Acute Coronary Syndrome

Acute Coronary Syndrome (ACS) represents a spectrum of clinical conditions ranging from unstable angina (UA) to myocardial infarction (STEMI and NSTEMI). According to the Fourth Universal Definition of Myocardial Infarction, an MI is defined by a rise and/or fall of cardiac troponin with at least one value above the 99th percentile URL plus evidence of myocardial ischaemia (symptoms, ECG changes, or imaging loss of viable myocardium). STEMI is characterized by ST-elevation in ≥2 contiguous leads (≥2mm in V2-V3 for men, ≥1.5mm for women; or ≥1mm in other leads) or new-onset Left Bundle Branch Block (LBBB). NSTEMI presents with ischaemic symptoms and elevated troponin but without persistent ST-elevation. Unstable angina presents as ischaemic symptoms at rest or with minimal exertion without biochemical markers of necrosis. The TIMI or GRACE scores are vital for risk stratifying NSTEMI patients to determine the urgency of invasive coronary angiography. Prompt reperfusion is the cornerstone of STEMI management, ideally via primary Percutaneous Coronary Intervention (PCI) if available within 120 minutes of diagnosis. Secondary prevention is critical to reduce the high risk of recurrence and heart failure, necessitating a lifelong commitment to lifestyle modification and pharmacological therapy.

The primary pathology in 90% of ACS cases is the rupture or erosion of a vulnerable atherosclerotic plaque. Atherosclerosis is a chronic inflammatory process involving the sub-endothelial accumulation of LDL-cholesterol, which becomes oxidized and triggers a macrophage response. These 'foam cells' form a fatty streak. Over time, a fibrous cap forms over a lipid-rich core. When this cap ruptures, the highly thrombogenic core is exposed to circulating blood. This triggers plate-let adhesion, activation, and aggregation, followed by the coagulation cascade. The resulting thrombus leads to partial (NSTEMI/UA) or total (STEMI) occlusion of the coronary vessel. Other mechanisms include coronary artery spasm (Prinzmetal angina), spontaneous coronary artery dissection (SCAD), or mismatch between myocardial oxygen supply and demand (Type 2 MI, e.g., in sepsis or severe anaemia). Irreversible myocyte necrosis begins within 20-40 minutes of total occlusion. Histologically, this progresses from coagulative necrosis to inflammatory infiltration, and eventually replacement with a non-contractile collagenous scar over 6-8 weeks.

The hallmark of ACS is 'cardiac-sounding' chest pain: typically central or retrosternal, heavy or pressure-like (crushing), radiating to the left arm, neck, or jaw. Pain is often associated with autonomic symptoms like diaphoresis (sweating), nausea, and vomiting. Silent MIs are common in elderly patients and those with diabetes, often presenting only with dyspnoea, syncope, or acute confusion. Physical examination may reveal signs of complications: a fourth heart sound (S4), signs of acute heart failure (basal crackles, raised JVP), or a new systolic murmur (mitral regurgitation due to papillary muscle rupture or a ventricular septal defect). Complication risks include arrhythmias (VF is the leading cause of pre-hospital death), cardiogenic shock, Dressler's syndrome (late pericarditis), and thromboembolism. The social history is vital, identifying modifiable risk factors such as smoking, sedentary lifestyle, and poor diet. Patients with STEMI are at immediate risk of re-infarction and sudden cardiac death; hence continuous ECG monitoring is mandatory in the acute phase.

1. Bedside: 12-lead ECG (repeat every 15-30 mins if symptoms continue), Serial vitals.
2. Bloods: High-sensitivity Troponin (at baseline and 3 hours per NICE), FBC (anaemia?), U&Es (renal function for contrast/drugs), LFTs (pre-statin), Glucose, Lipid profile.
3. Imaging: Chest X-ray (pulmonary oedema, widened mediastinum for dissection), Echocardiogram (assess LV function and mechanical complications).
4. Special: Coronary Angiography (Gold standard for anatomy), GRACE score calculation for NSTEMI (6-month mortality risk).

Acute (STEMI): Aspirin 300mg, Nitrates for pain. Primary PCI (if <120 mins) or Fibrinolysis (if >120 mins). Ticagrelor 180mg or Prasugrel 60mg. Heparin during PCI.
Acute (NSTEMI/UA): Aspirin 300mg + Ticagrelor 180mg (or Fondaparinux 2.5mg SC if no immediate PCI). Calculate GRACE score: if >3% risk, aim for angiography <72 hours. Note: Opioids (Morphine) are no longer recommended routinely in NSTEMI — ESC 2023 guidelines advise against routine opioid use due to evidence of increased mortality risk. Use nitrates for pain relief; escalate to senior review if pain is refractory.
Long-term: 1. Dual Antiplatelet Therapy (DAPT): Aspirin 75mg lifelong + second agent (e.g., Ticagrelor) for 12 months. 2. Beta-blocker (e.g., Bisoprolol). 3. ACE-inhibitor (e.g., Ramipril). 4. Statin (Atorvastatin 80mg). 5. Lifestyle: Smoking cessation, cardiac rehab, annual flu jab.