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

Effect of amiodarone in the Wolff-Parkinson-White syndrome. A clinical and electrophysiological study

Six patients with Wolff-Parkinson-White (WPW) syndrome were given long-term treatment with amiodarone. Symptomatic relief was obtained in all. Tolerance to the drug was good. Reversible corneal changes appeared after some weeks' treatment in five patients. No thyroid side-effects were noticed. Prior to treatment, dual atrioventricular (AV) conduction was demonstrated on His bundle electrograms in all six patients. Recordings were made at varied heart rates, using atrial and ventricular pacing. Reciprocating tachycardia was readily provoked by properly timed extra stimuli in all patients. When amiodarone treatment had become clinically effective, a second comparative study was made in four patients after 26--85 days' treatment. Amiodarone reduced heart rate and second degree AV block appeared at a lower atrial pacing rate. It increased the refractory periods of right atrium, AV node, and the accessory pathway in proportion to the duration of treatment. Induction of tachycardia was effectively prevented by the drug. It appears that amiodarone in chronic treatment has a predictable and unique depressant action on cardiac conduction, supporting the opinion that this compound, despite side-effects, has an important role to play in the treatment of refractory arrhythmias in patients with the WPW syndrome.

Electrophysiologic Characteristics and Radiofrequency Catheter Ablation in Children with Wolff-Parkinson-White Syndrome

BACKGROUND

The majority of cardiac arrhythmias in children are supraventricular tachycardia, which is mainly related to an accessory pathway (AP)-mediated reentry mechanism. The investigation for Wolff-Parkinson-White (WPW) syndrome in adults is numerous, but there is only limited information for children. This study was designed to evaluate the specific electrophysiologic characteristics and the outcome of radiofrequency (RF) catheter ablation in children with WPW syndrome.

METHODS

From December 1989 to August 2005, a total of 142 children and 1,219 adults with atrioventricular reentrant tachycardia (AVRT) who underwent ablation at our institution were included. We compared the clinical and electrophysiologic characteristics between children and adults with WPW syndrome.

RESULTS

The incidence of intermittent WPW syndrome was higher in children (7% vs 3%, P=0.025). There was a higher occurrence of rapid atrial pacing needed to induce tachycardia in children (67% vs 53%, P=0.02). However, atrial fibrillation (AF) occurred more commonly in adult patients (28% vs 16%, P=0.003). The pediatric patients had a higher incidence of multiple pathways (5% vs 1%, P<0.001). Both the onset and duration of symptoms were significantly shorter in the pediatric patients. The antegrade 1:1 AP conduction pacing cycle length (CL) and antegrade AP effective refractory period (ERP) in children were much shorter than those in adults with manifest WPW syndrome. Furthermore, the retrograde 1:1 AP conduction pacing CL and retrograde AP ERP in children were also shorter than those in adults. The antegrade 1:1 atrioventricular (AV) node conduction pacing CL, AV nodal ERP, and the CL of the tachycardia were all shorter in the pediatric patients.

CONCLUSION

This study demonstrated the difference in the electrophysiologic characteristics of APs and the AV node between pediatric and adult patients. RF catheter ablation was a safe and effective method to manage children with WPW syndrome.

Non-Invasive Diagnosis of Concealed Wolff-Parkinson-White Syndrome by Detection of Concealed Anterograde Pre-Excitation

Electrophysiological findings suggest that concealed anterograde conduction through accessory pathways may exist even during sinus rhythm in patients with so-called concealed Wolff-Parkinson-White (WPW) syndrome. To evaluate the pre-excitation characteristics in various types of WPW syndrome, high-resolution electrocardiograms were analyzed in 81 consecutive WPW syndrome patients and 50 age-matched normal subjects. The WPW group consisted of 30 cases of concealed WPW diagnosed by electrophysiological study, 38 cases of manifest WPW in which apparent delta waves were constant, and 13 cases of intermittent WPW in which the delta waves appeared periodically. The duration of the low-amplitude, high-frequency components of the signal-averaged filtered QRS complex that preceded the earliest upstroke of the surface QRS, including any delta waves (preceding potential duration, PPD), and the duration of low amplitude signals less than 10 microV (I-LAS10) or 20 microV (I-LAS20) were measured as parameters of pre-excitation. The PPDs in concealed and intermittent WPW were both significantly longer than in manifest WPW or in control subjects (6.8+/-2.7 ms, 7.9+/-3.5 ms vs 2.3+/-3.2 ms, 1.0+/-1.6 ms, both p<0.0001). Abnormally prolonged PPDs (>4 ms) were observed in 90% of concealed WPW cases and 76.9% of intermittent WPW, but in only 4% of normal subjects and 31.6% of manifest WPW. Both I-LAS10 and I-LAS20 in the 3 types of WPW syndrome were significantly longer than in normal subjects. The initial portion of the filtered QRS in concealed WPW closely resembled that of intermittent WPW. These results strongly suggest that in concealed WPW anterograde conduction through accessory pathways does occur and produces small amounts of pre-excitation even during sinus rhythm. The study concluded that, despite its name, concealed WPW is not completely concealed, and that non-invasive diagnosis during sinus rhythm is possible by using high-resolution electrocardiography to detect the concealed anterograde pre-excitation.

