The main aim of the present study was to develop an index of EMS response time for CVD-related calls between 2017 and 2019. Our main findings suggest that there is a significant variation in EMS response time over space and time, with significant clusters of low/or high response time and CVD-related mortality in Mashhad.
Previous studies highlight that clinical events and calls to clinical emergency services are not random, and follow a regular pattern. This pattern depends on specific time of the day, levels of car traffic, places of residence and commuting throughout the city, and other epidemiologic and demographic factors (17). Sudden myocardial infarctions, for example, follow a regular pattern of occurrence (22–25), with most events occurring between morning and noon (26, 27). Moreover, some studies report seasonal or weekly patterns of occurrence of myocardial events, with a reported increase on Mondays (28–31). Our study findings highlighted that the number of emergency requests follows a pattern of increased incidence between morning and noon, in line with the findings of previous studies. Moreover, we also observed an increasing pattern of emergency calls between 6 pm and midnight. This pattern was observed consistently across all days of the week from 2017 to 2019 (Fig. 4). Given the fact that a previous study (32) identified sudden wake-up and heavy workload as the main risk factors for myocardial infarction, these two factors could explain the higher rate of incidence in the morning (sudden wake-up) and evening (heavy workload). Moreover, while in some studies the weekly pattern of peak incidence rate was identified as occurring on Mondays, in our study this was found to be Saturdays (Fig. 5). This is likely to be due to the difference between the working week in Iran and that of the rest of the world. In Iran, Saturday is the first day of the week, and Friday is considered to be the weekend. The lowest rate of calls was recorded on Thursdays in the first year of study, and on Fridays in the second and third year of the study. Although Fig. 2 shows that the volume of delivered emergency services has increased by 15% in 2018 and 20% in 2019, a general look at the delivered services reveals that the ratio of cardiovascular-related emergency services to the total number of emergency services is 17.4, 17.5, and 17.3 for the past three calendar years, respectively. We could therefore interpret this to mean that not only CVD call requests, but all emergency calls, have increased.
Figure 6 shows the spatial distribution of EMS calls, demonstrating that the south-eastern areas of Mashhad have the highest number of emergency service requests. This is an area in proximity to the Holy Shrine, which is a central destination for tourists and a pilgrimage location. It is an area with a high concentration of hotels, residential complexes and shopping malls. As such, there is a high population density and heavy traffic congestion in this area as compared to the rest of Mashhad.
The most important temporal criterion in assessing the performance of the pre-hospital emergency services is response time. The standard response time is 8 minutes, which is directly related to higher survival rate and reduced mortality (33). The average response time for the three consecutive years was calculated as 11.35 ± 6.5 minutes, showing a pattern of decreasing response times: 12.33 ± 5.48 in 2017, 11.36 ± 6.46 in 2018 and 11.07 ± 6.77 in 2019. Another important criterion in assessing the performance of pre-hospital emergency services is scene interval, which represents the duration of time emergency technicians are present at the scene. The global gold standard for this criterion is 10 minutes (34). Patients should be managed in such a way so as to minimize delays in their transfer to clinical centers. In Iran, scene interval is typically less than twenty minutes (21). The average scene interval was calculated as 13.02 ± 7.77 minutes for the past consecutive three years, showing a decreasing pattern. Although both these criteria lag far behind global standards, this difference is not uniformly distributed across different areas of the city.
Cluster maps in Fig. 8 show significant differences in the performance of emergency departments across different areas of the city in relation to temporal criteria. A thorough analysis reveals that in the central areas of the city, where response time is high, there is no problem in terms of call to hospital time and scene to hospital time. The high response time may relate to a high volume of calls in this area due to its population density, leading to an increased response time in the central area of Mashhad. On the contrary, in the southern and rural areas of the city, which have a good response time, a weak call to hospital time and scene to hospital time is observed. This problem is likely due to the fact that the location of emergency dispatch centers is not properly linked with their respective hospitals. This should be taken into account to improve health standards and survival rate of patients.
The cluster map of Fig. 9 shows the mortality rate of patients with myocardial infarction who died before ambulance arrival. As can be observed, the south eastern area is associated with a significantly higher risk of mortality when compared to other areas. An analysis of the mean age for these subjects indicates that they have a higher mean age (71.91 ± 20.07). This is observed across all three years.
Previous studies report that a higher response time is directly associated with a higher rate of mortality (33). Although the response time is shorter in this group of patients (9.62-minute vs 11.35 for the entire population), the mortality rate is higher when compared to that of the total population. This needs to be investigated further to identify drivers (risk factors) of CVD related mortality other than response time. Some of these risk factors include patients’ age, delays in requesting emergency services, previous history of disease, lack of knowledge about heart disease, and loneliness and life style, which are mentioned in previous studies (35, 36). Given that the mean age of this group of patients is significantly higher than the rest of the population, it could be speculated that because of the higher age, other factors such as loneliness, low health literacy, previous disease history (more advanced disease, more comorbidities as a result of older age) could be the most significant driver of increased mortality despite quick response time in older people
Limitations:
No data was available about the time interval between the onset of chest cardiac symptoms and the decision by the patient to request emergency services, which is an important determining factor for patient survival.