Type 2 myocardial infarction : Aspects of diagnosis, prognosis and treatment

Unlike the coronary thromboembolic type 1 myocardial infarction (MI), a type 2 MI occurs secondary to other conditions causing an imbalance in myocardial oxygen supply and demand. Type 2 MI is associated with high mortality and evidence based treatment is lacking. It may also be difficult to differentiate type 2 MI from type 1 MI and myocardial injury, which causes uncertainty among physicians. Therefore, the aim of this thesis was to evaluate the current classification of MI types and myocardial injury with special emphasis on evaluating the therapeutic and prognostic importance of distinguishing and diagnosing type 2 MI. The validity of type 2 MI reports in the Swedish national register for MI (SWEDEHEART) was also investigated. The study populations consisted of 1328 patients with a clinical MI diagnosis from eight sites, whereof 792 had been reported to SWEDEHEART, as well as 281 patients with elevated cardiac troponins but without a clinical MI diagnosis from one site. The diagnosis of each patient was retrospectively adjudicated in accordance with the Third Universal Definition of Myocardial Infarction. Overall, the adjudicators agreed moderately when deciding the diagnosis and it was particularly difficult to distinguish type 2 MI and non-ischemic myocardial injury. Patients with type 2 MI were often treated outside cardiology departments which led to a significant underreporting to SWEDEHEART. Using the adjudicated diagnosis as a gold standard, type 2 MI registry reports had a positive predictive value of 62.5%. Receiving care outside cardiology departments was found to be associated with a lesser use of MI specific therapies and an adverse short and long term prognosis in MI patients overall. However, although clinically unrecognized type 2 MI patients received the least cardiology care in all aspects, this was still not observed to significantly affect the long term prognosis. In conclusion; the current MI classification defines type 2 MI as a very heterogeneous condition that is difficult to distinguish. This makes clinically defined type 2 MI populations, such as the one in SWEDEHEART, unreliable and it also makes it difficult to find and apply specific, prognostically relevant recommendations and therapeutic strategies for this serious condition