Autonomic control and innervation of the atrioventricular junctional pacemaker.

BACKGROUND: The main physiologic function of the AV junction is control of timing between atrial and ventricular excitation. However, under pathologic conditions, the AV junction may become the pacemaker of the heart. Unlike the well-characterized sinoatrial node (SAN), autonomic control of the AV junctional pacemaker has not been studied. OBJECTIVE: The purpose of this study was to characterize the autonomic control and innervation of the AV junctional pacemaker. METHODS: The response of rabbit AV junctional pacemaker to autonomic stimulation was investigated using optical mapping, autonomic modulation via subthreshold stimulation (n = 12), and quantitative immunohistochemistry (n = 5), and the density of parasympathetic and sympathetic innervation in optically mapped preparations was quantified. RESULTS: Subthreshold stimulation applied adjacent to the conduction system in the triangle of Koch autonomically modulates the junctional rate, and parasympathetic and sympathetic components can be separated with atropine and the beta-blocker nadolol. Subthreshold stimulation increased the rate maximally to 2.1 +/- 0.4 times when applied with atropine. Unlike the SAN pacemaker, which shifts significantly in response to autonomic stimulation, the AV junctional pacemaker remains stationary (most often in the inferior nodal extension), moving in only 5% of subthreshold stimulation trials. Staining with tyrosine hydroxylase and choline acetyltransferase revealed heterogeneous innervation within the AV junction. CONCLUSION: AV junctional rhythm can be autonomically modulated with subthreshold stimulation to produce junctional rates of 145 +/- 16 bpm (cycle length 412 +/- 29 ms), similar to sinus rates in rabbit. Unlike the SAN, the anatomic location of the AV junctional pacemaker is stable during autonomic modulation.

A permanent junctional reciprocating tachycardia with atypical location, treated with radiofrequency catheter ablation.

Permanent junctional reciprocating tachycardia (PJRT) is an incessant or almost incessant supraventricular tachycardia with a long RP interval, usually occurring in children and young adults. The differential diagnosis of PJRT includes an atrial tachycardia and atypical atrioventricular nodal reentrant tachycardia (AVNRT). The accessory pathways in PJRT are typically located in the posteroseptal region. We report a case of successful radiofrequency catheter ablation in a 28-year-old male patient with PJRT due to a left posterolateral accessory pathway.

[Familial junctional ectopic tachycardia: clinical and pathological findings]. / Forma familiar de la taquicardia ectópica de la unión: hallazgos anatomoclínicos.

We describe two brothers with a neonatal diagnosis of junctional ectopic tachycardia. The first brother presented hydrops fetalis secondary to narrow QRS tachycardia at a rate of 230-300 beats/min with atrioventricular dissociation. Although the ventricular rate was controlled with intravenous amiodarone the baby died a few hours after initiation of this treatment from ventricular fibrillation and electromechanical dissociation. Histological examination of the conduction system showed diffuse hemorrhage and necrosis of the atrioventricular node and His' bundle. The second brother presented fetal distress and polyhydramnios and the postnatal electrocardiogram revealed junctional ectopic tachycardia at a rate of 170 beats/min alternating with sinus rhythm, which was controlled without treatment.

[Focal junctional tachycardia in adults. Anatomo-electrophysiological aspects apropos of a case]. / Tachycardie jonctionnelle focale de l'adulte. Confrontation anatomo-électrophysiologique à propos d'un cas.

The authors report the case of a 65 year old patient with focal junctional tachycardia complicating infectious myocarditis which had a fatal outcome. The ECG recordings showed episodes of tachycardia alternating with junctional rhythm at 90/min. There were signs of retrograde conduction. The anatomopathological findings were typical of acquired myocarditic lesions in the lower part of the atrioventricular node with congenital abnormalities, in particular a bifid node and His bundle with an accessory paraseptal atrioventricular bundle. This is the first description, to the best of the authors's knowledge, of junctional tachycardia associated with a latent pre-excitation.

Histopathological findings in three children with His bundle tachycardia occurring subsequent to cardiac surgery.

This report concerns three children with His bundle tachycardia who died following cardiac surgery. At autopsy the conduction system was examined in detail. In all three, the sinus node was intact and supplied by a well-formed artery. Haemorrhagic tracks were identified invading the penetrating atrioventricular bundle. The tracks originated from stitches placed close to the conduction tissue. The hypothesis that disruption of the conduction tissue results in an arrhythmogenic focus is discussed.

Junctional tachycardias: anatomic substrate and its significance in ablative procedures.

The conduction system was studied by serial section in three patients with intractable supraventricular tachycardias originating from the atrioventricular (AV) junction who died suddenly. The three patients were a 6 month old girl (Case 1), a 5 month old boy (Case 2) and a 22 year old woman (Case 3). The latter had a pacemaker inserted after surgical ablation of the AV node. The heart was hypertrophied and enlarged in all. In Case 1, the AV node was partly within the central fibrous body and there was a left-sided AV bundle with acute necrosis in the summit of the ventricular septum, adjacent to the AV node and bundle. In Case 2, the coronary sinus was displaced cranially close to the central fibrous body, resulting in abnormality of the latter, with entrapment, distortion and division of the AV node and bundle into two distinct components within the central fibrous body. In Case 3, a left-sided AV node was connected to the atrial septum. The right AV node was completely interrupted by sutures and the penetrating and branching bundle and bundle branches were markedly fibrosed. In addition, the atrial septum and summit of the ventricular septum showed marked inflammatory reaction with fibrosis, which was more marked on the right ventricular side. Histologic examination of the conduction system in all three cases demonstrated congenital abnormalities of the AV junction that may be related to the tachycardia. These findings emphasize the need to carefully evaluate the atrial septum and AV junctional area, including the coronary sinus, before ablative procedures are undertaken.(ABSTRACT TRUNCATED AT 250 WORDS)

Permanent form of junctional reciprocating tachycardia involving an atrio-hisian accessory pathway: electrophysiologic and histologic correlations.

We present clinical, electrophysiologic and morphologic correlations of a patient with a permanent form of junctional reciprocating tachycardia, who died from a lung tumor. At electrophysiologic study, the tachycardia circuit was suspected to involve an atrio-Hisian accessory pathway antegradely and the AV node retrogradely; a ventriculo-atrial accessory pathway was excluded. Pathologic examination revealed a right-sided atrio-Hisian accessory pathway and an area of abnormal dispersion in the distal His bundle fibers. This case is consistently different from another previously reported case in which a concealed, serpiginous, septal atrioventricular accessory pathway was demonstrated by anatomic examination. Thus, different substrates seem to be responsible for the permanent form of junctional reciprocating tachycardia.