Arrhythmias Flashcards
What is an arrhythmia (dysrhythmia)?
A disturbance of the normal rhythmic beating of the heart, usually due to an ectopic (out of place) pacemaker
What features can the aberrant rhythm have?
- Too fast or too slow
- Regular or irregular
- Intermittent or permanent
How do you diagnose specific types of arrhythmias?
ECG
What are the main symptoms of arrhythmias?
- Palpitations (sensation of pounding heart)
- Breathlessness
- Dizziness, faintness, syncope
What are 4 important types of arrhythmias?
1) Complete heart block
2) Atrial fibrillation
3) Ventricular fibrillation
4) Ventricular tachycardia
What do all regions of the conducting system have the capacity to be?
Pacemakers
What is the phase 4 funny current?
A mixed sodium and potassium inward current
What is the effective refractory period?
When cells cannot fire another AP during most of an existing AP
What are 3 ways that arrhythmias are classified?
1) By rate
2) By location
3) By cause
What are the two classifications of arrhythmias by rate?
1) Inappropriate bradyarrhythmia (<60bpm)
2) Inappropriate tachyarrhythmia (>100bpm)
What are the two classifications of arrhythmias by location?
1) Supraventricular (atrial or AV nodal origin
2) Ventricular (ventricular origin)
Which type of arrhythmia (by location) is more dangerous and more difficult to treat?
Ventricular
What are the two classifications of arrhythmias by cause?
1) Disorders of impulse generation
2) Disorders of impulse conduction
How do bradycardia arrhythmias occur?
1) SAN slows down
2) impulse from SAN is blocked, slower distal pacemaker takes over
How do tachycardia arrhythmias occur?
1) Disorders of impulse generation → afterdepolarisations
2) Disorders of impulse conduction → re-entry
What is complete (third degree) heart block?
Blocked electrical connection between atria and ventricles
What are 3 causes of complete heart block?
1) Idiopathic bundle branch fibrosis
2) Atherosclerotic coronary heart disease
3) Dilated cardiomyopathy
What is the effect on cardiac rhythm of complete heart block?
1) Heartbeat is slow (doesn’t stop bc of distal pacemakers) → degree of slowing depends on location of block
2) Heart rhythm is driven by ‘escape beats’ originating from the distal pacemaker just below the block
What is a distal pacemaker?
A latent pacemaker in the conduction system becoming active
What happens when the AVN takes over from the SAN?
1) When the AVN is free of dominance from the SAN, it will take over
2) However, its pacemaker activity is intrinsically slower so the HR becomes slower
What happens to the HR when the bundle branches take over?
It slows down for the left bundle branch and then even slower for the right
Why does the HR slow down when the bundle branches take over?
Bc they have less channels involved in funny current further away from SAN
Why are all parts of the conduction system potential/latent pacemakers?
Bc they have the ion channels required for phase 4 depolarisation
Why does the intrinsic automaticity of the conduction system normally remain latent?
Bc of overdrive suppression by the SAN (the fastest pacemaker dominates)
What happens when latent pacemakers take over?
- If the conduction system is blocked between the atria and ventricles the heart will generally continue to beat more slowly
- The region of the pacemaker just distal to the block will take over from the SAN
- It paces the heart more slowly since its rate of intrinsic depolarisation is slower than that of the SAN
What symptoms occur when a latent pacemaker takes over (complete heart block)?
- Temporary syncope → as the heart stops bc it takes a few seconds for the latent pacemaker to take over
- Followed by recovery, with breathlessness, fatigue and possible chest pain, especially on effort
Why can chest pain occur in complete heart block?
CO drops with HR and if this is sufficient it can lead to chest pain
What is the prognosis of complete heart block?
- Episodes of syncope tend to get longer and exhale beats slow
- Most patients die within 2 months unless treated, some die immediately if distal pacemaker doesn’t take over
- Risk depends on location of block → more distal block = slower rhythm = greater risk of asystole
What is asystole?
Heart stopping
How is complete heart block treated?
- Implantation of a permanent pacemaker to generate the cardiac rhythm (unless risk is low or block is likely to be temporary)
- If risk of asystole is high, may need immediate temporary pacemaker as well
Describe the ECG in complete (3rd degree) heart block
- Hallmark = QRS complex becomes dissociated from the P wave (atrioventricular dissociation)
What causes the ECG pattern in 3rd degree heart block?
- QRS is generated by a distal pacemaker which has its own rhythm so the P wave happens more frequently than the QRS complex
- Atria and ventricles beat independently