Assessment of QT-measurement accuracy using the 12-lead electrocardiogram derived from EASI leads

The purpose of the present study is to assess QT-interval measurements from the EASI 12-lead electrocardiogram (ECG) as compared with the standard 12-lead ECG. The QT interval was automatically determined in simultaneously recorded standard and EASI 12-lead ECGs, using a validated wavelet-based delineator. The agreement between the 2 sets of measurements was quantified both on a lead-by-lead basis and a multilead basis with global definitions of QRS onset and T-wave end.The results show that the agreement between QT-interval measurements from the 2 lead systems is acceptable, with negligible mean differences and with correlation coefficients ranging from 0.91 to 0.98 depending on the lead studied. Although the SD shows a clear dependence on the selected lead (ranging from 9.2 to 26.4 milliseconds), differences are within the accepted tolerances for automatic delineation. In a few patients, large differences were found, mainly because of changes in morphology present in both lead systems. QT intervals measured by the multilead approach were considerably more stable than single-lead measurements and resulted in a much better agreement between the 2 lead systems (correlation coefficient, 0.98; QT difference, 1.1 ± 9.8 milliseconds). Thus, the EASI 12-lead ECG may be used for reliable QT monitoring when the multilead delineation approach is adopted.     

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 deltaEASI-gold standard versus deltaparamedic-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.     

EASI 3导联衍生的12导联心电图的应用研究

目的在亚洲人群中导出EASI导联和常规12导联心电图的转换系数和方程,比较亚洲人群与北美人群之间导联转换上的差异性,同时观察导联转换是否受年龄、性别、身高和体重的影响。方法627例受试者同步记录常规12导联心电图和EASI导联心电图。同时记录年龄、性别、身高和体重。结论在亚洲人群和北美人群之间,导联转换无显著性差异,年龄、性别、身高和体重对导联转换无显著影响。     

EASI 12导联心电监测系统的临床应用

目的探讨EASI12导联心电监测系统的临床意义。方法对CCU病房的530例（EASI12导联监测系统监测205例、传统单导联监测系统监测325例）患者持续心电监测24～72h，并对监测结果进行比较分析。结果应用EASI12导联监测系统监测的205例中，可见房性心律失常57例（27．8％），室性心律失常79例（38．5％），房室传导阻滞26例（12．7％），心肌缺血性ST段改变85例（41．5％），而应用传统单导联监测系统的325例中，可见房性心律失常56例（17．2％），室性心律失常82例（25．2％），房室传导阻滞22例（6．8％），心肌缺血性ST段改变81例（24．9％），前者检出率显著提高（x^2=6．103、6．898、4．218、10．456，P均〈0．05）。结论EASI12导联监测系统为临床提供了即时和准确的数据，有助于及时发现心律失常和心肌缺血事件。     

EASI 12导联与标准监护Ⅱ导联监测心肌缺血的观察

目的评价目前常规选择的标准监护Ⅱ导联和EASI12导联心电监测对于发现心肌缺血的有效性和敏感性。方法采用诊断试验的评价研究设计，将研究期间收住北京市宣武医院CCU病房的57例有ST段改变的病人作为病例组，43例无ST段改变的病人作为非病例组，选用标准12导联心电图为金标准，评价CCU标准监护Ⅱ导联和EASI12导联发现心肌缺血的有效性和敏感性。两组病人均同时描记标准12导联、EASI12导联和标准监护Ⅱ导联心电图。比较3种心电图中ST段的改变情况。结果标准监护Ⅱ导联心肌缺血检出率明显低于标准12导联心电图，敏感度、特异度、假阳性率和假阴性率分别为24．6％、95.3％、4.7％和75.4％，一致性检验Kappa值仅为0.178。而EASI12导联对心肌缺血的检出率与标准12导联心电图相仿，敏感度、特异度、假阳性率和假阴性率分别为89.5％、97．7％、2.3％和10．5％，Kappa=0．859。结论临床上通常选用的标准监护Ⅱ导联并不能有效地发现心肌缺血，而EASI12导联较标准Ⅱ导联能够更有效地发现心肌缺血，具有较好的敏感度和特异度。     

Detection of myocardial ischemia by vessel-specific leads derived from the 12-lead electrocardiogram and its subsets

