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.
1 The normal QRS axis range (+90Â° to -30Â°); this implies that the QRS be mostly positive (upright) in leads II and I. 2  right of +60Â°. 3  Septal q waves should not be confused with the pathologic Q waves of myocardial infarction. 4  Precordial leads: (see Normal ECG). 5  Small r-waves begin in V1 or V2 and progress in size to V5. The normal QRS axis range (+90Â° to -30Â°); this implies that the QRS be mostly positive (upright) in leads II and I. 2  right of +60Â°. 3  Septal q waves should not be confused with the pathologic Q waves of myocardial infarction. 4  Precordial leads: (see Normal ECG). 5  Small r-waves begin in V1 or V2 and progress in size to V5.