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.
In this way, the overall magnitude and direction of the heart's electrical depolarization is captured at each moment throughout the cardiac cycle. The graph of voltage versus time produced by this noninvasive medical procedure is referred to as an electrocardiogram (abbreviated ECG or EKG). typical ECG tracing is a repeating cycle of three electrical entities: a P wave (atrial depolarization), a QRS complex (ventricular depolarization) and a T wave (ventricular repolarization).