EKG Basics and 12-Lead Perspectives

Notes

Hello everyone, and welcome to our module on EKG basics. The EKG is a visual representation of electrical activity as it moves through the heart. To understand EKGs, we need to review how electricity moves through the heart under normal conditions. Normally, the sinoatrial (SA) node, located on the right atrial free wall, is the pacemaker of the heart. It depolarizes and sends a wave of depolarization spreading to the myocytes in the left and right atria. From there, depolarization funnels through the atrioventricular (AV) node, then to the His bundle, and subsequently to the left and right bundle branches. Finally, it reaches the Purkinje fibers, which are embedded in the myocytes of the left and right ventricles. When the Purkinje fibers depolarize, they lead to ventricular depolarization. Shown on the screen is a typical example of electrical activity as it moves through the heart, depicted by the EKG. The EKG detects electrical activity and plots it versus time. Time is always represented on the X-axis, and the Y-axis shows electrical activity. Any electrical event in the heart can generate either a positive or negative deflection on the EKG. A positive deflection is upward, an...