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.