ecg

1. EGG Interpretation
Presenter – Dr. Madhuri Sonone
Moderator-Dr. Leena Paulose

2. WHAT IS ECG
 Dignostic tool that records electrical activity of heart.

3. TYPES OF ECG
1. 12 Lead ECG :standard assessment tool that records the heart's
electrical activity from 12 different views of the heart and
provides a complete picture of electrical activity.
2. Rhythm strip :
 records the heart's electrical activity from a single lead.
 It's used to monitor a patient's heart rate and rhythm over a short
period of time.
 A standard rhythm strip is 10 seconds long and is usually recorded
from lead II on a 12-lead ECG.

4. Types of leads
LIMB LEADS
 Standard limb leads
 Lead I, II and III require a positive and negative electrode and are
hence called bipolar leads.
 Augmented limb leads
 aVR, aVF, aVL are augmented unipolar leads as they require only
positive electrode.
 In these leads the small waveforms are enhanced or augmented.
 The letter a stands for augmented and the letters R,L,F stands for
positive electrode position of lead.
 Electrodes placement is referred to as Einthoven’s triangle.

5. Einthoven's triangle

6.  Einthoven's triangle is an imaginary formation of three limb leads in a triangle .The
shape forms an inverted equilateral triangle with the heart at the center. It is named
after Willem Einthoven, who theorized its existence.
Lead placements
 Lead I — This axis goes from shoulder to shoulder, with the negative electrode placed
on the right shoulder and the positive electrode placed on the left shoulder. This results
in a 0-degree angle of orientation
I = LA-RA
 Lead II — This axis goes from the right arm to the left leg, with the negative electrode on
the shoulder and the positive one on the leg. This results in a +60 degree angle of
orientation.
II = LL-RA
 Lead III — This axis goes from the left shoulder (negative electrode) to the right or left
leg (positive electrode). This results in a + 120 degree angle of orientation.
III =LL-LA

7.  Chest or precordial leads
 V1, V2, V3, V4, V5 and V6 are unipolar leads as only positive electrode is required for
generating a waveform.
 The negative electrode being the center of the heart.

9. ELECTRICITY OF HEART

11. DIFFERENT PARTS OF ECG

12.  P wave-It represents atrial depolarisation .It is 3 mm in height (0.3 mV) or 3 mm
horizontally (0.12 sec)
 QRS complex-represents ventricular depolarization ,0.08–0.12s. Voltage varies
according to the leads, position of heart, and abnormality
 T wave-repolarization of the ventricles, 0.12 – 0.16s.
 U wave-represent repolarization of the papillary muscles or purkinje fibers
 PR interval : Interval between beginning of the P wave to the beginning of the QRS
complex. Represents the time taken by the electrical impulse to travel from the
sinus node through the AV node to bundle of his . Time-0.12 to 0.2 s
 QT interval-Interval between beginning of the QRS complex to the end of the T
wave. It represents the time for both ventricular depolarization and repolarization
(ventricular action potential). QTc- independent of heart rate
 QT: 0.2 to 0.4 seconds QTc: <0.44sec
 ST segment- It is the time at which the entire ventricle is depolarized and roughly
corresponds to the plateau phase of the ventricular action potential, 0.08 -0.12s

13.  The P wave
o First component of a normal ECG waveform.
o It represents atrial depolarization.
characteristics:
o Location—precedes the QRS complex
o Amplitude—2 to 3 mm high
o Duration—0.06 to 0.12 second
o Configuration—usually rounded and upright
o Deflection—positive or upright in leads I, II, aVF, and V2 to V6;
o Usually positive but variable in leads III and aVL;
o Negative or inverted in lead aVR; biphasic or variable in lead V1.

14.  If the deflection and configuration of a P wave are normal and if the P wave
precedes each QRS complex, we can assume that this electrical impulse originated
in the sinoatrial (SA) node.
 Peaked, notched, or enlarged P waves may represent atrial hypertrophy or
enlargement associated with chronic obstructive pulmonary disease, pulmonary
emboli, valvular disease, or heart failure.
 Inverted P waves may signify retrograde or reverse conduction from the
atrioventricular (AV) junction toward the atria.
 Varying P waves indicate that the impulse may be coming from different sites, as
with a wandering pacemaker rhythm, irritable atrial tissue, or damage near the SA
node.
 Absent P waves may signify conduction by a route other than the SA node, as with a
junctional or atrial fibrillation rhythm.

