Assessment of Coronary Microvascular Dysfunction After STEMI Using Continuous Saline Thermodilution

The goal of this observational study to measure the heart's microvascular function in the setting of a myocardial infarction (MI), or heart attack, using a method called continuous saline thermodilution (CST). The participants will include people who are experiencing MI from sudden and complete blockage of a coronary artery requiring immediate balloon and/or stent therapy. After getting the balloon and/or stent therapy, participants will have their heart's microvascular system tested using CST. The main questions it aims to answer are: * What measurements using CST can we expect from the heart's microvascular system during a treated MI? * Can CST measurements during a treated MI predict the amount of heart muscle that is injured and that recovers? For this study, participants will undergo measurement of their heart's microvascular function after balloon and/or stent therapy for the MI. They will then receive an MRI scan of the heart several days after the MI.

This will be a non-interventional, prospective, descriptive analysis on a cohort of patients experiencing ST-elevation myocardial infarction (STEMI) who present to the Cleveland Clinic cardiac catheterization laboratory (CCL) for emergent primary percutaneous coronary intervention (PCI). The aim is to study acute coronary microvascular dysfunction using the method of continuous saline thermodilution to provide absolute measurements of coronary blood flow, coronary microvascular resistance, and microvascular resistance reserve (MRR) following primary PCI for STEMI patients. Adult patients experiencing acute STEMI who present to the catheterization laboratory for emergent cardiac catheterization for STEMI, \<24 hours after symptom onset, who undergo primary PCI to an IRA. Only those able to provide initial oral consent upon CCL presentation and confirmatory written consent following cardiac catheterization will be included in the study. Study endpoints are part of usual standard practice, and include clinic visits with updated medical histories and physical examination, and echocardiography. Clinical endpoints of interest will include mortality, incident heart failure, anginal symptoms, and standard major adverse cardiac events including cardiac death, nonfatal MI, urgent coronary revascularization, or hospitalization for unstable angina.