Precordial Electrodes Research Articles

Specificity of Elevated Intercostal Space ECG Recording for the Type 1 Brugada ECG Pattern

Right precordial (V1-3) elevated electrode placement ECG (EEP-ECG) is often used in the diagnosis of Brugada syndrome (BrS). However, the specificity of this has only been studied in smaller studies in Asian populations. We aimed to study this in a larger European population. Two different populations consisting of healthy subjects were used. A total of 340 subjects were included, 80% were men, the median age was 43 year (interquartile range: 31-51) and all were of European ethnicity. No type 1 ECG patterns were identified but 16 (4.7%) subjects with a type 2 ECG and 32 (9.4%) subjects with a type 3 ECG were identified in any lead placement. In total 43 (13%) subjects had any BrS ECG pattern in any lead placement. The specificity was 100% (one-sided 97.5% CI: 99%) for the use of EEP-ECG to uncover type 1 pattern. For type 2 pattern the specificity was 95% (95% CI: 92-97%) and for type 3 pattern 91% (95% CI: 88-94%). Elevated electrode placement ECG in the diagnosis of BrS seems to have a very high specificity with regards to the finding of a type 1 ECG pattern in a European population; conversely a finding of a type 2 or 3 pattern is of a significantly lower specificity and should perhaps be disregarded.

Criteria to predict carriers of a novel SCN5A mutation in a large Portuguese family affected by the Brugada syndrome

Brugada syndrome (BrS) is a life-threatening arrhythmia disorder associated with autosomal-dominant mutations in the SCN5A gene. We aimed to characterize the diagnostic challenges and clinical manifestations of a novel SCN5A mutation associated with BrS. From a novel SCN5A mutation (c.664C>T; p.Arg222X) identified in a proband with the characteristic electrocardiographic pattern and the history of sudden collapse, 122 family members were studied including 40 carriers of the mutation. The electrocardiographic diagnosis of BrS requires type 1 Brugada electrocardiogram (ECG) pattern in >1 right precordial lead (V1-V3), but recently an isolated lead with coved-type ECG was proposed to be enough for the diagnosis. In this family, these proposed criteria (PC) were more sensitive in detecting mutation carriers than the conventional criteria without repercussion on the specificity. Carriers had, on average, longer P-wave duration, PR, and QRS intervals and higher transmural dispersion of repolarization. The prevalence of late potentials was higher in carriers, and individual signal average ECG (SAECG) parameters (QRSf, LAS, and RMS40) also were related to SCN5A gene mutation. Three non-carriers were found to be affected by BrS, two with a spontaneous type 1 ECG with alternative placement of the precordial electrodes, and one only after the pharmacological provocative test, suggesting that other genes may play a role in the pathophysiology of this disease. The PC for BrS diagnosis should be implemented. Some parameters from the spontaneous ECG and the SAECG are more effective tools than the characteristic repolarization pattern to discriminate between carriers of SCN5A mutations.

The utility of a 12-lead electrocardiogram electrode misplacement simulator in education

IntroductionA standard 12-lead electrocardiogram (ECG) is recorded using 6 precordial electrodes and 3 limb electrodes, all of which are positioned at precise anatomical landmarks. Nevertheless, up to 4% of all 12-lead ECGs are recorded with incorrect electrode placement. In these circumstances, the 12-lead ECG can emulate or conceal a pathological condition and, therefore, produce a misdiagnosis. This can be detrimental to the patient because it may yield unnecessary therapy. Despite this fact, ECG textbooks contain little or no information regarding the effects of electrode misplacement. In addition, current pedagogic tools, for example, physical mannequins, do not facilitate the free positioning of electrodes. In an attempt to address this issue, an intuitive Web-based application referred to as the Electrode Misplacement Simulator (EMS), has been developed to aid the classical teaching of electrocardiology. The EMS facilitates the free positioning of electrodes while rendering the corresponding ECG leads in real time. This study assessed the utility of the EMS as an educational tool.MethodsThe study population comprised 23 undergraduate students enrolled on the second year of a clinical physiology program. Eleven students were randomly selected and given access to the EMS for 1 week. The remaining 12 students did not use the EMS and relied solely on lectures for tuition. All students were informed that an examination relating to the effects of electrode misplacement would take place the following week. After 7 days, 9 students from the experimental group and 8 students from the control group completed the examination. The experimental group completed an additional questionnaire regarding the usability of the EMS.ResultsThe mean score of the control group was 11.56 (±2.83), whereas the mean score of the experimental group was 16.44 (±2.24). On interpretation, the experimental group performed approximately 30% better when compared with the control group. An unpaired 2-sample t test (t15 = 3.96, P = .00125) was used to examine this hypothesis. The P value rejected the null hypothesis and indicated a statistical significance at the 1% level (P < .01). Students who completed the usability questionnaire rated the usefulness, learnability, and the look and feel of the EMS between 4 and 5 on the Likert scale.ConclusionIn conclusion, the EMS was found to be a beneficial adjunct to the classical teaching of electrocardiology. This study hypothesized and proved that access to the EMS facilitated a better understanding of the effects of electrode misplacement as evidenced through an examination. In general, this study justifies the need for novel interactive tools to aid teaching in the field of electrocardiology.

