Guidelines for the Detection of ECG Limb Lead Misplacements

Suman Vardan, MD, Sandeep Vardan, MD, Disha Mookherjee, MD, Tapan K. Sarkar, PhD, Kishan G. Mehrotra, PhD, C. Thomas Fruehan, MD, and Sakti Mookherjee, MD

Published Online: January 16, 2008 - 9:59:09 PM (CST)

Physicians are often called upon to interpret a 12-lead electrocardiogram. Accurate interpretation depends, in part, on the ability to correctly place the 10 electrodes on their respective chest and limb positions. Electrocardiographic abnormalities caused by misplaced limb leads can mimic a variety of important clinical conditions, potentially leading to wrong diagnosis, unnecessary costs, and patient/physician anxiety. We examined electrocardiographic abnormalities that can occur with all 24 possible combinations of misplaced limb electrodes. Analysis of such diagnostic pitfalls enabled us to identify clues to uncovering the limb lead error responsible for the misleading electrocardiogram configurations. An accompanying ("web-extra") section, with additional examples, appears at the end of the article.

Electrocardiographic (ECG) abnormalities resulting from misplaced leads (electrodes) occur approximately 2% of the time in clinical practice, which means that about 2 million of the more than 100 million ECGs obtained in the United States each year may be recorded with misplaced leads.¹ Despite several recent reports of ECG electrode placement errors,^1-3 there have been few analyses of the ECG tracings that could result from all possible permutations of limb electrode misplacements. A routine 12-lead ECG recording is obtained by using 10 electrodes, each specifically labeled for its designated limb or chest position: 4 on the limbs and 6 on the chest. If we consider all possible interchanges involving the position of these 10 electrodes by permutation (N! factorial, ie, 10x9x8x7x6x5x4x3x2), the total number of variations would be 4,228,800?obviously an unyielding scenario in a clinical research setting. Therefore, we have limited our study to the frequently misplaced limb electrodes alone, which gave us a manageable number of 24 (4x3x2) variations.

Methods

In this study, we arbitrarily designed a method of intentionally misplacing ECG limb electrodes on a person who had a normal cardiac physical examination, a structurally normal heart on echocardiography, and a normal ECG. After being informed in detail about the procedure, the patient consented to participate in this study. The 24 possible variations of limb electrode placement were used in the ECG recordings of this volunteer (Table). Each of the 4 limbs got its correct electrode attached only 6 times, first with the left-leg electrode remaining on that limb during the first 6 recordings, while the other limb electrodes were switched around in a predetermined orderly fashion. In the next 3 sets of 6 recordings, the right-leg, left-arm, and right-arm electrodes remained attached to the left leg (x6 each), and the other limb electrodes were then switched for each of these sets. Each of the 24 examples was assigned a consecutive serial number on the ECG tracings (as well as in the Table). These serial numbers do not represent any sequential changes in ECG waveforms but serve only as identifiers of the limb electrode arrangements. The control tracing, with correctly attached electrodes, was assigned serial number 1 ("example 1") and those with misplacements, examples 2 through 24.

* Denotes correct placement of the electrode. Note: Serial number does not represent any sequential changes in the ECG wave forms.

In this article, we outline the diagnostic pitfalls resulting from such errors in ECG recordings and provide clues to identifying their source.

Analysis

The electrical activity of the heart is typically represented by vectors directed from the right arm to the left arm, the right arm to the left leg, and the left arm to the left leg, which are the conventional 3 bipolar limb leads I, II, and III, respectively. Einthoven's law translates these bipolar limb leads into the following equation: leads I + III ? II = 0 or I + III = II.

