Patterns of ventriculo-atrial conduction in the Wolff-Parkinson-White syndrome

Reflections on the early invasive clinical cardiac electrophysiology era through fifty manuscripts: 1967-1992

In 1967, researchers in The Netherlands and France independently reported a new technique, later called programmed electrical stimulation. The ability to reproducibly initiate and terminate arrhythmias heralded the beginning of invasive clinical cardiac electrophysiology as a medical discipline. Over the next fifty years, insights into the pathophysiologic basis of arrhythmias would transform the field into an interventional specialty with a tremendous armamentarium of procedures. In 2015, the variety and complexity of these procedures were major reasons that led to the recommendation for an increase in the training period from one year to two years. The purpose of this manuscript is to present fifty manuscripts from the early invasive clinical cardiac electrophysiology era, between 1967 and 1992, to serve as an educational resource for current and future electrophysiologists. It is our hope that reflection on the transition from a predominantly noninvasive discipline to one where procedures are commonly utilized will lead to more thoughtful patient care today and to inspiration for innovation tomorrow. In the words of the late Dr. Mark E. Josephson, "It is only by getting back to the basics that the field of electrophysiology will continue to grow instead of stagnate."

Clinical features of Wolff-Parkinson-White syndrome

Wolff-Parkinson-White syndrome is the most common form of ventricular preexcitation. Understanding this syndrome is fundamental for anyone interested in learning about arrhythmias. This review addresses (1) the historic sequence of events that led to the understanding of this syndrome; (2) the pathologic, embryologic, and electrophysiologic properties of accessory pathways; (3) the epidemiology and genetics of this syndrome; (4) the clinical diagnosis of this syndrome, with special emphasis on the arrhythmias that patients with ventricular preexcitation are predisposed to; and (5) the therapy for patients with Wolff-Parkinson-White syndrome.

Ventriculoatrial shortening achieved in Wolff-Parkinson-White syndrome by programmed right ventricular pacing

A 47-year-old woman with a left-sided Kent bundle showed marked reduction of the ventriculoatrial conduction time during extrastimuli at the right ventricular apex and outflow tract. The degree of reduction was greater than 6 years ago. A 'supernormal conduction' in the ventricle and the Kent bundle could have been responsible for this phenomenon.

Insights into the electrophysiology of accessory pathway-mediated arrhythmias provided by the catheter ablation experience: "learning while burning, part III"

The success of catheter ablation has greatly improved the care of patients with paroxysmal tachycardias and has caused a revolution in the practice of electrophysiology. Some investigators have expressed that concern over procedural success in an increasingly interventional specialty threatens to eclipse attempts to understand the physiology of arrhythmia syndromes. Alternatively, due to the precise and directed nature of the lesions created with radiofrequency energy, catheter ablation procedures have allowed investigation to continue at a more focused level. In this article, the insights provided by the catheter ablation experience into the physiology of arrhythmias mediated by accessory AV pathways will be reviewed. Although the learning process was sometimes delayed by the nearly immediate success of radiofrequency catheter ablation, difficult situations have continued to renew efforts for understanding at a deeper level. Conscious attempts at "learning while burning" will provide the opportunity to investigate aspects of bypass tract physiology that remain incompletely characterized, such as partial response to therapy and late recurrence.

Current management of the Wolff-Parkinson-White syndrome

In this review, we discuss the pathophysiology of the Wolff-Parkinson-White (WPW) syndrome and describe medical, surgical, and catheter based principles. WPW syndrome results from the congenital presence of impulse-conducting fascicles, known as accessory pathways (APs) or bypass tracts, which connect atria and ventricles across the annulus fibrosis and are capable of preexciting portions of the ventricular myocardium. Once triggered, atrioventricular reciprocating tachycardias (AVRTs) generally result from depolarization wavefronts moving anterograde through the AV node to the ventricles and returning retrograde to the atria along the AP. Rapid AVRT decreases ventricular filling time and cardiac output, resulting in symptoms. Medications that prolong AP refractory periods (flecainide, propafenone, and amiodarone) prevent rapid AP anterograde conduction (from atria to ventricles) in atrial tachycardias such as atrial fibrillation or flutter. In emergencies, adenosine can be used to terminate the AVRT of WPW syndrome. Otherwise, Class IA or IC antiarrhythmic agents are used to slow AP conduction either with or without AV nodal blocking agents. Open chest surgical ablation of a bypass tract in a symptomatic patient was first reported in 1968. The original endocardial surgical techniques for localizing and dividing APs were refined and an alternative epicardial approach has been developed. Reported mortality rates in experienced hands were 0% to 1.5% in large series for patients without additional cardiac abnormalities. Catheter delivered radiofrequency (RF) energy is now applied intravascularly to ablate APs. Since the first large series of patients undergoing RF ablation was reported in 1989, the procedure had proved safe, cost effective, and well tolerated. RF ablation has become the initial nonpharmacological treatment of choice for WPW syndrome; surgical ablation has become relegated to those cases where symptoms are intolerable and RF ablation is not feasible.

