ELECTRO CARDIOGRAM ECG BASIC PRINCIPLE LEARNING OBJECTIVES At the end of the lecture the student should be able to know • About ECG • Basic principle in generation of ECG waves • About ECG paper and its calibration • About different leads and their arrangement • About different components of ECG
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ELECTRO CARDIOGRAM ECG
BASIC PRINCIPLE
LEARNING OBJECTIVES
At the end of the lecture the student should be able to know
• About ECG
• Basic principle in generation of ECG waves
• About ECG paper and its calibration
• About different leads and their arrangement
• About different components of ECG
ELECTROCARDIOGRAM ECG
• Graph of electrical activity of heart
• Gold standard for diagnosis of cardiac arrhythmias
• Helps detect electrolyte disturbances (hyper- &
hypokalemia)
• Allows for detection of conduction abnormalities
• Screening tool for ischemic heart disease during stress
tests
• Helpful with non-cardiac diseases (e.g. pulmonary embolism or
hypothermia
PROPAGATING ACTIVATION WAVEFRONT
• At rest, cells have a negative transmembrane
voltage – surrounding media is positive
• When cells depolarize, they switch to a positive
transmembrane voltage – surrounding media
becomes negative
• This leads to a propagating electric vector
(pointing from negative to positive)
• PROPAGATING ACTIVATION WAVEFRONT
BASIC PRINCIPLE OF ECG RECORDING
• Wave of depolarization traveling towards a positive
electrode causes an upward deflection on the ECG
• Wave of depolarization traveling away from a
positive electrode causes a downward deflection on
the ECG.
COMPONENT OF ECG
WAVES
• P – atrial depolarization
• QRS complex – ventricular depolarization
• T – ventricular repolarization
SEGMENT—straight line between waves
• S-T segment
• end of ventricular depolarization to start of vent.
Repolariztion
INTERVAL---wave+segment
• P-R interval
• Q-T interval
RECORDING ECG
ECG PAPER
• Recorded on a calibrated graph paper
• Smallest divisions are 1mm square in both X and Y axis
• Runs at a paper speed of 25 mm/sec
• X axis represent time
• Y axis represents voltage
• On Y axis 1 mm=0.1 mV
• On X axis 1mm =0.04 sec
VERTICAL AXIS
• 1 small square = 0.1 mV
• 10 small square =10 mV
• 1 big square = 5 small square = 0.5 mV
• 2 big square = 10 smallsquare= 1 mV
• ECG PAPER HORIZONTAL AXIS
• 1 inch = 1 second
• Each inch is divided by dark black lines into 5 big square
• Each big square= 1/5=0.2 sec
• Each big square is further divided into 5 small square
• 1 small square = 0.2/5= 0.04 sec
• 1smallsquare = 0.04 sec =1mm
• 1 second =25 smallsquare
• 60second =1min =25 X 60=1500 small square =300 big square
ECG PAPER CALIBRATION
ECG LEADS SYSTEM
Lead
– two electrodes which are placed on body surface and connected to
ECG machine for measuring the potential fluctuations between two