understanding ecg
DESCRIPTION
ecg basics made easy, with description of most common ecg types especially in emergency situation. easy to memorize points and mnemonics included. approach to ecg diagnosis. sample ecgs.TRANSCRIPT
UNDERSTANDI NG ECG
By
Dr. Sy e d Sa ifudd in.
History
Development as a clinically useful tool – later half of nineteenth century.
12 lead standard ECG – early 20 th century – 1940
Alexander Muirhead – first to record human ECG.
Augustus D Waller – first to publish in 1887, of Robert Goswell.
Nomenclature
Waller - ABCD for the 4 deflectionsLater based on mathematical notation –
PQRST was started.First used by Einthoven.
What does the ECG actually record
Electrical activity of the heart.Also other muscles – skeletal muscles.A ECG from relaxed patient is easy to
elicit.
ECG Paper: Dimensions5 mm
1 mm
0.1 mV
0.04 sec
0.2 sec
Speed = rate
Voltage ~Mass
Measurements
ECG graphs:1 mm squares5 mm squares
Paper Speed:25 mm/sec standard
Voltage Calibration: 10 mm/mV standard
How does ECG look at the heart?
Electrodes vs leadsLimb vs chest leadsBipolar vs unipolar leadsCoranal vs transverse view
ECG Leads
The standard ECG has 12 leads:3 Standard Limb Leads
3 Augmented Limb Leads
6 Precordial Leads
The axis of a particular lead represents the viewpoint from The axis of a particular lead represents the viewpoint from which it looks at the heart.which it looks at the heart.
+-
RA
RA
LL+
+
--LA
LL
LA
LEAD II
LEAD I
LEAD III
Remember, the RLis always the ground
• By changing the arrangement of which arms or legs are positive or negative, three unipolar leads (I, II & III ) can be derived giving three "pictures" of the heart's electrical activity from 3 angles.
The Concept of a “Lead”
Leads I, II, and III
I
II III
Precordial Leads
Precordial Leads
Summary of Leads
Limb Leads Precordial Leads
Bipolar I, II, III(standard limb leads)
-
Unipolar aVR, aVL, aVF (augmented limb leads)
V1-V6
Direction of ECG deflection & direction of current
Generation of waves
Wave forms
Duration of waves & segments
Normal Heart rate = 60 – 100 bpm PR interval = 0.12 – 0.20 sec QRS interval <0.12 SA Node discharge = 60 – 100 / min AV Node discharge = 40 – 60 min Ventricular Tissue discharge = 20 – 40 min
Summary
Determining the Heart Rate
Rule of 300
10 Second Rule
Rule of 300
Take the number of “big boxes” between neighboring QRS complexes, and divide this into 300. The result will be approximately equal to the rate
Although fast, this method only works for regular rhythms.
10 Second Rule
As most ECGs record 10 seconds of rhythm per page, one can simply count the number of beats present on the ECG and multiply by 6 to get the number of beats per 60 seconds.
This method works well for irregular rhythms.
The QRS Axis
By near-consensus, the normal QRS axis is defined as ranging from -30° to +90°.
-30° to -90° is referred to as a left axis deviation (LAD)
+90° to +180° is referred to as a right axis deviation (RAD)
-90°-60°
-30°
0°
aVL
I
30°
60°
aVR
II
90°
120°III
150°
180°
-150°
-120°
aVF
Marked RAD
LAD
RAD
Normal Axis
-30° to +100°
Using leads I, II, III
LEAD 1 LEAD 2 LEAD 3
Normal UPRIGHT UPRIGHT UPRIGHT
Physiological Left Axis UPRIGHT
UPRIGHT / BIPHASIC NEGATIVE
Pathological Left Axis
UPRIGHT NEGATIVE NEGATIVE
Right Axis NEGATIVEUPRIGHTBIPHASICNEGATIVE
UPRIGHT
Extreme Right Axis
NEGATIVE NEGATIVE NEGATIVE
Normal Sinus Rhythm
Heart Rate Rhythm P Wave
PR Interval(sec.)
QRS (Sec.)
