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Factors influencing ambulance use in patients with ST-elevation myocardial infarction in Beijing, China

YAN, Hong-bing; SONG, Li; CHEN, Hui; ZHANG, Jian; LI, Shi-ying; LI, Qing-xiang; CHENG, Shu-juan; WANG, Jian; ZHAO, Han-jun; HU, Da-yi

Section Editor(s): WANG, Mou-yue; LIU, Huan

doi: 10.3760/cma.j.issn.0366-6999.2009.03.007
Original article
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SDC

Background Emergency medical service plays a key role in the early recognition and treatment of ST-elevation myocardial infarction (STEMI), but studies indicate that the patients experiencing STEMI symptoms often fail to call an ambulance as recommended. This study aimed to examine the current ambulance transport frequency and ascertain predictors and reasons for not choosing ambulance transportation by the patients with STEMI in Beijing.

Methods A prospective, cross-sectional survey was conducted from January 1, 2006 through until June 30, 2007 in two tertiary hospitals in Beijing and included consecutive patients with STEMI admitted within 24 hours of onset of symptoms. Data were collected by structured interviews and medical records review.

Results Of the 572 patients, only 172 (30.1%) used an ambulance, and the remaining 400 (69.9%) presented by self-transport. Multivariate analysis showed that age <65 years (OR: 1.220; 95% CI: 1.001–2.043), lower education level (OR: 1.582; 95% CI: 1.003–2.512), presence of pre-infarction angina (OR: 1.595; 95% CI: 1.086–2.347), and attribution of symptoms to non-cardiac origin (OR: 1.519; 95% CI: 1.011–2.284) were independent predictors for not using an ambulance. However, history of coronary artery disease (CAD), dyspnea, perceiving symptoms to be serious, and knowing the meaning of cardiopulmonary resuscitation appeared to be independent predictors of ambulance use. The main reasons for not using an ambulance were convenience and quickness of self-transport and the decreased severity of symptoms.

Conclusions A large proportion of patients in Beijing do not call for an ambulance after onset of STEMI symptoms. Several factors including demographics, previous CAD, symptoms and cognitive factors of patients are associated with the ambulance use. The public should be educated that an ambulance is not merely a transportation modality and that it also provides rapid diagnosis and treatment.

Edited by

Twenty-eighth Division, Beijing Anzhen Hospital, Capital Medical University, Beijing 100029, China (Yan HB, Song L, Li SY, Li QX, Cheng SJ, Wang J and Zhao HJ)

Beijing Emergency Medical Center, Beijing 100031, China (Chen H) Department of Emergency, China-Japan Friendship Hospital, Beijing 100029, China (Zhang J)

Heart Center, People’s Hospital of Peking University, Beijing 100044, China (HuDY)

Correspondence to: Prof. YAN Hong-bing, Twenty-eighth Division, Beijing Anzhen Hospital, Capital Medical University, Beijing 100029, China (Tel: 86–10–64456541. Email: yan591204@yahoo.com.cn)

This study was supported partially by Beijing Municipal Science and Technology Commission (No. [2005]593).

(ReceivedAugust 1, 2008)

In China, patient mortality due to coronary artery disease (CAD) has dramatically increased since the 1980s. For example, between the years of 1984 and 1999, CAD mortality in Beijing increased by 50% and 27% in men and women, respectively, aged 35–74 years.1 Further, it is estimated that of those who experience a fatal ST-elevation myocardial infarction (STEMI), more than half would die within 1 hour without receiving the required medical attention.2 Therefore, the greatest potential to improve survival lies outside the hospital. The emergency medical services (EMS) can dispatch ambulance crews who are trained to detect and treat life-threatening complications, such as cardiac arrest, at the accident scene and during transport. Additionally, the use of ambulance was associated with wider and quicker receipt of initial reperfusion therapies.3–5 Regrettably, previous studies6–10 indicated that almost half of the STEMI patients arrived at the hospital by other means rather than an ambulance.

