Chest pain in the ambulance; prevalence, causes and outcome - a retrospective cohort study

Chest pain is one of the most frequent symptoms among patients contacting the emergency medical services (EMS) and emergency departments (EDs) [1, 2]. In the United States, the estimated number of ED contacts due to chest pain exceeded 7 million in 2015 [3, 4]. Health care expenses for handling these patients are massive and are mainly driven by length of hospital stay [5]. Depending on the underlying cause, an acute EMS-response and subsequent hospitalization may prove relevant or non-relevant in chest pain patients.

Since chest pain is associated with potential life threatening conditions like acute myocardial infarction (AMI), pulmonary embolism or acute aortic dissection, the EMS response is most often dispatched in an “all or nothing”-fashion with a high triage level and immediate response. This level of triage is relevant in patients with a subsequent confirmed serious/adverse diagnosis and may favour an improved outcome [6, 7]. While patients with AMI often present with chest pain, the majority of patients presenting with chest pain may suffer from other more harmless conditions [8‐10]. A mismatch like this could lead to overtriage and an excess of non-relevant EMS responses in chest pain patients. Secondarily this leads to high EMS-resource consumption, crowding, and prolonged length-of-stay (LOS) in EDs and coronary care units (CCUs) [2, 8, 11].

Consequently, there is a need for evaluating prehospital over-triage and non-relevant EMS use in chest pain patients by examining diagnoses and mortality rates in patients presenting with chest pain and a need for addressing ways of early discrimination between high- and low-risk patients and thus support the decision of when an acute EMS response is relevant or may be down-graded. Structured use of patient characteristics and presence/absence of accompanying symptoms could be a key factor in improving the triage in chest pain patients [12]. Therefore, we aimed to compare EMS-patients according to presence of chest pain and to identify predictors of acute cardiac conditions and death.

This large study is based on all registrations of ambulance transports in the Central Denmark Region in a 1 year period, combined with diagnoses and vital status from validated national registers. However, we did exclude 6% of the cohort due to missing data on either symptom or diagnosis, and selection bias cannot be excluded. Available characteristics, diagnoses and outcome in these patients are presented in Additional file 2. In short, we see a very low incidence of AMI and other acute cardiac diagnoses (< 2%) in the symptom-missing patients and likewise a low incidence of chest pain (6%) in the diagnose-missing patients. Thirty-day mortality in the symptom-missing group is not different from the mortality rate in the overall cohort (6.2% vs 5.4%). Mortality in the diagnose-missing group was slightly higher (6.7%) but as mentioned, this group includes persons dying during ambulance transport or found dead, and subsequently transported to hospital for confirmation of death by a doctor, which can explain the observed higher mortality. We conclude that the risk of selection bias due to exclusion of these patients is very low. There is a risk of immortal time bias in our regression models, since we only include patients surviving to hospital admission. However, in prehospital terminated transports, 30-day mortality among chest pain patients was as low as 3.2%, disputing the possible immortal time bias.

In mortality analysis 70 patients are lost-to-follow-up, meaning that they are registered as inactive in the Danish civil registration system. However, only 13 of these where registered as inactive within 30 days after their chest pain event, while the remaining 57 where inactive at the time of their chest pain event (e.g. migrated or without residence in Denmark).

The study is limited by its retrospective design, which affects both the identification of symptoms (if specific information is missing) and potentially biases the effect of patient characteristics, symptoms and comorbidity, since we cannot definitely differentiate between correlation and causality. The identification of chest pain could be limited by the fact that only 37% of patients were triaged using symptom-based dispatch. Instead, symptom-identification relied on automatized text search in notes from electronical prehospital patient records. This method may be sensitive to spelling and abbreviation of words in the records. We sought to compensate for this by including several spellings and known abbreviations of each word, by excluding terms describing rejection of chest pain symptoms and by manual validation of the method in > 5% of the cohort. The automatized text search showed very good agreement with the manual reviews (kappa = 0.95), Additional file 3.

