Atrioventricular 2:1-conduction via an accessory pathway during left atrial flutter unmasking WPW syndrome: a case report.

Differential diagnosis of broad complex tachycardia with superior axis and positive concordance of chest leads consists of i) VT with a left ventricular exit at the posterior mitral annulus, ii) antidromic AVRT involving a left-posterior AP, and iii) supraventricular tachycardia predominantly conducted via a left-posterior AP. The absence of classic ECG criteria for preexcitation syndrome does not rule out AP sufficiently, highlighting the importance of minimal surface-ECG preexcitation criteria. In the case of detection of minimal surface-ECG preexcitation criteria, administration of adenosine rules out or proves the existence of an AP noninvasively and cost-effectively.