Estimation performance of a reduced lead system during continuous 12-lead ECG ST-segment monitoring.

BACKGROUND: Reduced lead systems utilizing patient-specific transformation weights have been reported to achieve superior estimates than those utilizing population-based transformation weights. We report upon the effects of ischemic-type electrocardiographic changes on the estimation performance of a reduced lead system when utilizing patient-specific transformation weights and population-based transformation weights. METHOD: A reduced lead system that used leads I, II, V2 and V5 to estimate leads V1, V3, V4, and V6 was investigated. Patient-specific transformation weights were developed on electrocardiograms containing no ischemic-type changes. Patient-specific and population-based transformations weights were assessed on 45 electrocardiograms with ischemic-type changes and 59 electrocardiograms without ischemic-type changes. RESULTS: For patient-specific transformation weights the estimation performance measured as median root mean squared error values (no ischemic-type changes vs. ischemic-type changes) was found to be (V1, 27.5 µV vs. 95.8 µV, P<.001; V3, 33.9 µV vs. 65.2 µV, P<.001; V4, 24.8 µV vs. 62.0 µV, P<.001; V6, 11.7 µV vs. 51.5 µV, P<.001). The median magnitude of ST-amplitude difference 60 ms after the J-point between patient-specific estimated leads and actual recorded leads (no ischemic-type changes vs. ischemic-type changes) was found to be (V1, 18.9 µV vs. 61.4 µV, P<.001; V3, 14.3 µV vs. 61.1 µV, P<.001; V4, 9.7 µV vs. 61.3 µV, P<.001; V6, 5.9 µV vs. 46.0 µV, P<.001). CONCLUSION: The estimation performance of patient-specific transformations weights can deteriorate when ischemic-type changes develop. Performance assessment of patient-specific transformation weights should be performed using electrocardiographic data that represent the monitoring situation for which the reduced lead system is targeted.

Prognostic significance of baseline ST-T-wave abnormalities in diagnostic stress echocardiography.

OBJECTIVE: The aim of this study was to determine whether resting ST-T wave abnormalities (ST-Ta) provide incremental prognostic information in patients with no history of coronary artery disease undergoing dobutamine stress echocardiography (DSE). METHODS: We evaluated 1308 consecutive patients without previous myocardial infarction (MI) or revascularization who underwent DSE. Ischemia was defined as new or worsening wall motion abnormalities. End points during follow-up were all-cause death and cardiac death/nonfatal MI. RESULTS: ST-Ta were detected in 162 (12%) patients. The incidence of ischemia was higher in patients with baseline ST-Ta than patients without [74 (46%) vs. 327 (28%), P=0.00001]. During a follow-up of 4.6 ± 3 years, cardiac death/nonfatal MI occurred in 42 (26%) patients with resting ST-Ta and in 157 (14%) patients without resting ST-Ta (P<0.001). Patients with ST-Ta had a higher annual cardiac death/nonfatal MI rate compared with patients without, both in the presence of normal DSE (3.2 vs. 1.4%, P=0.01) as well as abnormal DSE (5.3 vs. 3%, P<0.001). In a Cox proportional modeling, resting ST-Ta added incremental value over clinical and stress echocardiographic data for the prediction of death (global χ 125, 140, 150, respectively; P<0.05) and cardiac death/nonfatal MI (global χ 79, 100, 111, respectively; P<0.05). CONCLUSION: Baseline ST-Ta are associated with an increased risk of cardiac death/nonfatal MI and all-cause mortality, incremental to clinical data and DSE results. The associated risk is persistent among patients with normal DSE.

Effects of electrode placement errors in the EASI-derived 12-lead electrocardiogram.

