His bundle electrograms in two cases of Wolff-Parkinson-White (pre-excitation) syndrome

Localization of accessory pathways in the Wolff-Parkinson-White syndrome

Operative and ablative therapy in the Wolff-Parkinson-White syndrome requires accurate localization of accessory atrioventricular pathways. A reasonable first approximation to pathway location can be obtained by noninvasive techniques, the 12-lead electrocardiogram being the most readily available of these. Accurate characterization of the number and anatomic localization of accessory pathways still requires invasive electrophysiological assessment. The most useful technique for accessory pathway localization remains endocardial atrial mapping of the tricuspid and mitral (via the coronary sinus) ring during atrioventricular reciprocating tachycardia and ventricular pacing. Other techniques provide important confirmatory evidence and may be the only guides to accessory pathway location in selected individuals.

Interstitial potentials and their change with depth into cardiac tissue

The electrical source strength for an isolated, active, excitable fiber can be taken to be its transmembrane current as an excellent approximation. The transmembrane current can be determined from intracellular potentials only. But for multicellular preparations, particularly cardiac ventricular muscle, the electrical source strength may be changed significantly by the presence of the interstitial potential field. This report examines the size of the interstitial potential field as a function of depth into a semi-infinite tissue structure of cardiac muscle regarded as syncytial. A uniform propagating plane wave of excitation is assumed and the interstitial potential field is found based on consideration of the medium as a continuum (bidomain model). As a whole, the results are inconsistent with any of the limiting cases normally used to represent the volume conductor, and suggest that in only the thinnest of tissue (less than 200 micron) can the interstitial potentials be ignored.

Electrocardiography of arrhythmias: from deductive analysis to laboratory confirmation--twenty-five years of progress

Before the advent of the microelectrode, His bundle recording and direct cardiac pacing, electrocardiographic interpretation of arrhythmias in human beings was based on presumed mechanisms derived by deductive analysis. This indirect approach was forced by the fact that the surface electrocardiogram does not directly record the behavior of the specialized tissue that is the site of origin of most arrhythmias. In the past 25 years it has become possible to record directly from the specialized tissue. The result has been experimental confirmation of several underlying concepts of the electrocardiographic interpretation of arrhythmias and progress evidenced by the conversion of concept to fact.

Clinical electrophysiology--a decade of progress

During the past 14 years there have been major advances in the field of clinical electrophysiology. This progress is a result of a more extensive use of intracardiac electrode catheters with recordings from multiple sites in the right and left cardiac chambers, the introduction of programmed electrical stimulation techniques and the use of antiarrhythmic drugs for diagnostic and therapeutic purposes during acute electrophysiologic testing. This article examines the pioneering studies and the subsequent developments in the field of clinical electrophysiology. The specific topics that are reviewed include the sinus node and atrium, atrioventricular conduction, supraventricular tachycardia and ventricular tachycardia. The therapeutic implications of each topic are also discussed. Clinical electrophysiology in its initial stages was a descriptive technique, but has since become an important diagnostic and therapeutic tool. However, electrophysiologic testing is an intensive process, requiring specialized training and a substantial commitment of human and physical resources.

His bundle electrogram recording using a multipolar electrode catheter via the arm veins

In eighteen patients with atrioventricular conduction disturbance, His bundle electrograms were studied via the arm vein. A 6F Berkovits-Castellanos USCI hexapolar electrode catheter was introduced into the right atrium and looped across the tricuspid valve in a "golf club" shape. The main aim was to leave the two distal electrodes in contact with the atrial endocardium to perform atrial pacing, while displaying the other four electrodes along the superior angle of the tricuspid valve for proximal and distal His bundle recordings. His bundle electrograms were successfully obtained in all cases. The arm approach provides an alternate route whenever the femoral approach is not feasible. Moreover, the use of an hexapolar electrode catheter provides some practical advantages: 1) it enables atrial pacing to be performed, as well as proximal and distal His bundle recording to be obtained, by using the same multipolar electrode catheter; and 2) it allows long-term monitoring of His bundle potentials, in view of the stability of His bundle recordings. Finally, the arm approach could be the method of choice for the study of His bundle electrograms during leg supine exercise in selected patients.

