J. H. van Bemmel

QTc Dispersion Predicts Cardiac Mortality in the Elderly The Rotterdam Study

BACKGROUND Increased QTc dispersion has been associated with an increased risk for ventricular arrhythmias and cardiac death in selected patient populations. We examined the association between computerized QTc-dispersion measurements and mortality in a prospective analysis of the population-based Rotterdam Study among men and women aged > or = 55 years. METHODS AND RESULTS QTc dispersion was computed with the use of the Modular ECG Analysis System as the difference between the maximum and minimum QTc intervals in 12 and 8 leads (ie, the 6 precordial leads, the shortest extremity lead, and the median of the 5 other extremity leads). After exclusion of those without a digitally stored ECG, the population consisted of 2358 men and 3454 women. During the 3 to 6.5 years (mean, 4 years) of follow-up, 568 subjects (9.8%) died. The degree of QTc dispersion was categorized into tertiles. Data were analyzed using the Cox proportional hazards model, with adjustment for age. For QTc dispersion in 8 leads, those in the highest tertile relative to the lowest tertile had a twofold risk for cardiac death (hazard ratio, 2.5; 95% confidence interval [CI], 1.6 to 4.0) and sudden cardiac death (hazard ratio, 1.9; 95% CI, 1.0 to 3.7) and a 40% increased risk for total mortality (hazard ratio, 1.4; 95% CI, 1.2 to 1.8). Additional adjustment for potential confounders, including history of myocardial infarction, hypertension, and overall QTc, did not materially change the risk estimates. Hazard ratios for QTc dispersion in 12 leads were comparable to those found for QTc dispersion in 8 leads. CONCLUSIONS QTc dispersion is an important predictor of cardiac mortality in older men and women.

Diagnostic interpretation of electrocardiograms in population-based research : Computer program research physicians, or cardiologists?

We assessed the performance of diagnostic electrocardiogram (ECG) interpretation by the computer program MEANS and by research physicians, compared to cardiologists, in a physician-based study. To establish a strategy for ECG interpretation in health surveys, we also studied the diagnostic capacity of three scenarios: use of the computer program alone (A), computer program and cardiologist (B), and computer program, research physician, and cardiologist (C). A stratified random sample of 381 ECGs was drawn from ECGs collected in the Rotterdam Study (n = 3057), which were interpreted both by a trained research physician using a form for structured clinical evaluation and by MEANS. All ECGs were interpreted independently by two cardiologists; if they disagreed (n = 175) the ECG was judged by a third cardiologist. Five ECG diagnoses were considered: anterior and inferior myocardial infarction (MI), left and right bundle branch block (LBBB and RBBB), and left ventricular hypertrophy (LVH). Overall, sensitivities and specificities of MEANS and the research physicians were high. The sensitivity of MEANS ranged from 73.8% to 92.9% and of the research physician ranged from 71.8% to 96.9%. The specificity of MEANS ranged from 97.5% to 99.8% and of the research physician from 96.3% to 99.6%. To diagnose LVH, LBBB, and RBBB, use of the computer program alone gives satisfactory results. Preferably, all positive findings of anterior and inferior MI by the program should be verified by a cardiologist. We conclude that diagnostic ECG interpretation by computer can be very helpful in population-based research, being at least as good as ECG interpretation by a trained research physician, but much more efficient and therefore less expensive.

Shared care for diabetes: supporting communication between primary and secondary care

OBJECTIVE To assess the effects on information exchange of electronic communication between physicians co-treating diabetic patients. DESIGN Comparison of traditional paper-based communication for reporting and electronic communication. SETTING General practitioners and an internal medicine outpatient clinic of an urban public hospital. SUBJECTS A total of 275 diabetic patients, and the 32 general practitioners and one internal medicine consultant who cared for them. INTERVENTION An electronic communication network, linking up the computer-based patient records of the physicians, thus enabling electronic data interchange. MAIN OUTCOME MEASURES Number of letters sent and received per year by the general practitioners, the number of diabetes-related parameters (e.g. results of laboratory tests) in the patient records, and HBA1C levels. RESULTS INTERVENTION GPs received more messages per year (1.6 per patient) than control GPs (0.5 per patient, P<0.05). Significant higher availability (P<0.05) was achieved for data on HBA1C levels, fructosamine levels, blood pressure measurements, cholesterol levels, triglyceride levels and weight measurements. INTERVENTION patients showed a slight but significant decrease of HBA1C levels in the second semester of 1994 (from 7.0 to 6.8, P = 0.03), control patients also showed a slightly decreased group mean, but this change was not significant (from 6.6 to 6.5, P = 0.52). The magnitudes of these mean differences, however, were not significantly different (intervention group: 0.21; control group: 0.12, P = 0.68). CONCLUSIONS The electronic communication network for exchanging consultation outcomes significantly increased frequency of communication and the availability of data to the general practitioner on diagnostic procedures performed in the hospital, thus providing more complete information about the care that patients are receiving. A large-scale experiment over a longer period of time is needed to assess the effects of improved communication on quality of care.

