Investigations

• any ST elevation, particularly if in two 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 two 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

Why?

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 h)	ST elevation in two contiguous leads	62 (15 to 250)	93%	0.61 (0.51 to 0.74)	12%
attending emergency department with chest pain b (pre-test probability: 20%)	myocardial infarction (ECG and cardiac enzyme changes)	New ST segment elevation 1mm 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%
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 b (pre-test probability 20%)	myocardial infarction (ECG and cardiac enzyme changes)	New Q wave	5.3 to 25	57% to 86%
anterior chest pain b (pre-test probability 12%)	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 b (pre-test probability 12%)	myocardial infarction (ECG and cardiac enzyme changes)	T wave peaking and/or inversion 1mm or more	3.1	44%
anterior chest pain b (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 b (pre-test probability 12%)	myocardial infarction (ECG and cardiac enzyme changes)	Any conduction defect	2.7 (1.4 to 5.4)	28%	0.89 (0.79 to 1.00)	11%
anterior chest pain b (pre-test probability 12%)	myocardial infarction (ECG and cardiac enzyme changes)	Normal ECG	0.1 to 0.3	2% to 7%

Note

• Few patients with a normal ECG go on to have life-threatening complications (1.3%; 95% CI: 0.0 to 3.0%) c  

An abnormal admission ECG makes life-threatening complications more likely

Patient	Prognostic factor	Outcome	Control rate	RR (95% CI)	NNF+ (95% CI)
suspected MI c	abnormal admission ECG  not independent	VT, VF or heart block at discharge	1%	23.7 (3.29 to 171)	7  (1 to 73)