Thus, the amplitude of the waveforms in lead II approximates leads I and III combined, and the waveforms are transcribed in the same direction in all the 3 bipolar leads in a normal ECG. According to this equation, if we consider one of these leads as near zero, the remaining 2 leads will be equal to each other. The main composite vector is directed across lead II from the right arm to the left leg. The right-leg electrode is the ground and has little electrical activity. However, if the limb electrodes are connected erroneously to limbs other than the designated ones, then one needs to consider the possibility of 3 conceptual additional vectors connecting the left arm and the right leg, the right arm and the right leg, and the left leg and the right leg, which will be called "additional" bipolar leads IV, V, and VI, respectively, and which can be visualized on a 6-lead diagram (Figure 1). Because the major component of the cardiac vector is directed along lead II, it is clear that the component perpendicular to it given by additional lead IV will be of near-zero potential. In addition, there will be little electrical activity between the right leg and the left (as represented by additional lead VI), and additional lead V will follow the vector summation principle, depending on clockwise or counterclockwise orientation: I + IV ? V = O or II + VI ? V = 0 and V ? IV ? I = 0 or V ? VI ? II = 0, respectively.

Figure 1?The 6-lead diagram. To analyze misplaced limb electrode?generated ECG waveforms, follow these 5 steps: 1. Plot the limb electrode arrangements on this diagram. 2. Obtain the corresponding lead (conventional and additional). 3. Use the clockwise equation ( I + III ? II = 0, or I + IV ? V = 0, or II + VI ? V = 0, or III + VI ? IV = 0 ), or counter-clockwise equation ( II ? III ? I = 0, or IV ? VI ? III = 0, or V ? IV ? I = 0, or V ? VI ? II = 0). 4. Presume 1 of the 2 additional leads, IV and VI, to be at near-zero value if they occur together in any of the 3 bipolar lead combinations in either the clockwise or the counterclockwise equation. 5. Transform the leads obtained in step 3 into those recognized by the galvanometer according to its inherent design (I, II, III) to derive the directionality and the amplitude of the resultant ECG waveforms based on Einthoven's law (I + III ? II = 0) and its corollary (when one of I, II, or III is zero, the remaining 2 are equal in amplitude and direction to each other).

The ECG recording equipment (the galvanometer) has been conventionally designed to recognize the designated electrode for a particular limb, no matter where on the body that electrode may be placed (eg, the right-arm electrode misplaced anywhere on the body will always be interpreted as if it is correctly placed on the right arm). Thus, when the arm electrodes are correctly placed, the galvanometer finds the cardiac electrical current traversing from the right arm to the left arm and records predominantly positively directed waveforms. However, when the arm electrodes are reversed, the recorder interprets the cardiac impulse moving in the opposite direction and records predominantly negatively directed waveforms, in contradistinction to that recorded with the correctly attached arm electrodes. Furthermore, because there is little electrical activity between the 2 legs representing additional lead VI, switching the arrangement of the electrodes attached to the legs of normal individuals results in little change in their ECG waveforms.⁴ In any given combination of limb electrode misplacements in our study, switching leg leads resulted in negligible changes in the ECG configuration.

Therefore, the 24 ECG tracings obtained from all possible variations of limb electrode placements can, for all practical purposes, be grouped in 12 pairs (examples 1 and 7; 2 and 8; 3 and 13; 4 and 14; 5 and 19; 6 and 20; 9 and 15; 10 and 16; 11 and 21; 12 and 22; 17 and 23; 18 and 24), with each tracing of any particular pair having almost identical waveforms (see additional examples, web-extra). Therefore, we have analyzed the genesis of only the first tracing of each pair, using steps 1 through 5 outlined in the legend of Figure 1. (Analysis of each pair is provided in the web-extra section.)

The second tracing of each pair, which is nearly identical to the first tracing, is not analyzed in the text but can also be explained by these 5 steps.

Discussion

Lead placement errors occur in about 2% of routine ECGs.^1,2 In such cases, the ECGs are confused with significant cardiac conditions, including^4,5:

• Right-arm and left-arm lead reversal, resulting in the features of dextrocardia
• Right-arm and right-leg electrode switch, resulting in low-amplitude ECG complexes of approximately 5 mm
• Left-arm and left-leg electrode reversal, raising suspicion for inferior-wall myocardial infarction (MI)
• Right-arm and left-leg electrode switch, which can be confused with the combined features of lateralwall MI and low atrial rhythm.

