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**ELECTROCARDIOGRAM (ECG)**

بسم الله الرحمن الرحيم Cardiovascular System ANALYSIS Dr.Mohammed Sharique Ahmed Quadri Asst. Professor Physiology Almaarefa College ELECTROCARDIOGRAM (ECG)

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**The 12-Leads The 12-leads include: 3 Limb leads (I, II, III)**

3 Augmented leads (aVR, aVL, aVF) 6 Precordial leads (V1- V6)

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**Views of the Heart Left Lateral portion of the heart( I , Avl, v5,v6)**

Some leads get a good view of the: Anterior portion of the heart (V1,V2,- setum V3,V4-)- anterior Inferior portion of the heart II, III, aVF

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Basic components

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**The “PQRST” P wave - Atrial depolarization**

QRS - Ventricular depolarization T wave - Ventricular repolarization

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**Atrial depolarization**

The PR Interval Atrial depolarization + delay in AV junction (AV node/Bundle of His) (delay allows time for the atria to contract before the ventricles contract)

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**Segments & intervals PR interval: 0.12 – 0.20 sec**

QRS interval : 0.08 – 0.10sec QT interval : sec ST interval : sec

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**How to read the ecg Rhythm analysis**

Analyzing individual wave & segments Determine the mean electrical axis

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**Rhythm Analysis Step 1: Determine regularity. Step 2: Calculate rate.**

Step 3: Assess the P waves. Step 4: Determine PR interval. Step 5: Determine QRS duration.

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**1-Determine regularity**

Look at the R-R distances (using a caliper or markings with a pen on paper). Regular (are they equidistant apart)? Occasionally irregular? Regularly irregular? Irregularly irregular? Interpretation? R R Regular

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**2-Calculating heart rate**

H.R = NO OF SMALL SQURES BETWEEN R-R WAVES OR H.R = NO OF BIG SQURES BETWEEN R-R WAVES

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**Calculate Rate Option 2 R wave**

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

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**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

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**4-Determine PR interval**

Normal: seconds. (3 - 5 boxes) Interpretation? 0.12 seconds

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**5-QRS duration Normal: 0.04 - 0.12 seconds. (1 - 3 boxes)**

Interpretation? 0.08 seconds

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**Rhythm Summary Normal Sinus Rhythm Regularity regular Rate 90-95 bpm**

P waves normal PR interval s QRS duration s Interpretation? Normal Sinus Rhythm

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Calculate Heart Rate. What is Axis ? Normal ECG

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**Variations in Sinus Rhythm**

Rate? 35 bpm Regularity? regular P waves? normal PR interval? 0.12 s QRS duration? 0.10 s Interpretation? Sinus Bradycardia

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**Variations in Sinus Rhythm**

Rate? 130 bpm Regularity? regular P waves? normal PR interval? 0.16 s QRS duration? 0.08 s Interpretation? Sinus Tachycardia

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**SINUS ARHYTHMIA INTERPRETE THE ECG ?**

Observe Variation in Heart Rate during Inspiration and Expiration. [Increased Heart Rate during Inspiration]

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**Atrial Fibrillation Deviation from NSR**

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

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**Atrial Flutter Rate? 70 bpm Regularity? regular P waves? flutter waves**

PR interval? none QRS duration? 0.06 s Interpretation? Atrial Flutter

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AV Nodal Blocks 1st Degree AV Block 2nd Degree AV Block, MobitzType I 2nd Degree AV Block,MobitzType II 3rd Degree AV Block

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**Rate? 60 bpm Regularity? regular P waves? normal PR interval? 0.36 s**

Take a look at this ECG. What do you notice Rate? 60 bpm Regularity? regular P waves? normal PR interval? 0.36 s 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.

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**2nd Degree AV Block, Type I**

Take a look at this ECG. What do you notice Rate? 50 bpm Regularity? regularly irregular P waves? normal, but 4th no QRS PR interval? lengthens QRS duration? 0.08 s Interpretation? 2nd Degree AV Block, Type I 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.

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**2nd Degree AV Block, Type II**

Take a look at this ECG. What do you notice Rate? 40 bpm Regularity? regular P waves? normal, 2 & 3 no QRS PR interval? 0.14 s QRS duration? 0.08 s Interpretation? 2nd Degree AV Block, Type II 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.

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**Interpretation? 3rd Degree AV Block Rate? 40 bpm Regularity? regular**

Take a look at this ECG. What do you notice Rate? 40 bpm Regularity? regular P waves? no relation to QRS PR interval? none QRS duration? wide (> 0.12 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 beats/minute.

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Remember When an impulse originates in a ventricle, conduction through the ventricles will be inefficient and the QRS will be wide and bizarre.

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**Determination of Mean Electrical Axis**

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.

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When a vector is exactly horizontal and directed toward the person’s left side,the vector is said to extend in the direction of 0 degrees From this zero reference point, the scale of vectors rotates clockwise:

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**FORMATION OF HEXAAXIAL SYSTEM**

I III II

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**FORMATION OF HEXAAXIAL SYSTEM**

aVR aVL aVF

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**FORMATION OF HEXAAXIAL SYSTEM**

-90 aVR aVL I III II +90 aVF

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**Determination of Mean Electrical Axis**

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 +110o. A QRS axis that falls between -30o and -90o is abnormal and called left axis deviation. 0o 30o -30o 60o -60o -90o -120o 90o 120o 150o 180o -150o A QRS axis that falls between +110o and +180o is abnormal and called right axis deviation. A QRS axis that falls between +180o and -90o is abnormal and called Indeterminant (extende rt axis ) .

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**How to calculate the qrs axis**

Leads & there isoelectric partners

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**How to calculate the QRS axis**

… 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 aVF Axis normal left axis deviation right axis deviation right superior axis deviation/ indeterminant

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