Effects of limb electrode placement on the 12- and 16-lead electrocardiogram

The effects of three common limb electrode placement configurations on ECG signal morphology were examined, including the standard electrode placement of the electrodes on the extremities, the Mason-Likar placement, and the Lund placement. A non-traditional asymmetric configuration of placing the LA electrode on the upper arm with the RA electrode on the torso (below the clavicle) was also investigated. A series of 16-lead ECGs were acquired from 150 subjects representing a broad range of diseases. Effects of the limb electrode placement on axis measurements, QRS amplitudes, ST levels, and infarctions were studied. On average, the P, QRS, and T axes all exhibited rightward shifts as the electrodes were moved away from the extremities, but more generally, the axis became more vertical, with the largest shifts occurring when the standard ECG axis measurement was close to 0 degrees and tending to exhibit leftward shifts for ECGs with a standard axis measurement between 0 and –90 degrees. Voltage changes were consistent with axis shifts in the frontal plane (decreased lateral and increased inferior lead voltages), with the largest mean change a reduction in R wave amplitude of lead I going from the standard to the Mason-Likar configuration. In the precordial leads, Q and/or S magnitudes decreased in right-sided leads (V4r, V1, V2, V3) and R magnitudes increased in lateral leads (V3 – V9) as the arm electrodes moved toward the trunk, suggesting a posterior shift in the mean QRS axis. ST deviations in the lateral and posterior precordial leads tended to be mimicked in lead III when the electrodes were moved from the extremities to the torso. Over half (13 of 25) of the ECGs exhibiting criteria for inferior infarct in the standard configuration had that criteria erased when the electrodes were moved to the Mason-Likar positions. The largest single effect on the ECG resulted from moving the LA electrode from the shoulder to the clavicle. The asymmetric configuration with the RA electrode on the torso and the LA electrode on the upper arm may offer some compromise between noise and faithfulness to the standard configuration in noisy environments such as exercise testing or monitoring.     

Detection of acute ischemia from the EASI-derived 12-lead electrocardiogram and from the 12-lead electrocardiogram acquired in clinical practice

ST-segment measurements in the standard 12-lead electrocardiogram (ECG) of patients with acute coronary syndromes are crucial for these patients' management. Our objective was to determine whether the 12-lead ECG derived from the 3-lead EASI system can attain a level of diagnostic performance similar to that of the Mason-Likar (ML) 12-lead ECG acquired in clinical practice (CP) by paramedics and emergency department technicians. Using 120-lead body surface potential maps recorded before and during balloon inflation angioplasty from 88 patients (divided into “responders” and “nonresponders”), and electrode placement data from 60 applications of precordial leads in CP, we generated for the “nonischemic” and “ischemic” states of each patient the following lead sets: the ML 12-lead ECG, the EASI-derived 12-lead ECG, and 60 sets of 12-lead CP ECGs. We extracted ST deviations at J + 60 milliseconds, summed them for all 12 leads of each lead set to obtain ΣST, and, by using the bootstrap method, determined the mean sensitivity and specificity for recognizing the “ischemic” state at various thresholds of ΣST. Results were displayed as receiver operating characteristics, and the area under these curves (AUC) ± SE was used as the measure of diagnostic performance. AUC ± SE for all patients were ML ECG, 0.66 ± 0.03; EASI ECG, 0.64 ± 0.03; and CP ECG, 0.67 ± 0.03. Corresponding results for responders only were 0.81 ± 0.04 for ML ECG, 0.78 ± 0.04 for EASI ECG, and 0.81 ± 0.04 for CP ECG. The differences between the AUCs for the different lead sets were not significant (P > .05). Thus, the EASI-derived 12-lead ECG is as good for detecting acute ischemia as is the 12-lead ECG acquired in CP.     

