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ECG PART 9
This document outlines the steps for systematically reading a 12-lead ECG: 1. Calculate the heart rate 2. Determine the rhythm 3. Determine if the QRS axis is normal or shows left/right axis deviation 4. Calculate intervals between waves 5. Assess for signs of cardiac hypertrophy 6. Look for evidence of a myocardial infarction It provides guidance on analyzing each component, such as how to identify normal vs. abnormal QRS axis using leads I and II.
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Overview of reading and interpreting 12-lead ECGs.
Objective to systematically analyze a 12-lead ECG.
Modules include ECG Basics, Rhythm Analysis, Arrhythmias, Myocardial Infarction diagnosis, and Advanced Interpretation.
Introduction to systematically reading a 12-lead ECG using a 6-step approach, crucial for diagnostics.
Instruction on calculating the heart rate using the 12-lead ECG rhythm strip.
Reviewed systematic approach for rhythm analysis, including tips on identifying Atrial Fibrillation.
Explanation of QRS axis during ventricular depolarization, and visual guide to normal vs. abnormal axes.
Discussion on QRS axis abnormal deviations and their clinical significance.
Summary on QRS axis criteria for normal, left and right axis deviations.
Transition to advanced steps in 12-lead ECG interpretation.
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ECG PART 9
- 1. ECG Rhythm Interpretation Reading12-Lead ECG’s
- 2. Course Objective • Tosystematically analyze a 12-lead ECG.
- 3. Learning Modules • ECGBasics • How to Analyze a Rhythm • Normal Sinus Rhythm • Heart Arrhythmias • Diagnosing a Myocardial Infarction • Advanced 12-Lead Interpretation • Reading 12-Lead ECG’s
- 4. Reading 12-Lead ECGs •The 12-Lead ECG contains information that will assist you in making diagnostic and treatment decisions in your clinical practice. In previous modules you learned how to read and interpret parts of the ECG. Now, we will bring all that you have learned together so that you can systematically read and interpret a 12-lead ECG. • The information will be divided into two modules, VII a and VII b.
- 5. Reading 12-Lead ECGs Thebest way to read 12-lead ECGs is to develop a step- by-step approach (just as we did for analyzing a rhythm strip). In these modules we present a 6-step approach: 1. Calculate RATE 2. Determine RHYTHM 3. Determine QRS AXIS 4. Calculate INTERVALS 5. Assess for HYPERTROPHY 6. Look for evidence of INFARCTION
- 6. Rate Rhythm AxisIntervals Hypertrophy Infarct • In Module II you learned how to calculate the rate. If you need a refresher return to that module. • There is one new thing to keep in mind when determining the rate in a 12-lead ECG…
- 7. Rate Rhythm AxisIntervals Hypertrophy Infarct If you use the rhythm strip portion of the 12-lead ECG the total length of it is always 10 seconds long. So you can count the number of R waves in the rhythm strip and multiply by 6 to determine the beats per minute. Rate? 12 (R waves) x 6 = 72 bpm
- 8. Rate Rhythm AxisIntervals Hypertrophy Infarct • In Module II you learned how to systematically analyze a rhythm by looking at the rate, regularity, P waves, PR interval and QRS complexes. • In Modules III, IV and V you learned how to recognize Normal Sinus Rhythm and the 13 most common rhythm disturbances. • If you need a refresher return to these modules.
- 9. Rate Rhythm AxisIntervals Hypertrophy Infarct Tip: the rhythm strip portion of the 12-lead ECG is a good place to look at when trying to determine the rhythm because the 12 leads only capture a few beats. Lead II Rhythm? Atrial fibrillation Rhythm strip 1 of 12 leads
- 10. Rate Rhythm AxisIntervals Hypertrophy Infarct Axis refers to the mean QRS axis (or vector) during ventricular depolarization. As you recall when the ventricles depolarize (in a normal heart) the direction of current flows leftward and downward because most of the ventricular mass is in the left ventricle. We like to know the QRS axis because an abnormal axis can suggest disease such as pulmonary hypertension from a pulmonary embolism.
- 11. Rate Rhythm AxisIntervals Hypertrophy Infarct The QRS axis is determined by overlying a circle, in the frontal plane. By convention, the degrees of the circle are as shown. The normal QRS axis lies between -30o and +90o . 0o 30o -30o 60o -60o -90o -120o 90o120o 150o 180o -150o A QRS axis that falls between -30o and -90o is abnormal and called left axis deviation. A QRS axis that falls between +90o and +150o is abnormal and called right axis deviation. A QRS axis that falls between +150o and -90o is abnormal and called superior right axis deviation.
- 12. Rate Rhythm AxisIntervals Hypertrophy Infarct • Causes of left axis deviation include: – Left ventricular hypertrophy – Inferior wall MI – Left bundle branch block – Left anterior fascicular block – Horizontal heart 0o -90o 90o 180o • Causes of right axis deviation include: – Right ventricular hypertrophy – Lateral wall MI – Right bundle branch block – Pulmonary hypertension – Vertical heart
- 13. Rate Rhythm AxisIntervals Hypertrophy Infarct We can quickly determine whether the QRS axis is normal by looking at leads I and II. If the QRS complex is overall positive (R > Q+S) in leads I and II, the QRS axis is normal. QRS negative (R < Q+S) In this ECG what leads have QRS complexes that are negative? equivocal? QRS equivocal (R = Q+S)
- 14. Rate Rhythm AxisIntervals Hypertrophy Infarct How do we know the axis is normal when the QRS complexes are positive in leads I and II?
