Investigations

• 12-lead ECG looking for 
  • ischaemic changes ^a
  • evidence of arrhythmias ^a  

Why?

• An ECG helps diagnose a cause in 11% of cases (95% CI: 7% to 15%) ^b

No ischaemic changes on the first ECG make acute cardiac ischaemia less likely.

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
transient loss of consciousness a (pre-test probability: 7%)	cardiac ischaemia (serial ECG, cardiac enzymes and records)	ischaemic abnormalities on ECG	2.1 (1.8 to 2.4)	14%	0.0 (0.0 to 0.29)	0%

An abnormal ECG increases the risk of an arrhythmia

Patient	Prognostic Factor	Outcome	CER	RR (95% CI)	NNF+ (95% CI)
unexplained syncope a	abnormalities on ECG independent	syncope due to cardiac arrhythmia at 12 months	20%	23.5 (7.0 to 78.7)	2 (1 to 2)