Invalidation of the resting electrocardiogram obtained via exercise electrode sites as a standard 12-lead recording

The difficulty in interpreting the standard 12-lead electrocardiogram (ECG) due to the interference from muscle potentials produced by arm and leg motion makes it unsuitable during the exercise treadmill test. Likewise, the exercise lead placement ECG cannot substitute for the standard ECG due to significant errors in the former's diagnostic interpretation. This study compares the ECGs recorded via standard and exercise sites regarding frontal and horizontal plane axes, diagnosis and location of myocardial infarction and estimation of infarct size using the complete 54-criteria and 32-point Selvester QRS scoring system. The altered limb lead locations on the exercise ECG caused the QRS vectors to artifactually appear to be directed more inferiorly, posteriorly and rightward, producing a marked rightward mean frontal plane axis shift of +48 degrees (p less than 0.00001). No false positive or false negative anterior infarct was seen on the exercise lead placement ECG, whereas inferior and posterior infarcts were lost in 69% and 31% of patients, respectively. A false lateral infarct was seen in 19% of patients. Estimation of infarct size differed between the 2 ECG sets, with 11 patients increasing their infarct size by 3 to 9% and 14 others decreasing it by 3 to 15% on the exercise lead placement ECG. This study demonstrates that use of body torso positions for limb leads results in substantial QRS waveform variations that disqualify the exercise lead placement ECG as a "standard" recording. Such ECGs should therefore be labeled as "torso positioned" or "nonstandard" to prevent misuse for clinical and investigative purposes.     

Comparison of ST depression recorded by Holter monitors and 12-lead ECGs during coronary angiography and exercise testing

Data from previous studies are debatable regarding whether Holter monitors are a reliable electrocardiographic indicator of ischemia, for which the 12-lead electrocardiogram (ECG) is the standard. Simultaneous 12-lead and Holter ECGs were performed on 30 patients with typical angina pectoris during coronary angiography or exercise testing. ST depression recorded by both methods was directly compared, using the 12-lead ECG as the reference. The Holter tapes were also scanned by two automated ST analysis programs and the results were compared to 12-lead ECGs. Only 66 of the 178 12-lead ECG ST depression events were also present on the Holter recordings (37.1% Holter sensitivity). ST depression was underestimated by the Holter recordings compared to the 12-lead ECGs (p < 0.0001). The majority (67.0%) of ST depression events identified by one computer program were false positive events. The degree of ST depression was overestimated compared to 12-lead ECGs by the second program (p = 0.0033). Holter-detected ST depression may not be a reliable ECG indicator of myocardial ischemia.     

Similarity of ST and T waveforms of 12-lead electrocardiogram acquired from different monitoring electrode positions

Background

It is not always feasible to use standard electrode placement for limb leads when recording the 12-lead electrocardiogram (ECG). Other electrode placements have been accepted during monitoring. Nonstandard electrode positions, however, fail to produce waveforms identical to those recorded from the distal limb positions that are standard for diagnostic interpretation. The purpose of the present study was to validate the ST-T-segment for an alternative “Lund system” of proximal limb electrode sites.

Methods

Twelve-lead ECGs (standard, Mason-Likar, and Lund lead placement) were collected from 167 patients.

Results

There were systematic differences between measurements from standard vs Mason-Likar, but not vs the Lund system. The 95% confidence intervals of measurement agreement were similar or less when comparing measurements from the Lund system vs the first standard recording with measurements for the 2 standard recordings.

Conclusion

The Lund system might constitute a uniform convention for “diagnostic” ECGs as well as for monitoring ECG applications with regard to ST-T waveforms.     

Sensitivity of CIPS-computed PVC location to measurement errors in ECG electrode position: the need for the 3D Camera