Reciprocal tachycardias using accessory pathways with long conduction times

Three patients with reentrant tachycardia are described who had an accessory pathway with a very long conduction time that was incorporated in the tachycardia circuit. The accessory pathway was able to conduct in one direction only, in retrograde manner in two patients and in anteriograde manner in the remaining patient. Evidence is presented that reveals that in the first two patients the accessory pathway was septally located, had completely bypassed the normal atrioventricular (A-V) conduction system, had properties of decremental conduction, and had an atrial exit close to the coronary sinus and a ventricular exit relatively far from the atrioventricular A-V ring. In the third patient, who manifested wide QRS complex during tachycardia, the ventricular end of the accessory pathway seemed to be located close to the right ventricular apex. The atrial end of the pathway could not be localized exactly.

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.

Existence of automaticity in anomalous bundle of Wolff-Parkinson-White syndrome

Escape beats probably arising from the anomalous bundle were documented in 2 patients with the Wolff-Parkinson-White (WPW) syndrome. A third patient, in whom complete AV block developed both in the anomalous bundle and the normal pathway, showed the occurrence of escape beats (an escape-bigeminy pattern), as well as a regular idioventricular rhythm arising from the anomalous bundle. Phase 4 block in the anomalous bundle occurred in 7 other patients, in 4 of them spontaneously and in 3 only after the administration of ajmaline or amiodarone. Only 4 of 14 fully investigated patients (out of a total number of 23) showed absence of both escape beats and phase 4 block. The escape beats were considered as direct evidence, and the phase 4 block as indirect evidence, for the existence of automaticity in the anomalous bundle. Such evidence supports the view that the anomalous bundle, like the His bundle-branch system, may be composed of specialised tissue endowed with the property of automaticity.

Pre-excitation of the ventricle associated with total intra His bundle block

A case with total intra-His bundle block and intermittent pre-excitation syndrome is presented. During A-V conduction there was a P-delta interval of 130 msec. with a P-A interval of 20 msec., an A-H interval of 60 msec. and an H-V interval of 50 msec. During rapid atrial pacing the P-delta interval increased primarily due to an A-H1 prolongation and a Mobitz type 2 block and total A-V block occured at increasing rates showing H1 following every A spike. The escape beats showed a normal width of the QRS complexes with preceding H2 spikes. After administration of Ajmaline the bypass tract was blocked and constant total A-V block occurred. It was concluded that there was a constant total intra-His bundle block and a nodoventricular or fasciculoventricular bypass tract with prolonged conduction to the ventricle. This bypass tract blocked sometimes spontaneously and could also be blocked by rapid atrial pacing and administration of drugs. The close anatomic proximity of the His bundle and Mahaim fibers is responsible for the simultaneous block resulting in total atrioventricular block.

Recurrent paroxysmal supraventricular tachycardia: a complication of ventricular pacing in a patient with occult Wolff-Parkinson-White syndrome

A 60 year old man suffering from syncope believed to be due to the sick sinus syndrome was treated with a permanent demand ventricular pacemaker. This led to almost continous bouts of paroxysmal supraventricular tachycardia (SVT) over the ensuing two years, mistakenly believed to be part of the sick sinus syndrome. Careful study showed that this man had a type A Wolff-Parkinson-White accessory atrioventricular connection which consistently conducted retrogradely, but only rarely antegradely, during applications of carotid sinus massage. Episodes of SVT were repeatedly induced whenever ventricular-paced impulses captured the atria retrogradely. All episodes of SVT stopped when the ventricular pacemaker was removed. Following insertion of an atrial pacemaker, the patient had no episodes of SVT or syncope over a nineteen month follow-up period. This case illustrates the care required in selecting a proper site for protective pacing in patients who suffer from paroxysmal SVT.

