ECG Interpretation - Part II
Basic ECG Rhythm Identification
Part II
Learning Objectives
• By the end of the class, you will be able to:
• Identify the basic anatomy and conduction
system of the heart
• Describe electrode position for ECG and
telemetry equipment
• Identify basic ECG rhythms
• Identify dysrhythmias and relevant
implications and nursing interventions
• State policies and procedures related to ECG
monitoring
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ECG Interpretation - Part II
Atrioventricular Blocks
1° Heart Block
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P
<0.12 sec, upright, consistent morphology
PRI
> 0.20 sec
QRS
0.04 – 0.12 sec, consistent morphology
QRS complex is never dropped
Regularity
regular P-to-P interval, regular R-to-R interval
Rate
60 – 100 bpm or slower
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ECG Interpretation - Part II
1° Heart Block - Causes
• Conduction delay within the right atrium,
the AV node, the His-Purkinje system, or
a combination of these
• Higher prevalence reported in athletes
• Prevalence increases with age
• Coronary artery disease and angina
• Idiopathic degenerative diseases of the
conduction system
• Drugs: Calcium channel blockers, betablockers, digoxin, and amiodarone
1° Heart Block - Symptoms
• Generally asymptomatic at rest
• Markedly prolonged PR interval may
reduce exercise tolerance in some
patients with left ventricular systolic
dysfunction
• Syncope may result from transient
high-degree AV block
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ECG Interpretation - Part II
1° Heart Block - Interventions
• If possible, discontinue medications with
potential for AV block
• Permanent electronic pacemakers may be
indicated in those with severe bradycardia
or syncope
• Atropine
2° Heart Block Type I
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P
<0.12 sec, upright, consistent morphology
PRI
PRI gets progressively longer until a P wave is blocked,
cycle begins again following the blocked P wave
QRS
0.04 – 0.12 sec, consistent morphology
QRS complex is dropped if a P wave is blocked
Regularity
regularly irregular
Rate
variable
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ECG Interpretation - Part II
2° Heart Block Type I - Causes
• Disease of the AV node
• Can occur in individuals with high vagal
tone such as athletes or young children
• Can occur in infants and young children
with structural heart disease and in
individuals following valvular surgery
• Myocardial infarction
• Drugs: beta-blockers, calcium channel
blockers, amiodarone, digoxin
2° Heart Block Type I - Symptoms
• Most patients are asymptomatic
• May experience light-headedness,
dizziness, or syncope
• Patients often have a regularly irregular
heartbeat.
• Bradycardia may be present
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ECG Interpretation - Part II
2° Heart Block Type I - Interventions
• If asymptomatic, no intervention.
• If symptomatic, ACLS guidelines for
bradycardia, including the use of atropine
and transcutaneous pacing
• If MI suspected, treat with an appropriate
anti-ischemic regimen
• Re-evaluate medication regimen
2° Heart Block Type II
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P
<0.12 sec, upright, consistent morphology
PRI
may be normal or prolonged, but it is constant until one
P wave is not conducted to the ventricles
QRS
0.04 – 0.12 sec, consistent morphology
QRS complex is dropped if a P wave is blocked
Regularity
irregular due to dropped QRS
Rate
variable
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ECG Interpretation - Part II
2° Heart Block Type II - Causes
• Almost always a disease of the distal
conduction system (His-Purkinje System)
2° Heart Block Type II - Symptoms
• More likely to experience light-headedness,
dizziness, or syncope, although they may
be asymptomatic
• Patients may have chest pain if the heart
block is related to ischemia
• Bradycardia
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ECG Interpretation - Part II
2° Heart Block Type II - Interventions
• Same interventions as for Type I, plus
evaluation of patient for
• Transcutaneous pacing
• Transvenous pacemaker
• Type II can rapidly progress to complete
heart block
3° Heart Block
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P
<0.12 sec, upright, consistent morphology
PRI
variable when QRS present
QRS
0.04 – 0.12 sec, consistent morphology, but QRS may be wide,
there is no correlation between atrial and ventricular rates
Regularity
irregularly irregular
Rate
Atrial rate usually 60-100. Ventricular rate usually 20-40.
Atrial rate is always faster than ventricular rate.
