A predictive instrument to improve coronary-care-unit admission practices in acute ischemic heart disease. A prospective multicenter clinical trial.

Each year 1.5 million patients are admitted to coronary-care units (CCUs) for suspected acute ischemic heart disease; for half of these, the diagnosis is ultimately "ruled out." In this study, conducted in the emergency rooms of six New England hospitals ranging in type from urban teaching centers to rural nonteaching hospitals, we sought to develop a diagnostic aid to help emergency room physicians reduce the number of their CCU admissions of patients without acute cardiac ischemia. From data on 2801 patients, we developed a predictive instrument for use in a hand-held programmable calculator, which requires only 20 seconds to compute a patient's probability of having acute cardiac ischemia. In a prospective trial that included 2320 patients in the six hospitals, physicians' diagnostic specificity for acute ischemia increased when the probability value determined by the instrument was made available to them. Rates of false-positive diagnosis decreased without any increase in rates of false-negative diagnosis. Among study patients with a final diagnosis of "not acute ischemia," the number of CCU admissions decreased 30 per cent, without any increase in missed diagnoses of ischemia. The proportion of CCU admissions that represented patients without acute ischemia dropped from 44 to 33 per cent. Widespread use of this predictive instrument could reduce the number of CCU admissions in this country by more than 250,000 per year.

Cardiac nuclear imaging. Adoption of an evolving technology.

A national survey was conducted to examine the extent of adoption and use of nuclear imaging procedures in cardiology in hospitals by 1979 and to develop estimates for 1983. The data are based on the responses of 171 hospitals from a representative 200-hospital sample stratified for region, bed-size, and teaching status. Extrapolating the data, it is estimated that 2,106 hospitals nationally use cardiac nuclear imaging. In 1979, hospitals with at least 200 beds performed an estimated 396,000 cardiac nuclear imaging studies at a cost of $93 million. By 1983, it is estimated that 4,061 hospitals had the capability to perform cardiac nuclear imaging and that national expenditures would exceed $200 million ( noninflated dollars). Although cardiac nuclear imaging procedures have been demonstrated to be valuable in detecting coronary artery disease or measuring ventricular function, these procedures were rapidly being adopted by the medical community at a time when only limited information about their effectiveness and efficiency are available.

An aid for diagnosing acute ischemic heart disease in the emergency room.

A five-year study was undertaken to develop a valid mathematical model that could aid in diagnosing acute ischemic heart disease in the emergency room, thus reducing inappropriate admissions to the coronary care unit. The study was divided into two substudies. In the first, variables significantly predictive of ischemic heart disease were identified and a logistic function was developed and tested. In the second, a six-hospital study, the variables of the first substudy were validated and a final logistic regression was developed and tested prospectively. This model's availability proved to be successful in improving diagnostic accuracy and specificity and in reducing false positive predictive rates and admissions to coronary care units.

The logistic function as an aid in the detection of acute coronary disease in emergency patients (a case study).

We empirically developed a logistic function to predict acute coronary heart disease (ACHD) and then tested it to determine its usefulness to emergency room physicians in diagnosis and admission of patients with suspected ACHD to the coronary care unit. The function was based on nine clinical, historical and electrocardiographic variables from a set of 105 variables collected on 643 patients with suspected ACHD. In the second phase of the study, we provide the probabilities generated by the function to emergency room physicians during alternate months as a supplement to existing diagnostic modalities. Use of the probability of ACHD (401 patients with probabilities versus 455 patients without probabilities) resulted in statistically significant improvement in diagnostic rates and reduction in the number of inappropriate admissions to the coronary care unit.

Differential effects of experience on house officers' admission diagnoses for patients with possible myocardial infarction.

The effect of the level of training on house staff's abilities to accurately diagnose acute ischemic heart disease (AIHD) and admit patients presenting in an emergency room was assessed. A validated mathematical instrument, which calculates patients' probabilities of AIHD, was used to retrospectively stratify admitted patients. Sensitivity rates of house staff were similar for patients with high probabilities (greater than or equal to 40%) of AIHD (ns). When probabilities of AIHD were low (less than 40%), junior residents correctly admitted a significantly higher proportion of patients with confirmed AIHD than did interns (86% versus 63%, respectively; p less than 0.06). Specificity was unaffected by the level of house staff training for patients with probabilities of AIHD less than 40% (ns). In the high probability group of patients, the interns' specificity rate (54%) was significantly better than the 20% for junior residents (p less than 0.03); however, when clinical severity was controlled for, no differences by level of training were found.

An analytic method for the evaluation of rural Emergency Medical Service development.

