Determining the Mechanism of Myocardial Injury and Role of Coronary Disease in Type 2 Myocardial Infarction

Where patients are fit, coronary angiography will be performed via the femoral or radial artery with 6F arterial catheters. In patients with one or more stenoses in a major epicardial vessel, a coronary pressure guidewire (PressureWire™ Aeris™, St. Jude Medical, St. Paul, Minnesota) will be used to determine distal coronary pressure and the fractional flow reserve (FFR) calculated at maximal adenosine-induced (intravenous 140 μg/kg/min) hyperaemia. Optical coherence tomography (OCT) will be performed in all three coronary vessels using a Dragonfly® coronary imaging catheter (Abbott Diagnostics, Abbott Park, Illinois) with pullback at 20 mm/s to identify features consistent with vulnerable plaque or recent plaque rupture.(16) If there is evidence of inducible myocardial ischaemia due to coronary artery stenosis, revascularisation with percutaneous coronary intervention may be considered if in the patients best interests.

CT coronary angiography will be performed using a 128 multidetector row CT. Patients with a heart rate exceeding 65 beats/min will receive oral beta-blockade 1 hour before computed tomography. Additional intravenous beta blockers will be given depending on heart rate at the time of imaging. All patients will receive sublingual glyceryl trinitrate (300 μg) immediately prior to dual cardiac and respiratory-gated computed tomography imaging of the coronary arteries. The investigators will quantify total plaque burden using CT calcium scoring. A bolus of 80-100 mL of contrast will be injected intravenously at 5 mL/s. An assessment of the functional consequences of coronary artery stenosis will be made using the computed tomography fractional flow reserve (CT-FFR) technique, using the HeartFlow platform.

Cardiovascular magnetic resonance (CMR) will be performed using a 3T scanner. The MRI scan will consist of localisers, axial and coronal HASTE images, standard breath-held and ECG-gated cine sequences. Short-axis cine images will be obtained for the assessment of left ventricle function and volumes. Left ventricle volumes, mass and ejection fraction will be assessed using dedicated software and values indexed to body surface area. Breath-held, ECG-gated T2 mapping sequences of the myocardium will be performed in the short-axis as a marker of myocardial inflammation. T1-weighted imaging of the coronary arteries will be performed to look for evidence of recent intraplaque thrombus or haemorrhage. The late gadolinium enhancement and T2 mapping techniques will identify regions of new or old myocardial infarction as well as other patterns of injury. Where there are no contraindications, stress MRI will be performed using intravenous Regadenoson.