Describe the four phases of the typical myocardial action potential and the ions primarily responsible for each phase (not SA or AV nodes)
Phase 0: Na+ influx
Phase 1: K+ efflux
Phase 2: Ca2+/Na+ influx
Phase 3: K+ efflux
Phase 4: High conductace of K+ predominates
What channel is responsible for the slow upstroke in the SA and AV node?
What ion is responsible for the AP once the SA/AV nodes reach threshold?
The funny current (If); Calcium
What are 2 general mechanisms of arrhythmias?
1) Disturbance of Impulse Formation / Inappropriate Automaticity
2) Disturbance of Impulse Conduction
What are the two general classes of arrhythmias? (Give me some subtypes too!)
1) Bradyarrhythmia -
heart block (I, II, III)
2) Tachyarrhythmia - SVT, V-Tach
What bradyarrhythmias are cause by a problem with impulse initiation? Impulse conduction?
--sinoatrial exit block
What are the three general classes of tachyarrhythmia?
Which is most common? Least common?
Abnormal Impulse Initiation (Increased automaticity from other places besides SAN)
Triggered Automaticity - Early and Delayed Afterdepolarizations (Least Common)
Impulse Conduction: Reentry (Most Common)
What are three tachyarrhythmias that fall under increased automaticity? Causes?
1) Atrial tach - Impulse from atrial tissue other than SA
2) Junctional tach - abnormal impulse from AV junction
3) Ventricular tach - Abnormal impulse coming from ventricle
EADs/DADs are examples of triggered automaticity.
When during the AP do EADs occur? What can EADs cause?
When during the AP do DADs occur? What is an example of a DAD?
EADs: Phase 3; cause Long QT syndrome
DADs: Phase 4; Digoxin toxicity
3 Components necessary for Reentry Arrhythmia?
1. Parallel fast and slow conduction pathway
2. Unidirectional block
3. Final common pathway
Describe the mechanism for reentry arrhythmia.
1. Arrival of premature impulse while fast pathway is refractory, sending signal down slow pathway
2. Impulse then enters fast pathway in retrograde fashion
3. Proceeds to reenter slow pathway, starting re-entrant circuit