This presentation is about analysis and usefulness of electrocardiogram(ECG).

1. ‫الرحیم‬ ‫الرحمن‬ ‫هللا‬ ‫بسم‬

2. ANALYZE AN
ELECTROCARDIOGRAM
ECG

3. RATE
 The ECG is normally recorded at a speed of 25 mm/second so that each small
square, i.e. 1 mm represents 0.04 seconds.
 The atrial and ventricular rates are calculated by counting the number of small
squares between two consecutive P waves (P-P interval) and R waves (R-R
interval), respectively. Dividing 1500 by P-P and R-R intervals gives the atrial and
ventricular rates, respectively.
 Though normally both atrial and ventricular rates are equal, they should be
calculated separately since they can be different in complete AV block and
paroxysmal supraventricular tachycardia (PS VT) with 2° AV block.
 A heart rate > 100/minute is tachycardia and <60/minute is bradycardia.

4. RHYTHM
 See whether it is regular or irregular. If there is any doubt, use a piece
of paper to map out three or four consecutive beats and see whether
rate is same further along the ECG.
 Check for: P wave before each QRS complex, PR intervals (for AV
blocks) and QRS interval (for bundle branch block).

5. REGULAR RHYTHM
 In sinus rhythm, P wave precedes every QRS complex with consistent P-
R interval.
 In nodal or junctional rhythm no discernable P wave precedes each QRS
complex; the QRS complexes are narrow and regular with constant R-R
interval.

6. IRREGULAR RHYTHM
 In atrial fibrillation no discernable P waves precedes each QRS complex; the QRS
complexes are irregular with varying R-R intervals.
 Irregular rhythm with P wave preceding each QRS with consistent P-R interval is
sinus arrhythmia.
 Premature beats-After a premature beat the atria and the ventricles are in a
refractory state, and hence, the next expected sinus impulse is blocked. This
produces a pause that is known as compensatory pause. It is called complete when
the duration of R-R interval, including the premature beat is twice that of the normal
R-R interval, and incomplete when it is less than twice the duration of normal R-R
interval.
 Incomplete compensatory pause is a feature of supraventricular premature beats
whereas complete compensatory pause is seen in ventricular premature beats.

7. ABNORMALITIES IN IRREGULAR
RHYTHM
Irregularly Irregular Rhythm Regularly Irregular Rhythm
• Atrial fibrillation
• Multiple premature beats
• Complete compensatory pause:
Ventricular premature beats
• Incomplete compensatory pause:
Supraventricular premature beats
• Sinus arrhythmia
• Complete compensatory pause:
Ventricular premature beats
• Incomplete compensatory pause:
Supraventricular premature beats
• 2 ° AV block of varying type

8. AXIS
 Generally, the axis of leads I and a VF is used to calculate the axis of
QRS complex. For this, net deflection of QRS in each lead is calculated
by subtracting deflection of Q wave from deflection of R wave (e.g. if in
lead I, Q wave measures three small squares and R wave height is six
small squares, the net deflection is +3).
 The normal QRS axis is -30° to + 110°.
 Left axis deviation (LAD) is an axis between -30° and -90°.
 An axis between + 110° and + 180° indicates right axis deviation (RAD).

9. CAUSES OF AXIS DEVIATION
Left Axis Deviation (LAD) Right Axis Deviation
•Left bundle branch block
•Left anterior hemi block
• Myocardial infarction
• Hypertrophic cardiomyopathy
• Left ventricular hypertrophy
• Wolff-Parkinson-White syndrome
• Right ventricular hypertrophy
• Chronic obstructive airway disease
• Left posterior hemiblock

10. P WAVE
 P wave represents atrial depolarization. Normally, its duration is <0.1 seconds (
<2.5 small squares) and its amplitude is less than 2.5 mm.
 P waves are absent in atrial fibrillation and before ventricular premature beats.
 Normally, all P waves are followed by QRS complexes. In third degree AV block, P
waves do not bear any relation to QRS complexes.
 Morphology and duration of P waves are important to determine left and right
atrial hypertrophy.
 A tall P wave >2.5 mm in amplitude (P pulmonale) seen in right atrial
enlargement.
 A wide P wave >0.1 seconds (P mitrale) seen in left atrial enlargement.

