Monica C. Weisberg

A computer protocol to predict myocardial infarction in emergency department patients with chest pain.

To achieve more appropriate triage to the coronary care unit of patients presenting with acute chest pain, we used clinical data on 1379 patients at two hospitals to construct a simple computer protocol to predict the presence of myocardial infarction. When we tested this protocol prospectively in 4770 patients at two university hospitals and four community hospitals, the computer-derived protocol had a significantly higher specificity (74 vs. 71 percent) in predicting the absence of infarction than physicians deciding whether to admit patients to the coronary care unit, and it had a similar sensitivity in detecting the presence of infarction (88.0 vs. 87.8 percent). Decisions based solely on the computer protocol would have reduced the admission of patients without infarction to the coronary care unit by 11.5 percent without adversely affecting the admission of patients in whom emergent complications developed that required intensive care. Although this protocol should not be used to override careful clinical judgment in individual cases, the computer protocol for the most part yields accurate estimates of the probability of myocardial infarction. Decisions about admission to the coronary care unit based on the protocol would have been as effective as those actually made by the unaided physicians who cared for the patients, and less costly. Whether physicians who are aided by the protocol perform better than unaided physicians cannot be determined without further study.

Clinical characteristics and natural history of patients with acute myocardial infarction sent home from the emergency room

In a prospective multicenter investigation of emergency room patients with acute chest pain, physicians admitted 96% of patients with acute myocardial infarction (AMI) and discharged 4%. Of 35 patients who were sent home with AMI, only 11 (31%) returned to the same hospital because of persistent symptoms. Compared with a control group of 105 randomly selected patients with AMI who were admitted from the emergency room, patients in whom AMI was missed were significantly younger, had less typical symptoms and were less likely to to have had prior AMI or angina or to have electrocardiographic evidence of ischemia or infarction not known to be old. Despite the less typical presentations of patients in whom AMI was missed, after controlling for age and sex, the short-term mortality rate was significantly higher among patients in whom AMI was missed but in whom it was detected through our follow-up procedures than in admitted AMI patients. As determined by independent reviewers, 49% of the missed AMIs could have been diagnosed through improved electrocardiographic reading skills or by admission of patients with recognized ischemic pain at rest or ischemic electrocardiographic changes not known to be old.

The Value of the Autopsy in Three Medical Eras

To determine whether advances in diagnostic procedures have reduced the value of autopsies, we analyzed 100 randomly selected autopsies from each of the academic years 1960, 1970, and 1980 at one university teaching hospital. In all three eras about 10 per cent of the autopsies revealed a major diagnosis that, if known before death, might have led to a change in therapy and prolonged survival; another 12 per cent showed a clinically missed major diagnosis for which treatment would not have been changed. Among 1980 autopsies, renal disease and pulmonary embolus were less common causes of death than before, but systemic bacterial, viral, and fungal infections increased significantly and were missed clinically 24 per cent of the time. The introduction of radionuclide scans, ultrasound, and computerized tomography as diagnostic procedures did not reduce the use of conventional tests in patients who subsequently died and were studied by autopsy. Over-reliance on these new procedures occasionally contributed directly to missed major diagnoses. We conclude that advances in diagnostic technology have not reduced the value of the autopsy, and that a goal-directed autopsy remains a vital component in the assurance of good medical care.

Correlation between Preoperative Ischemia and Major Cardiac Events after Peripheral Vascular Surgery

Patients who undergo peripheral vascular surgery are at increased risk for postoperative cardiac events and are difficult to assess preoperatively because of limitations on their activity. We prospectively studied 176 consecutive eligible patients undergoing elective vascular surgery to determine the value in predicting a postoperative cardiac event of preoperative electrocardiographic monitoring to detect myocardial ischemia. Of the 176 patients, 32 (18 percent) had 75 episodes of monitored ischemic ST-segment depression preoperatively (of which 73 were asymptomatic), and 13 (7 percent) met strict criteria for major postoperative cardiac events, including 1 with a fatal myocardial infarction, 3 with nonfatal infarctions, 4 with unstable angina, and 5 with ischemic pulmonary edema. Of the 32 patients with ischemia before their operations, 12 had postoperative events (univariate relative risk, 54; 95 percent confidence interval, 7.2 to 400). Only 1 postoperative event occurred among 144 patients who did not have preoperative ischemia. The sensitivity of preoperative ischemia was 92 percent, the specificity 88 percent, the predictive value of a positive result 38 percent, and the predictive value of a negative result 99 percent. In multivariate analyses, preoperative ischemia was the most significant correlate of postoperative cardiac events and remained a statistically significant independent correlate even after we had controlled for all other preoperative factors (multivariate relative risk, 24.4; 95 percent confidence interval, 6.8 to 88). These preliminary data suggest that preoperative electrocardiographic monitoring to detect episodes of myocardial ischemia is a useful method for assessing cardiac risk in patients who undergo elective vascular surgery. In particular, the absence of ischemia during monitoring indicates a very low risk.

