1 Most episodes of acute lower back pain are caused by muscle strain, such as from lifting a heavy object, a sudden movement or a fall. 2  The low back pain can be very severe and last for several hours, several days or even a few weeks.
3. Characteristics of the Normal ECG. It is important to remember that there is a wide range of normal variability in the 12 lead ECG. The following normal ECG characteristics, therefore, are not absolute. It takes considerable ECG reading experience to discover all the normal variants.
For a routine analysis of the heartâs electrical activity an ECG recorded from 12 separate leads is used. A 12-lead ECG consists of three bipolar limb leads (I, II, and III), the unipolar limb leads (AVR, AVL, and AVF), and six unipolar chest leads, also called precordial or V leads, (, , , , , and).hapter V The 12-Lead EKG. This chapter presents an introduction to the 12-lead ECG. The 12-lead ECG gives a tracing from 12 different âelectrical positionsâ of the heart. Each lead is meant to pick up electrical activity from a different position on the heart muscle.