Renal adenocarcinoma with tumour thrombi in the inferior vena cava and right atrium in a pedestrian motor vehicle accident fatality: case report and medicolegal implications

Dramatic and unexpected natural disease processes may occasionally be encountered in the course of routine forensic pathology practice. The pathophysiological consequences of these processes may carry profound medicolegal implications which may have a bearing on the liability and culpability of the various parties involved. A pedestrian-vehicular incident involving a 53-year-old woman in whom a renal adenocarcinoma with tumour extension to the inferior vena cava and right atrium was discovered at autopsy is reported. The pathophysiological and biochemical disturbances associated with this tumour are discussed and their possible medicolegal implications evaluated.

Alternation of atrioventricular nodal conduction time during atrioventricular reentrant tachycardia: are dual pathways necessary?

INTRODUCTION

Alternation of atrial cycle length and AV nodal conduction time (NCT) is often observed during AV reentrant tachycardia. Both AV nodal dual pathway and rate-dependent function have been postulated to be involved in this phenomenon. This study was designed to determine the respective role of these two mechanisms in the alternation observed in an in vitro model of orthodromic AV reentrant tachycardia.

METHODS AND RESULTS

The tachycardia was produced by detecting each His-bundle activation and stimulating the atrium after a retrograde delay, thereby simulating retrograde pathway conduction, in six isolated rabbit heart preparations. After a 5-minute stabilization period at a fast rate, the retrograde delay was decremented by 2 msec every minute until nodal blocks occurred. We observed a sequential alternation of the cycle length and NCT in four preparations in the short retrograde delay range. The magnitude of the alternation gradually increased as the retrograde delay was decreased and reached 4.6 +/- 0.5 msec during 1:1 conduction. The alternation increased further just prior to termination of the tachycardia by an AV nodal block. None of the preparations showed discontinuous AV nodal recovery curves. Moreover, an electrode positioned over the endocardial surface of the node showed that the alternation developed distally to the nodal inputs, which are believed to constitute a major component of dual pathways. A mathematical model predicted the alternation from known characteristics of rate-dependent nodal functional properties.

CONCLUSIONS

NCT and cycle length alternation can arise during orthodromic AV reentrant tachycardia when the retrograde delay is sufficiently short. The characteristics of the alternation, presence of continuous recovery curves, intranodal location of the alternation, and mathematical modeling suggest that the alternation is predictable from the known functional properties of the AV node without postulating dual pathway physiology.

Significance of ventricular pacing site in manifest entrainment during orthodromic atrioventricular reentrant tachycardia with left-sided accessory pathway

We examined entrainment by ventricular pacing in six patients during orthodromic atrioventricular reentrant tachycardia (AVRT) utilizing a left-sided lateral accessory pathway. Constant fusion and progressive fusion were demonstrated in all patients by left ventricular pacing during tachycardia, but in none of the patients by right ventricular pacing. When left ventricular pacing was performed during AVRT, the antidromic wave front from the pacing impulse (n) collided with the orthodromic wave front of the previous pacing beat (n - 1) within the ventricle, therefore, constant fusion and progressive fusion were demonstrated in the surface electrocardiographic QRS complexes. On the other hand, when right ventricular pacing was performed during orthodromic AVRT, the antidromic wave front from the pacing impulse (n) collided with the orthodromic wave front of the previous paced beat (n - 1) within the normal atrioventricular pathway, and constant fusion and progressive fusion were therefore not demonstrated. These phenomena were explained by the relationship of the ventricular pacing site and the reentrant circuit. This study demonstrates the importance of the pacing site in manifest entrainment of orthodromic AVRT during ventricular pacing.