Anterograde and retrograde decremental conduction over left-sided accessory atrioventricular pathways in the Wolff-Parkinson-White syndrome

The electrophysiologic properties of left-sided accessory pathways (APs) were examined by cardiac stimulation in 55 patients with Wolff-Parkinson-White syndrome. Atrioventricular and ventriculoatrial conduction times were assessed at the coronary sinus level nearest to the AP and then plotted graphically as a function of coupling interval (for atrial and ventricular refractory period determinations). Of 29 patients with anterograde conduction over the AP, 10 (34%) exhibited decremental conduction. However, only two (7%) had a maximal decrement equal to or more than 30 msec. In the other eight (27%) patients the maximal decrement ranged from 10 to 20 msec. The longest coupling interval at which anterograde decremental conduction was demonstrated ranged from 260 to 440 msec (346 +/- 52 msec). The shortest coupling interval ranged from 240 to 320 msec (265 +/- 24 msec). The anterograde decremental conduction zone was 91 +/- 55 msec. Of 51 patients with retrograde conduction over the AP, 23 (45%) exhibited decremental conduction. However, only eight (15%) had a maximal decrement equal to or greater than 30 msec. In the other 15 (29%) patients the maximal decrement ranged from 10 to 25 msec. The longest coupling interval was 338 +/- 70 msec. The shortest coupling interval was 275 +/- 42 msec. The retrograde decremental conduction zone was 72 +/- 47 msec. There was a significant inverse correlation between the AP effective refractory period and the maximal decrement (r = -0.42; p < 0.05). The comparison of maximal ventriculoatrial conduction time with the maximal decrement revealed a positive correlation (r = 0.63; p < 0.01). These data reveal that minimal decremental conduction over left-sided APs is not an uncommon finding and stress that care should be taken in evaluation of conduction over these connections.

Physiological substrate for antidromic reciprocating tachycardia. Prerequisite characteristics of the accessory pathway and atrioventricular conduction system

BACKGROUND

Although the anatomic "substrate" for the occurrence of antidromic reciprocating tachycardia (ART) has been previously examined, the underlying physiological substrate for this unusual arrhythmia in patients with the Wolff-Parkinson-White syndrome has not been thoroughly characterized.

METHODS AND RESULTS

The electrophysiological properties of the accessory pathway and normal ventriculoatrial conduction system in 30 patients with ART and a single accessory pathway were compared with those observed in a control group of 36 patients without this arrhythmia to elucidate the critical physiological substrate essential for the development and maintenance of ART. Inducible ART had a mean cycle length of 286 +/- 31 msec. The average retrograde ventriculoatrial conduction system effective refractory period in ART patients was significantly less than that in the control group (244 +/- 32 versus 291 +/- 46 msec, p = 0.0002). All of the ART patients showed retrograde conduction over the normal conduction system at cycle lengths of less than or equal to 360 msec; 23 had 1:1 conduction to less than or equal to 300 msec, and 16 showed 1:1 propagation at cycle lengths of less than or equal to 260 msec. The shortest cycle length accompanied by 1:1 retrograde propagation over the normal conduction system in patients with ART was also significantly less than that observed in the control group (274 +/- 39 versus 347 +/- 73 msec, p less than 0.001). The accessory pathway anterograde ERP in ART patients with 1:1 retrograde conduction over the normal ventriculoatrial conduction system at cycle lengths of less than or equal to 360 was significantly less than that seen in comparable control patients (247 +/- 23 versus 284 +/- 56 msec, p = 0.001), and the accessory pathway location was significantly further from the atrioventricular node in 21 patients with ART undergoing surgery than that in 22 operated control patients (3.8 +/- 0.8 versus 2.9 +/- 0.8 mapping units, p = 0.0025) who also had retrograde ventriculoatrial conduction to cycle lengths of less than or equal to 360 msec. No significant differences in anterograde atrioventricular conduction system properties, retrograde accessory pathway refractoriness, or shortest ventricular pacing cycle lengths maintaining 1:1 conduction via the accessory pathway were observed between groups.

CONCLUSIONS

This quantitative characterization of the properties of conduction and refractoriness of both the accessory pathway and ventriculoatrial conduction system and the relation between these characteristics and the accessory pathway location in ART patients provides additional insight into the prerequisites for the initiation and maintenance of this rhythm disturbance.

Characteristics of accessory pathways exhibiting decremental conduction

The prevalence, electrophysiologic characteristics and functional significance of decremental conduction over an accessory pathway were examined in this retrospective study of 653 patients who had an accessory pathway demonstrated at electrophysiologic study. Decremental conduction was identified in 50 patients (7.6%). In 15 patients with anterograde decremental conduction, the accessory pathway was right parietal or septal in 14 patients and left parietal in 1 patient. In the 40 patients with retrograde decrement, the accessory pathway was left parietal in 19, posteroseptal in 13, right parietal in 2 and right anteroseptal in 6 patients. Anterograde conduction over the accessory pathway was absent in 11 of the 40 patients with retrograde decrement. Retrograde conduction over the accessory pathway was absent in 9 patients with anterograde decrement. There was no significant difference in the accessory pathway effective refractory period, or shortest cycle length with 1:1 conduction over the accessory pathway in anterograde and retrograde directions. The shortest RR interval in atrial fibrillation between 2 preexcited QRS complexes was longer in patients with anterograde decremental conduction than in a control group of patients with anterograde-conducting accessory pathways without decremental properties. These data demonstrate that decremental conduction over accessory pathways is uncommon. Anterograde decremental conduction usually occurs in right-sided or septal pathways that often do not conduct in the retrograde direction.

Clinical and electrophysiologic characteristics of patients with antidromic circus movement tachycardia in the Wolff-Parkinson-White syndrome

Antidromic circus movement tachycardia was documented in 36 of 345 consecutive patients with Wolff-Parkinson-White syndrome undergoing detailed electrophysiologic evaluation. Twenty-six patients were men and 10 were women (mean age +/- standard deviation 26 +/- 12 years [range 12 to 45]). Multiple accessory pathways were identified in 12 of these 36 patients (33%). Ten of the patients (67%) with clinically documented antidromic tachycardia had multiple accessory pathways. Dizziness and syncope occurred in 61 and 50% of patients with antidromic circus movement tachycardia. Six patients had clinical documentation of atrial fibrillation, and 4 patients (11%) were resuscitated from ventricular fibrillation. In the 36 patients, 56 distinct antidromic tachycardias were recorded and several different pathways were observed. Orthodromic tachycardia was the most frequently associated arrhythmia (72%). Dual atrioventricular nodal pathways were present in 12 patients (33%); however, atrioventricular nodal tachycardia could be initiated in only 2 of them. Interruption of the accessory pathway was successfully performed in all 20 patients undergoing surgery.

