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.
To meet criteria for LGL, the 12-lead ECG taken during a period of normal sinus rhythm must demonstrate a PR interval less than or equal to 0.12 second and a normal QRS upstroke and duration, as in the image below. ECG demonstrating a short PR interval of approximately 100 ms and normal QRS. One of the most useful diagnostic tools is a 12-lead ECG recorded during a paroxysm of tachycardia.