EGC Interpretation Basics Flashcards
Electrocardiogram (ECG)
Visual representation of the hearts electrical activity
Arrhythmia
Without normal rhythm
Dysrhythmia
Disturbance of rhythm
Electrophysiology
Studies the electrical properties of biological cells and tissues
Two functions for cardiac output
Electrical function, mechanical function
Electrical function
Electrical impulses stimulate the heart to contract; initiated by pacemaker cells
Mechanical function
Actual contraction of the heart to generate a palpable pulse; work of myocardial cells
Two types of cardiac cells
Myocardial cells, pacemaker cells
Myocardial cells
Form the muscular layers of the atrial and ventricular walls; contractile filaments, no spontaneous generation (no automaticity), rely on pacemaker cells for impulse
No impulse - No contraction
Pacemaker cells
Specialized cells of the electrical conduction system that; found in SA node and AV junction, purkinje fibres.
Increased contraction Ca++ in the blood increase automaticity
Decreased contractions K+ decrease automaticity
Four intrinsic properties of cardiac cells
Excitability (irritability), conductivity, automaticity, contractility
Excitability (irritability)
Ability of cardiac muscles to respond to an outside stimulus; chemical, mechanical, electrical.
Cardiac muscle is electrically irritable because of ionic imbalance
Conductivity
Ability of a cardiac cell to receive an electrical stimulus and conduct that impulse to an adjacent cardiac cell
Speed of conduction can be altered by factors such as sympathetic and parasympathetic stimulation
Automaticity
Ability of pacemaker cells to initiate an electrical impulse without being stimulated from another source
Contractility
The ability to contract/shorten in length
What two avenues does electrical stimulation occur through?
Sympathetic response, parasympathetic response
Response to sympathetic stimulation
Alpha 1 - arteries = constriction, Lungs = mild bronchoconstriction
Beta 1 - Heart = increased dromotropy, inotropy, chronotropy
Beta 2 - Lungs = smooth bronchial muscle dilation, Arteries = dilation
What is released from the adrenal medulla during sympathetic stimulation?
Norepinephrine / epinephrine
Depolarization
Myocardial cells are bathed in electrolyte solution, chemical pumps maintain the concentrations of ions within the cells, stimulus from the conduction system
Repolarization
Closing of the sodium and calcium channels, restores the negative charge, sodium-potassium pump ( 3 Na+ out, 2 K+in)
Cardiac action potential; phase 0
Depolarization, rapid influx of Na+, slow influx of Ca++, K+ leaves the cell, approx -90 millivolts to +30 millivolts
Cardiac action potential; phase 1
Na+ slowly closes, Cl- enters the cell, K+ still leaving the cell. This results in a slight decrease in positive electrical charges in the cell. Approx +30 millivolts - 0 millivolts
Cardiac action potential; phase 2
Plateau phase; Ca++ slowly enters cell, K+ slowly leaving cell, resulting in a similar positive and negative ion exchange across the cell membrane
Cardiac action potential - Phase 3
Repolarization; Na+ and Ca++ channels close
K+ quickly leaving cell
Resulting in a more negative charge inside the cell
