Cardiac enzymes + cardiac imaging + tamponade

Question 1

What cardiac enzymes rise first?

Answer 1

1. Myoglobin is the first to rise
2. CK-MB is useful to look for reinfarction as it returns to normal after 2-3 days (troponin T remains elevated for up to 10 days)

Question 2

What cardiac nuclear imaging is there?

Answer 2

These techniques use radiotracers which are extracted by normal myocardium:

1. Thallium
2. Technetium (99mTc) sestamibi: a coordination complex of the radioisotope technetium-99m with the ligand methoxyisobutyl isonitrile (MIBI), used in ‘MIBI’ or cardiac Single Photon Emission Computed Tomography (SPECT) scans
3. Fluorodeoxyglucose (FDG): used in Positron Emission Tomography (PET) scans

Question 3

What is SPECT?

Answer 3

• SPECT assesses myocardial perfusion and myocardial viability
• Two sets of images are usually acquired
• First the myocardium at rest followed by images of the myocardium during stress (either exercise or following adenosine / dipyridamole)
• By comparing the rest with stress images any areas of ischaemia can classified as reversible or fixed (e.g. Following a MI)

Question 4

What is MUGA?

Answer 4

• Multi Gated Acquisition Scan, also known as radionuclide angiography

1. Radionuclide (technetium-99m) is injected intravenously
2. Patient is placed under a gamma camera
3. May be performed as a stress test
4. Can accurately measure left ventricular ejection fraction.

​Typically used before and after cardiotoxic drugs are used

Question 5

What is cardiac CT?

Answer 5

Assess** **suspected ischaemic heart disease, using two main methods:

1. Calcium score: correlation between the amount of atherosclerotic plaque calcium and the risk of future ischaemic events. Cardiac CT can quantify the amount of calcium producing a ‘calcium score’
2. Contrast enhanced CT: allows visualisation of the coronary artery lumen

If these two techniques are combined cardiac CT has a very high negative predictive value for ischaemic heart disease

Question 6

What is cardiac MRI?

Answer 6

• Cardiac MRI (CMR) has become the gold standard for providing structural images of the heart
• Useful when assessing:
  
  • Congenital heart disease
  • Determining right and left ventricular mass
  • Differentiating forms of cardiomyopathy
  • Myocardial perfusion can also be assessed following the administration of gadolinium
  • Currently CMR provides limited data on the extent of coronary artery disease

Question 7

What is cardiac tamponade?

Answer 7

Cardiac tamponade is characterized by the accumulation of pericardial fluid under pressure

Question 8

What are classical features of cardiac tamponade?

Answer 8

Classical features - Beck’s triad:

• hypotension
• raised JVP
• muffled heart sounds

Question 9

What are some other features of cardiac tamponade?

Answer 9

Other features:

• dyspnoea
• tachycardia
• an absent Y descent on the JVP - this is due to the limited right ventricular filling
• pulsus paradoxus - an abnormally large drop in BP during inspiration
• Kussmaul’s sign - much debate about this
• ECG: electrical alternans

Question 10

What is the difference between cardiac tamponade and constrictive pericarditis?

Answer 10

Question 11

What is the management of cardiac tamponade?

Answer 11

• urgent pericardiocentesis

Question 12

What are some centrally acting anti-hypertensives?

Answer 12

1. Methyldopa: hypertension during pregnancy
2. Moxonidine: essential hypertension when conventional antihypertensives have failed to control blood pressure
3. Clonidine: the antihypertensive effect is mediated through stimulating alpha-2 adrenoceptors in the vasomotor centre