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.