Investigations Of Acute Coronary Syndromes

Question 1

What are acute coronary syndromes?

Answer 1

The classifications overlap and are far from perfect

• Pathology:
  
  • Atheromatous plaque rupture
• Rarer pathologies:
  
  • Coronary dissection
  • Coronary spasm.
• Not all that causes myocardial damages are coronary.

Question 2

How do you classify acute coronary syndromes based on an ECG?

Answer 2

ST elevation = STEMI or Aborted STEMI

No ST elevation = NSTEMI or Unstable Angina.

Troponin? = Yes - STEMI and NSTEMI. No - Aborted STEMI and UA

Question 3

What is the universal definition of an MI?

Answer 3

Cardiomyocyte necrosis in a clinical setting consistent with acute MI ischaemia.

Increased troponin and one of the following things:

• Symptoms of ischaemia
• New significant ST-T wave changes or left bundle branch block
• Pathological Q waves
• New loss of viable myocardium or regional wall motion abnormality.
• Intracoronary thrombus detected on angiopraphy or autopsy

Question 4

What are the subclassifications of MIs?

Answer 4

Type 1 MI: Thrombus in coronary arteries leading to decreased blood flow or distal embolisation and subsequent necrosis

Type 2 MI: A condition other than coronary plaque instability contributes to an imbalance between myocardial oxygen supply and demand. e.g. Anaemia and hypotension

Type 3 MI: MI resulting in death when biomarkers not available

Type 4 MI: MI related to Percutaneous Coronary Intervention

Type 5 MI: MI related to coronary artery bipass surgery

Question 5

How do you investigate an ACS?

Answer 5

You ask the following questions:

• What happened?
  
  • Coronary occlusion or narrowing?
• When did it happen?
  
  • Time frame
• How bad is it?
  
  • Anything else occured?
• Why did it happen?
  
  • Plaque rupture?
  • Dissection?
  • Triggering factors?

Question 6

How do you investigate what happened?

Answer 6

ECG - ST elevation, ST depression, T inversion

Invasive Coronary angiogram - occluded or stenosis.

Troponin level -raised or not (MI or not)

Question 7

How do you investigate “When did it happen”?

Answer 7

ECG - ST changes follow a timeline, Q waves imply established MI (Over 6 hours often over a day)

Profile of serial cardiac enzyme - e.g. troponin rise and fall (go up after 1-2 hours and peak after 1-2 days then tail off) , CK rise and fall.

Question 8

How do you investigate “Where did the MI happen?”

Answer 8

• ECG
  
  • Inferior changes - right coronary artery
  • Anterior changes - left anterior descending
  • Lateral changes - diagonal, obtuse marginal or circumflex.
• Invasive angiogram
• Identifed stenosis,, occlusion, dissection in the specific vessel.
• Echocardiogram - Regional wall motion abnormalities can correlate with the occlusion / stenosed territory

Question 9

How do you work out how bad the MI is?

Answer 9

• Chest X-ray
  
  • Pulmonary Oedema
• Urea and Electrolytes
  
  • Acute kidney injury e.g cardiogenic shock
• ECG and associated cardiac monitoring (bedside, telemetry)
  
  • AV conduction block (heart block)
  • VT, VF
• Echocardiogram
  
  • Ventricular septal defect due to septal infection
  • Mitral regurgitation
  • Left ventricular impairment

Question 10

How do you investiogate why an MI happened?

Answer 10

• Invasive coronary angiogram
  
  • plaque rupture? Vs dissection ect..
• CT aorta if worried about aortic dissection into RCA
• FBC - anaemia? polythaemia? sepsis?
• Lipid profile - triggering factors - e.g. CHD risk factors. Diabetes

Question 11

What does ST elevation on an ECH mean?

Answer 11

Implies sudden occlusion. It ca also persist long term as a mark of LV aneurysm (Q waves usually present)

Question 12

What does ST depression on a ECG mean?

Answer 12

• Usually implies under supply of blood to myocardium by not sudden coronary occlusion.
• If in the anterior leads, it can sometimes be due to sudden occlusion of a vessel at the back of the heart (Posterior STEMI).
• Other non-ischaemia related causes exist too.
• Digoxin can cause ST depression. And Severe Aortic stenosis

Question 13

What does T wave inversion on an ECG mean?

Answer 13

T wave inversion often implies under-supply of blood to myocardium but not sudden coronary occlusion.

There are other non-ischaemia related causes.

Question 14

What else can ECG pick up?

Answer 14

Heart block - various grades

Ventricular dyshythmia - VT, VF, ectopics

Question 15

What typical blood test should be conducted?

Answer 15

• FBC
• U and E
• Glucose
• Lipids
• Troponin
• Others as needed according to rarer conditions

Question 16

Troponin

Answer 16

• Troponin complex important in skeletal and cardiac muscle contractility.
• Cardiac Troponin T and I are highly sensitive and specific to cardiac origin.
• Measured using immunoassay.
• Typically raised within 3hrs of cardiac damage, peak at 24-48hrs and remains elevated for 2+ weeks.
• Raised in many conditions, not just coronary syndromes.

Question 17

Echocardiogram

Answer 17

• Evaluates structure and function.
  
  • Chambers, valves, flow patterns, Complications of MI, Pericardial space, allows interference about filling pressure of right heart.
• Can be small (smallest size of laptop)
• Provide real time imaging in a mobile setting.

Question 18

Invasive coronary angiogram.

Answer 18

This establishes the type of lesion and its location.

• Conducted under local anaesthetic.
• Radial or femoral artery.
• 30Mins procedure.
• Option of dilating narrrowed sections, stenting.
• Option to include intravascular ultrasound or optical coherence tomography.
• Can see lots as this is really high resolution

Question 19

What is the routine of investigations for acute coronary syndromes?

Answer 19

• Clinical History
• Blood tests - troponin, lipids, FBC, U and E
• ECG
• CXR
• Echocardiogram sometimes
• Coronary angiogram often
• Other investigations as necessary