Pharmacological characterization of conduction over a Mahaim fiber: evidence for adenosine sensitive conduction

The presence of a nodoventricular pathway (Mahaim fiber) has been invoked to explain certain distinctive electrocardiographic and electrophysiological observations. The presence of an atrioventricular or atriofascicular fiber with decremental conduction properties has been documented in many of these patients. We report the case of a patient with a Mahaim fiber and the response to conduction over this pathway after adenosine, procainamide, encainide, verapamil, edrophonium, phenylephrine and isoproterenol. Conduction over the Mahaim fiber was blocked by adenosine, but not verapamil. The time course of adenosine induced block over the Mahaim fiber differed from adenosine induced AV nodal block. Mahaim fibers are decrementally conducting pathways that are adenosine sensitive. These findings support the concept that conduction in accessory pathways manifesting decremental properties is not mediated by the calcium channel.

Electrophysiological demonstration of anterograde concealed conduction in accessory atrioventricular pathways capable only of retrograde conduction

Anterograde concealed conduction into the concealed accessory atrioventricular (AV) pathway has been postulated to be one of the factors preventing the reciprocating process via the accessory pathway in patients with the concealed Wolff-Parkinson-White(WPW) syndrome but its presence has not been documented. To demonstrate the occurrence of anterograde concealment, 12 patients with the concealed WPW syndrome were selected for study. A pacing protocol was designed in which the retrograde conduction of the ventricular extrastimulus over the accessory pathway was assessed during ventricular pacing alone (conventional method) and during the AV simultaneous pacing (simultaneous method); the results were then compared. When the high right atrium was simultaneously paced, the effective refractory period of the concealed accessory pathway shortened as compared with the conventional method in five of 12 patients (from 341.7 +/- 110.8 to 312.5 +/- 108.2 msec, n = 12), whereas, it decreased in all patients studied when the coronary sinus near the accessory pathway was simultaneously paced (from 375.7 +/- 135.0 to 287.1 +/- 116.1 msec, n = 7). These results demonstrate that the AV simultaneous pacing frequently shortens the refractoriness of the concealed accessory AV pathway and such facilitation seems to be well explained by the probable anterograde concealment in it and peeling back of the refractory barrier.

Conduction over an isthmus of atrial myocardium in vivo: a possible model of Wolff-Parkinson-White syndrome

Antiarrhythmic drugs appear preferentially to prolong refractoriness of accessory pathways compared with atrial or ventricular muscle in patients with the Wolff-Parkinson-White syndrome. This response may be due to intrinsic properties of accessory pathways or to depressed conduction associated with a narrow strip, or isthmus, of tissue. To test the latter possibility, in 16 anesthetized dogs we surgically isolated a portion of the right atrial myocardium in the form of an ellipse (10 to 25 X 8 to 15 mm). The ellipse was connected to the body of the right atrium by a narrow isthmus (cross-sectional area [CSA] 1 to 13.5 mm2) and was perfused by the sinus node artery or its branch. Diastolic threshold (mean +/- SE 0.16 +/- 0.05 vs 0.13 +/- 0.02 mA) and effective refractory period (ERP; 144 +/- 4 vs 139 +/- 5 msec) were the same proximal and distal to the isthmus. In eight dogs, determination of the ERP of the isthmus was limited by the ERP of the atrial tissue proximal and distal to the isthmus, and the CSA of the isthmus in these dogs was significantly larger than that in the remaining seven dogs in which the ERP of the isthmus could be determined (7.4 +/- 1.4 vs 3.2 +/- 0.6 mm2, p less than .05). The shortest pacing cycle length (PCL) with 1:1 conduction from the proximal to the distal segments did not differ from that in the opposite direction in 16 dogs (154 +/- 9 vs 153 +/- 7 msec). The CSA of the isthmus correlated inversely with the shortest PCL with 1:1 conduction in both directions via the isthmus (r = -.84, p less than .01). Vagal stimulation shortened the shortest PCL with 1:1 conduction from the distal to the proximal segment (153 +/- 14 vs 143 +/- 12 msec, p less than .02), but not in the opposite direction. Procainamide (10 to 20 mg/kg iv, serum concentration 8.6 +/- 0.8 micrograms/ml) prolonged the ERP of the proximal site from 145 +/- 5 to 170 +/- 5 msec (p less than .001), the ERP of the distal site from 143 +/- 6 to 168 +/- 6 msec (p less than .001) in 12 dogs, and the shortest PCL with 1:1 conduction (proximal to distal from 149 +/- 8 to 204 +/- 17 msec, p less than .001; distal to proximal from 149 +/- 7 to 197 +/- 12 msec, p less than .001) in 14 dogs.(ABSTRACT TRUNCATED AT 400 WORDS)

Reliability of retrograde atrial activation patterns during ventricular pacing for localizing accessory pathways

