الأحد، 18 أكتوبر 2015

ECG ( Electocardiogram ) 12 leads ECG

11:20 ص  ,   


ECG ( Electocardiogram )


Graphic surface recoding of electrical cardiac events, and allow 3D look at electrical activity.
The patient of resting on supine position. 


Electrophysiology

  • Pacemaker = Sinoatrial node
  • Impulse travels across atria
  • Reaches AV node
  • Transmitted along interventricular septum in Bundle of His
  • Bundle splits in two (right and left branches)
  • Purkinje fibers


Types of Leads
Composed of two type:
  • Frontal plane – Limb leads
* I, II, and III ( three augmented voltage ).
* aVR, aVL, and aVF.
  • Sagittal plane – Chest leads
            * Six chest ( Precardial Leads ) V1 – V6.

I, II, III, aVR, aVL, and avF called limb leads ( Frontal plane ).
V1 – V6 called procardial leads ( Sagittal plane ).



Precardial Lead Plasement
  1. Place your finger at the notch ( jugular notch ), then move your finger slowly downward until you feel a slightly horizontal ridge or elevation ( This is the angle of Louis, Sternal angle ).
  2. Follow the sternal angle until it articulates with 2nd rib. Move your finger below the 2nd rib ( 2nd intercostal space ).
  3. From 2nd intercostal space, the 3rd, and 4th intercostal spaces can be found below.
  4. V1 is placed in 4th intercostal space just right to the sternum.
  5. V2 is placed in 4th intercostal space just left to the sternum.
  6. V4 is placed in 5th intercostal space at mid clavicular line ( left sagittal ).
  7. V3 is placed directly between V2 and V4.
  8. V5 is placed at the same level as V4, at the anterior axillary line.
  9. V6 is placed at the same level as V5, at the mid axillary line.

The Leads on the chest are identified:
  • V1 – Right side of the sternum, 4th intercostal space.
  • V2 – Left side of the sternum, 4th intercostal space.
  • V3 – Midway between V2, and V4.
  • V4 – Left mid clavicular line, 5th intercostal space.
  • V5 – Left anterior axillary line at same level as V4.
  • V6 – Left mid axillary line at same level as V4.

What parts of the heart do the leads look at?
  1. I, aVL look at lateral Left ventricle.
  2. II, III, aVF look at Interventricular wall.
  3. avR looks at Right atrium.
  4. V1, V2 look at Septal wall.
  5. V3, V4 look at Anterior left ventricle.
  6. V5, V6 look at Lateral left ventricle. 

ECG time and voltage:
  • Major grid lines are 5 mm. At standard 5 mm corresponds to 0.2 seconds.
  • Minor grid lines are 1 mm. At standard 1mm corresponds to 0.04 seconds. 
  •           25mm/s (25 small squares /or 5 large squares) equals one second.
     


The QRS Axis:
  • Direction of ventricular depolarization, and described by the limb leads. 
  • Normal QRS complex equal 1.5 – 2.5 mm ( 60 – 80 ms ), and narrow.
 

  • P wave = atrial depolarization
  • QRS = ventricular depolarization
  • T = repolarization of the ventricles
QRS width

* The width of the QRS complex should be less than 0.12 seconds (3 small squares)
* It is useful to look at leads V1 and V6

The P wave

* The P wave represents atrial depolarization
* Height: a P wave over 2.5mm
* Length: a P wave longer than 0.08s (2 small squares)
* P wave  =  Normal sinus rhythm.

The PR interval

* The PR interval is measured between the start of the P wave to the start of the QRS complex.
* The PR interval corresponds to the time period between depolarization of the atria and ventricular depolarization.
* A normal PR interval is between 0.12 and 0.2 seconds ( 120 – 200 ms )3- 5 small squares.


      The ST segment

The ST segment should sit on the isoelectric line. It is abnormal if there is planar (i.e. flat) elevation or depression of the ST segment.
 



The heart rate

Use a calculator


Count the small (1mm) squares between two QRS complexes. The ECG paper runs at 25 mm/sec through the ECG printer; therefore:




What’s the heart rate?
the number of small boxes for the R-R interval is 22.5. The heart rate is 1500/21.5, which is 69.8.


The marker method
  1. Count the number of QRS complexes that fit into 3 seconds ( some ECG writers print this period on the ECG paper) . Multiply this number by 20 to find the number of beats/minute.
  2. Count the number of QRS complexes over a 6 second interval. Multiply by 10 to determine heart rate. This method works well for both regular and irregular rhythms.

 




What’s the heart rate?
7 QRS complexes, so the heart rate is 70.


Written by Mubark A. Wilkins
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