basics of ecg

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ECG interpretation
Dr mahesh batra Pg adult cardiology Nicvd
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Objectives

• Justify the reasons for performing an ECG
• Develop a structured approach to interpreting an
  ECG
• Practice interpreting ECGs

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The ECG

• The ECG (electrocardiogram) is a transthoracic
  interpretation of the electrical activity of the
  heart.

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21 yo presents for routine physical exam
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Why perform an ECG?

• Indicated by the patients symptoms
• - symptoms of IHD/MI
• - symptoms associated with dysrhythmias
• Indicated by the patients examination findings
• - cardiac murmur

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ECG interpretation

• Quality of ECG?
• Rate
• Rhythm
• Axis
• P wave
• PR interval
• QRS duration
• QRS morphology
• Abnormal Q waves
• ST segment
• T wave
• QT interval

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Intervals Small box large box
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Quality of the ECG

• Patient name
• Date of the ECG
• Is there any interference?
• Is there electrical activity from all 12 leads?
• Calibration
• - speed 25mm/second
• - height 1cm/mV

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Calibration
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ECG interpretation

• Quality of ECG?
• Rate
• Rhythm
• Axis
• P wave
• PR interval
• QRS duration
• QRS morphology
• Abnormal Q waves
• ST segment
• T wave
• QT interval

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Rate

• Rule of 300- Divide 300 by the number of boxes
  between each QRS rate
• Rate is either
• - normal
• - bradycardic
• - tachycardic

Number of big boxes Rate
1 300
2 150
3 100
4 75
5 60
6 50
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Rate How can you count it?
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Rate
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Rhythm
Not sinus
Sinus
Ventricular
Supravent.
Morphology
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Heart Rhythms, Lets Keep It Simple!

• Steps to Rhythm Interpretation
• Is it regular or irregular?
• What is the rate
• (too slow or too fast)?
• Is there a P for every QRS?
• Is there a QRS for every P?
• What is the P-R interval?
• Is the R to R interval regular?
• What is the QRS duration
• (QRS wide or narrow)?

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Mechanisms of Arrhythmogenesis

• Disorder of impulse formation.
• Automaticity.
• Triggered Activity.
• Early after depolarization.
• Delayed after depolarization.
• Disorder of impulse conduction.
• Block
• Reentry.
• Combined disorder.
• It may be clinically difficult to separate.
• Some tachyarrhythmias can be started by one
  mechanism and perpetuated by another. For
  example, an initiating tachycardia or premature
  complex caused by abnormal automaticity can
  precipitate an episode of tachycardia sustained
  by reentry.

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Normal Sinus Rhythm

• Originates in the SA node, follows appropriate
  conduction pathways.
• Rhythm Regular
• Rate 60-100 bpm
• Every P has a QRS and every QRS has a P
• PRI .12-.20 seconds
• QRS .8 -.12 seconds, narrow

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Is the Rhythm Regular?R to R interval should be
Regular
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Irregular Rhythm
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Premature Ventricular Contraction

• PVC complex may be isolated or occur in pairs or
  clusters
• Primary cause electrical irritability
• Potential for developing dysrhthmias increases in
  patients with ischemia or progressive heart
  disease
• Treatment none unless symptomatic
• Rhythm irregular
• P wave usually absent
• QRS greater than .12 seconds and wide and
  bizarre

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PVCs in Couplets

• A pattern of two PVCs following a normal
  complex. Remember Three or more PVCs in a row
  is VT
• A result of ventricular irritability
• QRS gt .12 and wide and bizarre
• Treatment close monitoring to assess
  possibility of ventricular tachycardia, monitor
  labs (potassium and magnesium)

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ECTOPIC BEATS
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Multifocal PVCs
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Bigeminy
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Trigeminy
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Ask why is the rhythm Irregular?

• Early (premature beats)
• Pauses
• Abnormal beats
• Is it slightly irregular?
• This is called Sinus Arrhythmia
• Normal in children and young adults
• Usually result of increased vagal tone

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Axis
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Axis
Positive in I and II NORMAL
Positive in I and negative in II LAD
Negative in I and positive in II RAD
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ECG interpretation

• Quality of ECG?
• Rate
• Rhythm
• Axis
• P wave
• PR interval
• QRS duration
• QRS morphology
• Abnormal Q waves
• ST segment
• T wave
• QT interval

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P Wave Size and Morphology

• Normal duration is less than 0.11 seconds wide(
  or 3 small boxes) and less than 2.5 mm high or
  less than 2.5 boxes high.
• The P-wave should be upright in leads II, III,
  and AVF
• Over 0.12 suggests an intra-atrial conduction
  defect
• The normal p-wave morphology looks like this.

