13 - Drugs on the CVS Flashcards
What are some causes of arrhythmias?
Tachycardia: Ectopic pacemaker, afterdepolarisations, AF, re-entry loop
Bradycardia: sick sinus syndrome, drugs, AV block
What are the two different types of after depolarisations?
Delayed: if intracellular Ca high more likely to occur as reverses NCX and can lead to tachycardia
Early: depolarisation as recovery occuring, if AP prolonged (long QT)
EACH OF THESE CAN TRIGGER AN ACTION POTENTIAL
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What is the rentrant mechanism of generating arrhythmias?
If you have multiple reentrant circuits you will get atrial fibrillation
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What is AV nodal reentry?
Leads to tachycardia
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What is ventricular pre-excitation?
Accessory pathway between atria and ventricles so impulse reaches ventricles earlier than it should so tachy
e.g Wolff-Parkinson-White syndrome
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What are the four different classes of anti-arrhythmic drugs?
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How do voltage-depend Na channel blockers prevent arrhythmia?
e. g Lidocaine
- They block depolarised tissue preventing automatic firing so A.P refractory period is longer, decreasing heart rate
- Damaged myocardium may be depolarised and fire automatically but these drugs stop this
- May give IV if patient has VT after MI to stop VF but not used prophylatically
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How do B-adrenoreceptorr antagonists help treat arrhythmias and what are some examples?
- Atenolol, Propranolol
- Block sympathetic action. Decrease slope of pacemaker potential in SA and slow conduction at AV
- Stops SVTs
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How do K+ channel blockers prevent arrhythmias?
- Prolong action potential, increasing absolute refractory period and heart rate but actually pro-arrythmic
- NOT VERY GOOD
What is the absolute refractory period of the ventricles corresponding with on the ECG?
- QT syndrome
- Longer QT can lead to torsades (ventricular tachycardia) which can turn into VF
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What is the only K+ channel blocker that is used?
- Amiodarone as non selective to K+
- Treats tachycardia associated with reentry loop syndrome called Wolff-Parkinson-White
- Can supress ventricular arrhythmias post MI
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How do Ca channel blockers prevent arrhythmias and what are some examples?
- Verapamil, diltiazem (Non-hydropyridines)
- Decrease slope of action potential at SAN, decrease AV nodal conduction and decreases force of contraction
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How do dihydropyridine Ca channel blockers differ to nondihydropyridines?
Dihydropyridines act on vascular smooth muscle, e.g nifedipine, to act as anti-hypertensive
How does adenosine act as an anti-arrhytmic drug?
- Produced endogenously but can be given IV
- Act on A1 receptors at AV node (short half life)
- Enhances K+ conductance hyperpolarising cell
- Terminates reentry SVT
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What is the definition of heart failure?
Chronic failure of the heart to provide sufficient output to meet the body’s requirements - can lead to peripheral and pulmonary oedema