BackgroundThe Cardiac Isochrone Positioning System (CIPS) is a non-invasive method able to localize the origins of PVCs, VT and WPW from the 12 lead ECG. The CIPS model integrates a standard 12-lead ECG with an MRI derived model of the heart, lungs, and torso in order to compute the precise electrical origin of a PVC from within the myocardium. To make these calculations, CIPS uses virtually represented ECG electrode positions. These virtual electrode positions, however, are currently assumed to represent the standard 12 lead positions in the model without taking into account the actual, anatomical locations on a patient. The degree of error introduced into the CIPS model by movement of the virtual electrodes is unknown. Therefore, we conducted a model-based study to determine the sensitivity of CIPS to changes in its virtually represented ECG electrode positions.MethodsPreviously, CIPS was tested on 9 patients undergoing PVC ablation, producing a precise myocardial PVC location for each patient. These initial results were used as controls in two different simulation experiments. The first moved all virtual precordial leads in CIPS simultaneously up and down to recalculate a PVC origin. The second moved each virtual precordial lead individually, using 8 points on multiple concentric circles of increasing radius to recalculate a PVC origin. The distance of the newly calculated PVC origin from the control origin was used as a metric.ResultsMoving either all electrodes simultaneously or each V1-6 precordial electrode independently resulted in non-linear and unpredictable shifts of the CIPS-computed PVC origin. Simultaneously moving all V1-6 precordial electrodes by 10 mm increments produced a shift in CIPS-computed PVC origin between 0 and 62 mm. Independently moving an electrode, a shift of more than 10 mm resulted in an unpredictable CIPS-computed PVC origin relocation between 0 and 40 mm. The effect of moving the virtual electrodes on CIPS modeling more pronounced the closer the virtual electrode was positioned to the actual PVC origin.ConclusionsSlight changes in the virtual positions of the V1-6 precordial electrodes produce marked, non-linear and unpredictable shifts in the CIPS-computed PVC origin. Thus, any variation in the physical ECG electrode placement on a patient can result in significant error within the CIPS model. These large errors would make CIPS useless and underscore the need for accurate, patient specific measurement of electrode position relative to the patient specific torso geometries. A potential solution to this problem could be the introduction of a 3D camera to incorporate accurate measurement of physical electrode placement into the CIPS model.Since the 3D camera software integrates the 3D imaged position of the electrode with the MRI derived torso model, it is conveniently incorporated in the next generation CIPS software to decrease the errors in modeled location of the electrodes. Thus, the 3D camera will be the III^rd component of the CIPS to increase its accuracy in PVC, VT, and WPW localization.     

Comparison of waveforms in conventional 12-lead ECGs and those derived from EASI leads in children

To investigate the possibility of simplifying electrocardiogram (ECG) recording in children, we compared waveforms in conventional 12-lead ECGs to those derived from EASI leads in 221 children of various ages. The conventional 12-lead ECGs and the ECGs using EASI electrode positions were collected simultaneously. We developed and determined the value of age-specific transformation coefficients for use in deriving 12-lead ECGs from the signals recorded at the EASI sites. We compared the results of using age-specific coefficients to the results of using adult coefficients and studied the "goodness-of-fit" between the conventional and the derived 12-lead ECGs. The age-specific coefficients performed slightly better than the adult coefficients, and good agreement was usually attained between the conventional 12-lead ECG and the EASI-derived 12-lead ECG. Our conclusion is that EASI leads in children have the same high levels of "goodness-of-fit" to replicate conventional 12-lead ECG waveforms, as reported earlier in adults.     

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 (EASIDeltastdECG) versus differences in waveform measurements between paramedic Mason-Likar and stdECG (PMLDeltastdECG) 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: EASIDeltastdECG and PMLDeltastdECG were identical in 28%, whereas EASIDeltastdECG was more than PMLDeltastdECG in 35%, and PMLDeltastdECG was accurate (both time) than EASIDeltastdECG 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.     

Potential solutions for providing standard electrocardiogram recordings from nonstandard recording sites

For a 12-lead resting electrocardiogram (ECG) to be considered “standard,” limb electrodes should be placed distally on the limbs. When resting ECGs are taken in conjunction with an ECG-monitoring situation, so-called monitoring sites (as described by Mason and Likar and also others) on the torso are used. Numerous publication have indicated that these ECGs are not identical with those recorded from distal sites, and this prohibits application of visual or computer-based interpretation criteria as well as serial comparison with standard ECGs. Loss of Q waves diagnostic for inferior wall myocardial infarction, as well as marked differences in frontal plane electrical axis, is the most commonly encountered problem with torso-recorded ECGs. This overview suggests 4 possible solutions to this dilemma.     

