Sinoatrial Node (SA node)
Rate?
Location & Area of intervention?
EKG?
Natural pacemaker of the heart
Rate: 60-100 bpm
Location: Upper portion posterior portion of the Right Atrium near superior vena cava
EKG: represented as the P wave
Atrioventricular node (AV node)
Rate?
Location?
�...
pathway for electrical signals to be transmitted to the ventricles
Rate: 40-45 bpm
Location: partially in right atrium and upper portion of interventricular septum that connects
the AV node and 2 bundle branches
Purkinjie Fibers
Rate?
hair-like fibers that spread out from bundle branches into the ventricles; innervate
myocardial cells directly; initiate ventricular depolarization
Rate: 20-40 bpm
Normal Conduction Pathway through the Heart
SA node
Interatrial tracts
AV node
Bundle of His
Bundle branches
Purkinje fibers
resting membrane potential
Electrical charge of cardiac muscle cells at rest
change in the electrical charge of a stimulated cell from negative to positive by the
flow of ions; Na+ allows for depolarization, except in AV node which depends on the
slow moving Ca2+
Repolarization
recharging of a cell to its normal polarity; K+ allows for repolarization
action potential
as cardiac cells reverse polarity, the electrical impulse generated during that event
creates an energy stimulus that travels across the cell membrane
What ion causes contraction?
Calcium
Phase 4
Phase 4: Resting State
Na+ and Ca2+ channels are closed; increase in K+ permeability to allow for a new cycle
Phase 0
Phase 0: Rapid depolarization
Opening of voltage-gated fast Na+ channels; cell fires to initiate transmission of electrical
impulse
Phase 1
Phase 1: Depolarization
Peak positive charge; K+ closes, Cl- enters to slow channels, slow Ca2+ channels open
Phase 2 Plateau
Opening of voltage gated slow Ca2+ channels and closing of some K+, some Na+ enters to
maintain; membrane potential is maintained or plateaued
Phase 3
Phase 3 Re-polarization
Opening of voltage-gated K+ channels and closing of Ca2+ channels; K+ moves from ICF to
ECF
Refractory periods
time from phase 0 until the repolarization of a myocyte or when enough Na+ have
recovered
Absolute refractory periods
occurs with the early part of the T-wave when most of the ventricle is depolarized and
is "refractory" to new stimuli
Relative refractory periods
occurs towards the end of the T-wave when most ventricular cells are repolarized and
vulnerable to new stimuli; can lead to VT if PVC lands during this time
Refractory = resistant
Normal P Wave
Measures: 0.5 - 2.5mm high
< 0.12 secs in width
1|Page| GradeA+ | 2 0 0 2 5
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