Currently used electrocardiographic criteria for identifying patients with ST-elevation myocardial infarction (STEMI) perform with high specificity but low sensitivity. Our aim was to enhance ischemia-detection ability of conventional STEMI criteria based on 12-lead electrocardiogram (ECG) by adding new criteria using 3 vessel-specific leads (VSLs) derived from 12-lead ECG. Study data consisted of 12-lead ECGs acquired during 99 ischemic episodes caused by balloon inflation in, respectively, left anterior descending coronary artery (LAD; n = 35), right coronary artery (RCA; n = 47), and left circumflex coronary artery (LCx; n = 17). ST deviation was measured at J point in 12 standard leads, and for 3 VSLs, its value was derived from 12-lead ECG by using 8 independent predictor leads or just a pair of precordial leads combined with a pair of limb leads. Mean values of sensitivity (SE) and specificity (SP) of ischemia detection achieved with conventional STEMI vs VSL criteria were then obtained from bootstrap trials. We found that the detection of ischemic state by conventional criteria achieved the mean SE/SP of 60%/96% in the total set of ischemic episodes, 74%/97% in the LAD subgroup, 60%/94% in the RCA subgroup, and 36%/100% in the LCx subgroup. In comparison, the mean SE/SP values of VSLs derived from 8 independent leads of 12-lead ECG were, at 125-μV threshold, 76%/96% in the total set, 91%/97% in the LAD subgroup, 70%/94% in the RCA subgroup, and 71%/100% in the LCx subgroup (with asterisk denoting a statistically significant increase). The mean SE/SP of VSLs derived from some of the 4-predictor lead sets (namely, those including lead V₃) matched or exceeded values achieved by VSLs derived from 8 predictors; for instance, with predictor leads I, II, V₃, V₆ derived VSLs attained at 125-μV threshold the mean SE/SP of 80%/95% in the total set, 91%/97% in the LAD subgroup, 74%/92% in the RCA subgroup, and 71%/100% in the LCx subgroup. Based on these results, we conclude that, in our data set, 3 VSLs derived from the complete standard 12-lead ECG—and even from its subsets—can identify acute ischemia better than existing STEMI criteria.     

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.     

Accuracy of the EASI 12-lead electrocardiogram compared to the standard 12-lead electrocardiogram for diagnosing multiple cardiac abnormalities

This study was performed to compare a derived 12-lead electrocardiogram (ECG) using a simple 5-electrode lead configuration (EASI 12-lead) with the standard ECG for multiple cardiac diagnoses. Accurate diagnosis of arrhythmias and ischemia often require analysis of multiple (ideally, 12) ECG leads; however, continuous 12-lead monitoring is impractical in hospital settings. EASI and standard ECGs were compared in 540 patients, 426 of whom also had continuous 12-lead ST segment monitoring with both lead methods. Independent standards relative to a correct diagnosis were used whenever possible, for example, echocardiographic data for chamber enlargement-hypertrophy, and troponin levels for acute infarction. Percent agreement between the 2 methods were: cardiac rhythm, 100%; chamber enlargement-hypertrophy, 84%–99%; right and left bundle branch block, 95% and 97%, respectively; left anterior and posterior fascicular block, 97% and 99%, respectively; prior anterior and inferior infarction, 95% and 92%, respectively. There was very little variation between the 2 lead methods in cardiac interval measurements; however, there was more variation in P, QRS, and T-wave axes. Of the 426 patients with ST monitoring, 138 patients had a total of 238 ST events (26, acute infarction; 62, angioplasty-induced ischemia; 150, spontaneous transient ischemia). There was 100% agreement between the 2 methods for acute infarction, 95% agreement for angioplastyinduced ischemia, and 89% agreement for transient ischemia. EASI and standard 12-lead ECGs are comparable for multiple cardiac diagnoses; however, serial ECG changes (eg, T-wave changes) should be assessed using one consistent 12-lead method.     

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.     