Factors influencing ambulance use among STEMI patients have been extensively explored in several countries. Demographics such as age and gender, previous medical history and symptoms were found to be related to the ambulance use.6–8,11 However, few data regarding these to date exist in China. The present study aimed to examine the current ambulance transport rates and ascertain predictors and reasons for not choosing ambulance transportation in the patients with STEMI in Beijing.

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METHODS

Study population and setting

This prospective, cross-sectional survey was conducted from January 1, 2006 through until June 30, 2007, and comprised consecutive patients with STEMI who were admitted to Beijing Anzhen Hospital and China-Japan Friendship Hospital in the Chaoyang district, Beijing.

Patients meeting the following criteria were included in this study: (1) ST-segment elevation >0.1 mV in ≥2 contiguous precordial leads or adjacent limb leads or new left bundle branch block; (2) elevated serum cardiac troponin I; (3) admission within 24 hours of symptom onset. Patients were excluded under the following conditions: (1) their mode of transport was unclear; (2) their clinical condition did not permit them to be interviewed; (3) they had communication problems (serious hearing and cognitive impairments); (4) they were transferred from outside Beijing; or (5) they refused to participate. Participants were categorized into 2 groups (either an ambulance group or a self-transport group) according to their mode of transport to the initial hospital. Especially, those who arrived by ambulance were included in the ambulance group, and those who arrived by other means, such as taxi, car and public transportation, etc, were included in the self-transport group.

The Chinese EMS system is a 1-tiered ambulance system,10 which is far from the ideal system that exists in the developed western countries. With a resident population of 16 millions in Beijing, on an average, each ambulance is responsible for almost 40 000 people. The average daily dispatch is 1014 times (370 000 people/year); among these, 20% dispatches are for emergency, severe, and critical rescue. The average radius for EMS is 10 kilometers, and the average response time ranges from several minutes to 30 minutes depending on the traffic conditions.

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Data collection

Data were collected via structured interviews and reviewing of medical records. A questionnaire was designed to obtain the following information: (1) demographics: age, gender, education level (≥college or <college), marital and work status, monthly income (≥ 2000 or <2000 RMB), health insurance coverage, and living arrangements (living alone or with others); (2) situational factors: time and place of symptom onset, presence of a bystander, self-treatment approaches, and consulting a doctor before seeking care; (3) symptoms: pre-infarction angina (PA) within 48 hours prior to the onset of the infarction, severity of symptoms (bearable or unbearable), location and duration of pain or discomfort, other associated symptoms, such as nausea, vomiting, perspiration, dyspnea, etc; (4) attribution of symptoms (cardiac or non-cardiac origin); (5) time of decision to seek medical care; (6) mode of transport; and (7) knowledge of STEMI and cardiopulmonary resuscitation (CPR). In addition, patients in the self-transport group were asked the question “what was the reason for you to not call for an ambulance”. All patients were interviewed by 4 trained investigators within 7 days after admission.

Medical records were used to obtain information regarding the time of hospital arrival, cardiovascular risk factors, and previous medical history.

Two time interval parameters were evaluated: time interval from the symptom onset to decision to seek medical care (patient delay) and time interval from the symptom onset to the door of the participating hospital (pre-hospital delay).

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Ethical considerations

The study protocol was approved by the Human Research Ethics Committees at the 2 participating hospitals and complied with the Declaration of Helsinki. The purpose of the study was explained and written informed consent was obtained as the same methods as we previously described.10

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Statistical analysis

Continuous data were expressed as mean ± standard deviation (SD). Chi-square test, unpaired Student’s t test and Mann-Whitney U test were used for analysis. A multivariate logistic regression analysis (backward method) was performed to identify the predictors for not choosing ambulance transportation using variables showing marginal association with P <0.10 according to univariate analyses. To ensure adequate sample size for the hypothesis under evaluation, we grouped variables into conceptually meaningful categories. For example, age was categorized as less than or at least 65 years and income as less than or at least 2000 RMB per month. Odds ratios (OR) and 95% confidence interval (CI) were calculated. All significant tests were 2-sided with a statistical significance of P <0.05.

