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.
Read More. Since we covered the first 6 leads of the 12 lead ECG in the 6-part tutorial on axis determination, a few words about the precordial leads might be in order. These are leads V1-V6, the unipolar leads that are placed directly on the patientâs chest.