Acute myocardial infarction: incidence and outcomes in an intensive care unit

Objective

To enhance the precision of the definition of acute myocardial infarction (AMI), the European Society of Cardiology/ American College of Cardiology (ESC/ACC) recently updated the diagnostic criteria for AMI. Given this change in AMI diagnostic criteria, little is known about the current incidence of AMI in the ICU and the associated clinical outcomes. We undertook a study to inform these issues.

Design

A prospective 2-month cohort study.

Setting

A 15-bed closed university-affiliated medical–surgical ICU.

Methods

We enrolled all consecutive ICU patients from 12 July to 12 September 2004. All aspects of patient management were at the discretion of the ICU team, which was unaware of the study to limit any influence on ECG or troponin test-ordering practices. As clinically indicated, 12-lead ECGs were performed by a technologist during the day, or by the ICU bedside nurse for emergencies, during the evenings and weekends. We adapted the Joint ESC/ACC redefinition of AMI for the ICU setting. Two investigators independently classified all patients as AMI or no AMI; discordance was resolved by discussion and criterion review. We used Wilcoxon Two-Sample Rank Sum Test to test for differences in continuous variables and Fisher's Exact Test for dichotomous variables.

Result

We screened 117 ICU admissions but considered only the first admission of two patients who were admitted twice. We enrolled 115 patients aged 64.1 (± 17.2) years with an APACHE II score of 21.9 (± 9.8); 83 (72.2%) patients were medical. Overall ICU mortality was 21.7% and hospital mortality was 27.8%. Of 115 patients 93 (80.9%) patients had both at least one ECG performed and one troponin measurement during ICU admission, seven (6.1%) patients had at least one ECG performed but no troponin measurement, 11 (9.6%) patients had at least one troponin measurement but no ECG performed, and four (3.5%) patients had neither an ECG nor troponin. Using the ESC/ACC criteria adapted to the ICU setting, 24 of 115 (20.9%) patients developed AMI (crude agreement between adjudicators was 88%).

Conclusion

One-fifth of these medical–surgical critically ill patients sustained an AMI. Patients with AMI had a significantly higher mortality than those who did not. More research is needed on appropriate AMI definitions in the ICU setting, risk factors, detection methods, mechanisms of myocardial necrosis during critical illness, optimal prevention and treatment strategies, and long-term prognosis.

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