Transcript Document

Advanced ECG’s for MLA’s
Cathie Cousins, RN, BScN, CCN(C)
Objectives
1. To review Basic Concepts for the 12-Lead ECG
To discuss the following on the 12-Lead ECG
2. Bradycardia
3. Tachycardia
4. Ventricular Ectopy
5. ST and T wave changes
6. Pacemakers
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1. Basic Concepts
• The heart is a pump with an electrical
conduction system
• 2 basic types of cardiac cells in the heart
• Myocardial cells or “muscle” cells
• Specialized cells of the conduction system or
“pacemaker” cells
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Electrical Axes and Vectors
• Each of the 12 leads on the ECG has a different
pattern because each lead views the hearts
electrical axis from a different position
• Atrial and ventricular depolarization and
repolarization generate an electric current
known as an electrical axis or vector (different
from the axis of a lead)
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• Average of all the ventricular vectors
points to the left and downward
• Knowing the electrical axis of the heart
enables us to determine the normal
pattern of each lead and the cause for
altered patterns in each lead
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Rate
• Both the atrial and ventricular rates should be
measured
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The Grid Method for Rate
• Uses the distance between 2 sequential
complexes on the ECG
• Each small square represents 0.04 seconds
- 1500 small squares in 1 minute
- 300 large squares in 1 minute
• Count the large squares between P waves for
atrial rate and R waves for ventricular rate
• 300 ÷ number of large squares = number of
beats/min
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Quick Tips
• 300 ÷ 5 large squares = 60 bpm
• 5 or > large squares per minute = Bradycardia
• 300 ÷ 3 large squares = 100 bpm
• 3 or > large squares per minute = Tachycardia
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2. Bradycardia
• Bradycardia is a heart rate < 60/min
• Bradycardia can be due a slow sinus rate, the
origin of the rhythm or an AV block:
- Sinus Bradycardia
- Junctional Rhythm
- Idioventricular Rhythm
- 2° AV Block Type I
- 2° AV Block Type II
- 3° AV Block
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Sinus Bradycardia
• Sinus node is pacing at a rate < 60/min
• P wave, QRS normal
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Junctional Rhythm
• Sinus node and atria fail to pace the heart.
AV junction paces at → 40-60/min
• No P wave or PR interval < 0.12, QRS normal
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Idioventricular Rhythm
• Sinus node, atria, and AV junction fail to pace.
Ectopic pacemaker in the ventricles paces at
→ 20-40/min
• No P wave, QRS wide, ST & T waves often
abnormal
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AV Blocks
• 2° Type I and 2°Type II AV Blocks, sinus node
paces the heart
• Not ever P wave results in QRS,
QRS normal or wide
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• 3° AV Block, sinus node paces the heart
• P waves do not result in QRS
AV junction paces, QRS normal
Ventricles pace, QRS wide
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3. Tachycardia
• Tachycardia is a heart rate > 100/min
• Tachycardia can be due to:
- Sinus Tachycardia
- Supraventricular Tachycardia
- Ventricular Tachycardia
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Sinus Tachycardia
• Sinus node is pacing at a rate > 100/min
• P wave, QRS normal
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Superventricular Tachycardia
• Ectopic focus in atria or AV junction paces the heart
or Abnormal conduction thru AV node
or Accessory pathway
• P wave or no P wave, QRS narrow or wide,
rate > 150/min
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Ventricular Tachycardia
• Ectopic pacemaker in ventricles paces the heart
• No P wave, QRS wide and bizarre
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4. Premature Ventricular Contractions
QRS Duration
• QRS duration - depolarization of right and left
ventricles, from the endocardium to epicardium
• Normal QRS duration - 0.06-0.10 sec
• QRS duration > 0.10 sec, a conduction delay
exists in the bundle branches, Purkinjie network
or ventricular myocardium, or ventricular ectopic
conduction exists
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• PVC’s, premature ventricular complexes:
the premature beat originates in an ectopic
focus in one ventricle, it depolarizes that
ventricle, then the other
• No P wave, QRS wide & bizarre, ST often
abnormal, T wave often opposite the rhythm
• Multifocal PVC’s come from more than one
ectopic focus, each foci has a different shape
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•
•
•
•
1 PVC
2 PVC’s
3 PVC’s
4 PVC’s
=
=
=
=
a PVC
couplet
triplet
ventricular tachycardia
• Every 2nd PVC = bigeminy
• Every 3rd PVC = trigeminy
• Bigeminy or trigeminy can refer to any ectopic
beat so clarify eg. bigeminal PVC’s or bigeminal PAC’s, etc.
