BACKGROUND: Intermittent accessory pathway conduction can obscure the electrocardiographic diagnosis of Wolff-Parkinson-White (WPW) syndrome on resting electrocardiograms (ECGs). Furthermore, sensory disruptions characteristic of multiple sclerosis (MS) can blunt symptom perception, masking potentially life-threatening hemodynamic instability.

CASE REPORT: A 54-year-old woman with secondary-progressive MS (SPMS) was admitted for a complicated urinary tract infection. The admitting ECG demonstrated sinus tachycardia without preexcitation. Telemetry subsequently revealed narrow-complex tachycardia at 220 beats per minute (BPM) with concurrent hypotension. Despite hemodynamic instability, the patient explicitly denied palpitations, chest pain, or presyncope. She had discontinued fingolimod several years earlier because of palpitations, a detail retrospectively suggestive of an accessory pathway. Review of records identified historical ECGs with intermittent delta waves and short PR intervals, confirming the presence of an accessory pathway with intermittent antegrade conduction. A 12-lead ECG during the acute event confirmed orthodromic atrioventricular reciprocating tachycardia (AVRT). The patient underwent successful synchronized cardioversion followed by radiofrequency ablation of a left-sided anterolateral accessory pathway via electrophysiological study (EPS).

CONCLUSIONS: This case illustrates the “ECG dilemma” of intermittent preexcitation, in which the absence of delta waves on a resting tracing does not exclude accessory pathway-mediated tachycardia. It further highlights that patients with neuro-modulating diseases, such as MS, may lack classical “alarm” symptoms for arrhythmia due to progressive autonomic and sensory dysfunction. Clinicians must maintain a high index of suspicion for concealed arrhythmias in this population, as neurological impairment can dissociate hemodynamic instability from subjective symptom perception. Objective monitoring with telemetry is essential to prevent adverse outcomes in this vulnerable population.

Keywords: Arrhythmias, Cardiac, Autonomic Nervous System, Demyelinating Diseases, Electrocardiography, Wolff-Parkinson-White Syndrome