Wolff-Parkinson-White Syndrome--current views

The Wolff-Parkinson-White (WPW) syndrome is an important clinical entity because of frequent recurrences of very rapid tachyarrhythmias. The electrocardiographic finding of the WPW syndrome often mimicks pseudo diaphragmatic (inferior) myocardial infarction which should not be misinterpreted. The most important diagnostic criterion is recognition of a delta wave; the short P-R interval or broad QRS complex may not be present in every case. The mechanism for the tachycardia is considered to be a reentry phenomenon via anomalous and normal atrioventricllar (A-V) pathways. The drug of choice for the treatment of regular supraventricular (reciprocating) tachycardia with narrow QRS complexes, which is the most common arrhythmia in the WPW syndrome, is propranolol. Digitalis is almost equally effective in this case. For tachyarrhythmias, particularly atrial fibrillation or flutter with anomalous conduction, intravenously-administered lidocaine is considered to be the drug of choice. Procainamide or quinidine is also frequently used under this circumstance with excellent therapeutic result. Many patients with the WPW syndrome require long-term maintenance drug therapy (propranolol, digitalis or quinidine in most cases). In urgent clinical situations, direct current (DC) shock should be applied immediately. In selected patients with refractory tachyarrhythmias, the use of an artificial pacemaker or surgical approach may be considered.

His bundle recordings in a case of complete atrioventricular block combined with pre-excitation syndrome

In a patient with complete A-V block suffering from attacks of dizziness an intermittent A-V conduction with a short P-R interval and a delta wave of the conducted ventricular complex were observed. After accelerating the sinus rate by atropine and by exercise, one-to-one conduction was established with QRS complexes of WPW type A configuration. His bundle recordings revealed a complete block within the normal conduction system at the level of the A-V node. A slow junctional rhythm with a normal H-V interval was activating the ventricle. During atrial pacing a one-to-one conduction through an accessory pathway could be documented at cycle lengths between 800 and 380 msec. sandwiched in between zones of complete block at smaller or longer cycle lengths. During ventricular stimulation no retrograde V-A conduction could be observed. The findings support the thesis of at least two functionally different A-V pathways in patients with pre-excitation syndrome.

Body-surface maps of heart potentials: tentative localization of pre-excited areas in forty-two Wolff-Parkinson-White patients

Heart potentials were recorded from the entire chest surface in 42 patients suffering from Wolff-Parkinson-White syndrome. We were able to identify six types of surface maps, according to the location of the potential maximum and minimum during the delta wave. For each of these types we suggested the most likely location of the pre-excited region around the A-V rings (types 1 to 5) or in the interventricular septum (type 6). In 13 patients belonging to Types 1, 2, 3, 5 and 6 our hypotheses were in agreement with intracardiac recordings, epicardial maps or surgical results obtained by others. Isopotential surface maps provide more information on the location of the pre-excited area than conventional ECGs, particularly when these exhibit intermediate features between Types A and B.

Wolff-Parkinson-White syndrome with 1:2 atrioventricular conduction

The QRS complex of the Wolff-Parkinson-White syndrome is thought to represent a fusion beat resulting from conduction over the normal pathway and an anomalous pathway. This report demonstrates utilization of both of these pathways resulting in two ventricular responses from a single supraventricular impulse. The presence of "1:2" atrioventricular conduction in this case firmly supports the fusion beat theory of the Wolff-Parkinson-White syndrome.