Other possible switches have been described^6,7:

• Left arm and right leg, as well as right leg and left leg, showing near-zero-potential complexes in lead III and a negligible change in lead III, respectively
• Clockwise as well as counterclockwise rotated right-arm/left-arm/left-leg leads (when the right-leg electrode remains attached to its correct limb), showing low atrial rhythm and inferior-wall MI and dextrocardia, respectively.

In light of such reports, one may tend to surmise that outside of the above 8 important scenarios (corresponding to examples 2, 6, 5, 22, 3, 7, 16, and 21 of our series), other combinations of limb misplacements "just never happen." Yet it is very plausible that other types of misplaced limb lead?generated ECG patterns may also be occurring, but they are not recognized because of the lack of systematically designed, comprehensive guidelines to identify such errors, which are therefore not reported.

Although computer programs do report "suspect arm lead reversal" and "low-voltage complexes"^1-3,8 in most situations the physician has to use his or her own clinical judgment based on a high index of suspicion, because none of these programs, to our knowledge, includes all 24 variations of limb lead placement in their database.

As noted earlier, the right-leg electrode is not included in the circuit of a bipolar limb lead recording. However, when the ground and the left-leg electrodes are mistakenly included in the circuit of any of the bipolar limb leads, little electric current will flow, and usually only a small "blip" of an approximate 1-mm deflection on the baseline of the ECG recording would appear. This blip is conventionally expressed as a near-zero-potential complex. Whenever the right-leg electrode?along with the left-leg, left-arm, or right-arm electrode?was misplaced separately on either arm, near-zero-potential ECG complexes were recorded respectively on leads I, II, and III (Figures 2, 3, 4).

Figure 2?Misplacement of the right- and left-leg electrodes, separately, on the arms resulted in the near-zero-potential recording of lead I ECG. Example 17 (and 23, web-extra) showed features of inferior-wall MI plus COPD; example 18 (and 24, web-extra) demonstrated low atrial rhythm.

Figure 3?Placement of the right-leg and the left-arm electrodes on the arms resulted in a near-zero-potential recording of lead II (examples 5, 6). In addition, example 5 (and 19, web-extra) showed features of dextrocardia, and example 6 (and 20, web-extra) showed features of lateral-wall MI plus COPD.

Figure 4?Placement of the right-leg and right-arm electrodes separately on either arm resulted in a near-zero-potential recording of lead III. Example 3 (and 13, web-extra) otherwise appeared normal, whereas example 4 (and 14, web-extra) mimicked COPD.

Of note, whenever the right-leg electrode (ground) is misplaced on the right arm (closest to the origination of the cardiac impulse) and the other 3 limb electrodes are switched around the overall ECG waveforms, the overall ECG waveforms result in significantly reduced amplitude QRS complexes of approximately 5 mm in all limb leads. This is suggestive of conditions such as chronic obstructive pulmonary disease (COPD), pericardial infusion, or generalized fluid overload (anasarca) (Figure 5). In subsequent descriptions of low-voltage states, COPD will be used as a generic term.

The examples of limb lead misplacement, in addition to showing near-zero-potential complexes in a bipolar limb lead, may be associated with the ECG morphology of COPD plus inferior-wall MI, showing Q waves in II, III, and aVF (Figures 2, 5, example 17); or COPD plus lateral-wall MI, showing Q waves in I and aVL (Figures 3, 5, example 6); or COPD alone (Figures 4, 5, example 4). Without COPD, near-zero-potential complexes in a limb lead may be associated with low atrial rhythm, showing inverted P waves in lead II, III, and aVF and upright P waves in aVR (Figure 2, example 18), or situs inversus dextrocardia showing inverted PQRST complexes in lead I and aVL, or upright in aVR (Figure 3, example 5) or may even appear normal (Figure 4, example 3). Therefore, a common denominator of near-zero-potential complexes in one of the bipolar limb leads in these examples (which account for 50% of all ECG limb lead misplacements) will usually serve as a clue to limb electrode placement errors.