New precordial bipolar electrocardiographic leads for detecting left ventricular hypertrophy

Background Novel small and wearable electrocardiogram (ECG) devices offer new means of recording cardiac activity in different applications. Our objective was to evaluate the performance of closely separated (6 cm) bipolar leads in differentiating subjects with left ventricular hypertrophy (LVH) from healthy subjects. Methods The material contained body surface ECG of 236 healthy and 116 LVH subjects. A total of 36 vertical, 30 horizontal, and 66 diagonal bipolar leads located on the anterior thorax were analyzed. The QRS amplitudes were calculated, and the leads' overall diagnostic performance was assessed by receiver operating characteristic (ROC) analysis. Results The best overall diagnostic performances were obtained from 2 areas: one near the precordial electrodes of standard leads V 1 to V 3 and the other on lower anterior thorax. Vertical and diagonal bipolar leads located at lower anterior thorax provided the highest ROC areas (≥0.79). These bipolar leads also provided similar sensitivities than the traditional Sokolow-Lyon method. Conclusion The new short distance vertical and diagonal bipolar leads are efficient in discriminating subjects with LVH from healthy subjects based on QRS amplitude.

Usefulness of Multichannel Holter ECG Recording in the Third Intercostal Space for Detecting Type 1 Brugada ECG: Comparison with Repeated 12‐Lead ECGs

Type 1 Brugada ECG is essential for the diagnosis of Brugada syndrome. We aimed to evaluate the usefulness of multichannel Holter ECG recording in the third intercostal space for detecting type 1 Brugada ECG. We enrolled 60 consecutive individuals with type 1 Brugada ECG and 31 individuals with type 2 or 3 Brugada ECG, in the presence or absence of Na+ channel blockers. All individuals underwent 12-lead ECGs recorded in the standard position and the third intercostal space at least 5 times every 3 months (4L-ECGs, 3L-ECGs, respectively) and multichannel Holter ECG. On multichannel Holter ECG, the precordial electrodes were attached at standard positions (4L-Holter) and the third intercostal space (3L-Holter) for leads V1 and V2. Among the 60 individuals, type 1 Brugada ECG in 4L-ECGs, 3L-ECGs, 4L-Holter, and 3L-Holter was detected in 15 (25%), 26 (43.3%), 23 (38.3%), and 33 individuals (55%), respectively, whereas detected in none of the 31 individuals. The documented duration of type 1 Brugada ECG on 3L-Holter was significantly longer than that on 4L-Holter (700 +/- 467 vs 372 +/- 422 min; P = 0.01, 3L-Holter vs 4L-Holter, respectively), and type 1 Brugada ECG was most frequently observed between 6 pm and 12 pm. Neither the presence nor the duration of the appearance of type 1 Brugada ECG differed significantly between symptomatic and asymptomatic individuals. Multichannel Holter ECG recording in the third intercostal space is more sensitive and useful for the diagnosis of type 1 Brugada ECG than repeated 12-lead ECGs or multichannel Holter ECG in the standard position.

Comparison of P-Wave Patterns Derived From Correct and Incorrect Placement of V1-V2 Electrodes

