Basic Interpretation of Electrocardiograms

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Basic Interpretation ofElectrocardiograms

• David Putnam, MD
• Albany Medical College

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ECG Reading

• Do not over-complicate

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ECG Reading

• Rhythm Strip
• A. Rate B. Rhythm C. Intervals
• Axis
• Chamber Enlargement
• Myocardial Infarction and Ischemia

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ECG Reading Rate

• Can be calculated by dividing the number of large
  boxes ( each 200 msec long ) contained in a R-R
  interval into 300

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ECG Reading Rhythm

• A. Analyze for the following
• Varying rhythm
• Rapid/Slow rhythm
• Extra beats
• Heart Blocks

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Supraventricular Rhythms

• Sinus rhythms
• Atrial rhythm
• Wandering atrial pacemaker
• Multifocal atrial tachycardia
• Paroxysmal atrial tachycardia
• Atrial fibrillation/flutter
• Junctional rhythm

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Sinus Rhythms

• P-wave preceeds each QRS complex
• PR interval is constant
• P-wave morphology remains constant

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Sinus Rhythms

• Sinus Rhythm rate 60 to 100 in adults ( some
  authors suggest 50 to 90 )
• Sinus Tachycardia rate greater than 90 to 100 (
  usually less than 160 to 170 )
• Sinus Bradycardia rate less than 50 to 60
• Sinus Arrhythmia rate 60 to 100, but P-P
  interval varies more than 160 msec

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Wandering Atrial Pacemaker

• Amplitude and morphology of P wave varies from
  beat to beat
• Variable PR, PP, RR intervals
• Atrial rate 60 to 100

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Multifocal Atrial Tachycardia

• P waves of varying morphology
• Absence of one dominant atrial pacemaker
• Variable PR, PP, RR intervals
• Atrial rate above 100

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Paroxysmal Atrial Tachycardia

• Abnormal P-waves
• Atrial rate 140 to 220
• Regular rhythm
• QRS complex after each P-wave ( Usually narrow,
  but may be wide from aberrant conduction )
• Secondary ST and T-wave changes may occur
• Abrupt onset and termination

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Atrial Tachycardia with AV Block

• Abnormal P-waves
• Atrial rate 150 to 220
• Isoelectric intervals between P-waves
• AV block

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Atrial Fibrillation

• P waves are absent
• Atrial activity represented by fibrillatory waves
• Ventricular rhythm ( in absence of AV block ) is
  irregularly irregular

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Atrial Flutter

• Atrial deflections consist of rapid regular
  undulations (F waves) giving rise to sawtooth
  appearance in some leads
• Atrial rate usually between 250 and 350
• Rate and regularity of ventricular complexes are
  variable
• QRS complex may be normal or abnormal

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Junctional Rhythm

• Rate normally 40 to 55
• QRS complex narrow
• P wave may precede , superimpose on, or follow
  QRS complex
• PR

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Ventricular Rhythms

• Idioventricular rhythm
• Accelerated idioventricular rhythm
• Ventricular tachycardia
• Ventricular fibrillation
• Paced rhythm

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Idioventricular Rhythm

• Abnormal and wide QRS complex
• Secondary ST and T wave changes
• Ventricular rate 30 to 40

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Ventricular Tachycardia

• Abnormal and wide QRS complex
• Secondary ST and T wave changes
• Ventricular rate 140 to 200
• Regular or slightly irregular
• AV dissociation
• Capture/fusion beats may be present

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Atrioventricular Blocks

• First degree
• Second degree
• Third degree

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First Degree AV Block

• P-R interval 200 msec
• Each P wave is followed by a QRS complex

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Type I Second-Degree AV Block

• Progressive lengthening of P-R interval until a P
  wave is blocked
• Progressive shortening of R-R interval until a P
  wave is blocked
• Group beating

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Type II Second-Degree AV Block

• Intermittent blocked P waves
• P-R intervals remain constant in the conducted
  beats

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Third Degree ( Complete ) AV Block

• Independence of the atrial and ventricular
  activities
• Atrial rate is faster than the ventricular rate
• Ventricular rate maintained by either a
  junctional or an idioventricular pacemaker

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Extra Beats

• Premature atrial contractions
• Premature junctional contractions
• Premature ventricular contractions

