Acute Coronary Syndrome

Acute coronary syndrome (ACS) occurs when an atherosclerotic plaque ruptures, leading to thrombus formation within a coronary artery, or coronary thrombosis.⁵ Patients who develop acute coronary syndrome symptoms such as chest pain and diaphoresis, require timely evaluation to determine the cause.^{9, 83} When ACS is diagnosed, further stratification into categories of ST-elevation myocardial infarction (STEMI), non-ST-elevation myocardial infarction (NSTEMI), and unstable angina guides therapeutic decision-making. Following recovery from an episode of ACS, patients continue to be at heightened risk of heart attack and stroke, for which a range of secondary preventive treatments are available.^{84, 85}

Risk assessment is a key step in the emergency management of patients with ACS. Stratifying patients by likelihood of morbidity and mortality guides management decisions. A range of risk-scoring systems have been devised to enable clinicians to select the appropriate antithrombotic or fibrinolytic therapy.⁸⁶

Patients with complete occlusion of a coronary artery can often be identified by ST-segment elevation on electrocardiogram (ECG). This group, representing approximately one in three patients presenting with ACS, should receive prompt reperfusion treatment with fibrinolytic therapy or percutaneous coronary intervention (PCI). The remaining two thirds of ACS patients do not have ST-segment elevation on initial ECG and require further risk stratification.⁹

Serial evaluation of biomarkers, including troponin, C-reactive peptide, and B-type natriuretic peptide, provide independent, additive prognostic data to complement history and physical examination findings and ECG results.⁸⁶ These findings determine whether the problem is non-ST-elevation myocardial infarction (NSTEMI) or unstable angina; the urgency of treatment for these conditions varies depending on a patient’s specific clinical situation.

The risk of cardiovascular death, recurrent myocardial infarction (MI), or progression to MI in patients initially presenting with unstable angina is greatest during the first two months after the acute event.⁸³ Subsequently, the clinical course of most patients with ACS is similar to that of patients with chronic stable coronary disease.

Because atherosclerotic plaque is often present throughout the arterial tree, patients who survive an episode of ACS live with an ongoing risk of a recurrent acute cardiovascular event, such as MI, sudden cardiac death, or stroke.⁸⁴ For patients who received a drug-eluting stent during revascularisation, there is an additional risk of late in-stent thrombosis.⁸⁷

A wide range of treatments are available to protect the heart and to decrease the propensity for recurrent atherothrombosis in survivors of ACS.⁸⁵

Calculating clinical risk scores can help to estimate the risk of morbidity and mortality in patients with suspected ACS. Widely employed systems include the GRACE (Global Registry of Acute Coronary Event) risk score, which evaluates the risk of death or myocardial infarction (MI) in patients with ACS, and the Thrombolysis In Myocardial Infarction (TIMI) risk score for STEMI and NSTEMI.²⁶² These scores are based on the following risk factors:

TIMI Risk Score Factors	GRACE Risk Score Factors
Age ≥ 65 years Over 3 risk factors for ischaemic heart disease (family history, hypertension, hypercholesterolaemia, diabetes, smoking) Known ischaemic heart disease Aspirin use in the past 7 days 2 episodes of severe angina in 24 hours ST segment changes ≥ 0.5 mm Positive troponin T	Age Heart rate Systolic blood pressure Killip class Cardiac arrest ST segment deviation Cardiac biomarker status

While the TIMI score is designed to be used acutely, the GRACE risk model provides prognostic estimates both at the time of initial presentation to the hospital and for a period of up to 6 months following hospital discharge.²⁶²

Patients with complete occlusion of a coronary artery can often be identified by ST-segment elevation on electrocardiogram (ECG). This group, representing approximately one in three patients presenting with ACS, should receive prompt reperfusion treatment with fibrinolytic therapy or percutaneous coronary intervention (PCI). The remaining two thirds of ACS patients do not have ST-segment elevation on initial ECG and require further risk stratification.⁹

The risk of cardiovascular death, recurrent myocardial infarction (MI), or progression to MI in patients initially presenting with unstable angina is greatest during the first two months after the acute event.⁸³ Subsequently, the clinical course of most patients with ACS is similar to that of patients with chronic stable coronary disease.

Because atherosclerotic plaque is often present throughout the arterial tree, patients who survive an episode of ACS live with an ongoing risk of a recurrent acute cardiovascular event, such as MI, sudden cardiac death, or stroke.⁸³ For patients who received a drug-eluting stent during revascularisation, there is an additional risk of late in-stent thrombosis.⁸⁷

A wide range of treatments are available to protect the heart and to decrease the propensity for recurrent atherothrombosis in survivors of acute coronary syndrome.^{23, 85} In 2007, the European Society of Cardiology (ESC) convened a task force that published evidence-based guidelines to assist clinician’s managing non-ST-segment elevation ACS. More recently, in 2010, a task force comprised of members from the ESC, the European Association for Cardio-Thoracic Surgery, and the European Association of Percutaneous Cardiovascular Interventions collaborated to develop guidelines on both surgical and percutaneous approaches to myocardial revascularisation.²⁸⁵