Comparison of Ambulance Officer Working Diagnosis of ST-Elevation Myocardial Infarction with Final Hospital Diagnosis: An Observational Study

Cardiac disease is a leading cause of morbidity and mortality around the world, accounting for more than one-third of total deaths. Cardiac disease causes myocardial infarction and affects thousands of New Zealanders each year. An ST-Elevation Myocardial Infarction (STEMI) is a myocardial infarction identifiable by an elevated ST-segment on the electrocardiograph. STEMI is thought to represent approximately 33% of myocardial infarction presentations and is associated with delayed diagnosis and an increased risk of death. There is evidence that ambulance officers can recognise STEMI from a 12-lead ECG, however, the accuracy of STEMI diagnosis varies between studies and there is no direct comparison to the New Zealand context. The primary aim of this thesis was to investigate whether those patients with STEMI were recognised as having STEMI by ambulance officers when compared with confirmed hospital diagnosis of STEMI. The secondary aim was to identify predictors of ambulance and hospital diagnostic agreement. This cross-sectional study linked data from the Auckland ambulance service electronic patient report forms, with patient data from hospital medical records, to explore diagnostic agreement. The observational study adopted a quantitative approach and included records for 268 cases. This study found that the sensitivity of ambulance officer STEMI diagnosis was 84.3% and the specificity was 53.5%. The high sensitivity indicated that the ambulance officer will rarely miss a STEMI for those patients who had the condition. The low specificity implied a potential to overestimate STEMI with a high number of false-positives. However, a low specificity may be acceptable when the patient is suspected of having a time-critical life-threatening medical emergency such as STEMI. The downside to this is the potential complications to the wider system of care such as incorrect early activation and/or bypass toward the cardiac catheterisation laboratory or the inappropriate administration of thrombolytic therapy. Results from the secondary outcomes indicated the strongest predictors for diagnostic agreement were the ambulance retrieval location type and patient symptom severity. When compared to the retrieval of a patient from the home location, a patient referred from a healthcare facility was three times less likely to have diagnostic agreement with the hospital. Finally, patients assessed with initial clinical symptom severity of Status Two, when compared to those assessed at Status One (more severe), were less likely to have diagnostic agreement with the hospital. This study highlights several important aspects regarding the current prehospital system of care within New Zealand. The diagnosis of STEMI by ambulance officers within the prehospital environment is possible, but there remains a high level of incorrect diagnosis to support a truly autonomous model of ambulance officer initiated hospital bypass or thrombolysis. This research provides an understanding of current clinical practice and can help to inform policy, education and most importantly, clinical practice