Definitive localization of accessory pathways is based on atrial activation patterns during orthodromic supraventricular tachycardia when retrograde conduction occurs exclusively through the accessory pathway. In some patients, supraventricular tachycardia cannot be induced or is deleterious. To determine whether accessory pathway sites can be identified accurately during ventricular pacing, retrograde atrial activation was assessed during orthodromic supraventricular tachycardia and ventricular pacing at multiple cycle lengths in 41 patients with a single accessory pathway. To obviate retrograde fusion due to concomitant conduction through the normal atrioventricular (AV) conduction system that may obscure the location of the accessory pathway, the difference in conduction time from the site of earliest atrial activation to the His bundle atrial electrogram (delta A-SVT) was measured during orthodromic supraventricular tachycardia and compared with values observed during ventricular pacing (delta A-VP). Characteristic values for the delta A-SVT interval were identified for left lateral (66 +/- 17 ms), left posterior (50 +/- 8 ms), posteroseptal (33 +/- 7 ms), right free wall (22 +/- 15 ms) and anteroseptal (0 +/- 0 ms) accessory pathway sites. During ventricular pacing, the site with the earliest atrial electrogram was used to define the accessory pathway location only if the maximal value of the delta A-VP interval over the range of cycle lengths assessed was comparable with the value of the delta A-SVT interval characteristic of that region. Values of the delta A-SVT interval correlated closely with the maximal values of the delta A-VP interval (r = 0.91). With this approach, 40 (98%) of 41 accessory pathway sites were identified correctly during ventricular pacing.(ABSTRACT TRUNCATED AT 250 WORDS)

Anatomic and electrophysiologic substrate of the permanent form of junctional reciprocating tachycardia

Data are reported on three patients with the permanent form of junctional reciprocating tachycardia, in whom conduction over a slow accessory pathway was observed after His bundle ablation. Tachycardia was almost incessant and showed a retrograde P wave (P') and RP' interval longer than P'R interval in all patients; during sinus rhythm, the PR interval was normal and there was no evidence of a delta wave. An accessory pathway with a long conduction time located in the posterior pyramidal space provided the retrograde limb of the reentry circuit. After His bundle ablation, the accessory pathway was capable of conducting in both anterograde and retrograde directions with decremental properties in all patients. Postmortem documentation of the accessory pathway was achieved in one patient. Serial sections revealed an accessory atrioventricular connection composed of ordinary myocardium joining the lower rim of the coronary sinus outlet to the uppermost ventricular muscle. This anomalous atrioventricular connection pursued a sinuous, tortuous path. As a result of changing cross-sectional area, such an accessory pathway might exhibit slow conduction, thus explaining its decremental characteristics.

Preexcitation syndromes. Mechanisms and management

Ventricular preexcitation occurs when, in relation to atrial events, some or all of the ventricular muscle is activated earlier by the atrial impulse than would be expected if conduction of the impulse activated the ventricles by way of the normal atrioventricular conduction system. The purpose of this article is to review the pathophysiology of the variants of preexcitation and to discuss the therapeutic approach to patients who have tachyarrhythmias.

Shortening of ventriculoatrial conduction in patients with left-sided Kent bundles

In six patients with electrophysiologic evidence of ventriculoatrial conduction through a left Kent bundle, we documented that programmed right ventricular stimuli falling within an interval of 60 to 160 msec from the end of the T wave propagated to the left atrium (distal coronary sinus unipolar lead) 10 to 20 msec earlier than the basic paced beats. This phenomenon could be reproduced 24 hours later in two patients, and it was abolished by procainamide and amiodarone in one instance. During this interval we were unable to induce reciprocating tachycardia. Our observations outline a new pattern in ventriculoatrial conduction in patients with left-sided Kent bundles. The findings suggest in addition, that (1) supernormal conduction may be responsible for the observed shortening in retrograde conduction and (2) this phenomenon does not facilitate induction of reciprocating tachycardia.

Retrograde (ventriculoatrial) conduction

Interest in retrograde VA conduction has been renewed with the advent of tachycardias induced by physiologic pacemakers with atrial sensing capabilities. Accurate representation of ventriculoatrial conduction requires detailed electrophysiologic analysis during sinus rhythm, during tachycardias whether or not associated with accessory pathways, and during ventricular pacing studies. Retrograde conduction should be assessed in patients considered for implantation of atrial sensing and tracking pacemakers (VAT, VDD, DDD), until technologic advances overcome the problems of endless loop tachycardias.

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.

Sequence of retrograde atrial activation in patients with dual atrioventricular nodal pathways

To characterize the sequence of retrograde atrial activation in the presence of dual atrioventricular (AV) nodal pathways, we analyzed electrophysiologic data from seven patients in whom discontinuous AV nodal and ventriculoatrial conduction curves could be induced with programmed electrical stimulation. In all patients, electrograms of the high right atrium (HRA), lateral right atrium (LRA), low septal right atrium (SRA) and proximal coronary sinus (PCS) near the coronary sinus ostium were simultaneously recorded at a paper speed of 150-250 mm/sec. During programmed ventricular extrastimulation and incremental ventricular pacing, ventriculoatrial conduction via the fast AV nodal pathway resulted in SRA activation before PCS, HRA and LRA activation. However, the sequence of retrograde atrial activation abruptly changed with a shift from retrograde fast to retrograde slow AV nodal pathway conduction. Characteristically, during ventriculoatrial conduction via the slow AV nodal pathway, activation of the PCS preceded SRA activation by 5-20 msec and was accompanied by an alteration of the temporal relationship between HRA and LRA activation in all patients. These observations suggest that anatomically, the proximal common AV nodal pathway is a broad area that permits the slow AV nodal pathway to have a retrograde exit located posteriorly, inferiorly and to the left of that of the fast AV nodal pathway, and that the retrograde atrial activation sequence recorded during tachyarrhythmias should be determined with caution attempting to differentiate retrograde normal AV pathway from retrograde anomalous bypass tract conduction.