In this study, we assess the effects of electrode placement error on the EASI-derived 12-lead electrocardiogram (ECG). The study data set consisted of 744 body surface potential map (BSPM) recordings. The BSPMs, each of which was made up of 117 leads, were recorded from a mixture of healthy, myocardial infarction, and left ventricular hypertrophy subjects. The BSPMs were interpolated to increase the number of data points in the region of the EASI recording electrodes I, E, and A and the precordial leads. This facilitated 3 experiments. Firstly, recording sites I, E, and A were simultaneously moved ±5 cm vertically, in 0.5 cm increments, from their correct locations. Secondly, recording sites I and A were moved horizontally, again up to ±5 cm, in 0.5 cm increments. Finally, all 6 precordial leads were moved vertically in 0.5 cm increments up to ±5 cm. At each movement step, the resulting 12-lead ECG was compared with the original 12-lead ECG. Root mean square error was determined along with the absolute difference in J-point amplitude. Although the EASI leads were found to be less sensitive to electrode misplacement than the standard precordial leads, it was found that when precordial leads were moved up to ±3 cm vertically, the resulting 12-lead ECG more accurately resembled the original 12-lead ECG than a 12-lead ECG reconstructed from accurately positioned EASI leads. Further work is required to establish the effects of electrode misplacement beyond the ±5 cm limits assessed in this study.

Abnormal spatial QRS-T angle predicts mortality in patients undergoing dobutamine stress echocardiography for suspected coronary artery disease.

OBJECTIVE: To investigate the association between (cardiac) mortality and spatial QRS-T angle in patients undergoing dobutamine - atropine stress echocardiography (DSE) for evaluation of known or suspected coronary disease. METHODS: Between 1990 and 2003, 2347 patients underwent DSE for evaluation of coronary disease at the Erasmus Medical Center. Echocardiographic images were analyzed offline using a 16-segment, 5-point scoring model for regional function. Twelve-lead resting ECGs were analyzed and patients were grouped in three categories according to their spatial QRS-T angle: normal (0-105 degrees), borderline (105-135 degrees), and abnormal (135-180 degrees). RESULTS: Mean age was 61+/-13 years, 66% were male, 32% had hypertension, 26% had hypercholesterolemia, 28% were smokers, and 12% were diabetic. During a mean follow-up of 7+/-3.4 years, 26.5% (623) of the patients died; 15.3% (359) died due to a cardiac cause. Abnormal QRS-T angle (135-180 degrees ) was present in 21% of the patients. Abnormal QRS-T angle was a predictor of cardiac death [hazard ratio: 3.2 (2.6-4.1)] and all-cause mortality [hazard ratio: 2.2 (1.8-2.6)]. After multivariate analysis abnormal and borderline QRS-T angle, peak wall motion score, age, male sex, history of diabetes, history of heart failure, smoking, and hypertension were independent predictors of (cardiac) death. CONCLUSION: Abnormal QRS-T angle is an independent predictor of (cardiac) death in patients undergoing DSE. Abnormal QRS-T angle should be considered as a risk factor in stable patients evaluated for coronary disease.

Clinically relevant QTc prolongation due to overridden drug-drug interaction alerts: a retrospective cohort study.

AIMS: To investigate whether, in patients in whom drug-drug interaction (DDI) alerts on QTc prolongation were overridden, the physician had requested an electrocardiogram (ECG), and if these ECGs showed clinically relevant QTc prolongation. METHODS: For all patients with overridden DDI alerts on QTc prolongation during 6 months, data on risk factors for QT prolongation, drug class and ECGs were collected from the medical record. Patients with ventricular pacemakers, patients treated on an outpatient basis, and patients using the low-risk combination of cotrimoxazole and tacrolimus were excluded. The magnitude of the effect on the QTc interval was calculated if ECGs before and after overriding were available. Changes of the QTc interval in these cases were compared with those of a control group using one QTc-prolonging drug. RESULTS: In 33% of all patients with overridden QTc alerts an ECG was recorded within 1 month. ECGs were more often recorded in patients with more risk factors for QTc prolongation and with more QTc overrides. ECGs before and after the QTc override were available in 29% of patients. Thirty-one percent of patients in this group showed clinically relevant QTc prolongation with increased risk of torsades de pointes or ventricular arrhythmias. The average change in QTc interval was +31 ms for cases and -4 ms for controls. CONCLUSIONS: Overriding the high-level DDI alerts on QTc prolongation rarely resulted in the preferred approach to subsequently record an ECG. If ECGs were recorded before and after QTc overrides, clinically relevant QTc prolongation was found in one-third of cases. ECG recording after overriding QTc alerts should be encouraged to prevent adverse events.