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5a. ST Segments
• ST segment = end of ventricular repolarization +
early part of ventricular repolarization
• ST segment normally isoelectric
• Ischemic + injured myocardial cells altered
membrane potentials, this allows a current to
flow as seen in ST elevation + depression
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Measuring ST Segments
• ST measurement = vertical difference between
the isoelectric line + end of QRS complex, the
“J” point”
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ST Segment Elevation
• ST segment elevation = >1 mm (>0.1 mV) above
baseline after the J point
• ST segment elevation due to severe injury
temporary until ischemia resolved or injured
heart tissue heals or dies
• ST segments elevate in leads facing the injury
• ST segments depress in leads opposite
(reciprocal ) leads
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Types of ST Elevation in AMI
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Other Common Causes of
ST Segment Elevation
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•
•
•
•
Coronary artery vasospasm
Acute pericarditis
Ventricular aneursym
Hyperkalemia
Non-specific ST-T wave changes
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ST Segment Depression
• ST segment depression = > 1 mm below
baseline after the J point
• ST segment depression due to severe ischemia
temporary until ischemia resolved or heart tissue
heals
• ST segments depress in leads facing the
ischemia
• ST segments elevate in opposite (reciprocal)
leads
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Types of ST Depression in AMI
Different types of
ST depression in AMI:
- downsloping
- horizontal
- upsloping
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Other Common Causes of
ST Segment Depression
• Left and right ventricular hypertrophy
• Left and right bundle branch block
• Digitalis in therapeutic and toxic doses
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Acute MI
Anterior
Septal
Anterior
Lateral
Inferior
Facing Leads Opposite Leads
V1-V2
V3-V4
I, aVL, & V5 or V6
II, III, & aVF
None
None
II, III, & aVF
I & aVL
Posterior
V7,V8, V9 on 18 lead V1-V4
Right Ventricle V4R, V5R, V6R on 18 lead None
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5b. T waves
• A T wave represents ventricular depolarization
• T waves normally upright, rounded, and slightly
asymmetrical. Normally negative in aVR.
• Normally 1/8 to 2/3 the height of the QRS
complex
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Abnormal T Waves in AMI
• Normal Heart positive T wave
• Subendocardial
Ischemia symmetrically
positive tall,
peaked T wave
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• Subepicardial
Ischemia symmetrically
negative deep T wave
• Late phases in AMI deeply inverted
T waves with
abnormal Q waves
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6. Pacemakers
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The 3 Functions of Pacing
1. Sensing – the ability of the pacemaker to
recognize the patient’s intrinsic heartbeat
2. Pacing – the pacemaker produces a stimulus
either when the sensing circuit does not detect
an intrinsic heartbeat or at a predetermined
time interval
3. Capturing – the depolarization of the
myocardium in response to pacing
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Pacemaker Codes
•
•
•
•
•
I
II
III
IV
V
Chamber(s) paced
Chamber(s) sensed
Response to sensing
Programmable function(s)
Antitachyarrhythmia function(s)
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Pacing Leads Sites - Permanent
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Pacing Leads Sites - Temporary
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Pacemaker Sites - Temporary
Transcutaneous
– External Pacing
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Pacemaker Strip 1
1. Sensing
2. Pacing
3. Capturing
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Pacemaker Strip 2
1. Sensing
2. Pacing
3. Capturing
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Thank You
• Remember: It is the team that assists the
patient in achieving wellness.
• Thank you and enjoy the exciting world of
12 Lead ECG’s.
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