Lecture 11: Anti-Arrythmic Drugs (Part I) Flashcards
____: Any change from normal sequence of cardiac impulse (may be fast, slow, or erratic beat) that result in ineffective pumping of blood to vital organs
Cardiac Arrythmia
True or False: A change in beat velocity or rhythm is considered arrhythmic
True
_____ is made up of continuous cycles of depolarization and re-polarization of cardiac muscle tissue. During this period, cardiac muscle cells are refractory to any further stimuli, which is known as ____
Cardiac action potential; effective refractory period (ERP) /absolute refractory period (ARP)
Which AP corresponds to pacemaker cells (SA/AV Node) and which correspond to non-pacemaker cells?
Left = non-pacemaker
Right = pacemaker cells
How many phases are present in pacemaker cell action potential?
How many phases are present in non-pacemaker cell action potential?
Pacemaker cell action potential = three phase s(Phase 4, 0, and 3)
Non-pacemaker cell action potential = five phases (Phase 0, 1, 2, 3, and 4)
What initiates Phase 4 in pacemaker cell action potential?
Slow and spontaneous depolarization by:
1) inward pacemaker current (inward funny current) - maintains automaticity
2) HCN channels
By the end phase 4 of pacemaker cell action potential, there is an increase in ___ (influx), which stimulates ___ entry
Na; Ca2+
Phase 0 of pacemaker cell action potential is characterized by rapid ____. What causes this?
rapid depolarization
- cause: opening of VG Ca2+ channel
What causes phase 3 of pacemaker cell action potential (repolarization phase)?
1) Opening of K+ selective channels via: delayed rectifier outward current
During phase 3 of pacemaker cell AP, are Ca2+ channels open or closed?
Closed
Following repolarization (phase 3 of pacemaker cell AP) - once the membrane potential reaches ___, it triggers the opening of __, for the next slow and spontaneous depolarization
-60 mV; If
True or False: In pacemaker cell action potential, phase 4 is associated with Na influx, phase 0 is associated with Ca influx, and phase 3 is associated with K efflux
True
What is the order in which the pacemaker cell AP phases occur in?
What is the order in which the non-pacemaker cell AP phases occur in?
Pacemaker: Phase 4→Phase 0 →Phase 3
Non Pacemaker: Phase 4→ 0 → 1→ 2 → 3 →4
What happens in phase 4 (first stage of non-pacemaker cell AP)?
K+ ions efflux via: delayed rectifier outward K+ currents - IKs - maintains negative potential
Which stage of the non-pacemaker cell action potential is associated with rapid depolarization (and, ultimately, a shift from negative (-90 mv) to positive potential) ?
A. Phase 1
B. Phase 4
C. Phase 0
C. Phase 0
During phase 0 of non-pacemaker cell AP, there is fast influx of __ ions. Which channels are closed at this time?
Na; Outward K
Which stage of the non-pacemaker cell action potential is associated with a rapid, transient repolarization stage? Cause?
Phase 1 is the initial rapid transient repolarization stage in Non-Pacemaker Cell Action Potential
- Due to opening of transient outward K+ channels
What factors lead to Phase 2 (plateau phase) of non-pacemaker cell action potential?
- Inward flow of calcium
- Outward K+ current
IKr and Iks are rapid and slow acting delayed rectifiers that allows for K+ efflux at what phase of non-pacemaker cell action potential?
Phase 2 (plateau) and Phase 3
By the end of phase 2 in the non-pacemaker cell action potential, the ___ channel closes and is following by steady and fast efflux of K+ via ___ and ___
Ca2+; IKr/IKs
What happens in phase 4 of the non-pacemaker cell action potential? How it it achieved?
Re-establishment of resting membrane potential
- Achieved by opening of outward K+ currents (IKr/IKs*) - time independent, but depends on potential of -90 mV
Which of the following corresponds to the following description?
“Atrial depolarization”
A. P wave
B. PR interval
C. QRS complex
D. ST segment
A. P wave
Which of the following corresponds to the following description?
“Time between atrial depolarization and ventricular depolarization”
A. P wave
B. PR interval
C. QRS complex
D. ST segment
B. PR interval
Which of the following corresponds to the following description?
“Ventricular depolarization”
A. P wave
B. PR interval
C. QRS complex
D. ST segment
C. QRS complex
Which of the following corresponds to the following description?
“Time taken for both ventricles to get completely depolarization - corresponds to plateu phase)”
A. P wave
B. PR interval
C. QRS complex
D. ST segment
D. ST segment
Which of the following corresponds to the following description?
“Ventricular repolarization”
A. P wave
B. PR interval
C. QRS complex
D. ST segment
E. T waves
E. T waves
Two types of defects that can lead to arrythmia?
1) Defects in impulse formation
2) Defects in impulse conduction
What are two factors that can cause defects in impulse formation?
1) Altered automaticity
2) Triggered activity
What is the normal path taken by electrical activity?
SA Node→AV Node→Bundle of His→Purkinje
____: a condition in which there is a defect in either pacemaker cells OR non-pacemaker cell activity, leads SA Nodal firing rate to become altered/impairs downstream conduction
Altered Automaticity
____: Process by which the initial AP triggers an immediate and addition depolarization PRIOR to completion of one cycle, leads to arrythmia
Triggered activity
What are the two types of triggered activity?
1) Early After Depolarization (EAD)
2) Delated After Depolarization (DAD)
When does Delayed After Depolarization commonly occur? When does Early After Depolarization occur?
DAD = Phase 3 or end of Phase 3
EAD = End of Phase 2 or early part of Phase 3
True or False: Early After Polarization is most likely to happen towards the enter of plateau or beginning of rapid repolarization
True
If Early After Depolarization persists, what condition could it lead to?
How is this condition characterized?
Torsade de Pointes
- characterized by:
1) ventricular tachyarrythmia
2) prolonged QT intervals
3) heart rate (200-250 beats/min)
What three drugs are known to induce Torsade de Pointes?
What three gene mutations are known to induce the condition?
Drugs: anti-arrythmic drugs; tricyclic antidepressants; anti-virals
Mutations: KCNQ1, HERG, SCN5A
True or False: Digitalis can induce torsade de pointes (TdP)
True - can be treated by MgSO4 IV infusion
Delayed After Depolarization typically occurs after repolarization (phase _) due to a rise in ___, leading another depolarization to occur before completion of one cycle
phase 3; Ca2+
Three factors that can lead to defects in impulse conduction?
1) Re-entry
2 ) Conduction block
3) Accessory Tract Pathways
What are two factors that lead to re-entry?
1) Uni-directional block
2) Slow retrograde conduction velocity
_____ is due to failure to propagate impulses due to damage induced reduced excitability of cardiac tissue. Often results in decrease contractility of ___
Conduction Block; myocyte
True or False: Accessory fibers, such as Bundle of Kent, can bypass SA-AV Path
True
Supraventricular Tachyarrythmia (WPW Syndrome) could lead to ______ if it is AV Nodal in origin
Paroxysmal Supraventricular Tachycardia
True or False: Impulses from accessory path and normal path can trigger impulses
True
What four drug classes are associated with QT Prolongation and TdP?
1) Anti-arrhythmics
2) Anti-microbials
3) Anti-depressants
4) Anti-psychotics
