ECG Monitoring – Reference Guide
Cardiac Conduction Pathway
The ECG Tracing
Label ECG tracing w/P,Q,R,
S, T and U
Label SA node, AV node,
bundle of His, bundle
branches and Purkinje
fibers
SA node= 60-100 beats/min
AV node= 40-60 beats/min
Bundle of His= 40-60 beats/min
Purkinje fibers= 20-40 beats/min
label PR Inteval, QRS
complex, ST segment and
QT interval
Normal measurements:
PR Interval: 0.12 – 0.20 sec.
QRS complex: less than 0.12 sec.
QT interval: less than ½ the distance
between two consecutive R waves
Representation of cardiac activity on the ECG:
P wave = atrial depolarization
QRS complex= ventricular depolarization
ST segment = early repolarization of the ventricles
T wave = later stages of ventricular repolarization.
ECG Monitoring – Guide to Leads
View of the heart provided by each lead:
264
Area
Lead
Lateral
I, AVL (high lateral)
V5, V6 (low lateral)
Inferior Wall
Anterior Wall
Septum
II, III, AVF.
V1-V4/ V2-V4
V1, V2.
American Heart Association’s standard color coding for ECG leads
Location
Inscription
Color
Right Arm
Left Arm
Right Leg
Left Leg
RA
LA
RL
LL
White
Black
Green
Red
Chest
V1
Brown
Lead placement for 5 lead ECGs
Lead placement mnemonic:
White is right.
Snow over trees (white over green).
Smoke over fire (black over red).
Chocolate (brown) is close to the heart.
ECG Monitoring – 5 Step Analysis
Step 1: Assess the regularity of the rhythm
Are the P waves (for atrial rhythm) or the R waves (for ventricular rhythm)
consistently equidistant from each other?
If there is a variation of more than 3 small boxes (0.12 seconds), the rhythm is
considered irregular.
Step 2: Calculating the heart rate
The Six-Second Method
This method can be used to easily measure the heart rate in nonregular rhythms. To calculate the ventricular rate, simply count the
number of QRS complexes in a 6 second strip and multiply by 10. To
calculate the atrial rate, count the P waves instead of the QRS
complexes.
The Large Box Method
For this method, count the number of large boxes between two sequential
R or P waves. Divide this number into 300 to obtain the rate.
The Square Counting, or Sequence, Method
The square counting method can be used for regular heart rhythms. First, find an R
wave that falls on a thick line. The next thick lines will be counted as follows: 300,
150, 100, 75, 60, 50, 43, 37. Stop the sequence at the next R wave. If the second R
wave falls between two thick lines, use the mean of the two numbers (for example, if
the R wave falls between 150 and 100, the rate would be 125)
The Small Box Method
Count the small boxes between two sequential R waves (for the ventricular rate) or
two sequential P waves (for the atrial rate). Divide this number into 1500 to obtain
the rate.
ECG Monitoring – 5 Step Analysis
3rd Step: Assessment of the P waves
The P wave represents atrial depolarization.
4th Step: Assessment of the PR interval
An absent P wave indicates that the electrical impulse is
being generated from somewhere other than the SA
node.
The PR interval reflects the total time it takes for the electrical impulse to travel from
the SA node through the AV node into the ventricles.
An inverted P wave can be seen with ectopic atrial and
junctional rhythms.
A shortened PR interval (> 0.12 seconds) can indicate a junctional rhythm where the
impulse originates in the AV junction, or an abnormal conduction pathway.
Peaked P waves may be seen with right atrial
enlargement, usually due to pulmonary hypertension
A prolonged PR interval indicates that the impulse is being delayed before entering
the ventricles. This is called first degree block and can be caused by myocarditis,
acute myocardial infarction, hyperkalemia, medication effects, AV septal defects and
enhanced vagal tone.
Notched P waves can be seen with left atrial
enlargement, usually due to mitral stenosis. (#2b)
Variable P waves are indicative of multifocal atrial
rhythms (meaning multiple sites within the atrium or AV
junction are acting as ectopic pacemakers).
5th Step: Assessment of the QRS Complex
The fifth step is to assess the QRS complex. The
QRS complex represents ventricular
depolarization.
As with the PR interval, the QRS complex needs to
be assessed for both duration (width) and
consistency.
The QRS can be classified as narrow (<0.10 sec) or
wide (>0.12 sec). An abnormally wide QRS
complex can indicate a delay or abnormality in
conduction through the ventricle. Causes of wide
QRS complexes can include bundle branch blocks,
Wolff-Parkinson White syndrome, hyperkalemia,
medication effects, and ventricular tachycardia,
fibrillation or ectopic beats.