60 - 100
Regular Before each QRS, Identical
.12 - .20 <.12
Sinus Rhythms
Sinus Bradycardia
Heart Rate Rhythm P Wave
PR Interval(sec.)
QRS (Sec.)
<60 Regular Before each QRS, Identical
.12 - .20 <.12
Sinus Rhythms
Sinus Tachycardia
Heart Rate Rhythm P Wave
PR Interval(sec.)
QRS (Sec.)
>100 Regular Before each QRS, Identical
.12 - .20 <.12
Sinus Rhythms
Sinus Arrhythmia
Heart Rate Rhythm P Wave
PR Interval(sec.)
QRS (Sec.)
Var. Irregular Before each QRS, Identical
.12 - .20 <.12
Sinus Rhythms
Sinus Arrest
Heart Rate Rhythm P Wave
PR Interval(sec.)
QRS (Sec.)
NA Irregular Before each QRS, Identical
.12 - .20 <.12
Sinus Rhythms
Sinus Arrest
Sinus Rhythms
Stop of sinus rhythm
New rhythm starts
One dropped beat is a sinus pause
Beats walk through
Sinus Pause
Atrial Fibri l lation
Heart Rate Rhythm P Wave
PR Interval(sec.)
QRS (Sec.)
Var. Irregular Wavy irregular NA <.12
Atrial Rhythms
Atrial Fibrillation No discernable p-waves preceding the QRS complex
The atria are not depolarizing effectively, but fibrillating Rhythm is grossly irregular HR <100 - controlled a-fib if >100 - rapid ventricular response AV node acts as a “filter”. Often a chronic condit ion, medical attention only
necessary if patient becomes symptomatic.
Atrial Rhythms
Atrial Flutter
Heart Rate Rhythm P WavePR
Interval(sec.)
QRS (Sec.)
Atrial=250 – 400
VentricularVar.
Irregular SawtoothNot
Measur-able
<.12
Atrial Rhythms
Ventricular RhythmsVentricular Tachycardia
Heart Rate Rhythm P Wave
PR Interval(sec.)
QRS (Sec.)
100 – 250
Regular
No P waves corresponding to
QRS, a few may be seen
NA >.12
Ventricular Rhythms
Ventricular Tachycardia No discernable p-waves with QRS Rhythm is regular Atrial rate cannot be determined, ventricular
rate is between 150-250 beats per minute Must see 4 beats in a row to classify as v-tach
Ventricular Rhythms
Ventricular Fibri l lation
Heart Rate Rhythm P Wave
PR Interval(sec.)
QRS (Sec.)
0 Chaotic None NA None
Ventricular RhythmsVentricular Fibrillation
No discernable p-waves No regularity Unable to determine rate Multiple irritable foci within the ventricles all
firing simultaneously May be coarse or fine This is a deadly rhythm
Patient will have no pulse Call a code and begin CPR
Asystole
Heart Rate Rhythm P Wave
PR Interval(sec.)
QRS (Sec.)
None None None None None
Heart Block
First Degree Heart Block
Heart Rate Rhythm P Wave
PR Interval(sec.)
QRS (Sec.)
Norm.
Regular Before each QRS, Identical
> .20 <.12
Heart BlockSecond Degree Heart BlockMobitz Type I (Wenckebach)
Heart Rate Rhythm P Wave
PR Interval(sec.)
QRS (Sec
.)
Norm. can be
slow
Irregular
Present but some not
followed by QRS
Progressively longer
<.12
Heart BlockSecond Degree Heart BlockMobitz Type II (Classical)
Heart Rate Rhythm P Wave
PR Interval(sec.)
QRS (Sec.)
Usually slow
Regular or
irregular
2 3 or 4 before each QRS,
Identical
.12 - .20
<.12 depend
s
Heart Block
Third Degree Heart Block(Complete)
Heart Rate Rhythm P Wave
PR Interval(sec.)
QRS (Sec.)
30 – 60
RegularPresent but no
correlation to QRS may be hidden
Varies<.12
depends
Identifying the cardiac rhythm
I hope that the advise given here will be sufficient to keep you out of trouble when trying to identify the cardiac rhythm in an emergency.
However, the recognition of some arrhythmias can be difficult, even for the specialist.
