Drugs On The Circulation (9) Flashcards
What are the main abnormalities that can affect the heart rate or rhythm?
- Bradycardia
- Tachycardia
- Atrial fibrillation
- Ventricular fibrillation
- Atrial flutter
What are the main effects drugs can have on the heart?
- Rate and rhythm
- Force of myocardial contraction
- Peripheral resistance and blood flow
- Blood volume
What are the three main causes of arrhythmia?
- Ectopic pacemaker activity
- Afterdepolarisations
- Reentry loop
What does ectopic pacemaker activity mean?
- Damaged myocardium becomes depolarised and spontaneously active
- Latent pacemaker region activated due to ischaemia
- Dominates over SAN
What is meant by a reentry loop?
- Conduction delay
- Conduction is blocked by damaged region
- If there’s incomplete conduction damage excitation can take a longer route through damaged area, mixing signals
What is meant by an afterdepolarisation?
- Abnormal depolarisations following AP
What are the 4 basic classes of anti-arrhythmic drugs?
- 1) blocks voltage sensitive Na channels
- 2) antagonists of B-adrenoreceptors
- 3) block K channels
- 4) block Ca channels
Give an example of a class I anti-arrhythmic drug and what does it do?
- Lidocaine only blocks open/inactive voltage gated Na channels
- Use dependent block
- Used following MI if ventricular tachycardia shown
- Damaged areas of myocardium may be depolarised and fire automatically, lidocaine blocks Na channels to prevent automatic firing and so less tachycardia
Give an example of a class II anti-arrhythmic drug and what does it do?
- B blockers
- Blocks sympathetic action to decrease slope of pacemaker potential in SAN
- Prevents ventricular arrhythmias (may be due to increased sympathetic action)
- Reduces O2 demand: reduce myocardial ischaemia
- Slow conduction in AVN can prevent supraventricular tachycardia
What do class III anti-arrhythmics do?
- Prolong AP
- Lengthens absolute refractory period
- Prevents another AP occurring too soon
What do class IV drugs do?
- Decrease slope of pacemaker AP at SAN
- Decrease AVN conduction
- Decrease force of contraction (can also cause some coronary and peripheral vasodilation)
What role does adenosine have as an anti-arrhythmic?
- Enhances K conduction
- Hyperpolarises cells of conducting tissue
- Decreases cAMP levels
- Short lived
- alpha 1 receptors at AVN
What are the main features of heart failure?
- Decreased cardiac output
- Decreased force of contraction
- Decreased tissue perfusion
- Oedema
What drugs are there to treat heart failure by increasing cardiac output?
- Positive inotropes
- Cardiac glycosides
- B- adrenergic agonists
What drugs are there to increase myocardial contractility?
- Cardiac glycosides
- Digoxin to block Na/K ATPase
- B adrenoreceptor agonists
What is the action of cardiac glycosides?
- Block Na/K ATPase
- Increase in Na concentration inside the cell lead ps inhibition of NCX
- Increases Ca concentration inside cardiac myocytes: -ve ionotropic effect & increase in contraction force
- Increases vagal activity: slows AV conduction, slows heart rate
What do ACE inhibitors do?
- Decrease vasomotor tone- decreasing blood pressure
- Reduce after load of heart
- Decrease fluid retention- decrease blood volume
- Reduce preload and work load of heart
Which two drugs are the main alleviators of workload for the heart?
- B blockers
- Diuretics (decreases blood pressure)
How is angina treated?
- Reduce the workload of the heart: B blockers, Ca channel antagonists and organic nitrates
- Improve blood supply to heart: organic nitrates and Ca channel antagonists
What do the organic nitrates do?
- React with triols (-SH) groups in vascular smooth muscle causes NO2- to be released
- NO2- -> NO (powerful vasodilator)
How does NO cause vasodilation?
- NO stimulates guanylate cyclase
- Guanylate cyclase acts as catalyst for GTP -> cGMP
- cGMP -> PKG -> Decreased Ca conc inside the cell -> vasodilation
What is the primary action of organic nitrates?
- Lowers preload by venodilation
- Decreases workload of heart
- Heart fills less therefore force of contraction decreases
- Lowers O2 demand
What is the secondary action of organic nitrates?
- Acts on coronary arteries to improve O2 delivery to ischaemic myocardium
- Acts on collateral arteries to improve blood supply to all of the heart including ischaemic areas
What heart conditions can increase the risk of forming a thrombus?
- Atrial fibrillation
- Acute MI
- Mechanical prosthetic heart valves
Give some examples of anticoagulants and what do they do?
- Heparin (IV): - inhibits thrombin
- short term - Fractionated heparin (subcutaneous)
- Warfarin (orally): - antagonises action of Vit K
- long term
What is a good example of an anti platelet drug used after an MI?
- Aspirin
What are the causes of hypertension?
- Increase in blood volume
- Increased TPR
What are the drugs that could be used in the treatment of hypertension?
- Diuretic
- ACE inhibitors
- B blockers
- Ca channel blockers (vasodilation)
- alpha 1 adrenoceptor antagonists (vasodilation)
