2. Sinus Rhythm
• Every beat starts with P wave
• One P wave before each QRS
• Every QRS complex come after P wave
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3. RhythmAnalysis
• Step 1: Calculate rate.
• Step 2: Determine regularity.
• Step 3: Assess the P waves.
• Step 4: Determine PR interval.
• Step 5: Determine QRS duration.
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4. Step 1: Calculate Rate
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5. Step 2: Determine regularity
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o Look at the R-R distances (using a caliper or markings
on a pen or paper).
o Regular (are they equidistant apart)? Occasionally
irregular? Regularly irregular? Irregularly irregular?
6. Step 3: Assess the P waves
• Are there P waves?
• Do the P waves all look alike?
• Do the P waves occur at a regular rate?
• Is there one P wave before each QRS?
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7. Step 4: Determine PR interval
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8. Step 5: QRS duration
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9. Normal Sinus Rhythm (NSR)
• Rate:
• Rhythm: Regular
• P Waves: Normal (upright and uniform)
• PR Interval:
• QRS:
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10. ♥ Clinical Tip
• A normal ECG does not exclude heart disease.
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12. Sinus Bradycardia
• Rate:
• Rhythm: Regular
• P Waves: Normal (upright and uniform)
• PR Interval:
• QRS:
Results from slowing of the SA node.
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13. ♥ Clinical Tip
• Sinus bradycardia is normal in athletes and during
sleep.
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14. Sinus Tachycardia
• Rate: ?
• Rhythm: ?
• P Waves: ?
• PR Interval: ?
• QRS: ?
Results from increased SA node discharge.
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15. ♥ Clinical Tip
• Sinus tachycardia may be caused by exercise,
anxiety, fever, hypoxemia, hypovolemia, or cardiac
failure.
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17. First degree heart block
• One P wave per QRS complex
• Prolonged PR interval
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• Rate:
• Regularity:
• P waves:
• PR interval:
• QRS duration:
19. Second degree heart block
• Failure of excitation completely to pass through
AV node or bundle of His.
• There are three variations of this:
1. Mobitz type 2
2. Wenckebach phenomenon
3. Two to one or three to one conduction
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20. Mobitz type 2
• Most beats are conducted with a constant PR interval,
but occasionally there is an atrial contraction without
subsequent ventricular contraction.
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21. What do you see
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22. Wenckebach
• Progressive lengetheninig of PR interval and then
failure of conduction of an atrial beat, followed by
a conducted beat with a shorter PR interval and
then repetition of this cycle.
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23. What do you see
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24. Two to one or three to one conduction
• Alternative conducted and non-conducted atrial beats
(or one conducted and then two non-conducted
beats), 2:1, 3:1.
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25. Third degree block (complete heart block)
• Atrial contraction is normal, but no beats are conducted
to the ventricles (no relationship b/w P waves and QRS).
• Wide QRS complex with rate < 50/min
• Some times narrow QRS complexes with rate 50-60/min
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26. What do you see?
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27. Bundle branch block
• Right bundle branch block: indicates problems in
the RT side of the heart, but with QRS complex of
normal duration is quite common in healthy people.
• Left bundle branch block: is always an indication
of heart disease, usually of the LT side
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28. Remember
oThe septum is normally depolarized from left to right
oThe left ventricle, having the greater muscle mass,
exerts more influence on ECG than does the right
ventricle.
oExcitation spreading towards a lead causes an
upward deflection within the ECG.
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29. Right bundle branch block
• Wide QRS complex
• RSR1 pattern in V1 and
• Deep S wave in lead V6
• Inverted T wave in lead V1 and s/t in V2-3
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35. Left Bundle Branch Block
• If conduction down the LT bundle branch fails,
the septum becomes depolarized from RT to LT,
causing a small Q wave in V1 and R wave in V6.
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37. LBBB
• The RT ventricle is depolarized before the LT, so
despite the smaller muscle mass there is an R wave
in V1and an S wave in V6.
• Remember that any upward deflection, however
small, is an R wave, and any downward deflection,
however small, following an R wave is called an S
wave.
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39. LBBB
• Subsequent depolarization of the LT ventricle
causes an S wave in V1 and another R wave in V6.
• LBBB is associated with T wave inversion in
lateral leads (I, VL, V5-6), though not necessarily
in all of there.
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42. What to remember
• RBBB is best seen in V1, where there is an RSR1
pattern.
• LBBB is best seen in V6, where there is a broad
complex with a notched top, which resembles the
letter ‘M’ and is thus known as an ‘M’ pattern.
• The complete picture, with a ‘W’ pattern in V1, is
often not fully developed.
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43. What do you see in this ECG
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ECG Interpretation
