Myocardial infarction with no obstructive coronary artery disease is more common in women

The Canadian Cardiovascular Society and the Canadian Women’s Heart Health Alliance have collaborated to develop guidelines on the diagnosis and management of myocardial infarction with no obstructive coronary artery disease (MINOCA). The guidelines focus on five key areas: 1) what MINOCA is and how not to miss it; 2) the importance of excluding diagnostic “mimickers”; 3) diagnostic pathways, including lab testing and noninvasive and invasive imaging; 4) the importance of understanding the underlying pathophysiology causing the MINOCA event to optimize treatment; and 5) the added benefit of post-acute care resources, including referral to cardiac rehabilitation and centres of excellence. MINOCA is defined as myocardial infarction (MI) without significant coronary artery stenosis (i.e., > 50%) on coronary angiography. It represents 6%–15% of all MIs, disproportionately affects women and is likely underdiagnosed. Compared to patients with MI caused by obstructive coronary artery disease (MI-CAD), MINOCA patients tend to be younger, are twice as likely to be female, and are less likely to have hyperlipidemia. Atherosclerotic causes account for about two-thirds of MINOCA. They most commonly include plaque disruption due to rupture, erosion and calcific nodules, all of which can result in thrombus formation and distal thromboembolization. Nonatherosclerotic coronary causes include epicardial coronary vasospasm, thromboembolism, spontaneous coronary artery dissection and coronary microvascular dysfunction.Patients with MINOCA usually present similarly to patients with MI-CAD, with symptoms of acute chest discomfort or dyspnea, and elevated cardiac troponin level. Symptoms might be accompanied by electrocardiogram changes and new left ventricular regional wall motion abnormalities. MINOCA occurs more frequently in the setting of a non-ST elevation MI compared with ST elevation MI (STEMI). The prognosis of patients who present with MINOCA is not benign. In a recent publication including 8,560 consecutive STEMI patients, five-year mortality hazard risk was 1.93 times higher in patients with MINOCA than in those with MI-CAD.Diagnosis The guidelines outline a comprehensive diagnostic pathway for MINOCA, including practical tips for making a diagnosis. Management is based on expert opinion, because of the lack of available data from randomized clinical trials evaluating the efficacy of pharmacologic therapy in patients with MINOCA.Nonpharmacologic treatment strategies include referral to a cardiac rehabilitation program to optimize a heart healthy lifestyle and to modify existing risk factors. Triggers should be avoided in patients who might have an allergic MINOCA precipitant. Read: An extremely effective and simple piece of preventative medicine? Get patients to cut down on salt.Pharmacologic treatments are based on the specific cause of MINOCA:Coronary plaque disruption (or erosion). Treatment is similar to MI-CAD because of the common pathophysiology. Patients should be prescribed cardioprotective therapies, including acetylsalicylic acid (ASA), a P2Y12 inhibitor (clopidogrel or ticagrelor), an angiotensin-converting enzyme inhibitor (ACEI)/angiotensin receptor blocker (ARB) and a β-blocker. Patients with significant left ventricular dysfunction (ejection fraction < 40%) and those with hypertension, diabetes or stable chronic kidney disease should receive an ACEI or ARB. Statins are also indicated. Coronary microvascular dysfunction. Small studies have reported improvement in chest pain with β-blockers and calcium channel blockers and to a lesser extent, nitrates. Ranolazine is a second-line therapy. Improvements in endothelial dysfunction markers, angina scores, coronary flow reserve and exercise-induced ischemia have been reported with statins and ACEIs.Coronary vasospasm. The mainstay of therapy includes calcium channel blockers (e.g., diltiazem) and nitrates. The development of tolerance might limit the long-term use of nitrates. In patients with ongoing angina, dual calcium channel blocker therapy (with nondihydropyridine and dihydropyridine agents) may be considered.Spontaneous coronary artery dissection (SCAD). Conservative medical therapy is recommended over acute revascularization, unless there is acute hemodynamic instability. ASA and β-blockers are the cornerstone of medical treatment. Patients who undergo percutaneous coronary intervention and stenting have a clear indication for dual antiplatelet therapy (DAPT), but the benefit of DAPT remains uncertain for those treated medically, and DAPT might increase bleeding risk. A common practice is to treat patients with lifelong ASA, as well as clopidogrel for three months (maximum 12 months). In premenopausal women who experience menorrhagia with DAPT treatment, low-dose ASA alone is recommended. Lipid-lowering therapy should only be prescribed to SCAD patients with a dyslipidemia indication. Coronary embolism. Anticoagulation is recommended in patients with atrial fibrillation, suspected or diagnosed prosthetic valve thrombosis, or intracardiac thrombus. Unknown underlying cause. The exact underlying mechanism leading to MINOCA cannot be confirmed in about 15% of cases. Therapy should be individualized to optimize the cardiovascular risk profile and treatment targeted to the probable underlying etiology. ACEI/ARB therapy should be considered in patients with MINOCA from plaque disruption or in whom an obvious other cause has not been identified. Statins should be considered in all patients when a specific cause has not been identified. Evidence is lacking to support the use of β-blockers in the absence of another indication. Currently, there is little evidence to support the systematic use of DAPT. Read: Updated Canadian guidelines on cardiovascular fitness to driveReferral to specialized centres should be considered in difficult to manage cases, to assist in management and to improve outcomes. As MINOCA disproportionately affects women, specialized care is often provided in women’s heart health centres or clinics, which currently exist in British Columbia, Ontario, Quebec and Nova Scotia.The guideline authors encourage the use of timely diagnostic and treatment protocols for MINOCA at each institution to avoid underdiagnosis. They also highlight the need for ongoing research to refine diagnostic algorithms and to establish randomized clinical trials specific for the MINOCA population.Reference:Pacheco C, Coutinho T, Bastiany A, et al. Canadian Cardiovascular Society/Canadian Women’s Heart Health Alliance clinical practice update on myocardial infarction with no obstructive coronary artery disease (MINOCA). Can J Cardiol 2024;40(6):953-68. (accessed June 13, 2024).

Register for free access or login.