A variable PR interval can indicate a wandering atrial pacemaker, Wenckebach
rhythm (2nd degree Mobitz Type I), 3rd degree (complete ) AV block.
Additional Assessments: The T wave & the QT interval
The T wave represents ventricular repolarization. It usually deflects upright in all
leads except aVR and V1. Assess the T wave for abnormalities in shape or
consistency and for inversion in leads where it normally is upright.
T wave abnormalities may be seen with myocardial ischemia or infarction, bundle
branch blocks, pulmonary embolism, electrolyte imbalances and ventricular
hypertrophy, among other conditions.
The QT interval represents the total time for ventricular depolarization and
repolarization. Abnormalities in the QT interval can indicate risk for serious
ventricular arrhythmias. Prolonged QT intervals can also be caused by medication
effects, hypocalcemia, myocarditis and CNS lesions.
ECG Monitoring
Arrhythmia Review
Sinus Rhythms
Normal Sinus Rhythm
Rate: 60-100 beats per minute (BPM)
Rhythm: Regular
P waves: upright, normal shape, consistent, one before each QRS complex
PR interval: 0.12 – 0.20 seconds (normal)
QRS: 0.10 seconds or less
Sinus Bradycardia
Rate less than 60 BPM
Can result in decreased cardiac output
Show strips from module
Causes : medication effects (calcium channel blockers, digoxin, beta blockers), increased vagal tone
sinus node disease, hypothyroidism, hypothermia, ischemia, increased intracranial pressure
Treatments: atropine (drug of choice), epinephrine or dopamine, transcutaneous of tranvenous
pacing
Sinus Tachycardia
Rate usually 100-160 bpm
Causes: increased activity, fever, anxiety/fear, pain, infection, hypoxia, acute MI, hypovolemia,
medication effects (epinephrine, atropine), stimulants (caffeine, nicotine, or cocaine), CHF
Treatment: Treat the underlying cause.
Sinus Arrhythmia
Rate usually 60-100 bpm but may be faster or slower
Rhythm is irregular (shortened R-R intervals during inspiration, lengthened during expiration)
There is not usually any treatment required for sinus arrhythmia.. If significant sinus bradydysrhythmia occurs and patient is symptomatic, treat for sinus bradycardia.
ECG Monitoring
Arrhythmia Review
Sinus Rhythms (continued)
Sinoatrial Block
Rate is usually normal but will decrease with pauses
Rhythm is irregular
Causes: SA node disease, acute MI, medication effects (digoxin, quinidine, procainamide), CAD,
myocarditis, CHF, increased vagal tone or stimulation.
Treatment: treatment is the same for symptomatic bradycardia, if present.
Sinus Pause/ Arrest
Rate is usually normal but will decrease with pauses
Rhythm is irregular
Causes: SA node disease, acute MI, medication effects (digoxin, quinidine, procainamide),
myocarditis, hyperkalemia, increased vagal tone or stimulation.
Treatment: treatment is the same for symptomatic bradycardia, if present.
Atrial Rhythms
Premature Atrial Contractions (PACs)
Rate is variable, depending on underlying rhythm
Rhythm will be irregular at point of PACs
Premature P waves will be different than sinus P waves , but vary depending on site
Causes : hypokalemia, hypomagnesemia, anxiety, stimulants (caffeine, tobacco or alcohol),digitalis
toxicity, and myocardial ischemia or injury.
Treatment: not usually required if PACs are infrequent; treat underlying cause
Ectopic Atrial Rhythms
Rate is less than 100 bpm
Regular rhythm
P waves are different than sinus P waves , but will depending on site; may be inverted
Causes : same as PACs.
Treatment: not usually required.
ECG Monitoring
Arrhythmia Review
Atrial Rhythms (continued)
Wandering Atrial Pacemaker
Rate is less than 100 bpm
Irregular rhythm
At least three different morphologies of P waves (all vary from sinus P waves)
Causes: digitalis toxicity, acute rheumatic fever, asthma, COPD, SA node disease, atrial hypertrophy
and acute MI.
Treatment: does not usually require treatment.
Multifocal atrial tachycardia
Rate is greater than 100 bpm
Irregular rhythm
At least three different morphologies of P waves (all vary from sinus P waves)
Causes: COPD, CHF, and hypoxia.
Treatment: treat the underlying disorder.
Atrial Flutter
Atrial rate is 250-350 bpm; ventricular rate is variable.
