12/6/2012
Arrhythmias Abnormal automaticity
Abnormalities in heart rate/rhythm caused by Occurs when SAN (heart’s normal pacemaker) activity
disorders of overridden by abnormal (latent) pacemaker activity in
Impulse generation cells of conduction system or myocardium
Abnormal automaticity Causes include ischaemia, hypokalaemia +
Triggered automaticity catecholamine activity
Impulse conduction
Re-entry circuits
Heart block
Triggered automaticity Re-entry circuits (circus movement)
Associated with extra depolarisation events arising during Re-excitation of myocardium by arrival or re-entry of
non-nodal cardiac action potential (afterdepolarisations), delayed impulse
either at the end of phase 2/commencement of phase 3
(early afterdepolarisations (EADs)) or in phase 4 (delayed Requires
afterdepolarisations (DADs)) Central inexcitable region
Caused by excessive calcium entry/accumulation in cell, Zone of slowed conduction
e.g. in response to
Zone of unidirectional block
Cardiac glycosides
Phosphodiesterase type III inhibitors
Catecholamines ( ß1-adrenoceptor agonists)
Hypercalcaemia
Ischaemia
Heart block
Partial or complete failure of conduction by AVN of
impulses from SAN to ventricles
3rd degree
Complete heart block (no conduction) Vaughan Williams classification
2nd degree
Fraction of impulses conducted
1st degree
Abnormally slow impulse conduction
1
Arrhythmias Abnormal automaticity
Abnormalities in heart rate/rhythm caused by Occurs when SAN (heart’s normal pacemaker) activity
disorders of overridden by abnormal (latent) pacemaker activity in
Impulse generation cells of conduction system or myocardium
Abnormal automaticity Causes include ischaemia, hypokalaemia +
Triggered automaticity catecholamine activity
Impulse conduction
Re-entry circuits
Heart block
Triggered automaticity Re-entry circuits (circus movement)
Associated with extra depolarisation events arising during Re-excitation of myocardium by arrival or re-entry of
non-nodal cardiac action potential (afterdepolarisations), delayed impulse
either at the end of phase 2/commencement of phase 3
(early afterdepolarisations (EADs)) or in phase 4 (delayed Requires
afterdepolarisations (DADs)) Central inexcitable region
Caused by excessive calcium entry/accumulation in cell, Zone of slowed conduction
e.g. in response to
Zone of unidirectional block
Cardiac glycosides
Phosphodiesterase type III inhibitors
Catecholamines ( ß1-adrenoceptor agonists)
Hypercalcaemia
Ischaemia
Heart block
Partial or complete failure of conduction by AVN of
impulses from SAN to ventricles
3rd degree
Complete heart block (no conduction) Vaughan Williams classification
2nd degree
Fraction of impulses conducted
1st degree
Abnormally slow impulse conduction
1
