Download Basic ECG Interpretation

Basic ECG Interpretation
Wendy Callaway, RN, BSN
Cardiopulmonary Rehab
Cardiac Anatomy
Four chambers
Atria (thin walls, low pressure)
Ventricles (thick walls, high pressure)
Four Valves
Atrioventricular -Tricuspid & mitral
Semilunar - Aortic & pulmonic
Cardiac Physiology
Systole
Ventricles in action
Aortic and pulmonic valves open
Diastole
Ventricles at rest
Tricuspid and mitral valves open
Conduction Pathway
SA – right atrium (60-100)
AV- non pacer cells that delay
impulses
Bundle of His- Left & Right bundle
branches
Purkinje Fibers – located deeper in
the muscle tissue
ECG Recordings
The heart’s electrical currents are
transformed into waveforms that
represent the heart’s depolarizationrepolarization cycle
ECG tracings represent the
conduction of electrical impulses
from the atria to the ventricles
ECG do not represent mechanical
activity or contraction
Leads
Electrode placement is different for
each lead
Different leads provide different views
of the heart
Current flows from negative to
positive
Color codes are often used for lead
placement
ECG Paper
Horizontal axis represents time
One small box = 0.04secs
6 sec strip is the standard for Single
ECG
Vertical axis represents energy
One small box = 0.1mV
P Wave
Represent atrial depolarization;
conduction of impulse through atria
Location – precedes the QRS
Amplitude – 2-3 mm high
Duration – 0.06-0.12 sec
Configuration – usually round and upright
Normal P waves originate from the SA
node
Abnormal P Waves
Peaked, notched or enlarged
Stretched atrial tissue
Inverted
Reverse or retrograde conduction
Varying
Originate from different sites
Absent
Blockage
PR Interval
Tracks the atrial impulse form the
atria , AV, Bundle of His, and
Branches
Location- from P to QRS
Duration – 0.12-0.20 sec
Abnormal
Shortened – impulse did not originate in
SA
Prolonged –represents conduction delay
QRS Complex
Represents depolarization of the ventricles
Location – follows the PR interval
Amplitude 5-30 mm high, depends on lead
Duration 0.06-0.10 sec; measured from
start of Q wave to end of S wave
Configuration – consist of Q wave first
negative deflection, R wave positive
deflection, S wave negative deflection
QRS Complex abnormalities
Deep and wide QRS
MI
Bundle branch block
Notched QRS
Absent QRS
AV Blockage or standstill
ST Segment
Represents the end of ventricular
conduction or depolarization
J point – the point that marks the end of the
QRS and the start of the ST segment
Location – extends from the S wave to the
start of T wave
Abnormal ST Segment:
Elevation – injury
Depression - ischemia
T Wave
Represents ventricular recovery or
repolarization
Location – follows S wave
Configuration- smooth and round
Deflection- usually upright in I, II,V3-V6
Abnormal
Notched – hidden p wave (indicates atrial
depolarization)
Tall, peaked, tented – injury or
hyperkalemia
Inverted (I, II, V3-V6) - ischemia
QT Interval
Measures ventricular depolarization
and repolarization
Location – extends from the start of Q
wave to the end of the T wave
Duration – varies 0.36-0.44
Shows time needed for ventricular
cycle
U Wave
Represents the recovery peroid of the
Purkinje conduction fibers
Usually not present
Location – follows the T wave
Configuration – usually round and upright
Deflection – upright
Prominent U wave – due to
hypercalcemia, hypokalemia or digitalis
toxicity
Steps in Strip Interpretation
Check rhythm
Calculate rate
Evaluate P wave
Check PR Interval
Check QRS
Examine T wave
Check QT interval
Check for abnormalities/ectopy
Naming the Strip
Origin of the rhythm
Pacemaker
Sinus, atria, ventricular
Rate characteristics
Bradycardia or tachycardia
