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.
When looking at a 12-lead ECG, there are a few logistics that must be known. First of all, the standard 12-lead ECG is a 10 second strip. The bottom one or two lines will be a full rhythm strip of a specific lead spanning the whole 10 seconds of the ECG. Other leads will only span about 2.5 seconds.