Figure 5?Misplacement of the right-leg electrode (ground) on the right arm (close to the origination of the main cardiac vector) resulted in the QRS complexes being reduced to <5 mm in all the limb leads, mimicking COPD. Depending on which limb electrode was placed on the left arm, near-zero potential was recorded in a bipolar lead with other associated conditions: in example 4 (and 14, web-extra), with the right-arm electrode attached to the left arm: COPD and near-zero potential in lead III; in example 6 (and 20, web-extra), with the left-arm electrode attached to the left arm: COPD with lateral-wall MI and near-zero potential in lead II; and in example 17 (and 23, web-extra), with left-leg electrode on the left arm: COPD, inferior-wall MI plus near-zero potential in lead I. Therefore, an ECG suggestive of COPD, with or without MI, and a near-zero potential in a bipolar limb lead were clues to limb lead misplacement.

Figure 6?Misplacement of left-leg electrode on the right arm resulted in the ECG morphology of low atrial rhythm with low atrial rhythm alone when the right-arm electrode was attached to the left arm in example 10 (and 16, web-extra); lateral-wall MI when the left-arm electrode remained attached correctly in example 12 (and 22, web-extra); and near-zero potential in lead I when the right-leg electrode was placed on the left arm in example 18 (and 24, web-extra). In examples 12 and 18, respectively, lateral-wall MI and near-zero potential in lead I were clues to electrode misplacement. There was no such clue in example 10.

Furthermore, when any one of the limb leads, other than the ground, remained misplaced on the right arm (close to where the cardiac impulse originates) and the other limb leads were switched around, the ECG morphology mimicked one of the following conditions:

• Low atrial rhythm mimics. Misplacement of the left-leg electrode on the right arm (Figure 6) resulted in the ECG morphology of low atrial rhythm, with or without features of lateral-wall MI, or near-zero-potential complexes in lead I. Thus, a combination of low atrial rhythm and lateral-wall MI morphology or near-zero-potential complexes in lead I (as seen in examples 12 and 18, respectively) should raise the suspicion of a misplaced left-leg electrode on the right arm. However, in example 10, which showed lone low atrial rhythm, no such clue was available.

• Situs inversus dextrocardia mimics. Misplacement of the left-arm electrode on the right arm resulted in the ECG morphology of dextrocardia in the limb leads, with or without inferior-wall MI, or near-zero amplitude limb lead complexes (Figure 7). However, examination of the precordial lead tracings (V₁ through V₆ showing the normal progression of R waves) would generally detect the error, and dextrocardia can be ruled out by the right-sided chest lead recordings of V₂R to V₆R.

Figure 7?Misplacement of the left-arm electrode on the right arm resulted in the ECG morphology of dextrocardia in the limb leads, with dextrocardia alone when the right-arm electrode was on left arm in example 2 (and 8, web-extra); near-zero-potential in lead II when the right-leg electrode occupied the left arm in example 5 (and 19, web-extra); and inferior-wall MI when the left-leg electrode was on the left arm in example 11 (and 21, web-extra). Near-zero potential in lead II and inferior-wall MI morphology were clues to misplaced leads in examples 5 and 11, respectively. There was no such indicator in example 2. However, examination of the precordial leads would detect the error promptly.

Figure 8?Misplacement of either leg electrode on the right arm when the left-arm lead was attached correctly resulted in the ECG morphology of lateral-wall MI, with <5-mm PQRST complexes in the limb leads mimicking COPD plus near-zero potential in lead II when the right-leg electrode occupied the right arm in example 6 (and 20, web-extra); and low atrial rhythm when the left-leg electrode was on the right arm in example 12 (and 22, web-extra). Therefore, features of COPD or low atrial rhythm with lateral-wall MI are clues to leg electrode misplacement on the right arm.

