ECG Basics

Normal Impulse Conduction
Sinoatrial node--AV node--Bundle of His--Bundle Branches--Purkinje fibers

The “PQRST”
►    P wave - Atrial   depolarization


        QRS - Ventricular    depolarization 
        T wave - Ventricular   repolarization




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)



Pacemakers of the Heart
►    SA Node - Dominant pacemaker with an intrinsic rate of 60 - 100 beats/minute.

►    AV Node - Back-up pacemaker with an intrinsic rate of 40 - 60 beats/minute.

►    Ventricular cells - Back-up pacemaker with an intrinsic rate of 20 - 45 bpm.



The ECG Paper

►    Horizontally
    One small box - 0.04 s
    One large box - 0.20 s 
►    Vertically
    One large box - 0.5 mV

►    Every 3 seconds (15 large boxes) is marked by a vertical line.
►    This helps when calculating the heart rate.