The document describes the basics of electrocardiograms (ECGs), including what parts make up a normal ECG trace. It explains that the P wave represents atrial depolarization, the QRS complex represents ventricular depolarization, and the T wave represents ventricular repolarization. It also discusses how depolarization and repolarization waves are generated and measured on an ECG. Finally, it provides steps for analyzing ECG rhythm, including calculating heart rate, determining regularity, and assessing intervals.

1. The electrocardiogram ECG or EKG The ECG is a measurement of the sum total of electrical activity generated by the heart measured from the surface of the body An electrical record of the heart’s activity It is one of the most valuable diagnostic tools for the recognition of a large variety of cardiac disorders

2. Characteristics of the normal electrocardiogram The normal electrocardiogram is composed of: P wave: is caused by electrical potentials generated when the atria depolarizebefore atrial contraction begins QRS complex: is caused by potentials generated when the ventricles depolarizebefore contraction The P wave and the components of the QRS complex aredepolarization waves

3. T wave: is caused by potentials generated as the ventricles recover from the state of depolarization. the T wave is known as a repolarizationwave The electrocardiogram is composed of both depolarization and repolarization waves.

4. The atrial repolarization wave, known as the atrial T wave, is usually obscured by the much larger QRS complex. For this reason, an atrial T wave seldom is observed in the electrocardiogram

7. Depolarization Waves Versus Repolarization Waves In figure (B) depolarization has extended over the entire muscle fiber, and the recording to the right has returned to the zero baseline because both electrodes are now in areas of equal negativity. The completed wave is a depolarization wave because it results from spread of depolarization along the muscle fiber membrane

8. Depolarization Waves Versus Repolarization Waves In figure (C) shows halfway repolarization of the same muscle fiber, with positivity returning to the outside of the fiber. At this point, the left electrode is in an area of positivity, and the right electrode is in an area of negativity Consequently, the recording, as shown to the right, becomes negative

9. Depolarization Waves Versus Repolarization Waves In figure (D) the muscle fiber has completely repolarized, and both electrodes are now in areas of positivity, so that no potential difference is recorded between them This completed negative wave is a repolarization wave because it results from spread of repolarization along the muscle fiber membrane

10. Relation of ventricle action potential to the QRS and T waves in the electrocardiogram No potential is recorded in the electrocardiogram when the ventricular muscle is either completely polarized or completely depolarized Only when the muscle is partly polarized and partly depolarized does current flow from one part of the ventricles to another part, and therefore current also flows to the surface of the body to produce the electrocardiogram

11. The time of the onset of the P wave to the onset of the QRS complex is termed as PR interval. It represent the conduction time from the atrial to the ventricle The time from the beginning of the Q wave to the end of the S wave is called the QRS interval. It indicates the time taken by the impulse to separate to the two ventricles

12. The time from the beginning of the Q wave to the end of T wave is called the QT interval. It represent the total electrical activity of ventricles The line between the QRS complex and T wave is called ST segment. It represent the time between completion of depolarization and onset of repolarization

13. The time interval from the apex of one R wave to the next R wave is called R-R interval R-R interval is related to the heart rate or rate of ventricular contraction The time interval from the beginning of one P wave to the beginning of the next P wave is called P-P interval

14. Vertical Axis = Voltage Vertical axis represents voltage on the EKG One small box (1 mm) represents 0.10 mV

15. Horizontal Axis = Time 1 small (1 mm) box = 0.04 seconds (40 ms) 1 large (5 mm) box = 0.20 seconds (200 ms) 5 large(5 mm) boxes = 1 second (1000 ms) 15 large(5 mm) boxes = 3 seconds and is marked on EKG paper

16. The ECG Paper Horizontally One small box - 0.04 s One large box - 0.20 s Vertically One large box - 0.5 mV

17. The ECG Paper Every 3 seconds (15 large boxes) is marked by a vertical line. This helps when calculating the heart rate. NOTE: the following strips are not marked but all are 6 seconds long. 3 sec 3 sec

18. Rhythm Analysis Step 1: Calculate rate. Step 2: Determine regularity. Step 3: Assess the P waves. Step 4: Determine PR interval. Step 5: Determine QRS duration.

19. Step 1: Calculate Rate Option 1 Count the # of R waves in a 6 second rhythm strip, then multiply by 10. Interpretation? 3 sec 3 sec 9 x 10 = 90 bpm

20. Step 1: Calculate Rate Option 2 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. (cont) R wave

21. Step 1: Calculate Rate Option 2 Interpretation? 300 150 100 75 60 50 Approx. 1 box less than 100 = 95 bpm

23. What is the heart rate?

24. Step 2 : Determine Regularity Regular: If the difference between the longest R-R interval in the ECG and the shortest R-R interval is less than 0.12 second Irregular: If the difference between the longest R-R interval in the ECG and the shortest R-R interval is greater than 0.12 second

25. Step 2: Determine regularity Look at the R-R distances (using a caliper or markings on a pen or paper). Interpretation? R R Regular

26. 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? Normal P waves with 1 P wave for every QRS

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

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

29. 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