It's All Greek to Me

Syncope and pre-syncope (because essentially they are treated as the same entity) are one of the most common presenting complaints to the emergency department, accounting for 1-2% of all ED visits (approximately 1 million visits per year)[1]. There are several possible causes of syncope, and several scoring systems that can help determine appropriate disposition. Neuro-cardiogenic syncope is from increased vagal tone and presents with syncope and bradycardia - classically the patient who just had a bowel movement, or that one friend who faints at the sight of their own blood. Orthostatic syncope occurs when a patient gets up too quickly after bingeing several hours of television. This type can occur due to several different causes including volume loss, medication side effects, and autonomic dysfunction. Neurologic syncope is not as common a cause of syncope, but it usually occurs due to seizures, TIAs, or even migraines. Cardiac causes of syncope include arrhythmias, cardiac tamponade, valvular heart diseases, or myocardial ischemia. The last and most common cause of syncope is actually “unknown”, essentially meaning that a thorough workup was unable to confirm the cause. This carries a 30% chance of mortality [2].

The most important component of syncope management in the emergency department is a thorough history and physical exam which can help determine which of the preceding causes of syncope is responsible for the patient’s presentation. Several adjunctive tests can also be used to help determine the cause; orthostatic vital signs, neuroimaging, labs, and ultrasonography are all important tools in the evaluation of syncope. In our emergency department, every patient with syncope gets an EKG. An EKG is an inexpensive, non-invasive test that can be performed and repeated as needed.

Multiple blogs and FOAMed sites exist that can help you determine whether the EKG you are looking at is concerning for myocardial ischemia, or what kind of tachyarrhythmia or bradyarrhythmia is the cause of the patients symptoms (assuming that they truly have concerning findings on an EKG). I want to talk about rare causes of syncope that are diagnosed on an EKG. These subtle findings and their associated disease processes are the Delta wave of Wolff-Parkinson-White Syndrome (WPW) and the Epsilon wave of Arrhythmogenic Right Ventricular Dysplasia (ARVD).

WPW is an uncommon pathology of the electrical conduction system of the heart. Classical conduction occurs from the SA node, to the AV node, and then the Bundle of His and the Purkinje system in the ventricles. The pathology of WPW occurs due to the presence of a bypass tract - commonly referred to as the Bundle of Kent, which allows electrical conduction to return from the ventricles to the atria. Most bypass tracts can conduct in both anterograde and retrograde directions, with 15% being retrograde only. Anterograde only is rarer still. Conduction through the accessory bundle can lead to the development of tachyarrhythmias, which can lead to cerebral hypoperfusion and syncope. The EKG finding of WPW is the Delta Wave (shown below), which is a shortening of the PR interval, with slurring of the initial positive deflection of the QRS complex[3]. In patients with resolved syncope, this may be the only sign of an resolved dysrhythmia.

ARVD is a congenital cardiac abnormality that is the second most common cause (10%) of sudden cardiac death in young patients after hypertrophic obstructive cardiomyopathy (HOCM). The pathophysiology of ARVD occurs due to fibro-fatty infiltration of the right ventricle, which causes conduction abnormalities between it and the surrounding normal cardiac tissue. These conduction abnormalities can lead to the development of ventricular ectopic beats or, in more severe cases, can lead to sustained ventricular tachycardia. These patients will usually have a family history of sudden cardiac death [4]. Syncope in these patients generally occurs due to a short run of ventricular tachycardia. The Epsilon wave, noted by the arrow in the picture below, is notching of the terminal portion of the QRS complex, and is pathognomonic of AVRD.

Any histologic changes in the overall cardiac tissue can be a source of ectopy, which can lead to problems in electrical conductance. In fact, one of the most common arrhythmias is atrial fibrillation, and its most common source is the entry of the pulmonary veins into the left atrium. This area is a common source of ectopy because the tissue is not just histologically different from the remainder of the left atrium, but due to neonatal development ,the tissue is also of a different embryological source than regular left atrial tissue.

Always look at the EKGs of your syncope patients! Sometimes in patients with completely normal physical exams and a noncontributory history this simple test can help you find significant and deadly pathology.

References:

1. Sun BC, Emond JA, Camargo CA Jr. Direct medical costs of syncope-related hospitalizations in the United States. Am J Cardiol. 2005 Mar 1;95(5):668-71. doi: 10.1016/j.amjcard.2004.11.013. PMID: 15721118.

2. Patel PR, Quinn JV. Syncope: a review of emergency department management and disposition. Clin Exp Emerg Med. 2015;2(2):67-74. Published 2015 Jun 30. doi:10.15441/ceem.14.049

3. Castellanos A Jr, Lemberg L, Claxton BW. Wolff-Parkinson-White syndrome: generalities. Chest. 1974 Mar;65(3):307-22. doi: 10.1378/chest.65.3.307. PMID: 4813838.

4. Marcus F, Towbin JA, Zareba W, Moss A, Calkins H, Brown M, Gear K; ARVD/C Investigators. Arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C): a multidisciplinary study: design and protocol. Circulation. 2003 Jun 17;107(23):2975-8. doi: 10.1161/01.CIR.0000071380.43086.29. PMID: 12814984.