The Case:
A 62-year-old F with a PMHx of osteoarthritis presented for two months of intermittent, unprovoked syncope, worse over thepast 24 hours. She was admitted one month prior and had TTE and 24 hours of observation without a noted event. She notes the day prior syncopizing without prodrome, chest pain, or SOB, and additionally experienced this 1-2 hours prior to presenting. She was brought to resus after syncopizing in the waiting room and being bradycardic. Figure 1 was obtained when the patient initially presented to the resus bay.
Figure 2: Repeat ECG following a witnessed episode of syncope.
She then syncopized, again following a 4-hour period without an interval event, normal cardiac biomarkers, and was noted to have an episode of sinus arrest for 10 seconds and sinus bradycardia. Figure 2 was immediately obtained following her episode of syncope.
Interpretation:
The first ECG was notable for Normal sinus rhythm, Left axis deviation axis, Normal intervals, and criteria for LVH
The second ECG was notable for Sinus bradycardia, Left axis deviation axis, Normal intervals, and criteria for LVH
Discussion:
The patient was ultimately diagnosed with SA node dysfunction, also known as sick sinus syndrome, and was admitted to the CCU for pacemaker placement. This dysfunction of the SA node results in impaired pacemaker function and a decrease in the automaticity of impulses, resulting in failure of impulse transmission (1). Sick sinus syndrome on ECG can be atrial bradyarrhythmias (e.g., atrial fibrillation with slow ventricular response, sinus arrest with or without junctional escape, etc.), atrial tachyarrhythmias (e.g., atrial fibrillation, atrial flutter, SVT, etc.), or tachycardia-bradycardia syndrome which is comprised of alternating episodes of tachyarrhythmias and bradyarrhythmias. As in the case of our patient, sinus pause or arrest of greater than 3 seconds without atrial activity is suggestive of sick sinus syndrome (2). The following escape rhythm can be atrial, ventricular, or junctional in origin. Additionally, severe, inappropriate, and abrupt sinus bradycardia or inappropriate bradycardia suggest sick sinus syndrome. Given sick sinus syndrome is a spectrum of disease, your patient's ECGs may be sinus at all times and do not necessarily have to have a junctional rhythm.
Etiologies can be intrinsic to the SA node or extrinsic to the SA node (3). Intrinsic dysfunction occurs secondary to congenital disorders (e.g., channelopathies), arrhythmias, infiltrative disorders (e.g., cardiac amyloidosis), or surgery. Ischemic injury is an unusual cause of sick sinus syndrome, given the proximal location within the atria. Extrinsic factors include abnormally increased vagal tone (e.g., vasovagal syndrome, autonomic dysfunction, carotid sinus dysfunction, etc.), metabolic (e.g., electrolyte abnormalities, hypoxia, hypothermia), or toxic (e.g., digoxin, lithium, antiarrhythmics, etc.). Increased intracranial pressure and sleep apnea can additionally result in this process.
Treatment is dependent on the underlying etiology resulting in dysfunction (1). Evaluation should begin by evaluating reversible causes, such as electrolyte dysfunction or hypothermia, and addressing reversible causes. A permanent pacemaker may be required if the syndrome continues despite addressing reversible causes or if no reversible causes are identified. Acutely, if the patient is unstable, transcutaneous or transvenous pacing may be required in bradycardias or cardioversion in tachycardias. Note, following cardioversion, a patient with sick sinus syndrome may have sinus arrest without a junctional escape rhythm and may require transcutaneous pacing. In our patient, a reversible cause was not identified. Given multiple months of symptoms, the appropriate management for her was pacemaker placement.
Take away points:
· Inappropriate bradycardia without sinus node blockers or sinus pause/arrest suggest sick sinus syndrome
· Sick sinus syndrome has variable presentations, including atrial bradycardias, atrial tachycardias, and tachy-brady syndrome
· The management for emergency physicians includes addressing reversible causes and expectant management in the stable patient
· Management in the unstable patient is dependent on the rhythm, namely electrical pacing for bradycardias and cardioversion for tachycardias
Authored by Jose Reyes, MD
References:
Hafeez Y, Grossman SA. Junctional Rhythm. [Updated 2023 Feb 5]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK507715/
Dakkak W, Doukky R. Sick Sinus Syndrome. [Updated 2023 Jul 17]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK470599/
Semelka M, Gera J, Usman S. Sick sinus syndrome: a review. Am Fam Physician. 2013 May 15;87(10):691-6. PMID: 23939447.