Bolivar Portillo

Entrainment of atrioventricular nodal reentrant tachycardias during overdrive pacing from high right atrium and coronary sinus: With special reference to atrioventricular dissociation and 2:1 retrograde block during tachycardias

Entrainment was attempted during electrophysiologic evaluation of 8 patients with atrioventricular (AV) nodal reentrant tachycardia. Entrainment could be performed while pacing from the high right atrium in 35 of 35 episodes, from proximal coronary sinus in 9 of 21 episodes and from distal coronary sinus in 10 of 20 episodes. The minimal rates required were 8 to 40 beats/min faster than those of the tachycardias. That the atria (as defined in electrophysiologic studies) were not a necessary component of the reentry circuit was suggested by the occurrence, during tachycardia, of short episodes of AV dissociation and of 1 episode of 2:1 retrograde block. For the tachycardia to be interrupted, the pacing rate usually had to be slightly faster than that required to entrain, as well as sufficiently rapid to produce anterograde block of an atrial impulse in the slow AV nodal pathway. Moreover, termination of tachycardia apparently was a function of the pacing site. In some episodes, either because of a proximity effect or because of a preferential input into the upper common pathway, coronary sinus pacing terminated the tachycardia at slower rates or with fewer stimuli than high right atrial pacing. Thus, patients with drug-resistant AV nodal reentrant tachycardias may benefit from recently introduced pacing techniques for termination of tachycardia through entrainment.

Quintuple pathways participating in three distinct types of atrioventricular reciprocating tachycardia in a patient with Wolff-Parkinson-White syndrome

Electrophysiologic studies were performed in a patient with recurrent supraventricular tachyarrhythmias. Sinus and paced atrial beats had QRS complexes characteristic of atrioventricular (A-V) conduction through a manifest left lateral accessory pathway (Wolff-Parkinson-White syndrome, type A). Three distinct types of A-V reciprocating tachycardia and three different modes of retrograde atrial activation were demonstrated. Type 1 tachycardia involved the slow A-V nodal pathway and a second (left lateral or left paraseptal) accessory A-V pathway capable of retrograde conduction only. Type 2 tachycardia was of the slow-fast A-V nodal pathway type. Type 3 tachycardia involved in heretofore undescribed circuit in that retrograde conduction occurred through an accessory A-V pathway with long retrograde conduction times and anterograde conduction through both the manifest left lateral accessory A-V pathway and fast A-V nodal pathway. Premature ventricular beats delivered late in the cycle of this tachycardia advanced (but did not change) the retrograde atrial activity without affecting the timing of the corresponding anterograde H deflection. In summary, this patient had five (three accessory and two intranodal) pathways participating in three different types of A-V reciprocating tachycardia; the recurrence of these were prevented with oral amiodarone therapy.

Right Atrial-ventricular Dissociation and Entrainment while Pacing from High Right Atrium and Coronary Sinus during Circus Movement Tachycardias

Thirteen patients with circus movement tachycardias [CMT] were studied. Twelve had left‐sided, and one, right‐sided, accessory pathways. Entrainment was possible during overdrive high right atrial stimulation in 13/13 patients, and during coronary sinus pacing in 10/12 patients. The minimal pacing rates required for this to occur were 10 to 31 beats/min faster than those of the tachycardias. Short episodes of right atrial‐ventricular dissociation occurred while pacing from the high right atrium [6/13 patients), but not from the coronary sinus (0/13 patients). It is possible to explain this phenomenon by postulating the existence of two distinct atrioventricular (AV) nodal inputs (one for right‐sided and the other for left‐sided impulses); it could also have been an expression of the close distance existing between the AV node and the coronary sinus. Entrainment, by defining a range of paring rates followed by resumption of the tachycardia upon the cessation of stimulation, indicated that faster rates were needed for the CMT to be interrupted. However, regardless of the pacing rate and pacing site, tachycardia termination occurred when an anterograde impulse was blocked at the. AV node. The information obtained from this study suggests that some patients with drug‐resistant CMT may benefit from pacing modes capable of terminating the arrhythmia “through entrainment” at the slowest atrial rate at which this is possible.

Treatment of Drug Resistant A‐V Reciprocating Tachycardias with Multiprogrammable Dual Demand A‐V Sequential (DVI,MN) Pacemakers

Programmable dual A‐V sequential demand (DVI,MN) pacemakers were implanted in eight patients with recurrent or incessant, drug‐refractory, A‐V reciprocating tachycardias. This was done after intracardiac studies had identified a variety of electrogenetic mechanisms which include tachycardias involving Kent bundles, (manifest or concealed Wolff‐Parkinson‐White syndrome), nodoventricular (Mahaim) fibers, enhanced A‐V node pathways (Lown‐Ganong‐Levine syndrome), and dual intranodal pathways. The antitachycardia features of the pacemaker were evaluated during the electrophysiological studies. No immediate postoperative complications occurred after implantation. Furthermore, during the follow‐up periods (4 to 20 months), clinical assessment, ambulatory (Holter) monitoring and invasive (as well as noninvasive) evaluations have confirmed continuous effectiveness in recognizing and automatically terminating the tachycardias. Late pacemaker system malfunction has not occurred. The frequency of the tachycardias and the dosage of concomitantly‐administered antiarrhythmic medications were significantly reduced. Furthermore, preliminary studies performed in our laboratory suggest that DVI,MN pacemakers may also be useful in certain types of intra‐atrial reentry tachycardias coexisting with sinus node dysfunction.