Identification and preliminary validation of predictors of major bleeding in hospitalized patients starting anticoagulant therapy

Among 617 hospitalized patients who started long-term anticoagulant therapy, major bleeding developed before discharge in 28 (5 percent) and minor bleeding in another 38 (6 percent), with daily incidence rates of 0.4 and 0.5 percent, respectively. The most common site of bleeding was gastrointestinal, and one patient died from bleeding. Four independent risk factors for major in-hospital bleeding were identified and weighted using multivariate discriminant analysis in a randomly chosen group of 411 patients: co-morbid conditions other than the indication for anticoagulant therapy (specific signs of heart, liver, or kidney dysfunction, cancer, and severe anemia); the use of heparin to begin therapy in patients age 60 years or older; the intensity of therapy (measured by the maximal prothrombin time or partial thromboplastin time); and liver dysfunction that worsened during treatment. These findings were validated in an independent testing group of 206 patients; the risk factors identified 151 patients at low (1 percent) risk of major bleeding, 33 at moderate (6 percent) risk, and 22 at high (23 percent) risk. The accuracy and clinical impact of this prediction rule should be evaluated further in other hospitals.

Clinical Characteristics and Outcome of Acute Myocardial Infarction in Patients with Initially Normal or Nonspecific Electrocardiograms (A Report from the Multicenter Chest Pain Study)

To determine the prevalence and characteristics of acute myocardial infarction (AMI) patients who present to emergency departments with normal or nonspecific electrocardiograms (ECGs), data were analyzed from 7,115 consecutive patients in the Multicenter Chest Pain Study. AMI patients with normal or nonspecific initial ECGs (n = 107) were less likely to have a past history of coronary artery disease or to be diaphoretic on presentation (p less than 0.01) than AMI patients with initial ECGs highly suggestive of AMI (n = 811). The overall probability of AMI among patients with chest pain and initially normal or nonspecific ECGs was 3%, but ranged from less than 1 to 17% depending on the patients age and sex and whether the patient had pressure-type pain or pain radiating to the shoulder, neck or arms. Among initially admitted patients, the time elapsed between onset of pain and presentation was similar in both groups. However, the time between onset of pain and definitive diagnosis of AMI by enzymes or clinical course was longer in patients with initially normal or nonspecific electrocardiograms (8.3 vs 7.5 hours, p less than 0.05), their peak creatine kinase levels were lower (mean 643 vs 1,032 mg/dl, p less than 0.001) and their mortality was slightly lower (6 vs 12%, p = 0.10). These findings suggest that AMI patients with initially normal or nonspecific ECGs may have a less severe short-term clinical outcome.

Sensitivity of routine clinical criteria for diagnosing myocardial infarction within 24 hours of hospitalization.

Myocardial infarction was diagnosed in 431 (30%) of 1460 patients with acute chest pain who had serial enzyme testing after admission to intensive or intermediate care units at three teaching and three community hospitals. The diagnosis was made within 12 hours of admission in 331 (77%) patients and within 24 hours in 415 (96%). Of the 16 patients with myocardial infarction who did not have enzyme abnormalities within 24 hours, 9 (56%) had recurrent ischemic pain during this 24-hour period. Of 451 patients who had neither enzyme abnormalities nor recurrent ischemic pain in the first 24 hours, only 7 (2%) ultimately met diagnostic criteria for myocardial infarction. These findings were prospectively validated in an independent testing set of 275 patients with myocardial infarction, 271 (99%) of whom either met diagnostic criteria for myocardial infarction or had recurrent ischemic pain within 24 hours of admission. These data suggest that 24 hours is nearly always a sufficient period to exclude myocardial infarction in patients without recurrent chest pain.

