How to read an ECG?

Let talk about how to read a 12 lead ECG,

At first you have to know ECG cnventions,those are

 

1) Depolarisation towards electrode: positive defection (‌ vid infra)

2) Depolarisation away frome electrode: Negative deflection

3) Sensitivity: 1mm=1mV

4) ECG paper speed: 25 mm/second

5)large square: 5mm, denoting time 0.2 seconds in duration in x axis,5 mV in Y axis

6) Small square: 1 mm, 0.04 seconds

৭)Heart rate= 1500/ RR interval বা 300/number of large squares between beats

When you see an ECG you must check the name,age of the patient,time and date when it is done.Then check for calibration that is the voltage what is used here,paper speed etc.

If the voltage is low it may indicate pericardial effusion, hypothyroidism etc or Emphysematous lung and obesity can also cause low voltage ECG.

Appearance of EV wave can be changed due to different speed.Norma speed of the paper 25mm/second

Now read the ECG wave by wave!

1) Rythm strip: Lead ll is called Rhythm strip.Here we see Heart rate and rhythm.

   Rate may normal

  May be tachycardia (more than 100 beats/min)

   May be Bradycardia ( rate less than 60 beats/min)

Rythmicity:

   Regular Rythm: RR interval normal throughout the ECG

Irrgular: RR wave irregular, it may be regularly irregular or irregularly irregular.

2)Cardiac axis: If QRS complex has positive deflection in  Lead l and  Lead ll এ QRS Complex  Cardiac axis normal.

   

3)P wave shape:

      *Tall P(pulmonale)=Right atrial enlargement

      * Notched P ( P mitrale)= Left Atrial enlargment

      *Absent or fibrillitory f: Atrial fibrillation

4)PR interval: 

       *Normal= 0.12-0.2 seconds

       * if more than 0.2 seconds AV block

       * less than 0.12 seconds WPW syndrome

5) QRS Complex Duration: If more than 0.12 seconds Ventricular conduction abnormal (Bundle branch block)

6)QRS Amplitude: 

       * In Slim person QRS complex may be large also in Letf ventricular hypertrophy.

7)Q wave: Q wave denoting previous MI

8) ST segment: Very important

         *Elevation: MI,pericarditis,Left ventricular aneurysm

         *Depression: Ischaemia or infarction

9) T wave:

        * Inversion: Myocardial ischaemia,Electrolytes disturbance

         * Tall T: Hyperkalemia,Hyperacute MI

10)QT interval: 

         * Normal: <0.042 seconds

         * QT prolong 

              Congenital long QT syndrome

              Low potassium,calcium,magnesium

             Drugs:       Disopiramide,Fleicanide,amitryptyline,sotalol,amiodarone,macrolids,chlorpramazine etc.