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Researchers examine the accuracy of current technology for diagnosing acute cardiac ischemia

The accurate diagnosis and triage of patients with acute cardiac ischemia (ACI, unstable angina and/or heart attack), should increase their survival and reduce unnecessary hospital admissions. Four new studies by the New England Medical Center Evidence-based Practice Center (EPC) are summarized here. The researchers examined the accuracy and clinical effect of current technologies for diagnosing ACI in the emergency department (ED). The EPC's work is supported by the Agency for Healthcare Research and Quality (contract 290-97-0019) and led by Joseph Lau, M.D.

According to the first study, many of the current technologies for diagnosing ACI in the ED remain under-evaluated, especially regarding their clinical effect. The second study shows that out-of-hospital electrocardiography (ECG) is excellent for diagnosing acute myocardial infarction (AMI, heart attack) and very good for diagnosing ACI. According to the third study, echocardiography and nuclear scans with technetium-99m sestamibi imaging appear to have good diagnostic performance for selected low- and moderate-risk patients. In the fourth study, the researchers conclude that biomarkers alone will greatly under-diagnose ACI and are inadequate to make triage decisions in the ED.

Lau, J., Ioannidis, J.P., Balk, E.M., and others (2001, May). "Diagnosing acute cardiac ischemia in the emergency department: A systematic review of the accuracy and clinical effect of current technologies." Annals of Emergency Medicine 37(5), pp. 453-460.

These investigators performed a meta-analysis of selected studies published from 1966 through 1998 on the accuracy and clinical effect of diagnostic technologies for ACI. This revealed that single measurements of biomarkers (proteins or enzymes in the heart muscle, such as troponin 1, creatine(CK)-MB, and myoglobin) of patients arriving at the hospital ED have low sensitivity for AMI, but they do have high specificity. Serial measurements greatly increased the sensitivity for AMI, while maintaining excellent specificity. Diagnostic technologies to evaluate ACI in selected populations, such as ECG, sestamibi myocardial perfusion imaging, and stress ECG (ECG readings while a patient runs on a treadmill) may have very good to excellent sensitivity. However, they have only been studied in small, restricted ED populations.

The Goldman Chest Pain Protocol had good sensitivity (about 90 percent) for AMI but did not result in any differences in hospitalization rate, length of stay, or estimated costs in the single clinical effect study performed. Also, its applicability to patients with unstable angina has not been evaluated. The use of an Acute Cardiac Ischemia-Time-Insensitive Predictive Instrument (ACI-TIPI) led to the appropriate triage of 97 percent of patients with ACI arriving at the ED and reduced unnecessary hospitalizations. Overall, biomarkers were the least costly but had the lowest effectiveness for appropriate triage. ACI-TIPI was the most effective and cost-effective diagnostic technology.

Ioannidis, J.P., Salem, D., Chew, P.W., and Lau, J. (2001, May). "Accuracy and clinical effect of out-of-hospital electrocardiography in the diagnosis of acute cardiac ischemia: A meta-analysis." Annals of Emergency Medicine 37(5), pp. 461-470.

Out-of-hospital ECG enables paramedics to begin thrombolytic (clot-busting) therapy for patients with suspected AMI before they arrive at the hospital. Out-of-hospital ECG has excellent diagnostic performance for AMI and very good performance for ACI, according to this study. Out-of-hospital thrombolysis also saved time from symptom onset to treatment and improved short-term mortality, with a less clear impact on long-term mortality. These findings are based on a meta-analysis of 11 studies involving 7,508 patients.

Five studies showed a pooled diagnostic sensitivity of 76 percent for ACI and a specificity of 88 percent. The respective figures in eight studies for AMI were a sensitivity of 68 percent and specificity of 97 percent. This diagnostic accuracy of out-of-hospital ECG for AMI and ACI was similar to that of the standard ECG, which is the gold standard in the management of patients with chest pain. Both in randomized and nonrandomized studies, out-of-hospital thrombolysis shortened the time from onset of symptoms to thrombolytic treatment by 40 to 60 minutes. Hospital mortality was reduced by 16 percent. There was no clear effect on long-term mortality, but data were sparse.

When combined with thrombolysis, out-of-hospital ECG may save about 45 minutes to 1 hour compared with waiting to give thrombolysis at the hospital. These findings were based on substantial evidence from patient groups with few exclusion criteria. Therefore, the evidence appears to support consideration of an out-of-hospital ECG for all patients with chest pain when first seen by paramedics.

Ioannidis, J.P., Salem, D., Chew, P.W., and Lau, J. (2001, May). "Accuracy of imaging technologies in the diagnosis of acute cardiac ischemia in the emergency department: A meta-analysis." Annals of Emergency Medicine 37(5), pp. 471-477.

Echocardiography and nuclear scans with technetium-99m sestamibi scanning offer two noninvasive options for assessing patients with suspected ACI. Both imaging technologies appear to have very good diagnostic performance for selected low- and moderate-risk patient groups. However, more evidence should be accumulated on their performance in the ED setting, conclude the researchers.

Their findings are based on a meta-analysis of 10 studies of rest echocardiography, 2 studies of dobutamine stress echocardiography, and 6 studies of technetium-99m sestamibi scanning. Patients often were highly selected to represent low- or moderate-risk groups. When limited to ED studies, rest echocardiography showed excellent sensitivity of 93 percent and good specificity of 66 percent. The results were similar when all studies were considered, including reports of patients admitted to the hospital and those sent to the cardiac care unit. There were insufficient studies on stress echocardiography in the ED to properly assess the technology.

Technetium-99m sestamibi scanning also showed excellent sensitivity (92 to 100 percent) and good specificity (49 to 84 percent) for AMI. For ACI, the random-effects pooled sensitivity was 89 percent, and pooled specificity was 77 percent.

Balk, E.M., Ioannidis, J.P., Salem, D., and others (2001, May). "Accuracy of biomarkers to diagnose acute cardiac ischemia in the emergency department: A meta-analysis." Annals of Emergency Medicine 37(5), pp. 478-494.

Biomarkers for ACI that have been studied include creatine kinase (CK) and CK-MB, myoglobin, and troponin I and T, which are heart muscle enzymes or proteins. The limited evidence available to evaluate the diagnostic accuracy of biomarkers for ACI suggests that biomarkers have very low sensitivity to diagnose ACI. Biomarker tests had sensitivities of 16 to 19 percent, and serial biomarker tests had sensitivities of 31 to 45 percent. Thus, many patients with unstable angina would be missed by using biomarkers alone, and biomarkers alone would be inadequate to make triage decisions in the ED.

Individual biochemical markers drawn in the ED had uniformly low test sensitivity for AMI (less than 50 percent) but high specificity (more than 85 percent). Myoglobin testing appeared to have slightly higher sensitivity than the other biomarkers, although few studies had examined the diagnostic performance of troponin testing. Myoglobin testing also had generally higher sensitivity than CK or CK-MB testing for diagnosis of AMI. For AMI diagnosis alone, multiple testing for individual biomarkers over time substantially improved sensitivity, while retaining high specificity, at the expense of additional time.

The researchers conducted a meta-analysis of studies published between 1966 and 1998 on the diagnostic performance of these biomarkers for AMI and ACI. Only four studies evaluated all patients with ACI: 73 focused only on diagnosis of AMI. The researchers conclude that further studies are needed on the clinical effects of using biomarkers for patients with ACI in the ED and on optimal timing of serial testing and in combination with other tests.

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