Body-surface map models for early diagnosis of acute myocardial infarction

Methods for presenting and visualising electrocardiographic data: From temporal signals to spatial imaging

INTRODUCTION

The electrocardiogram (ECG) is a recording of the electrical activity of the heart. It is commonly used to non-invasively assess the cardiac activity of a patient. Since 1938, ECG data has been visualised as 12 scalar traces (known as the standard 12-lead ECG). Although this is known as the standard approach, there has been a myriad of alternative methods proposed to visualise ECG data. The purpose of this paper is to provide an overview of these methods and to introduce the field of ECG visualisation to early stage researchers. A scientific purpose is to consider the future of ECG visualisation within routine clinical practice.

METHODS

This paper structures the different ECG visualisation methods using four categories, i.e. temporal, vectorial, spatial and interactive. Temporal methods present the data with respect to time, vectorial methods present data with respect to direction and magnitude, spatial methods present data in 2D or 3D space and interactive methods utilise interactive computing to facilitate efficient interrogation of ECG data at different levels of detail.

CONCLUSION

Spatial visualisation has been around since its introduction by Waller and vector based visualisation has been around since the 1920s. Given these approaches have already been given the 'test of time', they are unlikely to be replaced as the standard in the near future. Instead of being replaced, the standard is more likely to be 'supplemented'. However, the design and presentation of these ECG visualisation supplements need to be universally standardised. Subsequent to the development of 'standardised supplements', as a requirement, they could then be integrated into all ECG machines. We recognise that without intuitive software and interactivity on mobile devices (e.g. tablet PCs), it is impractical to integrate the more advanced ECG visualisation methods into routine practice (i.e. epicardial mapping using an inverse solution).

ECG-based signal analysis technologies for evaluating patients with acute coronary syndrome: a systematic review

BACKGROUND/OBJECTIVES

Timely identification of cardiac ischemia is critical in patients with acute coronary syndrome (ACS). The first test is often the standard, resting 12-lead ECG. Given its limitations, signal analysis enhancements have been proposed. We summarize the published evidence for commercially available ECG-based signal analysis technologies.

METHODS

This is a systematic review of the English-language published literature.

RESULTS

Published evidence meeting inclusion criteria was available for two devices: PRIME ECG and LP 3000. Meta-analysis of eight studies estimated a 68.4% sensitivity (95% CI, 35.1%-89.7%) and 91.4% specificity (CI, 83.6%-95.7%) for the PRIME ECG, compared with 40.5% sensitivity (CI, 19.6%-65.5%) and 95.0% specificity (CI, 87.9%-98.0%) for the standard 12-lead ECG.

CONCLUSIONS

Existing evidence is insufficient to confidently inform the appropriate use of ECG-based signal analysis technologies for detecting ischemia or infarct in ACS. Further research is needed to determine in what circumstances, if any, these devices might precede, replace, or add to the standard ECG in test strategies for detecting ischemia or infarct in ACS.

Noninvasive computational imaging of cardiac electrophysiology for 3-D infarct

Myocardial infarction (MI) creates electrophysiologically altered substrates that are responsible for ventricular arrhythmias, such as tachycardia and fibrillation. The presence, size, location, and composition of infarct scar bear significant prognostic and therapeutic implications for individual subjects. We have developed a statistical physiological model-constrained framework that uses noninvasive body-surface-potential data and tomographic images to estimate subject-specific transmembrane-potential (TMP) dynamics inside the 3-D myocardium. In this paper, we adapt this framework for the purpose of noninvasive imaging, detection, and quantification of 3-D scar mass for postMI patients: the framework requires no prior knowledge of MI and converges to final subject-specific TMP estimates after several passes of estimation with intermediate feedback; based on the primary features of the estimated spatiotemporal TMP dynamics, we provide 3-D imaging of scar tissue and quantitative evaluation of scar location and extent. Phantom experiments were performed on a computational model of realistic heart-torso geometry, considering 87 transmural infarct scars of different sizes and locations inside the myocardium, and 12 compact infarct scars (extent between 10% and 30%) at different transmural depths. Real-data experiments were carried out on BSP and magnetic resonance imaging (MRI) data from four postMI patients, validated by gold standards and existing results. This framework shows unique advantage of noninvasive, quantitative, computational imaging of subject-specific TMP dynamics and infarct mass of the 3-D myocardium, with the potential to reflect details in the spatial structure and tissue composition/heterogeneity of 3-D infarct scar.

