Sinus Node Dysfunction in a Young Female Without Identifiable Risk Factors

Background: Sinoatrial Node Dysfunction (SND) is a multifactorial disorder leading to symptomatic bradycardia and asystolic pauses. Epidemiological studies estimate the SND annual incidence at 0.8 per 1,000 person-years, with the majority of cases occurring over 75 years old. Case Presentation: A 32-year-old Caucasian female presented to the emergency department with sharp, episodic chest pain, radiating to the mid-back and jaw. Her episodes were associated with dizziness, diminished vision, and syncope, lasting approximately 5 minutes before resolving spontaneously. She had a history of PVCs, uncomplicated C-section, & LARC placement, but not for tobacco use, DVT/PE, CAD, immobilization, or cancer. Laboratory studies revealed prolonged PT (12.7), but troponin series, PTT, TSH, BNP, CBC, magnesium, I-STAT 6, and urine hCG were within normal limits. ECG showed sinus bradycardia. She was discharged home to follow up with electrophysiology. Two days later, episodes began occurring with higher frequency and shorter latency, necessitating admission to the cardiac intensive care unit. On admission, she appeared lethargic with a HR of 41bpm, BP of 108/60, and O2 saturation of 98%. Secondary assessment revealed normal heart sounds with no rubs, gallops, or murmurs. Laboratory assessment revealed prolonged PT and isolated lymphopenia (22.9%), but troponin series was within normal limits. ECG showed no ST-changes or T-wave inversions. Echocardiogram showed no evidence of valvular or structural heart disease. On Day 2, CBC revealed leukopenia (4,900mc/L) and CMP revealed low AST (10), calcium (7.6), albumin (3.1), and total protein (5.3), as well as high BUN/Cr (21.7). On Day 3, Lyme, Lupus Anticoagulant, and Rheumatoid Factor titers were within normal limits. BUN/Cr levels had also returned to 11.7. Coronary artery angiogram showed no evidence of aneurysm or pathologic vessel narrowing. Continuous telemetry showed an average heart rate of 50bpm while awake and 30bpm while asleep. Upon ambulation she achieved 66bpm, but was so fatigued afterwards that she had to return to bed. Given the degree of bradycardia and intolerance to ambulation, the decision was made to proceed with dual-chamber pacemaker implantation. The device was successfully placed without intraoperative complications. Conclusions: This case illustrates a unique presentation of SND in a highly atypical age group without contributory medical history or identifiable risk factors.