Should we always call 911/999 to get it right first time in suspected myocardial infarction?

Abstract

Public information campaigns have gone to great lengths to emphasise that a suspected myocardial infarction is a medical emergency requiring immediate medical attention. In the UK, the message is simple, ‘Time is Muscle’—dial 999. Highly skilled call handlers perform the challenging task of telephone triage to determine the urgency of response and the rapid dispatch of medical personnel. While standardised triage questions for chest pain are used to help make an informed judgement regarding the clinical severity, it is widely appreciated that the accuracy of these medical dispatching systems is very low and this results in an excessive deployment of emergency medical responders to mitigate any potential harm to patients. Indeed, even when senior medical input is involved in the triage decisionmaking, myocardial infarction only accounts for one in nine of chest pain callouts. In the prehospital setting, emergency medical services are aware of the modest sensitivity (approximately 80%) of an early triage assessment to safely rule out myocardial infarction, hence the high rate of transfers to hospital for early biomarker analysis. This simple pathway of dial 999—emergency medical services assessment—immediate hospital transfer is rightly considered the gold standard for achieving a timely assessment and early intervention to minimise the complications of ischaemia and subsequent infarction. However, despite the call for immediate medical attention being a critical part in initiating the ‘chain of survival’, there is a paucity of data regarding this prehospital decisionmaking. Importantly, does a deviation from this simple pathway by using alternative access points for health services result in more harm to patients with myocardial infarction? To address this question, Hodgins and colleagues performed a retrospective nationwide analysis using data linkage from Scottish healthcare records of 26 325 patients admitted with myocardial infarction over 2 years. Using International Classification of Disease 10th Revision (ICD) codes (I21 and I22) to capture the diagnosis of myocardial infarction, they were able to link multiple datasets from the Scottish National Health Service telephone triage service (NHS24), the Scottish Ambulance Service, outofhours primary care, emergency departments and acute hospital admissions units to ascertain the patient pathway which resulted in an acute hospital admission for myocardial infarction. Pathways which were ‘direct’ (those patients who had an uninterrupted admission from the call to an acute hospital bed) were compared with ‘indirect’ (those patients who had multiple prehospital assessments prior to an admission to an acute hospital bed) using a primary outcome measure of coronary artery disease mortality at 28 days. Quite surprisingly, there were 370 unique pathways by which patients were admitted to an acute hospital bed, of which only 15 were classified as ‘direct’ (figure 1). These 15 ‘direct’ pathways accounted for 92.1% of the myocardial infarction admissions in keeping with the recognised public health message that ‘Time is Muscle’. Reassuringly, if a patient’s pathway started by calling out an ambulance or by directly presenting to the emergency department, then over 95% of these patients would be appropriately admitted for further management. However, if the first point of contact was NHS24 or contact with an outofhours general practitioner, the rates of direct admission for the myocardial infarction fell to 76.9% and 62%, respectively. Of concern, the highest rates of coronary artery disease relatedmortality within 28 days of admission were in these later two groups (NHS24, 6.4%, n=318; outofhours primary care, 10.6%, n=23). Patients managed via an ‘indirect’ pathway had worse outcomes compared with those managed via a ‘direct’ pathway. In a model adjusted for age, sex, social deprivation