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RESULTS

Sample characteristics

A total of 626 patients met the inclusion criteria in this study. Of them, 54 (8.6%) were excluded because 15 provided incomplete interviews or with missing data, 6 had communication problems, 6 died before they could be approached, 22 were transferred from outside Beijing and 5 refused to participate in the study. An analysis comparing the cases included with those excluded indicated that there were no great differences with regard to age, gender, and means of transport.

For the remaining 572 patients, 76.2% were male with an average age of (61±13) years. The female was significantly older than the male ((68±11) vs (59±12) years, P <0.001). Only 172 (30.1%) arrived at the initial hospital by ambulance; the remaining 400 (69.9%) relied on other means of transport. Ambulance users had greatly shorter patient delays, median of 40 vs 88 minutes (P <0.001) and pre-hospital delays, median of 105 vs 178 minutes (P <0.001) than the patients in the self-transport group. The baseline characteristics of the sample and those of the 2 groups are summarized in Tables 1–4.

Table 1

Table 1

Table 2

Table 2

Table 3

Table 3

Table 4

Table 4

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Factors influencing ambulance use

Demographic variables

On an average, ambulance users were older than the patients who arrived by self-transport, and more likely to have health insurance coverage. Patients with an education level below college chose self-transport more frequently than patients with a college degree. In contrast, sex, marital and work status, income level and living arrangements did not influence the choice of means of transport (Table 1).

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Situational factors

At the onset of symptoms, the majority of the patients were at home and with others. Prior to seeking care, 51.0% attempted some form of self-management and 3.0% consulted a doctor. The use of self-management. was associated with increased ambulance use, whereas consulting a doctor before seeking care was not related to ambulance use. Regarding bystanders, coworkers, friends or strangers appeared to prompt the use of ambulance (P=0.011), whereas family members or relatives did not influence the choice of transport (P=0.098). Additionally, place and time of the symptoms onset seemed to have no effect on the patients’ decision to choose ambulance transport (Table 1).

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Risk factors and previous medical histories

Above 90% of the patients had at least one cardiovascular risk factor. Patients with a family history of CAD were less likely to use the ambulance than those without any family history of CAD. Other risk factors that were examined, such as hypertension, diabetes, dyslipidemia, smoking, and body mass index, were not related to ambulance use. Patients with a history of CAD or stroke used the ambulance more frequently. Additionally, patients with previous myocardial infarction also used the ambulance more frequently compared with patients without a history of myocardial infarction, but the difference was of marginal significance (P=0.057). The prevalence of a history of heart failure was similar between the two groups (Table 2).

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Symptoms

The 3 most commonly reported symptoms were chest pain (90.9%), perspiration (71.9%) and nausea or vomiting (32.3%). PA within 48 hours of onset of the infarction occurred in 50.3% of the sample population, and patients with PA were less likely to use an ambulance when compared with those without PA. Additionally, ambulance users reported more dyspnea, anxiety, and dizziness or syncope than patients in the self-transport group. However, location of pain and other associated symptoms were not associated with ambulance use (Table 3).

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Cognitive factors

Regarding the influence of cognitive factors, patients who attributed their symptoms to cardiac origin and perceived their symptoms to be serious were more likely to use the ambulance than those who did not. Only 12.9% of the patients knew what CPR meant, and far fewer (3.7%) had been trained in CPR. Patients who knew the meaning of CPR and had received CPR training used an ambulance more frequently than those who did not (Table 4).

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Predictors for not choosing ambulance transportation

As illustrated in Table 5, after multivariate logistic regression analysis, age <65 years, lower education level, presence of PA and attribution of symptoms to non-cardiac origin remained as the independent predictors for not using an ambulance. However, dyspnea, history of CAD, perceiving symptoms to be serious, and knowing the meaning of CPR appeared to be independent predictors of ambulance use.

