ECG Interpretation

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ECG Interpretation
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What is an ECG

• Electrocardiogram
• Traces the electrical activity of the heart
• 12 lead, 15 lead

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Uses of ECG Tracing

• Ischemia/infarct
• Arrhythmias
• Ventricular and atrial enlargements
• Conduction defects
• Pericarditis
• Effects of some drugs and electrolytes

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ECG
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How to Conduct an ECG

• Patient lies flat on back
• Electrodes are placed on the body
• Sites may need to be shaved or cleaned to ensure
  the leads will stick properly.
• Patient will lie as still as possible, hold
  breath, or put hands under bottom to keep from
  moving.
• The results are then printed out on paper for MD
  to review.

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ECG Strip
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Lead Placements

• V1 - Junction of the 4th ICS, Right sternal
  border
• V2 - Junction of the 4th ICS, Left sternal border
• V3 - Midway between V2 and V4
• V4 - Junction of 5th ICS, Mid clavicle
• V5 - Anterior aspect of axilla, same line as V4
• V6 - Mid axilla, same line a V4
• 4 limb leads (for grounding etc)

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Lead Placements Cont
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Normal Conduction Pattern
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Understanding the Waves
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Each wave

• P
• Q
• R
• S
• T

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ECG Strip r/t heart
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Understanding the Waves

• One small box 0.04 seconds
• One large box 0.2 seconds
• 5 large boxes 1 second

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Understanding the Waves

• Baseline (what is it?)
• P wave
• Length of time it takes the impulse to pass from
  the SA node to the AV node
• Should precede every QRS wave
• PR interval
• Should be no longer than 0.12 0.2

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Understanding the Waves

• QRS
• Should be no longer than 0.12
• If energy is going towards a positive electrode
  (camera), the picture will show a positive QRS
  complex
• If energy is going away from positive electrode,
  the picture will show a negative QRS complex
• If energy is toward the positive electrode and
  then passes by it, the QRS will be biphasic
• Ventricle contracting

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Understanding the Waves

• T wave
• Should always start from baseline
• Will indicate ischemia

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Understanding an ECG

• Is as easy as
• 1.
• 2.
• 3.
• rate
• intervals
• rhythm

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Step 1 Rate

• Different ways to calculate a rate
• a) ECG usually tells you
• b) Locate a QRS that is close to a big line and
  count to next big line 300, 150, 100, 75, 60, 50
• c) take a 6 second strip, count QRS and multiply
  by 10 (hint the middle of V3 on the lead II
  strip is 6 seconds)

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Step 1 Rate (cont)

• Checking the regularity
• map out QRSs

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Step 2 Intervals

• We assess intervals to see where the impulse is
  coming from (pacemaker beat)
• Remember
• PR interval normal is 0.12 - 0.2
• QRS interval normal is less than or equal to
  0.12

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Step 3 Rhythm

• The biggest question in relation to rhythm is

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• Is this rhythm affecting my patient?

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(Normal) Sinus Rhythm

• 60-80 bpm
• P preceding each QRS
• Normal intervals

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Normal ECG
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Other Sinus Rhythms

• Sinus bradycardia
• a sinus rhythm with a rate lt60 bpm

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Other Sinus Rhythms

• Sinus tachycardia
• a sinus rhythm with a rate gt80 bpm

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Atrial Arrhythmias

• Atrial fibrillation (A-fib)
• irregular rate
• no discernable P waves
• increased risk of strokes due to clots that might
  form due to fibrillation (patients are usually on
  anticoagulation therapy)

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Atrial fibrillation
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Atrial Arrhythmias Cont

• Atrial flutter
• saw tooth in appearance
• irregular rate

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Atrial flutter
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Blocks

• 1st degree AV block
• a PR interval that exceeds 0.20 sec

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Blocks Cont

• 2nd degree AV block (Mobitz)
• a) type I (Wenckebach)
• longer and longer PR intervals until a QRS is
  dropped

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Blocks Cont

• b) type II
• P waves and then suddenly a QRS is dropped
• Ps are regular

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Blocks Cont

• 3rd degree AV block
• HR lt40 bpm
• a complete block of electrical activity from
  atria to ventricle
• Ps are regular

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Ventricular Rhythms

• Ventricular fibrillation
• complete breakdown of all rhythm
• a) course
• b) fine

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V-fib

• Whats the first thing to do when coming up on a
  patient with this rhythm?

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Ventricular Rhythms Cont

• Ventricular tachycardia (V-tach)
• impulse originates in the ventricle
• always has a wide QRS complex

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V-tach Whats the first thing to do when coming
up on a patient with this rhythm?
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Asystole

• Pulseless

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Coronary Arteries
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MIs
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MIs
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MIs

• How can you tell on an ECG that your patient is
  having a heart attack?
• T waves
• Different views of heart will show different
  injured areas of heart

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MIs

• T wave shouldering is classic

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MIs

• How else can you tell that your patient has had
  an MI?
• Cardiac Markers
• CK will show in 4-6 hours (starts to come back
  down after 1 day)
• Troponin will show in 4-6 hours (may stay
  elevated for weeks)
• Others are LDH, CK-MB, myoglobin, AST

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Locating an MI
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I Lateral (circumflex) aVR V1 Anterior (Lt ant desc) V4 Anterior
II Inferior (Rt coronary) aVL Lateral V2 Anterior V5 Lateral
III Inferior aVF Inferior V3 Anterior V6 Lateral
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ECG Tissue Damage Locations
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Where is this MI?