- 15. Rate Rhythm AxisIntervals Hypertrophy Infarct The answer lies in the fact that each frontal lead corresponds to a location on the circle. 0o 30o -30o 60o -60o -90o -120o 90o120o 150o 180o -150o I II avF avLavR Limb leads I = +0o II = +60o III = +120o Augmented leads avL = -30o avF = +90o avR = -150o I IIIII
- 16. 0o 30o -30o 60o -60o -90o -120o 90o120o 150o 180o -150o Rate Rhythm AxisIntervals Hypertrophy Infarct Since lead I is orientated at 0o a wave of depolarization directed towards it will result in a positive QRS axis. Therefore any mean QRS vector between -90o and +90o will be positive. I
- 17. 0o 30o -30o 60o -60o -90o -120o 90o120o 150o 180o -150o Rate Rhythm AxisIntervals Hypertrophy Infarct Since lead I is orientated at 0o a wave of depolarization directed towards it will result in a positive QRS axis. Therefore any mean QRS vector between -90o and +90o will be positive. Similarly, since lead II is orientated at 60o a wave of depolarization directed towards it will result in a positive QRS axis. Therefore any mean QRS vector between -30o and +150o will be positive. I II
- 18. 0o 30o -30o 60o -60o -90o -120o 90o120o 150o 180o -150o Rate Rhythm AxisIntervals Hypertrophy Infarct Since lead I is orientated at 0o a wave of depolarization directed towards it will result in a positive QRS axis. Therefore any mean QRS vector between -90o and +90o will be positive. Similarly, since lead II is orientated at 60o a wave of depolarization directed towards it will result in a positive QRS axis. Therefore any mean QRS vector between -30o and +150o will be positive. Therefore, if the QRS complex is positive in both leads I and II the QRS axis must be between -30o and 90o (where leads I and II overlap) and, as a result, the axis must be normal. I II
- 19. 0o 30o -30o 60o -60o -90o -120o 90o120o 150o 180o -150o 0o 30o -30o 60o -60o -90o -120o 90o120o 150o 180o -150o Rate Rhythm AxisIntervals Hypertrophy Infarct Now using what you just learned fill in the following table. For example, if the QRS is positive in lead I and negative in lead II what is the QRS axis? (normal, left, right or right superior axis deviation) QRS Complexes I AxisI II + + + - normal left axis deviation II
- 20. 0o 30o -30o 60o -60o -90o -120o 90o120o 150o 180o -150o 0o 30o -30o 60o -60o -90o -120o 90o120o 150o 180o -150o Rate Rhythm AxisIntervals Hypertrophy Infarct … if the QRS is negative in lead I and positive in lead II what is the QRS axis? (normal, left, right or right superior axis deviation) QRS Complexes I AxisI II + + + - - + normal left axis deviation right axis deviation II
- 21. 0o 30o -30o 60o -60o -90o -120o 90o120o 150o 180o -150o Rate Rhythm AxisIntervals Hypertrophy Infarct … if the QRS is negative in lead I and negative in lead II what is the QRS axis? (normal, left, right or right superior axis deviation) QRS Complexes I AxisI II + + + - - + - - normal left axis deviation right axis deviation right superior axis deviation 0o 30o -30o 60o -60o -90o -120o 90o120o 150o 180o -150o II
- 22. Rate Rhythm AxisIntervals Hypertrophy Infarct Is the QRS axis normal in this ECG? No, there is left axis deviation. The QRS is positive in I and negative in II.
- 23. Rate Rhythm AxisIntervals Hypertrophy Infarct To summarize: – The normal QRS axis falls between -30o and +90o because ventricular depolarization is leftward and downward. – Left axis deviation occurs when the axis falls between -30o and -90o . – Right axis deviation occurs when the axis falls between +90o and +150o . – Right superior axis deviation occurs when the axis falls between between +150o and -90o . QRS Complexes AxisI II + + + - - + - - normal left axis deviation right axis deviation right superior axis deviation – A quick way to determine the QRS axis is to look at the QRS complexes in leads I and II.
- 24. SUMMARY Rate RhythmAxis Intervals Hypertrophy Infarct To summarize VII a: 1. Calculate RATE 2. Determine RHYTHM 3. Determine QRS AXIS – Normal – Left axis deviation – Right axis deviation – Right superior axis deviation
- 25. SUMMARY Rate RhythmAxis Intervals Hypertrophy Infarct In VII b we will cover the next 3 steps: 1. Calculate RATE 2. Determine RHYTHM 3. Determine QRS AXIS 4. Calculate INTERVALS 5. Assess for HYPERTROPHY 6. Look for evidence of INFARCTION