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Electrocardiogram
| Continuous visual display of the patient's ECG on an oscilloscope is the standard of care for all patients undergoing anesthesia. It detects (1) cardiac dysrhythmias, (2) myocardial ischemia as reflected by ST segment depression, and (3) electrolyte abnormalities, particularly potassium. The ability to save the ECG on the oscilloscope screen or to obtain a hard copy recording is helpful for more detailed analysis of the tracing. An audible indicator for each QRS complex allows the anesthesiologist to carry on other activities while listening for changes in heart rate or cardiac rhythm. Lead II is commonly used for detection of cardiac dysrhythmias because it parallels the P-wave vector, resulting in maximum amplitude of the P wave on the ECG. Inferior wall myocardial ischemia of the left ventricle may be reflected by ST segment depression in lead II. More common sites of myocardial ischemia, the anterior and lateral walls of the left ventricle, are best monitored by the precordial lead a V5 position (fifth intercostal space along the anterior axillary line). The equivalent of a V5 lead can be obtained with three electrodes by placing the left arm electrode in the V5 position and selecting lead a VL on the monitor. It must be recognized that the ECG reflects only the electrical activities occurring in the heart and in no way is a measure of heart function. For example, normal ECG complexes may persist on the oscilloscope in the absence of an effective cardiac output (pulseless electrical activity). |
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