Alan S. Berson

Utility of current risk stratification tests for predicting major arrhythmic events after myocardial infarction

OBJECTIVESnWe surveyed the literature to estimate prediction values for five common tests for risk of major arrhythmic events (MAEs) after myocardial infarction. We then determined feasibility of a staged risk stratification using combinations of noninvasive tests, reserving an electrophysiologic study (EPS) as the final test.nnnBACKGROUNDnImproved approaches are needed for identifying those patients at highest risk for subsequent MAE and candidates for implantable cardioverter-defibrillators.nnnMETHODSnWe located 44 reports for which values of MAE incidence and predictive accuracy could be inferred: signal-averaged electrocardiography; heart rate variability; severe ventricular arrhythmia on ambulatory electrocardiography; left ventricular ejection fraction; and EPS. A meta-analysis of reports used receiver-operating characteristic curves to estimate mean values for sensitivity and specificity for each test and 95% confidence limits. We then simulated a clinical situation in which risk was estimated by combining tests in three stages.nnnRESULTSnTest sensitivities ranged from 42.8% to 62.4%; specificities from 77.4% to 85.8%. A three-stage stratification yielded a low-risk group (80.0% with a two-year MAE risk of 2.9%), a high-risk group (11.8% with a 41.4% risk) and an unstratified group (8.2% with an 8.9% risk equivalent to a two-year incidence of 7.9%).nnnCONCLUSIONSnSensitivities and specificities for the five tests were relatively similar. No one test was satisfactory alone for predicting risk. Combinations of tests in stages allowed us to stratify 91.8% of patients as either high-risk or low-risk. These data suggest that a large prospective study to develop a robust prediction model is feasible and desirable.

Clinical application of a second generation electrocardiographic computer program

An electrocardiographic computer program based on multivariate analysis of orthogonal leads (Frank) was applied to records transmitted daily by telephone from the Veterans Administration Hospital, West Roxbury, Mass., to the Veterans Administration Hospital, Washington, D. C. A Bayesian classification procedure was used to compute probabilities for all diagnostic categories that might be encountered in a given record. Computer results were compared with interpretations of conventional 12 lead tracings. Of 1,663 records transmitted, 1,192 were selected for the study because the clinical diagnosis in these cases could be firmly established on the basis of independent, nonelectrocardiographic information. Twenty-one percent of the records were obtained from patients without evidence of cardiac disease and 79 percent from patients with various cardiovascular illnesses. Diagnostic electrocardiographic classifications were considered correct when in agreement with documented clinical diagnoses. Of the total sample of 1,192 recordings, 86 percent were classified correctly by computer as compared with 68 percent by conventional 12 lead electrocardiographic analysis. Improvement in diagnostic recognition by computer was most striking in patients with hypertensive cardiovascular disease or chronic obstructive lung disease. The multivariate classification scheme functioned most efficiently when a problem-oriented approach to diagnosis was simulated. This was accomplished by a simple method of adjusting prior probabilities according to the diagnostic problem under consideration.

Panoramic display of the orderly sequenced 12-lead ECG

The standard 12-lead electrocardiogram (ECG) has been developed over many years. The ECG has had a long and successful history of providing diagnostic information in clinical medicine. Cardiac arrhythmias have been elucidated by deductive reasoning from continuous ECG recordings with confirmation from electrophysiologic studies. Recently, there has been renewed interest in the morphology of the QRS complex, ST-segment, and T wave, which raises the important question of considering whether the usual method of display provides maximal diagnostic capabilities. The conventional display provides a logical visualization of precordial lead recordings representing the horizontal plane, but does not provide a logical visualization of the limb lead recordings representing the frontal plane. Many clinical problems require the consideration of serial ECGs necessitating the comparison of separate pages. An alternate format presenting serial recordings on a single page would be advantageous. Some automated ECG analysis systems already include the capability for multiple display formats, but these have not yet been widely used in clinical practice. This point of view paper introduces a new display format for the standard 12-lead ECG that includes: (1) a presentation of an orderly sequence of leads to facilitate scanning through different points in space and (2) a presentation of recordings of 12-lead sequences to facilitate scanning through different points in time. This display format could either replace or supplement the conventional ECG format.

