2. Abnormal rhythm
• Abnormal cardiac rhythms can begin in one of
three places:
1. The atrial muscle
2. The region around the AV node (this is called
junctional)
3. Ventricular muscle
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4. • These regions can be divided into:
1. Supraventricular: sinus rhythm, atrial rhythm
and junctional rhythm
2. Ventricular rhythm
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5. • In the supraventricular rhythms, the
depolarization wave spreads to the ventricles in
the normal way via the His bundle and its
branches.
• Therefore the QRS complex is normal, and is
the same whether depolarization was initiated by
the SA node, then atrial muscle, or the junctional
region.
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7. • In the ventricular rhythms, the depolarization
wave spreads through the ventricles by an
abnormal, and therefore slower, pathway through
the purkinje fibers.
• So the QRS complex is wide and abnormal.
• Repolarization is also abnormal, so the T wave is
of abnormal shape.
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9. Remember!
1. SV rhythms have narrow QRS complexes
2. Ventricular rhythms have wide QRS
complexes
3. The only exception to this rule occurs when
there is SVR with RT or LT BBB
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10. oAbnormal rhythms arising in the atrial muscle,
the junctional region or the ventricular muscle
can be categorized as:
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11. 1. Tachycardias: fast and sustained
2. Extrasystoles: occur as early single beats
3. Bradycardias: slow and sustained
4. Fibrillation: activation of the atria or ventricles
is totally disorganized.
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12. Atrial escape
• Def.: rate of depolarization of the SA node
slows down and a focus in the atrium takes
over control of the heart.
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13. oAfter one sinus beat the SA node fails to
depolarize
oAfter a delay, an abnormal P wave is seen
because excitation of the atrium has begun
somewhere away from the SA node
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14. oThe abnormal P wave is followed by a normal
QRS complex, because excitation has spread
normally down the His bundle.
oThe remaining beats show a return to sinus
arrhythmia
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16. Junctional escape
• Starts with sinus rhythm,
• Then sudden loss of P waves (indicates either
no atrial contraction or P wave lost in QRS
complex)
• Normal QRS complexes
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18. Ventricular escape
• Most commonly seen when conduction between
the atria and ventricles is interrupted by
complete heart block.
• It can occur without complete heart block and
can be single.
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19. Ventricular escape with complete HB
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21. Sinus Arrhythmia
• The SA node discharges irregularly.
• The R-R interval is irregular.
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22. ♥ Clinical Tip
• The pacing rate of the SA node varies with respiration,
especially in children and elderly people.
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23. Sinus Pause (Sinus Arrest)
■ The SA node fails to discharge and then resumes.
■ Electrical activity resumes either when the SA
node resets itself or when a lower latent pacemaker
begins to discharge.
■ The pause (arrest) time interval is not a multiple
of the normal P-P interval.
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25. ♥ Clinical Tip
• Cardiac output may decrease, causing syncope
or dizziness.
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26. Sinoatrial (SA) Block
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The block occurs in some multiple of the P-P
interval.
After the dropped beat, cycles continue on time.
27. ♥ Clinical Tip
• Cardiac output may decrease, causing syncope
or dizziness.
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28. Extrasystoles
• Atrial extrasystoles have abnormal P waves.
• Junctional extrasystole either is no P wave at all, or
it appears immediately before or immediately after
the QRS complex.
• QRS complexes of atrial and junctional
extrasystoles are the same as those of sinus rhythm.
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29. • Ventricular extrasystoles, however, have
abnormal QRS complexes, which are typically
wide but can be of almost any shape.
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32. • The effect of SV and ventricular extrasystoles on the
following P wave are as follows:
SV extrasystole resets the P wave cycle
Ventricular extrasystole does not affect the SA node,
so the next P wave appears at the predicted time.
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36. ♥ Clinical Tip
SVT may be related to caffeine intake, nicotine, stress,
or anxiety in healthy adults.
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