The AV nodal conduction curve generated by the atrial extrastimulus technique has been described only qualitatively in man, making clinical comparison of known normal curves with those of suspected AV nodal dysfunction difficult. Also, the effects of physiological and pharmacological interventions have not been quantifiable. In 50 patients with normal AV conduction as defined by normal AH (less than 130 ms), normal AV nodal effective and functional refractory periods (less than 380 and less than 500 ms), and absence of demonstrable dual AV nodal pathways, we found that conduction curves (at sinus rhythm or longest paced cycle length) can be described by an exponential equation of the form delta = Ae-Bx. In this equation, delta is the increase in AV nodal conduction time of an extrastimulus compared to that of a regular beat and x is extrastimulus interval. The natural logarithm of this equation is linear in the semilogarithmic plane, thus permitting the constants A and B to be easily determined by a least-squares regression analysis with a hand calculator.

We report three cases of corrected transposition (CT), all with Ebstein's disease, ventricular septal defect (VSD) and ventricular preexcitation. In cases 1 and 2, the ECG revealed sinus rhythm, with type A fusion preexcitation QRS complexes, suggesting left-sided Kent bundles and intact conduction system (CS). Complete serial section (SS) of the CS in both cases revealed an anterior CS and a Kent bundle in the posteroseptal wall of the morphologic right ventricle (MRV). Case 3 had intermittent preexcitation, with periods of complete atrioventricular (AV) block with narrow QRS escape rhythm. The preexcitation complexes suggested the presence of a left lateral Kent bundle. SS of the CS revealed a blind posterior and two anterior AV nodes, one on either side of the pulmonary trunk. The left anterior AV node was blind. The right anterior node formed the anterior bundle, which ended blindly. This bundle emerged again and joined a posterior bundle to form an interrupted sling around the closed VSD. In addition, there was a tenous Kent bundle at the posterolateral wall of the MRV. In summary: (1) preexcitation in CT with Ebstein's disease of the left AV valve is associated with Kent bundles; (2) fusion complexes reflected intact CS; and (3) intermittent preexcitation with AV block was associated with the presence of tenuous Kent bundl and discontinuity of the CS.

The saltatory pattern, characterized by wide and rapid oscillations of the fetal heart rate (FHR), remains a controversial entity. The authors sought to evaluate whether it could be associated with an adverse fetal outcome. Material and Methods: The authors report a case series of four saltatory patterns occurring in the last 30 minutes before birth in association with cord artery metabolic acidosis, obtained from three large databases of internally acquired FHR tracings. The distinctive characteristics of this pattern were evaluated with the aid of a computer system. Results: All cases were recorded in uneventful pregnancies, with normal birthweight singletons, born vaginally at term. The saltatory pattern lasted between 23 and 44 minutes, exhibited a mean oscillatory amplitude of 45.9 to 80.0 beats per minute (bpm) and a frequency between four and eight cycles per minute. Conclusions: A saltatory pattern exceeding 20 minutes can be associated with the occurrence of fetal metabolic acidosis.

suMMARY Three patients with accessory nodoventricular pathways and re-entry tachycardia are reported. In all three patients the accessory nodoventricular pathway formed the anterograde limb of the re-entry circuit while the His-Purkinje-atrioventricular node axis formed the retrograde limb of the tachycardia in two of the patients and a concealed accessory pathway formed the retrograde limb in the remaining patient. All three patients also manifested dual anterograde atrioventricular nodal pathways with conduction through the accessory nodoventricular pathways being associated with the atrioventricular nodal fast pathway. Type I antiarrhythmic drugs, especially disopyramide and quinidine, were effective for the treatment of the re-entry tachycardia because of their depressive action on the nodoventricular pathway. Beta blockers were also effective because of their action on the atrioventricular nodal portion of the re-entry circuit in one patient and most probably due to atypical (atrioventricular nodal like) properties of a retrogradely conducting accessory pathway in a second patient.One of the rare types of re-entrant paroxysmal tachycardia reflects the occurrence of re-entrance via nodoventricular fibres. In these unusual tachycardias anterograde conduction is usually via a right sided inserting nodoventricular pathway, producing a tachycardia resembling ventricular tachycardia with a left bundle branch block pattern.Nodoventricular pathways might respond with an increase in refractoriness to drugs which depress the atrioventricular node or quinidine like agents, or both. There are few systemic data concerning the pharmacology of nodoventricular fibres and circus movement tachycardias using these fibres.We report the drug responses, the electrophysiology of nodoventricular fibres as related to anterograde dual atrioventricular nodal pathways, and observations on the nature of retrograde conduction during nodoventricular circus movement tachycardia in three patients with re-entrant paroxysmal tachycardia. Case I A 20 year old man with a five year history of paroxysmal tachycardia and no evidence of organic heart disease was studied. Electrocardiograms during sinus rhythm were normal (Fig. 1). During episodes of tachycardia the electrocardiogram showed wide QRS complexes (0.12 s) with left bundle branch block morphology, an axis of -20", and a heart rate of 230 beats/min. ELECTROPHYSIOLOGICAL STUDIESElectrophysiological studies showed normal conduction intervals during sinus rhythm (AH: 70 msec, HV: 47 msec, QRS: 90 msec). With incremental atrial pacing from heart rates of 100 to 160 beats/min the AH interval gradually increased from 75 to 105 msec and concomitantly the HV interval gradually decreased from 30 to 10 msec with the appearance of partial pre-excitation. At atrial paced rates of 170 to 200 beats/min the His bundle electrogram merged into the QRS complex, which had a left bundle branch block appearance similar to his spontaneous tachycardia (Fig. 2). The time from stimulus to the onset of the QRS co...

Serial sections of the conduction system (CS) were performed in two patients with recurrent tachyarrhythmias. Case 1, a 34-year-old female who had dual atrioventricular (AV) nodal pathways with recurrent paroxysmal supraventricular tachycardia, committed suicide. Autopsy revealed an abnormally formed atrial septum with insertion of eustachian valve on the AV part of the pars membranacea. The intercuspid portion of the pars membranacea was muscular. The AV node was located adjacent to the membranous part of the ventricular septum rather than the central fibrous body. In addition, there was an accessory anterior AV node on the parietal wall of the right atrium. Case 2, a 13-year-old boy with history of recurrent ventricular tachycardia, died suddenly. CS revealed a right-sided, markedly septated bundle. The first part of right bundle branch was divided into three parts, which later joined together. Both cases showed fatty infiltration of the atrial septum, more than normal for the age of the patients. The relationship of the recurrent tachyarrhythmias to the congenital abnormalities in the CS in the two cases and the fatty infiltration is reviewed.