Echocardiography in Wolff-Parkinson-White syndrome

Twenty-six patients with Wolff-Parkinson-White (WPW) syndrome were studied by echocardiography. They were classified into the following WPW types: anterior right ventricular pre-excitation (Type I) - six patients; posterior right ventricular pre-excitation (Type II) - six patients; posterior left ventricular pre-excitation (Type III) - fourteen patients. Twenty-three patients were in WPW at the time of study. Four patients with Type I WPW had abnormal systolic motion of the interventricular septum: three paradoxical and one flat. Patients with Type II and Type III WPW had no septal motion abnormalities related to pre-excitation. Three patients had intermittent WPW, Type III; in all three only minor changes in normal septal motion were apparent on WPW beats. Associated cardiac abnormalities were evident in six patients: two mitral prolapse (one Type II WPS and one Tpe III); one idiopathic hypertrophic subaortic stenosis (Type III); one congestive cardiomyopathy (Type III); one hypertrophic nonobstructive cardiomyopathy (Type I); and one atrial septal defect (Type II). We conclude that abnormal interventricular septal motion may occur with Type I WPW abnormality. Other abnormalities are detectable by echocardiography in a high proportion of WPW patients, but do not appear to be associated with any single Wolff-Parkinson-White type.

Tachycardias and electrical pacing

Techniques of electrical pacing for the treatment of tachycardias are multiple. The choice of a suitable method for a particular tachycardia depends upon understanding the mechanism of the tachycardia and the pacing characteristics that will lead to interruption or suppression of the tachycardia, or to ventricular slowing. Electrical pacing is indicated for tachycardias when drug therapy alone has failed or cannot be initiated or continued, and only for those tachycardias that are likely to respond to this type of electrical stimulation. In either the circus movement type or the ectopic pacemaker type an ectopic tachycardia is more likely to be suppressed if the pacing site is near the site of origin of the tachycardia. Pacing more rapidly than the basic rate in order to prevent or abolish tachycardias is termed overdrive suppression. The mechanisms responsible for this phenomenon may be associated with release of acetylcholine, release of potassium, activation of an electrogenic sodium pump, increase in cardiac output and coronary flow, decrease in size of the heart with a consequent decrease in wall tension, and decrease in the inhomogeneity of recovery of excitability that occurs at more rapid rates in the non-ischemic heart. All of these effects of pacing suppress accelerated pacemaker activity or prevent emergence of conditions favorable for development of circus movement tachycardias. Paired, coupled, or rapid atrial pacing may improve ventricular performance or slow ventricular rate, or both, without abolishing the ectopic pacemaker activity. Atrial pacing with pacing sites located at endocardial, epicardial, coronary sinus, trans-septal, or esophageal locations may interrupt or prevent rapid supraventricular or ventricular arrhythmias. Similarly, ventricular pacing at endocardial, epicardial, myocardial, or transthoracic sites may be equally effective. Artificial pacing has abolished almost every type of tachycardia. Ventricular fibrillation always, and atrial fibrillation usually, require countershock if electrical treatment is to be employed, although defibrillation of the atria by rapid pacing has been reported once. Unipolar or bipolar pacemakers may be used temporarily, or permanently after implantation. Pacing rates used to abolish supraventricular tachycardias range from single premature beats to alternating current atrial pacing at 3600 cycles per minute. Artificial electrical stimulation of the heart may be on demand, or may be competitive (fixed rate). External magnets, induction coil coupling, and radio frequency signals allow competitive pacing to be used intermittently, with permanently implanted pacemakers. Thus, electrical pacing of the heart is a technique of major importance for the control of rapid heart rates.

Electrophysiologic demonstration of bilateral anomalous pathways in a patient with Wolff-Parkinson-White syndrome (type B preexcitation)

Pre- and postoperative electrophysiologic studies are described that were suggestive of two (right- and left-sided) anomalous atrioventricular (A-V) connections in a patient with type B Wolff-Parkinson-White syndrome and intractable arrhythmias, who underwent epicardial mapping and successful surgical ablation of the right-sided anomalous pathway. The presence of the right-sided anomalous pathway capable of both antegrade and retrograde conduction was suggested by the following observations: (1) Type B preexcitation on the surface electro-cardiogram; (2) maximal preexcitation and minimal stimulus-delta with low lateral right atrial pacing; (3) epicardial mapping of the atria and ventricles; and (4) disappearance of ventricular preexcitation after surgical ablation of the right-sided anomalous pathway. The presence of an additional left-sided anomalous pathway capable of only retrograde conduction (concealed on the surface electrocardiogram) was sugg-sted by the following observations: (1) Left to right retrograde atrial activation sequence during reentrant tachycardia and ventricular pacing at rapid rates and with coupled ventricular pacing postoperatively; (2) spontaneous conversion of wide ORS tachycardia utilizing the anomalous pathway for antegrade conduction to narrow QRS tachycardia with significant slowing in rate; and (3) smooth antegrade A-V nodal conduction curves with echo zone postoperatively. The demonstration of bilateral anomalous pathway in patients with preexcitation has important electrophysiologic and surgical implications.