Simultaneous comparison of 3 derived 12-lead electrocardiograms with standard electrocardiogram at rest and during percutaneous coronary occlusion.

AIM: The aim of the study was to simultaneously test the EASI lead system and two other derived ECG methods against the standard 12-lead ECG during percutaneous coronary intervention (PCI). METHODS: During 44 percutaneous coronary interventions, a simultaneously recorded 12-lead and EASI ECG were marked at the start of the PCI (baseline) and at known ischemia caused by balloon inflation (peak). ST deviations were measured 60 ms after the J point at baseline and peak in all leads and were summated (SUMST) to assess overall changes. For regional changes, the lead with the highest ST deviation (PEAKST) was marked. For each patient, derived 12-lead ECGs were computed from the EASI leads and a lead subset using patient-specific coefficients (PS) and coefficients based on a patient population (GEN). Absolute differences were computed between each derived and routine ECG for SUMST and PEAKST. RESULTS: SUMST was at baseline 567 microV (range: 150-1707) and increased at peak to 871 microV (range: 350-2101). SUMST difference at peak was for EASI: 163 microV (CI: 90-236, P <.001), GEN: 46 microV (CI: 2-91, P = .40), and PS: 16 microV (CI: 3-30, P = .15). PEAKST difference at peak was for EASI: 49 microV (CI: 19-220, P = .02), GEN: 48 microV (CI: -43-154, P = .26), and PS: 20 microV (CI: -51-32, P = .65). CONCLUSION: Simultaneous direct comparison of three derived ECG methods shows overall and regional differences in accuracy across PS, GEN, and EASI. Median SUMST and PEAKST differences for PS are lower than for GEN and EASI, and show a more accurate reconstruction.

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.

Reconstruction of the 12-lead electrocardiogram from reduced lead sets.

In clinical practice, continuous recording of all leads of the 12-lead electrocardiogram (ECG) is often not possible. We wanted to assess how well absent, noisy, or defective leads can be reconstructed from different lead subsets and how well lead reconstruction performs over time. A data set of 234 24-hour ECG recordings was divided into an equally sized training and test set. Precordial leads were systematically removed, and for all lead subsets including both limb leads and at least one precordial lead, the absent leads were reconstructed using general and patient-specific reconstruction templates. Reconstruction performance was measured by correlation between the original and reconstructed leads over the QRS and T waves, by average and maximum absolute ST differences, and by agreement when a clinical decision rule was applied. Reconstruction performance over time was evaluated at baseline, at 20 minutes, and 1, 6, 12 and 24 hours after the start of each recording. Reconstruction accuracy was high (correlation > or =0.932, average ST difference < or =30 microV, agreement > or =94.9%) with general reconstruction for lead sets with 1 or 2 precordial leads removed but was less satisfactory when more leads were missing. Patient-specific reconstruction performed well when up to 4 precordial leads were removed (correlation > or =0.967, average ST difference < or =26 microV, agreement > or =95.7%). Patient-specific reconstruction performance initially slightly decreased and then stabilized over time but remained much better than general reconstruction after 24 hours. Accurate reconstruction of the 12-lead ECG from lead subsets is possible over time. General reconstruction allows reconstruction of 1 or 2 precordial leads, whereas up to 4 leads can be reconstructed well using patient-specific reconstruction.