Interpretation of ECG lab session.ppt

Interpretation of ECG

1. Basics of Electrocardiogram
and its interpretation

2. At the end of the session, students should be able to:
•Identify the normal and abnormal waves of the ECG
in given ECG record
•Calculate rate, rhythm and electrical axis of the heart
•Interpret a normal electrocardiogram.
Learning Objectives…

3. Normal 12 Lead electrocardiogram.

4. Electrocardiogram Paper

5. ECG Analysis
1.Calculate rate.
2.Determine regularity.
3.Assess the P, T waves and identify
abnormal wave form
4.Determine PR interval & QT interval.
5.Determine QRS duration.
6.Determine electrical axis

6. Step 1: Calculate Rate
•Find a R wave that lands on a bold line.
•Count the # of large boxes to the next R wave. If the
second R wave is 1 large box away the rate is 300, 2
boxes -150, 3 boxes -100, 4 boxes -75, etc.
R wave

7. What is the heart rate?
(300 / 6) = 50 bpm

8. What is the heart rate?
(300 / ~ 4) = ~ 75 bpm

9. What is the heart rate?
(300 / 1.5) = 200 bpm

10. The Rule of 300
It may be easiest to memorize the following table:
# of big
boxes
Rate
1 300
2 150
3 100
4 75
5 60
6 50

11. 10 Second Rule
•As most ECGs record 10 seconds of
rhythm per page, one can simply
count the number of beats present
on the ECG and multiply by 6 to get
the number of beats per 60 seconds.
•This method works well for irregular
rhythms.

12. Step 1: Calculate Rate
•Count the # of R waves in a 6 second rhythm strip, then
multiply by 10.
•Reminder: all rhythm strips in the Modules are 6 seconds in
length.
Interpretation?
9 x 10 = 90 bpm
3 sec 3 sec

13. Step 2: Determine regularity
•Look at the R-R distances (using a caliper or markings
on a pen or paper).
•Regular (are they equidistant apart)? Occasionally
irregular? Regularly irregular? Irregularly irregular?
Interpretation?
Regular
R R

14. Step 3: Assess the P waves
•Are there P waves?
•Do the P waves all look alike?
•Do the P waves occur at a regular rate?
•Is there one P wave before each QRS?
Interpretation?

15. Step 4: Determine PR interval
•Normal: 0.12 -0.20 seconds. (3 -5 boxes)
Interpretation?0.12 seconds

16. Step 5: QRS duration
•Normal: 0.04 -0.12 seconds. (1 -3 boxes)
Interpretation?0.08 seconds

17. Step 5: QRS duration and QT interval
•Normal QRS Duration : 0.08 -0.12 seconds.(2 -
3 boxes)
Interpretation?
•Normal QT interval: 0.4 sec
0.08 seconds

18. Normal Sinus Rhythm (NSR)
•The electrical impulse is generated in the SA node
and conducted normally-called normal rhythm of the
heart;
•The rhythms that do not conduct via the typical
pathway are called arrhythmias.

19. Rhythm Summary
•Rate 90-95 bpm
•Regularity regular
•P waves normal
•PR interval 0.12 s
•QRS duration 0.08 s
Interpretation?Normal Sinus Rhythm

20. Sinus Bradycardia
•SA node is depolarizing slower than normal,
impulse is conducted normally i.e. normal PR
and QRS interval.

21. Sinus Tachycardia
•Cause:SA node is depolarizing faster than
normal, impulse is conducted normally.

22. Premature Atrial Contractions
•Cause:
•Ectopic beats originate in the atria (but not in
the SA node), therefore the contour of the P
wave, the PR interval, and the timing are
different than a normally generated pulse from
the SA node.

23. Premature Ventricular contractions
•Cause:One or more ventricular cells are
depolarizing and the impulses are abnormally
conducting through the ventricles.

24. Atrial Flutter
•“Saw tooth ” pattern with rate of 250 -350 bpm
•Cause:right atrium with every 2nd, 3rd or 4th
impulse generating a QRS (others are blocked in the
AV node as the node repolarizes).

25. Atrial Fibrillation
•Cause:
•No organized atrial depolarization, so no
normal P waves (impulses are not
originating from the sinus node).
•Atrial activity is chaotic (resulting in an
irregularly irregular rate).

26. Ventricular Fibrillation
•Etiology:The ventricular cells are excitable and
depolarizing randomly.
•Rapid drop in cardiac output and death occurs if
not quickly reversed

27. 1st Degree AV Block
•Feature:
•Prolonged conduction delay in the AV node or
Bundle of His.
•Rate and rhythm are typically normal

28. 2nd Degree AV Block-Mobitz type I
•Feature:
•PR interval progressively lengthens,
•The impulse is completely blocked (P wave
not followed by QRS).

29. 2nd Degree AV Block-Mobitz type II
•Feature:
•PR interval consistent
•Rhythm can be steady or unsteady depending
upon P to QRS ratio (2:1, 3:1, 3:2, etc.)
•Conduction block occurs in the Bundle of His.

30. 3rd Degree AV Block
•Features
•complete block of conduction in the AV junction,
•the atria and ventricles form impulses
independently of each other.
•Without impulses from the atria, the ventricles own
intrinsic pacemaker kicks in at around 30 -45
beats/minute.

31. The Electrical [QRS] Axis
•The QRS axis represents the net
overall direction of the heart’s
electrical activity.
•Normal QRS axis = -30 to +90°.
•Left axis deviation (LAD)= -30 to -
90°
•Right axis deviation (RAD) +90 to
+180°
•Abnormalities of axis can hint at:
•Ventricular enlargement
•Conduction blocks

32. Determining the Axis
Predominantly
Positive
Predominantly
Negative
Equiphasic

33. Quadrant Approach: Example 1

34. Quadrant Approach: Example 2

35. Quadrant Approach: Example 3

36. Quadrant Approach: Example 4