Narrative Syncope or transient loss of consciousness is a common problem seen in the emergency department (ED), accounting for 1% to 1.5% of ED visits annually. Cardiac syncope caused by cerebral hypoperfusion secondary to cardiopulmonary events such as arrhythmia or structural heart disease, accounts for 5% to 21% of syncope events. Cardiac syncope is associated with an increased risk of premature death and cardiac events., It is therefore important emergency providers differentiate cardiac syncope from other causes.
This systematic review by Albassam et al, evaluated patient characteristics, physical exam findings, and diagnostic tests to identify cardiac causes of syncope. The authors searched the MEDLINE, Embase, CINAHL and Cochrane databases, selecting 11 studies that met inclusion and exclusion criteria. Each study included at least 10 subjects aged 12 years or older, for a total of 4317 patients. Studies were assigned levels of evidence developed for the Rational Clinical Exam series.
Several historical factors were associated with an increased likelihood of cardiac syncope including: age at first syncopal spell 35 years or older, history of atrial fibrillation or flutter, known severe structural heart disease, dyspnea or chest pain prior to syncope, and witnessed cyanosis during syncope. An elevated cardiac troponin T or I, and an elevated B-type natriuretic peptide (BNP) both modestly increased the probability of cardiac syncope.
Factors that decreased the probability included age less than 35 years at first spell, normal cardiac troponin T or I, and normal BNP. Combinations of findings such as Evaluation of Guidelines in Syncope Study (EGSYS) score ≥3, Vasovagal score <-2, and abnormal electrocardiogram, heart disease, or both were more useful when absent than when present.
The results of this review should be interpreted cautiously. Included studies generally defined cardiac syncope based on cardiologist judgment. Five of 11 included specialty referral populations or inpatients, leading to the potential for spectrum bias. Applying these results to a general ED population might lead to additional testing or interventions in patients who have lower risk of cardiac syncope than the studied population. Misclassification may have further skewed the results as patients with unexplained syncope were excluded from a number of studies. Many of the clinical findings resulted from single studies. Studies often included a wide age range of patients despite the incidence of syncope, related ED visits, and serious outcomes increasing sharply after the age of 60.
Cardiac biomarkers such as troponin or BNP testing appear to be an attractive diagnostic option however they did not rule in or out cardiac syncope. Moreover, these levels were likely used to diagnose cardiac syncope leading to incorporation bias. ACEP clinical policy, appreciating these limitations, suggests a risk-stratification approach focusing on patient history and physical examination to avoid unnecessary testing and hospital admissions.
In summary, the accurate diagnosis of cardiac syncope is helpful in determining an appropriate plan of care. While no single variable can independently diagnose or exclude cardiac syncope, several clinical findings may be used cohesively to help guide healthcare providers.
The original manuscript was published in Academic Emergency Medicine
as part of the partnership between TheNNT.com and AEM.
Author Kathryn Wiesendanger, BSc; Daniel K. Nishijima, MD, MAS
Supervising Editor: Shahriar Zehtabchi, MD
Published/Updated October 16, 2019
What are Likelihood Ratios?
LR, pretest probability and posttest (or posterior) probability are daunting terms that describe simple concepts that we all intuitively understand.
Let's start with pretest probability: that's just a fancy term for my initial impression, before we perform whatever test it is that we're going to use.
For example, a patient with prior stents comes in sweating and clutching his chest in agony, I have a pretty high suspicion that he's having an MI – let's say, 60%. That is my pretest probability.
He immediately gets an ECG (known here as the "test") showing an obvious STEMI.
Now, I know there are some STEMI mimics, so I'm not quite 100%, but based on my experience I'm 99.5% sure that he's having an MI right now. This is my posttest probability - the new impression I have that the patient has the disease after we did our test.
And likelihood ration? That's just the name for the statistical tool that converted the pretest probability to the posttest probability - it's just a mathematical description of the strength of that test.
Using an online calculator, that means the LR+ that got me from 60% to 99.5% is 145, which is about as high an LR you can get (and the actual LR for an emergency physician who thinks an ECG shows an obvious STEMI).
(Thank you to Seth Trueger, MD for this explanation!)