Response of normal and abnormal sinus node to right ventricular stimulation

Right ventricular pacing at progressively increasing rates was performed in 25 patients with complete ventriculoatrial block, before and after autonomic blockade with intravenous propranolol and atropine. At the end of each ventricular pacing stage a right intraatrial electrogram and electrocardiographic leads were simultaneously recorded. The relation between right ventricular pacing and atrial rates was studied from the recordings obtained at each pacing stage in both group I, 8 patients with sick sinus syndrome, and group II, 17 patients with normal sinus function. Right ventricular pacing was associated with an increment in atrial rate that ws significantly smaller (probability [p] less than 0.001) in patients in group I (mean +/- standard error of the mean 8 +/- 6 beats/min) than in group II (mean 25 +/- 10 beats/min). The maximal atrial rate reached during right ventricular pacing exceeded 80 beats/min in all patients in group II but remained less than 74 beats/min in patients in group I. Because autonomic blockade did not significantly influence the preceding results, it is concluded that a mechanical effect on the sinus node may explain this phenomenon.

Role of retrograde His Purkinje block in the initiation of supraventricular tachycardia by ventricular premature stimulation in the Wolff-Parkinson-White syndrome

The precise mechanisms for paroxysmal reentrant supraventricular tachycardia (PSVT) initiation during right ventricular premature stimulation (V(2) method) were analyzed in 14 consecutive patients with Wolff-Parkinson-White Syndrome in whom the PSVT was inducible during retrograde refractory period studies. 9 patients had left-sided and the remaining 5 of 14 had right-sided ventriculo-atrial (VA) accessory pathway (AP). At the basic cycle lengths (V(1)V(1)) ranging from 550 to 900 ms (mean, 657.1+/-139.5), closely coupled V(2) (mean V(1)V(2), 357.3+/-59.2 ms, range 320-500) produced retrograde His bundle (H(2)) activation via the bundle branches and retrograde atrial (A(2)) activation via the AP. As the V(1)V(2) were further shortened, the V(2) showed a retrograde block in the His Purkinje system (HPS) and conducted to the atria via AP in 9 of 14 cases. Subsequently, the A(2) impulse conducted anterograde over the atrioventricular node-HPS to initiate a PSVT or an atrial echo response in all nine cases. In none of the patients was a PSVT induced by V(2) when the latter produced retrograde H(2) activation via the bundle branches. In 10 of 14 cases, however, the retrograde H(2) was followed by a V(3), due to macroreentry in the HPS. The V(3) in turn blocked retrogradely in the HPS while producing A(3) via the AP to initiate a PSVT or an atrial echo response in 9 of 10 cases. Retrograde block of V(2) and/or V(3) in the HPS resulted in PSVT initiation in 13 of 14 cases, whereas in the remaining 1 case the exact mechanism was not clear. In none of the patients in this series was the PSVT initiated with a retrograde block of V(2) in the atrioventricular node with or without concomitant retrograde A(2) activation via the AP. We conclude that within the ranges of cycle lengths tested, a retrograde block of V(2) and/or V(3) in the HPS is the most common mechanism for initiation of PSVT during ventricular premature stimulation in patients with the Wolff-Parkinson-White Syndrome.

Electrophysiological effects of lorcainide, a new antiarrhythmic drug. Observations in patients with and without pre-excitation

The electrophysiological effects of the intravenous administration of a new antiarrhythmic drug, lorcainide, were evaluated by programmed electrical stimulation of the heart in 23 patients with atrioventricular conduction disturbances (four patients), ventricular tachycardia (five patients), and accessory atrioventricular pathway (14 patients). Lorcainide did not affect the refractory period of the atrium, ventricle, atrioventricular node, or the AH interval. It lengthened the duration of the HV interval, the refractory period of the accessory pathway, and the width of the QRS complex. The drug terminated ventricular tachycardia in four of five patients. It is concluded that the drug may be of potential benefit in patients with ventricular tachycardia or accessory atrioventricular pathways (especially those with a short refractory period). Lorcainide is contraindicated in patients with bundle-branch block and prolonged HV interval.

Paroxysmal atrial fibrillation in the Wolff-Parkinson-White syndrome

Eighty-eight patients with preexcitation were studied to determine how 30 patients with documented spontaneous paroxysmal atrial fibrillation differed from 58 patients without this arrhythmia. Inducible reentrant tachycardia was present in 23 (77 percent) of the 30 patients with, versus 28 (48 percent) of the 58 patients without, atrial fibrillation (p less than 0.025). Heart disease was present in 13 (43 percent) of the 30 patients with, versus 15 (26 percent) of the 58 patients without, atrial fibrillation (not significant). Inducible reentrant tachycardia or heart disease, or both, were significant). Inducible reentrant tachycardia or heart disease, or both, were present in 29 (97 percent) of the 30 patients with, versus 34 (59 percent) of the 58 patients without, atrial fibrillation (p less than 0.0005). Of 51 patients with inducible reentrant tachycardia, 23 patients with atrial fibrillation did not differ from 28 patients without this arrhythmia with respect to clinical features and atrial, sinus nodal, or anomalous pathway properties, or cycle length of induced reentrant tachycardia. Spontaneous degeneration of induced reentrant tachycardia to atrial fibrillation was observed in 6 (26 percent) of 23 patients with, versus none of 28 patients without, atrial fibrillation (p less than 0.025). In summary, patients with preexcitation and documented spontaneous paroxysmal atrial fibrillation almost always have inducible reentrant tachycardia or heart disease, or both. It is likely that in many patients with inducible reentrant tachycardia, spontaneously occurring reentrant tachycardia relates to induction of atrial fibrillation. However, it is unclear why some patients with inducible reentrant tachycardia have atrial fibrillation and others do not. In many patients with organic heart disease, atrial fibrillation could relate to hemodynamic changes.

