Introduction

Angina is chest discomfort that occurs when the oxygen supply to the myocardium is insufficient to meet its metabolic demands. Classically, the patient will present with a history of substernal chest discomfort (often not described as a "pain" but as a tightness, squeezing, or pressure-like sensation) occurring with exertion and relieved within minutes with rest. This discomfort may radiate to the neck, jaw, or either arm and may be associated with shortness of breath. The diagnosis of angina depends largely on history. Physical exam and laboratory studies are often normal in the chronic stable angina patient. The electrocardiogram (ECG) will be normal in over a third of patients who are pain free on presentation, but may show evidence of prior infarction, an intraventricular conduction delay, or nonspecific ST-T wave abnormalities.

The differential diagnosis of angina includes a broad range of both cardiac and noncardiac causes of chest discomfort. These include gastroesphageal reflux, diffuse esophageal spasm, pericarditis, aortic dissection, musculoskeletal pain, and pulmonary embolus. By considering the quality, duration, location, and precipitating factors of the chest discomfort, it is usually possible to distinguish angina from these other causes of chest pain.

After establishing a diagnosis of angina, you should consider possible etiologies. The leading cause is certainly atherosclerotic coronary artery disease. As critical stenosis develops within the coronary arteries, myocardial oxygen supply/demand relationships with exertion are not met and angina occurs. Uncommon causes of angina in our active duty population include hypertrophic obstructive cardiomyopathy, severe aortic stenosis, pulmonic stenosis, pulmonary hypertension, and Prinzmetal's vasospastic angina. Descriptions of these entities may be found in standard medicine and cardiology texts. Also consider other factors that could produce angina like symptoms including anemia, thyrotoxicosis, underlying infection with tachycardia, and hypoxemia.

Management considerations

Unstable angina requires aggressive management. Unstable angina is variously defined as new onset angina at a low level of activity with significant worsening of a patient's existing anginal pattern, and angina at rest for patients with a suspected unstable angina syndrome. Urgent consultation with a subspecialist is needed. Through appropriate consultation, the required level of care for the unstable angina patient will be decided. Many of these patients will require admission to a coronary care unit for intravenous heparin, nitroglycerin, beta-blockers, aspirin, and telemetry monitoring. For discomfort persisting longer than 20-30 minutes, myocardial infarction should be excluded with serial enzymes and ECG's. The use of Spectralä slides for Myoglobin, CKMB, and Troponin may be available on some platforms.

If faced with an unstable angina patient in the field or on a ship, start treatment by administering oxygen (if available), have the patient chew one aspirin 325mg, administer sublingual nitroglycerin or nitropaste, and start an intravenous line. Ensure the systolic blood pressure remains above 90 mmHg. A beta-blocker should be initiated if not contraindicated. If there is ongoing pain and ST depression, an IV beta-blocker is preferred. Consider starting intravenous nitroglycerin or a heparin drip, if available. Arrange for urgent MEDEVAC.

Low molecular weight (LMW) heparin, enoxaprin, has been proven to be equally effective as titrated unfractionated heparin with simpler dosing at 1 mg/kg subcutaneous every 12 hours.

If presented with a patient diagnosed as chronic stable angina, treatment may be initiated with one aspirin/day and some combination of antianginal medications--nitrates, beta-blockers, or calcium channel blockers, tailored to your given patient. For the chronic stable angina patient, an aspirin/day, a low dose B-blocker (tenormin 50 mg PO BID or metropolol 50 mg PO QID), and SL nitroglycerin on an as needed basis is a reasonable starting point. Attention should be given to concomitant cardiac risk factors, for example hypertension, diabetes, tobacco abuse, and hypercholesterolemia. For the newly diagnosed chronic, stable patient, timely referral for exercise stress testing is appropriate to further risk-stratify the patient and aid in determination of suitability for full duty. Initial presentation is usually unhelpful in distinguishing patients with angina due to single vessel coronary artery disease from those with left main or three-vessel disease. Some patients will need cardiac catheterization, and possible interventional treatment or coronary artery bypass surgery.

Chronic stable angina can be managed comfortably by the general medical officer with timely subspecialty consultation. Patients with unstable angina syndromes require urgent referral to a higher echelon of medical care. In cases with diagnostic uncertainties, obtain an ECG, chest X-ray, and labs, and then phone consultation to the next higher level of care.

1. Braunwald, Eugene, Heart Disease. 4th Edition 1992 W.B. Saunders.

2. Silverman, K and Grossman, W. Angina Pectoris. NEJM 1984; 310:1712-17.

3. Agency for Health Care Policy and Research Guideline No. 10, Unstable Angina

4. Cohn M, et el: A comparison of low-molecular-weight heparin with unfractionated heparin fur unstable coronary artery disease (ESSENCE trial). NEJM 1997; 337: 447-452.