The relationship between intraoperatively assessed atrial and ventricular insertions of accessory pathways

To gain insight into the complex problems regarding the extension of the atrial and ventricular insertions of anomalous pathways, the activation patterns obtained from intraoperative epicardial mapping in 23 patients with Wolff-Parkinson-White syndrome were carefully analyzed. The atrial and ventricular activation times along the atrioventricular groove were measured at 15 predefined anatomical landmarks. The width of the region of earliest atrial and ventricular activation times and the extent of atrial and ventricular overlap were assessed. The relationship between the atrial and ventricular insertions was studied by predicting the ventricular insertions from the observed atrial insertions and vice versa. The mean extension of an atrial and a ventricular insertion at surgery was 1.9 +/- 0.2 (SE) and 1.6 +/- 0.2 (SE) anatomical landmarks, respectively. The width of the region of early atrial and ventricular activation times measured 2.7 +/- 0.3 (SE) landmarks, thus indicating an overlap of the atrial and ventricular insertions. The lateral distance between the sites of earliest atrial and ventricular activation times was, on average, 1.7 +/- 0.3 (SE) landmarks. The predicted atrial insertion from a known ventricular insertion, and vice versa was found to cover 4 to 6 anatomical landmarks. These observations suggest that wide surgical dissections along the atrioventricular groove are warranted even if epicardial mapping discloses only a single accessory pathway.

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.

Evaluation of flecainide acetate in rapid atrial fibrillation complicating Wolff-Parkinson-White syndrome

Flecainide is reported to be effective in patients with paroxysmal tachycardias, but its effect on rapid ventricular response over accessory atrioventricular pathway during atrial fibrillation is not known. The influence of flecainide on various electrophysiological properties of the accessory pathway with special emphasis on ventricular rate during atrial fibrillation was investigated in 9 patients with severe symptomatic Wolff-Parkinson-White syndrome. The shortest ventricular response during atrial fibrillation increased from 218 (190-270) to 320 (240-block) ms. In 4 patients sustained rapid atrial fibrillation converted to sinus rhythm. The rate of circus movement tachycardia decreased from 166/min to 130/min after flecainide, due to a lengthening of retrograde ventriculoatrial conduction time over the accessory pathway. Flecainide caused a significant prolongation of the effective refractory period of the accessory pathway in our subgroup with extremely fast AV conduction during atrial fibrillation and induced a depressant effect on retrograde accessory pathway conduction. This makes the drug very promising for the emergency treatment of dangerous rapid tachyarrhythias complicating this syndrome.

Evaluation of noninvasive tests for identifying patients with preexcitation syndrome at risk of rapid ventricular response

Intermittent preexcitation, block in the accessory pathway after intravenous injection of ajmaline or procainamide, and block in the accessory pathway during exercise usually exclude a short antegrade refractory period of an accessory pathway in patients with the Wolff-Parkinson-White syndrome. This report describes three patients with these findings suggestive of a relatively long antegrade effective refractory period of the accessory pathway in whom life-threatening ventricular response occurred during atrial fibrillation. In the first patient with a pattern of intermittent preexcitation, rapid ventricular response with wide QRS was present during atrial fibrillation. In the second patient in whom preexcitation disappeared after intravenous injection of ajmaline or procainamide as well as during exercise testing, atrial pacing showed 1:1 conduction over the accessory pathway at a cycle length of 220 msec and the shortest R-R interval during induced atrial fibrillation was 190 msec. The third patient, with no evidence of preexcitation during sinus rhythm, presented antidromic reciprocating tachycardia and atrial fibrillation with life-threatening ventricular response, the minimal R-R interval being 220 msec. Noninvasive tests in the preexcitation syndrome lack sufficient prognostic sensitivity. The evaluation of ventricular response during induced atrial fibrillation represents the most reliable means of identifying such patients at risk.