15. PR interval
 PR interval tracks the atrial impulse from the atria through the AV node, bundle of His, and
right and left bundle branches.
 Location—from the beginning of the P wave to the beginning of the QRS complex
 Duration—0.12 to 0.20 second.
 When evaluating a PR interval, look especially at its duration.
 Changes in the PR interval indicate an altered impulse formation or a conduction delay, as
seen in AV block
 Short PR intervals (less than 0.12 second) indicate that the impulse originated somewhere
other than the SA node.
 This variation is associated with junctional arrhythmias and preexcitation syndromes.
 Prolonged PR intervals (greater than 0.20 second) may represent a conduction delay through
the atria or AV junction due to digoxin toxicity or heart block—slowing related to ischemia or
conduction tissue disease

16. The QRS complex
 The QRS complex follows the P wave and represents depolarization of the ventricles.
 characteristics:
• location—follows the PR interval
• amplitude—5 to 30 mm high but differs for each lead used.
• duration—0.06 to 0.10 second, or half of the PR interval.
• Duration is measured from the beginning of the Q wave to the end of the S wave or from the
beginning of the R wave if the Q wave is absent.
• QRS complex represents intraventricular conduction time. If no P wave appears with the QRS
complex, then the impulse may have originated in the ventricles, indicating a ventricular
arrhythmia.

17. Configuration—
 Q wave- the first negative deflection after the P wave
 R wave- the first positive deflection after the P wave or the Q wave
 S wave -the first negative deflection after the R wave .
 The ventricles depolarize quickly, minimizing contact time between the stylus and the
ECG paper, so the QRS complex typically appears thinner than other ECG components.
 It may also look different in each lead. (See QRS waveform variety.
 Deflection—positive in leads I, II, III, aVL, aVF, and V4 to V6 and negative in leads aVR
and V1 to V3
 Deep and wide Q waves may represent myocardial infarction. In this case, the Q-wave
amplitude is 25% of the R-wave amplitude, or the duration of the Q wave is 0.04 second
or more.
 A notched R wave may signify a bundle-branch block.
 A widened QRS complex (greater than 0.12 second) may signify a ventricular conduction
delay.
 A missing QRS complex may indicate AV block or ventricular standstill.

20. The ST segment
 represents the end of ventricular conduction or
depolarization and the beginning of ventricular
recovery or repolarization.
 The point that marks the end of the QRS
complex and the beginning of the ST segment
is known as the J point.
 Location—extends from the S wave to the
beginning of the T wave
 Deflection—usually isoelectric (neither positive
nor negative);
 may vary from –0.5 to +1 mm in some
precordial leads.

21. A change in the ST segment may indicate myocardial damage.
 ST-segment depression - when it’s
0.5 mm or more below the base
line.
 May indicate myocardial ischemia
or digoxin toxicity.
 ST-segment elevation - when it’s 1
mm or more above the base line.
 may indicate myocardial injury.

23. CALIBRATION
 A standard signal of 1 millivolt (mV) should move the stylus vertically 1 cm (two large squares),
and this ‘calibration’ signal should be included with every record.

24.  Standardized sequence of steps to analyze the ECG are:
1. Rate
2. Rhythm
3. Axis
4. P wave
5. PR interval
6. QRS complex
7. ST segment
8. T wave
9. QT interval
10.U wave
11. Conclusion.

25. 1.RATE :
TIMES AND SPEEDS
 ECG machines record changes in electrical activity by drawing a trace on a moving paper
strip.
 ECG machines run at a standard rate of 25 mm/s and use paper with standard-sized
squares. Each large square (5 mm) represents 0.2 second (s), i.e. 200 milliseconds (ms)
 Therefore, there are five large squares per second, and 300 per minute. So an ECG event,
such as a QRS complex, occurring once per large square is occurring at a rate of 300/min.
CALCULATION OF RATE
 When rhythm is regular one can calculate rate by either:
1. Dividing 1500 by the number of small squares between one R-R interval
2. Dividing 300 by number of large squares between one R-R interval.
 When rhythm is irregular one can calculate rate by:–
1. Counting the number of R-R intervals in 3 sec (15 large squares) and multiplying by 20.
Example: Heart Rate = 300/4=75

27. 2 .RHYTHM :
 A regular rhythm is when the distance between R waves on an ECG is equal
 An irregular rhythm is when the distance between R waves varies.
 Sinus rhythm (which is the normal rhythm) has the following characteristics:
(1) heart rate 50–100 beats per minute;
(2) P-wave precedes every QRS complex;
(3) the P wave is positive in lead II.
(4) the PR interval is constant.
 Regularly irregular rhythm
 Irregularly irregular rhythm

