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.
The letter âaâ stands for âaugmentedâ as these leads are calculated as a combination of leads I, II and III. The 6 precordial leads are called leads V1, V2, V3, V4, V5 and V6. Below is a normal 12-lead ECG tracing. The different parts of the ECG will be described in the following sections.