5. Conduction System
• Each component of the conductive system has
its own intrinsic rate of self-excitation.
• SA node = 60–100 beats per minute
• AV node = 40–60 beats per minute
• Purkinje system = 15–40 beats per minute
7. Electrocardiographic
Monitoring
• Electrocardiogram (ECG) is a graphic record of the
heart’s electrical activity.
• Tells you nothing about the heart’s pumping ability,
which you must evaluate by pulse and blood pressure.
• The body acts as a giant conductor of electricity.
• The heart is its largest generator
• Electrodes on the skin can detect the total
electrical activity within the heart.
9. The Electrocardiogram
ECG Leads
Bipolar (Limb)
▪ Einthoven’sTriangle
▪ Leads I, II, III
▪ Provide only one view of the heart
Augmented (Unipolar)
▪ aVR, aVL, aVF
Precordial
▪ V1 –V6
▪ Measure electrical cardiac activity
on a horizontal axis
▪ Help in viewing the left ventricle
and septum
10. The Electrocardiogram
• Routine Monitoring
• Routine ECG monitoring generally uses only one lead
• Most common monitoring leads are either lead II or the
modified chest lead 1 (MCL1)
• Einthoven’s triangle offers a basis for placing the leads
• Place the electrodes on the chest wall
• Lead placement
11. Single Lead Monitoring
• Information from a single
lead shows:
• Rate
• Regularity
• Time to conduct an impulse
• Single lead cannot show:
• Presence of an infarct
• Axis deviation or chamber
enlargement
• Right-to-left differences in
conduction
• Quality or presence of
pumping action
12. The Electrocardiogram
• ECG Paper
• Speed
• A standard speed of 25
mm/sec
• Amplitude
and Deflection
• Should deflect two
large boxes when 1 mV
is present
• Calibration
21. The Electrocardiogram
• Time Intervals
• PR Interval (PRI) or PQ
Interval (PQI)
• 0.12–0.20 seconds
• QRS Interval
• 0.08–0.12 seconds
• ST Segment
• QT Interval
• 0.33–0.42 seconds
22. The Electrocardiogram
Refractory Periods
The all-or-none nature of myocardial depolarization
results in an interval when the heart cannot be
restimulated
Absolute
▪ Cannot accept stimulus
Relative
▪ If stimulus is strong enough, will cause depolarization
23. The Electrocardiogram
• ST Segment Changes
• The ST segment is usually an isoelectric line
• Ischemia causes deflections
• Infarctions usually follow this sequence:
• Ischemia
• ST segment depression or an invertedT wave
• Injury
• Elevates the ST segment
• Necrosis
• Significant Q wave presents
24. The Electrocardiogram
• Interpretation of Rhythm Strips
• Basic Criteria
• Always be consistent and analytical
• Memorize the rules for each dysrhythmia
• Analyze a given rhythm strip according to a specific format
• Compare your analysis to the rules for each dysrhythmia
• Identify the dysrhythmia by its similarity to established rules
25. The Electrocardiogram
• Five-Step Procedure
• Analyze the rate
• Analyze the rhythm
• Analyze the P waves
• Analyze the PR interval
• Analyze the QRS complex
31. The Electrocardiogram
• Analyzing PWaves
• Are P waves present?
• Are the P waves regular?
• Is there one P wave for each QRS complex?
• Are the P waves upright or inverted?
• Do all the P waves look alike?
• Analyzing the PR Interval
• Normal PR interval is 0.12–0.20 sec
• Analyzing the QRS Complex
• Do all the QRS complexes look alike?
• What is the QRS duration?
• Usually 0.04–0.12 sec
32. Cardiac Rhythms
• Normal Sinus Rhythm
• Rate
• 60–100
• Rhythm
• Regular
• P waves
• Normal, upright, only before each QRS complex
• PR Interval
• 0.12–0.20 seconds
• QRS Complex
• Normal, duration of <0.12 seconds
36. Causes of Dysrhythmias
• Myocardial Ischemia, Necrosis, or Infarction
• Autonomic Nervous System Imbalance
• Distention of the Chambers of the Heart
• Blood Gas Abnormalities
• Electrolyte Imbalances
37. Causes of Dysrhythmias
• Trauma to the Myocardium
• Drug Effects and DrugToxicity
• Electrocution
• Hypothermia
• CNS Damage
• Idiopathic Events
• Normal Occurrences
38. Dysrhythmias
• Mechanism of Impulse Formation
• Ectopic Foci
• Result of enhanced automaticity
• Cells other than the pacemaker cells automatically
depolarize
• PVC’s, PAC’s, and PJC’s
• Reentry
• Ischemia or another disease process alters two branches of a
conduction pathway
• Can result in rapid rhythms such as paroxysmal
supraventricular tachycardia or atrial fibrillation
40. Dysrhythmias
• Classification by Site of Origin
• Originating in the SA Node
• Originating in the Atria
• Originating within the AV Junction (AV Blocks)
• Originating in the AV Junction
• Originating in theVentricles
• Resulting from Disorders of Conduction
42. Dysrhythmias Originating
in the SA Node
NormalQRS
NormalPRI
Upright and normalP Waves
SA node
Pacemaker
Site
RegularRhythm
Less than 60Rate
Sinus Bradycardia
Rules of Interpretation
43. NormalQRS
NormalPRI
Upright and normalP Waves
SA node
Pacemaker
Site
RegularRhythm
Greater than 100Rate
Sinus Tachycardia
Rules of Interpretation
Dysrhythmias Originating
in the SA Node
