EKG Interpretation Essentials and QT Intro

Notes

- The 12-lead EKG records the same electrical activity from different vantage points. - When electrical activity moves towards a lead, it produces an upward deflection; when moving away, it produces a downward deflection. As mentioned earlier, the SA node is the dominant pacemaker under normal conditions. Other pacemakers exist but are slower, so the SA node controls the heart rate. A normal heart rate is about 60 to 100 beats per minute, dictated by the SA node's depolarization rate. If the SA node fails, the AV node can take over at 40 to 60 beats per minute, while the His bundle, bundle branches, and Purkinje fibers can serve as pacemakers at even slower rates of 25 to 40 beats per minute. Conduction velocity is slowest in the AV node, which is physiologically important because it allows more time for ventricular filling, making the heart a more effective pump. It is fastest in the Purkinje fibers, with conduction through atrial and ventricular myocytes being intermediate. The delay in the QRS complex after the P wave is mainly due to conduction time through the AV node, where conduction is slowest. To determine heart rate, measure the time between two QRS complexes, each repres...