cardiac electrophysiology Flashcards
polarization is
resting state of the cells
no deviation from the iso-electric line
depolarization is
cells’ state of excitability
during depolarization, changes in membrane permeability allow __ ions to cross the cell membrane and enter the cell
Na+
movement of NA+ ions causes the inside of the cell to become more __ than outside
electro positive
__ represents atrial depolarization
P wave
__ represents ventricular depolarization
QRS complex
Repolarization is
restoration of the cells to their resting state
repolarization is caused by
slower movement of ions leaving the cells
movement of __ ions out of the myocardial cells primarily accounts for repolarization
K+
___ represents atrial repolarization
Ta wavea
___ represents ventricular repolarization
T wave
Action potential represents
a full depolarization and repolarization sequence
AP of the atrial cells is represented by
P wave
AP of the ventricular cells is represented by
QRS
Membrane potential (MP) is
the voltage measurement of the cell’s membrane when at rest (polarized)
Threshold potential (TP) is
voltage to which a cell must be changed before it can be activated
allows cell to depolarize
MP of pacemaker cells is
-40 mV to - 70 mV
TP of pacemaker cells is
-35mV to -50mV
MP of a non-pacemaker cell is
-90mV
TP of a non-pacemaker cell is
-70 to -80mV
SA node depolarization and conduction through the atrial is reflected as a
rounded P wave
QRS shoots up because
the ventricular cells were resting until they boldly received a stimulus initiating their depolarization
phase 4
resting state
iso-electric line
phase 0
depolarization
fast Na+ channels then slow Ca++ channels
upward deflection R wave
phase 1,2,3
repolarization
phase 1
abrupt closure of fast NA+ channels
start of a downward wave (start of S)
phase 2
plateau stage of AP
K+ out, slow CA++ still opens
open of slow CA++ channels during phase 2 allows :
1.
2.
- bring more Ca++ for contraction
- prolong refractoriness by maintaining the cell in a prolonged depolarized state (allows complete contraction before initiate another one)
Phase 3
slow Ca++ channels close
increase K+ leaving
negative wave (S wave)
absolute refractory period (ARP)
phase 1, 2 and initial part of phase 3
ARP corresponds with
QRS and initial part of the ST segment
Relative refractory period (RRP) corresponds to
-60mV to -90mV in phase 3
conduction of premature impulses is possible slower than in a fully repolarized cell
Vulnerable period
before cell returning to MP(resting)
a weaker stimulus than is normally required (e.g. premature beat) can initiate an AP
vulnerable period corresponds with (on ECG)
peak of T wave
what’s a “R on T phenomenon”
when an impulse strikes during the vulnerable period
