arrhythmic drugs work on
L type (voltage gated calcium channels)
What are class 4 anti arrhythmic drugs
Voltage gated calcium channel blockers
What is the effect of class 4 anti arrhythmic drugs
Reduce depolarisation in SAN and AVN
What are non classified drugs
Drugs that do not get into classifications
Name 2 non classified drugs involved in the heart
Adenosine
Cardiac glycosides
Name an example of cardiac glycosides
Digoxin
Which receptors do adenosine binds to
Adenosine receptors
Where are adenosine receptros found
In the cells of SAN and AVN
What happens when adenosine binds to adenosine receptors
It opens potassium channels
What does opening of potassium channels cause
Hyperpolarisaton
What does hyper-polarisation mean in terms of refractory period
Increases the refractory period and the cell become further away from reaching threshold after hyperpolarisation
What is the role of cardiac glycosides
Increases vagal activity
What does increase in vagal activity do
Decrease AVN conduction rate due to activation of the parasympathetic NS
Why do we need drugs that affect force of contraction
To treat
Anaphylaxis
Heart failure
What happens to cardiac output in cardiac failure
Insufficient for metabolic needs of the body
How do we get cardiac myocytes contraction
Voltage gated calcium channels open due to depolarisation
This causes calcium influx
Calcium influx causes the release of other calcium from the sarcoplasmic reticulum
Calcium release moves regulatory complex from the actin binding site so myosin head binds to actin binding site to form a cross bridge and contraction
If drugs want to affect the force of contraction what do they need to effect
The intracellular calcium levels
Which drugs increase the intracellular calcium
Positive ionotrophic
What are the 3 inotrophic drugs
Sympothomimetics
Cardiac glycosides
Phosphodiesterase inhibitors
Give an example of cardiac glycosides
Digoxin
What is the mechanism of action of cardiac glycosides
Partial inhibition of sodium/potassium ATPase
How does the partial inhibition of sodium/potassium ATPase lead to the increase in intracellular calcium
1) after contraction some calcium will become stored back in the sarcoplasmic reticulum and some will be exchanged by sodium
2) calcium will leave out by a calcium/sodium transporter
3) another channel of sodium/potassium ATPase maintains the sodium concentration
4) dioxin partially acts on the sodium/potassium ATPase which causes a rise in sodium inside the cell
5) this makes the calcium/sodium exchanger less efficiency as there is lots of sodium in side the cell
6) this causes a rise in intracellular calcium
What are the side effects of cardiac glycosides
- Ionic disturbance which can cause excitability and therefore arrhythmia’s
- gynaecomastia- breast growth in both sexes
What are the other issues with using digoxin
Digoxin can interact with other drugs such as diuretics
Give an example of phosphodiesterase inhibitors
Milrinone
What is the mechanism of action of phosphodiesterase inhibitors
Inhibits the enzyme phosphodiesterase
What is the normal role of phosphodiesterase
Break 2nd messenger CAMP
How does calcium levels increase with phosphodiesterase inhibitors
Inhibiting phosphodiesterase increases CAMP
CAMP open calcium channels
Intracellular calcium therefore increases as calcium influx occurs
What channel does verapamil effect
Voltage gated calcium channels
What channel does lidocaine affect
Voltage gated sodium channel
What channel does metropol affect
Beta 1 adrenoceptors
What channel does amiodrone affect
Voltage gated potassium channel
What are the 2 roles digoxin
Increase vagal activity
Partially inhibit sodium/potassium ATPase
What channel does adenosine affect
Potassium channel
