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ECG ch2

Basic Electrophysiology

Specialized cells of the hearts electricial system also referred to as conducting or automatic cells Packemaker cells
The ability of cardiac pacemaker cells to creat an electrical impulse without being stimulated from another source Automaticity
Also called irritability referes to the ability of cardiac muscle cells to respond to an outside stimulus Excitability
Refers to the ability of a cardiac cell to receive an elecrtrical impulse and and conduct ut to an adjoining cardiac cell Conductivity
The ability of myocardial cells to shorten in response to an impulse which results in contraction Contractility
The flow of electrical charge from one point to another Current
The measurement of potential energy is Voltage
Elements or compounds such as NA+ K+ CA+ and CL- that break into charged particles (ions) when melted or dissolved in water or other solvent Electrolytes
Five phase cycle that reflects the difference in the concentration of these charged particles across the cell membrane at any given time Action potential
When the inside of a cell is more negative then the outside Polarized state
The voltage (difference in electrical charges) across the cell membrane Membrane potential
The ability of a membrane channel to allow passage of electtolytes once it is open Permeable
The movement of charged particles across a cell membrane causing the inside of the cell to become positive Depolarization
The movement of charged particles across a cell membrane in which the inside of the cell is restored to its negative charge Repolarazition
Phases 1,2,3 are referred to as Electrical systole
Phase 4 is referred to as Electrical diastole
This phase represents depolarazition. It is the rapid entry of NA+ into the cell Phase 0
During this phase the NA+ channels partially close, slowing the flow of NA+ into the cell. At the same time CL- enters and K+ leaves. Resulting in a decrease in the # of positive electrical charges within the cell Phase 1
The plateau phase. During this phase the CA++ slowley enters the cell as K+ continues to leave the cell slowley. It allows cardiac muscle to sustain an increased period of contraction Phase 2
This phase begins with the downslope of the action potential. The cell rapidly completes repolarazition as K+ quickly flows out of the cell which causes the inside to become more negative NA+ and CA+ channels close stopping the entry of the two. Phase 3
The resting membrane potential. During this phase an excess of NA+ is inside and K+ outside the cell. The NA+/K+ pump is activated to move NA+ outside and K+ back into the cell. The heart is polarized during this phase. Phase 4
The cell will not respond to further stimulation Absolute refractory period aka Effective refractory period
Some cardiac cell have repolarized to their threshold potential and can be stimulated to respond to a stronger than normal stimulus. This corosponds with the T wave Relative refractory period aka Vulnerable period
After the relative refractory period, a weaker then normal stimulus can cause cardiac cells to depolarize during this period. It extends from the end pf phase 3 to the beginning of phase 4 Supernomral period
The soecialized electrical cells in the heart are arranged in a system of pathways called Conduction system
When the AV junction is bypassed by an abnormal pathway the route is called Accessory pathway
The leads that view the inferior surface of the heart II, III, aVF
The leads that view the septal surface of the heart V1 and V2
The leads that view the anterior surface of the heart V3 and V4
The leads that view the lateral surface of the heart I, aVL, V5, and V6
It represents the spread of the impulse through the AV node, bundle of His, right and left bundle brnaches and the Purkinje fibers. It normally shortens as heart rate increases PR interval
Normal rate for PR interval .12-.20 secs
total ventricular activity- the time from ventricular depolarazition to repolarazition QT Interval
Duration of the QT interval under .38 secs
It represents activation of the AV node, the bundle of His, the bundle branches and the Purkinje fibers PR segment
It represents the early part of repolarazition of the right and left ventricels ST segment
Duration of the ST segment .5 to +2mm
Represents atrial depolarazition P wave
Duration of a P wave no more then .11 secs
Represents the spread of the electricial impulse through the ventricles (ventricular depolarazition) QRS Complex
Duration of a QRS complex .10 secs or less
Represents ventricluar repolarazition T wave
The primary pacemaker SA Node
The PR interval is considered prolonged if it is more then .20 secs
Which part of the conduction system receives an impulse from the bundle of His and relays it to the Purkinje fibers Right and left bundle branches
On the ECG the time necessary fot the spread of an electrical impulse through the AV nodes, bundle of His, right and left bundle branches and the purkinje fibers is represented by the PR segment
The portion of the ECG tracing used to determine the degree of ST segment displacement TP or PR segment
Part of the conduction system that reseives an impulse from the SA node but delays relaying that impulse to the bundle of His, allowing time for the atria to empty their contents into the venticles before the onset of ventricular contraction AV Node
Five large boxes each consisting 5 small boxes represents ? on ECG paper 1 second
When using a 12 lead ECG this surface of the heart is not directly viewed Right ventricle and posterios surface of the left ventricle
The appearence of coved ( frowny face) ST segment elevation is called Acute injury pattern
A line between waveforms is called Segment
The spread of an impulse through tissue already stimulated by that same impulse Reentry
The cells of the heart that contain contractile filaments are called Myocardial cells
Distortion of an ECG tracing by electrical activity that is noncardiac in origin is called Artifact
A waveform and a segment Interval
The relative refractory period is also called Vulnerable
An ECG machine is a sophisticated ? Voltmeter
This condition causes ST segment elevation in all or virtually all leads Pericarditis
An important electrolye that affects cardiac function Potassium
The difference in electrical charges across the cell membrane Membrane potential
The amplitude of a waveform is measured in millimeters
The ability of cardiac muscle cells to respond to an outside stimulus Excitability
The a in aVR, aVL and aVF Augmented
In leads I and II the right arm is Negative
This medication will increase the heart rate and force of contraction Epinephrine
A ? pacemaker is a pacemaker site other than the SA node Escape
Several waveforms Complex
The spread of an impulse through tissue already stimulated Reentry
When the inside of a cell is more negative then the outside Polarized
The stimulus that alters the electrical charges across the cell membrane may be electrical mechanical or ? Chemical
Depolarazition is caused by the movement of ? into the cell Sodium
Each electrode placed in the V position is a Positive electrode
Rate of SA node 60-100
Rtae of the AV node 40-60
rate of the ventricles 20-40
Four properties of cardiac cells 1.Automaticity 2.Excitability 3. Conductivity 4.Contractility
Created by: nju9552