Efficacy of amiodarone in the Wolff-Parkinson-White syndrome with rapid ventricular response via accessory pathway during atrial fibrillation

Sudden death in Wolff-Parkinson-White syndrome (WPW) is related to a very fast ventricular response to spontaneous atrial fibrillation (AF) conducted via accessory pathway (AP). The effect of oral amiodarone was studied in 12 patients with WPW syndrome and life-threatening rapid ventricular response via an AP during spontaneous AF. The effective refractory period of the AP in the anterograde direction was 280 ms or less during control study in all patients. After amiodarone therapy, the effective refractory period remained 280 ms or less in 7 of the 12 patients. During incremental atrial pacing, the longest atrial pacing cycle length that produced block over an AP ranged from 200 to 310 ms (mean 261 +/- 42) during the control period and 240 to 980 ms (mean 377 +/- 198) after amiodarone therapy. During AF the shortest ventricular response via the AP could be measured in 10 of 12 of the patients both before and after amiodarone treatment and ranged from 200 to 290 ms (234 +/- 30) and 250 to 500 (mean 302 +/- 75), respectively (p less than 0.01). The average RR interval during AF before and after the drug ranged from 200 to 390 ms (mean 280 +/- 55) and 280 to 650 ms (mean 396 +/- 116), respectively (p less than 0.01). Thus, the safety of amiodarone in the WPW syndrome should be established by electrophysiologic studies and induction of AF, because amiodarone is not protective in all patients with WPW.

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.

Ectopic left atrial rhythm that produces QRS changes in absence of Wolff-Parkinson-White syndrome

In an 18-year-old patient without manifest or concealed Wolff-Parkinson-White syndrome, spontaneous and paced left atrial impulses penetrated a left-sided AV nodal input and thereafter activated the ventricles in a normal fashion exclusively through the His-Purkinje system. On the other hand, sinus and paced right atrial impulses entered a right-sided atrioventricular nodal input that was completely dissociated from the left-sided input to subsequently activate the ventricles partly through Mahaim fibers and partly through the His-Purkinje system. The Mahaim fibers, which acted as "bystanders" during episodes of atrioventricular nodal reciprocating tachycardia, seemed to have extended from a "distal," common (right-sided) intranodal pathway (or "proximal" His bundle) to the right ventricle or, although this is less likely, to the right bundle branch. More studies are necessary to determine whether the association on the surface electrocardiogram of an ectopic slow left atrial rhythm with changes in QRS morphology (but not in QRS duration) always reflects the existence of Mahaim fibers.

Effectiveness of surgical management of the Wolff-Parkinson-White syndrome

In this report, the surgical experience with the treatment of Wolff-Parkinson-White syndrome in 190 patients who had 210 Kent bundles has been summarized. The patients with reentry tachycardia caused by the Kent bundle were relieved by Kent division or by His division, the latter being used only in 10 percent of the patients. A malignant ventricular arrhythmia was found in 25 percent of the patients and was due to a Kent bundle that conducted an atrial flutter-fibrillation 1:1 to the ventricle. This arrhythmia was corrected by Kent interruption, since the Kent bundle alone participated in the arrhythmia. Other unusual manifestations of Kent bundles were found, such as multiple pathways, unidirectional conducting pathways, and pathways causing incessant junctional tachycardia. Other cardiac problems were frequently present, such as hypertrophic cardiomyopathy and Ebstein's anomaly. Even in such a multifaceted problem caused by a minute congenital abnormality, careful application of sophisticated electrophysiologic measurements followed by appropriate surgical methods have proved to be effective in correcting the two arrhythmias associated with Wolff-Parkinson-White syndrome.

Localization of the accessory pathway in the Wolff-Parkinson-White syndrome from the ventriculo-atrial conduction time of right ventricular apical extrasystoles

In 18 consecutive patients with the Wolff-Parkinson-White syndrome undergoing electrophysiologic study, the ventriculo-atrial conduction time of right ventricular apical extrasystoles which advanced atrial activation during circus movement tachycardia was studied in relation to accessory pathway location. Accessory pathway location was determined by delta wave morphology during maximal pre-excitation, mapping of atrial activation during circus movement tachycardia and ventricular pacing, the effect of bundle branch block on ventriculo-atrial conduction time during circus movement tachycardia, and the effect of pacing from different sites in the atria on the stimulus-to-delta wave interval. In 7 patients with septal accessory pathways, ventriculo-atrial conduction time was similar during circus movement tachycardia and following right ventricular apical extrasystoles (mean difference 0 +/- 6 ms, range -5 to +10 ms). In contrast, in 11 patients with a left free wall accessory pathway, ventriculo-atrial conduction time increased by 46 +/- 15 ms (range 15 to 65 ms) following right ventricular apical extrasystoles. Therefore, measurement of the ventriculo-atrial conduction time of right ventricular extrasystoles during circus movement tachycardia provides an easy way to distinguish between septal and left free wall accessory pathways. This finding may be of particular use in determining the location of concealed bypass tracts.