• Lateral-wall MI mimics. Misplacement of the right- or the left-leg electrode on the right arm resulted in the ECG morphology of lateral-wall MI, with associated features of COPD plus near-zero potential in lead II and low atrial rhythm, respectively (Figure 8). Such ECG associations would serve as clues to the possibility that a leg lead was mistakenly placed on the right arm.

In contrast, when the left-leg electrode was placed on the left arm, and the other limb electrodes were switched around, the ECG demonstrated the morphology of inferior-wall MI (Figure 9). Associated terminally positive biphasic P waves in lead III, as seen in example 9 (normally biphasic P waves in lead III are terminally negative⁹), or features of dextrocardia (example 11) or COPD (example 17), were clues to left-leg electrode misplacement on the left arm.

Except for the lone low atrial rhythm, we were able to identify 92% of all ECG mimics of limb lead placement errors. The lone low atrial rhythm would be identified only when comparing it with an earlier (or even a later) ECG that was recorded with correctly attached limb leads.

Figure 9?Misplacement of the left-leg electrode on the left arm resulted in the ECG morphology of inferior-wall MI with the right-arm electrode attached correctly in example 9 (and 15, web-extra); inferior-wall MI with dextrocardia with the left-arm lead on the right arm in example 11 (and 21, web-extra); and COPD plus near-zero-potential lead I in example 17 (and 23, web-extra) when the right arm had the right-leg electrode. Thus, the clues to lead misplacement were near-zero-potential lead I, COPD, and inferior-wall MI in example 17, and dextrocardia with inferior-wall MI in example 11. In example 9, the clue for inferior-wall MI mimic was the terminally positive P wave of lead III.

Study Limitations

The findings resulting from all possible ECG limb lead misplacements apply to an individual having a normal ECG, with a frontal plane axis of 60?. Similar studies are needed to investigate patients whose ECGs show different frontal plane axes, as well as other abnormalities, to recognize the changes in their tracings that result from limb lead misplacements.

Conclusions

In 12 of the 24 ECGs resulting from all possible limb electrode placement variations mimicking COPD, with or without MI, low atrial rhythm, dextrocardia, or even a normal-appearing ECG, the error can be detected by a near-zero-potential bipolar limb lead tracing.

In the remaining 12 ECGs without near-zero-potential complexes, the following observations are useful:

• Example 1 had correct electrode placement with a normal ECG, and example 7 had the leg electrodes switched without significant change; the latter would go undetected with no clinical implications.
• In the lateral-wall MI mimics, an association with low atrial rhythm may raise suspicion for left-leg electrode misplacement on the right arm.
• In the case of inferior-wall MI mimics, terminally positive P waves in lead III or associated features of dextrocardia only in the limb leads are clues to misplaced left-leg electrodes on the left arm.
• In any case of dextrocardia mimics in the limb leads because of misplaced left-arm electrode on the right arm, the suspicion can easily be confirmed if an R-wave progression is evident in the precordial lead.
• In the remaining cases of low atrial rhythm mimics with no associated clues, one will have to depend upon the totality of the clinical presentation and a comparison with an earlier ECG or a repeat ECG taken with proper attention to correct lead placement.

A practical way to address limb lead placement errors would be to make graphics of Figure 1, the first pair of the web-extra examples, and Figures 2 through 9, along with the second tracing of each of their respective pairs from the web-extra examples, available as a pocket guide for physicians and technicians, and to have poster displays on the walls of ECG reading rooms, intensive care units, and emergency departments, similar to displays of echocardiographic and nuclear cardiology images.

Acknowledgments

The authors acknowledge the editorial advice of Aroor S Rao, MD, FACC, Peter Arquin, MD, FACC, and Harold Smulyan, MD, FACC. We also acknowledge the technical assistance of Ranjit Varma, BS, MBA, Jennifer Sickler, E. Pierce, M. Butts, A. Mullin, and N. Hill, RN.

