Tachy-brady Syndrome

Tachy-brady syndrome (sometimes called sick sinus syndrome) is characterized by alternating tachyarrhythmias and bradyarrhythmias. This syndrome primarily occurs in elderly patients with a history of cardiac disease, though can also occur in hypothyroidism, hyperkalemia, or syndromes with autonomic dysfunction. Most often, these patients have paroxysmal supraventricular tachycardias (ie atrial fibrillation with RVR) followed by periods of long pauses or bradycardia. Sinus pauses are defined by lack of atrial activity for at least 2 seconds. The periods of tachyarrhythmia can produce chest pain, palpitations, or SOB. Patients commonly have lightheadedness or syncope during the periods of bradycardia/pauses. It is often alarming for emergency medicine providers as one should not provide rate control or chronotropic agents due to the intermittent nature and requires supportive care until definitive management is obtained (typically pacemaker followed by initiation of rate control medications).

As mentioned, this usually occurs due to dysfunction of the sinus node. The SA node contains P (pacemaker) and T (transitional) cells. The P cells initiate the impulse and the T cells transmit them to the atria. Sick sinus syndrome and, ultimately tachy-brady syndrome, can result from dysfunction in either of these cells. There are actually different degrees of SA block that mimic our categories for AV block (not practically relevant for ED providers).

Examples:

Further Reading:

https://litfl.com/sinus-node-dysfunction-sick-sinus-syndrome/

http://hqmeded-ecg.blogspot.com/search/label/sick%20sinus