28. 3. CARDIAC AXIS
 The average direction of spread of the depolarization wave through the ventricles as seen
from the front is called the ‘cardiac axis’
 Cardiac axis represents the overall direction of electrical activity .
 Whenever the net direction of electrical activity is towards a particular ECG lead you
see a positive deflection in that lead on the ECG.
 Whenever the net direction of electrical activity is away from a particular ECG lead you
see a negative deflection in that lead on the ECG.
 In healthy individuals, cardiac axis lie between -30° (aVL) and +90º (aVF).
 the net direction of electrical activity spreads towards leads I, II and III (the yellow arrow
below). As a result, you see a positive deflection in all of these leads, with lead
II showing the most positive deflection as it is the most closely aligned to the
overall direction of electrical spread.
 The most negative deflection in aVR, due to aVR looking at the heart in
the opposite direction.

30.  The axis is calculated (to the nearest degree) by the ECG machine.
 The axis can also be approximated manually by judging the net direction of the QRS
complex in leads I and II.
The following rules apply:
• Normal axis: Net positive QRS complex in leads I and II.
• Right axis deviation: Net negative QRS complex in lead I but positive in lead II.
• Left axis deviation: Net positive QRS complex in lead I but negative in lead II.
• Extreme axis deviation (–90°to 180°): Net negative QRS complex in leads I and II.

31.  Right axis deviation
 The direction of depolarisation being distorted to the right (between +90º and +180º).
 The most common cause of RAD is right ventricular hypertrophy.
 Extra right ventricular tissue results in a stronger electrical signal being generated by
the right side of the heart.
 This causes the deflection in lead I to become negative and the deflection in lead
aVF/III to be more positive.
 RAD is commonly associated with conditions which result in the development of right
ventricular hypertrophy such as pulmonary hypertension.
 RAD can, however, be a normal finding in very tall individuals.

33.  Left axis deviation
 The direction of depolarisation being distorted to the left (between -30º and -90º).
 This results in the deflection of lead III becoming negative (this is only
considered significant if the deflection of lead II also becomes negative).
 LAD is usually caused by conduction abnormalities.

34. 4. P WAVE
 P-wave always positive in lead II, III and Avf
 P-wave duration should be < 0.12 in all leads.
 3 mm in height (0.3 mV) or 3 mm horizontally (0.12 sec).
 Abnormalities
1.Absent –Atrial fibrillation–Sino-atrial block–Nodal rhythm
2.Inverted–Dextrocardia–Incorrect electrode placement
3.Wide and notched P-mitrale—left atrial enlargement
4.Tall and peaked–P-pulmonale—in right atrial enlargement

35. 5.PR INTERVAL
 PR interval must be 0.12–0.22 s (all leads).
 PR interval >0.22 s: first-degree AV block.
 PR interval < 0,12 s: Pre-excitation (WPW syndrome)

36. 6.QRS COMPLEX
 QRS duration -0.08–0.12s.
 There must be at least one limb lead with R-wave amplitude >5 mm and at least one
chest (precordial) lead with R-wave amplitude >10 mm; otherwise there is low voltage.
 High voltage exists if the amplitudes are too high, i.e if the following condition is
satisfied: S wave V1 or V2 + R-wave V5 >35 mm.
 Wide QRS complex (QRS duration ≥0.12 s):
 Left bundle branch block.
 Right bundle branch block.
 Nonspecific intraventricular conduction disturbance.
 Hyperkalemia.
 Class I antiarrhythmic drugs.
 Ventricular rhythms and ventricular extrasystoles (premature complexes).
 Artificial pacemaker which stimulates in the ventricle.

37.  Short QRS duration: no clinical relevance.
 High voltage:
 Hypertrophy (any lead).
 Left bundle branch block (leads V5, V6, I, aVL).
 Right bundle branch block (V1 V3).
 Normal variant in younger and slender individuals.
 Low voltage:
 Normal variant.
 Misplaced leads.
 Cardiomyopathy.
 Chronic obstructive pulmonary disease.
 Perimyocarditis.
 Pneumothorax.
 Extensive myocardial infarction. Obesity.
 Pericardial effusion,Pleural effusion.
 Amyloidosis.

38.  Q waves are considered pathological if:
• > 40 ms (1 mm) wide
• > 2 mm deep
• > 25% of depth of QRS complex
• Seen in leads V1-3
 Pathological Q waves usually indicate current or prior myocardial infarction.
Differential diagnosis:
Left-sided pneumothorax.
Dextrocadia.
Perimyocarditis.
Cardiomyopathy.
Amyloidosis.
Bundle branch blocks.
.Ventricular hypertrophy.

39. 7.ST segment