Arrhythmias and antiarrhythmic drugs Flashcards
What is the definition of arrhythmias?
Abnormalities in heart rhythm
What are the symptoms of arrhythmias?
Palpitations, dizziness, fainting, fatigue, loss of conscious, cardiac arrest, blood coagulation (e.g. stroke, MI)
What are the causes of arrhythmias?
Cardiac ischemia (MI, angina), heart failure, hypertension,
coronary vasospasm, heart block, excess sympathetic stimulation
What is the origin of arrhythmias?
- Supraventricular(above the ventricles - SA node, atria, AV node)
- Ventricular
What are the effects of arrhythmias?
Tachycardia (>100 bpm) or Bradycardia (<60 bpm)
What happens in atrial fibrillation and how does it show on the ECG?
Quivering atria activity (no discrete P waves)
Irregular ventricular contraction
‘Clot-producing’ – risk of stroke
What happens in supraventricular tachycardia(SVT) and how does it show on the ECG?
P wave buried in T wave
Fast ventricular contractions
What happens in heart block and how does this show on ECG?
Failure of the conduction system
(e.g. SAN, AVN, or bundle of his)
Uncoordinated atria/ventricular
contractions
-P waves and QRS complexes are independent of each other. P waves and R waves are regular
What happens in ventricular tachycardia(VT)?
Fast, regular
What happens in ventricular fibrillation?
Fast, irregular
What are the mechanisms of arrhhythmogenesis?
- Abnormal impulse generation due to
-Automatic rhythms - increased SA node activity, ectopic activity
-Triggered rhythms - Early afterdepolarizations(EADs), Delayed-afterdepolarizations (DADs) - Abnormal conduction due to
-Re-entry electrical circuits in heart
-Conduction block
Where is pacemaker activity initiated?
Pacemaker activity is initiated in SAN but other areas of the heart can have
pacemaker activity to ‘safeguard’ if SAN becomes damaged
What is the frequency of the SA node?
60-70/s
What is the frequency of the AV node?
40-60/s
What is the frequency of the bundle of His?
30-40/s
What is the frequency of purkinje fibres?
15-25/s
What are the low frequency pacemaker areas enhanced by?
These other low frequency ‘pacemaker’ areas are greatly enhanced by sympathetic nerve activity:
-Increase heart rate
-Increasing AVN conduction
-Increase excitability of ventricular tissue
What can the continuous/enhanced stimulation of sympathetic nervous system lead to and what does this increase the risk of?
Continuous/enhanced stimulation of sympathetic nervous system
(stress, heart failure) can lead to arrhythmias
- increase risk of ectropic pacemaker activity -
Whats early afterdepolarization and what does it involve?
Altered ion channel activity
e.g. Abnormal increase
in Na or Ca channel activity
What is delayed afterdepolarization and what does it involve?
Abnormal levels of Ca2+ in SR
Ca2+ leaks out from RyR into cytosol
Stimulate Na/Ca exchanger (NCX)
Na+ influx – depolarisation
What is the basis for the SAN to ventricles ‘wave’ of conduction pathway of the heart/
Basis for the SAN to ventricles ‘wave’ of conduction pathway of the heart is:
Action potentials stop conducting because surrounding tissue is refractory
Cannot conduct anymore APs
What happens to conduction when there’s damage to the myocardium?
Damage to myocardium means that some areas of the heart are more
conductive than others – produces RE-ENTRY pathways