The Wolff-Parkinson-White syndrome: the value of the HIS bundle electrogram,

The HIS bundle electrogram has led to the aquisition of additional information on the physiology of the WPW syndrome and has become a useful technique for its diagnosis. The findings on the HBE and their interpretation in WPW are reviewed.

The Wolff-Parkinson-White syndrome: pharmacologic effects of procaine amide

The effect of procaine amide, 10 mg. per kilogram via intravenous infusion, was studied in 13 patients with the WPW syndrome. The delta wave was eliminated by procaine amide in 10 and modified in three patients. This effect lasted between 30 minutes and 8 1/2 hours and was unrelated to the total dose administered. Anterograde A-V conduction was assessed by atrial pacing with increasing rates. More rapid atrial pacing rates with 1:1 A-V conduction were observed in patients who maintained rather than lost their delta wave during pacing. Ventriculoatrial conduction was assessed with ventricular pacing at increasing rates; ventricular conduction time was fixed regardless on the pacing rate. Procaine amide significantly prolonged V-A conduction time in six and blocked V-A conduction in one patient. In addition, A-V and V-A refractory periods were measured by the extrastimulus technique. Two types of responses were observed: (1) Type I or (2) line of identity. A-V nodal refractoriness was observed to be within the normal range. Procaine amide converted anterograde line of identity responses to Type I responses in all patients who had their delta waves eliminated. In this patient group, bypass refractoriness was shorter than A-V nodal refractoriness. Procaine amide was not observed to alter significantly normal A-V conduction as assessed by atrial pacing or A-V refractory period measurements. Furthermore, a significant disparity between the effects of procaine amide on anterograde and retrograde bypass refractoriness was observed. Tachycardias could be induced in nine of the 13 patients with a mean rate of 167.2 +/- 7.9 beats per minute; delta waves were abent during all episodes of tachycardia. Procaine amide prevented tachycardia induction in six of the none patients. Procaine amide therefore demonstrates electrophysiologic effects which would be beneficial for prevention or treatment of reciprocating tachycardias in the WPW syndrome. Moreover, procaine amide would be an ideal agent for the prevention of rapid ventricular rates in patients with the WPW syndrome and atrial fibrillation.

Electrophysiological evaluation of the Wolff-Parkinson-White syndrome: problems in assessing antegrade and retrograde conduction over the accessory pathway

The effect of atrial pacing and recording site and ventricular pacing site on assessment of conduction over the accessory pathway (AP) was examined in a group of patients with the Wolff-Parkinson-White syndrome. The importance of initial localization of the AP by recording the sequence of retrograde atrial activation during circus movement tachycardia is demonstrated. Inability to record or pace near the AP may lead to significant errors in the assessment of the antegrade and retograde conduction properties of the AP. During ventricular pacing, retrograde atrial fusion was consistently demonstrated with laterally located APs.

Coexistence of functional Kent and Mahaim-type tracts in the pre-excitation syndrome. Demonstration by catheter techniques and epicardial mapping

An unusual patient with Ebstein's anomaly of the tricuspid valve and the Wolff-Parkinson-White syndrome is presented. Ventricular pre-excitation related to conduction over both a right posterior Kent bundle and Mahaim fibers coursing from the atrioventricular node to the right ventricle. Two types of supraventricular tachycardia were demonstrable. These were due to re-entry involving antegrade conduction over either the normal or Mahaim paths, and retrograde retrograde conduction via the Kent bundle. Surgical division of the Kent bundle has abolished the clinically debilitating arrhythmias.