Change in ST segment elevation 60 minutes after thrombolytic initiation predicts clinical outcome as accurately as later electrocardiographic changes

Objective—To compare prospectively the prognostic accuracy of a 50% decrease in ST segment elevation on standard 12-lead electrocardiograms (ECGs) recorded at 60, 90, and 180 minutes after thrombolysis initiation in acute myocardial infarction.
Design—Consecutive sample prospective cohort study.
Setting—A single coronary care unit in the north of England.
Patients—190 consecutive patients receiving thrombolysis for first acute myocardial infarction.
Interventions—Thrombolysis at baseline.
Main outcome measures—Cardiac mortality and left ventricular size and function assessed 36 days later.
Results—Failure of ST segment elevation to resolve by 50% in the single lead of maximum ST elevation or the sum ST elevation of all infarct related ECG leads at each of the times studied was associated with a significantly higher mortality, larger left ventricular volume, and lower ejection fraction. There was some variation according to infarct site with only the 60 minute ECG predicting mortality after inferior myocardial infarction and only in anterior myocardial infarction was persistent ST elevation associated with worse left ventricular function. The analysis of the lead of maximum ST elevation at 60 minutes from thrombolysis performed as well as later ECGs in receiver operating characteristic curves for predicting clinical outcome.
Conclusion—The standard 12-lead ECG at 60 minutes predicts clinical outcome as accurately as later ECGs after thrombolysis for first acute myocardial infarction.

Keywords: myocardial infarction;  thrombolysis;  ST segment elevation     

False ST elevation in a modified 12-lead surface electrocardiogram

Precise recording of the standard 12-lead electrocardiogram (ECG) is technically time consuming. Placing limb leads on the torso has the major advantages of ease of use, increased speed of application, and decreased artifact. This modified ECG frequently substitutes for the standard 12-lead ECG in intensive care units to detect ischemia, although its implementation should be limited to interpreting arrhythmias. We describe a patient who was misdiagnosed with acute inferior myocardial infarction in a modified 12-lead ECG. To the best of our knowledge, this is the first case report regarding detection of false ST elevations in this setting. Always, a standard 12-lead ECG is recommended to evaluate any ST-T changes.     

The impact of numeric and graphic displays of ST-segment deviation levels on cardiologists' decisions of reperfusion therapy for patients with acute coronary occlusion

The study purpose is to determine whether numeric and/or graphic ST measurements added to the display of the 12-lead electrocardiogram (ECG) would influence cardiologists' decision to provide myocardial reperfusion therapy. Twenty ECGs with borderline ST-segment deviation during elective percutaneous coronary intervention and 10 controls before balloon inflation were included. Only 5 of the 20 ECGs during coronary balloon occlusion met the 2007 American Heart Association guidelines for ST-elevation myocardial infarction (STEMI). Fifteen cardiologists read 4 sets of these ECGs as the basis for a “yes/no” reperfusion therapy decision. Sets 1 and 4 were the same 12-lead ECGs alone. Set 2 also included numeric ST-segment measurements, and set 3 included both numeric and graphically displayed ST measurements (“ST Maps”). The mean (range) positive reperfusion decisions were 10.6 (2-15), 11.4 (1-19), 9.7 (2-14), and 10.7 (1-15) for sets 1 to 4, respectively. The accuracies of the observers for the 5 STEMI ECGs were 67%, 69%, and 77% for the standard format, the ST numeric format, and the ST graphic format, respectively. The improved detection rate (77% vs 67%) with addition of both numeric and graphic displays did achieve statistical significance (P < .025). The corresponding specificities for the 10 control ECGs were 85%, 79%, and 89%, respectively. In conclusion, a wide variation of reperfusion decisions was observed among clinical cardiologists, and their decisions were not altered by adding ST deviation measurements in numeric and/or graphic displays. Acute coronary occlusion detection rate was low for ECGs meeting STEMI criteria, and this was improved by adding ST-segment measurements in numeric and graphic forms. These results merit further study of the clinical value of this technique for improved acute coronary occlusion treatment decision support.     

