Dr. Einthoven was a physiologist, who in the late 1800s, first established the 3-lead cardiac monitoring system; the three lead system maps the electrical workings of the heart with a triangular lead system – Leads I, II, III.
The three electrodes are colored white, black and red and form a triangle – Einthoven’s Triangle (see Figure 4.1). These colors are not universal. Two coloring schemes exist for electrode placement, originating from two standards bodies: the American Heart Association (AHA) and the International Electrotechnical Commission (IEC)Two coloring schemes exist for electrode placement, originating from two standards bodies: the American Heart Association (AHA) and the International Electrotechnical Commission (IEC). The coloring scheme followed in this book adheres to the standard advocated by the AHA (refer to.... The coloring scheme followed in this book adheres to the standard advocated by the AHA. See “Electrode Locations Standards of the AHA and IEC” for more info.
For monitoring purposes with the three lead system, the white electrode is placed just below the clavicle (collarbone) on the right shoulder. When utilized – in leads I and lead II – the white electrode has a negative polarity. In accordance with the AHA, the end of the electrode cable is labelled “RA” for right arm.
The red electrode, an electrode with positive polarity in lead in leads II and III, is connected below the left pectoral muscle near the apex of the heart. The end of the red electrode cable is usually labelled “LL” for left leg.
Electrodes are optimally placed directly on dry skin. Many electrode manufacturers stress: 1)shaving the skin if necessary; 2) removing dead skin cells by rubbing the area with a rough paper or cloth; 3) using electrodes from air tight packages; and 4) paying attention to expiry dates on the electrodes. While common practice may not place great importance on the later three items, these criteria may be especially useful when troubleshooting an unclear ECGElectrocardiogram; also called an EKG; a representation of electrical voltage measured across the chest over a period of time. 1. Six Second ECG Guidebook (2012), T Barill, p. 196 tracing.*
The black electrode is connected below the left clavicle near the shoulder. Often labelled “LA” for left arm, the black electrode switches polarity dependent on the lead chosen. With lead I, the black electrode becomes positive (white is always negative). The black electrode assumes a negative polarity in lead III.
Various mnemonics might help ensure correct lead placement. Two examples are:
– White to the right. Red to the ribs. Black on top.
– White to the right. Smoke (black) over fire (red).
Just the same, we can always just look for reference from the end of the electrodes and place them accordingly.
Electrodes are best connected to the skin in an area with minimal muscle activity. The cardiac monitor picks up any electrical activity, including any other muscle twitching in the vicinity. There is some question about whether the electrodes should be placed on bone, on muscle, under or over breasts. For dysrhythmiaUsed interchangeably with arrhythmia, refers to any abnormal rhythm – not normal sinus rhythm or sinus tachycardia. 1. Six Second ECG Guidebook (2012), T Barill, p. 196 monitoring, electrodes should be optimally placed to get the clearest tracing. Changing electrode positions, though, by very little often changes the ECG. The key is consistency.
The three lead system provides three views of the heart. Locating the positive electrode is crucial to determining which area of the heart is viewed electrically. Metaphorically, the positive electrode serves as a mini-video camera aimed at the heart in the direction of the negative electrode. These leads and their corresponding electrodes do not sit right on the heart. Rather, their vantage points offer a surface, frontal view of the heart.
Lead I provides a left lateral view of the heart. Perhaps the lead most often chosen for cardiac monitoring, lead II – an inferior lead – views the apex of the heart. Lead III also provides an inferior view.
An an important point to consider is that practically any lead will suffice for dysrhythmia monitoring. For tasks such as myocardial ischemiaInsufficient supply of oxygen to meet the oxygen demands of tissue. Anaerobic metabolism becomes increasingly important during periods of ischemia. Ischemia results from an inadequate blood flow that fails to meet the oxygen demands (energy demands) of tissues. If tissues... monitoring, though, each lead provides information specific only to the region viewed. For example, Lead I can provide signs of left ventricular ischemia, but only rarely signs of right ventricular ischemia.
Figure 4.1 depicts the standard three lead system that forms Einthoven’s triangle. Note that while the red electrode is usually placed near the left lateral base of the chest, the electrical reference point for the red electrode tends to reside as shown. The arrow that is directed parallel to lead III represents a vector. If the wave of electrical depolarizationThe rapid influx of positive ions (sodium and/or calcium) into a cell – depolarization is necessary for contraction to occur. A depolarizing wave moves through the myocardium on average along a trajectory or vector. A vector is a force moving... moves parallel and in the same direction as this vector, the waveforms will be upright and the tallest in amplitudeThe height or depth of waves and complexes of an ECG in millimetres; represents millivolts where 10 mm is 1 millivolt with a properly calibrated monitor. 1. Six Second ECG Guidebook (2012), T Barill, p. 190.
1. Six Second ECG GuidebookA Practice Guide to Basic and 12 Lead ECG Interpretation, written by Tracy Barill, 2012 Introduction The ability to correctly interpret an electrocardiogram (ECG), be it a simple six second strip or a 12 lead ECG, is a vital skill... (2012), T Barill, p. 64-65, 196