Rhythm abnormalities
Flutter, fibrillation, heart block
Normal Sinus Rhythm
Rhythm: Atrial &ventricular rhythms
regular
Rate: Atrial & ventricular rate: 60-100
P waves – round, smooth, upright in lead
II
PR interval – 0.12-0.20sec
QRS – less than 0.12sec
T wave – upright in lead II
QT interval – 0.36-0.44 sec
No ectopic or aberrant beats
Sinus Bradycardia
Rate less than 60 beats per minute
Normal during sleep, athletes
Normal response to reduced demand for blood
(45-59 tolerated by most)
Abnormal – MI, drugs, vagal stimulation etc…
Symptomatic Response (decreased CO)
S/S – hypotension, dizziness, altered
mentation, cool, clammy skin, blurred vision,
chest pain, syncope, crackles, dyspnea, S3
Sinus Tachycardia
Rate greater than 100 bpm
Rarely exceeds 180 except with
strenuous exercise
Increase myocardial oxygen demand
Causes
Exercise, fever, fear, pain, hemorrhage,
hypovolemia, MI, CHF…
Symptomatic - S/S decrease CO/reduced
ventricular filling time; increase O2
demand
Treatment – treat cause
Premature Atrial Contractions
Originate from an irritable spot or focus in
the atria that takes over as the
pacemaker
PACs may or may not be conducted
through the AV node
Blocked – p wave only (unlike normal p wave)
Usually followed by a pause
Pwave may be buried in preceding Twave
May cause the P to P intervals of the next two
occuring normal beats to be shorter
(noncompensatory)
Atrial Fibrillation
Chaotic, asynchronous electrical
activity in atrial tissue
Atrial Rate 400-600bpm (quivering)
Loss of atrial kick, decreased CO,
myocardial perfusion, CHF
No P waves – fibrillatory wave or f
waves
Irregular conduction & Irregular
rhythm
Atrial Flutter
SVT
Atrial Rate 250-400bpm (usually 300bpm)
Pwaves – saw-tooth appearance (flutter
waves)
Conduction Rate – 2:1, 3:1, 4:1
(atrial:ventricular response)
Rapid ventricular response reduce CO
and myocardial perfusion time
Premature Ventricular Contractions
A premature beat originating in the
ventricles
P wave is normal, but often buried when
PVC occurs
Wide QRS complex, > 0.12, may be
strangely shaped with an upside- down T
wave
Rhythm will be regular except for the single
beat interrupting the underlying rhythm
Bundle Branch Block
Conduction failure of the bundle
branch
Causes prolonged ventricular
depolarization on the affected side
QRS greater than 0.12sec
Ventricular Tachycardia
Three or more consecutive PVC’s at
>100 bpm
P wave is present or absent, QRS
complexes are not preceded by
associated P waves
QRS is wide, >0.12, and bizarre
Atria rate is immeasurable, Ventricular
rate is 150-200 bpm
Ventricular rhythm is usually regular
Ventricular Fibrillation
Quivering ventricular movements
No Pulse
PQRST non-identifiable
Chaotic
Asystole
Cardiac standstill
Absence of all ventricular activity
Treat with pacemaker, CPR, and
related drug intervention
Paced Rhythm/ Pacer Spike
Appears as a vertical line or spike on
the ECG strip
Atrial – followed by P wave….
Ventricular – followed by QRS
A/V – as above
The type of pacemaker used and the
patient’s condition may affect whether
every beat is paced
12 Lead EKG
Diagnostic test used to identify
pathologic conditions
Provide a more complete view of
cardiac electrical activity than rhythm
strip
Must be viewed with other clinical
evidence i.e. history, physical,
laboratory results and medication
ST segment elevation and
depression
Depression indicates myocardial
ischemia, lack of O2 to heart muscle
Elevation indicates heart muscle
injury or infarct
12 lead EKG can identify the area, but
not the extent of an infarct
Final Thought!
Even with your current knowledge of
rhythm strips, always remember to
treat the patient, and not the monitor!!