Should a site outside the electrical system initiate an impulse (for example, a ventricular site), a different mechanism of depolarization occurs. Because the impulse occurs outside the specialized electrical system cells, asynchronous activation of the right and left ventricle occurs and in addition the conduction velocity is slowed through the myocardial cells. This results in a wide bizarre qRs. THE ELECTROCARDIOGRAM An electrocardiogram is a graphic tracing of voltage produced by depolarization and repolarization of the heart muscle. It is important to remember that the ECG shows you only the electrical activity of the heart – it shows nothing related to the mechanical function of the heart muscle. When no current is flowing, the stylus (writing point) of the electrocardiograph does not move, and a straight line is recorded. A current flow causes a deflection (movement) of the stylus, so that a wave is inscribed on the ECG paper. Normal movements from the baseline are called waves and are designated P, q, R, s, T and U. The spaces between the waves, which usually appear as straight lines, are called segments and are named by the waves they separate (for example, ST segment between the S and T waves). Intervals are also named by the waves at their beginning and end, for example, PR interval, but their measurement is from the beginning of the first wave, unlike the segments whose measurement starts at the end of the first wave. An interval ends with the start of the wave at its end just like a segment does, with one exception; the qT interval is measured from the start of the q wave to the end of the T wave. A complex includes more than one wave (qRs complex). Each wave recorded on the electrocardiogram corresponds to a particular event in the cardiac cycle. Although the heart consists of several layers, it is only the heart muscle cell layer (myocardium) that generates currents large enough to be recorded by the electrocardiograph. The current recorded by the electrocardiograph at any moment is the sum of all the currents flowing in cells throughout the heart at the particular instant. Deflections that emanate above the isoelectric line are called positive deflections. Deflections that radiate below the isoelectric line are considered negative deflections. Positive Isoelectric Negative
16 ELECTRODE PLACEMENT Electrodes are small patches which are placed on the chest to transmit electrical activity from the heart to the telemetry system. Correct electrode placement is critical in order to correctly identify cardiac rhythms and rhythm disturbances. “Research has shown that when an electrode is misplaced by 1 intercostal space, the morphology of the qRs can change dramatically and missed …diagnosis may occur… There are certain leads that are appropriate for specific dysrhythmias.
You've reached the end of your free preview.
Want to read all 70 pages?
- Spring '18
- Normal sinus rhythm