This post is based on a personal medical care experience of mine that occurred two years ago. My surgeon appropriately ordered a screening electrocardiogram for me prior to an elective surgery that required general anesthesia.
My electrocardiogram was performed at an excellent hospital in my community. At the time of the test, I noted that the technician was placing the V1 and V2 precordial leads way too high on my chest (at the second intercostal space) and the rest of the V leads were also misplaced based on the V1 and V2 leads.
I also noted that the technician had me elevated at a 60 degree angle for the electrocardiogram.
The electrocardiogram interpretation, signed by the cardiologist, said “age indeterminate anterior [infarction or ischemia – I can’t remember which] suggested”.
I have never had any cardiac symptoms during or after vigorous exercise nor at any other time. Two years prior to the electrocardiogram, I had a heart coronary calcium score which was interpreted as zero calcium score [There was no indication for the test, I just wanted it and I paid cash for it].
I had a complete transthoracic echocardiogram performed after the electrocardiogram which was interpreted as completely normal.
I chose not to have an exercise stress test as I felt that the likelihood of my having significant coronary artery disease was less than the likelihood of a false positive test leading to further tests [meaning coronary angiography] that I was unlikely to need.
I checked my reasoning with my surgeon and my primary care physician and both agreed with me.
And so the above is the reason for this post.
The following are excerpts from Resource (1), Recommendations for the standardization and interpretation of the electrocardiogram. Part I: the electrocardiogram and its technology [PubMed] [Full Text HTML], below:
Location of Standard Limb and Precordial Electrodes
Technology
The standard 12-lead ECG (5,24) consists of 3 limb leads (leads I, II, and III), 3 augmented limb leads in which the Goldberger modification of the central terminal of Wilson serves as a derived indifferent electrode that is paired with the exploring electrode (leads aVR, aVL, and aVF), and 6 precordial leads in which the Wilson central terminal serves as a derived indifferent electrode that is paired with the exploring electrode (V1 through V6). All leads are effectively “bipolar,” and the term “unipolar” in description of the augmented limb leads and the precordial leads lacks precision. Reference is made to the comprehensive study of lead systems for various types of electrocardiography by Macfarlane (77). Skin preparation by cleaning and gentle abrasion before electrode application can reduce noise and improve the quality of the recorded ECG (78–80). Historically, limb lead electrodes have been attached at the wrists and the ankles, with the patient in the supine position, generally with a pillow under the head. Historically, limb lead electrodes have been attached at the wrists and the ankles, with the patient in the supine position, generally with a pillow under the head. For routine 12-lead recording, the AHA statement of 1975 recommended placement of the 4 limb lead electrodes on the arms and legs distal to the shoulders and hips (5,81), and thus not necessarily on the wrists and ankles. Evidence exists that different placement of electrodes on the limbs can alter the ECG, a phenomenon that appears to be more marked with respect to the left arm electrode (81). Therefore, reevaluation of the magnitude of changes due to variation in limb electrode placement in clinical practice is required, as discussed below. Six electrodes are placed on the chest in the following locations: V1, fourth intercostal space at the right sternal border; V2, fourth intercostal space at the left sternal border; V3, midway between V2 and V4; V4, fifth intercostal space in the midclavicular line; V5, in the horizontal plane of V4 at the anterior axillary line, or if the anterior axillary line is ambiguous, midway between V4 and V6; and V6, in the horizontal plane of V4 at the midaxillary line.
