Atypical Presentations of Acute Myocardial Infarction: Medical and Legal Consequences
Special Feature
Atypical Presentations of Acute Myocardial Infarction: Medical and Legal Consequences
By William J. Brady, MD
Patients presenting to the emergency department (ED) with acute chest discomfort of potentially ischemic origin are evaluated with a history and physical, a 12-lead electrocardiogram (ECG), and serum markers of myocardial injury. Using any combination of these tools, acute myocardial infarction (AMI) most often is either clinically suspected or correctly diagnosed on presentation or early in the ED course. However, atypical presentations are encountered in as much as one-third of the AMI population.1 Numerous factors may impact upon securing the correct diagnosis of AMI, including patient age, alternate chief complaints, atypical symptomatology, comorbid states, confounding ECG patterns, and the normal nondiagnostic ECG. The patient’s medical outcome and the potential legal consequences for the emergency physician (EP), are not favorable if the AMI diagnosis is missed initially and the patient is subsequently released from the ED.
Medical Issues and Consequences
The characteristics of patients released from the ED with an acute coronary ischemic syndrome (ACIS) that progresses to AMI are of great interest. Studies have documented that 2-10% of patients with chest discomfort and AMI are released from the ED.1,2 Based on an estimate of 800,000 patients admitted each year in the United States with AMI and a 5% release rate, approximately 40,000 AMI patients will be released from the ED. These patients represent considerable risk for potential liability.
In one study, 4% of AMI patients released from the ED were significantly younger, had atypical symptomatology, and were less likely than a control group of patients with recognized AMI to have electrocardiographic evidence of ischemia or infarction.3 Mortality for the group released from the ED tended to be higher than those admitted, possibly because of a return to normal activity and the lack of appropriate therapies. In this study, improved ECG reading skills and the admission of patients with obvious ischemic pain at rest would have led to the correct diagnosis in 49% of patients with missed AMI.3
From another study with 9% of AMI patients discharged from the ED, three of five patients were young men between 30 and 45 years of age with nonspecific clinical and electrocardiographic findings.4 Another large, multicenter study found a 2.9% ED release rate among AMI patients.2 Similarly, improved ECG interpretation skills would have decreased the number of AMI patients released from the ED. A recently published large investigation reported a 2.1% ED release rate of AMI patients and a similar rate of 2.3% for unstable angina pectoris.1 Factors associated with unrecognized ACIS were female gender younger than age 55, nonwhite race, and either a normal or nondiagnostic ECG. ACIS patients discharged from the ED had considerably higher rates of poor outcome compared to admitted patients. As with other studies, misinterpretation of the patient’s history as well as the ECG contributed significantly to the misdiagnosis.
The prognosis for AMI patients who present atypically usually is worse than for those with classic symptoms. Uretski and colleagues found a three-fold increase in mortality among patients presenting atypically (50%) vs. patients with classical descriptions of chest discomfort (18%); cardiogenic shock was the chief cause of death in patients with unusual AMI presentations, followed by myocardial rupture and dysrhythmias.5 A large survey of AMI patients presenting without chest pain reported that these patients often were diagnosed at a later time, and less often received early reperfusion therapy, compared to patients presenting in typical fashion; their medical outcome, understandably, was less favorable than those patients who presented with chest pain.6 Advanced age with associated comorbidity is considered partially responsible for the increased mortality of the atypical presentation group in this study; less frequent use of early pharmacotherapy in those AMI patients without chest pain accounted for approximately 28% of the higher mortality rate. Those time-dependent therapies include thrombolysis, aspirin, heparin, and beta-blockade.5,6 The Framingham study demonstrated an in-creased long-term mortality rate for unrecognized in-farctions; a 10-year, 45% mortality rate was observed for patients with unrecognized infarctions, whereas individuals with symptoms had a 39% mortality rate.7,8
Legal Issues and Consequences
