dr.noha elsayed cardiovascular monitoring electrocardiogram
TRANSCRIPT
DR.NOHA ELSAYED
Cardiovascular Monitoring
Electrocardiogram
, Cardiovascular System
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Electrocardiography
Electrical activity is recorded by electrocardiogram (ECG)
P wave corresponds to depolarization of SA node
QRS complex corresponds to ventricular depolarization
T wave corresponds to ventricular repolarization
Atrial repolarization record is masked by the larger QRS complex
Cardiovascular System: Intrinsic Conduction System
Chapter 18, Cardiovascular System
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Electrocardiography
Figure 18.16
Isoelectric line
No electrical activity baseline
EKG Records
1. Amount of voltage generated by ht – vertical scale
2. Time required for voltage to travel thru ht – horizontal scale
ECG Interpretation
What is your approach to reading an ECG?1. Rate 2. Rhythm3. Axis4. P wave5. PR interval6. QRS complex7. QT interval 8. ST segment – T wave
EKG Interpretation: 8 criteria
1. What is the rate? Quick estimate:
Count # R waves in a 6 second strip x 10 6 second strip = 3 “tic” marks
Square Counting: 300-150-100-75-60-50-42A
Role of 300
Take the number of “big boxes”between neighboring QRS complexes, and divide this into 300. The result will be approximately equal to the rate
Although fast, this method only works for regular rhythms.
10 Second Rule
As most EKGs record 10 seconds of rhythm per page, one can simply count the number of beats present on the EKG and multiply by 6 to get the number of beats per 60 seconds.
This method works well for irregular rhythms.
Rythm
2. Is rhythm regular or irregular? Measure distance between RR interval Measure throughout full 6 second strip
Axis
3.Left or right axis deviation?Look at limb leads I and aVF.Normal: I +, aVF + LAD: I +, aVF – RAD: I -, aVF +
Axis Deviation
QRS-axis
4-P WaveFirst component of a normal ECGRepresents the spread of electrical activity over
the atrium, atrial depolarization. The normal depolarization begins at the sinoatrial (SA) node near the top of the atrium. Because of the top-to-bottom, right-to-left path, the P wave is normally largest in Lead II
Configuration: usually rounded and upright in all leads except R
Amplitude is usually 2-3 mv in any lead
Are P waves present? Should be 1:1
Abnormal rhythms with P waves
5. What is the PR Interval? PRI
PR Interval
Measured from the beginning of the P wave (atrial depolarization) to the beginning of the QRS complex (ventricular depolarization)
Represents the time it takes for an impulse to travel from the SA node through the atria and the AV node
Normally between 0.12 to 0.20 seconds in durationIf prolonged, > 0.20 seconds
indicates conduction delay through the AV node and is called a 1st degree AV block
6. What is the width of QRS complex?
Normal QRS duration is 0.06 to 0.12 seconds
QRS Complex
Represents activation of the ventricles, ventricular depolarization Special conducting bundles spread the wave of depolarization
rapidly over the bundles May have one, two or all three components : Q R S Q wave is the first negative wave after the P wave and before the
R wave. The Q wave represents activation of the ventricular septum
R wave is the first positive wave after the P wave. Most of the ventricle is depolarized during the R wave. S wave is the negative wave after the R wave. Lengthening of the QRS indicates some blockage of the electrical
conduction system either due to ischemia, necrosis of the conducting tissue, electrolyte imbalance or hypothermia
Sinus Rhythm Impulse originates in SA node (normal pacemaker site)
Normal Sinus Rhythm - NSR Regularity – regular Rate - 60 – 100 / minute P waves = 1:1 PRI = .12 - .20 QRS = .12 or <
7-Q-T Interval
QT interval represents total ventricular activity. It is the summation of ventricular depolarization to repolarization
Can vary with heart rateMeasured from the beginning of the Q wave to the end
of the T waveCorrected QT interval (QTc) takes heart rate into
account and provides various normal values based on the rates
Rule of thumb – QT interval should be less than half the preceeding R-R interval
The U wave represents repolarization of the Purkinje fibers but isn’t always seen on paper. A prominent U wave may be caused by hypercalcemia or hypokalemia
8.ST segment & T wave
Normal Values
PR interval: 0.12-0.21 sQRS complex: 0.06-0.1
sQT interval: < 0.44 s- HR dependent, cave:
long QT syndrome!ST segment changes:- significant if > 1mm
in limb leads, > 2mm in precordial leads
Q waves: significant if > 1/3 of
total QRS complex