This document provides an overview of electrocardiography (ECG) basics. It defines ECG as a graphical representation of the heart's electrical activity used to assess cardiovascular diseases. It discusses the conduction system of the heart and the 12 standard chest leads used in ECG. It outlines the key steps in ECG interpretation including analyzing rate, rhythm, intervals, chambers, and waveform durations. It describes how to calculate heart rate from the ECG and defines the normal P wave, PR interval, QRS complex, ST segment, QT interval, and ECG axis.

1. ELECTROCARDOGRAPHY
(ECG) BASICS
AIC LITEIN MISSION HOPSITAL CME
DR. MATE SHILULI

2. DEFINITION
• A graphical representation of the electrical activity of the heart
• Used in assessment of cardiovascular diseases
• Most important test in interpretation of the cardiac rhythm, detection of
myocardial ischemia & infarction, conduction system abnormalities, pre-
excitation, long QT syndromes, atrial abnormalities, ventricular hypertrophy,
pericarditis….

3. CONDUCTION SYSTEM OF THE HEART

4. STANDARD CHEST LEADS
• Comprises of 12 leads in various dimensions (coronal and transverse
to give a 3D picture of the heart).
3 bipolar leads – I, II, III
9 unipolar leads – AVR, AVL AVF, V1-V6

5. .

6. ECG waves, intervals and segments

8. STEPS IN INTERPRETATION
• Rate – normal vs tachycardia/bradycardia
• Rhythm – regular vs irregular
• Intervals – PR, QRS, QT
• Chamber abnormality – atrial enlargement, ventricular hypertrophy
• QRST duration – Q waves, poor R wave progression, ST segment depression/elevation or
T wave changes.

9. ECG GRID

10. HEART RATE
• In regular cardiac rhythm, HR is determined by interval between two successive
QRS complexes.
• On a std ECG paper, HR can be calculated by dividing the number of large boxes
btwn 2 successive QRS complexes into 300.
• If the HR is irregular, count the number of QRS complexes and multiply by 6 to
obtain the average HR

11. Example;

12. P WAVE
• Represents atrial depolarization.
• Normally is upright morphology in leads I, II & AVF but inverted in lead AVR
• Usually biphasic (positive-negative), but when the negative terminal component
exceeds 0.04 secs in duration, it is abnormal.
• Left atrial enlargement usually associated with increased P wave duration
• Right atrial enlargement suspected when P waves are peaked, i.e, more than
2.5mm in inferior leads and 1.5mm in V1 and V2

13. Normal P wave

14. PR INTERVAL
• Represents time from depolarization of sinus node to the onset of
ventricular depolarization
• Marks beginning of P-wave to start of QRS complex.
• Normal duration is between 0.12 – 0.20

15. QRS COMPLEX
• Represents time for ventricular depolarization
• Normal duration is 0.06 – 0.10 seconds

16. ST SEGMENT
• Interval between ventricular depolarization and ventricular
repolarization.
• Starts at end of QRS complex to beginning of T wave
• ST segment elevation signifies ACS

17. ST SEGMENT…

18. QT INTERVAL
• Measure depolarization and repolarization of the ventricles.
• QT prolongation usually associated with development of ventricular
arrythmias and sudden death.
• Dependent on HR, FASTER hr associated with shorter QT interval
while SLOWER HR has a longer QT interval

19. ECG AXIS

20. ECG AXIS…
• There are shortcut methods to determine the axis.
• For example, if the QRS complex is upright in both leads I and II, then the axis
must fall somewhere between -30º and 90º and the axis is normal:
• If the complexes are negative in lead I and positive in lead aVF, then the axis is
rightward.
• If the complexes are positive in lead I but negative in lead II, then the axis is
leftward.

21. ECG AXIS…
• If the complexes are negative in both leads I and aVF, then the axis is extreme.
• The causes of left axis deviation include normal variation, left ventricular hypertrophy,
left anterior fascicular block, congenital heart disease with primum atrial septal defect or
endocardial cushion defect, ventricular ectopic beats, and preexcitation syndromes
• The causes of right axis deviation include normal variation, right ventricular hypertrophy,
left posterior fascicular block, ventricular ectopic beats, preexcitation, and dextrocardia.

22. R WAVE PROGRESSION
• Should progress in size across leads V1 to V6
• Poor progression can a sign of previous anterior MI