Reproducibility of computerized ecg measurements and coding in a nonhospitalized elderly population

The standard 12-lead electrocardiogram (ECG) is used in many epidemiologic studies to diagnose and predict cardiovascular disease. In view of this, knowledge about the reproducibility of ECG measurements and coding is essential. Minute-to-minute, day-to-day, and year-to-year variability of ECG measurements, composite scores, and Minnesota Code classification were assessed by use of a computer program, in 101 nonhospitalized elderly men and women. Interval ECG measurements were more reproducible than amplitude measurements. The best reproducibility was found for the overall QTc interval (coefficient of variation 3.1%, 4.0%, and 5.2% for the minute-to-minute, day-to-day, and year-to-year groups, respectively) and the poorest was found for the Cardiac Infarction Injury Score (coefficient of variation 67.1%, 78.5%, and 94.3%, respectively). Minnesota Code discrepancies occurred in 16%, 19%, and 22% of the ECGs in the minute-to-minute, day-to-day, and year-to-year groups, respectively. Reproducibility within specific code categories was much better. Overall, variability tended to increase with time. In the routine setting, electrode positioning had relatively little effect on total variability.

Interpolation of body surface potential maps

The performance of four methods for interpolation of body surface potential maps (BSPMs) for different electrode grid densities was assessed. This study is part of a research project on the influence of the variability of 12-lead electrocardiograms on computer interpretation due to small electrode position changes. Interpolated BSPMs can be used to simulate this variability. The set of BSPMs studied, derived from a 117-electrode grid with relatively many electrodes on the left precordial part of the thorax, consisted of 232 cases without abnormalities, 277 with infarction, and 237 with left ventricular hypertrophy. The interpolation methods used were fast Fourier transforms, Chebyshev polynomials, linear functions, and cubic splines (CS). In the horizontal plane, a reference signal was first interpolated and, thereafter, resampled using 11 different sets of electrodes with the number of electrodes ranging from 18 down to 8. In the vertical direction, five grids with electrodes only on the front of the thorax and nine grids with electrodes on the front and back were examined. As a performance measure for interpolation, mean absolute error (MAE) was used: the absolute differences between the reference signal and the interpolated signal, averaged over the QRS on all maps. All methods showed deteriorating performance for decreasing grid density. In the horizontal direction, CS proved to be slightly superior to other methods for the left precordial electrodes for all but the densest grid (e.g., MAE = 22.8 microV vs MAE > 24.8 microV for a 12-electrode grid). For electrodes not in that area, CS performed the best as well (MAE = 16.1 microV for the same grid), with differences with the other methods being small (MAE > 16.4 microV). In the vertical direction, CS showed the best results on the front, both for the dense nonperiodic (MAE = 19.1 microV vs MAE > 26.6 microV for a 6-electrode grid) and periodic grids (MAE = 25.1 microV vs MAE > 26.6 microV for a 12-electrode grid). Linear functions performed best for sparse nonperiodic grids and sparse periodic grids for electrodes on the back, with the difference with CS for the last case being small. The method CS performed best overall, and is recommended for interpolating BSPMs.