Saw-toothed flutter waves (no regular P waves)
Causes: stimulants (alcohol, nicotine, etc.), stress, fatigue, electrolyte imbalances, acute MI,
ischemic heart disease, valvular disease, pulmonary embolism, digitalis or quinidine toxicity. It can
also occur following open-heart surgery.
Treatment: may include: cardioversion, calcium-channel blockers, beta-blockers, digoxin, warfarin
(to prevent emboli)
Atrial Fibrillation
Atrial rate is usually >350-400 bpm; ventricular rate is variable
Fibrillatory waves (no regular P waves)
Causes: stimulants (alcohol, nicotine, etc.), stress, fatigue, electrolyte imbalances, acute MI, openheart surgery, ischemic heart disease, valvular disease, and hypertension.
Treatments : cardioversion, calcium-channel blockers, beta-blockers, digoxin, warfarin (to prevent
emboli)
Atrioventricular Nodal Reentrant Tachycardia (AVNRT)
Rate is 150-250 bpm
P waves may be hidden in QRS or may appear a pseudo S or R wave
In AVNRT, reentry is due to the presence of both a fast and slow pathway within the AV node that
can allow the electrical impulse to reverse direction and generate another heartbeat.
Treatments: Vagal maneuvers are the initial treatment for stable AVNRT.
If vagal maneuvers are unsuccessful, adenosine may be administered.
ECG Monitoring
Arrhythmia Review
Junctional Arrhythmias
Premature Junctional Complexes
Rate depends on underlying rhythm
Regular rhythm with premature beats
P waves may be before, after or hidden in QRS; if visible, inverted in leads II, III and aVF.
Causes: stimulants (caffeine, tobacco, alcohol), electrolyte imbalance, heart disease, ischemia or
MI, hypoxia, digitalis toxicity and sinus node dysfunction.
Treatments: no treatment is usually necessary; treat the underlying cause.
Junctional Escape Beats & Rhythms
Junctional escape rhythm is comprised of three or more junctional escape beats in a row.
Rate is 40-60 bpm
P waves may be before, after or hidden in QRS;
if visible, inverted in leads II, III and aVF.
Causes: heart disease, acute MI, hypoxia, sinus node dysfunction, cardiac surgery and with certain
medications (digitalis toxicity, beta-blockers, calcium-channel blockers).
Treatment: if infrequent, treatment may not be necessary. If patient is symptomatic, may include
atropine, pacing, or digibind (if related to digitalis toxicity).
Accelerated Junctional Rhythms & Junctional Tachycardia
Rate is 60-100 for accelerated junctional rhythm; 100-150 for junctional tachycardia
P waves may be before, after or hidden in QRS;
if visible, inverted in leads II, III and aVF.
Causes: electrolyte imbalances, digitalis toxicity, ischemia, MI and myocarditis.
Treatment: depends on severity of symptoms; may include vagal maneuvers, adenosine, digibind
(if related to digitalis toxicity), antiarrhythmics, pacing or ablation therapy.
ECG Monitoring
Arrhythmia Review
Ventricular Rhythms
Premature Ventricular Complexes (PVCs)
*Frequent PVCs (more than 6 per minute) can be life
threatening.
Rate depends on underlying rhythm
Regular rhythm with premature beats
No P waves with PVC
Wide, abnormal QRS ; T wave is usually in opposite direction of QRS complex.
Causes: stimulants (caffeine, nicotine, alcohol), stress, and fatigue, ischemia, MI,
CHF, electrolyte imbalance, acid-base imbalance, digitalis toxicity, and medication effects
(sympathomimetics, beta-agonists, tricyclic antidepressants).
Treatments: based on the cause and the patient’s symptoms.
Idioventricular rhythms (IVR)
Idioventricular rhythms are composed of 3 or more continuous ventricular escape beats.
Ventricular rate is 20-40 bpm (atrial rate not discernible)
No P waves
Wide, abnormal QRS ; T wave is usually in opposite direction of QRS complex.
Causes: electrolyte imbalances, digitalis toxicity, myocardial ischemia or injury, and
cardiomyopathy.
Treatment: increase heart rate, may require transcutaneous pacing, atropine
Accelerated Idioventricular Rhythm (AIVR)
Ventricular rate is 40-100 bpm (atrial rate not discernible)
No p waves
Wide, abnormal QRS complex; T wave is usually in opposite direction of QRS complex.
Causes: digitalis toxicity, MI, myocardial ischemia or injury, and cardiomyopathy.
Treatment: if unstable, cardioversion or pacing may be needed.
