Type 3 myocardial infarction unusual in clinical practice
It is rare to encounter type 3 myocardial infarction (MI) in clinical practice, comprising less than 5 percent of all types of MI, according to a recent study. However, if autopsy data are taken into account, the number of type 3 MIs appears to increase to about 50 percent.
“The occurrence of type 3 myocardial infarction is rare in clinical practice, with an annual incidence of 7.3/100,000 person-years and a frequency of 3 to 4 percent among all patients having the diagnosis of a myocardial infarction,” researchers said.
“Our results indicate that the number of type 3 myocardial infarctions increases if information from autopsies is included in the definition,” they added.
Of the 246,723 adult residents in the study region, 2,766 (aged >18 years) had died during the indicated 1-year period. A total of 1,596 deaths occurred out of hospital, while 1,170 deaths took place within the hospital. Of these, 18 individuals were diagnosed with type 3 MI, corresponding to an annual incidence of 7.3/100,000 person-years. [Am J Med 2017;130:862.e9–862.e14]
“The documents of the Universal definition of myocardial infarction do not specify the settings or surroundings in which a type 3 myocardial infarction may occur,” researchers said. [Eur Heart J 2007;28:2525–2538; Eur Heart J 2012;33:2551–2567]
“Thus, it is not clear whether it is a requirement that the patient has reached the hospital before the type 3 myocardial infarction definition comes into play, or whether the type 3 myocardial infarction criteria can be used in patients that are managed out of hospital,” they added.
Both in-hospital and out-of-hospital deaths were included in this study. If the latter group was excluded from the cohort study, the frequency of type 3 MI would be reduced from 3.6 to 2.8 percent, according to researchers.
A total of 488 patients indicated other types of MI during the same 1-year period. This denoted a type 3 MI frequency of 3.6 percent (18 of 506) among all MIs.
In the 2007 Universal definition of MI, a type 3 MI included “sudden, unexpected cardiac death” and “evidence of fresh thrombus by coronary angiography and/or autopsy.” This was modified in 2012, wherein the wording “sudden unexpected” was omitted and the statement “evidence of fresh thrombus by coronary angiography and/or autopsy” was moved to be included in the criteria for type 1 MI. [Eur Heart J 2007;28:2525–2538; Eur Heart J 2012;33:2551–2567]
“However, even so, fatal myocardial infarctions without elevated biomarkers are supposed to be categorized as type 3 myocardial infarctions,” researchers said.
In this study, the authors retrieved data on the occurrence of deaths in a well-defined geographic region from the Danish Civil Registration System from 2010 to 2011. Complementary data regarding the causes of deaths were obtained from the Danish Register of Causes of Death, and ambulance and hospital patient files. Two local experts and one external senior cardiologist adjudicated the diagnosis.
The study has several limitations, including its partly retrospective design and the fact that the symptom history may be absent in patients who die from MI prior to measurement of cardiac troponin. Also, the observations are done on a limited geographic region with only one referring hospital. Finally, the adjudication process was difficult in some cases due to insufficient data.
“Cardiac death in a patient with symptoms and electrocardiographic changes indicative of myocardial ischaemia but without available measurements of cardiac biomarkers is designated a type 3 myocardial infarction,” researchers said.