Acute Coronary Syndrome

Question 1

Define acute coronary syndrome (ACS), what it encompasses and its common pathology

Answer 1

ACS encompasses a spectrum of unstable coronary artery disease.

Includes; Unstable angina, STEMI & NSTEMI

Common pathology; ruptured plaque, thrombus formation & inflammation (with vasoconstriction due to platelets releasing serotonin & thromboxane-A2)

Question 2

Define unstable angina

Answer 2

A type of angina pectoris caused by disruption of an atherosclerotic plaque with partial thrombosis & possible embolisation.

Severe pain at rest in crescendo fashion.

Question 3

What are the ECG findings in unstable angina?

Answer 3

• ST depression

Question 4

Define STEMI and explain ECG findings

Answer 4

ST-elevated myocardial infarction

• Transmural necrosis occurs to myocardium due to prolonged ischaemia
• ECG, on leads facing MI;
  
  • ST elevation (transmural infarct causes current flow towards injury (towards +ve electrode..))
  • Hyperacute (tall) T wave which then depress and then return to normal (due to potassium channel changes?)
  • Later Q waves (ECG sees through infarcted tissue to other side of heart, where current in going the opposite way, causing increased negative Q wave)
  • First T waves go up, then ST seg follows, then T waves depress, then ST seg goes normal, then T wave goes normal, then Q wave is born

Question 5

Define NSTEMI and explain ECG findings

Answer 5

Non ST-elevated myocardial infarction

• Subendocardial necrosis occurs to myocardium due to prolonged ischaemia
• ECG, on leads facing MI;
  
  • ST normal/ depressed (subendocardial infarct causes current flow towards injury (away from +ve electrode..))
  • Hyperacute (tall) T wave which then depress and then return to normal (due to potassium channel changes?)
  • No Q waves

Question 6

Outline the risk factors for ACS

Answer 6

• Sex: male
• Age : older
• Diabetes mellitus
• BP high
• Elevated cholesterol (hyperlipidaemia)
• Tobacco
• Sedentary
• Family history
• Obesity

Others include;

• Stress
• Type A personality
• High apoprotein A, fibrinogen, insulinaemia, homocysteine
• Cocaine use

Question 7

What are the symptoms & signs of MI?

Answer 7

Symptoms

• Acute central chest pain lasting >20mins
  
  • Also; nausea, sweatiness, dyspnoea, palpitations
  • OR no pain (silent infarct (elderly, diabetics)
  • May radiate to arms/ neck/ jaw/ teeth

Signs

• Distress, anxiety, pallor, sweatiness
• Inc or dec pulse/ BP
• 4th heart sound (sound of atrium contracting with extra effort [to push blood into ventricles which are stiff due to infarct])
• Heart failure signs;
  
  • Inc JVP
  • 3rd heart sound (due to dilated ventricles which rapidly fill..)
  • Basal crepitations
• Pansystolic murmur
• Low grade fever
• Later;
  
  • Pericardial friction rub
  • Peripheral oedema

Question 8

What are the investigations of and how do you diagnose an MI?

Answer 8

Acute MI;

• Cardiac biomarkers; tropnonin T & I, creatine kinase, myoglobin
• ECG;
  
  • Hyperacute (/inverted) T waves
  • ST elevation (/depression)
  • Q waves
  • New LBBB
• CXR;
  
  • Cardiomegaly
  • Pulmonary oedema
  • Widened mediastnum (aortic rupture)
• Cholesterol (within 12h of onset of symptoms)
• Glucose & HbA1C - Hyperglycaemia common with ACS, indicator of poor survival/ inc. complications
• FBC - anaemia & baseline
• INR, APTT

Question 9

Explain what & why cardiac enzymes are used in investigations

Answer 9

Cardiac troponin (T & I) [gold standard]

• Inc within 3-12hrs after chest pain onset
• Peak 24-48hr
• Baselin 5-14days

Creatinine Kinase

• CK-MM (skeletal muscle); inc after trauma, activity, myositis, afrocaribs, hypothyroidism
• CK-BB (brain)
• CK-MB (heart); THE ONE TO LOOK FOR.

Myoglobin

• Highly sensitive but not specific
• Rice within 1-4hr of chest pain onset

Question 10

Outline differentials for ACS!

Answer 10

• Angina
• Pericarditis
• Myocarditis
• Aortic dissection
• PE
• Oesophageal reflux/ spasm

Question 11

Outline the immediate treatment & management of an Non-/STEMI

Answer 11

Immediate treatment

• Aspirin 300mg
• Atenolol (B-blocker)
• Diamorphine (pain)
• Metoclopramide (antiemetic due to morphine side effect)
• Oxygen

STEMI

• Clopidogrel/ prasugrel (anti platelet’s)
• PCI!!

NSTEMI

• Fondaparinux (similar to LMWH)
• Clopidogrel (anti platelet)
• PCI/ CABG!!

Question 12

Outline the complications of MI

Answer 12

• Cardiac arrest
• Cardiogenic shock
• Unstable angina
• Bradycardias/ heart block
  
  • Sinus bradycardia
  • 1stº - PR > 0.2s (inf MI)
  • 2ndº Type 1 - progressive prolongation of PR until 1 drops
  • 2ndº Type 2 - P wave blocked all or nothing (high risk of complete block, pace them)
  • 3rdº - ALL P waves blocked, atria/ ventricles beating seperatly (usually resolved within days, pace them)
  • Bundle branch block
• Tachyarrhythmias [caused by calcium influx in reperfusion into ischaemic cells (damaged membrane) raising resting membrane potential, also low K+, hypoxia & acidosis)
• Pericarditis [acute MI pericarditis, chemical mediators diffuse to pericardium]
• Dressler’s syndrome [post MI pericarditis, antigens from MI released into circulation, antibodies react with pericardium [[cause pleural effusions, fever, anaemia & inc ESR]]
• Cardiac temponade [rupture & rapid effusion into pericardium (no time to stretch) putting pressure on heart, pulsus paradoxus, inc JVP, muffled heart sounds]
• DVT & PE [prophylactically heparinized]
• Systemic embolism [mural thrombus]
• Mitril regurgitation [papillary muscles]
• Ventricular;
  
  • Septal defect [MI & rupture, pansystolic murmur, inc JVP, cardiac failure]
  • Right ventricular failure [low CO & inc JVP]
  • Left aneurysm [occurs late due to weak wall bulging out, LVF, angina, recurrent VT, systemic embolism]