Inconsistent measurement of acute coronary syndrome patients' pre-hospital delay in research: a review of the literature

Background: Patients' treatment-seeking delay remains a significant barrier to timely initiation of reperfusion therapy. Measurement of treatment-seeking delay is central to the large body of research that has focused on pre-hospital delay (PHD), which is primarily patient-related. This research has aimed to quantify PHD and its effects on morbidity and mortality, identify contributing factors, and evaluate interventions to reduce such delay. A definite time of symptom onset in acute coronary syndrome (ACS) is essential for determining delay, but difficult to establish. This literature review aimed to explore the variety of operational definitions of both PHD and symptom onset in published research.

Methods and results: We reviewed the English-language literature from 1998-2013 for operational definitions of PHD and symptom onset. Of 626 papers of possible interest, 175 were deemed relevant. Ninety-seven percent reported a delay time and 84% provided an operational definition of PHD. Three definitions predominated: (a) symptom onset to decision to seek help (18%); (b) symptom onset to hospital arrival (67%), (c) total delay, incorporating two or more intervals (11%). Of those that measured delay, 8% provided a definition of which symptoms triggered the start of timing.

Conclusion: We found few and variable operational definitions of PHD, despite American College of Cardiology/American Heart Association recommendations to report specific intervals. Worryingly, definitions of symptom onset, the most elusive component of PHD to establish, are uncommon. We recommend that researchers (a) report two PHD delay intervals (onset to decision to seek care, and decision to seek care to hospital arrival), and (b) develop, validate and use a definition of symptom onset. This will increase clarity and confidence in the conclusions from, and comparisons within and between studies.