ecg an introduction
TRANSCRIPT
BASICS of
ECG
BY:Mohd Faisal
BASICS OF ECG
Presented by:فیصل محمد
احمد: معاونین نزیر،وسیم ،جنید اختر دانشP.G Scholars
DEPARTMENT OF ILMUL JARAHAT NATIONAL INSTITUTE OF UNANI MEDICINE, KOTTIGEPALYA, MAGADI MAIN
ROAD. BANGALORE-91.
1. History2. What is an ECG?3. HOW TO DO ELECTROCARDIOGRAPHY4. How does an ECG work?5. ECG Paper6. Calibration of ECG 7. LEADS8. Rate9. Rhythm10.Cardiac Axis11.P – wave12.PR - interval13.QRS Complex14.ST Segment15.QT interval (Include T and U wave)
Contents
HISTORY
• 1842- Italian scientist Carlo Matteucci realizes that electricity is associated with the heart beat
• 1876- Irish scientist Marey analyzes the electric pattern of frog’s heart
• 1895 - William Einthoven , credited for the invention of EKG
• 1906 - using the string electrometer EKG, William Einthoven diagnoses some heart problems
CONTD…
• 1924 - the noble prize for physiology or medicine is given to William Einthoven for his work on EKG
• 1938 -AHA and Cardiac society of great Britan defined and position of chest leads
• 1942- Goldberger increased Wilson’s Unipolar lead voltage by 50% and made Augmented leads
• 2005- successful reduction in time of onset of chest pain and PTCA by wireless transmission of ECG on his PDA.
MODERN ECG INSTRUMENT
It can provide evidence to support a diagnosis, but remember…..
LOOK AT THE PATIENT NOT JUST THE PAPER
ECG……………….
What is an ECG?
•The electrocardiogram (ECG) is a representation of the electrical events of the cardiac cycle.
•Each event has a distinctive waveform •the study of waveform can lead to greater insight into a patient’s cardiac pathophysiology.
With ECGs we can identify
•Chamber hypertrophy•Arrhythmias•IHD•Pericarditis•Electrolyte disturbances (i.e. hyperkalemia, hypokalemia)•Drug toxicity (i.e. digoxin and drugs which prolong the QT interval)
1. Place the patient in a position. If the patient cannot tolerate being flat, you can do the ECG in a more upright position.
2. Instruct the patient to place their arms down by their side and to relax their shoulders.
3. Make sure the patient's legs are uncrossed.
4. Remove any electrical devices, such as cell phones, away from the patient as they may interfere with the machine.
5. If you're getting artifact in the limb leads, try having the patient sit on top of their hands.
6. Causes of artifact: patient movement, loose/defective electrodes/apparatus, improper grounding.
HOW TO DO ELECTROCARDIOGRAPHY
An ECG with artifacts.
Patient, supine position
The ECG works mostly by detecting and amplifying the tiny electrical changes on the skin that are caused when the heart muscle
"depolarizes" during each heart beat.
How does an ECG work?
Simply Electrical stimulation through the atria and ventricles------depolarizationReturn to resting state after stimulation (depolarization) iscalled repolarization.
BASIC ECG WAVEFORMS: P, QRS, ST, T, AND U WAVES
The basic ECG waves are labeled alphabetically and begin with the P wave:▪ P wave—atrial depolarization (stimulation)▪ QRS complex—ventricular depolarization (stimulation)▪ ST segment, T wave, and U wave—ventricular repolarization (recovery)
ECG PAPER
• Horizontally– One small box - 0.04 s– One large box - 0.20 s
• Vertically– One large box - 0.5 Mv– One page of ECG - 10 sec
STANDARDIZATION (CALIBRATION) MARKER
The electrocardiograph must be properly calibrated so that a 1-mV signal produces a 10-mm deflection.
ECG paper (25 mm/sec, 10 mm/mV).
A, Electrocardiograph set at normal standardization. B, One half standardization. C, Two times normal standardization.
ECG illustrating the 12 leads. The leads can be subdivided into two groups: The six limb(extremity) leads And the six chest (precordial) leads
The six limb leads—I, II, III, aVR, aVL, and They can be further divided into two subgroupsThree standard “bipolar” limb leads (I, II, and III), and three augmented “unipolar” limb leads(aVR, aVL, and aVF).
LEADS
Lead I, for example, records the difference in voltage between the left arm (LA) and right arm (RA) electrodes:
Lead I = LA – RALead II records the difference between the left leg (LL) and right arm (RA) electrodes:
Lead II = LL – RA
Lead III records the difference between the left leg (LL) and left arm (LA) electrodes:
Lead III = LL – LA
Einthoven's triangle
Lead I + Lead III = Lead II
I =LA-RAIII=LL-LAI+III=LL-RA=II
Einthoven’s equation
A, Einthoven's triangle.B, The triangle is converted to a triaxial diagram by shifting leads I, II, and III so that they intersect at a common point.
