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Importance of patient selection in evaluating a cardiac ambulance service
Insights
Special cardiac ambulances may seem effective for heart attack patients, but selection bias complicates results. Low-risk cases were chosen, making true effectiveness hard to determine.
Area of Science:
- Emergency medicine
- Cardiology
- Health services research
Background:
- Cardiac ambulance services aim to improve outcomes for patients experiencing heart attacks.
- Assessing the true effectiveness of specialized emergency medical services can be challenging due to patient selection factors.
Purpose of the Study:
- To evaluate the effectiveness of a dedicated cardiac ambulance service compared to routine ambulances for patients with heart attacks.
- To identify potential biases in patient selection for the cardiac ambulance.
Main Methods:
- A comparative study following patients transported by a special cardiac ambulance versus routine ambulances.
- Analysis of mortality rates and patient characteristics between the two transport groups.
Main Results:
- Patients in the cardiac ambulance group had a lower mortality rate (40%) compared to routine ambulances (51%).
- However, patients with similar risk profiles who did not use the cardiac ambulance when available showed higher mortality (68%), suggesting selection of lower-risk patients for the cardiac ambulance.
- Factors like short symptom duration and public-initiated calls were associated with cardiac ambulance use.
Conclusions:
- The study highlights the difficulty in evaluating cardiac ambulance effectiveness due to unintentional selection of lower-risk patients.
- Further research with methods to mitigate selection bias is needed to accurately assess the impact of cardiac ambulance services.
Abstract:
All patients brought to hospital by a special cardiac ambulance were followed up and compared with patients carried by routine ambulances to assess the effectiveness of a cardiac ambulance service. The overall mortality of patients with heart attacks was 51% among those carried by an ordinary ambulance and 40% among those carried by the cardiac ambulance. The apparently low mortality in the latter group was balanced, however, by a high mortality (68%) among patients carried by ordinary ambulances when the cardiac ambulance was available but not used; these patients tended to have a short duration of symptoms and heart attacks away from home, and their ambulance was more often called by a member of the public than a general practitioner. It seems therefore that low-risk cases were inadvertently selected for transport by the cardiac ambulance; such unintentional selection makes it difficult to evaluate a cardiac ambulance service.