Precordial electrode misplacement is an important source of error in electrocardiogram (ECG) interpretation. Previous studies have shown important changes affecting P wave morphology when V1 and V2 electrodes are placed in higher intercostal spaces. We aimed to identify ECG signs that could alert professionals performing or interpreting the ECG about the incorrect placement of V1 and V2 electrodes. This cross-sectional study included 101 apparently healthy individuals. Five P wave patterns were compared, placing electrodes V1 and V2 on the fourth (correct position), third, and second intercostal spaces (incorrect position). Incorrect V1-V2 electrode placement produced statistically significant differences in 3 of 5 ECG patterns. The presence of a negative component of the P wave in V2 (P < .001), negative P wave in V1 (P < .001), and rSr' preceded by negative P wave (P < .001) was strongly indicative of high placement. Patterns where the amplitude ratio between the positive and negative components of the P wave in V1 was less than or equal to 1 were observed in 27 of 101 cases with correct placement. However, on comparing correct and incorrect electrode placement, significant differences were found (P < .001) Patterns that indicate high placement of V1 and V2 were (1) negative component of the P wave in V2 lead recorded in either second and third intercostal spaces, (2) negative P wave in V1 lead recorded in either second and third intercostal spaces, and (3) rSr' preceded by negative P wave recorded only when V1 is placed on the second but not on the third intercostal space.

Would different routine precordial electrode positions be more useful? Answer: not likely.

There are reasons to wonder if the current precordial electrode positions are the best ones to study the electrical forces of the heart. Theoretically, more horizontal electrode positions and several superior and inferior electrode positions that are perpendicular to the horizontally placed electrode positions should make a superior lead system. A study was designed to determine if that was true. The result of the study indicated that such a system did not solve all of the problems that were posed by the current system. Although the new system was easier to use, the findings did not justify a change from the presently used system of precordial electrode placement.

Abstract 2147: Utility of Multichannel Holter ECG Recording at the Third Intercostal Space to Diagnose A Type 1 Brugada ECG; Comparison with Repeated 12-Lead ECGs

The detection of a type 1 Brugada ECG is essential for diagnosis and risk stratification in Brugada syndrome. In this study, we evaluated the detection rate of a type 1 ECG on the multichannel Holter ECG, compared with the 12-lead ECGs recorded repeatedly. We enrolled consecutive 60 patients who had eventually exhibited a diagnostic type 1 ECG in the presence or absence of Na+ channel blockers at either standard or the third intercostal position. All patients underwent 12-lead ECGs recorded at both standard and the third intercostal position at least 5 times between 0 p.m and 2 p.m (4L-ECGs, 3L-ECGs, respectively). The 24-hour Holter ECG was performed in all patients, using a 12-lead Holter recording system. The precordial electrodes were attached at the standard position of V1, V2, V5, V6 and the third intercostal space of V1 and V2 (V1 IC3 , V2 IC3 , respectively). The leads V1 and V2, and V1 IC3 and V2 IC3 on the Holter ECG were expressed as 4L-Holter and 3L-Holter, respectively. The diagnostic type 1 ECG on the Holter ECG was defined as a presence of a coved-type ST-segment elevation &gt;0.2mV over continuous 60 seconds at least one lead. We evaluated the detection rate of the type 1 ECG in 4L-ECGs, 3L-ECGs, 4L-Holter and 3L-Holter, and compared them among the 4 different recording methods. Among 60 patients, the patients showing the type 1 ECG on 4L-ECGs, 3L-ECGs, 4L-Holter and 3L-Holter were 15 (25%), 26 (43.3%), 23 (38.3%) and 33 patients (55%), respectively. The detection rate in 3L-ECGs and 3L-Holter was significantly larger than that in 4L-ECGs (p=0.03, p&lt;0.001, respectively). Additionally, in 8 (23.5%) out of 34 patients with drug-induced type 1 ECG at standard and/or the third intercostal position, a spontaneous type 1 ECG was detected in 3L-Holter. Although the detection rate of a type 1 ECG in 3L-Holter was not significantly different with that in 3L-ECGs, the 3L-Holter was the most sensitive to detect a type 1 ECG among the 4 recording methods. In patients with Brugada type ECG, the Holter ECG recorded in the right precordial leads at the third intercostal space is more sensitive method to detect a diagnostic type 1 ECG than repeated 12-lead ECGs or the Holter ECG at standard position.

Abstract 2055: Non-Invasive Measurements for Predicting Duration of Untreated Cardiac Arrest

