![]() ![]() 23 Normal sinus rhythm is illustrated in Figure 5-4 and premature ventricular contractions (PVCs) in Figure 5-5.Īlthough not recommended for use in all procedures, the ECG does increase one's ability to detect possibly significant changes in the functioning of the myocardium at a time when corrective treatment may usually restore a normal rhythm. Textbooks on basic electrocardiography are available, enabling the reader to become proficient at the interpretation of ECG tracings. Although 12 leads may be used, standard lead I (right arm → left arm) or lead II (right arm → left leg) are most commonly used during anesthesia because they permit excellent detection of dysrhythmias. The ECG ( Figure 5-3) monitors both the heart rate and rhythm and provides a warning of the development of changes in the electrical activity of the myocardium. Malamed DDS, in Sedation (Fifth Edition), 2010 Electrocardiography ![]() The standard setting of 25 mm/sec must be used when the duration of various ECG components, such as PR interval or QT interval, are calculated manually. A sweep speed of 50 mm/sec is occasionally useful to show waveforms more clearly, particularly the identification of P waves. This setting must be used when the amplitude of ECG components, such as R wave height and ST segment deviation, are measured manually (parameters calculated automatically take the gain setting into account). The standard gain setting used when recording a 12-lead ECG is 10 mm = 1 mV. In certain situations, altering the default settings is useful: if the QRS complex is large, reducing the gain minimizes overlap between waveforms and reduces the likelihood of double-counting the heart rate if the QRS complexes are small, increasing the gain may improve detection of the R wave, which is necessary for the calculation of heart rate and for the synchronization of shocks during electrical cardioversion. ![]() To display a range of ECG waveforms accurately, a frequency range of 0.05 to 100 Hz should be used, although this may be reduced if there is marked interference.Īdjusting the gain or calibration controls can alter the size of the displayed ECG. The lower frequency limit must be sufficiently low to display accurately low-frequency waveforms such as the P and T waves, and the higher limit must be sufficiently high to record high-frequency waveforms such as the QRS complex and to display rapid tachycardias. High-frequency filters reduce electrical interference low-frequency filters reduce movement artifact and signal distortion resulting from poor electrode contact. David Sidebotham, in Cardiothoracic Critical Care, 2007 Filtering, Gain, and Sweep SpeedĪll ECG machines use filters to reduce artifacts. ![]()
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