ECG

3. DR ABDUL SAMI
MPHIL EASTERN MEDICINE
The Islamia University of
Bahawalpur
Pakistan

4.  Electrocardiography
 Electrocardiography is the technique by
which the electrical activities of the
heart are studied. The spread of
excitation through myocardium
produces local electrical potential. This
causes flow of small currents through
the body which acts as volume
conductor. These small currents can be
picked up from the surface of the body
by using suitable electrodes and
recorded in the form of
electrocardiogram.

5. ELECTROCARDIOGRAPH
 Electrocardiograph is the instrument (ECG machine)
by which the electrical activities of the heart are
recorded.

6. Electrocardiogram
This is (cardiology) the visual output that an
electrocardiograph produces.

7. The paper that is used for recording ECG is called
ECG paper. Electrocardiographic grid refers to the
markings (lines) on ECG paper. ECG paper has
horizontal and vertical lines at regular intervals of 1
mm. Every 5th line (5 mm) is thickened.

8. ECG is recorded by placing series of electrodes on the
surface of the body. These electrodes are called ECG leads
and are connected to the ECG machine. Electrodes are
fixed on the limbs. Usually, right arm, left arm and left leg
are chosen. Heart is said to be in the center of an
imaginary equilateral triangle drawn by connecting

9.  Baseline or Isoelectric line: The flat or straight line present in the graph paper of
ECG.
 Wave: Any deviation from baseline is called wave. Wave always starts from
baseline and ends on baseline.
 Waveform: Movement away from the baseline, up or down.
 Segment: A line between waveforms or a line (baseline) joining the two waves
(successive waves).
 There are three segments in one ECG:-
 1) PQ Segment
 2) ST Segment
 3) TP Segment
 Complex: Two or more waves having no segment between them is called
complex. Eg QRS complex in which there are three waves having no segment.

10.  Interval: A waveform plus a segment is called interval.
 PR Interval: The time duration between beginning of P
wave and beginning of QRS complex. Normal duration is
0.12 sec to 0.20 sec.
 QRS Interval:The time duration in which ventricles
depolarize, it is also called ventricular activation (VAT). Its
normal duration is less than 0.11 sec.
 QT Interval:The time duration between the beginning of Q
wave and end of T wave. Its normal duration is 0.35 sec.
 RR Interval:It is the time duration between two successive
R waves. Its normal duration is 0.8 sec.

13. Horizontally:
 One small box (1mm)= 0.04 sec
 One large box (5mm)= 0.20 sec
 Five large boxes (25mm)= 1sec
Vertically:
 One large box (5mm)= 0.5mv
 Two large boxes (10mm)= 1mv

14. SA Node - Heart pacemaker; located in the RA;
initiates next step

15. P Wave - Atrial depolarization and contraction

16. AV Node - Slows the depolarization of the atria;
connects atria and ventricles electrically

17. QRS complex - ventricular depolarization; begins in
Bundle of His

18. ST Segment - Initial plateau phase of
ventricular repolarization

19. T wave - Rapid phase of ventricular
repolarization

20. U wave – Positive deviation after T wave and preceding the
next P wave

21.  Look at the whole tracing.
Rhythm: Is there a P wave before each QRS complex?
− Yes: sinus rhythm No: AV junctional or heart block
Rate: Count boxes; use caliper, ruler
PR interval: Normal - 0.20 sec. or less
QRS complex: Skinny (0.10 sec. or less) or broad (BBB or
ventricular)
ST segment: Isoelectric (normal), elevated or depressed
T wave: Upright, flat or inverted
Interpretation: Normal or abnormal.
− Is the rhythm dangerous?

22.  Electrocardiogram is useful in determining and
diagnosing the following…
 Heart rate
 Heart rhythm
 Abnormal electrical conduction
 Poor blood flow to heart muscle (ischemia)
 Heart attack
 Coronary artery disease
 Hypertrophy of heart chambers.