Use of the standard 12-lead ECG to simulate electrode displacements

Placement of the precordial electrodes for recording a 12-lead electrocardiogram (ECG) is subject to variation. Previous research has shown that displacement, especially in the longitudinal direction, can lead to changes in diagnosis. In practice, both the displacement and the effects of displacement on an individual ECG are unknown. To assess this effect for a given ECG, the authors developed a method to simulate ECGs at different displacements using only the recorded ECG. The material consisted of 746 body surface potential maps (BSPMs) containing 232 cases without abnormalities, 277 with myocardial infarction (MI), and 237 with left ventricular hypertrophy. By interpolating BSPMs, ECGs from closely spaced electrode positions could be derived. Taking electrode positioning errors that may be encountered in practice, 40 ECGs at different electrode displacements (displaced ECGs) for each BSPM were derived. Using half of the BSPMs, for each displacement, a transformation matrix that transforms the ECG at the standard 12-lead electrode positions (standard ECG) to the displaced ECG was determined. Using the other half of the BSPMs, each displaced ECG was compared with the ECG yielded by the corresponding transformation matrix (transformed ECG). For each comparison, the differences were assessed between the two sets of ECG signals and between the diagnostic computer classifications of the two sets. Signal differences were expressed as mean absolute amplitude differences over the QRS. Computer interpretation of MI and left ventricular hypertrophy was graded in five levels of certainty (no, consider, possible, probable, definite). For instance, for the largest longitudinal displacement studied of about one intercostal space, the 96th percentile mean absolute amplitude difference over the test set was 204 microV. The percentage of cases showing a change in MI classification of more than two certainty levels was 2.7% for this displacement. When comparing the standard ECG with the displaced ECG, these figures were 434 microV and 8.3%, respectively. It is concluded that ECGs from displaced electrodes can be well simulated by transforming the standard ECG, both for the ECG signal and diagnostic classifications.

Medical Informatics Is Interdisciplinary avant la Lettre

Objective: To discuss the elements of interdisciplinary research and to analyze its contribution to (bio)medical informatics. Method: Commenting on ‘Informatics and Medicine – From Molecules to Populations‘ from K. A. Kuhn et al. in this issue of Methods of Information in Medicine. Referring to examples of successfully established interdisciplinary research. Results and Conclusions: Medical informatics is an interdisciplinary field avant la lettre. Experience with successful interdisciplinary research already exists for many decades: Interdisciplinary research is not a category of research but a consequence of addressing a complex problem in society, involving the collaboration between and methods drawn from multiple disciplines. Because research is people, personal interactions are critical for interdisciplinary research. Collaboration takes extra time to develop, to build consensus and to understand new methodologies, languages, and each other‘s culture. Interdisciplinary research requires leaders with vision and expressive skills. Effective scientific and institutional leadership is critical to the success of interdisciplinary groups. Interdisciplinarity begins in the classroom. Interdisciplinary research cannot be effective without interdisciplinary education. Researchers and teachers should immerse themselves in the culture of other disciplines, learning to explain their work in terms understood by people outside their own discipline. Teams that perform interdisciplinary research should promote collaboration, meet regularly, and recognize that it requires a commitment toward good communication and clear goals. Although much progress is achieved by interdisciplinary research, basic monodisciplinary research is still required to advance the frontiers of scientific knowledge, such as in physics or biology.

Integration and communication for the continuity of cardiac care (I4C)

The project I4C (Integration and Communication for the Continuity of Cardiac Care) is carried out for the advancement of cardiac care, from prevention to follow-up. The goals of I4C are: (1) integrated access to patient data, wherever they are stored; (2) support of evidence-based care; (3) consistent recording of patient data (eg, patient history, electrocardiograms IECGs] or cine-angios) in a multimedia patient record; and (4) a documented reference data set for research. In several clinics, workstations are being installed to serve the four goals. Integration with other information systems in clinical care is realized by encapsulation. A computer-based patient record (ORCA) has been developed to support the collection, consultation, and sharing of patient data. In I4C, ORCA is intended for use in a research setting as well as routine patient care. The functionality of ORCA covers the collection of patient history data in a highly structured manner, the recording of drug prescriptions, an overview of laboratory test results, and viewers for ECGs and angiographic images. At present, structured data entry and consultation is supported in six European languages.

A prototype integrated medical workstation environment

In this paper the requirements, design, and implementation of a prototype integrated medical workstation environment are outlined. The aim of the workstation is to provide user-friendly, task-oriented support for clinicians, based on existing software and data. The prototype project has been started to investigate the technical possibilities of graphical user-interfaces, network technology, client-server approaches, and software encapsulation. Experience with the prototype encouraged discussion on both the limitations and the essential features for an integrated medical workstation.

Common Standards for Quantitative Electrocardiography : The CSE Pilot Study

A four year concerted action project has been started in the European Communities (EC) with the aim of “Common Standards for Quantitative Electrocardiography” (CSE Project). Standards for computer derived ECG measurements are urgently required because more and more quantitative diagnostic ECG criteria are now being derived by ECG computer programs and in view of the existing differences, first of all with respect to time measurements of present computer programs.