NEWS
Dr Pierre Margent | 04 June 2024
Each year in the United States, 750,000 patients are diagnosed with myocardial infarction (MI). Far more patients are evaluated for suspected MI. The diagnosis is often considered during an emergency department visit, sometimes with atypical signs, nonspecific symptoms, or even in the absence of symptoms.
Up to 20% Misdiagnoses
Misdiagnosing MI is not trivial, often leading to unnecessary additional tests, including costly and potentially harmful cardiac imaging. It can also result in treatments causing side effects, unnecessary hospitalisations, and potential impacts on employment and health insurance coverage.
The risk of overdiagnosing MI appears to be higher than underdiagnosing it. Some studies have estimated a 9% diagnostic error rate in patients clinically suspected of having an MI. In certain clinical trials, these diagnostic errors were found to be as high as 15%-20% after secondary analysis and strict application of MI definitions.
Cardiac magnetic resonance imaging could prove useful. For instance, in the Women’s Heart Attack Research Program study, only half of the clinically diagnosed MI cases were confirmed by magnetic resonance imaging, with 20% receiving a different diagnosis indicating other types of myocardial damage.
A Universal Definition of Myocardial Infarction?
The working group on the universal definition of MI retained as a definition the association of symptoms and/or signs of coronary ischaemia accompanied by myocardial injury, primarily indicated by changes in troponin levels. However, while abnormal troponin levels are necessary to diagnose MI, they are not sufficient alone, given the wide normal range. In the US, nearly a quarter of emergency room patients are tested for troponin, although only half report chest pain.
It is also noteworthy that the sensitivity of available tests has increased, reducing posttest validity. Consequently, these tests often yield abnormal results even for noncoronary conditions. Additionally, the risk of an abnormal troponin level without MI increases with patient age and comorbidities. In unselected cohorts of patients admitted to emergency departments, approximately one in seven have elevated troponin levels. Even though troponin is currently the most specific biomarker for myocardial necrosis, its elevation involves complex mechanisms, such as apoptosis and exocytosis, which can occur in noncoronary diseases.
An Essential but Insufficient Upper Troponin Limit
Therefore, troponin abnormalities, even evolving over time and taking into account a reference higher than the 99th percentile of high-sensitivity troponin levels, do not necessarily indicate ischemic myocardial necrosis. Moreover, this upper limit, crucial for diagnosing MI, was established in populations of young or middle-aged adults under 60 years. For older adults, aged 60 years or above, the limit could be 1.5-2 times higher, increasing the possibility of overdiagnosis in older patients. For these reasons, an abnormal troponin level has a low predictive value, of the order of only 15% in the US, compared with 60% in the UK. This low positive predictive value in the US reinforces the hypothesis of possible overdiagnosis or misdiagnosis of myocardial necrosis.
Strategies to Reduce Overdiagnoses
Several strategies should be explored to reduce the excessive number of overdiagnosed cases. One approach could be to modify practitioner liability laws by capping damages, thereby reducing the tendency toward defensive medicine. This could potentially lower healthcare costs without compromising care quality. Secondly, troponin testing should be reserved for patients suspected of having acute coronary syndrome and not performed nonselectively on many patients presenting to the emergency room.
It is also possible to better define the 99th percentile value of troponin levels, adapting it to patient age. Additionally, focusing on parameters other than biomarkers in defining MI and developing new, more specific necrosis markers would be very beneficial. Lastly, cardiac imaging in complex cases could improve diagnostic accuracy.
In conclusion, diagnostic errors for MI are more often due to overdiagnoses than underdiagnoses. Overdiagnosing myocardial necrosis is far from trivial, potentially causing unnecessary tests, unwarranted treatments, increased costs, and unnecessary hospitalisations. Future studies are needed to better analyse the frequency and consequences of MI overdiagnosis in order to develop more accurate detection strategies.
This story was translated from JIM using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.
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