Instrumentation and practice standards for electrocardiographic monitoring in special care units. A report for health professionals by a Task Force of the Council on Clinical Cardiology, American Heart Association.

The proposed recommendations for continuous electrocardiographic monitoring systems represent goals for future development. Description of a technique in the report does not constitute an endorsement of its clinical use. Lead systems for ECG monitoring must adequately sense the cardiac electrical field and the leads should be standardized. Future monitors should be capable of simultaneously displaying and analyzing multiple leads. Recommendations for electrode placement and position of patient are made. Important parameters in each category of standards for instrumentation published in 1983 in the American National Standard for Cardiac Monitors, Heart Rate Meters, and Alarms are listed. Selected procedures proposed by the Association for the Advancement of Medical Instrumentation to inform users of minimally acceptable accuracy of computerized systems in a standardized manner are presented. Emphasis is placed on the importance of nursing and medical staff capabilities. Personnel qualifications and training as well as systems to assure and maintain quality of immediate ECG diagnosis are highlighted.

Long-term mechanical circulatory support system reliability recommendation: American Society for Artificial Internal Organs and The Society of Thoracic Surgeons: Long-term mechanical circulatory support system reliability recommendation

Jointly developed by members of the American Society for Artificial Internal Organs and the Society of Thoracic Surgeons along with staff from the Food and Drug Administration, the National Heart, Lung and Blood Institute and other experts, this recommendation describes the reliability considerations and goals for Investigational Device Exemption and Premarket Approval submissions for long-term, mechanical circulatory support systems. The recommendation includes a definition of system failure, a discussion of an appropriate reliability model, a suggested in vitro reliability test plan, reliability considerations for animal implantation tests, in vitro and animal in vivo performance goals, the qualification of design changes during the Investigational Device Exemption clinical trial, the development of a Failure Modes Effects and Criticality Analysis, and the reliability information for surgeons and patient candidates. The document will be periodically reviewed to assess its timeliness and appropriateness within five years.

Recommendations for Safe Current Limits for Electrocardiographs A Statement for Healthcare Professionals From the Committee on Electrocardiography, American Heart Association

The release of a revised American National Standard1 that permits an increase in current limits purported to be safe makes it urgent that the American Heart Association review its recommendations regarding safety and electrical shock hazards for electrocardiographs. These recommendations cover two aspects of electrical safety. The first is the level of current allowable in any patient-connected lead that may flow through the myocardium without inducing ventricular fibrillation. The second is the allowable chassis leakage current that may flow from the electrocardiograph to ground, passing through patient or operator. These recommendations for safe current limits reaffirm the levels of allowable current established for patient-connected leads and revise the amount of allowable chassis leakage current established in previous AHA recommendations. nnRecommendation : The electrocardiographic (ECG) or vectorcardiographic apparatus shall be designed so that no more than 10 μA root mean square, from direct current to the tenth harmonic of power line frequency, shall flow through any patient-connected lead under either normal or single-fault conditions. nnJustification : In 1972 the AHA, in an amendment to its 1967 report,2 recommended an upper limit of 10 μA for current between any patient electrode and either power line ground or the accessible part of the electrocardiograph. The concept of a single fault was introduced to define the occasional failure of one component of the ECG equipment, an error in power distribution connections, or a wiring error on the part of the operator. The AHA recommended that the 10 μA limit not be exceeded, even in the presence of a single fault, to address occurrences such as an insulation failure in a line-operated component, an incorrectly wired power line receptacle, a single failure in an electronic circuit, or a disconnected power line ground. The AHA based its 1972 recommendation on the fact that the …

Distortions in infant electrocardiograms caused by inadequate high-frequency response

Frank lead ECGs from infants were studied for frequency content by introducing low-pass filters of 50, 75, 100, and 150 150 Hz bandwidths before obtaining computer measurements. Results indicated that a minimum bandwidth of 100 Hz is required to avoid amplitude error of 10 per cent or greater. This bandwidth requierement is essentially the same as that required for adult ECGs despite the fact that infant QRS durations are usually about half those of adults. Although the average infant ECG spectrum is likely to contain higher frequencies than the average adult ECG spectrum, duration values for Q, R, and S waves overlap in these populations to such an extent that bandwidth requirements are practically identical.

