Contribution of Myocardial Perfusion Imaging in the Initial Assessment of Acute Coronary Syndromes Without ST Elevation for the Diagnosis of Myocardial Infarction or Differential Diagnoses

Patients with myocardial infarction require invasive treatment via coronary angiography to confirm the diagnosis and, in most cases, treatment by angioplasty/stenting. In the case of acute coronary syndrome without ST segment elevation (NSTEMI), myocardial infarction is suspected but cannot be confirmed. The recommendations suggest that, in cases of low suspicion, a non-invasive ischaemia test should be performed, but in cases of high suspicion, coronary angiography should be performed immediately (1). In cases of NSTEMI, segmental kinetic abnormalities on echocardiography place the patient under high suspicion of infarction and justify coronary angiography without prior ischaemia testing. However, certain kinetic abnormalities may be related to causes other than infarction: stress cardiomyopathy (TakoTsubo), left bundle branch block, pacemaker stimulation, myocarditis, leading to unnecessary and potentially harmful invasive examinations. Transthoracic echocardiography (TTE) is central to the initial management of patients hospitalised for NSTEMI, both to confirm the diagnosis and to detect any immediate complications.The use of contrast agents during TEE is already recommended to improve the quality of the examination, as it increases the echogenicity of patients, and several studies have demonstrated its usefulness in analysing myocardial perfusion (2). The only contrast agent currently available in France is Sonovue® (Bracco Imaging). Microbubbles are lipid 'shells' containing a gas (sulphur), with a diameter similar to that of red blood cells (less than 7 μm). The behaviour of microbubbles in the circulation and capillaries can therefore be likened to that of red blood cells, which allows for better visualisation of all the structures through which blood flows (3). Its use is not contraindicated in the acute phase of a myocardial infarction and has few adverse effects (4).

Several studies have shown that the use of contrast agents during perfusion ultrasound can improve the diagnosis of ischaemic heart disease (5) and distinguish stress-induced heart disease (TakoTsubo) from myocardial infarction (6-8). No studies have looked at patients with kinetic disorders of other aetiologies (bundle branch block, pacemaker).

Furthermore, in certain patients presenting with actual myocardial infarction with segmental kinetic abnormalities but no significant coronary lesions on coronary angiography, myocardial MRI is of definite value in confirming or ruling out the diagnosis of healthy coronary artery infarction (1). However, the use of MRI in routine practice is severely limited by the lack of MRI facilities in many centres or by delays in obtaining results that are incompatible with the urgency of diagnosis.

Compared to computed tomography (CT) and MRI, the advantages of contrast-enhanced ultrasound are 1) the possibility of real-time imaging and 2) the absence of nephrotoxicity, risk of hyperthyroidism and radiation exposure. The aim of our study is therefore to compare perfusion ultrasound with coronary angiography and MRI in this population so that, if the results are satisfactory, certain invasive examinations currently considered essential can be avoided.