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ECG Interpretation - Part II
3° Heart Block - Causes
• Co-administration of AV-nodal, betaadrenergic- and calcium channel- blocking
agents.
• MI
• Cardiomyopathy (Lyme disease,
rheumatic fever)
• Profound hypervagotonicity
• Metabolic disturbances such as
hyperkalemia
3° Heart Block - Symptoms
•
•
•
•
•
•
•
•
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Confusion, lethargy, syncope
Tachypnea, dyspnea
Severe chest pain
Hypotension, tachycardia
Pallor, diaphoresis
Sudden death
Signs/symptoms of (concurrent) MI
Signs/symptoms of CHF
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ECG Interpretation - Part II
3° Heart Block - Interventions
•
•
•
•
•
•
ACLS guidelines
Prepare for transcutaneous pacing
Evaluation for permanent pacemaker
Avoid valsalva
AV nodal medications should be withheld
Anti-ischemic therapy should be started
Critical Points: AV Blocks
Are there any lonely P’s?
Yes
No
1° AVB
Gradually prolonged
2° Type I
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How is the PR interval before the lonely P’s?
Constant
2° Type II
Not gradually prolonged
Not constant
3°
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ECG Interpretation - Part II
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ECG Interpretation - Part II
Ventricular Rhythms
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ECG Interpretation - Part II
Idioventricular Rhythm
P
not present
PRI
unmeasurable
QRS
> 0.12 sec
Regularity
usually regular
Rate
20 - 40 (IVR)
40 - 100 (accelerated IVR)
Idioventricular Rhythm - Causes
• Subordinate or second-order pacemakers
fire when the prevailing sinus rate
becomes too low (or lower than the rate of
the second-order pacemaker cells)
• Sinus bradycardia combined with
enhanced automaticity of the subordinate
site is the common pathophysiology.
• Myocardial ischemia
• Digoxin toxicity
• Electrolyte imbalance (hypokalemia)
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ECG Interpretation - Part II
Idioventricular Rhythm - Symptoms
•
•
•
•
Similar to acute myocardial infarction.
May present with bradycardia
Hypotension
An irregular heart rhythm may develop
because of the alternating predominance
of the sinus rate and idioventricular rate
Idioventricular Rhythm - Interventions
• Treat the primary disease process that
allows the escape rhythm to take over
pacemaker control of the heart
• Pharmacological or electrical suppressive
therapy is rarely needed because the
ventricular rate is usually less than 100 bpm
• If symptomatic or hemodynamically
compromised, increasing the atrial rate with
atropine, isoproterenol, or atrial pacing
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ECG Interpretation - Part II
Premature Ventricular Contraction
Unifocal
P
<0.12 sec, upright, consistent morphology
may be blocked by PVC
PRI
0.12 – 0.20 sec except during PVC
QRS
> 0.12 sec for PVC, morphology of PVC will vary from other
QRS complexes but all PVCs will have the same morphology
Regularity
regular P-to-P interval, regular R-to-R interval except during PVC
Rate
variable
Premature Ventricular Contraction
Multifocal
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P
<0.12 sec, upright, consistent morphology
may be blocked by PVC
PRI
0.12 – 0.20 sec except during PVC
QRS
> 0.12 sec for PVC
morphology of PVCs vary because of multiple ectopic sites
Regularity
regular P-to-P interval, regular R-to-R interval except during PVC
Rate
variable
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ECG Interpretation - Part II
Premature Ventricular Contraction
Bigeminy
P
<0.12 sec, upright, consistent morphology
may be blocked by PVC
PRI
0.12 – 0.20 sec except during PVC
QRS
> 0.12 sec for PVC, every other QRS complex is a PVC,
morphology will vary if more than one ectopic site
Regularity
regular P-to-P interval, regular R-to-R interval except during PVC
Rate
variable
Premature Ventricular Contraction
Couplet
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P
<0.12 sec, upright, consistent morphology
may be blocked by PVC
PRI
0.12 – 0.20 sec except during PVC
QRS
> 0.12 sec for PVC, PVCs will appear in pairs
morphology will vary if more than one ectopic site
Regularity
regular P-to-P interval, regular R-to-R interval except during PVC
Rate
variable
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ECG Interpretation - Part II
Premature Ventricular Contraction
Burst or Run of VT
P
<0.12 sec, upright, consistent morphology
may be blocked by PVC
PRI
0.12 – 0.20 sec except during PVC
QRS
> 0.12 sec for PVC, burst or run: 3 or more consecutive PVCs
morphology will vary if more than one ectopic site
Regularity
regular P-to-P interval, regular R-to-R interval except during PVC
Rate
variable
PVCs - Causes
• Reentry occurs when there is a blockage
in the Purkinje fibers and a second area of
slow conduction
• Creation of areas with differing conduction
and recovery times due to MI
• During ventricular depolarization, the area
of slow conduction activates the blocked
part after the rest of the ventricle has
recovered, resulting in an extra beat.
