Electrophysiology Flashcards
Depolarization
Stimulates contraction
Repolarization
Resting cell, recovery from depolarization
Sodium (Na+) electrolyte roll in cardiac function
Flows into cell to initiate depolarization
Potassium (K+) electrolyte roll in cardiac function
Flows out of cell to initiate repolarization
Calcium (Ca++) electrolyte roll in cardiac function
Moves slowly into the cell, depolarization of pacemakers, maintains depolarization and myocardial contractility
Magnesium (Mg++) electrolyte roll in cardiac function
Stabilizes cell (works with K+), opposes Ca++
Hypercalcemia
High Ca++
High contractility
Hypocalcemia
Low Ca++
Low contractility
High myocardial irritability
Hypermagnesemia
High Mg++
High myocardial irritability
Hypagnesemia
Low Mg++
Decreased conduction
Hyperkalemia
High K+
High myocardial irritability
Hypokalemia
Low K+
Decreased automaticity/conduction
Cardiac Action Potential Phase 0
Cell depolarizes & begins to contract
Cells receive impulse
Na+ enters cell (positive change in TMP to meet threshold of -70 mV)
More sodium rapidly shoots up to +30 mV
Calcium start to enter slowly
QRS complex (really RQ segment)
Cardiac Action Potential Phase 1
Repolarization starts
Inward Na+ channels close
Negative chloride ions enter cell
Outward K+ channels open briefly (slight decrease in TMP, negative charge)
QS segment
Cardiac Action Potential Phase 2
Plateau phase (longest phase)
Na+ & Ca++ slowly enters cell while K+ flows out of cell (prolongs depolarization, creating plateau
Ends when outward flow of K+ exceeds Na+ & Ca++
ST segment
Cardiac Action Potential Phase 3
Final phase
Slowly Ca++/Na+ channels close
K+ rapidly leaves cell (causing TMP to drop and go negative)
T wave
Cardiac Action Potential Phase 4
Resting phase
Membrane potential of -90 mV
Transmembrane potential (TMP)
Change in the charge of a myocardial cell (-90 mV at rest)
Absolute refractory period (ARP)
Cardiac cells are unable to respond to any stimulus
Phase 0-3 of cardiac action potential
“If you flush a toilet, it needs time to refill”
Relative refractory period (RRP)
Enough cells have repolarized sufficiently to depolarize again
Mid phase 3 to beginning of phase 4
Time AV node delays pulse
0.12 seconds
Allows atria to empty blood into ventricles
AV junction includes:
AV node, surrounding tissue, non-branching portion of bundle of His
Time for pulse to spread across ventricles?
0.08 seconds
Ischemia definition
Tissue injury caused by hypoxia
Secondary pacemaker (bpm): AV node
40-60 bpm
Secondary pacemaker (bpm): Purkinje fibers
20-40 bpm
Bundle of Kent
Between left atrium and left ventricle
Triggers early depolarization in L. Ventricles
ECG - Delta waves
Sympathetic nervous system on heart, enzyme,
Accelerator
Norepi to SA node, AV node, ventricles
Parasympathetic nervous system on heart, nerve, enzyme,
Inhibitory, vagus nerve, acetylcholine
Vagus nerve stimulation, cause on heart
Increases corotid sinus pressure, straining/forced exhalation (valsalva maneuver), distention of hollow organ (bladder/stomach)
Bradycardia
Common drug to fight parasympathetic nervous system/bradycardia
Atropine
Baroreceptor
Detects changes in blood pressure in blood
creates CNS response
Chemoreceptor
Detects change in hydrogen ions (pH), O2, CO in blood
Creates CNS response