Selection of optimal recording sites for limited lead body surface potential mapping in myocardial infarction and left ventricular hypertrophy

A lead selection algorithm was applied to find optimal recording sites for limited lead body surface potential maps. The studied population consisted of a set of 117 lead body surface potential maps recorded from 744 subjects (229, normal; 278, with myocardial infraction [MI]; and 237, with left ventricular hypertrophy [LVH]). One generic lead set derived from all disease groups was found. Also found were 3 disease-specific lead sets (normal, MI, and LVH) and one specific to abnormal subjects (MI and LVH combined). The performance of each lead set in estimating data from other disease groups was largely similar. This was with the exception of leads specific to LVH in the estimation of normal data and normal leads in the estimation of LVH data. Here, the difference was found to be significant (P < .001). The top 6 recording sites in each lead set did not occupy the same positions as the 6 precordial leads. Although disease-specific lead sets are of limited practical use, this study has illustrated that, largely, there is little difference between the performance of different lead sets. The suboptimality of the 6 precordial leads has also been illustrated.

Estimated body surface potential maps in emergency department patients with unrecognized transient myocardial ischemia

BACKGROUND

We report on 5 patients who presented to the emergency department (ED) with chest pain, had negative serum troponin levels, and were discharged with a presumed noncardiac diagnosis. Thereafter, retrospective analysis of Holter monitoring data recorded for a clinical trial revealed ST events indicative of transient myocardial ischemia that was unrecognized clinically.

STUDY AIM

The purpose of this analysis was to determine whether initial body surface potential maps estimated from optimal ischemia electrode sites estimated body surface potential map (EBSPM) showed signs of ischemia in the missed ischemia group that could have prevented misdiagnosis.

METHODS

This is a secondary analysis of data from a prospective clinical trial in which patients were attached to 2 Holter monitor devices for simultaneous recordings. One Holter device recorded a standard Mason-Likar 12-lead electrocardiogram (ECG) and the other recorded a 10-electrode lead set considered optimal for ischemia detection. A body surface potential map was then estimated from the optimal lead set.

RESULTS

At 1 year, 2 of the 5 patients with missed ischemia died and a third had an acute myocardial infarction (MI) (40% mortality, 60% death/nonfatal MI). In comparison, 1-year mortality was 5.7% in 159 similar patients treated for unstable angina at the same institution over the same period (P = .037). The initial standard ECG showed no abnormalities in 3 patients and showed left ventricular hypertrophy in 1. The fifth patient with a history of recent MI had slight ST elevation in leads III and aVF and Q waves that were considered indicative of recent (not acute) MI. EBSPM data recorded at the time of ED presentation matched the standard ECG (normal in 3, left ventricular hypertrophy or inconclusive in 2). During transient ischemia, all 5 EBSPMs showed areas of ischemia overlapping with standard electrode sites.

CONCLUSION

Patients evaluated in the ED for chest pain are at high risk for death or nonfatal MI if they have ischemic events with continuous ST-segment monitoring that are unrecognized clinically. In this small cohort with unrecognized ischemia, the initial body surface potential maps estimated from optimal ischemia electrode sites did not improve on 12-lead ST-segment monitoring to identify this high-risk group.

Comparative Analysis Using the 80-Lead Body Surface Map and 12-Lead ECG With Exercise Stress Echocardiograms

This retrospective study constituted of 144 patients who were recruited at the University of California Davis Medical Center (UCDMC) Echo and Stress Laboratory during a 10-month period by referrals for standard ESE to assess for CAD. Participation criteria included referral for a standard ESE, age older than 18 years, and the same criteria as standard stress tests. Standard stress test exclusion criteria were applied as well (Table 1).12 All patients gave informed consent. The study group, called the 80-lead BSM group, consisted of 72 participants. Seventy-two random participants comprised the 12lead ECG group (see Table 2). Twenty-two participants in the 80-lead group had poor image quality ESE or incomplete data for exercise cessation and/or image acquisition real time; as a result, these participants were excluded from the study. None of the ESE of the 12-lead ECG group was considered of poor image quality, nor were any data incomplete. STRESS ECHOCARDIOGRAMS

How many ECG leads do we need?