Onset of atrial fibrillation during antidromic tachycardia: association with sudden cardiac arrest and ventricular fibrillation in a patient with Wolff-Parkinson-White syndrome

Electrophysiologic evaluation in an 18 year old youth with the Wolff-Parkinson-White syndrome who had a sudden cardiac arrest while playing racquetball revealed two types of paroxysmal reciprocating tachycardia: (1) A normal QRS tachycardia with a short ventriculoatrial (V-A) interval fulfilled the criteria for reentry within the atrioventricular (A-V) node; and (2) a wide QRS tachycardia with a QRS configuration of maximal preexcitation was demonstrated to be the result of an antidromic mechanism. During laboratory study, the wide QRS tachycardia spontaneously degenerated into atrial fibrillation. In the basal state, the shortest R-R interval between preexcited QRS complexes was 270 ms, but after infusion of isoproterenol (1.6 microgram/min intravenously), the shortest R-R interval became 180 ms. Consequently, this electrophysiologic study suggested that evolution of antidromic reciprocating tachycardia into atrial fibrillation with a rapid ventricular response during exercise-induced catecholamine release may have been the mechanism for ventricular fibrillation in this patient.

Strength-interval relations in a chronic canine model of myocardial infarction. Implications for the interpretation of electrophysiologic studies

Fifteen adult mongrel dogs underwent two-stage occlusion of the mid- or distal left anterior descending coronary artery and then a reperfusion stage. The dogs were studied 3-30 days later to determine strength-interval relations in a canine model of chronic myocardial infarction. These dogs were susceptible to the initiation of sustained ventricular tachyarrhythmias with the introduction of one, two or three ventricular extrastimuli. Using unipolar cathodal stimuli with a pulse width of 2 msec, strength-interval curves were constructed from measurements made at multiple sites in the distribution of occluded and nonoccluded vessels during drive pacing at a cycle length of 300 msec. At 56 normal sites, ventricular refractory periods measured at twice-diastolic-excitability threshold approximated the relative refractory periods (mean absolute difference 3 msec), but were variably longer than effective refractory periods (mean difference 18 msec, range 4-29 msec). At 51 infarct sites, differences between ventricular refractory periods measured at twice-diastolic-excitability threshold and both relative refractory periods (mean difference 13 msec, range -60 to +18 msec) and effective refractory periods (mean difference 28 msec, range 1-60 msec) were markedly disparate. These differences were further exaggerated after administration of i.v. procainamide. These findings suggest limitations in interpreting the results of programmed pacing studies performed using stimuli of twice-threshold intensity.

Initiation of sustained ventricular tachyarrhythmias in a canine model of chronic myocardial infarction: importance of the site of stimulation

The importance of the site of stimulation to the initiation of sustained ventricular tachyarrhythmias was determined in 24 adult mongrel dogs. Studies were performed 3-30 days after two-stage occlusion of the mid- or distal left anterior descending coronary artery, modified by a reperfusion stage. Unipolar cathodal stimuli of twice-threshold intensity and 2 msec duration were introduced at five to 24 sites in each dog in the distribution of occluded and nonoccluded vessels. Strength-interval curves were constructed from 232 measurements at these sites and local properties of excitability and refractoriness were correlated with the ability to initiate arrhythmias. All dogs had sustained ventricular tachyarrhythmias inducible from at least one site. Intramyocardial sites with normal excitability and refractoriness within 2 cm of an area of infarction were most often successful (27 of 44, 61%) in the initiation of sustained arrhythmias. Less successful sites included normal left ventricular plunge electrode sites less than 2 cm from an area of infarction (eight of 32, 25%) (p = 0.002), left ventricular plunge electrode sites within an area of infarction (20 of 103, 19%) (p less than 0.001), normal right ventricular sites (five of 24, 21%) (p less than 0.001), and endocardial catheter sites (six of 29, 21%), (p less than 0.001). These findings suggest that local properties of excitability and refractoriness at the site of stimulation, as well as anatomic and geometric factors, may be critical in the initiation of sustained ventricular tachyarrhythmias using the technique of programmed electrical stimulation.