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Premature Atrial Contractions

• Originates from ectopic focus in atrium
• P-wave is premature in relation to the basic
  sinus rhythm
• P-wave morphology is abnormal
• P-R interval may be normal, short, or long
• Ventricular complex may be normal, aberrant, or
  blocked
• Cycle length after APC is long but not full
  compensatory pause

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Premature Junctional Contractions

• Originates from ectopic focus in AV node
• P-waves inverted in II, III, aVF
• P-wave may precede, superimpose on, or follow the
  QRS complex
• P-R interval less than 110 msec
• Ventricular complex may be normal, aberrant, or
  blocked
• Cycle length after premature beat is long but not
  full compensatory pause

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Premature Ventricular Contractions

• VPCs from the same focus tend to have constant
  coupling interval
• QRS complex is abnormal in duration and
  configuration
• Secondary ST and T-wave changes
• Retrograde capture of the atria may or may not
  occur

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ECG Reading Normal Intervals

• PR 120 to 200 msec
• QRS 60 to 100 msec
• QT 30 to 46 msec
• Increases with bradycardia, decreases with
  tachycardia
• Tends to be longer in women
• Should be less than half of the R to R interval

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Intraventricular Conduction Delays
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Left Bundle Branch Block

• QRS duration 120 msec or greater
• Monophasic R in I, V5, V6, which is usually
  notched or slurred
• Absence of Q wave in I, V5, V6

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Right Bundle Branch Block

• QRS duration 120 msec or greater
• Secondary R wave (R) in right precordial leads
  with Rinitial R wave
• Wide S wave in I, V5, V6

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ECG Reading Axis

• Normal Axis QRS upright in I, aVF
• Left Axis Deviation QRS upright in I, inverted
  in aVF
• Right Axis Deviation QRS inverted in I, upright
  in aVF
• Extreme Right Axis Deviation QRS inverted in I,
  aVF

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Chamber Enlargement
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Left Atrial Enlargement

• Wide P wave, 110 msec in duration in any lead
• Notch in the P wave in any lead with the two
  peaks 400 msec apart
• Negative deflection in terminal portion of P wave
  in V1 1 mm deep and 1mm wide

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Right Atrial Enlargement

• P wave tall and peaked in II, III, aVF
• P wave amplitude 2.5

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Left Ventricular Hypertrophy

• Major Criteria
• Increased QRS voltage in standard leads ( R wave
  in I plus S wave in III 25 mm )
• Increased precordial voltage ( S wave in V1 plus
  R wave in V5/V6 35 mm
• ST segment and T wave abnormalities
• Left atrial abnormality

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Left Ventricular Hypertrophy

• Other Criteria
• R wave in aVL 11 mm
• R or S wave in any limb lead 20 mm
• R wave in V5/V6 30 mm
• S wave in V1/V2 30 mm

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Left Ventricular Hypertrophy

• Possible LVH 1 of first 3 criteria
• Probable LVH 2 of major criteria
• Definite LVH 3 of major criteria

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Right Ventricular Hypertrophy

• Tall R wave in V1 ( 7 mm )
• Right axis deviation
• R/S ratio in V1 1
• rSR in V1 with R 10 mm
• Inverted T waves in V1 and sometimes in V2, V3
• Deep S waves V4 to V6 are common

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Myocardial Infarction/Ischemia
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Myocardial Infarction/Ischemia

• ST segment depression subendocardial ischemia
• ST segment elevation transmural ischemia
• Q-wave transmural infarction

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Q Waves

• Pathological Q waves are at least 40 msec in
  duration and as deep as 1/4 to1/3 the height of
  the QRS complex
• Normal, non-pathological Qs are often seen in I,
  aVL, V5, V6 from septal depolarization
• Normal, non-pathological Q may be seen in III

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Infarct Location

• II, III, aVF
• V1 to V2
• V1 to V2
• V2 to V4
• V3 to V5
• V5 to V6
• I, aVL

• Inferior
• Posterior
• Right
• Anteroseptal
• Anterior
• Apical
• High Lateral

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LBBB ECG Diagnosis of Acute MI

• Concordant ST-segment elevation 1 mm
• Discordant ST-segment elevation 5 mm
• ST-segment depression V1, V2, or V3
• NEJM 1996(Feb)334481-7.