Investigations

If there is a left bundle branch block, look for ^{a b}

• ST-elevation of 1 mm concordant with the QRS complex
• ST-elevation of 5 mm discordant with QRS complex
• ST-depression of 1 mm in leads V1, V2 or V3

Why?

LBBB: ECG changes make a myocardial infarction more likely

Patient	Target Disorder and Reference Standard	Diagnostic Test	LR+ (95% CI)	Post-test Probability	LR- (95% CI)	Post-test Probability
possible myocardial ischaemia and LBBB on ECG b (pre-test probability: 13%)	myocardial infarction (rise and fall in CK-MB)	ECG change	6.6 (3.2 to 13)	50%	0.58 (0.40 to 0.84)	8%
		new or indeterminate LBBB	1.4 (1.1 to 1.8)	18%	0.41 (0.16 to 1.0)	6%
		elevated initial CK-MB x 100)/CK or ECG with concordant ST-elevation or depression	44 (11 to 180)	88%	0.38 (0.23 to 0.64)	6%