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P wave

• Are there P waves present?
• Bifid P mitrale (LA hypertrophy)
• Pointy P pulmonale (RA hypertrophy)

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P mitrale
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P pulmonale
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PR interval

• Start of P wave to start of QRS complex
• Normal 0.12 - 0.2 seconds (3-5 small squares)
• Decreased can indicate an accessory pathway
• Increased indicates AV block (1st/2nd/3rd)

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Bradycardia Disturbances of cardiac impulse
conduction

• Defined as HR less than 60
• CAUSES
• First degree AV heart block
• Second degree
• Mobitz I
• Mobitz II
• Unifasicular block
• R bundle branch block
• L bundle branch block
• Bifasicular block
• Third degree (trifascicular ) heart block

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First Degree AV Block

• Occurs when impulses from the atria are
  consistently delayed during conduction through
  the AV node.
• First degree AV block is a constant and prolonged
  PR interval.
• May result from insult to the AV node, hypoxemia,
  MI, ischemia, increased vagal tone, aging, beta
  blockers, calcium channel blockers, digitalis
  toxicity but is also seen in normal conduction.
• Rhythm Regular
• Every P has a QRS and every QRS has a P
  
• PRI gt .20 seconds
• QRS lt .12

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Second Degree AV BlockMobitz I (Wenkebach)

• Wenckebach is characterized by progressive delay
  at the AV node until the impulse is completely
  blocked. Possible causes are insult to the AV
  node, hypoxemia, MI, digitalis toxicity,
  ischemia, and increased vagal tone. This
  conduction usually does not progress to higher
  degree heart blocks.
• No treatment needed if patient is asymptomatic
• Rhythm Irregular
• PRI progressive lengthening of PRI until
  dropped beat.
• (long, longer, drop)
• QRS is usually lt .12

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Second Degree AV Block, Mobitz II

• Because the ventricle rate is slow, cardiac
  output may be decreased
• May progress to third degree heart block.
• Occurs when some impulses from SA node fail to
  reach the ventricles
• Usually occurs with AMI, degenerative changes in
  conduction, progressive CAD
• Problem usually occurs at the Bundle of HIS or
  its branches
• Rhythm is irregular (because of dropped beats)
• PRI remains constant until a block of the AV
  conduction, resulting is a P wave not being
  followed by a QRS
• Is there a P for every QRS (YES) is there a QRS
  for every P (NO)?
• Treatment the aim is to improve cardiac output.
  Consider temporary pacing or permanent
  pacemaker. Close monitoring and BP support.

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Third Degree Heart Block

• No conduction through the AV node (divorced
  heart).
• Atrial and Ventricular rate and rhythm are
  independent of one another
• Treatment temp. or permanent pacing
• Rhythm is regular (ventricular and atrial, but at
  diff. rates)
• Rate
• Atrial 60 to 100
• Ventricular 40 to 60
• PRI will vary with no pattern or regularity
• QRS origin of impulse determines QRS width.
• From AV node QRS will be normal
• From Purkinje system QRS will be wide, rate lt 40

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ECG interpretation

• Quality of ECG?
• Rate
• Rhythm
• Axis
• P wave
• PR interval
• QRS duration
• QRS morphology
• Abnormal Q waves
• ST segment
• T wave
• QT interval

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Q wave

• The Q-wave is the first negative deflection after
  the p-wave
• It should not exceed 0.03-0.04 millivolts in
  length or 1 small box.
• Pathological Q waves
• are defined as those that
• are 25 or more of the
• height of the R wave and/or
• greater than 0.04 seconds in height.

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QRS complex

• Normal lt0.12 seconds
• gt0.12 seconds Bundle Branch Block

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QRS complex

• Is there LVH?
• Sum of the Q or S wave in V1 and the tallest R
  wave in V5 or V6
• gt35mm is suggestive of LVH

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Q waves

• Q waves are allowed in V1, aVR III
• Pathological Q waves can indicate previous MI

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ECG interpretation

• Quality of ECG?
• Rate
• Rhythm
• Axis
• P wave
• PR interval
• QRS duration
• QRS morphology
• Abnormal Q waves
• ST segment
• T wave
• QT interval

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ST segment

• ST depression
• - downsloping or horizontal ABNORMAL
• ST elevation
• - infarction
• - pericarditis (widespread)

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ST segment
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ST segment
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ST segment
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T wave

• Small hypokalaemia
• Tall hyperkalaemia
• Inverted/biphasic ischaemia/previous infarct

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T wave
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T wave
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T wave
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QT interval

• Start of QRS to end of T wave
• Needs to be corrected for HR
• Normal QTc lt 400ms
• Long QT can be genetic or iatrogenic

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QT interval
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ECG quiz
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ECG 2
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ECG 3
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ECG 4
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Summary

• Discussed the indications for performing an ECG
• Introduced an approach to interpreting ECGs
• Discussed common ECG abnormalities

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Any questions?
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