Cardiac and Pacemaker Cell APs
Define: Cardiac arrhythmia
What is...Any change from the normal sequence of cardiac impulse. Can be slow, fast, or erratic resulting in ineffective pumping of blood in vital organs.
How many phases are in non pacemaker cell APs? What is the order?
What is...5 phases
4,0,1,2,3,4 (Phase 4 connects the loop)
What is the QRS complex representing on an EKG? What is the normal time interval?
What is...Ventricular depolarization & between
0.06-0.1 seconds
What is Early After Depolarization?
What is... It mostly occurs at the end of phase 2 or early part of phase 3. Towards the end of plateau or at the beginning of rapid repolarization phase respectively.
What can accessory fibers like bundle of Kent do?
What is...bypass the SA-AV-path. Impulses from accessory paths and normal path could trigger impulses.
Define: Cardiac action potential
ERP and ARP
What is...comprises of continuous cycles of depolarization and re-polarization of the cardiac muscle.
During this period they are refractory to any other stimulus: ERP (effective refractory period) or ARP (absolute refractory period).
What is different about Phase 0's rapid depolarization in non-pacemaker cell APs than pacemaker cell APs?
What is... Phase 0 in non-pacemaker cell APs has to do with Na+ ions entering fast; these channels are open and active. And the K+ channels are closed. While Phase 0 in pacemaker cell APs has to do with the opening of voltage-gated Ca2+ channels.
What does the QT interval indicate?
What is...it denotes the total time taken for ventricular depolarization AND re-polarization.
What is persistent EAD?
What is...Torsade de pointes. This is characterized by Ventricular tachyarrhythmia and prolonged QT interval and will have a beat rate between 200-250 beats/min.
What drugs are associated with QT prolongation?
Pacemaker cell AP: What are the phases? Which ones are depolarization phases and which are the re-polarization phases? Fast or slow?
What is...
Phase 4 - Slow and spontaneous depolarization
Phase 0 - rapid depolarization
Phase 3 - re-polarization (no speed indicated)
What is the difference between in non-pacemaker cell APs and pacemaker cell APs regarding phase 4?
What is...Phase 4 in non-pacemaker cell APs have to do with the movement of K+ ions, while pacemaker cell APs have to do with the inward funny current and HCN-gated channels, Na+ ions responsible.
Name and describe the 2 defects in impulse formation regarding the electrical dysfunction leading to arrhythmia?
What is...Altered automaticity & Triggered activity
What are...re-entry, conduction block, accessory tract pathways.
What are the 2 major factors which are interconnected?
What are...unidirectional block and slow retrograde conduction velocity.
How do Phase 4 in pacemaker cell action potentials work? What currents and channels are at work? What ions are involved?
What is...The inward pacemaker current (funny current inward) is what leads to the slow and steady depolarization. This maintains automaticity. Channels responsible are HCN <- non-selective.
Na+ ions are responsible for this phase.
The ^ of Na+ then stimulates Ca2+ by the end of this phase.
What is Phase 2 in non-pacemaker cell APs?
What is...The plateau due to the inward flow of Ca2+ (by opening transient T-type and L-type Ca2+ channels) and due to outward current of K+.
What is altered automaticity?
What drugs can induce Torsade de pointes?
What is...Anti-arrhythmic drugs, tricyclic antidepressants, and antiviral drug.
What is a conduction block?
What is...failure in propagation of impulses due to damage induced reduced excitability of cardiac tissue.
How are Phase 0 and Phase 3 of pacemaker cell APs different? What specific channels are open and which are closed?
What is...Phase 0: rapid depolarization
Opening of voltage-gated Ca2+ channels.
Phase 3: re-polarization
Opening of K+ selective channels and during this phase Ca2+ channels are closed. Cannot go back to phase 4 until the membrane potential reached -60mV.
What is Phase 1 in non-pacemaker cell APs?
What is...Initial rapid transient re-polarization stage due to I K to (transient inward K+ channels); also short lived.
What is Triggered activity?
What is...The initial action potential triggers an immediate and additional depolarization before the completion of one cycle-leading to arrhythmia --> after depolarization.
What is delayed after depolarization and when does it occur?
What is...it occurs mostly after repolarization (phase 3). A rise in Ca2+ overload, leading to another depolarization before the completion of one cycle is considered a major reason.
Treatment of ________ is also known to induce ______. How is it treated?
What is... digitalis; TdP. Treated by MgSO4 IV infusion or as a bolus dose?