Wolff-Parkinson-White syndrome. The problem, evaluation, and surgical correction

Physiological studies of the type we have described, when performed in patients with the WPW syndrome, can yield diagnostic information regarding the mechanism of arrhythmia, demonstrate functional properties of therapeutic import, facilitate therapeutic decision-making about drug regimens and presumptively localize the site of pre-excitation as a basis for possible surgical intervention. Based on our experience, we feel that in selected patients, surgical correction of the WPW syndrome is entirely feasible, and can be accomplished in the majority of patients in whom free wall A-V connections are present. The continuing challenge of identification and correction of septal accessory pathways directs our present work with the WPW syndrome.

Wolff-Parkinson-White syndrome type B with His depolarization occurring after the QRS. Further evidence that WPW-QRS is a fusion beat

His bundle electrograms were recorded in a patient with Wolff-Parkinson-White syndrome (type B) during atrial pacing studies and during the induction of premature atrial depolarization at varying coupling intervals. Early ventricular depolarization (preexcitation) occurred simultaneously with the His depolarization, suggesting that conduction occurred via both the Kent and the normal A-V nodal-His-Purkinje pathway during sinus rhythm. Atrial pacing at increasing rates showed progressive advance of the His spike into the QRS and increasing duration of the delta wave until the appearance of broad bizarre QRS complexes with prolonged P-J intervals, suggesting major, if not total, depolarization of the ventricle by the Kent pathway. PAD's induced at coupling intervals of 360, 330, and 300 msec caused progressive delay of the His bundle depolarization, with the His spike occurring after the QRS at S(1)-H intervals of 230, 265, and 325 msec, respectively, and Q-H intervals of 123, 160 and 220 msec, respectively. These findings suggest that during sinus rhythm the QRS was a fusion beat. With early premature atrial stimulation, conduction occurred solely via the Kent pathway, with conduction via the normal A-V nodal pathway encountering increasing delay. The finding of His depolarization occurring after the QRS suggests retrograde myocardial-His block, and may explain the absence of paroxysmal supraventricular tachycardias in this patient.

Contribution of cardiac pacing to our understanding of the Wolff-Parkinson-White syndrome

This review discusses the information which can be obtained by cardiac pacing in patients with the Wolff-Parkinson-White syndrome. Programmed electrical stimulation when combined with the recording of intracardiac electrograms and surface electrocardiograph leads, can be extremely useful in the following areas. 1) Determining the type of the accessory atrioventricular connexions; 2) determining the electrophysiological properties of the accessory atrioventricular pathway; 3) localizing the position of the accessory atrioventricular pathway; 4) determining the mechanisms of any tachycardia; 5) assessing effect of drugs; 6) identifying patients likely to be at high risk; and 7)evaluating postoperative conduction.

Classification of ventricular pre-excitation. Vectorcardiographic study

In a study of 45 cases of ventricular pre-excitation, 19 were classified as type A and 20 as type B according to Rosenbaum's criteria, which depend on the polarity of the major deflections in the right praecordial leads and not, as is commonly thought, on the direction of the delta vector. Six cases that could not be classified as type A or type B were termed intermediate. Vectorcardiograms were recorded from 29, and these showed a wide but continuous range of values for both the delta and the main QRS vectors in all three planes. Any classification based on these features must, therefore, depend on arbitrary quantitative data. Three patients in this series had associated right bundle-branch block. A review of the published reports on the association of pre-excitation and bundle-branch block failed to provide a rational basis for the classification of pre-excitation. It is emphasized that Rosenbaum's classification is empirical and its validity is questioned.

