Limitations of prehospital predictors of acute myocardial infarction and unstable angina

Studies have attempted to define predictive indicators of diagnosis and/or prognosis for acute myocardial infarction (AMI) in the emergency department and to identify the need for hospital admission in patients with chest pain. Because prehospital predictors have not been defined, dispatchers, paramedics, and base station physicians continue to triage based on patient history. We reviewed 401 patients presenting in one year to an urban paramedic system with chest pain, normal vital signs, and stable rhythms to identify predictors of AMI and unstable angina. Thirty-one percent (123) had a diagnosis of AMI, 26% (105) unstable angina, and 43% (173) “other” diagnoses. Two-hundred seventy-eight patients required nitroglycerin administration, 182 required IV morphine, 14 developed arrhythmias requiring lidocaine, and two suffered cardiac arrest in the field. Nine other patients had a cardiac arrest after arrival in the ED. When comparing AMI and unstable angina patients to the “others”, 64% (132) versus 36% (74) had radiation of pain (P < .003), 72% (95) versus 28% (37) had diaphoresis (P < .0001). Neither difficulty breathing, nausea/vomiting, vital signs, initial rhythm, nor past history of myocardial infarction were helpful in discriminating AMI and unstable angina from others. Comparing AMI alone versus others, the presence of ST segment elevation on lead II was present in 15% (18) AMIs, 3% (3) unstable angina, and 8% (14) others (P = .005). Diaphoresis also was a predictor of diagnosis with 51% (63) of the AMIs and 25% (69) of others exhibiting this sign (P < .001). For stable prehospital chest pain patients, sex, age, radiating pain, and diaphoresis have a sensitivity of 79% and a specificity of 45% in discriminating acute cardiac ischemia from other diagnoses. These figures are unacceptably low for a disease with significant mortality and morbidity. Given the consequences of missing an AMI or unstable angina we recommend that all chest pain patients be transported by an advanced life support unit and managed as AMIs.