Objective. Initial chest compression rather than defibrillation has evolved as the initial intervention when the duration of untreated cardiac arrest exceeds 4 min. Accordingly, we sought methods by which the duration of untreated cardiac arrest could be reliably estimated and communicated to the rescuer. Both AMSA (the amplitude spectrum area) together with measurements of tissue PCO 2 in the buccal mucosa (P BU CO2) were investigated. We hypothesized that decreases in AMSA, reflecting reduced myocardial electrical function, and increases in P BU CO 2 , reflecting the severity of anaerobic metabolism, would fulfil this need. Materials and Methods. In 9 domestic male pigs weighing 41 ± 2 kg, ventricular fibrillation (VF) was electrically induced and untreated for 15 min. AMSA was analyzed by fast Fourier transform from the ECG signal obtained through conventional precordial electrodes. P BU CO 2 was continuously measured utilizing a miniature optical sensor system (CO 2 ABG Module, Vasomed, Minneapolis, MN) applied non-invasively on to the buccal mucosa. Results . After 3 min of untreated VF, the AMSA value decreased significantly (p &lt; 0.01, Figure ). P BU CO 2 progressively increased, exceeding threshold levels after 4 min. AMSA and P BU CO 2 were remarkably highly correlated with the durations of untreated cardiac arrest (r = 0.99 and r = 0.92, p &lt; 0.0001) and with each other (r = −0.95, p &lt; 0.0001). Conclusion. AMSA and P BU CO 2 both represent methods by which the duration of untreated cardiac arrest may be identified such as to prompt rescuer to immediately defibrillate or begin chest compression.

Precordial low voltage in patients with ascites

Electrocardiographic (ECG) changes in patients with ascites are not well studied. The aim of this study was to evaluate ECG changes in patients with ascites. Prospective analysis of patients with ascites who were referred for paracentesis. Three ECGs were recorded before paracentesis. ECG 1 was a standard 12-lead ECG. For ECG 2 the precordial leads were placed 1 intercostal space (ICS) and for ECG 3, 2 ICS cranially. The sums (Sigma) of the QRS in ECG1 were compared with ECG 2 and 3. In six patients the same ECG protocol was performed after removal of ascites. Ten hospitalized patients without ascites served as controls. Twenty patients with ascites were analysed. Limbs leads low voltage was present in 11 patients and precordial low voltage in four patients. Cranial placement of the precordial electrodes increased SigmaQRS in all patients with ascites. The most prominent voltage changes appeared in the leads V4-V6 (+62%). Paracentesis of ascites normalized precordial leads low-voltage, while limbs leads low voltage remained. Cranial placement of the precordial electrodes in patients without ascites decreases SigmaV1-V6. We describe a phenomenon of precordial voltage changes in patients with ascites, not reported in the literature yet. By placing the precordial electrodes 1 and 2 ICS cranially the voltage changes can be 'corrected' and this should be done in all patients prior to further diagnostic workup. Removal of the ascites normalizes the precordial leads low voltage.

Accuracy in ECG lead placement among technicians, nurses, general physicians and cardiologists

The objective of the study was to determine the reliability of ECG precordial electrode placement by doctors and nurses involved in the emergency care of patients admitted with suspected cardiac diseases. A total of 120 subjects were recruited within 2 days from six hospitals. They comprised physicians, nurses and cardiac technicians involved in the clinical assessment and care of patients with suspected cardiac disease. Subjects were asked to complete a questionnaire and marked on two diagrams of the chest wall the positions they would place precordial electrodes V1-V6. This study showed wide inter-individual and inter-group variations in the placement of electrodes. Notably, V1 and V2 were frequently incorrectly positioned in the second intercostal space, especially by physicians. The correct position of V1 in the fourth right intercostal space was identified by 90% of cardiac technicians, 49% of nurses, 31% of physicians (excluding cardiologists) and--most disappointing of all--only 16% of cardiologists (p<0.001 for inter-group differences). V5 and V6 were also often mispositioned, too high on the lateral chest wall. Nurses and doctors (especially cardiologists) do not know the correct positions for ECG electrodes. Because incorrect positioning of the precordial electrodes changes the ECG significantly, patients are at risk of potentially harmful therapeutic procedures. Equally, doctors who are aware of the possibility of lead misplacement may be inclined to ignore some ECG changes that may be genuine evidence of ischaemia. The only safe solution is proper precordial electrode placement, which requires training and an environment supporting precision.

Adaptation of the standard 12-lead electrocardiogram system dedicated to the analysis of atrial fibrillation

Objective The objective of the study was to design a lead system aimed at studying atrial fibrillation (AF), while being anchored to the standard 12-lead system. Methods The location of 4 of the 6 precordial electrodes was optimized while leaving the remaining 5 of the 9 electrodes of the standard 12-lead system in place. The analysis was based on episodes of 11 different variants of AF simulated by a biophysical model of the atria positioned inside an inhomogeneous thorax. The optimization criterion used was derived from the singular value decomposition of the data matrices. Results While maintaining VR, VL, VF, V 1 and V 4, the 4 new electrode positions increased the ratio of the eighth and the first singular values of the data matrices of the new configuration about 5-fold compared with that of the conventional electrode positions. Conclusion The adapted lead system produces a more complete view on AF compared with that of the standard 12-lead system.