• Enhanced automaticity with hyperkalemia
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ECG Interpretation - Part II
PVCs - Symptoms
•
•
•
•
Patients are usually asymptomatic
Palpitations
Syncope with frequent PVCs
Runs of PVCs can result in hypotension
PVCs - Interventions
• Correct underlying contributory causes
when appropriate
• PVCs are usually not problematic any may
not need intervention other than closer
monitoring
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ECG Interpretation - Part II
Torsades de Pointes
P
if present, may be obscured
PRI
unmeasurable
QRS
variable but usually wide and bizarre morphology; may
progress to ventricular tachycardia or ventricular fibrillation
Regularity
irregular
Rate
150-250 bpm
Torsades de Pointes - Causes
• Triggered by an early premature ventricular
contraction (R-on-T phenomenon)
• Unlike ventricular tachycardia, TdP is most
often preceded by a prolonged QT interval
• With prolonged repolarization, myocardial
cells become less refractory to electrical
stimuli and more likely to depolarize
prematurely.
• Hypokalemia and hypomagnesemia
• Antiarrhythmic drugs
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ECG Interpretation - Part II
Torsades de Pointes - Symptoms
• QT interval increased markedly (usually to
600 msec or greater)
• Torsades usually occurs in bursts that are
not sustained; the rhythm strip usually
shows the baseline QT prolongation.
• No physical findings are typical of
Torsades
Torsades de Pointes - Interventions
• Administration of beta blockers to decrease
risk of stress-induced arrhythmias.
• Treat hypokalemia, hypomagnesemia
• Isoproterenol infusion
• Electrical cardioversion or defibrillation
• Overdrive pacing to reduce pauses
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ECG Interpretation - Part II
Ventricular Tachycardia
P
unmeasurable, usually absent or my be hidden by QRS
PRI
unmeasurable
QRS
> 0.12 sec, wide and bizarre morphology, tombstone look
Regularity
regular or irregular
Rate
100 – 250 bpm
Ventricular Tachycardia - Causes
•
•
•
•
•
•
•
•
•
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Coronary artery disease
MI with scarring
Cardiomyopathy
Cardiac hypertrophy
Cardiac surgery with scarring
Sleep apnea
Hypokalemia
Hypomagnesemia
Aggressive adrenergic stimulation
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ECG Interpretation - Part II
Ventricular Tachycardia - Symptoms
•
•
•
•
•
•
•
Palpitation, tachycardia
Decreased level of consciousness
Lightheadedness and syncope
Chest pain may be due to ischemia
Anxiety
Dyspnea, tachypnea
Pallor and diaphoresis
Ventricular Tachycardia - Interventions
• Defibrillation per ACLS protocols
• If the hemodynamic status is stable, rhythm
conversion may be achieved with
cardioversion or intravenous medication
• AICD
• Correct underlying causes
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ECG Interpretation - Part II
Ventricular Fibrillation (V Fib)
P
unmeasurable, usually absent or my be hidden by QRS
PRI
unmeasurable
QRS
unmeasurable, no QRS complex is discernable because
multiple ventricular sites are firing at the same time
Regularity
irregular
Rate
unmeasurable
Ventricular Fibrillation - Causes
• Coronary artery disease is the most
common cause
• Signal reentry
• Electrolyte abnormalities (low K and Mg)
• Ischemia
• Sleep apnea
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ECG Interpretation - Part II
Ventricular Fibrillation - Symptoms
• Palpitation, lightheadedness, and syncope
from diminished cerebral perfusion
• Chest pain may be due to ischemia
• Anxiety
• Pallor and diaphoresis
• Tachypnea
• Hypotension
• Decreased level of consciousness
• Syncope
Ventricular Fibrillation - Interventions
• If the hemodynamic status is stable:
rhythm conversion with cardioversion or
intravenous medication
• AICD
• Endocardial catheter ablation
• Meds: procainamide, lidocaine,
amiodarone, and a handful of intravenous
beta-adrenergic blocking agents
(metoprolol, esmolol, propranolol)
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ECG Interpretation - Part II
Ventricular Standstill / Asystole
P
none
PRI
none
QRS
none
Regularity
none
Rate
none
Asystole - Causes
• Heart fails to generate ventricular
