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Type 2 myocardial infarction — ABIM Board MCQ

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ModerateCardiovascularType 2 myocardial infarctionABIM Board

A 74-year-old man with severe COPD is admitted with pneumonia, marked hypoxemia, and sinus tachycardia. He has no chest pain. During worsening hypoxemia, an ECG shows new horizontal ST-segment depressions in the lateral leads. High-sensitivity troponin I levels are 24, 96, and 41 ng/L at 0, 3, and 12 hours, respectively (99th-percentile upper reference limit, 19 ng/L). The ECG abnormalities resolve after oxygenation and treatment of the pneumonia. Echocardiography shows normal left ventricular systolic function without a regional wall-motion abnormality. Which of the following is the most likely mechanism of his myocardial infarction?

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Correct answer: E — Hypoxemia-induced myocardial oxygen supply-demand mismatch

The correct answer is E. The rise and fall in high-sensitivity troponin above the 99th percentile establishes acute myocardial injury, and the transient new ST-segment depression provides evidence of myocardial ischemia. Severe hypoxemia and tachycardia from pneumonia increase myocardial demand while reducing oxygen supply, producing type 2 myocardial infarction without acute atherothrombosis. Plaque rupture with thrombosis causes type 1 myocardial infarction and is less consistent with the close relationship between the ischemic findings and reversible respiratory stress. Immune checkpoint myocarditis requires relevant drug exposure and is not defined by supply-demand ischemia. Coronary arteritis and embolization from a vegetation would require supporting vascular, systemic inflammatory, bacteremic, or valvular findings.

Reference: Januzzi JL Jr, Mahler SA, Christenson RH, et al. Recommendations for Institutions Transitioning to High-Sensitivity Troponin Testing, section “Troponin and Acute MI.” Journal of the American College of Cardiology. 2019;73:1059-1077. https://www.acc.org/~/media/Non-Clinical/Files-PDFs-Excel-MS-Word-etc/Tools%20and%20Practice%20Support/Quality%20Programs/Emergency-Department-2020/Session-1/Recommendations%20for%20Institutions%20Transitioning%20to%20High-Sensitivity%20Troponin%20Testing.pdf?la=en