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ECG Interpretation
Chapter 22
ECG Interpretation
1. Rate
a. Atrial rate: PP interval
b. Ventricular rate: RR interval
2. Rhythm
a. P wave
b. PR interval
c. QRS
i. voltage (height)
ii. width
3. Axis
4. Hypertrophy
5. Blocks
6. Infarct
7. Ischemia
Standardization
Standardization mark10 mm vertical deflection = 1 mVolt
Rate
Ventricular rate (heart rate)RR interval
Atrial ratePP interval
3rd degree AV block
Heart Rate Calculation
1500 divided by the number of small boxes between two R waves
•most accurate•take time to calculate•only use with regular rhythms
1 lg sq = 300 bpm2 lg sq = 150 bpm3 lg sq = 100 bpm4 lg sq = 75bpm5 lg sq = 60 bpm6 lg sq = 50 bpm
300 divided by the number of large boxes between two R waves
•quick•not too accurate•only use with regular rhythm
10 multiplied by the number of R waves in 6 seconds
•less precise•use with irregular rhythms•very quick
Rhythm
Sinus rhythm - consistent P wavesAtrial rhythm - irregular P wavesJunctional/Nodal rhythm - no P waves, late P waves, or inverted P wavesVentricular rhythm - no P waves, wide QRS
AV Junctional Rhythms
Retrograde P waves immediately preceding the QRS complexes in aVR and II.Retrograde P waves immediately following the QRS complexesAbsent P waves
ECG Waves
P waveatrial depolarization
≤ 2.5 mm in amplitude< 0.12 sec in width
PR interval (0.12 - 0.20 sec.)time of stimulus through atria and AV node
prolonged interval = first-degree heart block
P wave
Tall = RAEWide = LAE
PR Interval
Long PR interval = first degree AV blockShort PR interval = WPWShort PR interval with inverted P waves = ectopic atrial or junctional pacemaker
Classification of AV Heart Blocks
Degree AV Conduction Pattern
1St Degree Block Uniformly prolonged PR interval
2nd Degree, Mobitz Type I Progressive PR interval prolongation
2nd Degree, Mobitz Type II Sudden conduction failure
3rd Degree Block No AV conduction
Wolff-White-Parkinson
Wide QRSdue to early depolarization not due to a delay in depolarization
Shortened PR intervalUpstroke QRS complex is slurred; delta wave
ECG Waves
QRSwidth 0.12 second or less
Normal QRS
V1? V1?
V6? V6?
Fig. 4-6
Normal Q waves
• Septal r wave
• Septal q wave
Q WavesAbnormal if wider than 0.04 sec
Leads I, II, III, aVf or leads V3 - V6.Greater than 25% of the R waveNote: Not all Q waves are abnormal, Not all Q waves are the result of MI.
QRS Width
WideRBBB or LBBBPremature ventricular beatsWPW
QRS Voltage
RVHLVH
Mean QRS Axis
Axis Deviation
LEAD ILEAD aVF
(or Lead II or III)
LEAD aVR
Normal Positive Positive
LAD Positive Negative
RAD Negative Positive Positive (or Negative)
Intermediate axis Negative Negative
R Wave Progression
Transmural MI
Ischemia Tall T waves (and/or reciprocal T wave inversion)
InjuryST segment elevation.T wave inversion of the previously tall T waves
InfarctPathalogical Q waves
(at least one small box wide or 11/3 the entire QRS height)
Overview
LEAD AREA OF THE HEART
V1-V2 Anterior/Septum
V3-V4 Anterior Wall
V5-V6 Anterior/Lateral
II, III, aVF Inferior
I and aVL Lateral
V1-V2 Posterior (reciprocal)
ST SegmentsJ point:
end of QRS wavebeginning of ST segment
ST segmentbeginning of ventricular repolarizationnormally isoelectric (flat)changes, elevation or depression, may indicate pathological condition
Subendocardial Ischemia
ST segment depression criteria1 mm or morehorizontal or downwardlasts 0.08 secondsdepression of only the J point with rapid upward sloping are considered normal.