depolarization
• Ischemia or from degeneration of the SA
node or AV conduction system
• Severe tissue hypoxia with metabolic
acidosis
• suffocation, near drowning, stroke, pulmonary
embolus, hyperkalemia, hypothermia
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ECG Interpretation - Part II
Asystole - Symptoms
• Patient will be unconscious and
unresponsive
• Agonal breaths
• No detectable heart sounds
• No palpable peripheral pulses
Asystole - Interventions
• Only 3 drugs recommended by the AHA:
epinephrine, vasopressin, and atropine
• ACLS
• Transcutaneous or transvenous pacing
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ECG Interpretation - Part II
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ECG Interpretation - Part II
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ECG Interpretation - Part II
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ECG Interpretation - Part II
Bundle Branch Blocks
Bundle Branch Blocks
• When a bundle branch becomes injured, it
may not conduct electrical impulses
appropriately, resulting in altered
pathways for ventricular depolarization.
• Electrical impulses cannot use the
preferred pathways, so it may move
instead through muscle fibers
• Electrical movement is slower and the
direction of the impulses changes, leading
to loss of ventricular synchrony
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ECG Interpretation - Part II
Bundle Branch Blocks
• A mnemonic to remember the
ECG changes is WiLLiaM MuRRoW:
• With a LBBB there is a W in V1
and an M in V6
• With a RBBB there is a M in lead V1
and a W in lead V6
Left Bundle Branch Block
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ECG Interpretation - Part II
Left Bundle Branch Block
P
<0.12 sec, upright, consistent morphology
PRI
0.12 – 0.20 sec
QRS
> 0.12 sec because of bundle branch block
notch seen in QRS complex (going counter clockwise/left)
Regularity
regular or irregular
Rate
variable
Right Bundle Branch Block
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ECG Interpretation - Part II
Right Bundle Branch Block
P
<0.12 sec, upright, consistent morphology
PRI
0.12 – 0.20 sec
QRS
> 0.12 sec because of bundle branch block
notch seen in QRS complex (going clockwise/right)
Regularity
regular or irregular
Rate
variable
Paced Rhythms
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ECG Interpretation - Part II
Indications for Cardiac Pacing
• Sinus bradycardia
• Sick sinus syndrome
• Atrial arrhythmias
• to restore atrial kick
• to overdrive pace
• 3rd degree HB
• Congenital
• Iatrogenic
• Acquired (“senile”)
TYPES OF PACING
• Transcutaneous
• Transvenous
• Epicardial
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ECG Interpretation - Part II
TRANSCUTANEOUS PACING
• Non-invasive via skin and chest wall
• Mostly used for emergent pacing
• Electrodes:
• placed on anterior and posterior chest walls
• connected to pulse generator by pacing
cables
TRANSCUTANEOUS PACING
• Preferred electrode placement
• Round (-) electrode
• left anterior chest
• over the heart (closer to the apex)
• Square (+) electrode
• left posterior chest
• over the back of
the heart
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ECG Interpretation - Part II
TRANSCUTANEOUS PACING
• Anterior - anterior placement
(if anterior-posterior is not possible)
• round electrode
• left anterior chest
• mid-axillary over 4th ICS
• Square electrode
• right anterior chest
• below clavicle
Transcutaneous Pacing
• Apply to clean, dry skin
• Clip, do not shave excessive hair
• Assess for both electrical and mechanical
capture
• Skeletal muscle contraction does not
indicate mechanical capture by heart
• May cause pain with impulse delivery
• Analgesia and/or sedation PRN
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ECG Interpretation - Part II
TRANSVENOUS PACING
•
•
•
•
Electrode inserted into RV via introducer
Tip comes in direct contact with RV wall
Can be left in place for 72 hrs
Complications:
•
•
•
•
•
•
Infection/ phlebitis/thrombosis
Pneumothorax
RV wall perforation
Dysrhythmias
Dislodgement
Diaphragmatic pacing
EPICARDIAL PACING
• Pacing wires:
• attached to atrial or ventricular
epicardium
• exits chest wall to right or left