Clinical Implications
Skin preparation and electrode placement have important effects on the ECG, and patient positional change, such as elevation and rotation, can change recorded amplitudes and
axes. It has been widely accepted for many years that ECG
amplitudes, durations, and axes are independent of the distal
or more proximal location of the limb electrodes. As a result,
routine recording of the ECG from the upper arm rather than
from the wrist to “reduce motion artifact” has become popular and is facilitated by the development of disposable tab electrodes. However, one study has shown that electrode placement along the limbs can affect ECG voltages and
durations, most importantly in the limb leads (81). Whether
these differences are large enough to alter routine diagnostic
criteria, such as voltage for left ventricular hypertrophy or
Q-wave duration for inferior infarction, is unknown. Further
confounding this situation is the variability in electrode
placement that might have been present during the actual
derivation of the diagnostic criteria involved, because studies
during the past several decades have rarely described electrode
placement in detail.From the time of their initial standardization by a joint committee of the AHA and the Cardiac Society of Great
Britain and Ireland (82,83), the normal precordial electrode
positions have been relatively horizontal in orientation. When
precordial electrodes are positioned without reference to the
underlying bony landmarks, the placement pattern often is
erroneously vertical in orientation (84). Mapping data document the often profound alterations in waveforms that can
result from precordial electrode misplacement (85,86). A common error is superior misplacement of V1 and V2 in the
second or third intercostal space. This can result in reduction
of initial R-wave amplitude in these leads, approximating 0.1
mV per interspace, which can cause poor R-wave progression
or erroneous signs of anterior infarction (87). Superior displacement of the V1 and V2 electrodes will often result in rSr’
complexes with T-wave inversion, resembling the complex in
lead aVR. It also has been shown that in patients with low diaphragm position, as in obstructive pulmonary disease (88,89), V3 and V4 may be located above the ventricular boundaries and record negative deflections that simulate anterior infarction. Another common error is inferior placement of V5 and V6, in the sixth intercostal space or even lower, which can alter amplitudes used in the diagnosis of ventricular hypertrophy. Precordial lead misplacement explains
a considerable amount of the variability of amplitude
measurements that is found between serial tracings (90).
Some residual disagreement persists in current guidelines and
texts on the standard for location of V5 and V6, with some
sources retaining an early recommendation that these leads
follow the course of the fifth intercostal space rather than the
horizontal plane of V4. In addition, it is common to refer to
the anterior axillary line as an anatomic marker for the
placement of V5. These alternatives are discouraged because
the course of the intercostal space is variable and the definition of an anterior axillary line only vague. Placement of precordial electrodes in women with large breasts remains problematic. Electrodes are most commonly placed beneath the breast, which should reduce amplitude attenuation caused by the higher torso impedance in women and, intuitively, would seem to favor reproducibility of positioning during routine practice. Conversely, one study has suggested that reproducibility of ECG measurements is slightly increased when electrodes are positioned on top of the breast (91). Another study using precisely ascertained electrode placement has suggested that precordial potential attenuation by the breast is very small (92). Yet another study has found attenuation only in V3 and an increase in voltage in V5 and V6 (93) when electrodes are placed over the breast; this may result from V5 and V6 being correctly placed at the level of V4 rather than more inferiorly when V4 is positioned under the breast. Clearly, the magnitude of this effect in ordinary ECGs will depend greatly on the care with which electrodes are ordinarily placed and also on breast size, breast shape, and small changes in patient position. Similar considerations apply in relation to subjects with breast implants and in subjects who are obese.Recommendations
Technicians and other medical personnel responsible for the
recording of ECGs should have periodic retraining in skin
preparation, proper electrode positioning, and proper patient
positioning. All leads are effectively “bipolar,” and the
differentiation between “bipolar” and “unipolar” in the description of the standard limb leads, the augmented limb
leads, and the precordial leads is discouraged. Neither term
should be used. Studies to clarify the effect of distal versus
proximal limb lead electrode placement on ECG magnitudes
and durations are required. Validity of test performance
criteria for current diagnostic algorithms may be dependent
on placement of limb leads in the same positions that were
used for criteria development. Pending resolution of this
issue, all ongoing studies used for criteria development must
clearly document electrode placement with precision. The
horizontal plane through V4 is preferable to the fifth intercostal
interspace for the placement of V5 and V6 and should be
used for placement of these electrodes. Definition of V5 as
midway between V4 and V6 is conducive to greater reproducibility than occurs for the anterior axillary line, and this should be used when the anterior axillary line is not well
defined. In the placement of V6, attention should be directed
to the definition of the midaxillary line as extending along the
middle, or central plane, of the thorax. For the time being, it
is recommended that electrodes continue to be placed under
the breast in women until additional studies using electrodes
placed on top of the breast are available.
The following are excerpts from Resource (2), The effect of precordial lead displacement on ECG morphology [PubMed Abstract] [Full Text HTML] [Full Text PDF]. Med Biol Eng Comput. 2014; 52(2): 109–119, below:
Introduction
Electrocardiography is nowadays one of the most widely used diagnostic methods in screening tests for early detection of cardiac diseases. Examinations are noninvasive and have a large impact on clinical diagnosis and on further medical treatment. The ECG signals reflect the electrical activity of the heart muscle as it is sensed by electrodes placed on the body surface. In clinical practice, the most commonly used electrodes layout is 12-lead standard ECG system. Standard ECG has, however, limited sensitivity (30–70 %) and specificity (70–95 %) in detection of acute coronary syndromes [7]. To improve effectiveness of the ECG diagnostic, high-resolution measurement technique and body surface potential mapping (BSPM) were proposed [3, 29] and validated [5, 15, 31]. However, due to time-consuming procedure of large number ECG electrodes placement, the method is still not widely used in clinical practice.