The number of leads needed in clinical electrocardiography depends on the clinical problem to be solved. The standard 12-lead ECG is so well established that alternative lead systems must prove their advantage through well-conducted clinical studies to achieve clinical acceptance. Certain additional leads seem to add valuable information in specific patient groups. The use of a large number of leads (eg, in body surface potential mapping) may add clinically relevant information, but it is cumbersome and its clinical advantage is yet to be proven. Reduced lead sets emulate the 12-lead ECG reasonably well and are especially advantageous in emergency situations.

Diagnosing Old MI by Searching for a Linear Boundary in the Space of Principal Components

Body surface potential mapping (BSPM) is a technique employing multiple electrodes to capture, via noninvasive means, an indication of the heart's condition. An inherent problem with this technique is the resulting high-dimensional recordings and the subsequent problems for diagnostic classifiers. A data set, recorded from a 192-lead BSPM system, containing 74 records is investigated. QRS isointegral maps, offering a summary of the information obtained during ventricular depolarization, were derived from 30 old inferior myocardial infarction and 44 normal recordings. Principal component analysis was applied to reduce the dimensionality of the recordings and a linear classifier was employed for classification. This perceptron-based classifier has been adapted so that the final weight and bias values are estimated prior to the learning process. This estimation process, referred to as the linear hyperplane approach (LHA), derives the estimated weights from a bisector hyperplane, placed orthogonal to the means of two class distributions in an n-dimensional Euclidean space. Estimating weights encourages a network to exhibit better generalization ability. Utilizing a number of different principal components as input features, the LHA achieved an average sensitivity and specificity of 79.58% and 76.45%, respectively, across all experiments. The average accuracy of 76.73% achieved with this approach was significantly better than the other benchmark classifiers evaluated against it.

Body surface mapping versus the standard 12 lead ECG in the detection of myocardial infarction amongst emergency department patients: a Bayesian approach

OBJECTIVE

To determine if body surface mapping (BSM) is better than the standard 12 lead ECG in the diagnosis of acute myocardial infarction amongst emergency department patients.

SETTING

A University affiliated inner-city emergency department.

PARTICIPANTS

People presenting to an emergency department with symptoms compatible with myocardial ischaemia/infarction.

MAIN OUTCOME MEASURES

Myocardial infarction as defined by either standard 12 lead ECG changes with associated cardiac marker rise, Troponin T >0.1 microg/ml at > 12 h or autopsy/surgical findings of fresh macroscopic infarction.

RESULTS

BSM had an overall sensitivity of 47.1% versus 40% for the 12 lead ECG (P < 0.001). Specificity for the BSM was 85.6% versus 93.7% for the 12 lead ECG (P < 0.001). These findings were consistent for low/moderate and high risk subgroups. Bayesian analysis demonstrates that indiscriminate use of BSM would result in a clinically important overdiagnosis of myocardial infarction amongst emergency department patients.

CONCLUSIONS

BSM has a higher sensitivity, but a lower specificity for the diagnosis of myocardial infarction.

Body surface mapping in the ED evaluation of the patient with chest pain: use of the 80-lead electrocardiogram system

Body surface mapping (BSM) is an electrocardiographic (ECG) technique that uses numerous leads on a patient's anterior and posterior chest, enabling more complete visualization of cardiac electrical activity. The rationale behind BSM is an extension of additional lead ECG. Output from BSM is displayed in a 12-lead ECG format, an 80-lead ECG format, and on color contour maps. The color contour maps can be displayed on a torso image or as a flat map.