side of sternal incision
• must be clearly labeled atrial
(right of sternum) or
ventricular (left of sternum)
• must be kept dry, insulated
and intact
• Gloves should be worn at all
times when handling wires
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ECG Interpretation - Part II
mA versus mV
• mA (milliamps)
• electrical energy to pace heart
• higher mA setting means a
higher amount of electricity
delivered to the heart
• mV (millivolts)
• measure of sensitivity
• amplitude or height of intrinsic
impulse that will be assessed
by the pacemaker to prevent it
from firing
SENSITIVITY
• Sensing - ability of the pacemaker to “see”
intrinsic electrical activity
• The higher the mV, the less sensitive the
device is to intrinsic events
• The higher the “fence”, the less is seen
“behind the fence”
• The lower the mV setting, the higher the
sensitivity to native beats)
• The lower the “fence”, the more is seen
“behind the fence”
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ECG Interpretation - Part II
SENSITIVITY
The lower the mV,
the more intrinsic beats are seen
Amplitude (mV)
5.0
2.5
1.25
Time
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ECG Interpretation - Part II
The higher the mV,
the fewer intrinsic beats are seen
Amplitude (mV)
5.0
2.5
1.25
Time
Pacemakers
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ECG Interpretation - Part II
Pacemaker Components
• Pulse generator or box
• houses battery and circuitry that delivers
electrical charge and directs pacing
• Pacing lead or wire
• insulated wire which carries impulse from
pulse generator to heart muscle
• Electrode tip
• non-insulated part of wire which carries
impulse from pulse generator to heart muscle
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ECG Interpretation - Part II
Pacemaker Codes
•
•
•
•
Remember P - S - R
First letter - chamber Paced
Second letter - chamber Sensed
Third letter - Response of the pacemaker
when atrial or ventricular activity is sensed
(inhibit or trigger)
1st Letter
2nd Letter
3rd Letter
Chamber(s)
paced
A = atrium
Chamber(s)
sensed
A = atrium
Response to
sensing
I = inhibit
(demand mode)
V = ventricle
V = ventricle
T = triggered
D = dual
(both atrium &
ventricle)
D = dual
(both atrium &
ventricle)
O = none
D = dual
(both atrium &
ventricle)
O = none
(asynchronous)
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ECG Interpretation - Part II
COMMON PACEMAKER CODES
•
•
•
•
•
D
A
D
V
D
D
A
V
V
O
D
I
I
I
O
DDD - Universal Pacemaker
• Chamber paced - atrium and ventricle
• Chamber sensed - atrium and ventricle
• Response to sensing for atrial or ventricular
activity:
•
•
•
•
Intrinsic P (followed by QRS)  No pacing
Intrinsic P (with no QRS)  pacing
Intrinsic P below set rate  pacing
Intrinsic QRS below set rate  pacing
• Mimics physiologic cardiac cycle and
maintains AV synchrony
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ECG Interpretation - Part II
AAI - Atrial Demand
• Chamber paced – atrium
• Chamber sensed – atrium
• Response when intrinsic atrial activity is
sensed  no pacing
• Must have functioning AV node &
ventricular conduction system
• Used in sinus bradycardia or
sick sinus syndrome
DVI - AV Sequential
• Chamber paced – atrium and ventricle
• Chamber sensed – ventricle
• Response to sensing for ventricular activity:
• No intrinsic QRS  pacing (atrium & ventricle)
• Intrinsic QRS  no pacing
• Used in heart blocks or sick sinus
syndrome
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ECG Interpretation - Part II
V V I - Ventricular Demand
• Chamber paced – ventricle
• Chamber sensed – ventricle
• Response when intrinsic ventricular activity is
sensed  no pacing
• Response when there is no intrinsic
ventricular activity  pacing
• Used in complete heart block
Paced Beats
• Pacing spike
• represents electrical impulse that the
pacemaker sends to the heart
• in atrial pacing, occurs before P wave
• in ventricular pacing, occurs before QRS
• P wave
• different in shape from intrinsic beat, wave
may be inverted
• QRS complex
• wide and bizarre
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ECG Interpretation - Part II
Review Of Terminology
• Demand pacing
• pacing in which the pacemaker fires only
when the intrinsic heart rate falls below a
