Spontaneous and Induced Reentrant Tachycardia

184

Supraventricular tachycardia in an isolated rabbit heart preparation was repeatedly initiated and terminated by carefully timed atrial premature beats. Transmembrane action potentials of AV nodal cells were recorded simultaneously by a "brush electrode" consisting of 10 microelectrodes. Surface electrograms of atrium and His bundle were also recorded. The moments of activation of 54 different AV nodal cells, both during regular driving of the atrium and during tachycardia were ascertained. Premature atrial beats introduced during tachycardia would either "reset" the tachycardia or terminate it. The sequence of activation of the AV nodal cells when initiating tachycardia, during tachycardia itself, and when premature beats were interpolated during tachycardia warrant the conclusion that a circus movement in the AV node, based on functional longitudinal dissociation of the upper AV node, was the underlying mechanism of the arrhythmia. KEY WORDS reciprocating tachycardia echo beats longitudinal dissociation transmembrane potentials atrial premature beats initiation and termination of tachycardia• On the basis of experiments on turtle hearts, Mines (1) described the basic mechanism underlying a reciprocating rhythm: "A slight difference in the rate of recovery of two divisions of the AV connexion might determine that a extrasystole of the ventricle . . . should spread up to the auricle by that part of the AV connexion having the quicker recovery process and not by the other part. In such a case, when the auricle became excited by this impulse, the other portion of the AV connexion would be ready to take up the transmission back to the ventricle. Provided the transmission in each direction was slow, the chamber at either end would be ready to respond . . . and thus the condition once

mentioning

confidence: 99%

Circus Movement within the AV Node as a Basis for Supraventricular Tachycardia as Shown by Multiple Microelectrode Recording in the Isolated Rabbit Heart

Janse

Capelle

Freud

et al. 1971

184

“…• One type of supernormal conduction, i.e., the paradoxical propagation of closely coupled stimuli when stimuli at longer coupling intervals are blocked, reflects a gap phenomenon (1)(2)(3)(4)(5)(6). This phenomenon occurs when the refractory period of a distal conduction site limits conduction.…”

mentioning

confidence: 99%

Nature of the Gap Phenomenon in Man

Denes

Dhingra

et al. 1974

The atrioventricular (AV) gap phenomenon occurs when the effective refractory period of a distal site is longer than the functional refractory period of a proximal site and when closely coupled stimuli are delayed enough at the proximal site to allow distal site recovery. According to previous studies, in type 1 gap, the distal site of block is distal to the His bundle (ventricular specialized conduction system) and the proximal site of block is in the AV node. In type 2 gap, both the proximal and the distal sites of conduction block are within the ventricular specialized conduction system. Using His bundle recordings and atrial extra-stimulus techniques in man, we observed three previously undescribed types of gaps between (1) the AV node (distal) and the atrium (proximal), (2) the His bundle (distal) and the AV node (proximal), and (3) the ventricular specialized conduction system or a bundle branch (distal) and the His bundle (proximal). The delays at the His bundle in the second and third types of gaps seen in this study were demonstrated as splitting of His bundle potentials. Gaps between the AV node or the His bundle and the ventricular specialized conduction system were more easily demonstrated at long cycle lengths, but gaps between the atrium and the AV node were more easily demonstrated at short cycle lengths. Therefore, the previous subdivision of gaps into two types is an oversimplification, because gaps can occur between multiple sites in the conduction system. The gap phenomenon may be potentiated by both long and short cycle lengths; long cycle lengths increase the effective refractory period of a distal site, e.g., the His bundle and the ventricular specialized conduction system, and the short cycle lengths decrease the functional refractory period of a proximal site, e.g., the atrium and the AV node. KEY WORDS atrial extra stimuli functional block cycle length His bundle electrogram supernormal conduction refractory period split His bundle potentials intra-atrial conduction delay• One type of supernormal conduction, i.e., the paradoxical propagation of closely coupled stimuli when stimuli at longer coupling intervals are blocked, reflects a gap phenomenon (1-6). This phenomenon occurs when the refractory period of a distal conduction site limits conduction. With closely coupled stimuli, enough proximal delay occurs so that the impulse arrives at the distal conducting site late enough to be conducted. Gallagher and co-workers (5) have defined two types of gaps. In type 1 gap, the initial distal site of block is distal to the His bundle recording site, and the proximal site of delay is in the atrioventricular (AV) node. In type 2 gap, both the distal and the proximal site of conduction delay are distal to the His bundle recording site (5). A third kind of gap has recently been described by Agha and co-workers (6) in a patient with AV block; however, this kind of gap appears to reflect supernormal conduction, and proximal and distal sites of delay have not been defined (6).In the present st...

“…Curves relating ventricular intervals to the intervals between basic and premature atrial responses have been used as an index to determine the refractory periods of the A-V conduction system in both the canine and human hearts (2,3,5,11,(16)(17)(18)(19). Since conduction delay and block of premature atrial impulses can occur in the VSCS, the recording of His bundle activity enables values for the refractory periods of the A-V node to be distinguished from His-Purkinje conduction delay and block.…”

mentioning

confidence: 99%

Patterns of Atrioventricular Conduction in the Human Heart

Wit

Weiss

Berkowitz

et al. 1970

309

Atrial, His bundle (H), and ventricular electrograms were recorded by an electrode catheter in unanesthetized man. Conduction time through the atrioventricular (A-V) conduction system was subdivided into A-V nodal (A-H interval) and ventricular specialized conduction system (H-V interval). The right atrium was driven at a constant rate and the pattern of A-V conduction of premature atrial test impulses was determined as they occurred progressively earlier in the cardiac cycle. In the type 1 response, conduction delay and block were limited to the A-V node only. The type 2 response was characterized by progressive conduction delay in both the A-V node and ventricular specialized conduction system with block occurring in several instances in the latter. In the type 3 response there was also a progressive delay in A-V nodal conduction time, and a sudden marked delay in conduction in the ventricular specialized conduction system. Conduction block occurred distal to the His bundle depolarization. The relevance of conduction delay and block in the different regions of the A-V conduction system to the full recovery time and the relative, functional, and effective refractory periods of A-V conduction are indicated. ADDITIONAL KEY WORDS premature atrial impulses functional refractory period effective refractory periodHis bundle electrogram conduction block conduction delay full recovery time relative refractory period • Conduction of impulses from the atria to the ventricles involves propagation through a series of elements known as the atrioventricular (A-V) conduction system. This system includes the A-V node and the ventricular specialized conduction system (VSCS), which includes the bundle of His, the bundle branches and peripheral Purkinje network (1).Previous investigations in dogs have shown some of the physiological properties of A-V conduction by studying the propagation of premature atrial impulses (2-5). The characteristic types of A-V delay differed in different