ECG Interpretation Flashcards
Without normal rhythm
Arrhythmia
Disturbance of rhythm
Dysrhythmia
Studies the electrical properties of biological cells and tissues
Electrophysiology
Two functions of Cardiac Output
- Electrical Function
- Mechanical Function
Electrical impulses stimulate the heart to contract. Initiated by Pacemaker cell
Electrical Function
Actual contraction of the heart to generate a palpable pulse. Work of myocardial cells
Mechanical Functions
Two types of Cardiac Cells
- Myocardial cells
- Pacemaker cells
- No automaticity
- No impulse
- No contraction
Myocardial Cells
- Automaticity
- Increased concentrations of Ca++ in the blood increases automaticity
- Decreased concentrations of K+ decreases automaticity
Pacemaker Cells
4 intrinsic properties of Cardiac Cells
- Excitability (irritability)
- Conductivity
- Automaticity
- Contractility
Ability of cardiac muscle cells to respond to an outside stimulus such as that from a chemical, mechanical or electrical source
Excitability (irritability)
Ability of a cardiac cell to receive an electrical stimulus and conduct that impulse to an adjacent cardiac cell
Conductivity
Ability of pacemaker cells to initiate an electrical impulse without being stimulated from another source
Automaticity
The ability to contract/shorten in length
Contractility
Electrical Stimulation occurs through two avenues
- Parasympathetic
- Sympathetic
Alpha 1 receptor
Arteries= constrict
Lungs= mild bronchoconstriction
Beta-1 receptor
Heart= increased dromotropic, inotropic, Chronotropic
Beta-2 receptor
Lungs= smooth bronchial muscle dilation
Arteries= Dilate
Change in heart rate
Chronotropic
Strength of contractility
Inotropic
Speed of conduction
Dromotropic
Prepares body to respond to various stresses. Norepinephrine/epinephrine release from adrenal medulla
Sympathetic Nervous System
Sympathetic Nervous system also known as
Adrenergic System
Another name for Parasympathetic Nervous system
Cholinergic System
Cardiac cells contain a large number of mitochondria and abundant reserves of myoglobin that store O2. WHY?
So that the heart doesn’t fatigue
Polarization
Resting
Depolarization
Stimulation
- Myocardial cells are bathed in electrolyte solution
- Chemical pumps maintain concentration of ions within cell
- Stimulus from the conduction system
Depolarization
- Closing of the sodium and calcium channels
- Restores the negative charge
- Sodium-potassium pump (3 Na+ out, 2K+ in)
Repolarization
- rapid influx of Na+
- Slow influx of Ca++ K+ leaves cell
- Approximately -90 millivolts to +30 millivolts
Phase 0- Depolarization (contraction)
- Na+ slowly closes
- Cl- enters cell
- K+ still leaving cell
- Resulting in a slight decreases in positive electrical charges in cell
Phase 1
- Ca++ slowly enters cell
- K+ still slowly leaving cell
- resulting in a similar positive and negative ion exchange
- Across the cell membrane
Phase 2- Plateau phase
- Na+ and Ca++ channels close
- K+ quickly leaving cell
- Resulting in a more negative charge inside cell
Phase 3- Repolarization
- Sodium-potassium pump
- 3 Na+ out, 2 K+ in
- Resulting in relaxation of the cardiac muscle
Phase 4- Resting Membrane Potential
Myocardial cell will not respond to stimulus. Corresponds with onset of QRS to peak of T wave. Phase 0, 1, 2 and part of 3
Absolute Refractory Period
Can be stimulated. Corresponds with downslope of T wave
Relative Refractory Period