Nine leads have been added to the original three “bipolar” extremity leads.
In the 1930s, Dr. Frank N. Wilson and his colleagues at the University of Michigan invented the “unipolar” limb leads and also introduced the six “unipolar” chest leads, V1 through V6.
A short time later, Dr. Emanuel Goldberger invented the three augmented unipolar limb leads: aVR, aVL, and aVF.
The abbreviation a refers to augmented; V tovoltage; R, L, and F to right arm, left arm, and left foot (leg), respectively. Today 12 leads are routinely employed, consisting of the six limb leads (I, II, III, aVR, aVL, and aVF) and the six precordial leads (V1 to V6).
Augmented Limb Leads
aVR + aVL + aVF = 0
Precordial Leads
Arrangement of Leads on the ECG
Anatomic Groups (anterior wall):
Anatomic Groups(Septum)
Anatomic Groups(Lateral Wall)
Anatomic Groups(Inferior Wall)
Anatomic Groups(Summary)
ECGINTERPRETATION
The More You See, The More You Know
RateRhythm
Cardiac AxisP – wave
PR - intervalQRS ComplexST Segment
QT interval (Include T and U wave)
Other ECG signs
The best way to interpret an ECG is to do it step-by-step
CALCULATING RATE
300the number of BIG SQUARE between R-R interval
Rate =
As a general interpretation, look at lead II at the bottom part of the ECG strip. This lead is the rhythm strip which shows the rhythm for the whole time the ECG is recorded. Look at the number of square between one R-R interval. To calculate rate, use any of the following formulas:
1500the number of SMALL SQUARE between R-R interval
OR
Rate =
CALCULATING RATE
300Rate =
For example:
3
150015
Rate =or
Rate = 100 beats per minute
If you think that the rhythm is not regular, count the number of electrical beats in a 6-second strip and multiply that number by 10.(Note that some ECG strips have 3 seconds and 6 seconds marks) Example below:
CALCULATING RATE
1 2 3 4 5 6 7 8
= (Number of waves in 6-second strips) x 10= 8 x 10= 80 bpm
Rate
There are 8 waves in this 6-seconds strip.
You can also count the number of beats on any one row over the ten-second strip (the whole lenght) and multiply by 6. Example:
CALCULATING RATE
= (Number of waves in 10-second strips) x 6= 13 x 6= 78 bpm
Rate
Look at p waves and their relationship to QRS complexes. Lead II is commonly usedRegular or irregular?If in doubt, use a paper strip to map out consecutive beats and see whether the rate is the same further along the ECG.Measure ventricular rhythm by measuring the R-R interval and atrial rhythm by measuring P-P interval.
RHYTHM
RHYTHM
ECG rhythm characterized by a usual rate of anywhere between 60-99 bpm, every P wave must be followed by a QRS and every QRS is preceded by P wave. Normal duration of PR interval is 3-5 small squares. The P wave is upright in leads I and II
Normal Sinus Rhythm
Sinus Bradycardia
RHYTHM
Rate < 60bpm, otherwise normal
RHYTHM
Sinus Tachycardia
Rate >100bpm, otherwise, normal
RHYTHM
Atrial Fibrillation
A-fib is the most common cardiac arrhythmia involving atria.Rate= ~150bpm, irregularly irregular, baseline irregularity, no visible p waves, QRS occur irregularly with its length usually < 0.12s
RHYTHM
Ventricular Fibrillation
A severely abnormal heart rhythm (arrhythmia) that can be life-threatening. Emergency- requires Basic Life SupportRate cannot be discerned, rhythm unorganized
RHYTHM
Ventricular tachycardia
fast heart rhythm, that originates in one of the ventricles- potentially life-threatening arrhythmia because it may lead to ventricular fibrillation, asystole, and sudden death.Rate=100-250bpm
CARDIAC AXIS
Electrical impulse that travels towards the electrode produces an upright (positive) deflection (of the QRS complex) relative to the isoelectric baseline. One that travels away produces negative deflection. And one that travels at a right angle to the lead, produces a biphasic wave.
The cardiac axis refers to the general direction of the heart's depolarization wavefront (or mean electrical vector) in the frontal plane. With a healthy conducting system the cardiac axis is related to where the major muscle bulk of the heart lies.
The normal QRS axis should be between - 30 and +90 degrees.
Left axis deviation is defined as the major QRS vector falling between -30 and -90 degrees.
Right axis deviation occurs with the QRS axis is between +90 and +180 degrees.
Indeterminate axis is between +/- 180 and -90 degrees.
CARDIAC AXIS
Axis Lead I Lead II Lead III
Normal Positive Positive Positive/Negative
Right axis deviation
Negative Positive Positive
Left axis deviation
Positive Negative Negative
To determine cardiac axis look at QRS complexes of lead , II, III.
Remember, positive(upgoing) QRS omplex means the impulse travels towards the lead. Negative means moving away.