Comparison of EASI-derived 12-lead electrocardiograms versus paramedic-acquired 12-lead electrocardiograms using Mason-Likar limb lead configuration in patients with chest pain

Introduction Monitoring or serial 12-lead electrocardiogram (ECG) recordings are the accepted requirement for prehospital data acquisition in patients with chest pain. The purpose of this study was to determine whether waveforms and clinical triage decision are similar in EASI-derived ECGs and paramedic-acquired 12-lead ECGs using Mason-Likar limb lead configuration when compared with standard 12-lead ECGs (stdECG). Method Twenty patients with chest pain had a prehospital 12-lead ECG recorded in the ambulance, and paramedic-applied electrodes retained in place at hospital arrival. An ECG technician applied standard precordial and EASI electrodes in their correct positions. Twelve-lead ECGs were obtained from the paramedic-applied electrodes, using their Mason-Likar limb lead configuration, and derived from the EASI leads for comparison with the stdECG. Three computer-measured QRS-T waveform parameters were considered, and differences in waveform measurement between EASI and stdECG (EASI ΔstdECG) versus differences in waveform measurements between paramedic Mason-Likar and stdECG (PML ΔstdECG) were calculated. Two physicians determined whether the EASI-derived or the paramedic Mason-Likar ECG contained information that would change their clinical triage decision from that indicated by the stdECG. Results EASI ΔstdECG and PML ΔstdECG were identical in 28%, whereas EASI ΔstdECG was more than PML ΔstdECG in 35%, and PML ΔstdECG was accurate (both time) than EASI ΔstdECG in 37% ( P = .62). The physicians were more likely to change the level of patient care based on the EASI-derived ECGs compared with the paramedic ECGs; however, this difference was not statistically significant ( P = .27), but this may only be caused by the small study population. Conclusions There are similar differences from stdECG waveforms in EASI-derived ECGs and those acquired via paramedic-applied precordial electrodes using Mason-Likar limb lead configuration. Either method can be used as a substitute for monitoring, but neither should be considered equivalent to the stdECG for diagnostic purposes.

Comparison of the Five-Electrode–Derived EASI Electrocardiogram to the Mason Likar Electrocardiogram in the Prehospital Setting

This study compared the 5-electrode-derived EASI electrocardiogram (ECG) with the conventional Mason-Likar ECG in 200 consecutive patients with chest pain transported to 3 hospitals by 2 different emergency medical services. No significant differences were observed between the 2 systems for the detection of relevant electrocardiographic abnormalities. A questionnaire administered to participating emergency medical personnel revealed a high degree of acceptability of the EASI ECG, with some participants commenting that the sternal and mid-axillary locations of the EASI electrodes made them easier to apply, especially to women, than conventional precordial electrodes.

Assessment of derived 12-lead electrocardiograms using general and patient-specific reconstruction strategies at rest and during transient myocardial ischemia

Twelve-lead ST-segment monitoring is a widely used tool for capturing focal ischemia and transient intermittent episodes. However, continuous registration of all 10 electrodes is impractical in clinical settings. This study investigated the accuracy of 2 derived 12-lead strategies that required 6 electrodes, including all limb leads, and 2 precordial leads by using population-based (generalized) and individualized (patient-specific) reconstruction coefficients to derive the additional 4 chest leads. A total of 26,880 simultaneous digital conventional 12-lead generalized and patient-specific electrocardiograms were monitored over 112 hours in 39 patients during percutaneous coronary intervention, including 159 balloon occlusions in 63 arteries, to test accuracy at rest and during ischemia. Occlusion duration was 78 seconds (range 42 to 96) in the left main coronary in 2 patients, the left anterior descending artery in 15, the right coronary artery in 10, the circumflex artery in 2, and graft segments in 5 patients. Average summated 12-lead ST deviation over the study population at baseline was 377 microV (range 104 to 1,718), which increased at peak ischemia to an average of 1,086 microV (range 282 to 4,099). Median absolute differences at peak ischemic ST deviation were 25 microV in lead V(1), 0 microV in lead V(2), 35 microV in lead V(3), 34 microV in lead V(4), 0 microV in lead V(5), 11 microV in lead V(6), and 114 microV for summated 12-lead ST deviation with the generalized method and 7 microV in lead V(1), 4 microV in lead V(2), 1 muV in lead V(3), 5 microV in lead V(4), 4 microV in lead V(5), 9 microV in lead V(6), and 83 microV for the summated 12-lead ST deviation with the patient-specific method. Limb leads (I, II, III, aVR, aVL, and aVF) were identical in all patients. Thus, generalized and patient-specific methods derived from 12-lead electrocardiography using actual limb and 2 precordial electrodes accurately derived the additional chest leads at rest and during ischemia. These approaches appear to be more practical than conventional 10-electrode monitoring but preserve high accuracy.

