Demonstration of intra-atrial conduction delay, block, gap and reentry: a report of two cases

Biatrial pacing for paroxysmal atrial fibrillation: a randomized prospective study into the suppression of paroxysmal atrial fibrillation using biatrial pacing

OBJECTIVES

The purpose of this study was twofold: to assess whether biatrial pacing is superior to single-site pacing and capable of reducing the frequency of episodes of paroxysmal atrial fibrillation (PAF); and to compare pacing of the proximal coronary sinus (PCS) with the distal coronary sinus (DCS) and the effects of sequential or simultaneous biatrial pacing.

BACKGROUND

Interatrial conduction abnormalities have a role in the initiation of PAF. Biatrial pacing alters the site and timing of atrial depolarization and may benefit those with drug-resistant PAF.

METHODS

Nineteen patients with PAF who were intolerant of or refractory to medication were studied. All received right atrial (RA) and coronary sinus (CS) leads (either PCS or DCS). For three months the pacemaker was set in sensing mode only. Subsequently each patient completed three-month periods in random order in the following modes: RA pacing, CS pacing, biatrial pacing using inter-atrial delays of 15 and 70 ms.

RESULTS

Sixteen patients received a benefit from one or more pacing modes. The greatest reduction in PAF episodes was seen during biatrial pacing, especially with leads sited at the high right atrium (HRA) and distal CS (p = 0.0048). There was no difference for sequential or simultaneous pacing. Three patients derived no benefit.

CONCLUSIONS

In selected patients, biatrial pacing causes a significant decrease in atrial fibrillation episodes. Optimal lead sites were at the HRA and DCS. Simultaneous pacing conferred no benefit over sequential pacing.

Abnormal automaticity as mechanism of atrial tachycardia in the human heart--electrophysiologic and histologic correlation: a case report

INTRODUCTION

A 32-year-old woman was operated upon because of drug refractory atrial tachycardia.

METHODS AND RESULTS

Electrophysiologic study was performed prior to operation. During surgery, epicardial mapping of the electrical activity of the left atrium was performed. The left atrial appendage was resected and studied in a tissue bath. Thereafter, histologic examination was performed. Polarity of the P wave in the surface ECG suggested that the tachycardia originated high in the left atrium. Epicardial mapping disclosed earliest activation in the apex of the left atrial appendage. Intracellular recordings from surgical specimen made at the site of origin, which was marked during surgery, revealed cells with phase 4 depolarization at cycle lengths ranging from 360 to 540 msec. Exit block prevented spread of activation from the spontaneously firing cells to surrounding tissue. Histology showed that spontaneous activity arose in an area with abnormal cells--characterized by an amorphous, pale eosinophilic staining cytoplasm and absence of nuclei--surrounded by normal myocytes.

CONCLUSION

The observations indicate that the mechanism of the atrial tachycardia was based on abnormal automaticity in an area consisting of a conglomeration of normal and abnormal myocytes.

Mechanisms of clinical tachycardias

Animal data suggest that cardiac arrhythmias can result from a variety of mechanisms. In clinical settings, arrhythmias that are easily initiated and terminated with programmed electrical stimulation are often designated as reentry tachycardias. However, proof of reentry is contingent upon demonstration of the entire circuit; this relation has been proposed for arrhythmias associated with large circuits, such as those seen in the Wolff-Parkinson-White syndrome. Reentry has also been proposed as the mechanism responsible for a variety of other tachycardias, including bundle branch and atrioventricular nodal reentry tachycardia, permanent junctional reentrant tachycardia, reentry tachycardia associated with nodoventricular Mahaim fibers and inducible atrial and ventricular tachycardia. Documentation of triggered rhythms as the mechanism responsible for clinical arrhythmias has been even more difficult. Examples of arrhythmias resulting from triggered activity may include those associated with digitalis toxicity arising from the atria, the atrioventricular junction or the ventricles. Clinical arrhythmias due to triggered activity in the absence of digitalis have also been described. Cardiac arrhythmias that cannot be induced by electrical stimulation are presumably due to normal or abnormal automaticity. Examples of normal automaticity in the human heart are sinus rhythm and junctional and idioventricular escape rhythms. Tachycardias by abnormal automaticity have seldom been investigated for the purpose of documenting the mechanism and therefore the limited data available make it difficult to draw any final conclusions.

Atrioventricular nodal reentrant tachycardia

This entity represents the most common type of recurrent, regular, narrow QRS tachycardia in the absence of preexcitation syndrome. Electrophysiologic basis for the arrhythmia is reentry within the AV node resulting from dissociation between intranodal pathways. A better understanding of these intranodal pathways helps in the selection of a rational approach to management of these cases.

Evidence that AV nodal re-entrant tachycardia does not require participation of the entire AV node

Electrophysiologic studies in a case of AV nodal re-entrant tachycardia showed that a programmed atrial premature depolarization induced during the tachycardia did not change the tachycardia cycle but caused a delay in the following atrial echo. Analysis of such a phenomenon suggests that the atrial premature depolarization was conducted to the upper part of the AV node but not to the site of the re-entry. Therefore, AV nodal re-entry can persist without the participation of the upper part of the AV node. This case illustrates that the upper common pathway connecting the dual AV nodal pathways cranially is most likely located within the AV node and consists of AV nodal tissue.

Mechanism and clinical significance of atrial repetitive responses in man

We have studied the electrophysiological correlates of atrial repetitive responses, induced by single extrastimuli, in a group of 25 patients undergoing electrophysiologic studies for a variety of supraventricular and ventricular arrhythmias. The incidence of repetitive responses was not related to a previous history of atrial tachyarrhythmias. Repetitive responses were observed only when the extrastimulus elicited a significant intra-atrial conduction delay, as measured from the extrastimulus artifact, to two or three points in the atria. This condition was fulfilled only when the basic atrial rhythm was paced, and it was also facilitated by increasing atrial rate, which shortened the atrial effective refractory period. Atrial pacing thus seemed to facilitate the production of atrial repetitive responses by both promoting intra-atrial conduction delays during extrastimulation, and by shortening the atrial refractory period. Atrial repetitive responses are probably a nonspecific phenomenon, unrelated to a tendency towards atrial tachyarrhythmias; their mechanism is probably local re-entry, related to slow conduction of impulses during incomplete repolarization, and under favorable conditions they may precipitate atrial flutter or fibrillation in predisposed patients.

Atrioventricular nodal dysfunction in patients with atrial septal defect. Abnormalities of conduction and reciprocal rhythms

Electrophysiologic studies were performed in 17 unselected patients (mean age, 20 years) with atrial septal defect (ASD) of the ostium secundum type. In nine (52.9 percent) signs were found of atrioventricular (A-V) nodal dysfunction, in seven (41.1 percent) prolonged A-H interval, and in three (17.6 percent) prolonged effective refractory period of A-V node and in five (29.4 percent) A-V nodal tachycardia and reentry. Three of the four cases showed anterograde conduction (Ae-H interval) faster than retrograde conduction (H-A3 interval) during the tachycardia. In one patient with reentry a similar phenomenon was observed. In the remaining patient the conduction time was reversed (Ae-H longer than H-Ae). In two patients infrahisian and intrahisian block (first and second degree) with persistence of the tachycardia was observed. Patent or latent abnormalities in A-V node function are a frequent finding in patients with ASD. In the sinus node, any kind of significant abnormality can be found.