Presumed Postural Tachycardia Syndrome: 12-Lead Electrocardiograms During Tilt Table Testing Unmask an Atrial Tachycardia

Tilt table testing is commonly used to evaluate orthostatic intolerance and syncope and is typically performed with three-lead electrocardiography (ECG) monitoring, which limits P-wave interpretation. A 21-year-old woman with congenitally corrected transposition of the great arteries presented with recurrent tachy-palpitations and near syncope and was presumed to have postural tachycardia syndrome (POTS) after extensive noninvasive testing. During head-up tilt table testing incorporating intermittent 12-lead ECGs, she developed a sustained narrow-complex tachycardia that reproduced her symptoms. Careful P-wave analysis demonstrated P-wave morphologies that localized the rhythm to a left atrial focus, which was later confirmed on an electrophysiology study. This case highlights the diagnostic value of 12-lead ECGs during tilt table testing for the analysis of P-wave morphology and axis. Ectopic atrial tachycardia may mimic orthostatic syndromes and remain undetected with limited-lead testing. Incorporation of 12-lead ECGs during tilt table testing enables ECG-based localization of atrial arrhythmias, preventing misdiagnosis of orthostatic syndromes.