Improving the approach to non-cardiac syncope in the emergency department observation unit

Syncope is a rather frequent condition, responsible for 1.0%–1.5% of emergency department (ED) visits.[1] Even if the development of clinical guidelines has improved the ED management of syncope,[2] the hospitalization rate is still very high (up to 50%), especially compared with the incidence of short-term adverse events, which is 11% globally, but decreases to less than 4% when events already diagnosed in the ED are excluded,[1] meaning that most patients will not benefit from admission.

The current classification[3] differentiates between three main clinical forms, cardiac syncope, reflex syncope and orthostatic syncope. Non-cardiac forms constitute the absolute majority, both in the ED and in other areas,[3] and are associated with a better prognosis than cardiac syncope, which is instead associated with high morbidity and considerable mortality.[1,4]

However, prognostic stratification of patients with syncope in the ED is challenging, as it has been observed that the risk of adverse events is more influenced by the presence of underlying cardiovascular diseases than by the clinical form itself.[1] It has also been observed that syncope due to orthostatic hypotension (OH) is far from benign in elderly patients, as the risk of death, coronary artery disease, heart failure, and stroke in these patients’ is twice that of the general population, largely caused by the greater severity of comorbidities.[1]

Moreover, the differential diagnosis between cardiac and non-cardiac forms can be difficult in the ED, particularly in elderly subjects, since in these patients atypical presentation, “double diagnosis” (presence of multiple potential mechanisms, in association), overlap with unintentional fall, amnesia for the event (the so-called “amnesia for amnesia”) are very frequent as well as the absence of witnesses.

According to the current guidelines,[1] the assessment of the severity of syncope must also consider factors other than the clinical form, such as the recurrence over time and the shortness of prognosis with the risk of traumatic injury.

All of these data suggest that prognostic stratification of syncope in ED is very tricky; not surprisingly, it has been observed that the incidence of adverse events in patients discharged from the ED as being considered at low risk is not meaningless, either in the short or long term.[5,6]

Recent advances in the management of non-cardiac syncope

The latest update of the European Society of Cardiology guidelines on syncope (ESC GL),[3] as the previous ones,[7] states that the first step of the diagnostic work-up should aim at recognizing patients with a likely high-risk cardiovascular condition requiring urgent investigation and admission. The approach to other forms of syncope has been recently implemented according to a new classification, based on the underlying mechanism,[8] which defines two main syncope phenotypes with different predominant mechanisms:[9] the hypotensive phenotype, where hypotension or vasodepression prevails, and the bradycardic phenotype, where cardioinhibition prevails, whose typical pattern are, classical OH and adenosine syncope due to paroxysmal atrioventricular (AV) block, respectively. Once a cardiac form has been excluded, diagnostic investigations are therefore aimed at discovering the underlying mechanism leading to syncope.[8,9]

Table 1 shows the clinical features, main causes and the diagnostic tests useful for the diagnosis of the two phenotypes.

Table 1.

New classification of non-cardiac syncope based on the underlying mechanism

Application of the new classification to the ED approach to syncope

The new classification may further enhance the method suggested by the ESC GL, but its application in the ED can be problematic, as the identification of the dominant phenotype mostly relies on diagnostic tools not applicable in the ED, requiring an amount of time beyond the optimal length of stay in an emergency setting.

However, some aspects of the ED management of patients with syncope can be improved based on these new insights into the approach to non-cardiac syncope, as detailed below.

ED risk stratification flow-chart

The flowchart can be modified as shown in Figure 1. Compared to previous studies,[3,10] the following aspects become more relevant: i) the need not to directly discharge from ED with evidence of acute diseases underlying syncope or risk factors for cardiac syncope (see Table 2, showing diagnostic findings and suggestive features for cardiac syncope); these patients should be admitted, in the case of severe acute principal diseases (such as acute cardiovascular diseases or other conditions needing hospitalization per se) or major criteria for cardiac syncope, for diagnostic or therapeutic purposes, or be managed in the emergency department observation unit (EDOU), in the case of non-serious acute condition with pain or fluid loss (eliciting hypotensive syncope) or minor criteria for cardiac syncope; ii) the importance of stratifying the prognosis of syncope based on the frequency and severity of episodes (the “consequential risk”), not just the presence, suspected or proven, of an underlying cardiovascular disease (the “causal risk”).

Figure 1.

Emergency department risk stratification flow-chart for patients underlying syncope. TLOC: transient loss of consciousness; APDs: acute principal diseases; ED: emergency department; EDOU: emergency department observation unit.

Table 2.

