Coronary Microvascular Dysfunction in Myocardial Infarction with Non-Obstructive Coronary Arteries

Study group : MINOCA – patients with myocardial infarction and non-obstructive coronary arteries. All participants will undergo Breathing-Induced Myocardial Oxygenation Reserve (B-MORE) oxygen-sensitive cardiac magnetic resonance imaging (OS-CMR) to assess myocardial oxygenation, enabling comparison across the four study groups. Device description The intervention will use a clinical whole-body 3 Tesla cardiac magnetic resonance imaging system equipped with standard multi-channel cardiac radiofrequency coils. Oxygenation-sensitive imaging will be performed using a validated blood-oxygen-level–dependent (BOLD) CMR pulse sequence, which will be sensitive to changes in myocardial oxygenation and will not require ionising radiation or intravenous contrast administration. What participation will involve Participants will attend a single CMR study visit. Following routine MRI safety screening, participants will be positioned supine within the scanner. Standard cardiac localiser and cine sequences will be acquired, followed by oxygenation-sensitive imaging performed at rest and during a controlled hyperventilation manoeuvre. This will include baseline image acquisition, followed by a 60-second period of paced hyperventilation at a rate of 30 breaths per minute. Hyperventilation will be guided by a metronome delivered through the CMR speaker system. Immediately following hyperventilation, participants will perform a voluntary maximal breath-hold, during which oxygenation-sensitive CMR images will be continuously acquired until normal breathing is resumed. Participants will then rest and breathe normally for 180 seconds to allow physiological parameters to return to baseline. Following the recovery period, the breathing manoeuvre will be repeated in accordance with the same protocol. Duration and frequency The intervention will be performed once only. The total scan duration will be approximately 45 to 60 minutes. Who will deliver the intervention The CMR examination will be conducted by accredited cardiac MRI radiographers. The hyperventilation protocol will be supervised by trained clinical staff in accordance with institutional CMR procedures. Location/setting The intervention will be conducted within a hospital-based clinical MRI facility at Flinders Medical Centre, South Australia Adherence and fidelity monitoring Adherence to the intervention will be ensured by completion of the imaging protocol during the scheduled visit. Fidelity will be maintained through the use of a standardised OS-CMR acquisition protocol and a predefined hyperventilation procedure. Compliance with the hyperventilation manoeuvre will be monitored in real time by radiographers via direct communication with participants and review of respiratory pattern and image quality. Image datasets will be reviewed by experienced CMR investigators to confirm protocol adherence and adequacy of the physiological stress response.