Electrophysiologic effects of ouabain in patients with preexcitation and circus movement tachycardia

Effects of intravenous ouabain were evaluated in 19 patients with an anomalous conduction pathway (14 with manifest and 5 with concealed preexcitation (utilizing intracardiac stimulation and recording. Anterograde conduction through the anomalous pathway was present in all 14 patients with manifest preexcitation at a maximal atrial paced rate of 140 to 250 beats/min (mean +/- standard error of the mean 214 +/- 7.2) before and at 150 to 240 beats/min (mean 206 +/- 7.1) after ouabain (difference not significant [NS]). The anterograde effective refractory period of the anomalous pathway, measured at an equivalent atrial paced rate in 10 patients, was 250 to 450 ms (mean 309 +/- 19.7) before and 260 to 450 ms (mean 300 +/- 17.2) after ouabain (NS). Retrograde conduction through the anomalous pathway was possible at maximal ventricular paced rates (17 patients) of 160 to 250 beats/min (mean 222 +/- 6.6) before and 190 to 250 beats/min (mean 221 +/- 4.4) after ouabain (NS). Sustained atrioventricular (A-V) reentrant paroxysmal supraventricular tachycardia was inducible in all 19 patients before and in 17 patients (89 percent) after ouabain (tachycardia could not be induced in two patients because of increased A-V nodal refractoriness). The mean cycle length of tachycardia in the 17 patients was 320 +/- 6.7 ms before and 340 +/- 8.1 ms after ouabain (p < 0.01). In conclusion, ouabain has no significant effect on either anterograde or retrograde anomalous pathway refractoriness. Although ouabain slightly increases the cycle length of tachycardia, it does not interfere with induction of tachycardia in most patients with preexcitation. Oral cardiac glycosides alone would appear to be of limited value in patients with preexcitation and recurrent supraventricular tachycardia.

Accessory atrioventricular pathways that conduct only in the antegrade direction

Patients with accessory atrioventricular pathways that conduct only in the antegrade direction represent an unusual variant of the Wolff-Parkinson-White syndrome. This report describes such patients and compares them with patients with accessory pathways that demonstrate bidirectional conduction. Of 143 patients with single accessory pathways, seven demonstrated exclusive antegrade conduction (study group), 111 demonstrated bidirectional conduction (control group), and 25 demonstrated exclusive retrograde conduction. Study group patients were significantly older than patients in the control group (42 +/- 9.8 years and 31.4 +/- 13.9 years, respectively, p < 0.0001). Refractoriness and conduction characteristics of the accessory pathways in the antegrade direction in the study group were not different from those in the control group. Control group patients presented with atrioventricular reentrant tachycardia (58 of 111), atrial fibrillation (23 of 111), both of these arrhythmias (19 of 111), or no documented arrhythmia (11 of 111). Study group patients presented with only atrial fibrillation (six of seven). An accessory pathway with only antegrade conduction is a rare cause of symptoms in the Wolff-Parkinson-White syndrome. These patients are asymptomatic until atrial fibrillation develops as the patient ages. Despite the absence of retrograde conduction over the accessory pathway, its antegrade functional properties are similar to pathways that demonstrate bidirectional conduction.

Superficial accessory pathway in the Wolff-Parkinson-White syndrome--electrophysiological, surgical and histologic demonstration

A superficial accessory pathway was demonstrated by electrophysiologic techniques and surgical histopathology in 30-year-old male with Wolff-Parkinson-White syndrome, severe mitral valve disease and medically uncontrollable arrhythmias. In this patient, electrode catheter studies in the cardiac catheterization laboratory revealed antegrade and retrograde function of an accessory pathway between the anterior right atrium and the right ventricle. During surgery, electrophysiologic mapping confirmed the anterior location of this pathway. Blunt dissection in the fat pad of the A-V groove between the right atrium and ventricle revealed the accessory pathway which consisted of tissue strands superficial to the A-V ring. These were removed and on histological examination were composed of ordinary myocardial cells. Concomitant replacement of the patient's calcified stenotic and regurgitant mitral valve was carried out. Postoperatively, there was complete regression of the preexcitation and arrhythmias.

Effect of drugs in the Wolff-Parkinson-White syndrome. Importance of initial length of effective refractory period of the accessory pathway

The effect of procainamide, quinidine, ajmaline and amiodarone on the effective refractory period of the accessory pathway in the (A-V) anterograde and retrograde directions was studied in relation to the length of this period before drug administration. All patients had the Wolff-Parkinson-White syndrome and were studied with intracavitary recordings and programmed electrical stimulation of the heart using identical basic cycle lengths and test stimulus intervals before and after drug administration. The patients were separated into two groups, those in whom the effective refractory period of the accessory pathway was 270 ms or greater (Group 1) and those in whom it was less than 270 (Group 2). In the anterograde direction the magnitude of increase in the length of the effective refractory period of the accessory pathway after drug administration was related to its initial length. Only modest lengthening of this period could be accomplished in patients with an initially short period. In evaluating the effect of drugs in patients with the Wolff-Parkinson-White syndrome, the role of the initial length of the effective refractory period of the accessory pathway should be considered.