A vector-based, 5-electrode, 12-lead monitoring ECG (EASI) is equivalent to conventional 12-lead ECG for diagnosis of acute coronary syndromes

AIMS: The conventional 12-lead electrocardiogram (cECG) derived from 10 electrodes using a cardiograph is the gold standard for diagnosing myocardial ischemia. This study tested the hypothesis that a new 5-electrode 12-lead vector-based ECG (EASI; Philips Medical Systems, formerly Hewlett Packard Co, Boeblingen, Germany) patient monitoring system is equivalent to cECG in diagnosing acute coronary syndromes (ACSs). METHODS: Electrocardiograms (EASI and cECG) were obtained in 203 patients with chest pain on admission and 4 to 8 hours later. Both types of ECGs were graded as ST-elevation myocardial infarction if at least 1 of the 2 consecutive recordings showed ST elevation more than 0.2 mV, as ACS if one or both showed ST elevation less than 0.2 mV, T-wave inversion, or ST depression. Otherwise, the ECG was graded negative. RESULTS: Final diagnosis was identical in 177 patients (87%; 95% confidence interval [CI], 82%-91%; kappa = 0.81; SE = 0.035). ST-elevation myocardial infarction was correctly identified or excluded by EASI with a specificity of 94% (95% CI, 89%-97%) and a sensitivity of 93% (95% CI, 86%-97%; using cECG as the gold standard). Of 118 patients with enzyme elevations, an almost identical number (72 [61% by EASI] and 73 [62% by cECG]) had ST elevations. Both techniques were equivalent in predicting subsequent enzyme elevation (identical, 108/143; 75% of ACS and ST-elevation myocardial infarction ECGs by EASI and cECG). Thus, both ECG methods had exactly the same specificity of 59% (95% CI, 48%-69%) and sensitivity of 91% (95% CI, 85%-96%) for detecting myocardial injury. CONCLUSION: EASI is equivalent to cECG for the diagnosis of myocardial ischemia.     

A comparison of 2-lead, 6-lead, and 12-lead ECGs in patients with changing edematous states: implications for the employment of quantitative electrocardiography in research and clinical applications

OBJECTIVE: Precordial ECGs reveal significant intrasubject variability due to the inexact employment of the recommended V(1)-V(6) chest landmarks. Also, as per the Einthoven law, the six limb leads can be derived from leads 1 and 2. The purpose of this study was to evaluate whether the 12-lead ECG could be substituted by ECG sets with a limited number of leads. MATERIALS AND METHODS: The performance of three ECG systems (ie, the 12-lead ECG, a 6-lead ECG comprising the limb leads, and a 2-lead ECG comprising exclusively leads 1 and 2) was evaluated in data from 28 patients with anasarca (AN), 28 control patients, 10 patients who had undergone hemodialysis, and 3 patients with idiopathic dilated cardiomyopathy. RESULTS: Linear regression analyses of changes in ECG data with the weight gain of patients with AN and the intercorrelations of the three ECG systems in the various patient subgroups were found to be statistically significant at p = 0.0005 and r values ranging from 0.61 to 0.99, which are suggestive of good/excellent correlations. However, regression analyses of peak weight (PW) gain with changes in the 2-lead ECG (r = 0.43; p = 0.02) and 6-lead ECG (r = 0.48; p = 0.01), and half of PW gain and 12-lead ECG (r = 0.41; p = 0.03), 6-lead ECG (r= 0.18; p = 0.35), and 2-lead ECG (r = 0.43; p = 0.02) revealed poor correlations. CONCLUSION: ECG systems, comprising 2 or 6 leads, can be substituted for the 12-lead ECG for certain clinical and research applications (pertaining to the amplitude of QRS complexes), attesting to the inherent redundancy of the information from the 12-lead ECG.     

