Heart Lecture 5: Mechanism of Cardiac Arrhythmias Flashcards
Cardiac arrhythmias result from disturbances in impulse _________ or __________
formation; conduction
What are the three mechanisms of cardiac dysrhythmias?
1) altered automaticity (meaning mediated by pacemaker conduction system)
2) re-entry of excitation (ALWAYS pathological - conduction problem)
3) triggered activity (ALWAYS pathological - formation problem)
What does automaticity mean?
that the impulse is traveling through the normal, automatic pacing system
Tachycardia definition
heart rate over 100bpm
Bradycardia definition
heart rate under 60bpm
What causes tachycardia?
1) sympathetic nervous activity (NE stimulation)
2) stimulants/amphetamines (like caffeine)
3) ischemia (current of injury)
4) stretching (ventricular aneurysm
5) sick sinus syndrom, fever, hyperthyroidism
What causes bradycardia?
1) drugs (anti-arrhythmics, beta blockers, Ca++ antagonists, digitalis)
2) barbituates, anesthetics
3) ischemia or infact
4) sick sinus syndrome
5) aging (fibrosis)
Where does re-entry of excitation occur?
Anywhere in the heart
What are the 3 requirements for re-entry of excitation?
1) geometry for conduction loop
2) slow or delayed conduction
3) unidirectional conduction block
What causes re-entry?
1) ischemia (MOST COMMONly found after MI)
2) infarction (cell death - plugs up part of heart)
3) congenital bypass tracts (Wolf-Parkinson White)
Describe the flow of re-entry
1) impulse comes down on tissue
2) hits blockade but AP still occurs right before damaged tissue
3) meanwhile, finds excitable tissue and conducts normally
4) go through damaged region (which has greater membrane potential so some Na+ channels are already activated) and has slow conduction so AP is just barely longer than the one that occurred neighboring it. Therefore, once it ends, the area next to it is excitable again
What is Wolf-Parkinson-White?
A congenital abnormality that connects right atria to right ventricle (has functional characteristics of Purkinje fibers - aka rapid conduction and long refractory periods)
SVT travels _______ through the AV node and _________ through the bypass tract
anterograde; retrograde
What is triggered activity?
random impulse formation
What is a delayed afterdepolarization (DAD)?
a transient release of Ca++ from the SR that leads to abnormally elevated intracellular [Ca++] which increases strength of contraction