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.

Ventricular tachycardia in infancy: evidence for a reentrant mechanism

Ventricular tachycardia is unusual in infancy. Three infants are described in whom this arrhythmia was documented by electrophysiologic studies. The ability to start and terminate this rhythm by critically timed premature ventricular stimulation suggests a reentrant mechanism. All three patients have remained free of arrhythmias on oral propranolol therapy.

Enhanced atrioventricular nodal conduction in a patient with dual extranodal pathways

A patient was admitted to the hospital with wide complex tachycardia and a history of recurrent palpitations. Electrophysiologic studies showed evidence of dual atrioventricular (AV) accessory pathways. One proved to be an anteroseptal (possible right anterior) pathway probably capable of only unidirectional conduction. The other pathway was in the posterior septum and conducted only in the retrograde direction. The tachycardia circuit involved anterograde conduction via either the AV node-His axis or the anteroseptal pathway and retroconduction over the posteroseptal accessory pathway. In addition, enhanced AV nodal conduction coupled with two accessory AV nodal pathways has rarely been described in English medical literature. Previous reports have carefully described anatomic, electrocardiographic, and electrophysiologic evidence of more than one accessory pathway in patients with the Wolff-Parkinson-White syndrome. The introduction of surgical techniques for ablation of an accessory pathway demands precision in the electrophysiologic evaluation of patients with ventricular preexcitation. Reported herein is a patient with the unique finding of two extranodal accessory pathways and enhanced atrioventricular (AV) nodal conduction (or AV nodal bypass).

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.

Ventricular fibrillation during programmed ventricular stimulation: incidence and clinical implications

Ventricular fibrillation occurred in 10 (3.3 percent) of 300 patients consecutively studied with programmed ventricular stimulation. One hundred twenty-five of these patients were studied with double ventricular extrastimuli including 68 patients with and 57 patients without documented or suspected ventricular tachycardia or fibrillation, or both. Ventricular fibrillation did not develop in response to a single ventricular extrastimulus delivered during sinus rhythm, ventricular pacing or ventricular tachycardia or in response to ventricular pacing at cycle lengths of 300 msec or greater and occurred only in response to double ventricular extrastimuli. All 10 patients who manifested ventricular fibrillation during programmed stimulation were in the group of patients with suspected or documented ventricular tachycardia or fibrillation. Ventricular fibrillation was initiated in seven patients with double ventricular extrastimuli delivered during sinus rhythm or ventricular pacing and in three patients with double ventricular extrastimuli delivered during ventricular tachycardia. Four patients had spontaneous conversion to sinus rhythm and the remainder underwent defibrillation without sequelae. Recurrent ventricular fibrillation occurred clinically in 7 of the 10 patients. This study suggests that ventricular fibrillation occurs uncommonly during programmed ventricular stimulation and only in response to double ventricular extrastimuli in patients in whom spontaneous episodes are likely to occur.

Effects of metoprolol on heart rate in patients with digitalis treated chronic atrial fibrillation

Adequate control of ventricular rate in patients with chronic atrial fibrillation (AF) may not be achieved with digitalis alone. In the present study the additional effect of two different doses (50 mg and 50 +/- 50 mg) of oral metoprolol, a new selective beta-blocking agent, on ventricular rate in patients with longstanding AF has been studied. A decrease in the mean ventricular rate during rest and during exercise at various work loads was observed after both doses. The effect was more pronounced at the highest work load of 80 W, both after 50 mg (p less than 0.002) and after 50 +/- 50 mg (p less than 0.01) of the drug. A high initial heart rate at rest or during exercise was reduced more by the drug than a lower one. Exercise tolerance was reduced in 2 patients. These results suggest that patients with AF in whom satisfactory control of heart rate cannot be achieved with digitalis alone may benefit from addition of individualized metoprolol therapy.

