Download Chapter_036_Dysrhythmias

(Relates to Chapter 36,
“Nursing Management: Dysrhythmias,”
in the textbook)
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 Abnormal
cardiac rhythms are termed
dysrhythmias.
 Prompt assessment of dysrhythmias
and the patient’s response to the
rhythm is critical.
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 Automaticity
 Excitability
 Conductivity
 Contractility
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Fig. 32-4. A, Conduction system of the heart. AV, Atrioventricular; SA, sinoatrial. B, The normal
electrocardiogram (ECG) pattern. The P wave represents depolarization of the atria. The QRS
complex indicates depolarization of the ventricles. The T wave represents repolarization of the
ventricles. The U wave, if present, may represent repolarization of the Purkinje fibers or it may
be associated with hypokalemia. The PR, QRS, and QT intervals reflect the length of time it takes
for the impulse to travel from one area of the heart to another.
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 Autonomic
nervous system controls:
• Rate of impulse formation
• Speed of conduction
• Strength of contraction
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 Parasympathetic
nervous system
Vagus nerve
• Decreases rate
• Slows impulse conduction
• Decreases force of contraction
 Sympathetic nervous
system
• Increases rate
• Increases force of contraction
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 Graphic
tracing of electrical impulses
produced by the heart
 Waveforms of ECG represent activity
of charged ions across membranes of
myocardial cells.
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Fig. 36-1. Phases of the cardiac action potential. The electric potential, measured in millivolts (mV), is
indicated along the vertical axis of the graph. Time, measured in seconds (sec), is indicated along the
horizontal axis. There are five phases of the action potential, labeled as phase 0 through phase 4. Each
phase represents a particular electrical event or combination of electrical events. Phase 0 is the upstroke
of rapid depolarization and corresponds with ventricular contraction. Phases 1, 2, and 3 represent
repolarization. Phase 4 is known as complete repolarization (or the polarized state) and corresponds
to diastole. TP, Threshold membrane potential; RP, resting membrane potential.
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Fig. 36-4. A, Lead placement for MCL, using a three-lead system. B, Lead placement for V1 or V6 using a
five-lead system. C, Typical electrocardiogram tracing in lead MCL1. C, Chest; LA, left arm; LL, left leg;
MCL, modified chest lead; RA, right arm; RL, right leg.
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 Rhythm strip
provides documentation
of patient’s rhythm.
 Allows
for measurement of complexes
and intervals
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 Heart
rate ( 60 – 100)
 Is there a P wave before each QRS
 Is PR ( 0.06-0.12 sec) and QRS ( 0.08 –
0.20 sec) intervals WNL
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Fig. 36-5. Time and voltage on the electrocardiogram; 6-second
strip.
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 Count
• The number of QRS complexes in 1
minute
• The R-R intervals in 6 seconds, and
multiply by 10
• Number of small squares between one RR interval, and divide this number into
1500
• Number of large squares between one R-R
interval, and divide this number into 300
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Fig. 36-6. When the rhythm is regular, heart rate can be determined at a glance. The estimated heart rate
is 70.
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 Clip
excessive hair on chest wall.
 Rub
skin with dry gauze.
 May
need to use alcohol for oily skin
 Apply
electrical conductive gel.
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Fig. 36-7. Artifact. A, Muscle tremor. B, Loose
electrodes.
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 Observation
of HR and rhythm at a
distant site
 Two types
• Centralized monitoring system
• Sophisticated alarm system alerts
when it detects dysrhythmias,
ischemia, or infarction.
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 Sinus
node fires 60 to 100 bpm.
 Follows normal conduction pattern
Fig. 36-8. Normal sinus rhythm in lead II.
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Fig. 36-9. The electrocardiogram complex as seen in a normal sinus rhythm. 1, P wave; 2, PR interval; 3,
QRS complex; 4, ST segment; 5, T wave; 6, QT interval. Isoelectric (flat) line represents the absence of
electrical activity in the cardiac cells. (See Table 36-2 for timing of intervals.)
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 Sinus
node fires <60 bpm.
 Normal rhythm in aerobically trained
athletes and during sleep
Fig. 36-11. A, Sinus bradycardia.
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 Clinical
associations
• Occurs in response to
 Carotid sinus massage
 Hypothermia
 Increased vagal tone
 Administration of parasympathomimetic
drugs
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 Clinical
associations
• Occurs in disease states
 Hypothyroidism
 Increased intracranial pressure
 Obstructive jaundice
 Inferior wall MI
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 Clinical
significance
• Dependent on symptoms
 Hypotension
 Pale, cool skin
 Weakness
 Angina
 Dizziness or syncope
 Confusion or disorientation
 Shortness of breath
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 Treatment
• Atropine
• Pacemaker may be required.
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 Discharge
rate from the sinus node is
increased as a result of vagal inhibition
and is >100 bpm.
Fig. 36-11. B, Sinus tachycardia.
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 Clinical
associations
• Associated with physiologic stressors
 Exercise
 Pain
 Hypovolemia
 Myocardial ischemia
 Heart failure (HF)
 Fever
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 Clinical
significance
• Dizziness and hypotension due to
decreased CO
• Increased myocardial oxygen
consumption may lead to angina.
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 Treatment
• Determined by underlying cause
 -adrenergic blockers to reduce HR and
myocardial oxygen consumption
 Antipyretics to treat fever
 Analgesics to treat pain
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