Shedding light on the grey zone: characterisation and predictors of poor outcome in patients with suspected myocardial infarction triaged to the observe zone
Authors: Hartikainen T , Gossling A , Soerensen N A , Haller P M , Lehmacher J , Toprak B , Zeller T , Blankenberg S , Twerenbold R , Westermann D , Neumann J T 
Published: October 2022

Abstract

Background
To facilitate a rapid triage of patients with suspected myocardial infarction (MI), the European Society of Cardiology (ESC) recommends the application of a 0/1h-algorithm based on cardiac troponin. Patients, in whom neither rule-in nor rule-out of MI is possible, are assigned to the observe zone. Management of these patients can be challenging due to their heterogeneous nature. We aimed to characterize patients in the observe zone and identify predictors of incident cardiovascular events in these patients.

Methods
Patients with suspected MI presenting to the emergency department of a German tertiary center were prospectively enrolled. High-sensitivity cardiac troponin I (hs-cTnI) was measured at baseline and after 1 hour. Based on the ESC 0/1h algorithm, patients were stratified into rule-in, rule-out and observe zones. The final diagnosis was adjudicated according to the 4th Universal Definition of MI. We performed uni- and multivariable Cox regression analyses to identify predictors of major cardiovascular events (MACE), defined as the composite of all-cause mortality, recurrent MI and cardiac hospitalisation at 1 year in the observe zone.

Results
We included 2491 patients, of which 1046 (42.0%) were triaged to the rule-out zone, 512 (20.6%) to the rule-in zone and 933 (37.4%) to the observe zone. Observe patients were significantly older (median age 71 years vs. 56 years for rule-out vs. 69 years for rule-in) and more often male than patients in the rule-in and rule-out zone, respectively (67.1% vs. 58.8% vs. 66.6%). Cardiovascular risk factors were comparably frequent in observe and rule-in patients, but significantly more common than in rule-out patients. Angiography and consecutive percutaneous interventions during the index presentation were performed less frequently in observe patients (22.6% and 9.2%) than in rule-in patients (62.5% and 36.5%) but more often than in rule-out patients (9.9% and 3.8%).
Among observe patients, 50 (5.4%) were diagnosed with MI and 452 (48.4%) with acute or chronic myocardial injury. At 1 year, the rate of MACE in the observe zone was significantly higher (25.0%) than in rule-out patients (12.2%) but only slightly lower than in rule-in patients (29.7%). Univariable and consecutive multivariable analyses with a backward selection process identified atrial fibrillation, hs-cTnI at 1h, hypertension, diabetes and a higher NYHA class as independent predictors of MACE (Table 1).

Conclusion
About one third of patients with suspected MI are categorized into the observe zone. These patients had almost comparably poor outcome as rule-in patients. Atrial fibrillation, hs-cTnI at 1h, hypertension, diabetes and a higher NYHA class were identified as predictors of an impaired outcome. These predictors could contribute to improving the identification of subjects at high risk in the observe zone and thereby facilitate management of these patients.

Funding Acknowledgement
Type of funding sources: None.