A minority of AMI patients (2-4%) are sent home from the ED, and most are associated with atypical presentations or young age.2,3 However, missed myocardial infarction is the third leading cause of medical malpractice claims, accounting for 20% of legal damage awards. Forty percent of claims result in payment to the plaintiff, with an average indemnity of $220,000. EPs represent the third most frequent specialty to be sued for medical malpractice concerning the missed AMI, and are the leading physician group in terms of amount of paid indemnity (approximately $280,000/case).9
The following information is drawn from the 1996 Physician Insurers Association of American (PIAA) survey of the "missed myocardial infarction" malpractice claim;9 these findings are characteristic of the successful claim due to missed myocardial infarction and do not necessarily correspond to the features of the medically unrecognized AMI. The clinical presentation of the missed AMI in the PIAA survey involves all age groups, though 50% of such patients are younger than 50 years of age. Seventy percent lack a history of ischemic heart disease. Chest discomfort is the chief or secondary complaint in most cases, with the majority described as typical; anginal equivalent complaints were encountered in a minority of cases. The ECG was misinterpreted and/or used incorrectly in 25% of cases; incorrect use applies to over-reliance on a single "negative" study or the interpretation of nonspecific ST segment-T wave findings as normal. Additional diagnostic testing was misused in 6% of cases (i.e., over-reliance on a single negative serum marker). Incorrect initial diagnoses included gastrointestinal, musculoskeletal, and noncardiac chest pain syndromes (listed in order of occurrence). As determined during litigation, factors leading to misdiagnosis included: failure to order study (ECG); diagnosis not considered; inappropriate discharge from ED; incorrect interpretation of tests; and over-reliance on negative studies (i.e., "negative" ECG or single serum marker).
Conclusions
Issues from the medical literature associated with atypical and/or unrecognized AMI are similar to many points noted from the malpractice perspective. These include female gender, young patient, no history of ischemic heart disease, anginal equivalent complaint, atypical discomfort, over-reliance on the ECG and single serum markers, and incorrect interpretation of studies.2,3,7-10 When one considers both medically unattended and inappropriately discharged AMIs, young patients without a history of heart disease frequently are noted; women and older men also represent at-risk populations. One large ED-based study of missed AMI found that ECG misinterpretation accounted for 25% of undiagnosed cases; a similar percentage was incorrectly felt to have stable presentations of ischemic heart disease rather than acute infarction.2 The outcome from missed AMI is considerably worse in the immediate post-infarction period. With appropriate medical attention, prognosis should be similar to the recognized AMI—similar in terms of type of patient and infarct (age, comorbidity, and coronary anatomy) as well as outcome measures (death, left ventricular function, arrhythmia).
References
1. Pope JH, et al. Missed diagnosis of acute cardiac ischemia in the emergency department. N Engl J Med 2000;342:1163-1170.
2. McCarthy BD, et al. Missed diagnoses of acute myocardial infarction in the emergency department: Results from a multicenter study. Ann Emerg Med 1993;22:579.
3. Lee TH, et al. Clinical characteristics and natural history of patients with acute myocardial infarction sent home from the emergency room. Am J Cardiol 1987;60:219-224.
4. Hedges JR, et al. Use of cardiac enzymes identifies patients with acute myocardial infarction otherwise unrecognized in the emergency department. Ann Emerg Med 1987;16:248-252.
5. Uretski B, et al. Symptomatic myocardial infarction without chest pain: Prevalence and clinical course. Am J Cardiol 1977;40:498-503.
6. Canto JG, et al. Prevalence, clinical characteristics, and mortality among patients with acute myocardial infarction presenting without chest pain. JAMA 2000;283:3223-3229.
7. Margolis JR, et al. Clinical features of unrecognized myocardial infarction—silent and symptomatic. Eighteen year follow-up: The Framingham Study. Am J Cardiol 1973;32:1-7.
8. Kannel WB, Abbott RD. Incidence and prognosis of unrecognized myocardial infarction. An update on the Framingham study. N Engl J Med 1984;311:1144-1147.
9. Physician Insurers Association of American. Acute myocardial infarction study. Rockville, MD; May 1996.
10. Yano K, MacLean CJ. The incidence and prognosis of unrecognized myocardial infarction in the Honolulu, Hawaii, Heart Program. Arch Intern Med 1989;149:1528-1532.
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