ECG Monitoring
Arrhythmia Review
Ventricular Rhythms (continued)
Ventricular Tachycardia
*Life threatening arrhythmia
Ventricular rate 100-250 bpm (atrial rate not discernible)
P waves may or may not be present; not associated with QRS complex
Wide, abnormal QRS complex
Causes : electrolyte imbalance, acid-base imbalance, myocardial ischemia or infarction, drug
toxicity (digitalis, other antiarrhythmics), cardiomyopathy, infection (myocarditis, Chagas disease),
CNS stimulants (cocaine, amphetamines)
Treatment: If the patient is symptomatic and has palpable pulses, cardioversion is the treatment
of choice. If the patient does not have palpable pulses, immediate defibrillation is required.
Torsades de pointes
*Life threatening arrhythmia
Ventricular rate 150-250 bpm (atrial rate not discernible)
No P waves
Wide, abnormal QRS complex
Changes in QRS shape, amplitude (height) and width
Causes: conditions associated with prolonged QT interval , including medications (quinidine and
procainamide, among others) and electrolyte imbalances (hypokalemia, hypomagnesia,
hypocalcemia).
Treatment : address the cause of the prolonged QT interval. Unstable patients should be treated
with defibrillation.
Ventricular fibrillation
*Life threatening arrhythmia
No discernible rate
Chaotic, rapid, irregular rhythm
No discernible P waves or QRS complexes
Causes: myocardial ischemia or infarction, electrolyte imbalance, cardiomyopathy, hypoxia,
congenital conditions, electrocution, untreated ventricular tachycardia, R-on-T PVCs.
Treatment: Unless advanced life support is started immediately, ventricular fibrillation is a fatal
rhythm. VF requires defibrillation as soon as possible. Vasopressors (epinephrine, vasopressin) and
antiarrhythmics (amiodarone) may also be used – follow current ACLS protocol.
ECG Monitoring
Arrhythmia Review
Atrioventricular Blocks
First Degree Atrioventricular (AV) Block
PR interval >0.20 seconds
Causes: acute MI,medication effects (digitalis, calcium channel blockers, beta-blockers, among
others), electrolyte imbalances, myocarditis, AV node disease
Treatments: usually no treatment needed for first-degree AV block.
Second Degree Atrioventricular (AV) Block, Mobitz Type 1
PR interval lengthens after each P wave until QRS is eventually dropped, then cycle starts again
Causes: acute MI,medication effects (digitalis, calcium channel blockers, beta-blockers, among
others), electrolyte imbalances, myocarditis, AV node disease
Treatments: usually no treatment needed.
Second-Degree Atrioventricular (AV) block, Mobitz Type II
Impulses intermittently blocked resulting in dropped QRS complexes
P waves occur at consistent intervals
Causes: anteroseptal MI, structural heart disease ,cardiac surgery, medication effects , infiltrative
conditions , inflammatory conditions , autoimmune conditions , hyperkalemia
Treatment: temporary pacing until a permanent pacemaker can be placed.
Mobitz type II is a more serious condition than type I and can rapidly progress to third-degree heart
block.
Third-degree Atrioventricular (AV) block
Atrial impulse are not conducted to the ventricles. Secondary pacemaker in the AV node or below
pace s the ventricles.
No correlation between P waves and QRS complexes.
QRS will be narrow if secondary pacemaker is junctional, wide if it is ventricular.
Causes: same as second-degree AV block
Treatment: most patients will require placement of a permanent pacemaker.
ECG Monitoring
Arrhythmia Review
Pulseless Electrical Activity
Pacemakers
Pulseless electrical activity (PEA) is not a specific
arrhythmia, but occurs when an organized rhythm is seen on
the ECG tracing but ventricular contraction does not occur
and, therefore, the patient is pulseless.
Pacemakers can pace either the atria or the ventricles (single
chamber pacemakers) or both (dual chamber pacemakers).
Show strip from module
•
Pulseless electrical activity can present as various rhythms on the
ECG tracing, including sinus rhythm, bradycardias and tachycardia.
•
•
In atrial pacing, a spike will be seen prior to the P wave.
In ventricular pacing, a spike will be seen before the QRS
complex.
Spikes before the P wave and QRS complex will be present
when the patient has a dual chamber pacemaker.
Show pacemaker
strips from
module
Pacemaker Problems Notable on
the ECG
Failure to pace
Absence of pacemaker spikes when the
patient’s heart rate is below the
pacemaker rate.
Failure to capture
Pacemaker spikes will be seen on the
ECG but they will not be followed by a
P wave (in atrial pacing) or a QRS
complex (in ventricular pacing).
Failure to sense
The pacemaker spike will be seen in an
inappropriate place on the ECG (for
example, after or near a QRS complex
in ventricular pacing).