The Effect of Conductivity on ST-Segment Epicardial Potentials Arising from Subendocardial Ischemia

We quantify and provide biophysical explanations for some aspects of the relationship between the bidomain conductivities and ST-segment epicardial potentials that result from subendocardial ischemia. We performed computer simulations of ischemia with a realistic whole heart model. The model included a patch of subendocardial ischemic tissue of variable transmural thickness with reduced action potential amplitude. We also varied both intracellular and extracellular conductivities of the heart and the conductivity of ventricular blood in the simulations. At medium or high thicknesses of transmural ischemia (i.e., at least 40% thickness through the heart wall), a consistent pattern of two minima of the epicardial potential over opposite sides of the boundary between healthy and ischemic tissue appeared on the epicardium over a wide range of conductivity values. The magnitude of the net epicardial potential difference, the epicardial maximum minus the epicardial minimum, was strongly correlated to the intracellular to extracellular conductivity ratios both along and across fibers. Anisotropy of the ischemic source region was critical in predicting epicardial potentials, whereas anisotropy of the heart away from the ischemic region had a less significant impact on epicardial potentials. Subendocardial ischemia that extends through at least 40% of the heart wall is manifest on the epicardium by at least one area of ST-segment depression located over a boundary between ischemic and healthy tissue. The magnitude of the depression is a function of the bidomain conductivity values.

The Effect of Low Force Chiropractic Adjustments for 4 Weeks on Body Surface Electromagnetic Field

OBJECTIVE

To study the effects of 4 weeks of low-force chiropractic adjustments on body surface electromagnetic fields (EMFs).

METHOD

Thirty-five chiropractic students randomly assigned into control (17 subjects) and experimental groups (28 subjects). A triaxial fluxgate magnetometer was used for EMF detection. The subjects' body surface EMF was determined in the prone position before and after the chiropractic adjustment. A Toftness low-force chiropractic adjustment was applied to the cervical, thoracic, lumbar, and sacral areas as determined by the practitioner. Heart rate variability analysis was recorded once a week to determine autonomic nervous system activity in both the control and experimental groups.

RESULTS

The EMF on the subjects' body surface decreased after chiropractic adjustment at the cervical, thoracic, lumbar, and sacral regions in all 6 visits during the 4-week treatment period. The EMF showed a downtrend over the 4-week period after the low-force adjustment. The same changes were not observed in the control group. The chiropractic adjustment group had a slight decrease in heart rate over the 4-week treatment period, and no significant change was observed in the control group. Heart rate variability analysis did not show consistent changes before and after the low-force adjustments during the treatment period.

CONCLUSION

Low-force chiropractic adjustment in the cervical and thoracic areas resulted in a consistent reduction of the body surface EMF after 4 weeks of active treatment. No statistically significant differences were found in the heart rate and heart rate variability in the 4-week study.

Mechanism for ST depression associated with contiguous subendocardial ischemia

INTRODUCTION

A mechanism for ST depression arising on the epicardial surface over the border between normal and ischemic tissue is proposed. Depression is caused by current flowing in a transmural loop that begins and ends at the lateral boundary between healthy and ischemic tissue and passes through the transmural boundary between healthy and ischemic tissue. The result is ST depression at the epicardium over the lateral boundary. The size and direction of current flow are dictated by differences in the magnitude and orientation of anisotropic conductivity between those boundaries.

METHODS AND RESULTS

Computer simulations verified and quantified the relationship between ST depression and conductivity differences. We used computer simulations based on an anatomically accurate, anisotropic model of canine ventricles and a bidomain representation of the effects of ischemia to verify the biophysical basis of this mechanism.

CONCLUSION

ST depression at the epicardium appears over a lateral boundary between healthy and ischemic tissue.

Body surface potential mapping improves detection of ST segment alteration during percutaneous coronary intervention

BACKGROUND

The 12-lead electrocardiogram underestimates ST segment alteration in acute coronary syndromes compared with multi-lead body surface mapping. We assessed whether 80-lead mapping would improve detection of ST alteration during percutaneous coronary intervention.