SELF-ASSESSMENT TEST

1. According to Einthoven's law, what does the amplitude of the waveforms in lead II approximate?
   
   1. Lead I
   2. Lead III
   3. Leads I and III combined
   4. Lead III minus lead I


2. Terminally positive P waves in lead III is a clue to misplaced electrodes on which limb?
   
   1. Reversal of left- and right-arm electrodes
   2. Reversal of left-arm and left-leg electrodes
   3. Reversal of right-arm and left-leg electrodes
   4. Reversal of right-arm and right-leg electrodes


3. Which limb lead misplacement can mimic the ECG of dextrocardia?
   
   1. Reversal of left- and right-arm electrodes
   2. Reversal of left-arm and left-leg electrodes
   3. Reversal of right-arm and left-leg electrodes
   4. Reversal of right-arm and right-leg electrodes


4. A near-zero potential in lead I suggests which of the following limb lead misplacements?
   
   1. Left-leg electrode on the right arm and right-leg electrode on the left arm
   2. Left-leg electrode on the right arm and right-arm electrode on the left arm
   3. Left-leg electrode on the right arm and left-arm electrode attached correctly
   4. The 2 arm electrodes are reversed


5. Which limb lead misplacement is suggested by an ECG showing features of COPD plus near-zero-potential waveforms in lead II?
   
   1. Left-leg electrode on right arm
   2. Left-leg electrode on left arm
   3. Right-leg electrode on left arm
   4. Right-leg electrode on right arm

(Answers at end of references list)

References

1. 1. Hed?n B, Ohlsson M, Holst H, et al. Detection of frequently overlooked electrocardiographic lead reversals using artificial neural networks. Am J Cardiol. 1996;78:600-604.
2. 2. Hed?n B, Ohlsson M, Edenbrandt L, et al. Artificial neural networks for recognition of electrocardiographic lead reversal. Am J Cardiol. 1995;75:929-933.
3. 3. Kors JA, van Herpen G. A novel method to detect electrocardiographic electrode interchanges. J Electrocardiol. 2000;33(suppl): 209-210.
4. 4. Peberdy MA, Ornato JP. Recognition of electrocardiographic lead misplacements. Am J Emerg Med. 1993;11:403-405.
5. 5. Lee YC, Buser G. ECG lead reversal: a common source of misinterpretation. Primary Cardiol. 1992;18:64-74.
6. 6. Haisty WK Jr, Pahlm O, Edenbrandt L, et al. Recognition of electrocardiographic electrode misplacements involving the ground (right leg) electrode. Am J Cardiol. 1993;71:1490-1495.
7. 7. Marriott HJL. Electrodes and leads. In: Practical Electrocardiography. 7th ed. Baltimore, Md: Williams and Wilkins; 1983:1-6.
8. 8. Hed?n B. Electrocardiographic lead reversal. Am J Cardiol. 2001; 87:126-127.
9. 9. Abdollah H, Milliken JA. Recognition of electrocardiographic left arm/left leg lead reversal. Am J Cardiol. 1997;80:1247-1249.

Answers: 1. C; 2. B; 3. A; 4. A; 5. D.

WEB EXTRA

Example 1. The electrodes are correctly attached to all 4 limbs (leads I, II, and III of the conventional design) with clockwise orientation. According to Einthoven's law, I + III ? II = 0 (ie, I + III = II). Thus, the ECG waveforms have mainly upright orientation, with lead II recordings being tallest and equal to the combined amplitude of leads I and III, and the amplitude of lead III is smallest due to both of its electrodes being situated farthest from the origin of the cardiac impulse.

Example 2. The arm electrodes are reversed, therefore lead I is recorded in the opposite direction, with inverted PQRST waves, mimicking situs inversus dextrocardia in the limb leads. The electrodes of lead III are now attached at the site of conventional lead II; therefore, the former recorded the tallest and upright ECG waveforms, whereas lead II, now recorded from the conventional position of lead III, has the smallest amplitude, because it is farthest from the origin of the cardiac impulse.

