Arrhythmias Flashcards
What are the causes of abnormal automaticity?
lack of cardiac blood supply (reflecting myocardial damage induced by cardiac ischaemia, which can make the resting membrane potential unstable)
hypokalaemia
catecholamine activity (involving excessive cardiac β1-adrenoceptor signalling in response to noradrenaline and adrenaline)
What is required for Re entry
Central inexcitable region
Zone of slowed conduction
Zone of unidirectional block
The myocardial cell absolute refractory period (RP) is typically an effective barrier to a _______________
Re-entrant impulse and inappropriate re-excitation.
Explain what happens at each stage during heart block.
3rd degree
2nd degree
1st degree
complete heart block (no conduction)
fraction of impulses conducted
abnormally slow impulse conduction
During heart block partial or complete failure of conduction by ___ of impulses from _______
AVN
SAN to ventricles
what is arrhythmais?
Abnormalities in heart rate/rhythm
another name for automaticity?
impulse generation
Abnormalities in heart rate/rhythm caused by disorders of what?
*Impulse generation
Abnormal automaticity
Triggered automaticity
*Impulse conduction
Re-entry circuits
Heart block
what drives normal or sinus rhythm and acts as the normal pacemaker in the acts?
sinoatrial node (SAN)
abnormalities in heart rate or rhythm (abnormal automaticity, leading to departures from normal or sinus rhythm can lead to either _________ or _______________–
increase (tachyarrhythmia) or decrease (bradyarrthythmia) in pulse rate
On some occasions, arrhythmias can lean to ______________
atrial or ventricular fibrillation (AF or VF), where cardiac contractions become chaotic and uncoordinated.
explain the problems with atrial or ventricular fibrillation (AF or VF)?
This means the heart stops working as a single functional unit and this has immediate, lethal consequences for maintaining cardiac output in VF; while AF poses a major risk of stroke owing to atrial-centred thromboembolism. These rhythm abnormalities are underpinned by disorders either in the generation or conduction (i.e. transmission) of cardiac electrical impulses.
what is abnormal automaticity?
Occurs when sinoatrial node (SAN) activity is overridden by abnormal (latent) pacemaker activity in cells of conduction system or myocardium
due to spontaneous impulse generation
what is triggered automaticity?
Associated with extra depolarisation events arising during non-nodal cardiac action potential (afterdepolarisations), either at the end of phase 2, commencement of phase 3 (early afterdepolarisations (EADs)) or in phase 4 (delayed afterdepolarisations (DADs))
What are the causes of triggered automaticity
excessive net inward depolarising current (in the case of EADs);
and intracellular calcium accumulation (in the case of DADs)
Impulse generation may go awry in respect of what?
the establishment of re-entry circuits (where impulses are maintained in a perpetual circus movement)
the development of heart block (where impulses are delayed or not conducted at all between the atria and ventricles).
what is re-entry
due to a circuit within the myocardium, re-entry occurs when a propagating impulse fails to die out after normal activation of the heart and persists as a result of continuous activity around the circuit to re-excite the heart after the refractory period has ended
explain myocadiac cell absolute refractory period
The absolute refractory period of the cardiac muscle action potential refers to the time interval when the voltage gated sodium channels are inactivated
The cause after-depolarizations is linked to what and what
is linked to excessive net inward depolarising current (in the case of EADs);
and intracellular calcium accumulation (in the case of DADs)
what causes abnormal automaticity
spontaneous impulse generation
AF poses a major risk of stroke because__________
due to atrial-centred thromboembolism
what type of after depolarization for each phase
phase 2
phase 3
phase 4
phase 2- EADs
phase 3 - EADs
phase 4 - DADs