Surgical correction of anomalous left ventricular pre-excitation: Wolff-Parkinson-White (type A)

This report describes two patients with the Wolff-Parkinson-White syndrome including episodes of supraventricular tachycardia and atrial fibrillation. Both patients had Type A electrocardiograms. Electrophysiological studies demonstrated pre-excitation and evidence that the site of pre-excitation involved the left ventricle. The effective refractory periods of the accessory pathway during atrioventricular conduction were 240 and 220 msec respectively. Epicardial mapping at the time of surgery showed that anomalous excitation began adjacent to the annulus of the mitral valve near a marginal branch of the left circumflex coronary artery. An incision which separated the atrial muscle from the annulus of the mitral valve at the region of anomalous excitation abolished the delta wave. Epicardial maps after surgery showed normal ventricular activation and follow-up studies have shown normal electrocardiograms and no arrhythmias.

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

In 36 patients with the Wolff-Parkinson-White syndrome, ventriculo-atrial (VA) conduction was studied using the single test stimulus method. In 22 patients no significant change in VA conduction time occurred following test stimuli with increasing prematurity suggesting exclusive VA conduction by way of the accessory pathway, an accessory pathway with a shorter refractory period than the His-AV node pathway, or identical refractory periods in both pathways. In 14 patients showing this VA conduction pattern tachycardias could be initiated by a single early ventricular premature beat. This finding lends credence to the hypothesis that the accessory pathway is an essential link in the tachycardia circuit. In two of the five patients showing exclusive VA conduction over the His-AV node pathway single re-entrant beats with antegrade conduction over the accessory pathway could be elicited by appropriately timed ventricular premature beats. In one patient showing this pattern a sustained tachycardia with AV conduction over the accessory pathway could be initiated. A total of eight patients did not show VA conduction over the accessory pathway.

A new catheter technique for His bundle recordings via the arm veins

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Effect of digitalis on atrioventricular conduction and circus-movement tachycardias in patients with Wolff-Parkinson-White syndrome

During regular driving of the right atrium using the single-test stimulus method, atrioventricular conduction and initiation of tachycardias were studied in six patients with the Wolff-Parkinson-White syndrome (W-P-W), before and 45 min after the administration of ouabain (0.75-1.5 mg into the right atrium).

Following ouabain (1) all patients showed shortening of the refractory period of their anomalous pathway; (2) at least five of them showed lengthening of the refractory period of the A-V nodal-His pathway; and (3) all patients showed prolongation of the A-V nodal transmission time (prolongation of the A-H interval). In four patients who suffered from circus-movement tachycardias these changes resulted in two patients in marked shortening of the range of premature beat intervals during which a tachycardia could be initiated and complete inability to initiate a tachycardia in the other two. These results suggest that digitalis can be of prophylactive value in patients with the Wolff-Parkinson-White syndrome and circus-movement tachycardias.

Wolff-Parkinson-White Syndrome. A review

Recent developments in the field of electrophysiology and surgical therapy in selected cases of Wolff-Parkinson-White syndrome (W-P-W) support the concept of anomalous A-V pathways. Impulse transmission usually occurs simultaneously through both the normal and anomalous pathways resulting in a fusion QRS complex. Atrial tachycardia is usually due to reentry through the normal and anomalous A-V pathways. However, reentry may occur independently in the A-V node alone exclusive of the anomalous pathway. Anomalous connections, despite varying anatomic locations, may result in similar electrocardiographic manifestations characteristic of W-P-W. His bundle recordings together with electrophysiologic studies may be clinically useful (1) to differentiate various types of anomalous connections, (2) for possible determination of the reentry circuit, (3) to predict the maximum ventricular rate possible during supraventricular tachycardia by evaluating the refractory period of the A-V pathways, or (4) to compare the efficacy of different drugs in a given patient. Surgical interruption of the anomalous pathway in selected cases with W-P-W (type B) is feasible but is most commonly not necessary. The indications for medical and surgical management of symptomatic cases with W-P-W are reviewed.

The His bundle electrogram

The His bundle electrogram is discussed with respect to its rationale, methods for its recording and evaluation, findings with its use in the various forms of heart block and arrhythmias, its clinical value, and its limitations.