Positive
Positive
Positive
Normal Axis Deviation
CARDIAC AXIS
Positive
Negative
Negative
Left Axis Deviation
CARDIAC AXIS
Negative
Positive
Positive
Right Axis Deviation
CARDIAC AXIS
Cardiac Axis CausesLeft axis deviation Normal variation in pregnancy, obesity; Ascites,
abdominal distention, tumour; left anterior hemiblock, left ventricular hypertrophy, Inferior MI
Right axis deviation normal finding in children and tall thin adults, chronic lung disease(COPD), left posterior hemiblock, anterolateral MI.
North West emphysema, hyperkalaemia. lead transposition, artificial cardiac pacing, ventricular tachycardia
CARDIAC AXIS
Normal P- wave3 small square wide, and 2.5 small square high.Always positive in lead I and II in NSRAlways negative in lead aVR in NSRCommonly biphasic in lead V1
P -WAVE
P -WAVE
P pulmonaleTall peaked P wave. Generally due to enlarged right atrium- commonly associated with congenital heart disease, tricuspid valve disease, pulmonary hypertension and diffuse lung disease.
Biphasic P waveIts terminal negative deflection more than 40 ms wide and more than 1 mm deep is an ECG sign of left atrial enlargement.
P mitraleWide P wave, often bifid, may be due to mitral stenosis or left atrial enlargement.
PR INTERVAL
NORMAL PR INTERVAL
PR-Interval 3-5 small square (120-200ms)(start of P to start of Q)
PR-INTERVAL
First degree heart block
P wave precedes QRS complex but P-R intervals prolong (>5 small squares) and remain constant from beat to beat
Second degree heart block
1. Mobitz Type I or Wenckenbach
Runs in cycle, first P-R interval is often normal. With successive beat, P-R interval lengthens until there will be a P wave with no following QRS complex. The block is at AV node, often transient, maybe asymptomatic
PR-INTERVAL
Second degree heart block
2. Mobitz Type 2
P-R interval is constant, duration is normal/prolonged. Periodically, no conduction between atria and ventricles- producing a p wave with no associated QRS complex. (blocked p wave). The block is most often below AV node, at bundle of His or BB,May progress to third degree heart block
PR-INTERVAL
Third degree heart block (Complete heart block)
No relationship between P waves and QRS complexesAn accessory pacemaker in the lower chambers will typically activate the ventricles- escape rhythm.Atrial rate= 60-100bpm. Ventricular rate based on site of escape pacemaker. Atrial and ventricular rhythm both are regular.
PR-INTERVAL
QRS complex< 3 small square (0.06 - 0.10 sec)
QRS COMPLEX
Normal duration- 0.06 - 0.10 sec (upto 3 small squares)
Depth of the S wave must not exceed 30 mm.
Non pathological Q waves may present in I, III, aVL, V5, and V6.
The R wave must grow from V1 to at least V4The S wave must grow from V1 to at least V3 and disappear in V6
ST SEGMENT
• ST Segment is flat (isoelectric)
• Elevation or depression of ST segment by 1 mm or
more is abnormal.
• “J” (Junction) point is the point between QRS and ST
segment
• S in V1 or V2 + R in V5 or V6 should be less than 35
mm.
• V1 R/S ratio or V6 S/R ratio should be less than1mm.
T WAVE
• Normal T wave is asymmetrical, first half having a gradual slope than the second
• Should be at least 1/8 but less than 2/3 of the amplitude of the R
• T wave amplitude rarely exceeds 10 mm.
• Abnormal T waves are symmetrical, tall, peaked, biphasic or inverted.
QT interval1. Total duration of Depolarization and Repolarization.
2. QT interval decreases when heart rate increases.
3. For HR = 70 bpm, QT<0.40 sec.
4. QT interval should be 0.35 0.45 s,
5. Should not be more than half of the interval between
adjacent R waves (R R interval).
QT Interval
U wave
• U wave related to depolarizations which follow
repolarization.
• U waves are small, round, symmetrical and positive in lead
II, with amplitude < 2 mm
• U wave direction is the same as T wave
• More prominent at slow heart rates
RULE 1
PR interval should be 120 to 200 milliseconds or 3 to 5 little squares
RULE 2
The width of the QRS complex should not exceed 110 ms, less than 3 little squares
RULE 3
The QRS complex should be dominantly upright in leads I and II
RULE 4
QRS and T waves tend to have the same general direction in the limb leads
RULE 5
All waves are negative in lead aVR
RULE 6
The R wave must grow from V1 to at least V4The S wave must grow from V1 to at least V3 and disappear in V6
RULE 7
The ST segment should start isoelectric except in V1 and V2 where it may be elevated
RULE 8
The P waves should be upright in I, II, and V2 to V6.
RULE 9
There should be no Q wave or only a small q less than 0.04 seconds in width in I, II, V2 to V6
RULE 10
The T wave must be upright in I, II, V2 to V6
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