Table 5

Table 5

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Reasons for not calling for an ambulance

The main reasons for not calling for an ambulance were that most patients perceived self-transport to be more convenient (42.0%, n=168) due to their close proximity to the hospital; some patients believed that the symptoms were not severe enough (30.3%, n=121), and that the use of self-transport would enable them reach the hospital more quickly (21.0%, n=84). Additionally, 3.5% (n=14) stated that the cost of using an ambulance was an issue, 1.0% (n=4) stated that they were not aware of the emergency service numbers, and 2.2% (n=9) could not provide a reason for their decision.

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Modes of transport in the self-transport group

In the self-transport group, the most common modes of transport were taxi (45.0%, n=180), private car (38.0%, n=152), and foot (8.3%, n=33). Additionally, 2.5% (n=10) arrived by bicycle, 3.0% (n=12) used the public transport, and 3.3% (n=13) used other means.

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DISCUSSION

Three major findings are as follows: (1) a large proportion of patients did not call for an ambulance after the onset of STEMI symptoms; (2) the independent predictors influencing ambulance use included age >65 years, lower education level, presence of PA and attribution of symptoms to non-cardiac origin, whereas history of CAD, dyspnea, perceiving symptoms to be serious, and knowing the meaning of CPR appeared to be independent predictors of ambulance use; and (3) the main reasons for not using an ambulance were convenience and quickness of self-transport and the decreased severity of symptoms.

In accordance with the results of two other Chinese reports10,12 and several western studies,13–17 ambulance users had shorter pre-hospital delays than self-transport patients. Thus, an effective way to shorten the pre-hospital delay is to encourage the STEMI patients to use EMS in a timely manner. Calling for an ambulance is the recommended response for patients with STEMI in China, as it is in other countries. In the event of STEMI symptoms, contacting the EMS may improve survival in the long term because properly trained ambulance staff can record electrocardiograms (ECGs), administer relevant medical therapy and in the case of an obvious STEMI promote triage directly to a regional heart centre prepared to perform emergent percutaneous coronary intervention (PCI). Unfortunately, the study showed that above two-third of the STEMI patients in Beijing presented to the hospital by self-transport; this is greatly higher than previous data obtained from western countries including Japan and South Korea.6–8,13

In this study, ambulance users were older than the non-ambulance users; this corroborates the findings of other research.18–22 Previous studies indicated that women used an ambulance more frequently.3,18 However, gender did not predict ambulance use in the present study. Hjälte et al20 reported that STEMI patients with a college degree were less likely to call for EMS when compared with those without a college degree. However, in contrast with their results, higher education level was associated with increased ambulance use in the present survey. Although the reasons for the decreased use of ambulance among patients with a lower education level are unknown, our finding at least partly reflects their difficulty in gaining and understanding health-related knowledge, failure to recognize the seriousness of STEMI symptoms and limited awareness of the importance of calling for an ambulance. Thus, it suggests that public health education should be provided through varied approaches, and the education programs must be sensitive to the capabilities of the targeted individuals with different education levels. It is logical that EMS use among underinsured and low-income patients may be influenced by economic considerations. Previous studies have found that ambulance use varied according to the income and type of health insurance.5,23,24 Unexpectedly, neither income level nor insurance status influenced ambulance use after controlling for other baseline characteristics. It should be noted that we did not differentiate the types of health insurance coverage in this study. Consequently, the association between health insurance and ambulance use may warrant further investigation.

Johansson et al7 found that of the patients calling for an ambulance, very few dialed the emergency service number themselves; it was usually the spouse (40%) or the general practitioner (32%) who called for the ambulance. In a survey of 962 community members enrolled in the REACT trial, Brown et al11 reported that 89% of the participants indicated that they would call “911” if they witnessed a cardiac event; however, only 23% of the patients who experienced symptoms of suspected acute coronary syndrome actually called the EMS. These findings suggest that bystanders may increase deliberative coping strategies in the event of a cardiac emergency. In the present study, we also found that coworkers, friends or strangers appeared to prompt the use of an ambulance, whereas family members or relatives did not influence the choice of transport. This suggests that family members and other significant people related to the high-risk individuals should be included while providing education as they play a key role in eliciting care-seeking behaviors.