Candidates for Thrombolysis among Emergency Room Patients with Acute Chest Pain: Potential True- and False-Positive Rates

STUDY OBJECTIVE To assess the potential clinical impact of thrombolytic therapy for acute myocardial infarction by determining true-positive and false-positive rates of criteria for eligibility among emergency room patients with acute chest pain. DESIGN Prospective multicenter cohort study. SETTING Emergency rooms of three university and four community hospitals. PATIENTS Emergency room patients (7734) with acute chest pain. MEASUREMENTS AND MAIN RESULTS Only 261 (23%) of 1118 patients with acute myocardial infarctions were 75 years of age or younger, presented within 4 hours of the onset of pain, and had emergency room electrocardiograms showing probable acute myocardial infarction: 60 (0.9%) of the 6616 patients without infarction also met these criteria (positive predictive value, 261/321 = 81%; CI, 77% to 86%). The positive predictive value could increase to about 88% (CI, 82% to 93%) if eligibility were based on the official hospital electrocardiogram reading. CONCLUSIONS Because experience from published studies suggests that about one third of patients who meet these three eligibility criteria have other contraindications to thrombolysis, we estimate that about 15% of patients with acute myocardial infarction would meet the criteria for eligibility for thrombolysis that have been used in clinical trials at the time of emergency room presentation. Further, for every eight patients with true-positive results who are treated, one to two patients with false-positive results may also be treated if decisions are based on the interpretation of a single electrocardiogram.

The effect of gender on the probability of myocardial infarction among emergency department patients with acute chest pain: a report from the Multicenter Chest Pain Study Group.

Objective: To identify differences in the incidences of myocardial infarction in women and men with chest pain.Design: Prospective multicenter cohort study.Setting: Emergency rooms of three university and four community bospitals.Patients: 7,734 emergency room patients with acute chest pain.Measurements and main results: Myocardial infarction was diagnosed in 10% of the 3,896 women, compared with 19% of the 3,838 men, yielding an age-adjusted relative risk of myocardial infarction for women of 0.54 (95% confidence interval 0.48, 0.60). Physicians were equally adept at admitting women and men with myocardial infarctions, but men without myocardial infarction or unstable angina were significantly more likely to be admitted than were women without these diagnoses. Most clinical and electrocardiographic features indicating a risk of myocardial infarction were present in both women and men, but several high-risk features were less commonly present in women. After adjusting for the other factors that correlate with each patient’s probability of having acute myocardial infarction, the relative risk of myocardial infarction was the same in women as men when the emergency department electrocardiogram showed the classic changes associated with acute myocardial infarction, but the risk was 40% lower in women when such electrocardiographic changes were not present.Conclusions: Clinical features that predict myocardial infarction in men predict myocardial infarction in women to a similar extent. However, female gender is associated with about a 40% lower rate of myocardial infarction except when classic electrocardiographic evidence is present on the emergency department electrocardiogram.

Outcome of patients who were admitted to a new short-stay unit to “rule-out” myocardial infarction☆

For emergency room patients with a low probability of acute myocardial infarction, we established a new short-stay coronary observation unit, a 2-bed nonintensive care unit with telemetry monitoring adjacent to the emergency room. Of 512 consecutive admissions to the coronary observation unit, 425 (83%) were discharged home without evidence of acute myocardial infarction or serious complications (mean length of stay, 1.2 days; median length of stay, 1 day); 87 (17%) were transferred to other hospital beds. The rate of acute myocardial infarction was 3%. No deaths and only 1 serious complication occurred in the coronary observation unit. At 6 month follow-up, the cardiac survival rate was 99% for patients sent home directly from this unit. It is concluded that the coronary observation unit is safe and adequate for ruling out acute myocardial infarction in a defined subset of patients. Short-stay units, however, encourage early discharges which, when premature, may miss patients who are at risk of having complications shortly thereafter. Strategies such as mandatory but expeditious predischarge stress testing to encourage early but not premature discharge may augment the efficiency of coronary observation units.