Comparison of value of leads from body surface maps to 12-lead electrocardiogram for diagnosis of acute myocardial infarction

We aimed to develop 12-lead electrocardiographic (ECG) models testing ST-elevation criteria with QRST variables and compare their performance with the 80-lead body surface map (BSM) in detection of acute myocardial infarction (AMI). Because the prevalence of non-ST-elevation AMI is increasing worldwide, advances in early ECG detection of AMI are urgently needed. The study population was 755 consecutive patients presenting with ischemic chest pain from January 2002 to June 2004. All patients had electrocardiography and body surface mapping performed at initial presentation. AMI occurred in 519 patients (69%, cardiac troponin T or I level > or =0.1 ng/ml). Of these 519 patients, 303 (58%) had no ST-elevation on the initial 12-lead electrocardiogram. Ten patients were classified as having an "aborted AMI" and were included in the AMI analysis. The American College of Cardiology/European Society of Cardiology criteria for ST-elevation on 12-lead electrocardiogram identified 236 patients with AMI (sensitivity 45%, specificity 92%). Additional QRST features improved sensitivity (51% to 68%) but with decreased specificity (71% to 89%), with the optimal multivariate ECG model having a c-statistic of 0.75. The optimal BSM model identified 402 patients as having AMI (sensitivity 76%, specificity 92%, c-statistic 0.84). This improvement in sensitivity over the 12-lead electrocardiogram was due mainly to detection of ST-elevation in the high right anterior, posterior, and right ventricular territories and AMI in the presence of left bundle branch block. In conclusion, QRST variables added to criteria for ST-elevation result in improvement in sensitivity of the 12-lead electrocardiogram, although with decreased specificity. The BSM is superior in detecting AMI and demonstrates the importance of electroanatomic evaluation of patients with acute coronary syndromes.     

EASI与标准12导心电图监测QT及QTd的研究

目的以标准12导联心电图为金标准,评价EASI 12-导联心电监测系统对QT间期及QTd监测的有效性。方法同时记录EASI 12-导联心电图和标准12导联心电图,测量并比较两种心电图各导联的QT间期并计算QTd。结果共采集了216例冠状动脉综合征患者的EASI 12-导联心电图和标准12导联心电图,两种心电图各导联的QT间期具有很好的的相关性(r=0.630~0.843,p0.05);各导联QT间期配对t检验差异均无统计学意义(p0.05)。EASI 12-导联心电图和标准12导联心电图的QTd配对t检验差异均无统计学意义(p0.05)。结论 EASI 12-导联与标准12导联心电图在QT间期及QTd测量上具有一致性,为临床QT及QTd的持续监测提供了依据。     

Comparison of epicardial potential maps derived from the 12-lead electrocardiograms with scintigraphic images during controlled myocardial ischemia

Our aim was to cross-validate electrocardiographic (ECG) and scintigraphic imaging of acute myocardial ischemia. The former method was based on inverse calculation of heart-surface potentials from the body-surface ECGs, and the latter, on a single photon emission computed tomography (SPECT). A boundary-element torso model with 352 body-surface and 202 heart-surface nodes was used to perform the ECG inverse solution. Potentials at 352 body-surface nodes were calculated from those acquired at 12-lead ECG measurement sites using regression coefficients developed from a design set (n = 892) of body-surface potential mapping (BSPM) data. The test set (n = 18) consisted of BSPM data from patients who underwent a balloon-inflation angioplasty of either the left anterior descending coronary artery (LAD) (n = 7), left circumflex coronary artery (LCx) (n = 2), or the right coronary artery (RCA) (n = 9). Body-surface potential mapping distributions at J point for 352 nodes were estimated from the 12-lead ECG, and an agreement with those estimated from 120 leads was assessed by a correlation coefficient (CC) (in percent). These estimates yielded very similar BSPM distributions, with a CC of 91.0% ± 8.1% (mean ± SD) for the entire test set and 94.1% ± 1.4%, 96.7% ± 0.8%, and 87.4% ± 10.3% for LAD, LCx, and RCA subgroups, respectively. Corresponding heart-surface potential distributions obtained by inverse solution correlated with a lower CC of 69.3% ± 18.0% overall and 73.7% ± 10.8%, 84.7% ± 1.1%, and 62.6% ± 21.8%, respectively, for subgroups. Bull's-eye displays of heart-surface potentials calculated from estimated BSPM distributions had an area of positive potentials that qualitatively corresponded, in general, with the underperfused territory suggested by SPECT images. For the LAD and LCx groups, all 9 ECG-derived bull's-eye images indicated the expected territory; for the RCA group, 6 of 9 ECG-derived images were as expected; 2 of 3 misclassified cases had very small ECG changes in response to coronary-artery occlusion, and their SPECT images showed indiscernible patterns. In conclusion, our findings demonstrate that noninvasive ECG imaging based on just the 12-lead ECG might provide useful estimates of the regions of myocardial ischemia that agree with those provided by scintigraphic techniques.