This retrospective study in a large cohort of patients being transported by ambulance has three major findings. Firstly, chest pain is a very common reason for acute ambulance transport and hospital admission, accounting for one in six emergent ambulance transports. Secondly, acute ambulance transport in chest pain patients is associated with a high degree of overtriage with more than 50% of transported chest pain patients discharged without any diagnosis of disease and with a very low (< 0.5%) 30 day-mortality risk. Thirdly, it may be possible to identify a very-low-risk group already at the time of emergency call based on patient characteristics and symptomatology, indicating a potential for downgrading the response in selected chest pain patients.

The rate of chest pain patients transported by ambulance was comparable to the chest pain rate found in recent Swedish and Danish studies, but substantially higher than earlier reported in studies from Norway and the UK [2, 20‐23]. The most likely reason for this higher rate is a temporal increase in chest pain cases also reported in other studies [23, 24]. This increase may be explained by an increased focus in the general population and in health care professionals on the need for acute assessment in cases with chest pain. Both chest pain and AMI rates in the present study are also comparable to rates previously reported from European and American ED cohorts [1, 25].

When compared to patients without chest pain, chest pain patients were more often diagnosed with an acute cardiac condition including AMI (13% vs 2%), but also more often discharged with no final diagnosis (51% vs. 19%). This is a paradox and reflects on one hand the relevance of chest pain as a symptom of acute cardiovascular disease, but on the other hand also an overtriage of chest pain patients compared to patients presenting with other symptoms. The burden added to the EMS by chest pain patients is exaggerated by the fact that 88% of these patients were allocated a “grade A” response, thus representing 31% of all “grade A” responses. The decision to dispatch a “grade A” response is currently not based on an individual risk-estimation, but rather a “no miss” strategy, where the majority of patients with symptoms with even the slightest risk of AMI, are offered the highest level of care. The result is a significant overtriage, where more than half of all chest pain patients are discharged with no disease specific diagnosis and extremely low 30-day mortality below 0.5%. This advocates the use of a systematic differentiation between high-risk chest pain patients with urgent need of treatment and very low-risk chest pain patients without need for hospital admission. In the EMCC, this may be achieved by including patient characteristics and symptoms (readily accessible at the time of emergency call) in a risk assessment tool.

In explorative analyses on the present cohort (Tables 3 and 4) female gender, younger age, chronic pulmonary disease, absence of dyspnoea, absence of radiation/severe pain for > 5 min and absence of clammy skin/uncomfortable/nausea were associated with being discharged without an acute cardiac diagnosis and surviving 30 days after a chest pain event. Applied in a diagnostic model for the composite endpoint of no acute cardiac diagnosis during index admission and surviving 30 days from chest pain event, Model 2 presented acceptable sensitivity, NPV and negative likelihood ratio. However, since these data were retrospective, they were not gathered with this in mind. Thus, though risk assessment using patient characteristics and clinical presentation/ accompanying symptoms seems promising, safety of such a strategy should be further refined and explored in prospective studies. Future studies should aim at confirming that an estimated very low risk justifies a lower prehospital dispatch priority and potentially prehospital rule out of AMI and other acute conditions already at medical emergency call.

Clinical implementation of a risk assessment strategy may further unfold as the patient pass through the EMS system. Early rule-out of AMI in the ED using patient characteristics and clinical presentation in combination with high-sensitive troponin has been validated in several recent studies [26‐28]. Even earlier rule-out of AMI could be achieved by combining high-sensitive troponin with copeptin, maybe even in the prehospital setting, when equipment for point-of-care copeptin measurement is developed [29‐31]. The prerequisites for this dual marker approach are examined in an ongoing randomized controlled study [32]. With a risk assessment tool used at time of emergency call, resource downgrading after ambulance dispatch may be based on incorporation of subsequent clinical assessment, ECG-findings and biomarker results in a stepwise, individual risk assessment model, even before reaching hospital.

Chest pain is the reason for 16% of all ambulance transports. AMI is only diagnosed in 11% of chest pain patients. The mortality in chest pain patients is lower than in other patients transported to hospital by ambulance, and particularly low in chest pain patients not receiving a diagnosis of disease during index admission. Structured risk assessment using patient characteristics and symptoms seems to hold a potential for early resource downgrading in low risk chest pain patients, already in the prehospital setting.