Acute Coronary Syndrome (ACS)
Acute coronary syndrome (ACS) is a group of cardiac conditions caused by interruption of blood flow to the heart muscle, with varying degrees of severity. These include:
ST-elevation myocardial infarction (STEMI): A severe type of heart attack in which one of the heart's major arteries is blocked. This is the classic form of myocardial infarction.
Non-ST-elevation myocardial infarction (NSTEMI): An intermediate form of ACS in which a blockage occurs either in a smaller coronary artery or causes partial obstruction of a larger coronary artery. Symptoms may be similar to STEMI, but the extent of myocardial damage is usually smaller.
Unstable angina: A thrombus partially or intermittently blocks a coronary artery.
Stable angina is not considered an acute coronary syndrome.
ACS is a type of coronary artery disease (CAD), which is responsible for one third of all deaths in people over 35 years of age. Some forms of CAD may be asymptomatic, but ACS is always symptomatic.
Epidemiology
Acute coronary syndrome (ACS) and sudden death are major causes of mortality related to ischemic heart disease (IHD), which accounts for 1.8 million deaths annually. The incidence of IHD and ACS increases with age, although it generally occurs 7–10 years earlier in men than in women. ACS is far more common in men than women below the age of 60, while women make up the majority of patients over 75. Lifetime risk of acute coronary events is related to exposure to traditional cardiovascular risk factors.
There are major differences between European and global regions in the incidence and prevalence of IHD and ACS, as well as in mortality rates.
Causes
The most common cause of ACS is rupture of an atherosclerotic plaque in the coronary arteries. Other, less common causes include:
Aortic or coronary artery dissection
Vasculitis
Connective tissue diseases
Use of recreational drugs, such as cocaine
Coronary artery spasm
Evaluation
The first assessment performed is an ECG, which helps distinguish between STEMI, NSTEMI and unstable angina. According to American Heart Association guidelines, all patients with symptoms that may indicate ACS should have an ECG performed within 10 minutes of arrival.
The catheterization laboratory should be activated as soon as STEMI is confirmed at a center that performs percutaneous coronary intervention (PCI).
Cardiac biomarkers, particularly troponin and the CK-MB/CK ratio, are important when evaluating NSTEMI versus myocardial ischemia without tissue necrosis.
A chest X-ray may be useful for diagnosing other causes of chest pain, such as pneumonia or pneumothorax. Blood tests including a complete blood count (CBC), chemistry panel, liver function tests and lipase can help distinguish intra-abdominal pathology that may present with chest pain.
Clinical manifestations
The clinical manifestations of acute coronary syndrome (ACS) vary, but typical symptoms include:
Angina pectoris (chest pain), which may indicate unstable angina or acute myocardial infarction.
Chest pain, often described as a squeezing or pressure sensation that may radiate to the arms, neck, jaw, back or abdomen.
Shortness of breath (dyspnea), which may occur during exertion or at rest.
Nausea, dizziness and sweating may also occur together with the pain.
Other manifestations may reflect angina, myocardial infarction or coronary artery disease, all of which can form part of the acute coronary syndrome spectrum.
Treatment
Reperfusion therapy:
A diagnosis of STEMI requires immediate reperfusion therapy to restore normal coronary blood flow and limit infarct size. Percutaneous coronary intervention (PCI) is associated with an approximately 30% reduction in mortality and a lower risk of intracranial bleeding and stroke, making it the preferred option for older adults and people at increased bleeding risk. Under optimal conditions, PCI can restore coronary blood flow in more than 90% of cases, whereas fibrinolytic drugs restore blood flow in approximately 50–60% of cases.
Oxygen therapy:
Supplemental oxygen should be administered to patients with signs of respiratory distress, heart failure, shock or an arterial oxyhemoglobin saturation below 94%.
Nitroglycerin:
Nitroglycerin has beneficial effects in ACS. It dilates the coronary arteries, peripheral arterial vessels and venous capacitance vessels. Nitroglycerin is administered cautiously, particularly when its use may limit other beneficial medications. Patients with ischemic symptoms may receive up to three doses of 0.4 mg at 3–5 minute intervals, until chest pain is relieved or low blood pressure limits further use.
Antiplatelet therapy:
This treatment involves medications that are mainly taken orally, including aspirin, ADP receptor blockers and glycoprotein IIb/IIIa inhibitors.
Beta-blockers:
Beta-blockers have been shown to reduce mortality and infarct size when administered intravenously early and may help prevent arrhythmias. They reduce cardiac workload and oxygen demand by lowering contractility, heart rate and blood pressure.
Anticoagulation:
Anticoagulant medications such as unfractionated heparin (UFH), low-molecular-weight heparin (LMWH) or bivalirudin have been shown to reduce the risk of reinfarction after reperfusion therapy.
Prevention and lifestyle modification
To help prevent acute coronary syndrome, modifiable risk factors should be addressed, including diet, physical activity, management of hypertension and diabetes, and smoking cessation. In line with NICE guidance, healthcare professionals should recommend a Mediterranean-style diet, 20–30 minutes of daily physical activity to the point of mild breathlessness, and smoking-cessation support. Policy changes in Scotland, including legislation banning smoking in public places and workplaces, have been associated with a substantial reduction in hospital admissions for ACS.
Cardiac rehabilitation and education can improve prognosis and reduce mortality associated with ACS.
Sources:
Verywell Health Non-ST Segment Myocardial Infarction Overview:https://www.verywellhealth.com/non-st-segment-elevation-myocardial-infarction-nstemi-1746017
Radiopaedia ACS: https://radiopaedia.org/articles/acute-coronary-syndrome
Aragam, K.G. & Bhatt, D.L., 2011. Antiplatelet therapy in acute coronary syndromes. Journal of cardiovascular pharmacology and therapeutics, 16(1), pp.24–42
Singh A, Museedi AS, Grossman SA. Acute coronary syndrome.: https://www.ncbi.nlm.nih.gov/books/NBK459157/
Davies MJ. The pathophysiology of acute coronary syndromes. Heart. 2000 Mar 1;83(3):361-6.: https://oxfordmedicine.com/view/10.1093/med/9780198784906.001.0001/med-9780198784906-chapter-305
Davies, M.J., 2000. The pathophysiology of acute coronary syndromes. Heart (British Cardiac Society), 83, pp.361–366.
