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Acute Coronary Syndrome

Acute Coronary Syndrome (ACS) includes myocardial infarction and unstable angina

Definition

  • Ischemic heart disease caused by blockage to the coronary arteries, resulting in ischemic damage and sometimes infarction

 

Risk factors

  • Hypertension
  • High cholesterol
  • Low HDL
  • Smoking
  • Age
  • Male
  • Diabetes
  • Family history
  • Alcohol
  • Inactivity/sedentary lifestyle
  • Q-risk and risk visualisers are often used to estimate risk

 

Differential diagnoses

  • Angina/NSTEMI/STEMI (whichever it is not)
  • Pleural effusion
  • Pneumothorax
  • GORD
  • Peptic ulcer
  • Pericarditis
  • Cardiac tamponade
  • Aortic dissection
  • Pneumonia
  • Skeleto-muscular injury

 

Epidemiology

  • Coronary heart disease is biggest cause of death in the UK
  • Mortality from CHD is decreasing
  • More common in men
  • North/south divide in mortality
  • More common in SE Asian

 

Aetiology

  • Atheroma rupture and thrombus lodging in coronary arteries
  • Blocks oxygen supply to the myocardium
  • Ischemia, which is transient in angina, but causes infarction in MI

 

Clinical features

  • Angina
    • Central crushing and severe chest pain (usually on exertion)
    • Pain relief on rest
    • Associated SOB
    • Angina pain at rest is ‘unstable angina’
    • Pain relieved by NO spray
  • MI
    • Central crushing chest pain
    • May radiate to left (or right) arm, shoulder and jaw
    • SOB
    • Pallor
    • Clammy
    • Nausea/indigestion
    • Sense of impending doom
    • ST elevation on ECG (unless is an NSTEMI)

 

Pathophysiology

  • Ischemia of over 20 minutes causes irreversible damage – infarction
  • Fibrous cap rupture – thrombus stuck in coronary artery
  • Platelet adhesion and further thrombus ‘growth’
  • The severity of an MI depends on three factors:
    • The level of the occlusion in the coronary artery
    • The length of time of the occlusion
    • The presence/absence of collateral circulation.
  • The larger the myocardial infarction, the greater the chance of death because of a mechanical complication or pump failure.
  • Survival of an MI results in some lasting damage to the myocardium that takes time to develop

 

Investigations

  • ECG
    • ST elevation of >2 squares in 2 adjacent leads
    • NSTEMI does not have ST elevation – may instead show ST depression
  • Blood test – cardiac enzymes
    • Elevated troponin I, myoglobin, creatinine kinase
  • Angiogram
    • Contrast medium and imaging highlights areas of narrowing
    • Can be invasive or CT angiography
  • Angina: ECG/exercise tolerance ECG, angiogram, trial of NO

 

Management

  • Angina
    • GTN spray: vasodilation, mainly of peripheral arteries, so reduction in afterload and preload, so reducing the work required of the heart
    • Beta blockers – reduces contractility (reduced O2 requirement) and reduces heart rate (increases diastole and coronary artery filling)
    • Calcium channel blocker –
      • Dihydropyridine class: relaxes arteriolar smooth muscle, reduces afterload therefore reduces the amount heart has to work/contract: so reduced O2 requirement
      • Non-dihydropyridine class (verapamil) – relaxes arteriolar smooth muscle, reduces contractility and reduces heart rate
  • MI
    • Loading dose of aspirin (300mg)
    • Sublingual GTN spray
    • O2 if sats are below 94%
    • Pain relief (eg morphine and anti-emetics)
    • PCI (Percutaneous intervention) – catheter inserted, and clot cleared, balloon inflated, stent put in (may be drug-eluting stent)
    • Anticoagulation with fondaparinux/heparin alongside PCI
    • Thrombolysis only used for STEMI if cannot reach a centre with a cath lab, or too much time has passed
    • Thrombolysis may be used for NSTEMI
    • Thrombolytic agents:
      • Streptokinase
      • Altepase/recombinant tissue plasminogen activator (rtPA)
    • Antiplatelet drugs:
      • Aspirin given during acute MI
      • Aspirin and clopidogrel given for 6 months after

 

Prognosis

  • 3 out of 10 die from heart attack
  • Figure is lower in the community – out of hospital cardiac arrest survival rate is about 1 in 10 (NB MI doesn’t necessarily mean cardiac arrest)
  • Around 1 admission due to heart attack every 3 minutes
  • MI is likely to lead to heart failure because of the damage to the myocardium
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