Consistent with the published literature,3,4,17,21 we found that patients with a history of CAD used an ambulance more frequently than those without such a medical history. It is conceivable that recognition of previous CAD symptoms, more knowledge and better understanding of the disease, including the possible seriousness of new onset of symptoms, promoted EMS contact. However, none of the cardiovascular risk factors examined were found to be related to ambulance use, this may raise some questions regarding the efficacy of our health education interventions targeting high-risk patients.

The study indicated that patients with PA were less likely to call for an ambulance than those without PA. No reports have previously described the association between PA and ambulance use by STEMI patients. Nevertheless, it is easy to justify our finding. The clinical feature of PA is characterized by short anginal attacks preceding STEMI. Therefore, patients experiencing PA usually believed that the symptom would vanish or the pain would resolve by itself similar to prior short attacks. A previous study has demonstrated that patients who believed that their symptoms would resolve by themselves were less likely to avail an EMS. 15 Additionally, the incidence of intermittent pains prior to the attack may contribute to the failure to realize the life-threatening condition. McKinley et al24 reported that intermittent symptoms were related to increased patient delay in response to the STEMI symptoms. It is well known that STEMI patients, with preceding PA, usually have smaller infarcts and a better short- and long-term outcomes than those without PA.25,26 However, negative consequences of failure to call for an ambulance in a timely manner may greatly offset the protective effects of PA in these patients. Thus, our results suggest that interventions are required to provide awareness and knowledge regarding typical and atypical symptoms of STEMI as well as early warnings or prodromal symptoms, such as PA. In accordance with the previous studies,8,20 we also found that the patients who attributed their symptoms to non-cardiac origin were less likely to use an ambulance. The above findings further reinforce the importance of symptom interpretation in relation to care-seeking behavior.

As might be expected, knowledge of the value of CPR increased ambulance use in this study. It has been suggested that bystander CPR at least doubles the survival from cardiac arrest.27 In the study, a lot of patients were with family members at the time of symptom onset; the most common modes of self-transport were taxi and private car. Thus, it is important that family members of high-risk individuals and taxi drivers are taught to perform CPR effectively. However, our findings showed poor levels of knowledge and CPR training in Beijing. Thus, developing community resuscitation training program may be an effective strategy to further reduce mortality due to STEMI.

The reasons for under use of ambulances by patients with STEMI are not entirely understood. In this study, the main reasons for not calling an ambulance were as follows: the patients believed self-transport to be more convenient, the symptoms were not severe enough and they believed that self-transport would be quicker. Accordingly, we also found that perceiving symptoms to be serious is the strongest predictor of ambulance use. The last 2 reasons have been detected in other studies as well.6,7,18 These findings suggest that both the risks of self-transport and the potential benefits of using an ambulance were underestimated by many patients. Thus, the public health education system should emphasize that the ambulance is not merely a transportation modality and that it also provides rapid diagnosis and treatment; further, it can save lives, especially during cardiac events.

There are several limitations of this study that require mentioning. First, a cross-sectional observational design may pose concerns related to residual confounding. Second, information collected during the interview relied on the recall of events by the patients. However, in order to minimize the recall bias, the interview was conducted within a week of admission. Third, our sample only represented hospitalized STEMI patients who were admitted in two tertiary hospitals in Beijing within 24 hours of onset of symptoms. It did not include those who were pronounced dead at the site of an accident or who died on route and those who were admitted to other hospitals. Thus, caution should be exercised in generalizing our results to the entire STEMI population in Beijing.

In conclusion, a large proportion of patients residing in Beijing, China did not call for an ambulance after the onset of STEMI symptoms. Several factors including demographics, previous cardiovascular history, symptoms, and cognitive factors of patients were associated with the use of ambulance. The public should be educated that ambulance is not merely a transportation modality and that it also provides rapid diagnosis and treatment.

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REFERENCES

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Keywords:

myocardial infarction; predictors; ambulance use

© 2009 Chinese Medical Association