Diagnostic findings and suggestive features for cardiogenic syncope

Role of acute principal diseases associated with syncope

As stated by ESC GL,[3] various factors such as volume depletion (haemorrhage, low fluid intake, diarrhoea, vomiting), alcohol use or pulmonary diseases causing a reduction in brain oxygen supply may facilitate syncope, especially in case of a reflex or orthostatic form. This assumption perfectly complements the approach proposed by ESC GL for the management of syncope in the ED, focused on the prompt identification of acute principal diseases underlying the transient loss of consciousness (TLOC), with recent advances in the management of non-cardiac syncope. In fact, these hemodynamic or metabolic factors due to an acute disease, even if not severe, can exacerbate a hypotensive, constitutional of drug-related, susceptibility, leading to a non-cardiac syncope with a hypotensive phenotype.

Assessment of the dominant mechanism of syncope

Although the identification of hypotensive and bradycardic phenotypes, in a non-cardiac syncope, can exceed the resources of the ED, in terms of timing and instrumental equipment, the authors believe that the recent advances in the management of non-cardiac syncope could be applied in an EDOU, leading to an improvement in the ED management of patients with TLOC. These acquisitions may help define the diagnostic protocol to be used in patients with syncope managed in EDOU, so that it includes the following points:

• i) clinical reassessment, also aimed at pointing out suggestive features for hypotensive (advanced age and frailty; vasoactive drugs; comorbidities with fluid loss; relationship with orthostatic stress, postprandial or post-exercise) [9] or bradycardic phenotypes (younger age; absence of hypotensive drugs; shortness or absence of prodromes [typical premonitory symptoms preceding syncope, such as pallor, sweating and/or nausea]) and at stratifying cardiovascular and syncopal risk, to define appropriate therapeutic targets in the case of hypertensive patients with syncope.

• ii) thorough blood pressure evaluation, including a careful orthostatic challenge, as an active standing test (to identify classical OH according to ESC GL and delayed OH with prolonged blood pressure monitoring) and tilt table test.[11]

• iii) ECG monitoring (bedside or by telemetry), for a minimum of 6 to 24 h.

• iv) carotid sinus massage (CSM), to be performed in all patients over the age of 40 years with syncope compatible with a reflex mechanism, unless contraindicated (a previous stroke or already known carotid stenosis> 70%), preferably during continuous ECG and non-invasive beat-to-beat BP monitoring, on both sides, supine and upright (for 10 seconds each) to allow symptoms to develop.[1] Unfortunately, the few available data show that CSM is performed in a small minority of ED patients,[12] but the authors believe that a strong effort should be made to spread the execution of this maneuver, as neurological complications are extremely rare (0.24%).[3]

• v) tilt table test, it plays a central role in identifying the prevalent syncope phenotype, as it can highlight the presence of hypotensive susceptibility,[13] which plays a role in causing syncope regardless of the aetiology and mechanism of syncope (in OH orthostatic vasovagal syncope but also in case of cardiac syncope) and diagnose a cardioinhibitory reflex syncope, with reproduction of an asystolic syncope during the test. In clinical practice, this test is mostly performed as an outpatient, but according to the 2018 ESC GL[3] it should be performed as an additional evaluation after the initial evaluation, so the authors think that there is a need to strengthen the collaboration between EDOU and the syncope unit (SU) to perform this exam during the ED stay, if indicated.

Organizational and educational aspects

To improve the ED management of patients with non-cardiac syncope, it is necessary to implement pathways and adopt innovative organizational solutions. In this regard, we consider the following aspects to be essential: i) to spread the presence of EDOUs with adequate instrumental equipment, into EDs of any complexity and size, as required by ministerial guidelines in our country;[14] ii) to strengthen the link between EDOU and SU, with early involvement of the syncope expert to define the diagnostic path, to be carried out in ED or with a fast track to SU or other services, if further investigations that cannot be performed in ED are needed (such as 24-hour ambulatory pressure monitoring, prolonged ECG monitoring with internal loop recorder (ILR) or external loop recorder (ELR); autonomic function test); iii) to enhance collaboration between EDOU and geriatrics (consultancies, referral to outpatient clinics, acute geriatric units, care pathways) for the management of elderly patients with non-cardiac syncope. This management could be very challenging due to peculiarities of syncope in these patients, as mentioned above, or risk factors (injuries, comorbidities, polypharmacy, disability, frailty); iv) active dissemination (including through decision-making software, dedicated applications, e-learning or web-based courses) of the recent acquisitions, as shown in Table 3.

Table 3.

Main educational points from recent acquisitions on non-cardiac syncope management

CONCLUSIONS

Recent advances in the management of non-cardiac syncope along with the contribution given to ED management by ESC GL, with a focus on the role of acute principal diseases underlying syncope, pathways and organizational issues and risk stratification based on causal and consequential risk, allow a further step along the road that leads to the ambitious target of zero admission for unexplained syncope. To combine this goal with patient safety, there is a strong need for organizational implementation, to ensure a widespread diffusion of the EDOU facilities with adequate equipment in the EDs and to further strengthen connections between these structures, syncope outpatient clinics or other hospital services.