Ongoing Opioid Treatment and Symptoms of Myocardial Infarction in Calls to the Emergency Medical Services

Background: Ongoing opioid treatment can potentially modify symptoms of myocardial infarction (MI) and cause a lack of recognition and treatment delay. Objectives: The purpose of this study was to examine MI symptoms and the time to hospitalization for patients in ongoing opioid treatment compared to patients without ongoing opioid treatment. Methods: We evaluated calls to the Copenhagen Emergency Medical Services in Denmark from 2014 to 2018. Calls were included when followed by hospitalization and a diagnosis of MI. Symptoms of MI and the time from call to hospitalization in patients in ongoing opioid treatment initiated prior to the onset of MI were compared to a control group of MI patients without opioid treatment. Results: In total, 6,633 calls were included; 552 calls from patients in opioid treatment and 6,081 calls from controls. Patients in opioid treatment were older and had more comorbidities than controls. Chest pain was less prevalent in MI patients in opioid treatment compared to controls (adjOR: 0.70; 95% CI: 0.57-0.85). The median time from the call to hospitalization was longer in patients in opioid treatment than in controls (50 vs 47 minutes; P = 0.006). Conclusions: In calls to the Emergency Medical Services, opioid treatment initiated prior to the onset of MI was associated with less frequent chest pain in MI. Therefore, awareness of ongoing opioid treatment may improve telephone triage of patients with MI, as symptom presentation in opioid-treated patients may differ and potentially challenge and delay the emergency response.