Example 3. Only the electrodes of the left arm and the right leg are switched, resulting in II, VI, and V lead positions on the 6-lead diagram (Figure 1), with a clockwise orientation (II + VI ? V = 0 or II + VI = V). Transformed into conventional leads (as seen by the galvanometer), leads II, VI, and V become leads II, III, and I, respectively. Because lead VI has near-zero potential and lead VI = III, lead III will also have near-zero potential. Therefore, in the equation I + III ? II = 0, when III is 0, I will equal II, resulting in normal ECG waveforms of similar amplitude in leads I and II, along with near-zero-potential complexes in lead III.

Example 4. The right arm has the right-leg electrode, the left arm has the right-arm electrode, the right leg has the left-arm electrode, and the left leg has its own electrode. This arrangement resulted in leads III, VI, and IV positions on the 6-lead diagram (Figure 1), with clockwise orientation (III + VI ? IV = 0 or III + VI = IV). Because this equation involves 2 additional leads, VI and IV (both with little electrical current), we presumed that one of them, VI in this case, has near-zero value. Transformed into conventional leads (as seen by the galvanometer), leads III, VI, and IV become leads II, III, and I, respectively. Because lead VI has near-zero potential and lead VI = III, lead III will also be near zero. Thus, in the equation I + III ? II = 0, when III is 0, lead I approximates lead II. In addition, lead I electrodes, from the position of the additional lead IV, recorded small-amplitude ECG waveforms, because they were perpendicular to the composite cardiac vector. In contrast, lead II electrodes from lead III position recorded the ECG waveforms similar to the normal lead III waveforms seen in example 1. In general, the overall ECG showed significantly low-amplitude waveforms in all limb leads.

Example 5. The right arm has the left-arm electrode, the left arm has the right-leg electrode, the right leg has the right-arm electrode, and the left leg has its own electrode. This arrangement resulted in leads II, VI, and V positions on the 6-lead diagram (Figure 1), with clockwise orientation (II + VI ? V = 0 or II + VI = V). Transformed into conventional leads (as seen by the galvanometer), leads II, VI, and V become leads III, II, and I, respectively. Because lead VI has near-zero potential and VI = II, lead II will also be near zero. Thus, in the equation I + III ? II = 0, when II is 0, then III equals minus I, resulting in equal-amplitude waveforms in leads I and III, with negative and positive orientation, respectively, and near-zero potential in lead II.

Example 6. The right-arm and right-leg electrodes are switched; the left-arm and left-leg electrodes remain intact. This arrangement resulted in leads III, IV, and VI positions on the 6-lead diagram (Figure 1), with a clockwise orientation (III + VI ? IV = 0 or III = VI = IV). Because this equation involves 2 additional leads, VI and IV (both with little electrical current), we presumed one of them, VI in this case, has near-zero potential. Transformed into conventional leads, leads III, VI, and IV become leads III, II, and (?) I, respectively. Because lead VI has near-zero potential and lead VI = II, lead II will also be near zero. Thus, in the equation I + III ? II = 0, when II is near zero, then III = minus I. Hence, lead I being perpendicular to lead II position recorded smaller-amplitude waveforms, with negative P waves and inverted R mimicking Q, along with inverted T waves. In general, the overall ECG waveforms were of low amplitude in all limb leads.

Example 9. The left arm has the left-leg electrode, the left leg has the right-leg electrode, the right leg has the left-arm electrode; the right-arm electrode is intact. This arrangement resulted in leads I, IV, and V positions on the 6-lead diagram (Figure 1), with clockwise orientation (I + IV ? V = 0 or I + IV = V). Transformed into conventional leads, leads I, IV, and V become leads II, (?) III, and I, respectively. Because lead IV has near-zero potential and lead IV = III, lead III will also have near-zero potential. Thus, in the equation I + III ? II = 0, when III is near zero, then I = II, resulting in normal-appearing equal-amplitude upright waveforms in leads I and II and negatively oriented small-amplitude waveforms mimicking Q waves in III.