CR leads in cardiac emergencies. A preliminary study

The purpose of this study was to find a set of simplified electrocardiographic (ECG) leads that would be useful in cardiac emergencies. In 27 ambulatory cardiac patients and in 15 patients admitted to the hospital, we found that ECG records obtained with six bipolar CR leads were, in most respects, similar to records obtained previously in the same patients with six V leads. Records obtained with two abdominal-upper extremity leads, tested as possible alternatives to limb leads 2 and 3, were quite similar to records obtained with leads 2 and 3 in patients with an inferior wall infarction. Records obtained with leads CR7, CR8, and CR9 in a patient with a posterior wall infarction revealed a QS pattern that was not seen in the conventional 12-lead hospital record. In patients with anterolateral and inferior myocardial infarctions and in patients with unstable angina, the diagnostic patterns recorded with 11 bipolar leads described in this report were identical to patterns recorded with 12-lead ECGs. Although a larger number of observations, including patients with arrhythmias, would be required to reach a definitive conclusion, our results provide preliminary evidence that cardiac potentials may be adequately analyzed by using only two electrodes, using CR and abdominal leads, in succession. The technique described in this report, in which the reference electrode is attached to the right arm, and the exploring electrode is moved successively over nine preselected chest sites and over the umbilicus, can be completed in less than 3 minutes in a given patient, and provides records that are comparable to those obtained with the conventional 12-lead system.     

The effects of electrode misplacement on clinicians' interpretation of the standard 12-lead electrocardiogram

IntroductionThis study investigates how a particular incorrect electrode configuration affects the 12-lead Electrocardiogram (ECG).MethodsA correct and an incorrect 12-lead ECG were extracted from a 192-lead BSPM. This was done for 232 BSPMs yielding 464 12-lead ECGs. The particular incorrect ECG involved displacing electrodes V1 and V2 in the second intercostal space whilst also offsetting the remaining electrodes. These ECGs were examined in two stages: (a) analysis of the effects of electrode misplacement on signal morphology and (b) analysis of how often the incorrect electrode configuration changed the diagnosis of two clinicians in a random sample of 75 patients.ResultsAccording to the Root Mean Square Error (RMSE) of the difference between PQRST intervals in the correct and incorrect ECGs, lead V2 is the most affected lead (mean: 185 μV ± 82 μV), followed by lead V4 (mean: 114 μV ± 59 μV) and lead V1 (mean: 100 μV ± 47 μV). It was found that if the incorrect electrode configuration is applied, there is a 17% to a 24% chance the diagnostic interpretation will be different. Quantified using Similarity Coefficient (SC) leads V1 and V2 were found to be more alike when misplaced in the second intercostal space. The average SC between these leads when correctly placed was 0.08 (± 0.65), however when incorrectly placed, the average SC was 0.43 (± 0.3).ConclusionThere is a reasonable chance this particular incorrect electrode configuration will change the diagnosis of the 12-lead ECG. This highlights the importance of developing algorithms to detect electrode misplacement along with better education regarding ECG acquisition.     

Prehospital 12-lead ST-segment monitoring improves the early diagnosis of acute coronary syndrome

Aims/MethodsWe studied 620 patients who activated “911” for chest pain symptoms to determine the sensitivity and specificity of 12-lead electrocardiogram (ECG) ST-segment monitoring in the prehospital period (PH ECG) for diagnosing acute coronary syndrome (ACS) and to assess whether the addition of PH ECG signs of ischemia/injury to the initial hospital 12-lead ECG obtained in the emergency department would improve the diagnosis of ACS.ResultsThe sensitivity and specificity of the PH ECG were 65.4% and 66.4%. There was a significant increase in sensitivity (79.9%) and decrease in specificity (61.2%) when considered in conjunction with the initial hospital ECG (P < .001). Those with PH ECG ischemia/injury were more than 2.5 times likely to have an ACS diagnosis than those who had no PH ECG ischemia/injury (P < .001).ConclusionsPrehospital ECG data obtained with 12-lead ST-segment monitoring provides diagnostic information about ACS above and beyond the initial hospital ECG.     

Precordial ST-segment mapping 1. Clinical studies in the coronary care unit.