There are many independent factors affecting the ECG examination results related to ECG measurement procedure and physiological inter-individual variability [27]. One of the main sources of mistakes is inaccurate ECG electrode placement in suggested anatomical landmarks, e.g., in proper intercostal spaces [14]. On the other hand, since differences in inter-individual human anatomies, the exact heart position in the thorax is never precisely known. Both factors, dependent and independent on medical staff, can cause the change of the distance between the electrodes and source of the signal in the heart as well as the solid angle at which outline of ventricular mass is seen from the body surface [34]. The displacements of the precordial electrodes located nearby the signal source have a greater influence on the ECG signal than shifts of the distant limb electrodes [20, 34]. Precordial electrodes need sometimes to be shifted to apply bandages, drains, and to undertake an echocardiographic study [19]. However, displacement of the ECG electrodes from determined ‘standard’ positions [14] can arise also from mistakes of medical staff [9, 18, 20, 23] as well as by patients at home who participate in ECG monitoring programs. A common mistake is placing V1 and V2 electrodes too high, in second or third intercostal space [20], which could result in superior misplacement of remaining precordial electrodes. Electrodes V5 and V6 are also placed frequently in the fifth intercostal space and not in the recommended parallel position to electrode V4 [14], which is usually not precisely positioned according to visual estimation of midclavicular line [21].
Thus, one important issue which should be taken into account is poor reproducibility of precordial lead placement in serial ECG recordings. Kerwin et al. [12] reported that correct lead positions with an error less than 1 cm were achieved by trained technicians only in case of 50 % of studied men and 20 % of studied women. They found that electrode placement error often was in the range of 2–3 cm, but occasionally reached even 6 cm.
A number of methods for controlling variation in chest electrodes’ position were suggested and validated. Soliman [30] recently proposed to add simple measurement of the distance from suprasternal notch to the V1–V2 position assuring the same position of electrodes between clinical trials. Herman et al. [9] invented a sliding ruler that facilitates correct lead placement and for documenting its position on the chest. Kerwin et al. [12] advise to use the grid printed on non-stretchable material to record and later on, if needed, to relocate wrong positioned electrodes. Unlikely, all methods, even the simplest, are not accepted by clinicians, meaning that ECG electrodes are often placed not precise according to subjective visual inspection.
The analysis of ECG signals recorded from misplaced electrodes can lead to misinterpretation or even to significant diagnostic errors like incorrect recognition of anterior infarction, anteroseptal infarction, ventricular hypertrophy [9, 14], false diagnosis of ischemia, or Brugada syndrome [16, 24]. Bond et al. have shown that incorrect electrode placement could lead to wrong diagnosis in 17–24 % of patients [1]. Precordial electrode displacement could cause wrong diagnosis made by human expert as well as by computer-based analysis [26].
The aim of this study was to investigate in detail the effect of displacement of the precordial ECG electrodes on the morphology of the recorded multilead high-resolution ECG signals, in particular, to answer the questions what kind of changes in the recorded ECG signal could be expected while moving the electrode in any direction at a short distance (up to 5 cm) and which precordial ECG leads are most sensitive to electrodes displacement.
Resources (1) and (3) are guidelines on technical aspects of electrocardiography.
Resources:
(1) Recommendations for the standardization and interpretation of the electrocardiogram. Part I: the electrocardiogram and its technology [PubMed] [Full Text HTML] . A scientific statement from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society. Heart Rhythm. 2007;4(3):394–412. doi: 10.1016/j.hrthm.2007.01.027.
(2) The effect of precordial lead displacement on ECG morphology [PubMed Abstract] [Full Text HTML] [Full Text PDF]. Med Biol Eng Comput. 2014; 52(2): 109–119
(3) Recommendations for the standardization and interpretation of the electrocardiogram: part II: electrocardiography diagnostic statement list a scientific statement [PubMed Abstract] [Full Text HTML] [Full Text PDF] from the American Heart Association Electrocardiography and Arrhythmias Committee, Council on Clinical Cardiology; the American College of Cardiology Foundation; and the Heart Rhythm Society Endorsed by the International Society for Computerized Electrocardiology. J Am Coll Cardiol. 2007 Mar 13;49(10):1128-35.
