Concealed retrograde conduction of an atrial echo in second degree A-V block of the Wenckebach type with modified ventricular acceleration.

Whereas second degree A-V block showing the classical pattern of the Wenckebach phenomenon is easily diagnosed, variant forms of the Wenckebach phenomenon in second degree A-V block may pose difficulties to the interpretor. A case is presented, where modified acceleration of the ventricles--a crucial "pointer" to the Wenckebach A-V block -- is disturbed by concealed conduction of an atrial echo. Differences in the electrocardiographic manifestation between this and the classical type of second degree A-V block of the Wenckebach type are discussed.