Recommended Citation: Reyes J. Heart of the Matter - A Case of Intermittent Bradycardia and Tachycardia [Internet]. Cook County Emergency Medicine Residency;Available from: https://cookcountyem.com/blog/2023/11/24/6okq744wg2ovowxwk0iggw11pemtn8
The Case:
A 47-year-old M with a PMHx of unspecified substance use was transferred from the medium acuity team to the high acuity team for progressive altered mental status, fever, and episodes of severe bradycardia with confusion (ECG from Cook County). Figure 1 was obtained when the patient initially arrived at our resuscitation bay, and 40 minutes later, Figure 2 was obtained, with the patient having intermittent tachycardia and bradycardia in between.
Figure 2. ECG 40 minutes after index ECG notable for junctional bradycardia with intermittent sinus conducted ventricular depolarizations.
Rate?
Rhythm?
Axis?
Intervals?
QRST?
Interpretation:
The first ECG was notable for Sinus tachycardia, Normal axis, Normal intervals, Diffuse ST-segment depressions with borderline elevation of aVR
The second ECG was notable for Sinus bradycardia with competing junctional rhythm, Normal axis, Normal intervals, Non-specific ST changes
Discussion:
A junctional rhythm is defined as ventricular depolarization originating at the level of the AV node or His bundle independent of the SA node (1). Pathophysiologically, this occurs either because the electrical activity of the SA node is blocked or the automaticity is insufficient to stimulate the AV node, resulting in the AV node's native pacemaker function occurring. The AV node’s native pacemaker function results in 40 to 60 spontaneous depolarizations per minute when stimulus from the SA node or atria is absent. The terminology for junctional rhythms is dependent on the resultant heart rate. It includes junctional bradycardia (40 bpm or less), junction escape rhythm (40 to 60 bpm), accelerated junctional rhythm (60 to 100 bpm), or junctional tachycardia (100 bpm or greater).
This patient’s condition was ultimately that of sick sinus syndrome, which is the dysfunction of the SA node resulting in impaired pacemaker function and a decrease in the automaticity of impulses resulting in failure of impulse transmission (2). 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.
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 (2). 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, but the syndrome spontaneously resolved, and it was, therefore, believed to be secondary to a toxic metabolic process.
Take away points:
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
Rarely is this process secondary to ischemia, but it should always be evaluated
Authored by Jose Reyes, MD
References:
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/
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/
Semelka M, Gera J, Usman S. Sick sinus syndrome: a review. Am Fam Physician. 2013 May 15;87(10):691-6. PMID: 23939447.