Example 10. The right arm has the left-leg electrode, the left arm has the right-arm electrode, the left leg has the right-leg electrode, and the right leg has the left-arm electrode. This arrangement resulted in leads I, IV, and V positions on the 6-lead diagram (Figure 1), with clockwise orientation (I + IV ? V = 0 or I + IV = V). Transformed into conventional leads, leads I, IV, and V become leads (?) II, I, and (?) III, respectively. Because lead IV has near-zero potential and lead IV = I, lead I will also have near-zero potential. Therefore in the equation I + III ? II = 0, when I is near zero, then (?) III = (?) II, resulting in small-amplitude upright waveforms in lead I and inverted PQRST waves of equal amplitudes in leads II and III.

Example 11. All the leads are misplaced. The right arm has the left-arm electrode, the left arm has the left-leg electrode, the left leg has the right-leg electrode, and the right leg has the right-arm electrode. This arrangement resulted in leads I, IV, and V positions on the 6-lead diagram (Figure 1), with clockwise orientation (I + IV ? V = 0 or I + IV = V). Transformed into conventional leads, leads I, IV, and V become leads III, (?) II, and (?) I, respectively. Because lead IV has near-zero potential and lead IV = (?) II, lead (?) II will also have near-zero potential. Therefore, in the equation I + III ? II = 0, when II is near zero, then III = (?) I, resulting in inverted PQRST waves of normal size in I, small-amplitude inverted R mimicking Q in II, and upright waveforms of normal size in III.

Example 12. The right arm has the left-leg electrode, the left leg has the right-leg electrode, the right leg has the right-arm electrode; the left-arm electrode is intact. This arrangement resulted in leads I, IV, and V positions on the 6-lead diagram (Figure 1), with clockwise orientation (I + IV ? V = 0 or I + IV = V). Transformed into conventional leads, leads I, IV, and V become leads (?) III, (?) I, and (?) II, respectively. Because lead IV has near-zero potential and lead IV = (?) I, lead (?) I will also have near-zero potential. Therefore in the equation I + III ? II = 0, when I is near zero, III = II. Because orientation of all these leads is in the reverse direction, lead I recorded small-amplitude waveforms inverted R mimicking Q, whereas leads III and II recorded inverted PQRST waves of equal amplitudes.

Example 17. The right-arm and right-leg electrodes have been switched, as have the left-arm and left-leg electrodes. This arrangement results in leads III, VI, and IV positions on the 6-lead diagram (Figure 1), with clockwise orientation (III + VI ? IV = 0 or III + VI = IV). Because this equation involves the additional leads VI and IV (both with little electrical activity), we presumed one of them, VI in this case, has near-zero potential. Transformed into conventional leads, leads III, VI, and IV become leads (?) III, (?) I, and (?) II, respectively. Because lead VI has near-zero potential and lead VI = (?) I, lead (?) I will also have near-zero potential. Therefore, in the equation I + III ? II = 0, when I is near zero, then (?) II = (?) III. This resulted in near-zero-potential waveforms in lead I and negative waveforms of small amplitude in leads II and III, mimicking Q waves.

Example 18. All the limb leads have been misplaced. The right arm has the left-leg electrode, the left arm has the right-leg electrode, the left leg has the left-arm electrode, and the right leg has the right-arm electrode. This arrangement results in leads II, VI, and V positions on the 6-lead diagram (Figure 1), with clockwise orientation (II + VI ? V = 0 or II + VI = V). Transformed into conventional leads, leads II, VI, and V become leads (?) III, (?) I, and (?) II, respectively. Because lead VI has near-zero potential and lead VI = (?) I, lead (?) I will also have near-zero potential. Therefore, in the equation I + III ? II = 0, when I = 0, (?) II = (?) III. This results in near-zero amplitude waveforms in lead I and inverted PQRST waves of equal amplitude in II and III.

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- March 14, 2010 - 9:36:40 (CDT)

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