Accessory pathway unmasked by adenosine in a patient with unexplained cardiac arrest: a case report.

Background: Survivors of sudden cardiac arrest require detailed diagnostic evaluation to identify reversible causes and guide therapy. Underlying mechanisms may include ischaemia or electrophysiological abnormalities. The conventional diagnostic workflow may fail to uncover occult arrhythmic substrates, highlighting the need for targeted testing strategies in selected cases.

Case summary: A 35-year-old man, a former endurance athlete, experienced a witnessed sudden cardiac arrest during sleep. Ventricular fibrillation was terminated with direct-current shock, achieving return of spontaneous circulation. The initial 12-lead ECG showed ST-segment elevation in V1-V3 with a coved Brugada-like pattern, but reciprocal ST-segment depression. Myocardial ischaemia was ruled out with coronary angiography, and Brugada syndrome was excluded by a negative ajmaline test. No further abnormalities were found. Persistent clinical suspicion prompted an adenosine test, which revealed a left lateral accessory pathway. Electrophysiological testing demonstrated high-risk properties of the accessory pathway, with haemodynamic collapse during pre-excited atrial fibrillation. Catheter ablation successfully eliminated the accessory pathway without changes in QRS complex morphology, and the patient remained asymptomatic at follow-up, with no arrhythmic recurrence.

Discussion: Unexplained cardiac arrest in patients with structurally normal hearts presents significant diagnostic challenges. In this case, adenosine testing unmasked an accessory pathway as the reversible cause of cardiac arrest. Though not routinely included in cardiac arrest evaluations, adenosine testing was crucial in this patient's diagnosis and management, preventing unnecessary implantable cardioverter-defibrillator placement. Comprehensive diagnostic strategies, including targeted use of adenosine testing, can reveal occult arrhythmic substrates, improving outcomes and avoiding overtreatment in selected cases.