Twenty-one patients were studied in whom ventricular preexcitation (VP) had been recorded in the past and had later disappeared, indicating antegrade block in the accessory pathway (AP), either spontaneously (10 patients) or under the effect of chronic treatment with amiodarone (11 patients). VP reappeared in nine cases during vagal stimulation, and in five cases during an i.v. isoproterenol in...

INCOMPLETE TRANSMISSION of impulses across the atrioventricular (A-V) junction has held a special fascination for many investigators.'14 Varied investigational techniques including venous pulse waves, standard electrocardiograms, and direct catheter electrode recordings from the cardiac chambers have been used to further the understanding of retrograde transmission of impulses into the A-V junc...

Concealed anterograde penetration of the atrioventricular (AV) node has been used to explain a wide variety of electrocardiographic findings. The effects of atrial rate acceleration on this phenomenon remain undefined. To examine the dynamic interrelations between conducted and nonconducted beats at different atrial rates, a unique atrial pacing protocol of functional 2:1 AV block was used in 1...

Exit block from a parasystolic focus is recognized when automatic discharges fail to become manifest during the excitable phase of the ventricular cycle. In the present study, an apparently complete exit block and a persistently concealed ventricular parasystole (VP) resulted from an exit refractory period (ExRP) longer than the sinus cycle length. Slowing of the heart rate caused the concealed...

Multiple areas of concealed intraventricular conduction are deduced on the basis of aftereffects observed in His bundle recordings. Electrocardiograms and His bundle recordings are presented from two patients with unstable bilateral bundle branch block, the instability of which depended on the interval at which ventricular depolarization was initiated by sinus or paced impulses. This circumstan...

We studied antegrade concealed conduction of atrial extrastimuli (A2) that blocked in the atrioventricular (AV) node in eight subjects, using a third extrastimulus (A3), coupled at decreasing coupling intervals to A2. Three A1-A2 intervals were tested in each subject: late (just shorter than AV nodal effective refractory period), intermediate, and early (just longer than atrial functional refra...

We studied the electrophysiologic characteristics of atrioventricular (AV) nodal conduction in patients with reciprocating tachycardia (RT) without ventricular preexcitation, and the relation of these characteristics to RT cycle length (CL). Thirty-five symptomatic patients who had a normal PR interval (0.13-0.20 second) during sinus rhythm underwent detailed intracardiac electrophysiologic stu...

In the present report, A-V dissociation with concealed retrograde conduction into the A-V node, caused SINUS beats to exhibit antegrade A-V nodal conduction delay sufficient to result in episodes of supraventricular tachycardia (SVT). In this patient, atrial ectopic premature depolarizations were never observed. The primary role of A-V nodal conduction delay in the genesis of paroxysmal SVT is ...