Pharmacological Management of Dysrhythmia Flashcards
What are dysrhythmias and what causes them?
- Dysrhythmia describes conditions where the coordinated sequence of electrical activity in the heart is disrupted.
- Can be due to:
- Changes in the heart cells
- Changes in the conduction of the impulse through the heart.
- Combination of these.
Describe the Vaughan Williams system of classifying anti-dysrhythmic drugs.
- Sodium channel blockers (divided into 1a, 1b, 1c).
- β-adrenoceptor blockers.
- Potassium channel blockers.
- Calcium channel blockers.
- Unclassified.
How do sodium channel blockers work?
- They inhibit action potential propagation and reduce the rate of cardiac depolarisation during phase 0.
- They bind to the open and refractory states of the channels and so are viewed as use-dependent.
- This means that they work more efficiently if there is high activity and so are more effective against abnormal high frequency activity and not so much against normal beating rates.
- They can block from the cytoplasmic side or the luminal side.
What is Disopyramide and what are the indications for its use?
- Disopyramide is a class 1a sodium channel blocker.
- Indications for use:
- Ventricular and supraventricular dysrhythmia.
- Prevention of recurrent atrial fibrillation triggered by vagal over-activity.
- Maintenance of sinus rhythm after cardioversion.
What is Lignocaine and what are the indications for its use?
- Lignocaine is a class 1b sodium channel blocker.
- Indication for use:
- Treatment and prevention of ventricular tachycardia and fibrillation during and immediately after MI.
- To be given during CPR as an alternative if amiodarone is not available.
What is Flecainide and what are the indications for its use?
- Flecainide is a class 1c sodium channel blocker.
- Indications for use:
- Suppresses ventricular ectopic beats.
- Prevents paroxysmal atrial fibrillation and recurrent tachycardia associated with abnormal conducting pathways.
What are the contraindications of Disopyramide (class 1a sodium channel blocker)?
- Bundle branch block associated with first-degree AV block.
- Second- and third- degree AV block (unless pacemaker fitted).
- Severe heart failure (unless secondary to arrhythmia).
- Severe sinus node dysfunction.
What are the contraindications of Lignocaine?
- All grades of AV block.
- Severe myocardial depression.
- Sinoatrial disorders.
How do β-Adrenoceptor blockers work?
- Block β-1 receptors, slowing the heart rate and decreasing cardiac output.
- β-1 receptor activation increases the rate of depolarisation of th pacemaker cells, so blocking them decreases this.
- β-1 receptor activation enhances calcium entry in phase 2 of the cardiac action potential, so blocking them reduces this.
- β-blockers increase the refractory period of the AV node, so prevent recurrent attacks of supraventricular tachycardias.
- Basically increased sympathetic drive and influence tend to promote dysrhythmias and so attenuating their influence will slow the heart and decrease their occurrence.
Give examples of β-blockers.
What are the indications for their use?
- Sotalol, bisopralol, atenolol.
- Indications for use:
- Reduce mortality following MI
- Prevent recurrence of tachycardias provoked by increased sympathetic activity.
- Also used in hypertension, angina, arrhythmias, heart failure and thyrotoxicosis.
What are the contraindications for β-blocker use?
- Symptomatic bradycardia
- AV block
- Decompensated heart failure
- Asthma
What are the common adverse effects of β-blockers?
- Nausea, weakness and dizziness.
- Cold hands and feet.
- Fatigue.
- Slow heart rate.
- Swelling of hands and feet.
How do potassium channel blockers work?
Give an example of a potassium channel blocker.
- They prolong the cardiac action potential by prolnging the refractory period.
- Amiodarone
What are the indications for use of a potassium channel blocker?
- Amiodarone is used to treat tachycardia associated with Wolff-Parkinson_white syndrome.
- Sotalol combines class 3 with class 2 actions. It is used in supraventricular dysrhythmias and suppress ventricular ectopic beats and short runs of tachycardia.
What is Wolff-Parkinson-White Syndrome?
- Wolff-Parkinson-White syndrome is a heart condition featuring episodes of an abnormally fast heart rate.
- Episodes can last for seconds, minutes, hours, or (in rare cases) days.
- They may occur regularly, once or twice a week, or just once in a while.