METHODS

Simultaneous maps and 12-lead electrocardiograms were recorded pre-procedure, during balloon inflation and post-procedure from patients undergoing elective intervention to native coronary arteries. Recordings were obtained from 39 inflations (19 patients). All arteries were successfully stented.

RESULTS

Mean 'lead specific' ST alteration (the difference in ST elevation/depression between pre-procedure and inflation recordings in the lead showing maximal ST alteration) was greater on the map than on electrocardiogram, both for ST elevation (0.16+/-0.02 vs. 0.06+/-0.01 mV; p<0.001) and ST depression (0.11+/-0.017 vs. -0.03+/-0.006 mV; p<0.001). During first inflations (n=19), mean lead specific ST elevation and depression on map were greater than on electrocardiogram (0.20+/-0.034 vs. 0.07+/-0.015 mV; p<0.001 and 0.11+/-0.029 vs. 0.03+/-0.009 mV; p=0.001, respectively). Mapping detected greater summated ST elevation and depression during inflation than electrocardiogram (0.04+/-0.005 vs. 0.021+/-0.003 mV; p<0.001 and 0.026+/-0.004 vs. 0.011+/-0.002 mV; p<0.001, respectively). Qualitative analysis of maps and electrocardiograms showed that 21/39 (53.8%) maps recorded during inflation met criteria for myocardial ischaemia compared with 7/39 (17.9%) electrocardiograms (p<0.001).

CONCLUSION

Body surface mapping compared with the 12-lead electrocardiogram improves detection of myocardial ischaemia during intervention.

A novel method for the detection of transient myocardial ischaemia using body surface electrocardiac mapping

BACKGROUND

The limitations of the 12-lead ECG in the detection of myocardial ischaemia are well known. This study sought to test the hypothesis that a Body Surface Mapping (BSM) system can detect and localise the transient regional ischaemia induced by elective percutaneous coronary intervention (PCI) in patients with stable angina.

METHODS AND RESULTS

25 patients undergoing elective single vessel PCI were studied: 11 with RCA lesions, 9 with LAD lesions and 5 with circumflex lesions. Patients had BSM readings every 30 s following the inflation of a dilating balloon in the target vessel for 1 min. BSMs were analysed for ST segment change at 60 ms after the J point (ST60). Peak ST changes were analysed and colour map reconstruction made. Characteristic ST segment changes in each arterial domain were observed following inflation of the balloon. Maximal change occurred in a standard V lead on only 2/46 occasions. Statistically significant rapid rise and fall of ST 60 readings were observed indicating the onset recovery and location of the transient ischaemia. A novel method for the presentation of colour map reconstruction that removes baseline noise has been developed.

CONCLUSIONS

These data confirm the hypothesis that this BSM system can detect and display transient myocardial ischaemia. BSM may represent a novel clinical tool for the assessment of clinical ischaemia.

The use of calculated epicardial potentials improves significantly the sensitivity of a diagnostic algorithm in the detection of acute myocardial infarction

Inverse electrocardiography can calculate epicardial potentials (EP) from body surface potentials (BSP) taking into account a thoracic volume conductor model (TVCM). Previous studies have shown that a tailored TVCM is superior to a general TVCM in calculating EP. However, construction of a tailored TVCM for a patient in an acute clinical setting is impractical. In this study we used a general TVCM in our EP calculations to determine whether this improves detection of acute myocardial infarction (AMI) using a diagnostic algorithm. BSP were derived from the 80-lead body surface map (BSM). Consecutive patients (n=379) with ischemic type chest pain were recruited. The BSM and a 12-lead electrocardiogram (ECG) were recorded at initial presentation and creatine kinase (CK) and/or CK-MB were measured initially, 12 and 24 hours postsymptom onset. A physician interpreted the 12-lead electrocardiogram and documented ST elevation if present. AMI was defined by the World Health Organization (WHO) criteria. The diagnostic algorithm result for each patient using BSP and calculated EP were documented. AMI occurred in 171 patients. The diagnostic algorithm using BSP identified 106 of these as ST elevation AMI (STEMI) (sensitivity 62%, specificity 80%). The same algorithm using EP identified 133 as STEMI (sensitivity 78%, specificity 80%). Calculated EP improved the algorithm's diagnostic sensitivity by a factor of 1.25 (P<.001) with no significant difference in specificity. Calculated EP using a general TVCM significantly improves the sensitivity of a diagnostic algorithm based on BSP in detection of AMI with no significant loss in specificity.