The relative accuracies of ECG precordial lead waveforms derived from EASI leads and those acquired from paramedic applied standard leads

Accurate precordial electrode placement can be difficult in emergency situations leading either to loss of time or diminished accuracy. A possible solution is the quasi-orthogonal EASI lead system, with only five electrodes and easily defined landmarks to provide a derived 12-lead electrocardiogram (ECG). The purpose of this study was to test the hypothesis that precordial waveforms in EASI-derived ECGs have no greater deviation from those in gold standard ECGs, than do the precordial waveforms in paramedic acquired standard ECGs. Twenty paramedics applied the standard precordial electrodes employing the routine procedure. A certified ECG technician applied the 6 standard precordial electrodes in their correct gold standard positions, and the EASI electrodes. 12-lead ECGs were obtained from the paramedics’ standard leads, and derived from the EASI leads, for comparison with the gold standard ECG. In each precordial lead recording, 6 computer-measured QRS-T waveform parameters were considered. Differences between ΔEASI-gold standard versus Δparamedic-gold standard were calculated for every waveform in every lead resulting in 720 comparisons. EASI and paramedic results were “equally accurate” in 47%, the paramedic was more accurate in 31%, and EASI was more accurate in the remaining 22%. The differences from gold standard recording of precordial waveforms in ECGs derived from the EASI leads and those acquired via paramedic-applied standard electrodes are similar. The results suggest that the EASI lead system may provide an alternative to the standard ECG precordial leads to facilitate data acquisition and possibly save valuable time in emergency situations.

The evaluation of a precordial ECG BELT: Technologist satisfaction and accuracy of recording

The standard method for performing electrocardiogram (ECG) recordings presents a challenge to technicians because of the need to correctly position the individual precordial electrodes according to 6 bony thoracic landmarks. A proposed new method using a 6-lead ECG BELT for precordial application was compared to the standard method to determine the level of agreement among automated interpretations. A comparison of automated interpretations from repeat standard recordings served as the control. Results indicate that BELT and standard automated interpretations disagreed significantly more frequently than repeat standard recording automated interpretations of the cardiac rhythm. The BELT's most obvious weakness was the inability to obtain a recording with a stable ECG baseline, triggering automated detection of “baseline artifact or wander,” and requiring a repeat recording. These findings suggest that the ECG BELT is not adequate for clinical application in its current form.

Computer simulation of defibrillation threshold (DFT) for pre-cordial electrodes replacing the RV electrode

Computer simulation of defibrillation threshold (DFT) for pre-cordial electrodes replacing the RV electrode

Computer simulation of defibrillation threshold (DFT) for pre-cordial electrodes replacing the RV electrode

Computer simulation of defibrillation threshold (DFT) for pre-cordial electrodes replacing the RV electrode

Variability of precordial electrode placement during routine electrocardiography

Placement of precordial electrodes by 30 experienced technicians during routine electrocardiography was compared with anatomically ascertained sites marked by ink visible only under ultraviolet “black light” in three men and five women. The distance and direction from each marked site to the center of the applied electrode was measured to allow calculation of both the linear magnitude of difference (derived from the square root of the sum of the squares of rise and run) and also the direction of difference (in quadrants) between the anatomically established location and the electrode at each precordial site. The average difference from the applied electrodes to the corresponding marked sites was 1.14 inches, ranging from a mean of 1.31 inches at lead V 1 to 0.98 inches at lead V 4. Overall, 64% of precordial electrodes were placed within a radius of 1.25 inch, ranging from 56% for lead V 6 to 74% for lead V 4, and 27% of precordial electrodes were placed within a radius of 0.625 inch. There was superior quadrant displacement of more than 0.625 inch in more than 50% of routine applications of leads V 1 and V 2, indicating that these electrodes are commonly placed both high and wide of their anatomically defined precordial sites. Similarly, there was an inferior and left-ward displacement of more than 0.625 inch in 30–50% leads of routine applications of V 4 through V 6, indicating that these lateral precordial electrodes are commonly placed both low and wide of their respective anatomic sites.