Acute Myocardial Infarction Diagnosis: Atypical Presentations
By William J. Brady, MD
The emergency physician (ep) will encounter atypical features of acute myocardial infarction (AMI) in approximately 10-30% of myocardial infarction cases.1-6 Factors contributing to this diagnostic challenge include patient age, alternate chief complaints, atypical discomfort, and certain comorbid states.
A Broad Spectrum of Atypical Complaints
Anginal equivalent complaints, which occur in the "painless" AMI setting, classically include dyspnea, diaphoresis, nausea, and emesis. Other anginal equivalent symptoms to consider are cough, palpitations, and anxiety. Among chief complaints, the most frequently encountered anginal equivalent is dyspnea, which is found in 10-30% of AMI patients, often because of pulmonary edema.1-3 Isolated emesis and diaphoresis are quite rare, with a 1-3% prevalence.2,3 The geriatric patient also may present atypically with acute weakness (3-8%) and syncope (3-5%).4 Unexplained sinus tachycardia, bronchospasm resulting from cardiogenic asthma, and new-onset lower extremity edema all have been reported as anginal equivalent presentations for AMI. Anginal equivalent syndromes often involve neurologic presentations with acute mental status abnormalities and cerebrovascular attacks (CVA), frequently among the elderly. From the perspective of acute delirium, less than 1% of such patients with altered mentation in an emergency department (ED) population will have AMI. Less pronounced mental status abnormalities, including confusion and lethargy, are classically reported findings in the elderly AMI patient and are described in approximately 5% of cases. Myocardial infarction associated with acute stroke is noted in approximately 5-9% of patients, usually older than 60 years.4
When discomfort or another painful sensation is the complaint associated with AMI, it may be atypical from a number of different perspectives. The patient may complain of pain in an atypical location. The discomfort may be located in non-chest portions of the body (e.g., the epigastrium, anterior neck or jaw, or left upper extremity). While not the classic presentation of an AMI, these symptoms usually do not challenge the EP’s diagnostic ability; in the appropriate patient, such pain distributions are suggestive of a coronary ischemic source. The discomfort may be located in the back, posterior neck, and right arm in the rare patient, suggesting another explanation for the unpleasant sensation. Other highly unusual presentations include cephalgia, as well as hip and lower back pain.
The actual chest discomfort description may range from the classic "crushing, pressure-like, heaviness" to the atypical "sharp, knife-like" or "burning." Taking into account all ED patients presenting with typical terms such as "crushing" or "pressure-like," only slightly more than one-half experienced an acute coronary syndrome (ACS) (approximately 50% AMI and 50% unstable angina).7 The remaining patients had gastrointestinal, pulmonary, and musculoskeletal diagnoses. Chest discomfort is described as "burning" or "indigestion-like" in an adult chest pain population of which 23% have AMI and 21% have unstable angina.7 Interestingly, a minority of AMI cases presenting with burning chest discomfort may relate a favorable response to the infamous "GI cocktail." In 19-23% of instances, patients note "sharp," "knife-like," or pleuritic pain because of an ACS.8 Lastly, the physical examination may mislead the EP with reproducible chest pain being present in as many as 15% of confirmed AMI patients.
The Elderly: Atypical May Be Typical
A patient’s advanced age almost always effects the EP’s ability to evaluate the patient and assess the potential of AMI. In fact, several studies have demonstrated that the evaluation of acute chest pain with confirmation of the correct diagnosis and initiation of appropriate therapies is very difficult in geriatric patients. Numerous disease states, syndromes, and medications contribute to making the elderly AMI presentation a significant diagnostic challenge. This increased rate of atypical presentation in the elderly translates into the possibility of clinically unrecognized AMI. For example, in one large autopsy series of elderly patients, correct AMI diagnosis was made in less than one-half the patients antemortem; this was especially true in the very old.4 As a patient ages, a multitude of factors—including autonomic neuropathy, injury to cardiac sensory afferent nerves due to past ischemic heart disease, cortical failure resulting from cerebrovascular or other central nervous system disease, extensive comorbidity, higher pain thresholds, and pre-existing mental status abnormalities—contribute to a higher rate of atypical presentation and unrecognized AMI. Among the geriatric populace, these factors result in an increased prevalence of anginal equivalent chief complaints, "silent" myocardial infarction, and a preponderance of neurologic syndromes.
Atypical presentations are encountered with increasing frequency in sequentially older populations.4 In elderly patients younger than 85 years, chest pain becomes less frequent while equivalent complaints are noted more often; however, chest pain still is found in the majority of cases. Stroke, weakness, and altered mentation become more common with increasing age and frequently are not accompanied by typical chest discomfort. Atypical presentations occur, yet still are in the minority in this relatively younger geriatric population.
In the patient older than 85 years, atypical presentations are the norm and should be anticipated. The incidence of "painless" AMI increases dramatically with age; 60-70% of elderly AMI patients older than 85 years will present with an anginal equivalent complaint or syndrome—most often with a change in mental status. If one considers all elderly patients with altered mental status in an ED population, however, the AMI diagnosis is found only in 1% of cases. In most acutely ill patients older than 85 years, the clinician should consider not only the potential for AMI but also should actively exclude the diagnosis with appropriate investigations.
The elderly also frequently present with complications of AMI rather than the actual symptoms of the acute ischemic event. For example, very elderly patients presenting with new-onset, unexplained congestive heart failure should be screened for acute ischemia. Similarly, the elderly patient presenting with malignant bradycardia, atrioventricular block, or ventricular arrhythmia should have AMI excluded while appropriate therapies and other evaluations are performed.4
Atypical Presentations Common in Diabetics
Patients with diabetes mellitus (DM) suffer AMI more often than the general public; they also experience AMI at an earlier age, present more frequently with atypical manifestations, and suffer more commonly an unrecognized myocardial infarction. Medically unrecognized AMI is felt to occur in approximately 40% of DM patients compared to 25% of the non-DM population.5 Autopsy studies have demonstrated that myocardial scar without an antemortem diagnosis of myocardial infarction—indicative of the medically unattended, past infarct—is three times more frequent in the diabetic than the nondiabetic patient.5 The medical and legal literature discussing the missed AMI frequently cite DM history as a risk factor for an unrecognized event. In fact, DM often is implicated in legal cases as a medical factor leading to the diagnosis error. As with the elderly AMI patient, numerous factors contribute to atypical manifestations of acute ischemic heart disease in the DM patient, including polyneuropathy, an altered perception of cardiac pain, and extensive comorbidity.
The diabetic patient’s abnormal perception of myocardial infarction may lead to atypical or less impressive symptoms of AMI. Accurate diagnosis based on historical grounds—the primary tool available to the EP—is made much more difficult. In the diabetic patient, atypical symptoms such as dyspnea, confusion, fatigue, and emesis may be the presenting complaint in as many as 40% of AMIs.5 The diabetic also may experience more frequently the less-than-classic pain syndromes, including discomfort in unusual locations and with abnormal characteristics. The atypical presentations reduce the rate at which the patient is able to receive adequate medical care. The patient may not feel the pain or may attribute the abnormal sensation to some other malady, and therefore, may not consult a physician at all or may wait until later in the course of the event. If the patient does seek medical attention, the presentation may be such that the physician misses the actual diagnosis, leading to an inappropriate disposition and therapy.
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