Precordial ST-segment mapping Was applied serially in the coronary care unit for the study of 46 patients with myocardial infarction (MI), using a 49-lead system. Data from the maps were compared with clinical status of patients, conventional ECGs obtained simultaneously, and serum enzyme levels. Stability of the maps over a one hour period was noted in the early phase of admission. However, a drop of 32% of the sum of ST-segment elevations (+sigma ST) was detected in eight patients with uncomplicated anterior MI over the first 24 hours after admission. Extension of infarction was associated with abrupt rise of + sigma ST, and was diagnosed in two cases from maps in the presence of unchanged standard ECGs. The course of ST elevations was followed more accurately by the map than the standard ECG in eight patients. Pericarditis invalidated the technique completely, due to persistent + sigma ST. The standard ECG was superior to the map in following patients with inferior MI. A case of true posterior MI was more accurately delineated by maps of the posterior thorax than by the standard ECG. Intraventricular conduction defects and pacemaking interfered with maps. Early repolarization produced stable maps; however, mapping showed no advantages over the standard ECG. Preinfarction angina can probably be followed by serial mapping of ST-segment depression.     

On designing and testing transformations for derivation of standard 12-lead/18-lead electrocardiograms and vectorcardiograms from reduced sets of predictor leads

The aim of this study was to develop and evaluate transformation coefficients for deriving the standard 12-lead electrocardiogram (ECG), 18-lead ECG (with additional leads V7, V8, V9, V3R, V4R, V5R), and Frank vectorcardiogram (VCG) from reduced lead sets using 3 “limb” electrodes at Mason-Likar torso sites combined with 2 chest electrodes at precordial sites V1 to V6; 15 such lead sets exist and each can be recorded with 6-wire cable. As a study population, we used Dalhousie Superset (n = 892) that includes healthy subjects, postinfarction patients, and patients with a history of ventricular tachycardia. For each subject, 120-lead ECG recordings of 15-second duration were averaged, and all samples of the QRST complex for leads of interest were extracted; these data were used to derive—by regression analysis—general and patient-specific coefficients for lead transformations. These coefficients were then used to predict 12-lead/18-lead ECG sets and 3-lead VCG from 15 reduced lead sets, and the success of these predictions was assessed by 3 goodness-of-fit measures applied to the entire QRST waveform and to the ST deviation at J point; these 3 measures were similarity coefficient (SC in percentage), relative error (in percentage), and RMS error (in microvolts). Our results show that the best pair for predicting the standard 12-lead ECG by either general coefficients (mean SC = 95.56) or patient-specific coefficients (mean SC = 99.11) is V2 and V4; the best pair for deriving the 18-lead set by general coefficients (mean SC = 93.74) or by patient-specific coefficients (mean SC = 98.71) is V1 and V4; the best pair for deriving the Frank X, Y, Z leads is V1 and V3 for general coefficients (mean SC = 95.76) and V3 and V6 for patient-specific coefficients (mean SC = 99.05). The differences in mean SC among the first 8 to 10 predictor sets in each ranking table are within 1% of the highest SC value. Thus, in conclusion, there are several near-equivalent choices of reduced lead set using 6-wire cable that offer a good prediction of 12-lead/18-lead ECG and VCG; a pair most appropriate for the clinical application can be selected.     

Electrocardiographic Findings of Severe Left Main Coronary Artery Stenosis

Studies have documented the occurrence of ST elevation in lead aVR and/or diffuse ST depression in the setting of acute coronary syndromes (ACS) in patients with left main coronary stenosis (LMCS). We sought to describe the baseline ECG characteristics in LMCS patients outside of the ACS setting. Seventeen patients with ≥90% LMCS and 129 patients with 70–89% LMCS met criteria for the study. None of the 17 patients in the ≥90% LMCS group and 2/129 patients in the 70–89% LMCS group had ST elevation in aVR. None of the 17 patients in the >90% LMCS group and 3/129 patients in the 70–89% LMCS group had ST depression in ≥6 leads. Twenty-four percent of patents in the >90% LMCS group and 29% of patients in the 70–89% LMCS group had normal ECGs. While patients with severe LMCS outside of the ACS setting did not demonstrate ischemia, many exhibited normal ECGs. The authors have no conflict of interest and there was no financial support for this research project.