An analytic method is presented for assessing the marginal impact of incremental changes in rural Emergency Medical Services (EMS) on cardiac mortality, morbidity, EMS system process and performance, and health care system utilization. The method incorporates a model of the EMS system. This model specifies five sets of interactive variables characterizing EMS system development and effectiveness. The analytic method quantifies the contribution of each of these sets of interactive variables on the outcome variables (cardiac mortality, morbidity, EMS process/performance, and health care system utilization) for three target populations: those who utilize the EMS system, all hospitalized patients with acute ischemic heart disease independent of EMS system use, and the population of all patients dying from acute ischemic heart disease on a communitywide basis. By including in the model those factors unique to rural areas, such as scarcity of fiscal and health care system resources, geographical constraints, and the skewed severity of case mix due to the clinical and socioeconomic conditions found among rural patients, the analytic method is able to quantify and help explain the impact of these factors on the EMS system and the limitations which they impose. The analytic method affords planners and administrators and rational basis for decisions regarding future rural EMS system development through its identification of those system characteristics amenable to change and worth pursuing from a health policy perspective.

Effectiveness of a prehospital medical control system: an analysis of the interaction between emergency room physician and paramedic.

Medical control for paramedics by means of radio and ECG telemetry is costly, time consuming, and of unproved value. We assessed the interaction between emergency room physicians and paramedics during ambulance transport of "seriously ill" cardiac patients (cardiac arrest, acute myocardial infarction, or new onset of crescendo angina pectoris) with paramedics in service. Thirty-five percent of all arrhythmias and 35% of potentially life-threatening arrhythmias were misclassified. Correct treatment was rendered in 74% of the cases, although only 65% were correctly diagnosed (p < 0.01). The principal predictive variable for misdiagnosing or incorrectly treating a patient was the presence of a potentially life-threatening arrhythmia, precisely the condition for which medical control and the paramedic system has the most to offer. Only 39% of patients with life-threatening arrhythmias were correctly diagnosed and correctly treated, whereas 64% of patients without life-threatening arrhythmias were correctly diagnosed and correctly treated (p < 0.001). Mortality reflected correct diagnosis and treatment. In-hospital and overall mortalities were 12% and 33%, respectively, for patients who were correctly diagnosed and treated (p < 0.06), compared with 20% and 43%, respectively, for patients who were incorrectly diagnosed or incorrectly treated (p < 0.04). More rigorous medical control is needed to improve the quality of patient care and outcome and to further integrate the advanced life support program into the health care system.

The usefulness of a predictive instrument to reduce inappropriate admissions to the coronary care unit.

A mathematical instrument was developed to supplement the diagnostic information available to physicians in the emergency room to improve physicians' diagnostic accuracy in managing patients with acute ischemic heart disease and thereby reduce inappropriate coronary care unit admissions. The instrument was empirically derived and is based on nine clinical, historical, and electrocardiographic predictive variables. Probabilities of acute ischemic heart disease generated by the instrument were given to the house staff in an emergency room during alternate months. Comparison of the control months (455 patients) with the experimental months (401 patients) showed the following: The overall diagnostic accuracy increased from 83% to 91% (P less than 0.005), the overdiagnostic accuracy increased from 51% to 33% (P less than 0.01), and the admission rate to the coronary care unit fell from 26% to 14% (P less than 0.001), while the inappropriate discharge rate from the emergency room did not change, 3% versus 3% (not significant).

Implications of alternative sampling strategies for emergency medical service evaluation.

Evaluations of emergency medical service (EMS) programs have been ambiguous, due in part, to problems of sample definition. Four different sampling strategies were studied: 1) all patients in cardiac arrest; 2) patients with a final diagnosis of myocardial infarction (MI); 3) patients with an emergency room diagnosis of "rule out MI"; and 4) patients identified by the ambulance team as a possible MI. Using a regional data base of all ambulance runs, we created study samples based on each of these strategies and measured the error that may be introduced as a result of sample selection. Bias was measured along three parameters of EMS system performance: 1) observed incidence of MI in the ambulance system; 2) condition recognition--the ability of the ambulance team to correctly identify acute cardiac patients; and 3) emergency room and hospital mortality rates. The emergency room diagnosis strategy systematically excludes all false-positives, while samples based on the ambulance team's assessment omit all false-negatives. The final diagnosis strategy yields significant underestimates of cardiac mortality. Samples restricted to cardiac arrests result in biased estimates of both the incidence of MI and the number of deaths.

Ambulance utilization by patients with acute myocardial infarction.

