Treating Arrythmias Flashcards
Where is the heart beat initiated?
In the SA node
Via what channels is the resting potential controlled in the SA node?
If- funny channels which are cAMP activated. They transport Na+ and K+ across the membrane leading to slowly reach the threshold for depolarisation
Which channels cause the upstroke of the slow cardiac action potential?
Ca2+ channels.
Which channels cause the repolarisation of the slow cardiac action potential?
K+ channels
How many stages are there in the fast cardiac action potential?
5
0,1,2,3,4
At which stage do voltage gated sodium channels open in the fast cardiac action potential causing the first upstroke?
Stage 0
What is the mechanism in the fast cardiac action potential causing the plateau?
Transient outflow of potassium ions, influx of Ca2+ into the cell via L type Ca2+ channels which are slow to close.
Which pump in the cell membrane is responsible for maintaining the resting potential in the fast cardiac action potential?
NaK ATPase.
What are the two broad categories of how an arrhythmia may arise?
Abnormal impulse generation
Abnormal conduction
What types of arrhythmias can cause abnormal impulse generation?
Triggered rhythms such as early after depolarisations or delayed after depolarisations.
Ectopic foci
Enhanced normal automaticity = increased frequency of action potentials from SA node.
What kinds of arrhythmias can cause abnormal conduction to develop?
Re entry mechanisms eg WPW syndrome, circus movement, reflection
Conduction block- 1st, 2nd, 3rd degree
What are the different classifications of anti arrhythmic drugs? Briefly describe what each class does.
Class Ia- sodium channel blocker
Class IIa- sodium channel blocker
Class Ic- sodium channel blocker, also some K+ and Ca2+ blockade.
Class II- Beta blocker
Class III- K+ channel blocker
Class IV- calcium channel blocker
Digitalis glycosides- positive inotropy, AV nodal blockade
Adenosine- enhances outward flow of K+- hyperpolarisation. Causes sinus bradycardia. Also AV node blocker
Atropine- antimuscarinic- reduces inhibitor effect of vagus nerve on heart.
Which drugs are used for treatment of bradycardias?
Atropine
What can cause sinus bradycardia?
MI
Overdose of beta blocker
What are the categories of arrythmias?
Bradycardias
Supraventricular tachycardia
Nodal tachycardia
Ventricular tachycardia
What are the different types of SVTs?
Atrial flutter
Atrial tachycardia
Atrial fibrillation
Atrial premature beats.
What are the key pathophysiological features of atrial flutter?
2:1 conduction ratio to ventricles
Usually arises fro a macro re entrant circuit in right atrium
Atrial rate is 250-250bpm.
What characteristic sign is often seen on ECG in patient with atrial flutter?
Sawtooth appearance
What is the treatment for atrial flutter?
Commonly DC cardioversion. Pharmacological treatment- class Ic agents are sometimes used but must be given together with an AV nodal blocker to prevent a 1:1 conduction to the ventricles.
What is the pathophysiology of atrial tachycardia?
Infrequent rhythm disturbance arising from automatic ectopic foci producing an atrial rate of 150-250bpm.
What is the pharmacological treatment of atrial ectopic foci?
Flecainide to reduce heart rate and restore sinus rhythm+ AV node blocker- beta blocker or CCB
What is the pathophysiology of atrial fibrillation?
Often occurs without any underlying cause
Often arises from multiple re-entrant circuits in the atria.
Why does having atrial fibrillation increase the risk of stroke?
The condition predisposes to left atrial thrombus formation and subsequent systemic emboli
What are the aims of treatment in atrial fibrillation?
Treatment of underlying cause
Restoration of sinus rhythm
Control of rapid ventricular response in persistent or permanent AF
What are common underlying causes of AF?
Hypertension, valvular heart disease, heart failure, ischaemic heart disease
Chest infections, pulmonary embolism, lung cancer
Systemic causes- excessive alcohol intake, thyrotoxicosis, electrolyte depletion, infections, DM
How is sinus rhythm restored in atrial fibrillation?
DC or drug induced cardioversion Pharmacologically this is done using a single oral dose of flecainide. Sinus rhythm can be maintained with a class Ic drug, sotalol or amiodarone (CCB)
How do we control the rapid ventricular response to persistent atrial fibrillation?
Digoxin- used to control HR
Av node blocker- CCB or beta blocker
What is the first step of treatment in nodal tachycardias?
Carotid sinus massage, or sometimes adenosine may be used.
How do nodal tachycardias arise?
What is a classic example?
Arise from a reentry circuit and are usually initiated by an ectopic beat.
Wolff parkinson white syndrome
AV node reentrant tachycardia is another example of a nodal tachycardia. How is it treated?
Beta blockers, dilitiazem or verapimil can be used to treat acute episodes.
Junctional tachycardias also respond well to flecainide, sotalol or amiodarone
What are the major types of ventricular tachycardias?
vetricular fibrillation
Ventricular tachycardia
Ectopic beats
When can ventricular ectopic beats occur?
In healthy individuals or after an MI
What drugs are used to treat ventricular ectopic beats after an MI to reduce the risk of sudden cardiac death?
Beta blockers
How does ventricular tachycardia present on ECG?
Broad QRS complexes
What pharmacological treatment is given to non sustained ventricular tachycardia?
Beta blockers
What pharmacological treatment is given to sustained ventricular tachycardia?
Class Ib agents such as lidocaine or amiodarone