Linking phenomenon during atrial stimulation with accessory pathways

Linking is an electrophysiologic phenomenon in which each successive impulse entering a macroreentry circuit propagates preferentially along 1 limb because of the functional impedance to conduction in the contralateral limb produced by the previous impulse. Electrophysiologic studies were performed in 12 patients with a bidirectionally conducting accessory pathway. Linking was analyzed while 1:1 atrioventricular conduction took place through the normal pathway. When atrial pacing (at the same cycle length) could be initiated during sinus rhythm in patients with rapidly conducting accessory pathways, linking was dynamically maintained by repetitive local refractoriness (interference). When it could be initiated during the usual type of orthodromic circus movement tachycardia, linking was sustained by actual impulse collision, the underlying mechanism having also been called entrainment. When it could be initiated during sinus rhythm in a patient with a slowly conducting accessory pathway, linking was maintained by impulse collision, but the underlying mechanism could not be called entrainment because stimulation had not been started during tachycardia. This study showed that 2 terms--linking and entrainment--may be applied to the same mechanism and, conversely, that the same name could not be used in reference to the same mechanism when pacing was initiated under different circumstances. However, using the proposed conceptual formulation for linking, it is apparent that seemingly diverse mechanisms associated with macroreentry circuits involving accessory pathways are, in fact, variations on a common electrophysiologic theme.

Entrainment of circus movement tachycardia utilizing an accessory pathway with long retrograde conduction times during ventricular and atrial stimulation

An unusual case is presented in which a circus movement tachycardia incorporating an accessory pathway with long retrograde conduction time was transiently entrained. Overdrive high right atrial stimulation produced entrainment without atrial fusion since collision of anterograde and retrograde impulses took place within the accessory pathway. Tachycardia termination occurred when, at a faster pacing rate, an atrial impulse that collided in the accessory pathway was blocked at the atrioventricular (AV) node. In contrast, the entrainment seen during right ventricular apical stimulation was characterized by the occurrence of both fusion and collision within the ventricles. The tachycardia was terminated when a pure paced impulse that collided in the normal pathway was blocked in a retrograde direction in the accessory pathway. These data indicate that: 1) transient entrainment of this arrhythmia (circus movement tachycardia) can be identified by the classical criteria used to diagnose it, provided that fusion and collision occur within the ventricles; and 2) the accessory pathway is the weak link for tachycardia termination only during ventricular pacing since the AV node is the weak link during atrial stimulation.

Attempted entrainment of circus movement tachycardias by ventricular stimulation

. Entrainment was attempted while pacing the right ventricle in 12 patients with circus movement tachycardias. At the onset of stimulation eight patients had short episodes of intraventricular and atrioventricular dissociation during which the paced impulses activated the various ventricular recording sites (right and left), but did not reach the atria. The latter occurred because the ventricular olectrograms were recorded from parts of the ventricles which were not essential components of the reentry circuit. Relatively long (greater than 5 s) runs of entrainment were not possible in any case because of the relatively prompt termination of the tachycardias. Whereas in three patients this was due to the abrupt appearance of retrograde block in the accessory pathway, in nine patients it happened when the sequential, anterograde and retrograde, penetration of the AV node resulted in AV nodal block of the subsequent, reentering atrial impulse. The findings in this study showed that, with the methodology used, entrainment of circus movement tachycardias by ventricular stimulation had to be defined conceptually, by the fulfillment of requirements which did not include its occurrence for at least 5 seconds. Furthermore, the results also suggested that entrainment and tachycardia termination were best demonstrated by a technique which allowed the emission of the first stimulus in a constant (late) moment of the cycle, with deliverance of one additional stimulus at the same cycle length in successive pacing runs.

Tachycardias in which the Reentry Circuit Includes Atrioventricular Bypass Tracts

The possibilities for an atrial or ventricular impulse to bypass all or part of the AV node, the His bundle, or both, are [52A]: (a) unidirectionally or bidirectionally conducting accessory atrioventricular pathways (APs) with short or long conduction times [144B, 123CJ; (b) nodoventricular tracts (Mahaim fibers extending from AV node to ventricles); (c) fasciculoventricular tracts (Mahaim fibers connecting His bundle and ventricles; (d) atriofascicular (atrio-His bundle) tracts; and (e) intranodal bypass tracts (see table 7–1). The latter two will not be discussed in this communication.