Investigations

Perform

• a blood count ^b
• urea, electrolytes and creatinine ^d
• glucose ^d
• lipid levels ^d
• serial cardiac enzymes, ideally CK-MB ^c

• troponin T  ^{a b c} or troponin I ^c
• myoglobin ^c
• serial creatine kinase (CK) ^{b c}, aspartate transaminase (AST) ^a, lactate dehydrogenase (LDH) ^a, taken over 24 hours ^a
• a 12-lead ECG ^{a b} - read it carefully! ^a

• any ST elevation particularly if in 2 or more leads or not known to be old ^{a b}
• any ST depression particularly if not known to be old ^b
• any Q waves particularly if in 2 leads or more or not known to be old ^{a b}
• any T wave inversion particularly if not known to be old ^b
• any conduction defect particularly if not known to be old ^b

• acute injury: ST elevation in 1 mm or more in 2 contiguous limb leads, or 2 mm or more in 2 contiguous precordial leads,
• acute ischaemia : ST depression 1 mm or more in 2 contiguous leads or symmetrical T wave inversion of 3 mm or more in 2 contiguous leads,
• in patients with BUNDLE BRANCH BLOCK: ST depression or elevation 1 mm or more towards deflection of main QRS deflection in 2 contiguous leads, or 7 mm or more away from QRS deflection and > 50% amplitude of T wave in 2 contiguous leads   

Perform a chest X-ray ^a, looking for 

• a lobar infiltration ^c

• widening of the ^b

• aorta (particularly the aortic knob)
• mediastinum
• pleural effusion ^b
• tracheal shift ^b
  
• cardiomegaly ^b
• interstitial oedema ^b
• inverted pulmonary blood-flow distribution ^b

Use the following clinical prediction rule to rank your patient for risk of a myocardial infarction ^a

If clinical finding not present, go onto next question a			probability of MI
ST elevation or Q waves in 2 or more leads, not known to be old			75%
			.
chest pain began 48 hours ago or more	=>	ST-T changes of ischaemia or strain, not known to be old	22%
		no changes or old	1.6%
previous history of angina or MI	=>	ST- T changes of ischaemia or strain, not known to be old	26%
		longest pain episode < 1 hour	4.0%
		pain worse than prior angina or the same as a prior MI	11%
.		pain not as bad	1.0%
pain radiates to neck, left shoulder or left arm	=>	aged < 40	2.4%
.		chest pain reproduced by palpation	1.3%
		pain radiates to back, abdomen or legs	7.7%
.		chest pain stabbing	1.8%
		chest pain not stabbing	17%
-
ST- T changes of ischaemia or strain, not known to be old			26%
no changes or old			2.0%

Patients at low-risk for a myocardial infarction can be assessed in a rapid evaluation unit ^b by

• CK-MB at 0, 4, 8, 12 hours
• serial 12-lead ECGs
• clinical assessment at 0, 6, 12 hours
• exercise ECG
  if all the above negative

• pain worse than prior angina or the same as the pain associated with a prior myocardial infarction
• systolic blood pressure <110 mmHg
• rales above the bases bilaterally
• ST elevation or Q waves, not known to be old, in two or more leads
• ST segment or T wave changes, not known to be old, indicative of myocardial ischaemia   

For patients with possible coronary artery disease, but no clear evidence, consider

• adding 3 right precordial leads to the 12-lead ECG ^a
• stress testing, using any of 
  • exercise ECG   ^a looking for ^a
    • horizontal or down sloping ST slope and 1 mm or more of depression ^b in any lead
    • angina during test
  • exercise echocardiography ^a
  • scintigraphy ^{a b} - Look for a reversible perfusion defect ^b
  • exercise SPECT (single-photon emission computed tomography) ^a
  • electron-beam CT ^a
  • angiography ^a

Patients with normal coronary arteries and chest pain can be found to have multiple potential causes on exhaustive testing - including psychiatric disorders ^c