acute myocardial infarction
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acute myocardial infarctionCardiology The abrupt death of heart muscle due to acute occlusion or spasm of the coronary arteries Epidemiology ±1.5 million MIs/yr–US, 75,000 AMI follow strenuous physical activity, of whom1⁄3 die; ±1⁄4 of all deaths in the US are due to AMIs; > 60% of the AMI-related deaths occur within 1 hr of the event; most are due to arrhythmias, in particular ventricular fibrillation Triggers Heavy exertion in ±5% of Pts, which is inversely related to Pt's habitual physical activity Etiology Occlusion of major coronary artery–CA, in a background of ASHD, due primarily to the plugging of the vessel with debris from an unstable plaque–see Uncomplicated plaque Clinical Main presenting symptom–retrosternal chest pain accompanied by tightness, discomfort, & SOB; cardiac pain often radiates to the arm & neck, and less commonly to the jaw; the pain of AMI generally is. not relieved with nitroglycerin, in contrast to esophageal pain, which is often identical in presentation, and may respond, albeit slowly, to nitroglycerin; the characteristic clinical picture notwithstanding, there is a high rate of false negative diagnoses of AMIs Diagnosis Clinical presentation, physical examination, EKG–sensitivity in diagnosing AMI is 50–70%, and is lower in lateral MIs than in anterior and inferior MIs; CXR may demonstrate left ventricular failure, cardiomegaly Echocardiography M-mode, 2-D & Doppler Radioisotopic studies Radionuclide angiography, perfusion scintigraphy, infarct-avid scintigraphy, & PET can be used to detect an AMI, determine size & effects on ventricular function, and establish prognosis; a radiopharmaceutical, 99mTc-sestamibi, has become the perfusion imaging agent of choice, given its usefulness for measuring the area of the myocardium at risk for AMI, and for recognizing the myocardium salvaged after thrombolytic therapy Other imaging techniques–eg, CT, and MRI Lab CK-MB, troponin I DiffDx AMI is the most common cause of acute chest pain in older adults, other conditions must be excluded–Prevention ↓ Smoking, ↓ cholesterol, ↓ HTN; ↑ aerobic exercise; influence of other factors-eg maintaining normal body weight, euglycemic state in diabetes, estrogen-replacement therapy, mild-to-moderate alcohol consumption, effect of prophylactic low-dose aspirin-on incidence of AMI is less clear. See AIMS, ASSET, EMERAS, EMIP, GISSI, GISSI-2, GUSTO-1, INJECT, ISIS-2, ISIS-3, LATE, MITI-1, MITI-2, RAPID, TAMI-5, TAMI-7, TEAM-2, TIMI-2, TIMI-4, Trial.
Differential diagnosis of acute myocardial infarction
- Arm pain
- Myocardial ischemia, cervical/thoracic vertebral pain, thoracic outlet syndrome
- Epigastric pain
- Myocardial ischemia, GI tract–esophagus, peptic ulcers, pancreas, liver disease–cholecystitis, hepatic distension, pericardial pain, pneumonia
- Retrosternal pain
- Myocardial ischemia, aortic dissection, esophageal pain, mediastinal lesions, pericardial pain, PTE
- Shoulder pain
- Myocardial ischemia, cervical vertebra, acute musculoskeletal lesions, pericardial pain, pleuritis, subdiaphragmatic abscess, thoracic outlet syndrome