Electrocardiogram (ECG) Lecture Notes PDF

‫جامعة بالد الرافدين‬ ‫كلية التقنيات الصحية والطبية‬ ‫قسم التخدير‬ ‫المرحلة الثالثة‬ ‫‪anesthetic equipment‬‬ ‫)‪electrocardiogram (ECG‬‬ ‫‪Dr. Ammar Hoom‬‬  Electrocardiogram (ECG) This monitors the electrical activity of the heart with electrical potent...

‫جامعة بالد الرافدين‬ ‫كلية التقنيات الصحية والطبية‬ ‫قسم التخدير‬ ‫المرحلة الثالثة‬ ‫‪anesthetic equipment‬‬ ‫)‪electrocardiogram (ECG‬‬ ‫‪Dr. Ammar Hoom‬‬  Electrocardiogram (ECG) This monitors the electrical activity of the heart with electrical potentials of 0.5-2 mV at the skin surface. It is useful in determining the heart rate, ischemia, the presence of arrhythmias and conduction defects.  The bipolar leads (I, II, III, AVR, AVL and AVF) measure voltage difference between two electrodes.  The unipolar leads (V1-6) measure voltage at different electrodes relative to a zero point.  Components 1. Skin electrodes detect the electrical activity of the heart. Silver and silver chloride forms a stable electro combination. 2. Color-coded cables to transmit the signal from electrodes to the monitor. All the cables of a particular set should have the same length to minimize the effect of electromagnetic interference. 3. The ECG signal is then boosted using an amplifier. The amplifier covers a frequency range of 0.05-150 Hz. It also filters out some of the frequencies considered to be noise. The amplifier has ECG filters that are used to remove the noise/ artifacts from ECG and produce a clean signal. 4. An Oscilloscope that displays the amplified ECG signal. A high-resolution monochrome of color monitor is used.  Mechanism of action 1. Proper attachment of ECG electrodes involves cleaning the skin, gently abrading the stratum corneum and ensuring adequate contact using conductive gel. 2. Modern ECG monitors use multiple filters for signal processing. The filters used should be capable of removing the unwanted frequencies, leaving the signal intact. Two types of filters are used for this purpose: the high-pass filters and the low-pass filters. 3. The ECG monitor can have two modes: a) the monitoring Mode has a limited frequency response to reduce environmental artifacts. b) The diagnostic mode has a wider frequency response allows the assessment of the ST segment, QRS morphology and tachyarrhythmia. 4. There are many ECG electrode configurations. Usually during anesthesia, three skin electrodes are used (right arm, left arm and indifferent leads left leg). The three limb leads used include two that are active and one that is inactive (earth). Sometimes five electrodes are used. Lead II is ideal for detecting arrhythmias. CM5 configuration is able to detect 89% of ST-segment changes due to left ventricular ischemia.  Problems in practice and safety features 1. Incorrect placement of the ECG electrodes in relation to the heart is a common error, leading to false information. 2. Electrical interference because of capacitance or inductive coupling effect. Any electrical device powered by AC can act as one plate of a capacitor and the patient acts as the other plate. 3. Muscular activity, such as shivering, can produce artifacts. 4. High and low ventricular rate alarms and an audible indicator of ventricular rate are standard on most designs. More advanced monitors have the facility to monitor the ST segment. 5. Absence of or improperly positioned patient diathermy plate can cause burns at the site of ECG skin electrodes. This is because of the passage of the diathermy current via the electrodes causing a relatively high current density.