6. Cardiac Arrhythmias Flashcards
How do class 1 drugs act?
Block Na channels
Marked slowing conduction in tissue
Minor effects on action potential duration
How do class 2 drugs act?
Beta blockers
Reduction in effluent of Ca
Diminish phase 4 depolarisation and automaticity
How do class 3 drugs act?
Block K channels
Increase action potential duration
Longer refractor period
How do class 4 drugs act?
Calcium channel blockers
Decrease inward Ca currents resulting in a decrease of phase 4 spontaneous depolarisation
Affect plateau phase of action potential
What are the effects of Ca channel blockers on slow action potential (SAN, AVN)?
Extend slope of phase 0
Increase refractory period
Harder for node to beat again
Where are fast action potentials found?
Cardiac and atrial myocytes
Where are slow action potentials found?
SA or AV node
What causes a re-entry rhythm?
- An accessory pathway in heart connecting atrium to ventricle
- Present only in small populations
- Wolf-Parkinson-White syndrome (WPW) - Two pathways within AVN
- causes supraventricular tachycardia (AVNRT) - Scarring
In general, what do drugs work to do in arrhythmias?
Reduce abnormal impulse generation
Slow conduction through tissue
Block AV node to terminate some rhythms
Give 2 examples of class 1b agents
Lidocaine (IV)
Mexiletine (oral)
What are the effects of class 1B agents on cardiac activity?
No change in phase 0 in normal tissue
Action potential duration slight decreased
Increase threshold (Na+)
Decrease phase 0 conduction in fast beating or ischaemic tissue
What are the effects of class 1B agents on ECG?
None in normal heart
In fast beating or ishcaemic heart, prolongation of QRS
What are the uses of class 1B agents?
Acute - ventricular tachycardia
Not used in atrial arrhythmias or AV junctional arrhythmias
What are the side effects of class 1B drugs?
Less pro arrhythmic than class 1A Dizziness, drowsiness Abdominal upset
Name 2 class 1C agents
Flecanide Propafenone (used less)
What are the effects of class 1C agents on cardiac activity?
Substantially decreased phase 0 (Na+) in normal heart
Decreased automaticity (increased threshold)
Increased action potential duration and increased refractory period
What are the effects of class 1C agents on ECG?
Prolonged PR, QRS and QT
What are class 1C agents used for?
Wide spectrum
Used for supraventricular arrhythmias (fibrillation and flutter)
Premature ventricular contractions (ectopic beats)
WPW syndrome
What are the side effects of class 1C agents?
Pro-arrhythmia and sudden death especially with chronic use and in structural heart disease
Increase ventricular response to supraventricular arrhythmias
CNS and GI effects
Name some class II agents
Propranolol
Bisoprolol
Metoprolol
Esmolol (very short acting)
What are the effects of class II agents on cardiac activity?
Increase action potential duration and refractory period in AV node to slow AV conduction velocity
Decrease phase 4 depolarisation
What are the effects of class II agents on ECG?
Prolonged PR
Slower heart rate
What are class II agents used for?
Treating sinus and catecholamines dependent tachycardia
Converting reentrant arrhythmias at AV node
Protecting the ventricles from high atrial rates in atrial flutter or atrial fibrillation
What are the side effects of class II agents?
Bronchospasm
Hypotension
Name some class III agents
Amiodarone
Sotalol
What are the cardiac effects of amiodarone?
Increase refractory period and action potential duration Decrease phase 0 and conduction Increase threshold Decrease phase 4 Decrease speed of AV conduction
What are the effects of amiodarone on ECG?
Prolonged PR, QRS and QT
Decreased heart rate
What is amiodarone used for?
Effective for most arrhythmias
What are the side effects of amiodarone?
Increase with time Pulmonary fibrosis Hepatic injury Increase LDL cholesterol Thyroid disease Photosensitivity Optic neuritis
What are the cardiac effects of sotalol?
Increased Acton potential duration and refractory period in atrial and ventricular tissue
Slow phase 4
Slow AV conduction
What are the ECG effects of sotalol?
Prolonged QT
Reduced heart rate
What are the uses of sotalol?
Supraventricular and ventricular tachycardia
What are the side effects of sotalol?
Proarrhythmia, fatigue, insomnia
Name 2 class IV agents
Verapamil
Diltiazem
What are the cardiac effects of class IV agents?
Slow conduction through AV
Increased refractory period in AV node
Increase slope of phase 4 in SA to slow HR
What are the effects on ECG of class IV agents?
Prolong PR
May increase or decrease heart rate depending on blood pressure response and baroreflex
What are the uses of class IV agents?
Control ventricles during supraventricular tachycardia
Convert supraventricular tachycardia
Can be used in asthma patients when beta blockers can’t
What are the side effects of class IV agents?
Caution when partial AV block present, can get asystole if beta blocker is on board
Caution when hypotension, decreased cardiac output
Some GI problems (constipation)
What is the mechanism of adenosine?
Natural nucleoside that binds A1 receptors and blocks adenylyl cyclase thus reducing cAMP which in turn activated K+ currents in AV and SA node, causing hyperpolarisation
Therefore leads to decrease in heart rate
What are the cardiac effects of adenosine?
Slows AV conduction
What are the uses of adenosine?
Convert re-entrant supraventricular arrhythmias
What is the mechanism of ivabradine?
Blocks If ion current which is highly expressed in sinus node
What are the cardiac effects of ivabradine?
Slows the sinus node but does not affect blood pressure
What are the side effects of ivabradine?
Flashing lights
Teratogenicity not known (avoid in pregnancy)
What are the uses of ivabradine?
Reduce inappropriate sinus tachycardia
Reduce heart rate in heart failure and angina
What is the mechanism of digoxin?
Enhances vagal activity
Slows AV conduction and slows HR
What are the uses of digoxin?
Treatment to reduce ventricular rates in atrial fibrillation and flutter
What is the mechanism of atropine?
Selective muscarinic antagonist
What are the cardiac effects of atropine?
Block vagal activity to speed AV conduction and increase HR
What are the uses of atropine?
Treat vagal bradycardia