Reciprocating tachycardia using bilateral anomalous pathways: electrophysiologic and clinical implications

A patient who had disabling supraventricular tachycardia showed electrophysiologic evidence of coexistent right and left Kent bundles. The supraventricular tachycardia was accelerated by sequential antegrade and retrograde conduction over the right and left Kent bundles, respectively. Spontaneous blocking of the conduction through the right Kent bundle was associated with a slowing of the tachycardia and with the appearance of right bundle branch block (RBBB). Antegrade conduction was through the left bundle branch and was followed by an early retrograde atrial activation through the left Kent bundle, with consequent shortening of the ventriculoatrial (VA) interval. Thus, the coexistence of bilateral Kent bundles can be suspected whenever shortening of the VA interval in external electrocardiographic recordings occurs in the presence of a tachycardia with a RBBB pattern in a patient with right-sided preexcitation. Our data also showed that bilateral accessory pathways may have different electrophysiologic properties and that unequal response to antiarrhythmic drugs may be expected.

Unmasking of ventricular preexcitation by vagal stimulation or isoproterenol administration

Twenty-one patients were studied in whom ventricular preexcitation (VP) had been recorded in the past and had later disappeared, indicating antegrade block in the accessory pathway (AP), either spontaneously (10 patients) or under the effect of chronic treatment with amiodarone (11 patients). VP reappeared in nine cases during vagal stimulation, and in five cases during an i.v. isoproterenol infusion. Retrograde conduction over the AP was studied in four of the remaining seven patients and was found to be present in three and absent in one. Although these patients differ from the ordinary patient with concealed AP in that antegrade preexcitation had been demonstrated in the past, this study suggests that concealed VP may result from the following mechanisms: 1) an extremely prolonged refractory period in the AP, causing a rate-dependent VP that can be identified during vagal stimulation; 2) a rate-independent depression of antegrade conduction that can be reversed by isoproterenol; 3) a depression of conduction that is apparently no longer reversible. Only in the latter case is a study of retrograde conduction needed to identify the concealed VP. These three mechanisms are likely to be a natural sequence of events leading to complete antegrade block in the AP.

Atypical patterns of retrograde conduction over accessory atrioventricular pathways in the Wolff-Parkinson-White syndrome

Patterns of ventriculoatrial conduction have been used to distinguish retrograde conduction over an accessory atrioventricular pathway from that over the normal atrioventricular conduction system. Ventriculoatrial conduction at a constant interval during incremental ventricular pacing and during progressive prematurity of ventricular extrastimuli has been considered characteristic of conduction over an accessory pathway. We describe three patients with the Wolff-Parkinson-White syndrome who had progressive or sudden increments in ventriculoatrial conduction over an accessory pathway during fixed-rate ventricular pacing or during introduction of ventricular extrastimuli. Such properties have been considered characteristic of conduction over the normal atrioventricular conduction system. We conclude that retrograde conduction over accessory pathways may resemble conduction over the normal atrioventricular conduction system.

The response of regular re-entrant supraventricular tachycardia to right heart stimulation

The study was designed to assess the effect of various forms of right atrial or ventricular stimulation on the termination of re-entrant "supraventricular" tachycardias. Standard electrophysiological techniques were used in 81 patients to study 86 stable tachycardias. All tachycardias were initiated by single or double atrial or ventricular premature stimuli or incremental atrial pacing. Eight groups of tachycardia circuit were defined in terms of the anterograde and retrograde pathways. Termination of each tachycardia was studied by atrial underdrive, ventricular underdrive, rapid atrial stimulation and single or double atrial and ventricular premature extrastimuli. Intranodal re-entrant tachycardias formed 33% of the total and WPW tachycardias as a whole formed 55% of the total number of arrhythmias. The remainder were comprised of atrial tachycardia (5%), tachycardias in association with a partial AV nodal bypass (3%) and pre-excited tachycardias (5%). A single atrial extrastimulus was most effective where the circuit involved the right atrium. Atrial underdrive was consistently less successful than a single atrial extrastimulus in all groups. Rapid atrial pacing was effective in all groups, but caused transient atrial flutter or fibrillation in a proportion of each group except one. Ventricular underdrive stimulation was most effective in those groups where the right ventricle was involved in the circuit, but tended to be less effective than programmed single or double ventricular extrastimuli. Pacemakers designed to deliver appropriately timed single or double extrastimuli may offer an important alternative to other pacing modalities.

The electrophysiologic effects of intravenous propranolol in the Wolff-Parkinson-White syndrome

Fourteen patients with the Wolff-Parkinson-White (WPW) syndrome were studied by means of intracardiac stimulation techniques, before and after the intravenous administration of propranolol, 0.1 mg./Kg. There were no significant change, or only a slight increase, in the effective refractory periods of all parts of the re-entry tachycardia circuit studied, in either anterograde or retrograde directions. Re-entry tachycardia was initiated in nine patients in the control state, and in 10 patients after propranolol. The rate of re-entry atrioventricular node-accessory pathway tachycardia was decreased, but by only 10 per cent. The duration and outer limit of the tachycardia zone of atrial extrastimuli were not significantly decreased. Propranolol, by rapid intravenous infusion administration, is unlikely to be effective primary therapy for PSVT in the WPW syndrome.

