Myocardial infarction: ST elevation in 2 contiguous leads on the initial ECG diagnosed it

Clinical bottom line (level 2b)

  1. One in six patients presenting to an emergency department with central or left-sided chest pain had a myocardial infarction.
  2. ST elevation in 2 contiguous leads on the initial ECG diagnosed a myocardial infarction (LR+61) .
  3. An elevated total CK (LR+6.0) , elevated leukocyte count (LR+6.8) or a decreased relative lymphocyte percentage (LR+6.3) made a myocardial infarction more likely but were not diagnostic.
Thomsen et al: Annals of Internal Medicine 1995; (122): 335-341
Expires March 2003

The study

Setting: emergency department, university hospital, USA

384 patients (aged , % male) presenting with anterior or left lateral chest pain

Excluded if
  • insufficient data to exclude MI
  • failed to return after 24 hours for repeat blood tests
  • infection in the previous week
  • exogenous glucocorticoid use in the previous month
  • malignancy in previous 5 years
  • transferred from another hospital
  • major trauma, major gastrointestinal bleeding, surgery, dialysis or resuscitation in the previous week
  • aged < 20
Independent blinded reference standard, applied in all patients from a non-consecutive appropriate spectrum.
Reference standard:
  • one of
    • CK-MB level > 9.6 mg/dl within 48 hours
    • sudden unexplained death within 72 hours
Diagnostic test:
  • ECG: ST elevation 1 mm or more in 2 contiguous leads
  • creatine kinase
  • leukocyte count

The evidence

pre-test probability of myocardial infarction: 18%, (95% CI: 14% to 22%)

diagnostic test myocardial infarction no myocardial infarction LR+
(95% CI)		 post-test probability LR-
(95% CI)		 post-test probability
positive ECG 27 2 62
(15 to 250) 		93% 0.61
(0.51 to 0.74) 		12%
elevated creatine kinase 29 22 6.0
(3.7 to 9.8) 		57% 0.62
(0.50 to 0.76) 		12%
elevated leukocyte count 33 22 6.8
(4.3 to 11) 		60% 0.56
(0.45 to 0.70) 		11%
decreased relative lymphocyte percentage 40 29 6.3
(4.2 to 9.4) 		58% 0.46
(0.35 to 0.61) 		9%
total 69 315

Comments

  1. The study also reported elevated rapid CK-MB levels, but since CK-MB is included in the reference standard the test characteristics are inaccurate.

Citation

  1. Thomsen SP, Gibbons RJ, Smars PA, et al: Incremental value of the leukocyte differential and the creatine kinase-MB isoenzyme for the early diagnosis of myocardial infarction. Annals of Internal Medicine 1995; (122): 335-341
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Contributor: Chris Ball, February 2000
Reviewer:

Clinical Question.
Patient chest pain
Intervention or Exposure creatine kinase, ECG, leukocyte count, lymphocyte count
Outcome myocardial infarction