Monitors that require three electrodes use positive, negative, and ground electrodes that are placed in the right arm (RA), left arm (LA), and left leg (LL) positions on the chest as designated by markings on the monitor cable.
When the electrodes are placed appropriately, the standard leads (leads I, II, III) may be obtained by moving the lead selector on the bedside monitor to the lead I, II, or III position (Fig. 17-15). The lead selector automatically adjusts which electrode is positive, which electrode is negative, and which electrode is ground to obtain an appropriate tracing. When lead I is selected, the LA is positive, the RA is negative, and the LL is ground. For a lead II configuration, the LL is positive, the RA is negative, and the LA is ground. To obtain a lead III, the LL is positive, the LA is negative, and the RA is ground. The configuration of leads I, II, and III, known as Einthoven’s triangle, is illustrated in Figure 17-16.
To obtain a chest lead on the monitor that replicates the chest lead from the 12-lead ECG, a five-wire system is
needed. When only three wires are available, a modified version of any of the six chest leads may be obtained. To
configure a modified chest lead (MCL), the goal is to position the positive electrode in the designated chest position.
For example, an MCL1 would require the positive electrode to be placed in a V1 position (fourth intercostal space, right sternal border). The negative electrode is always positioned under the left clavicle. The ground electrode can be positioned anywhere.
To obtain an MCL1 lead, the monitor is set to lead I (Box 17-13). (By setting the monitor to lead I, the LA electrode is positive, the RA electrode is negative, and the leg wire is ground [Einthoven’s triangle].) The positive
electrode (LA) is placed in a V1 position (fourth intercostal space, right sternal border), and the negative electrode (RA) is positioned under the left clavicle. The
ground electrode (LL) can be positioned anywhere, but if it is placed in a V6 position, it is helpful when switching to an MCL6 lead.
To obtain an MCL6 lead, the goal is to place a positive electrode in a V6 position, a negative electrode under the left clavicle, and a ground wire anywhere. By setting the monitor to lead II, the LL electrode is positive, the RA electrode is negative, and the LA electrode is ground (Einthoven’s triangle). The positive electrode (LL) is placed in the V6 position (midaxillary line, same horizontal level as V4), and the negative electrode (RA) is placed under the left clavicle. The ground wire can be placed anywhere, but if it is placed in a V1 position, it will be helpful when switching to an MCL1 lead.
By arranging the electrodes as described, the nurse can monitor both MCL1 and MCL6 merely by switching the monitor from a lead I to a lead II without changing the electrode
placement on the patient’s chest. MCL1 and MCL6 are ideal leads for detecting bundle branch block (BBB) rhythms and for differentiating supraventricular wide-QRS tachycardias
from VT.
When the electrodes are placed appropriately, the standard leads (leads I, II, III) may be obtained by moving the lead selector on the bedside monitor to the lead I, II, or III position (Fig. 17-15). The lead selector automatically adjusts which electrode is positive, which electrode is negative, and which electrode is ground to obtain an appropriate tracing. When lead I is selected, the LA is positive, the RA is negative, and the LL is ground. For a lead II configuration, the LL is positive, the RA is negative, and the LA is ground. To obtain a lead III, the LL is positive, the LA is negative, and the RA is ground. The configuration of leads I, II, and III, known as Einthoven’s triangle, is illustrated in Figure 17-16.
To obtain a chest lead on the monitor that replicates the chest lead from the 12-lead ECG, a five-wire system is
needed. When only three wires are available, a modified version of any of the six chest leads may be obtained. To
configure a modified chest lead (MCL), the goal is to position the positive electrode in the designated chest position.
For example, an MCL1 would require the positive electrode to be placed in a V1 position (fourth intercostal space, right sternal border). The negative electrode is always positioned under the left clavicle. The ground electrode can be positioned anywhere.
To obtain an MCL1 lead, the monitor is set to lead I (Box 17-13). (By setting the monitor to lead I, the LA electrode is positive, the RA electrode is negative, and the leg wire is ground [Einthoven’s triangle].) The positive
electrode (LA) is placed in a V1 position (fourth intercostal space, right sternal border), and the negative electrode (RA) is positioned under the left clavicle. The
ground electrode (LL) can be positioned anywhere, but if it is placed in a V6 position, it is helpful when switching to an MCL6 lead.
To obtain an MCL6 lead, the goal is to place a positive electrode in a V6 position, a negative electrode under the left clavicle, and a ground wire anywhere. By setting the monitor to lead II, the LL electrode is positive, the RA electrode is negative, and the LA electrode is ground (Einthoven’s triangle). The positive electrode (LL) is placed in the V6 position (midaxillary line, same horizontal level as V4), and the negative electrode (RA) is placed under the left clavicle. The ground wire can be placed anywhere, but if it is placed in a V1 position, it will be helpful when switching to an MCL1 lead.
By arranging the electrodes as described, the nurse can monitor both MCL1 and MCL6 merely by switching the monitor from a lead I to a lead II without changing the electrode
placement on the patient’s chest. MCL1 and MCL6 are ideal leads for detecting bundle branch block (BBB) rhythms and for differentiating supraventricular wide-QRS tachycardias
from VT.
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