Departure of principal investigator

In the management of acute myocardial infarction treated with primary angioplasty, despite effective epicardial clearance obtained in 95% of cases, microvascular obstruction (MVO) in the damaged territory concerns 50% of patients. The Index of Microvascular Resistance (IMR) allows early assessment of the microcirculatory state during the angioplasty procedure. A value of IMR>40 indicates MVO and is correlated with morbi-mortality. A new method for immediate evaluation of MVO using thermodilution with a new Rayflow® microcatheter has been described: it no longer allows the estimation but the measurements of absolute coronary resistance and coronary flow. We hypothesize that these measurements allows a better evaluation of the microcirculatory state after primary angioplasty, comparing to IMR.

The main objective is to study the diagnostic performance of Rayflow® to predict MVO - no reflow (NR) - in ST-Elevation Myocardial Infarction (STEMI) patients in order to determine an absolute coronary resistance threshold by thermodilution for early diagnosis of MVO.

The main secondary objectives will be to compare the different microcirculatory assessment parameters with each other, not indexed and indexed to the myocardial mass at risk (coronary resistance, IMR, CFR, Resistance Reserve Ratio) and to establish a link between high resistance or IMR and the occurrence of rhythm disorders at D1, D2 and D3.

All patients presenting for STEMI by occlusion of a proximal coronary artery, vascularizing a large volume of myocardium corresponding to an APPROACH score> 21, in the first 12 hours following the onset of chest pain, will be included.

Data relating to medical history, lifestyle (sedentary lifestyle, smoking, drug use), cardiovascular risk factors will be collected.

The management of acute coronary syndrome will be carried out in accordance with the European Society of Cardiology guidelines of 2015. An emergency coronary angiography will be used to revascularise the patient as indicated. Thromboaspiration, stenting, antithrombotic agents and other treatments will be administered according to angiographic and clinical criteria.

The FFR guide (PressureWire® Certus® from St Jude Medical Abbott) will be used to make pressure and temperature measurements. It has been used in daily practice since the FAME study in 2011 to guide the therapeutic decision in patients with an intermediate lesion.

An injected cardiac magnetic resonance imaging (MRI) will be performed between 48 hours and 7 days following the infarction in accordance with current practices.The initial trans-thoracic ultrasonography as well as the various blood samplings will be performed according to standard practice.

The Rayflow® microcatheter will be used to allow the optimal delivery of physiological saline solution into the studied artery. It will be mounted on the FFR guide already in place as part of the angioplasty procedure. Bayer's Medrad® Mark 7 Arterion® infuser will be used to deliver saline continuously at a flow rate of 15-20 mL/min through the Rayflow® microcatheter

Inclusion Criteria:

• Acute ST + coronary syndrome seen within 12 hours after the initial pain: ST offset in 2 contiguous leads ≥ 1mm or ≥ 2mm in precordial or inaugural left branch block, permanent or transient with chest pain > 20 min
• Patient with an indication for emergency coronary angiography with angioplasty
• Acute occlusion of a large caliber artery corresponding to an APPROACH score ≥21: proximal or mean anterior interventricular artery, proximal circumflex artery or proximal right coronary artery
• Final Thrombolysis In Myocardial Infarction (TIMI) of 2 or 3 at the end of the angioplasty procedure regardless of the initial TIMI score
• Free and informed written consent to participate in the study

Exclusion Criteria:

• Known history of infarction in the same territory : STEMI or NSTEMI (angioplasty programmed for angina does not constitute a criterion for non-inclusion)
• Haemodynamic instability requiring the initial use of vasopressive amines or circulatory assistance (counterpulse balloon or extracorporeal membrane oxygenation) or mechanical ventilation (a recovered cardiopulmonary arrest does not constitute an exclusion criterion)
• Technical impossibility of performing IMR or Rayflow® measurements (tortuous or calcified artery)
• Persistent high-grade atrioventricular block after primary angioplasty
• Cardiomyopathy or severe valvulopathy which can induce microcirculatory abnormalities (congenital heart diseases, dilated cardiomyopathy, cardiac amyloidosis, hypertrophic heart disease, mitral regurgitation, aortic regurgitation, tricuspid regurgitation or pulmonary regurgitation grade 3 or 4, tight aortic stenosis or pulmonary stenosis with average gradient > 40 mmHg or vmax > 4m/sec , tight mitral stenosis or tricuspid stenosis with average gradient > 10mmHg)
• Contraindication to performing cardiac MRI: wearing a pacemaker, intracerebral clip, intraocular foreign body, neurostimulator, severe renal failure with glomerular filtration rate < 30 mL/min, body weight > 150 kg
• Age < 18 years
• Pregnant or breastfeeding woman
• Inclusion in another research protocol < 30 days
• Patient not affiliated to a social security scheme
• Patient under guardianship or curatorship