11. P-R INTERVAL
 • The P R- interval (normally 0.12-0.20 seconds) reflects
intra-atrial, AV nodal and His- Purkinje conduction. It is the
interval between the beginning of P wave and the
beginning of QRS complex.

12. ABNORMALITIES IN P-R INTERVAL
Prolongation of P-R interval (first
degree AV block)
Short P-R interval
• Rheumatic fever (carditis)
• lschaemic heart disease
• Digitalis effect
• Wolff-Parkinson-White syndrome
• AV nodal rhythm
• Supraventricular tachycardia
Progressive prolongation of P-R interval
• Wenckebach's second degree block

13. QRS COMPLEX
 The QRS complex, representing ventricular depolarization, has a normal duration of 0.04- 0.10 seconds.
 Abnormal Q waves are present in myocardial infarction.
 Wide and bizarre QRS complexes are seen in ventricular ectopic, ventricular tachycardia and supraventricular tachycardia with
aberrant conduction.
 Increase in the height of QRS complexes indicates right or left ventricular hypertrophy.
 Left ventricular hypertrophy
 Sum of S wave in lead VI and R wave in lead V 5 or V 6 > 35 mm
 S wave inV1 >25mm or R wave inV5 orV6 >25mm
 R wave in lead aVL >12 mm
 In systolic overload, q waves in leads I, aV L,V 5 andV 6 may disappear, ST become depressed and T wave becomes inverted.
 In diastolic overload, q waves become deep in leads I, aV L, V5 and V6 , and T waves become tall inV 5 -V6 . Right ventricular
hypertrophy Right axis deviation
 Predominant R wave in VI and V 2 (R:S ratio > 1) or R wave >5 mm in V 1
 Sum of R wave in V1 or V2 and S wave in V5 or V6 > 10 mm

14. CAUSES OF TALL R WAVES IN V1
• Right ventricular
hypertrophy
• Right bundle branch block
• Wolff-Parkinson-White
syndrome (type A)
•Dextrocardia
•Hypertrophic
cardiomyopathy
•Posterior wall myocardial
infarction

15. ST SEGMENT
 ST segment elevation or depression is seen in ischemic heart disease,
cardiomyopathies, myocarditis and conduction blocks.
 Some drugs like digitalis can also produce ST segment depression.

16. T WAVES
 T waves represent ventricular repolarisation.
 Inverted T waves are frequently seen in cases with ischemic heart
disease, bundle branch blocks, atrial fibrillation with rapid ventricular
rate and in PSVT (due to relative coronary insufficiency).
 A tall, peaked T wave is seen in hyperkaliemia.

17. QT INTERVAL
 From beginning of QRS complex to end of T wave
 Corrected QT interval (QTc) is calculated using the following formula:
 QTC
 QTJRR
 QTc >0.45 is abnormal that can be seen in hypokalaemia, hypocalcaemia
and congenital QT prolongation
 syndrome.
 Prolonged QTc interval may produce torsades de pointes and sudden
death.
 QTc below 0.32 may also predispose to cardiac arrhythmias and sudden
death (short QT syndrome).

18. USEFULNESS OF
ELECTROCARDIOGRAM
 Electrocardiography is useful in the following situations:
 Myocardial ischemia and infarction
 Cardiac arrhythmias
 Conduction defects
 Chamber (atrium or ventricle) hypertrophy
 Electrolyte abnormalities (hypokalemia, hyperkaliemia, hypocalcaemia,
hypercalcemia)
 Effects of drugs (Digitalis)
 Hypothermia
 Pericarditis