Myocardial infarction: a new LBBB or ST elevation concordant with the QRS complex made it more likely

Clinical bottom line (level 1b)

  1. One in eight patients presenting to an emergency department with suspected cardiac ischaemia had a myocardial infarction.
  2. A new LBBB on ECG made a myocardial infarction more likely (LR + 12) .
  3. ST elevation 1 mm or more concordant with the QRS complex made a myocardial infarction more likely.
  4. No ECG criteria studied could safely rule out a myocardial infarction.
Li et al: Ann Emerg Med 2000; 36 : 561-565
Expires February 2004

The study

Setting: urban teaching hospital, USA

190 patients (aged mean 73, 85% male) with suspected ischaemia (chest pain, dyspnoea, palpitations, syncope, epigastric pain or cardiac arrest) and LBBB

Excluded if
  • underwent thoracotomy or cardiac catheterisation before MI could be diagnosed or excluded
  • incomplete set of cardiac enzymes over 24 hours
  • incomplete medical records


Independent blinded reference standard, applied in all patients from a consecutive appropriate spectrum.
Reference standard:
  • elevated CK-MB (at least 5% of total CK)
Diagnostic test: ECG interpreted by 2 physicians. MI diagnosed if any of the following:
  • ST elevation 1 mm or more concordant with QRS complex
  • ST elevation 5 mm or more discordant with QRS complex
  • ST-depression in leads V1 to V3

The evidence

pre-test probability of myocardial infarction: 13%, (95% CI: 8.4% to 18%)

diagnostic test myocardial infarction no myocardial infarction LR+
(95% CI)		 post-test probability LR-
(95% CI)		 post-test probability
new LBBB 11 6 12
(4.9 to 30) 		65% 0.58
(0.41 to 0.82) 		8%
ST elevation 1 mm or more and concordant with QRS 4 0 -
(8.9 to infinity) 		100% 0.84
(0.71 to 1.00) 		11%
ST elevation 5 mm or more discordant with QRS 2 8 1.7
(0.37 to 7.3) 		20% 0.97
(0.86 to 1.1) 		13%
ST depression in leads V1 to V3 0 3 0.0
(0.0 to 6.2) 		0% 1.0
(1.0 to 1.0) 		13%
Any of the above 3 present 5 12 2.8
(1.1 to 7.1) 		29% 0.86
(0.71 to 1.1) 		12%
total 25 165

K interobservor: ST elevation 1 mm or more and concordant with QRS: 0.97 (95% CI: 0.94 to 0.99)
K interobserver: ST elevation 5 mm or more and discordant with QRS: 0.92 (95% CI: 0.87 to 0.96)
K interobserver: ST depression in leads V1 to V3: 0.96 (95% CI: 0.93 to 0.99)

Comments

  1. The study was performed retrospectively, and validated a set of rules derived by Sgarbossa et al.

Citation

  1. Li SF, Walden PL, Marcilla O, et al: . Ann Emerg Med 2000; 36 : 561-565
Search Terms: from ACP Journal Club other articles noted
Contributor: Chris Ball, February 2002
Reviewer:

Clinical Question.
Patient suspected cardiac ischaemia and LBBB
Intervention or Exposure ECG criteria
Outcome myocardial infarction