Body surface mapping improves early diagnosis of acute myocardial infarction in patients with chest pain and left bundle branch block

OBJECTIVE

To test prospectively depolarisation and repolarisation body surface maps (BSMs) for mirror image reversal, which is less susceptible to artefact, in patients with acute ischaemic-type chest pain, and to compare these BSM criteria with previously published 12 lead ECG criteria.

METHODS

An 80 lead portable BSM system was used to map patients presenting with acute ischaemic-type chest pain and a 12 lead ECG with left bundle branch block (LBBB). Acute myocardial infarction (AMI) was defined by serial cardiac enzymes. Each 12 lead ECG was assessed by the criteria of Sgarbossa et al and Hands et al for diagnosis of AMI. Depolarisation and repolarisation BSMs were assessed for loss of mirror image reversal of QRS with ST-T isointegral map patterns and a change in vector angle from QRS to ST-T outside 180+/-15 degrees -findings typically seen in LBBB with AMI.

RESULTS

Of 56 patients with chest pain and LBBB, 18 had enzymatically confirmed AMI. Patients with loss of BSM image reversal were significantly more likely to have AMI (odds ratio 4.9, 95% confidence interval 1.5 to 16.4, p = 0.007). Loss of BSM image reversal was significantly more sensitive (67%) for AMI than either 12 lead ECG method (17%, 33%) albeit with some loss in specificity (BSM 71%, 12 lead ECG 87%, 97%). Patients with AMI compared with those without AMI had a greater mean change in vector angle outside the normal range (180+/-15 degrees ), particularly between QRS isointegral and ST60 isopotential (the potential 60 ms after the J point at each electrode site) BSMs (19 degrees v 9 degrees, p = 0.038). Loss of image reversal and QRS-ST60 vector change outside 180+/-15 degrees had 61% sensitivity and 82% specificity for AMI (odds ratio 7.0, 95% confidence interval 2.0 to 24.4, p = 0.001).

CONCLUSIONS

BSM compared with the 12 lead ECG improved the early diagnosis of AMI in the presence of LBBB.

Comparison of the 80-lead body surface map to physician and to 12-lead electrocardiogram in detection of acute myocardial infarction

Diagnosis of non-ST-elevation acute myocardial infarction (AMI) by a 12-lead electrocardiogram has poor sensitivity and specificity and, therefore, relies on biochemical markers of myocardial necrosis, which can only be reliably detected within 14 to 16 hours from symptom onset. The body surface map (BSM) improves AMI detection but is limited by its interpretation by inexperienced medical staff. To facilitate interpretation, an automated BSM algorithm was developed and is evaluated in this study. One hundred three patients with ischemic-type chest pain were recruited for this study from December 2001 to April 2002. A 12-lead electrocardiogram (Marquette Mac 5K) and BSM (PRIME-ECG) were recorded at initial presentation, and cardiac troponin I and/or creatine kinase-MB levels measured at 12 hours after symptom onset. The admitting physician's 12-lead electrocardiographic (ECG) interpretation, 12-lead ECG algorithm (Marquette 12 SL V233) diagnosis, and BSM algorithm diagnosis were documented for each patient. AMI, defined by elevation of troponin I to >1 microg/L and/or creatine kinase-MB to >25U/L, occurred in 53 patients. The admitting physician diagnosed 24 patients with AMI (sensitivity 45%, specificity 94%), the 12-lead ECG algorithm diagnosed 17 patients with AMI (sensitivity 32%, specificity 98%), and the BSM algorithm diagnosed 34 patients with AMI (sensitivity 64%, specificity 94%). The BSM algorithm improved the diagnostic sensitivity by 2.0 (p <0.001) and 1.4 (p = 0.002) compared with the 12-lead ECG algorithm or the admitting physician, respectively. There was no significant difference in specificity. Thus, the BSM algorithm improves detection of AMI compared with the 12-lead ECG algorithm or physician's 12-lead ECG interpretation.