- The combination of Wolff-Parkinson_white syndrome and atrial fibrillation can be life-threatening.
What are the contraindications of potassium channel blockers?
- Severe conduction disturbances (unless pacemaker fitted).
- Sinus node disease.
- Iodine sensitivty.
- Sinoatrial heart block (except in cardiac arrest).
- Sinus bradycardia (except in cardiac arrest).
- Thyroid dysfunction.
What are the general adverse effects of potassium channel blockers?
- Arrhythmias
- Hepatic disorders
- Hyperthyroidism
- Nausea
- Respiratory disorders
- Skin reactions
How do calcium channel blockers work?
Give an example of a calcium channel blocker.
- Blocks cardiac voltage-gated L-type calcium channels.
- Slow conduction through the SA and AV nodes where the conduction of the action potential relies on the slow calcium currents.
- They shorten the plateau of the cardiac action potential and reduce the force of contraction of the heart.
- Verapamil is the main drug.
What are the indications for using a clacium channel blocker?
- Used to prevent recurrence of supraventricular tachycardias (SVTs).
- Also used in paroxysmal tachyarrhythmias, angina and hypertension.
- Used to reduce the ventricular rate in patients with atrial fibrilation provided they do not have Wolff-Parkinson-White syndrome.
What are the contraindications for using calcium channel blockers?
- Dizziness
- Flushing
- Headache
- Nausea
- Palpitations
- Peripheral oedema
- Rash
- Tachycardia
- Vomiting
What is adenosine?
An endogenous nucleoside occurring in all cells of the body and is not chemically related to other anti-dysrhythmic drugs.
What is the mechanism of action of adenosine?
- It relaxes ventricular smooth muscle through the reduction in calcium uptake by inhibition of slow inward calcium current and activation of adenylate cyclase in smooth muscle cells.
- Adenosine may reduce vascular tone by modulation of sympathetic neurotransmission.
- It acts on A1 receptors which are responsible for affecting the AV node. These receptors are linked to the same cardiac conducting tissue and slows the heart rate.
- It decreases pacemaker activity.
What are the indications for use of adenosine?
- Rapid reversion to sinus rhythm of paroxysmal supraventricular tachycardias, including those associated with accessory conducting pathways (e.g. Wolff-Parkinson-White syndrome).
- Used to aid diagnosis of broad or narrow complex ventricular tachydardias.
What are the contraindications for use of adenosine?
- Asthma
- COPD
- Decompensated heart failure
- Long QT syndrome
- Second- or third- degree AV block
- Sick sinus syndrome (unless pacemaker fitted)
- Severe hypotension
What are the common adverse effects of adenosine?
- Abdominal discomfort
- Arrhythmias
- AV block
- Chest discomfort or chest pain
- Dry mouth
- Dyspnoea
- Flushing
- Headache
- Hypotension
- Pain
- Paraesthesia
- Throat discomfort
What is digoxin?
What does it do?
- Digoxin is a cardiac glycoside.
- It increases vagal efferent activity to the heart by an unknown mechanism.
- Parasympathomimetic action - reduces sinoatrial firing rate (which decreases heart rate) and reduces conduction velocity of electrical impulses through the AV node.
What is the effect of toxic concentrations of digoxin?
- Toxic concentrations disturb sinus rhythm.
- Digoxin can inhibit the sodium-potassium ATPase pump; this can cause depolarisation and therefore ectopic beats.
What are the indications for the use of digoxin?
- Rapid digitalisation for atrial fibrillation or atrial flutter.
- Maintenance for atrial fibrillation or flutter.
- Heart failure (for patients in sinus rhythm).
What are the contraindications for the use of digoxin?
- Constrictive pericarditis
- Hypertrophic cardiomyopathy
- Intermittent complete heart block
- Myocarditis
- Second-degree AV block
- Supraventricular arrhythmias associated with accessory conducting pathways.
- Ventricualar tachycardia or fibrillation
What are the adverse effects of digoxin?
- Arrhythmias
- Cardiac conduction disorder
- Cerebral impairment
- Diarrhoea
- Dizziness
- Eosinophilia
- Nausea
- Skin reactions
- Vision disorders
- Vomiting