REMEMBER
IF IN DOUBT ABOUT A PATIENT’S CARDIAC RHYTHM, DONOT HESITATE TO SEEK THE ADVISE OF A CARDIOLOGIST.
Analysing the rhythm
Two questions in your mind—
1. Where does the impulse come from?
2. How is the impulse conducted?
Narrowing down on the possible diagnosis!!!
1. How is the patient?
2. Is ventricular activity present?
3. What is the ventricular rate?
4. Is the ventricular rhythm regular or irregular?
5. Is the QRS complex width normal or broad?
6. Is atrial activity present?
7. How is the atrial activity and ventricular activity related?
How is the patient?
Never analyse ECG without the clinical context in which it was recorded.
NSR vs PEA Arrhythmia vs Artifact ALWAYS ---
1. Insist on knowing the clinical context
2. Make a note of the clinical context at the top of the ECG
Is ventricular activity present?
Check for the electrical activityAsystole – check for the electrodes and of
course the patientP waves only – responds to emergency
pacing manoeuvresIf QRS present – proceed next
What is the ventricular rate?
Bradycardia - <60 beats/minNormal - 60-100 beats/minTachycardia - 100 beats/min
Is the ventricular rhythm regular or irregular?
Spacing of the QRS complexes1. Regular – equal2. Irregular – variable Using a strip of paper Irregular cardiac rhythms –1. Atrial fibrillation2. Sinus arrhythmia3. Any supraventricular rhythm with intermittent
AV block4. Ectopic beats
Is the QRS complex width normal or broad?
Clue about the origin of the rhythm.Narrowed to one half of the heart.Supraventricular vs ventricularVentricular repolarisation via AV node –
0.12s – narrow QRS complex.Any block/impulse directly from ventricular
muscle – myocyte to myocyte conduction – prolonged depolarisation - broad QRS complex.
Broad QRS complex –
1. Ventricular rhythm
2. Supraventricular rhythm with aberrant conduction.
A GOOD GENERAL RULE IS THAT BROAD COMPLEX TACHYCARDIA IS ALWAYS ASSUMED TO BE VT UNLESS PROVEN OTHERWISE.
VT vs SVT
Elderly H/o Cardiac disease Atypical broad
complexes Diagnostic of VT –
Independent P wave activity, fusion beats, capture beats.
Young No H/o Cardiac
disease Typical LBBB/RBBB
morphology.
Is atrial activity present?
4 categories –
1. P waves (atrial depolarization) – check for orientation
2. Flutter waves – 300/min
3. Fibrillation waves – 400-600/min
4. Unclear activity – Hidden in QRS complex – AVNRT Absent – SA block / sinus arrest
How is the atrial activity and ventricular activity related?
Association between QRS complex and P wave –
Every QRS followed by P wave – activated by common source – SA / AV node
More P waves than QRS – Block (partly/completely)
More QRS complexes than P waves – AV dissociation
ST segment changes
Anatomic Groups(Summary)
Ventricular hypertrophy
LVH
Bundle branch blocks
Artefacts
If you encounter abnormalities that appear atypical or do not fit with the patients clinical condition, always consider the possibility that they are artefacts caused by –
1. Electrode misplacement
2. External electrical interference
3. Incorrect calibration
4. Incorrect paper speed
5. Patient movement
Deflections occurring at a rate of 400-to-500 times/minute especially in view of the morphology, irregularity, and clinical history (of tremor) in this case.
ventricular fibrillation in a awake and alert patient.
ECG-1
ECG-2
ECG-3
ECG-4
ECG-5
ECG-6
ALWAYS KEEP THINGS SIMPLE AND TRY TO AVOID GETTING SIDE TRACKED BY UNNESSARY DETAIL – THE DIAGNOSIS WILL OFTEN OFTEN BE OBVIOUS ONCE YOU HAVE IDENTIFIED THE KEY FEATURES OF ECG.
--- THANK YOU !!!
Study resources
www.ecglibrary.com www.skillstat.com/6sECG_rdm.html http://www.randylarson.
rhythmst.htmlcom/acls/master/ Rapid Interpretation of EKG’s, Dale Dubin M.D.