Noninvasive assessment of reperfusion after fibrinolytic therapy for acute myocardial infarction

Assessment of reperfusion by the 12-lead electrocardiogram (ECG) or biochemical markers is limited by suboptimal sensitivity and/or specificity. Body surface mapping (BSM) improves the spatial sampling of the 12-lead ECG. Serial 12-lead ECGs and 64-lead anterior BSMs were recorded from 67 patients with acute myocardial infarction undergoing coronary angiography 90 minutes after fibrinolytic therapy. ECG-1 and BSM-1 were recorded before/shortly after therapy (median 18 minutes). ECG-2 and BSM-2 were recorded after the 90-minute angiogram (median 30 minutes). The maximum ST elevation on ECG-1 was noted and > or = 30% ST resolution on ECG-2 was taken to represent partial/complete reperfusion. Patients were randomly divided into a training set and validation set. Isointegral and isopotential ST-T variables from BSMs of training-set patients were compared with Thrombolysis In Myocardial Infarction (TIMI) trial flow using discriminant analysis to identify which variables best classified reperfusion. Reperfusion (TIMI 2/3 flow) occurred in 32 of 34 training-set patients and in 29 of 33 validation-set patients. In the training set, > or = 30% ST resolution correctly classified reperfusion with 72% sensitivity (23 of 32) and 50% specificity (1 of 2). In the validation set, > or = 30% ST resolution classified reperfusion with 59% sensitivity (17 of 29) and 50% specificity (2 of 4). In comparison, a model containing 24 BSM variables correctly classified all training-set patients, and when prospectively tested in the validation-set, correctly classified 28 of 29 patients who achieved reperfusion (97% sensitivity) and all 4 patients who failed to reperfuse (p = 0.035). In conclusion, BSM is more useful than the 12-lead ECG for noninvasive assessment of reperfusion after fibrinolytic therapy for acute myocardial infarction.

Early diagnosis of right ventricular or posterior infarction associated with inferior wall left ventricular acute myocardial infarction

Right ventricular (RV) or posterior infarction associated with inferior wall left ventricular acute myocardial infarction (AMI) has important therapeutic and prognostic implications. However, RV and posterior chest leads in addition to the 12-lead electrocardiogram are required for accurate detection. Body surface mapping (BSM) has greater spatial sampling and may further improve inferior wall AMI classification. Consecutive patients with chest pain lasting <12 hours were assessed to identify those with AMI and > or =0.1 mV ST elevation in > or =2 contiguous inferior leads of the 12-lead electrocardiogram (bundle branch block or left ventricular hypertrophy excluded). A 12-lead electrocardiogram, RV leads (V(2)R, V(4)R), posterior chest leads (V(7), V(9)), and a BSM were recorded. From each BSM, the 12 electrodes overlying the RV region (regional RV map) and 10 electrodes overlying the posterior wall (regional posterior map) were assessed for ST elevation. Infarct size was estimated by serial cardiac enzymes. AMI occurred in 173 of 479 patients. Of the 62 patients with inferior wall AMI, ST elevation > or =0.1 mV occurred in 26 patients (42 in V(2)R or V(4)R compared with 36 patients (58%) in > or =1 electrode on the regional RV map (p = 0.0019). ST elevation > or =0.1 mV occurred in 1 patient (2%) in V(7) or V(9) compared with 17 patients (27%) in > or =1 electrode on the regional posterior map (p = 0.00003). ST elevation > or =0.05 mV occurred in 6 patients (10%) in V(7) or V(9) compared with 22 patients (36%) in > or =1 electrode on the regional posterior map (p = 0.00003). Patients with ST elevation on regional RV and/or posterior maps had a trend toward larger infarct size (mean peak creatine kinase 1,789+/-226 vs. 1,546+/-392 mmol/L; p = NS). Thus, BSM, when compared with RV or posterior chest leads, provides improved classification of patients with inferior wall AMI and RV or posterior wall involvement.