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Electrocardiogram ECG II. ANALYSIS Dr. Amel Eassawi. Electrocardiogram . The 12 leads include: 3 Limb leads (I, II, III) 3 Augmented leads ( aVR , aVL , aVF ) 6 Precordial leads (V 1 - V 6 ). Normal ECG. 1. Rhythm analysis. 2. Analyzing individual wave & segments.
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Electrocardiogram ECG II ANALYSIS Dr. AmelEassawi
Electrocardiogram • The 12 leads include: • 3 Limb leads (I, II, III) • 3 Augmented leads (aVR, aVL, aVF) • 6 Precordial leads (V1- V6)
1. Rhythm analysis. 2. Analyzing individual wave & segments. 3. Determine the mean electrical axis. The ECG can be used to diagnose: Abnormal heart rate. Arrhythmias. Damage of heart muscle. How to read the ecg
Rhythm Analysis • Step 1: Determine regularity. • Step 2: Calculate heart rate. • Step 3: Assess the P waves. • Step 4: Determine PR interval. • Step 5: Determine QRS duration. • Step 6: Interpretation. How to read the ecg
1. Determine Regularity • Look at the R-R distances • Regular = equidistant apart • Interpretation = Regular How to read the ecg R R
How to read the ecg • 2. Calculating Heart Rate • HR = 1500 ÷ NO OF SMALL SQURES BETWEEN R-R WAVES • OR • HR = 300 ÷ NO OF BIG SQURES BETWEEN R-R WAVES R R
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 How to read the ecg
4. Determine PR Interval Normal: 0.12 - 0.20 seconds (3 - 5 boxes) Interpretation = normal 0.12 seconds How to read the ecg
5. Determination of QRS Duration Normal: 0.04 - 0.12 seconds (1 - 3 boxes) Interpretation = normal = 0.08 seconds How to read the ecg
Rhythm Analysis: • Regularity Regular • Rate 90-95 bpm • P waves Normal • PR interval 0.12 s • QRS duration 0.08 s Interpretation Normal Sinus Rhythm Normal Sinus Rhythm
Electrocardiogram and cardiac arrhythmias Arrhythmia: is any abnormality in the origin and/or the conduction of the cardiac impulse (action potential). A. Normotopic arrhythmias The site of origin is still in the sinus node; however, the firing of action potentials by the pacemaker is either: An abnormally slow rate, sinus bradycardia An abnormally high rate, sinus tachycardia. Irregular, sinus arrhythmias. B. Ectopic arrhythmias: Atrial ectopic arrhythmias: Atrial flutter Atrial fibrillation 2. Ventricular ectopic arrhythmias: Ventricular fibrillation
Variations in Sinus Rhythm • Regularity Regular • Rate 35 bpm • P waves Normal • PR interval 0.12 s • QRS duration 0.10 s Interpretation? Sinus Bradycardia Normotopic arrhythmias
Variations in Sinus Rhythm • Regularity Regular • Rate 130 bpm • P waves Normal • PR interval 0.16 s • QRS duration 0.18 s Interpretation? Sinus Tachycardia Normotopic arrhythmias
Deviation From Normal Sinus Rhythm: • Regularity Regular • Rate 70 bpm • P waves flutter waves • PR interval none • QRS duration 0.06 s Interpretation? Atrial Flutter Atrial ectopic arrhythmias
Atrial Fibrillation • No organized atrial depolarization, so no normal P waves (impulses are not originating from the sinus node). • The atrial rate is usually above 350 beats per minute • Atrial activity is chaotic (resulting in an irregularly irregular rate). • Common, affects 2-4%, up to 5-10% if > 80 years old Atrial ectopic arrhythmias
Regularity Regular • Rate 60 bpm • P waves normal • PR interval 0.036 • QRS duration 0.08 s Interpretation? 1st Degree AV Block PR Interval > 0.20 s Etiology: Prolonged conduction delay in the AV node or Bundle of His. First Degree AV Block
Regularity Regularly irregular • Rate 50 bpm • P waves normal, but 4th no QRS • PR interval lengthens • QRS duration 0.08 s Interpretation? 2nd Degree AV Block PR interval progressively lengthens, then the impulse is completely blocked (P wave not followed by QRS). Etiology: Each successive atrial impulse encounters a longer and longer delay in the AV node until one impulse (usually the 3rd or 4th) fails to make it through the AV node. SECOND Degree AV Block
Regularity Regular • Rate 40 bpm • P waves normal, but 2 and 3 no QRS • PR interval 0.14 s • QRS duration wide (> 0.12 s) Interpretation? 2nd Degree AV Block Occasional P waves are completely blocked (P wave not followed by QRS). Etiology: Conduction is all or nothing (no prolongation of PR interval); typically block occurs in the Bundle of His. SECOND Degree AV Block
Regularity Regular • Rate 40 bpm • P waves no relation to QRS • PR interval none • QRS duration 0.08 s Interpretation? 3rd Degree AV Block Etiology: There is complete block of conduction in the AV junction, so 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. Third Degree AV Block
Ventricular ectopic arrhythmias When an impulse originates in a ventricle, conduction through the ventricles will be inefficient and the QRS will be wide and bizarre.
Ventricular ectopic arrhythmias • Ventricular fibrillation produces an irregular electrocardiogram due to irregular stimulation of the ventricles. • Once the ventricles are fibrillating, they have to be defibrillated by applying a strong electrical current for a short period of time. Then the SA node may be able to reestablish a coordinated beat. • Ventricular fibrillation is of special interest because it can be caused by an injury or drug overdose. • It is the most common cause of sudden cardiac death in a seemingly healthy person over age 35.
Human physiology, Lauralee Sherwood, seventh edition. • Text book physiology by Guyton &Hall,11th edition. • Physiology by Berne and Levy, sixth edition. References