Investigations

• ECG

Look for features suggestive of cardiac ischaemia

• 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

ST elevation or depression, Q waves and T wave inversion help diagnose MI

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
central or left-sided chest pain b (pre-test probability: 18%)	myocardial infarction (CK-MB at 24 hours)	ST elevation in 2 contiguous leads	62 (15 to 250)	93%	0.61 (0.51 to 0.74)	12%
attending emergency department with chest pain (pre-test probability: 20%) b	myocardial infarction (ECG and cardiac enzyme changes)	new ST-segment elevation 1 mm or more	(5.7 to 54)	59% to 93%
anterior chest pain b (pre-test probability: 12%)	myocardial infarction ( ECG and cardiac enzyme changes )	any ST-segment elevation	11 (7.1 to 18)	61%	0.45 (0.34 to 0.60)	6%
attending emergency department with chest pain b (pre-test probability: 20%)	myocardial infarction ( ECG and cardiac enzyme changes )	new ST depression	(3.0 to 5.2)	43%
attending emergency department with chest pain (pre-test probability: 20%)	myocardial infarction ( ECG and cardiac enzyme changes )	new ST depression	(3.0 to 5.2)	43%
anterior chest pain b (pre-test probability: 12%)	myocardial infarction ( ECG and cardiac enzyme changes )	any ST-segment depression	3.2 (2.5 to 4.1)	31%	0.38 (0.26 to 0.56)	5%
attending emergency department with chest pain (pre-test probability: 20%) b	myocardial infarction ( ECG and cardiac enzyme changes )	new Q wave	(5.3 to 25)	57% to 86%
anterior chest pain (pre-test probability: 12%) b	myocardial infarction ( ECG and cardiac enzyme changes )	any Q wave	3.9 (2.7 to 5.7)	36%	0.60 (0.47 to 0.76)	8%
anterior chest pain (pre-test probability: 12%)	myocardial infarction ( ECG and cardiac enzyme changes )	T-wave peaking and/or inversion 1 mm or more	3.1	44%
anterior chest pain (pre-test probability: 12%)	myocardial infarction ( ECG and cardiac enzyme changes )	new T-wave inversion	(2.4 to 2.8)	38% to 41%
attending emergency department with chest pain b (pre-test probability: 20%)	myocardial infarction ( ECG and cardiac enzyme changes )	new conduction defect	6.3 (2.5 to 16)	61%
anterior chest pain (pre-test probability: 12%) b	myocardial infarction ( ECG and cardiac enzyme changes )	any conduction defect	2.7 (1.4 to 5.4)	28%	0.89 (0.79 to 1.0)	11%
anterior chest pain (pre-test probability: 12%)	myocardial infarction ( ECG and cardiac enzyme changes )	normal ECG	(0.1 to 0.3)	2% to 7%