Patterns of atrial activation during right ventricular pacing in patients with concealed left-sided Kent pathways

A 'concealed' accessory pathway was suspected in 12 patients because of eccentric left atrial activation during tachycardia. Retrograde conduction during ventricular pacing may occur over the atrioventricular node, the accessory pathway, or both. There were 4 patterns of ventriculoatrial conduction in response to ventricular extrastimuli (V2) at various coupling intervals: (1) exclusive accessory pathway conduction throughout the cardiac cycle in 2 patients; (2) exclusive accessory pathway conduction at long coupling intervals and exclusive atrioventricular node conduction at short coupling intervals in 2 patients; (3) variably fused accessory pathway/atrioventricular node conduction at long coupling intervals but exclusive accessory pathway conduction at short coupling intervals in 4 patients; (4) fused accessory pathway/atrioventricular node conduction at long coupling intervals but exclusive atrioventricular node conduction at short coupling intervals in 4 patients. With increased prematurity of V2 the ventricle to right atrial interval prolonged conspicuously in 11 of 12 patients whereas the ventricle to left atrial interval remained constant until the refractory period of the accessory pathway in all but 2 instances where intraventricular delay occurred. This study emphasises the importance of left atrial recordings in these patients.

Multiple reentrant tachycardias due to retrograde conduction of dual atrioventricular bundles with atrioventricular nodal-like properties

A patient is presented who had two paroxysmal supraventricular tachycardias, one slow and incessant and the other fast. Both paroxysmal tachycardias appeared to be atrioventricular (A-V) reentrant, with anterograde conduction by way of a normal A-V pathway. Two pathways conducting in retrograde manner were demonstrated, characterized by different conduction times (fast and slow), identical abnormal atrial activation sequence and A-V nodal-like properties (retrograde Wenckebach periodicity with rapid ventricular pacing, and depression with ouabain and propranolol). Thus, there appeared to be two anomalous A-V bundles with nodal-like properties conducting in retrograde fashion. Whether the paroxysmal tachycardia was fast or slow depended on which of these pathways was utilized. Spontaneous cure of incessant paroxysmal tachycardia was observed and coincided with unexplained total loss of ability for ventriculoatrial conduction.

The fast-slow form of atrioventricular nodal reentrant tachycardia in children

An unusual form of atrioventricular (A-V) nodal reentry is described as the underlying mechanism for incessant tachycardia in two children. During tachycardia a fast pathway was utilized for anterograde conduction and a slow pathway for retrograde conduction. This is the reverse of the usual form of A-V nodal reentrant tachycardia, in which the slow pathway is utilized for anterograde conduction and the fast pathway for retrograde conduction. One patient had a smooth ventriculoatrial (V-A) conduction curve demonstrating exclusive utilization of the slow pathway for retrograde conduction. The other had a discontinuous V-A conduction curve demonstrating failure of retrograde fast pathway conduction with resultant slow pathway conduction. In both cases the retrograde effective refractory period of the fast pathway was longer than that of the slow pathway, resulting in the establishment of this unusual reentry circuit. Both patients had a superior P axis with a P-R interval shorter than the R-P interval during tachycardia, features described in a significant number of children with incessant tachycardia. This unusual form of reentrant tachycardia can be suggested by its electrocardiographic pattern and is another mechanism for reentrant tachycardia not previously documented in children.

Symptomatic sinus node disease: natural history after permanent ventricular pacing

Fifty-nine patients between the ages of 13 and 88 with sinus node disease, who received a permanent ventricular pacemaker between 1965 and 1976 at one institution, were followed to determine the natural history of the disorder after permanent pacing. Nineteen had ischemic heart disease, six had primary myocardial disease, and eight valvular heart disease. In 26, no etiology for the arrhythmia was apparent. The one- and five-year survival was 85.5% and 73.1%, respectively. Patients with underlying heart disease had a significantly poorer survival when compared to those without (58% versus 94% at 36 months) and all but 3 of 13 deaths in the first 36 months were in those with ischemic heart disease. There was a distinct trend toward poor survival in those with heart failure prior to pacemaker implant and those over age 65. Patients with sinus bradycardia alone did best (91% survival three years after implant), while those with bradycardia-tachycardia syndrome and those with sinoatrial arrest alone did distinctly worse (76% and 65% survival at three years, respectively). Twelve of 18 deaths were due to progression of underlying heart disease. The long-term prognosis with symptomatic sinus node disease can be predicted in part by (1) etiology of the underlying heart disease, (2) pre-implant arrhythmia, and (3) ventricular function prior to implant.

Ebstein's anomaly in association with anomalous nodoventricular conduction. Pre-operative and intra-operative electrophysiological studies

A 13 year old girl with Ebstein's anomaly was investigated for refractory paroxysmal tachycardias and ventricular pre-excitation. Intracardiac electrophysiological studies demonstrated that ventricular pre-excitation was due to conduction in an anomalous nodo-ventricular pathway. Tachycardia occurred as a result of re-entry within the A-V node with pre-excitation during tachycardia due to conduction in the nodo-ventricular pathway. These tachycardias were controlled initially by medical therapy but because of increasing frequency of attacks, occasionally requiring D.C. conversion, further electrophysiological studies and epicardial mapping were undertaken. The epicardial surface of the right ventricle and right atrium were mapped during tachycardia. The results of the studies confirmed that a direct anomalous atrio-ventricular pathway was not present and that re-entrant tachycardia did not involve an accessory pathway of this type. A rapid atrial pacing system was implanted and paroxysmal tachycardias have been successfully controlled.

Multiple mechanisms of tachycardias in a patient with the Wolff-Parkinson-White syndrome

In a patient with the Wolff-Parkinson-White Syndrome we observed atrial fibrillation and three distinct paroxysmal re-entrant tachycardias. Intracardiac electrograms obtained during the tachycardias showed the mechanisms to be A-V nodal, accessory pathway and sinus node re-entry. When P wave morphology, R-P relationship and QRS configuration are considered, it is illustrated how these four tachyarrhythmias may be successfully diagnosed on the surface electrocardiogram. The therapeutic implications of multiple arrhythmias with different mechanisms in the Wolff-Parkinson-White Syndrome are discussed.