Fifty-five per cent (73/133) of myocardial infarction (MI) patients on Cape Cod during a three-month period reached the hospital by ambulance. the 45 per cent (60/133) not using ambulances were compared to users to identify a subpopulation to which public health programs might be directed to increase appropriate use of cardiac ambulances. Univariate analyses showed a distnce of more than ten miles from the hospital, and a prior history of MI distinguished ambulance users from non-users. Demographic/economic status, delay in seeking care, presenting symptoms, Killip class, and in-hospital mortality rates were not signigicantly different. Step-wise discriminant analysis identified four predictive variables in rank order: distance from the hospital, past history of MI, symptoms of fainting, and negative history for hypertension which correctly classified 72 per cent of our population with respect to ambulance utilization.

An assessment of emergency medical technicians' performance as related to seasonal population influx.

The periodic influx of large numbers of people into resort areas substantially increases the use of emergency medical services. This investigation assesses the effects of such a threefold increase in the summer population of the Cape Cod area upon the accuracy of emergency medical technicians' diagnoses and treatments. The technicians' diagnoses for ambulance patients were evaluated against those given by the emergency room physicians during the months of August 1975 and February 1976. The distribution of conditions was similar for both months and the observed frequency of correct diagnoses for common conditions was more than 90% in both months. The overdiagnosis rate of 25% to 50% for common conditions and the correct treatment rate for suspected myocardial infarction of 65% did not vary significantly between summer and winter. Thus, a large influx in population does not seem to affect adversely EMT diagnosis rates. Although misdiagnoses were uncommon, a failure to follow through with a correct treatment for patients with suspected myocardial infarctions, thus indicating the need for better quality control on EMT performance.

Prognostic efficacy of early clinical categorization of myocardial infarction patients.

To assess the prognostic validity of "low risk" classification at 24-36 hours as the basis for early transfer to an intermediate coronary care unit, Killip and Hutter/Sidel criteria for risk classicication were applied to 410 patients with acute myocardial infarction (MI) and prospectively compared with respect to mortality and morbidity. Six percent of "low risk" patients by the Killip classification subsequently died and were therefore misclassified. No patients in the group classified as "low risk" by the Hutter/Sidel criteria died; however, more than two and a half times as many potentially "low risk" patients were excluded from this group. With respect to morbidity, 35 of 87 patients (40%) classified as "low risk" by Hutter/Sidel criteria developed 43 major complications during their hospitalization. Nine of these patients developed 11 of the 43 complications (26%) on day six or later, and for five of these patients, this was their first major complication during hospitalization. This significant incidence of morbidity in "low risk" patients, despite their low mortality rates as a group, must be taken into account in developing intermediate coronary care units.

A nurse rehabilitator's impact on patients with myocardial infarction.

A nurse rehabilitator, supplementing routine physician/nursing coronary care unit (CCU) care, was found to be effective in increasing the return to work rate (p less than .05) and decreasing smoking (p less than .05) in a randomized trial of 102 patients with acute myocardial infarction (MI). These outcomes were thought to be due to the nurse rehabilitator's efforts in increasing patient knowledge of heart disease (p less than .01) and individual counseling.

Studies of ambulance patients with ischemic heart disease. 1. The outcome of pre-hospital life-threatening arrhythmias in patients receiving electrocardiographic telemetry and therapeutic interventions.

Patient delay in seeking medical assistance for acute ischemic heart disease and the incidence of potentially life-threatening arrhythmias en route to the hospital were examined in a 22-month community trial of ambulance telemetry. Of 7,654 patients transported, 179 who had electrocardiograms (ECGS) transmitted were found to have had acute MIs or acute myocardial ischemic events. Fifty per cent of these patients summoned an ambulance within 30 minutes and 72 per cent within two hours after the onset of acute symptoms. Fifty-eight patients had potentially life-threatening arrhythmias. Interventions with drugs and/or defibrillation was required in 22 patients with or without cardiopulmonary resuscitation (CPR); intervention with CPR alone was required in six patients. Twelve of these 28 patients survived through hospital admission and six were alive at three months. The relatively low outcome/input ratio of this experience necessitates re-evaluation of the epidemiological characteristics and patient selection criteria in populations considered for telemetry.

Studies of ambulance patients with ischemic heart disease. 11. Selection of patients for ambulance telemetry.

One hundred eighty-two of 1,928 patients (9.4 per cent) transported by ambulance during a six-month period in Baltimore had ECGs transmitted. Review of the remaining 1,746 records by two cardiologists indicated that an additional 113 patients should have had their ECGs transmitted because of life-threatening conditions. Of patients with acute ischemic heart disease, 47 had ECG monitoring and 24 did not. There were 22 per cent more Killip 111/1V patients with a 19 per cent higher mortality at three months among the "non-transmitted" patients as compared to the "transmitted" patients, controlling for all other relevant variables. Critical presentations inappropriately affect ambulance staffs' selection of patients for monitoring.