Cardiovascular pharmacology 1 Flashcards
What is inotropy?
Contractility of the cardiac muscle
What is lusitropy?
Relaxation of the ventricles
Affecting preload will have which affect which 2 things?
Circulating volume
Vascular resistance
Affecting afterload will affect the…?
Vascular resistance
What are the overall effects of the following drugs on the heart:
- Positive inotropes
- Lusiotropes
- Positive chronotropes
- Negative inotropes
- Negative chronotropes
- Increase contractility
- Change relaxation
- Increase heart rate
- Decrease contractility
- Decrease heart rate
Which drug is used in the case of atrioventricular block?
Positive choronotropes
Which drug is used in dilated cardiomyopathy cases?
Positive inotropes
- it is disease of the heart muscle that causes the ventricle to stretch and dilate
Rate is determined and altered by which 2 factors?
- CV centre in the medulla oblongata
- Autonomic NS
Conduction of the action potential is reliant on which 3 factors?
- Normal activity of Na+, K+ and Ca++ channels
- Normal intracellular and extracellular levels of these ions
- Correct function of intercalated discs
What may cause control of heart rate and rhythm to go wrong?
- Ectopic pacemakers
- Damage to conducting tissue
- Depression of the CV centre
What is a tacharrhythmia?
A heart rate that exceeds the normal resting rate
What is the problem with tacharrhythmias?
- ↓diastolic filling time = ↓EDVV = ↓SV = ↓CO
- Can be severe and cause fainting and sudden death
- Increased cardiac work leads to myocardial hypertrophy
What factors can we change to slow heart rate?
- Reduce firing rate
- Slow conduction of impulses
Which group of drugs do we use to slow the heart down?
Antidysrhythmics
What is the overall function of each of the 4 classes of antidysrhythmics?
I = drugs which block fast sodium channels II = β blockers III = drugs which prolong the AP by blocking some K channels IV = Drugs which block calcium channels
Out of class I A,B and C, which is a weak, moderate and strong sodium ion channel blockade?
B = weak A = moderate C = strong
How do class I A, B and C each effect the effective refractory period?
A - increases the ERP
B - decreases the ERP
C - doesn’t change the ERP
How does the type of sodium channel effect the drugs?
What is the importance of this?
They are more likely to act on an active sodium channel than an inactive channel.
Reduce heart rate in tachyarrhythmias while not significantly affecting normal heart rates.
What are class I antidysrhythmics dependant on?
Normal extracellular potassium for function
What is the effect of hyper- and hypo- kalaemia on class I antodysrhytmics?
Hyperkalemia increases their function
Hypokalemia reduces their function
Name the Class Ia and Class Ib antidysrhythmic used in practice
Ia = Quinidine Ib = Lidocaine
What are the adverse effects of using quinidine?
- Various rhythm disturbances as blockade persists
- Negative inotropy & vasodilation –> Congestive heart failure
- GI signs, Nervousness, depression
- Need 24 hour monitoring
How are quinidine and lidocaine administered?
Quinidine = Oral route preferred Lidocaine = slow IV parental
What are the predicted effects of Class II antidysrhythmics (Beta blockers)?
- Slow the pacemaker potential by slowing the calcium influx
- Slow conduction through the AV bundle as increases the refractory period
- Also negative inotropy and reduced lusitropy
Where might beta blockers be useful?
- Supraventricular or ventricular tachycardias
- Hypertension
What is the Class II antidysrhythmic used in practice?
Atenolol
What are the mechanisms of action of class III antidysrhythmic?
- Prolong the cardiac AP
- Block potassium ion channels which slows repolarisation (so cells are depolarised for longer, slowing the HR) and increases the refractory period
What is the Class III antidysrhythmic used in practice?
Sotalol
What makes up Sotalol?
A mixture of two isomers:
I-isomer which is a non-selective beta blocker
D-isomer which inhibits potassium ion channels
What are the effects of Class IV antidysrhythmics?
- Block Ca channels
- Shorten the plateau phase
- Slows conduction in the SA and AV nodes
- Cause partial AV block
What effect do Class IV antidysrhythmics have on inotropy and lusitropy?
Negative inotropes
Positive lusitropes
Describe the Class IV antidysrhythmic is used in practice?
Diltiazem
- administered orally and parentally
- coronary and systemic vasodilator
Which class does Digoxin belong to?
Class V -miscellaneous
What is digoxin used for?
- Negative chronotropic effects (decreases HR)
- Enhances the action of the vagus nerve in the heart, mimicking the action of the parasympathetic NS
- Slows conduction through the AV node by increasing the refractory period
What do most bradyarrhythmias require if they are causing clinical signs?
Pacemaker implantation
Which 2 groups of autonomic drugs can be used to treat bradyarrhythmias?
- Sympathomimetics
- Anticholinergics