specified parameter
• Asynchronous pacing
• pacing in which the pacemaker fires at a fixed
rate, independent of underlying cardiac
activity
Review Of Terminology
• Firing
• the generation of an electrical signal from the
pacemaker in order to generate a
physiological response
• Capture
• when a pacer spike is followed by a P wave
(atrial) or a QRS complex (ventricular)
• Sensing
• the ability of the pacemaker to detect the
intrinsic electrical activity of the heart
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ECG Interpretation - Part II
Failure To Fire Or Pace
• The pacemaker does not work when it is
supposed to work
• Most common causes
• oversensing
• battery failure
• generator malfunction
Failure To Capture
• The heart does not contract in response to pacing
• Most common causes:
•
•
•
•
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setting set too low
battery failure
generator malfunction
change in patient’s condition
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ECG Interpretation - Part II
Oversensing
• Extraneous electrical signals are inadvertently
sensed, inhibiting pacemaker from firing when it
was supposed to
• Most common causes:
• sensitivity too high
• electromagnetic interference
• loose connections
Failure To Sense
• Pacemaker does not detect the intrinsic beat
and generates a spike during or after the beat
• Most common causes:
• sensitivity too low
• pacing wire problems
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ECG Interpretation - Part II
Myocardial Ischemia/Infarction
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ECG Interpretation - Part II
ST Segment
• Segment between the J point and the
beginning of the T wave
• Need to use a reference point
• Compare ST segment to TP segment
• Do not use PR segment as reference
ST
TP
ST Segment
• ST elevation (b)
• > 1 mm above baseline
• concave or coved
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• ST depression (c)
• > 1 mm below baseline
• horizontal or downward
sloping
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ECG Interpretation - Part II
ST Segment Analysis
• For each complex, determine whether the
ST segment is elevated one millimeter or
more above the TP segment
Policies & Procedures
Please review:
Cardiac Monitoring (General)
Policy: Adult Telemetry Monitoring
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ECG Interpretation - Part II
Monitored Patients
Policy: Adult Telemetry Monitoring
Procedure: Cardiac Monitoring (Adult)
• Outside critical care settings, cardiac and
pulse oximetry monitoring is provided on
the LSU, 8 South, 10 CVT, 13 L and 14 M
• Telemetry is available to all services
• The clinical indication for ECG monitoring
must be specified on the order form
• The provider order must
also specify parameters for
notification of the provider
Monitored Patients
• Triage of telemetry beds will be performed
by the charge nurse in conjunction with the
ordering provider and hospital supervisor
• Whenever possible, patients will be
admitted to the monitored unit that is most
appropriate for the admitting service
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ECG Interpretation - Part II
How do you determine the most
appropriate units for patients who
require cardiac/CPO monitoring?
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ECG Interpretation - Part II
Monitored Patients
• Routine rhythm analysis is performed and
documented at least q 12 hours and within
the first 2 hours of the shift
• Bedside RNs must verify and co-sign the
tele tech’s rhythm assessment, even when
another RN is acting as the tele tech
• Changes in rhythm will be documented
and communicated to provider
• The charge nurse will assess competency
of float nurses caring for telemetry patients
The Telemetry-Competent RN
• If you provide care to a monitored patient,
you must have documentation of your
competency:
• ECG rhythm interpretation test
• Telemetry CBO (competency-based
orientation)
• Know your resources
• Know how to escalate a situation using the
chain of command
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ECG Interpretation - Part II
Questions?
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