Unrecognised myocardial infarction and its relationship to outcome in critically ill patients with cardiovascular disease

Abstract

Purpose: To establish the incidence of myocardial infarction (MI) in ICU patients with co-existing cardiovascular disease (CVD), and explore its association with long-term survival.

Methods: In a multi-centre prospective cohort study in 11 UK ICUs, we enrolled 273 critically ill patients with co-existing CVD. We measured troponin I (cTnI) with a high sensitivity assay for 10 days; ECGs were carried out daily for 5 days and analysed by blinded cardiologists for dynamic changes. Data were combined to diagnose myocardial 'infarction', 'injury' or 'no injury' according to the third universal definition of MI. Patients were followed-up for 6 months. Regression and mediation analyses were used to explore relationships between acute physiological derangements, MI, and mortality.

Results: cTnI was detected in all patients, with a rise/fall pattern consistent with an acute hit. In 73% of patients, this peaked on days 1-3 [median 114 ng/l (first, third quartiles: 27, 393)]. Serial ECGs indicated 24.2% (n = 66) of patients experienced MI, but > 95% were unrecognized by clinical teams. Type 2 MI was the most likely aetiology in all cases. A further 46.1% (n = 126) experienced injury (no ECG changes). Injury and MI were both associated with 6-month mortality (reference: no injury): OR injury 2.28 (95% CI 1.06-4.92, p = 0.035), OR MI 2.70 (95% CI 1.11-6.55, p = 0.028). Mediation analysis suggested MI partially mediated the relationship between acute physiological derangement and 6-month mortality (p = 0.002), suggesting a possible causal association.

Conclusions: Undiagnosed MI occurs in around a quarter of critically ill patients with co-existing CVD and is associated with lower long-term survival.

Keywords: Cardiovascular disease; Cohort study; Critical care; Myocardial infarction; Troponin.