Differences caused by changes in electrode positions in two corrected orthogonal lead systems

Summary Frank and McFee corrected orthogonal lead systems were compared for electrode displacement errors on 10 normal and 12 abnormal (enlarged hearts) individuals. All of the normal and 6 of the abnormal subjects were recorded using both lead systems. Chest and back electrodes were individually and collectively displaced 2.5 centimeters from their correct locations and errors in scalar and vector amplitudes were measured using a digital computer. The McFee lead showed some superiority over the Frank lead for scalar amplitudes when percentage errors were compared but no significant difference between the systems was observed when comparing absolute magnitude of errors. For the Frank lead the normal group performed better than the abnormal group while no such difference occurred for the McFee lead. The Frank lead was most sensitive to longitudinal electrode displacement while the McFee lead was most sensitive to lateral displacement of the left side and anterior chest wall electrodes. For the Frank lead it appears that a level slightly below the 4th interspace was optimum for the majority of subjects.

Differences between supine and sitting Frank-lead electrocardiograms

Frank-lead electrocardiograms (ECGs) were recorded from 59 adult males with suspected coronary artery disease. Three records were recorded consecutively on frequency modulated tape for each patient in (1) supine position, (2) sitting position with arms relaxed, and (3) sitting position on bicycle with arms on bicycle handles. Electrodes were applied at the level of the fifth intercostal space with patients in the sitting position. Computer measurements of electrocardiographic amplitudes were averaged over ten seconds of each record with these results: (1) QRS spatial amplitudes and R amplitudes in lead z were significantly higher and R amplitudes in lead y lower for sitting than for supine positions. (2) Except for slightly higher R and S amplitudes in lead x for sitting with arms on bicycle, no significant differences were observed between the two sitting positions. (3) These postural differences are significantly greater than those resulting from day-to-day variability of electrode locations. It is hypothesized that electrode level shifts with postural changes are responsible for the observed x- and z-lead changes. For the y-lead changes, it is hypothesized that shifting blood volumes with postural changes are the cause. It is concluded that reference electrocardiographic measurements for stress testing should be obtained from resting ECGs with the patient in the same postural position as that maintained during exercise.

NHLBI workshop on the utilization of ECG databases: Preservation and use of existing ECG databases and development of future resources

Baseline examinations and periodic reexaminations in longitudinal population studies, together with ongoing surveillance for morbidity and mortality, provide unique opportunities for seeking ways to enhance the value of the electrocardiogram (ECG) recorded with digital technology as an inexpensive and noninvasive tool for prognosis and diagnosis. Clinicians, epidemiologists, and engineers from industry, government, and academic medical centers gathered at a workshop sponsored by the National Heart, Lung, and Blood Institute (NHLBI) on June 11-12, 1997, to discuss the research potential of ECG databases, their preservation and accession, and standards for recording and storage. Databases considered were those acquired in ongoing and future NHLBI-funded studies and in clinical settings in which the ECG continues to provide valuable information for evaluation and treatment. The accessibility of existing databases, the quality of their data, and the availability of ancillary demographic and clinical information were major themes. Also discussed were appropriate statistical methodologies to be used with these data for developing and testing ECG algorithms. The workshop participants affirmed the value of these databases and urged the establishment of an ECG advisory and review group to (1) resolve technical and proprietary issues for the utilization of currently existing databases; (2) develop standards for recording, storage, and utilization of ECGs in future NHLBI-supported studies; (3) oversee the creation of a national ECG database resource, consisting of an archive of ECG databases from past and ongoing NHLBI-supported studies, and a registry of ECG databases that would eventually include digital ECGs from populations currently underrepresented in the demographic spectrum of the NHLBI databases.