A 79-year-old female with hypertension, CKD Stage 4, history of breast cancer s/p tamoxifen therapy, osteoporosis presenting to the emergency department for pleuritic chest pain radiating to back. Laboratory work-up is significant for a troponin of 0.24, a d-dimer of 2.40., and a creatinine of 2.4 (baseline 1.8). The plan is for the patient to be admitted to medicine for V/Q scan to evaluate for pulmonary embolism. The patient’s EKG (Figure 1) is shown.
Interpretation:
Rate: 87 bpm; Rhythm: irregularly irregular; Axis: normal axis (I: pos., II:pos., aVF: pos) Intervals: PR: n/a; QRS: 110, normal; QT: 414, normal; P-Waves: absent; QRS Complex: normal, good R wave progression; ST Segment/T-waves: diffuse T-wave flattening without obvious elevations, depression, or inversions
The initial EKG demonstrates new onset atrial fibrillation. While waiting for admission, the telemetry alarm sounds for asystole and shows the following rhythm strip (Figure 2):
Figure 2.
The patient is brought to the resuscitation bay and the monitor now shows the following rhythm strip (Figure 3):
Figure 3.
What is this set of electrocardiographic tracings most concerning for? What is your disposition?
Discussion
This constellation of findings is consistent with a diagnosis Tachycardia-Bradycardia Syndrome with Sinus Arrest, a type of Sinus Node Dysfunction, also known as Sick Sinus Syndrome. This condition can be caused by either extrinsic or intrinsic causes and is most commonly identified in the elderly.
Intrinsic causes include degenerative fibrosis, ischemia, cardiomyopathy, infiltrative disease, and congenital causes. Extrinsic causes include medications (digoxin, beta blockers, calcium channel blockers), autonomic dysfunction, hyperkalemia, hypothyroidism, and other electrolyte abnormalities [1, 2].
Patients with atrial fibrillation often develop fibrosis from remodeling of the sinoatrial node over time [3], and in this patient with new undiagnosed atrial fibrillation, this is a plausible precipitating cause. The patient was noted to be taking carvedilol 180 mg BID for hypertension. And, on further review of the work-up in this case for possible etiologies, the potassium was revealed to be 4.3 (normal), despite the AKI on CKD, and thyroid studies demonstrated subclinical hypothyroidism with a TSH of 11.2 (elevated) and T4 of 0.85 (low normal), a possible contributing factor but unlikely the sole reason for this patient's sick sinus.
Specifically, this patient presented with Tachycardia-Bradycardia Syndrome with Sinus Arrest. Tachy-Brady Syndrome is defined as paroxysmal bradycardia alternating with an atrial tachyarrhythmia (e.g. SVT, AFib RVR). The stretch of tachyarrhythmia is often followed by a sinus pause, with more concerning pauses known as sinus arrest lasting longer than 6 seconds [1, 3].
The sinus pauses in this patient had a max duration of 8-10 seconds noted on telemetry and, in discussion with Cardiology and Electrophysiology, the patient was admitted to the CCU for close monitoring and ultimately underwent permanent pacemaker placement.
Take Away Points:
This case demonstrates why it is so important that we keep our chest pain, palpitations, syncope, and arrhythmia patients on telemetry! It actually catches real pathology that changes outcomes for our patients.
Think Sick Sinus Syndrome when patients have alternative tachycardia and bradycardia
Capture your sinus pause on EKG or rhythm strip as this help Cardiology determine next steps (medical management, holter monitoring, PPM placement)
Sinus pauses >6 seconds are high risk for syncope and complications and require ICU admission for PPM placement
References
Burns E, Buttner R, Buttner EB and R. Sinus node dysfunction (sick sinus syndrome). Life in the Fast Lane. October 8, 2024. Accessed May 28, 2025. https://litfl.com/sinus-node-dysfunction-sick-sinus-syndrome/.
Thery C, Gosselin B, Lekieffre J, Warembourg H. Pathology of sinoatrial node. Correlations with electrocardiographic findings in 111 patients. Am Heart J. 1977;93:735–740. doi: 10.1016/S0002-8703(77)80070-7.
Padda I, Sebastian SA, Khehra N, et al. Tachy-brady syndrome: Electrophysiology and evolving principles of management. Dis Mon. 2024;70(2):101637. doi:10.1016/j.disamonth.2023.101637