Re-entry via Mahaim fibres as a possible basis for tachycardia

Paroxysmal tachycardia with widened QRS complexes was recorded in a 21-year-old man. In sinus rhythm there was no evidence of pre-excitation. His bundle studies revealed an abnormally short HV interval of 30 ms. Premature atrial stimuli produced an increased PR interval. At short coupling intervals the His bundle activity became incorporated within the QRS complex. Concurrently, a left bundle-branch block pattern appeared identical to that seen during tachycardia. Closely coupled ventricular extrastimuli initiated a tachycardia identical to the initial episode. A re-entry mechanism via anterograde Mahaim fibres and retrograde His bundle -AV node pathway is postulated.

The anatomical substrates of wolff-parkinson-white syndrome. A clinicopathologic correlation in seven patients

Clinicopathological correlations were made on the hearts from seven patients known to have exhibited electrocardiographic evidence of the Wolff-Parkinson-White syndrome. In each case, clinical and pathological investigations were conducted independently, neither group of investigators having knowledge of the other's results. In all seven hearts, the entire atrioventricular junctions were serially sectioned. Accessory atrioventricular connections were predicted in all seven cases following electrocardiographic investigation. Connections were identified histopathologically in four hearts in the predicted site. In another case two connections were identified, one being considered responsible for the pre-excitation. In the sixth case a right lateral connection was anticipated, but only accessory nodo-ventricular fibers were identified following histopathologic studies. In the final case, a posterior septal connection was predicted but the entire septum had fibrosed following previous operation. These findings are discussed in the light of the investigative techniques used, the theories of pre-excitation and the embryogenetic mechanisms producing accessory atrioventricular connections.

Value and limitations of programmed electrical stimulation of the heart in the study and treatment of tachycardias

A review is given on the use of programmed electrical stimulation of the heart in patients suffering from tachycardia. The application of this technique makes it possible to evaluate mechanisms of tachycardia directly in the human heart. By repeating the same stimulation program following drug administration the effect of drugs on arrhythmia mechanisms can be studied. There are several factors, however, that influence the amount of information on mechanism and pathway of tachycardia and selection of appropriate therapy that can be obtained during the study. These factors as well as how information obtained programmed electrical stimulation of the heart has resulted in a better use of the 12-lead electrocardiogram as a diagnostic tool are discussed.

Identical twins with differing forms of ventricular pre-excitation

Identical 10-year-old twins, both with electrocardiograms showing a short PR interval and a normal QRS complex but with dramatically different electrophysiological characteristics, are described. One twin experienced episodes of rapid palpitation and on one occasion was resuscitated from ventricular fibrillation. An intracardiac electrophysiological study confirmed the presence of an atrioventricular nodal bypass tract and in addition revealed the presence of an accessory atrioventricular pathway, thus demonstrating that the patient had both the Lown-Ganong-Levine and Wolff-Parkinson-White syndromes. Re-entry tachycardia and atrial fibrillation, with a very rapid ventricular rate, were precipitated. After treatment with amiodarone, the patient became asymptomatic and a repeat study showed that the features of the atrioventricular nodal bypass tract were no longer present and though re-entry tachycardias using the accessory atrioventricular pathway could still be induced, their rates were slower than before treatment. The other twin, in spite of an identical surface electrocardiogram, was asmymptomatic. An electrophysiological study showed the features of an atrioventricular nodal bypass tract but there was no evidence of additional atrioventricular accessory connections and a tachycardia could not be induced.

The value of the electrocardiogram in the differential diagnosis of a tachycardia with a widened QRS complex

To determine the value of the electrocardiogram for differentiating aberrant conduction from ventricular ectopy, findings were retrospectively reviewed from patients with a widened QRS complex during tachycardia in whom the site of origin of tachycardia was determined by His bundle electrography. Seventy episodes of sustained ventricular tachycardia from 62 patients and 70 episodes of aberrant conduction during supraventricular tachycardia from 60 patients were available for study. Findings suggesting a ventricular origin of tachycardia were (1) QRS width over 0.14 sec, (2) left axis deviation, (3) certain configurational characteristics of QRS and (4) atrioventricular (A-V) dissociation. Capture or fusion beats resulting from A-V conduction of dissociated atrial complexes during ventricular tachycardia were seen during only four of 33 episodes of sustained tachycardia.

The preexcitation syndromes

Current methodology permits one to define the functional basis of the preexcitation syndromes with reasonable certainty and to develop a rationale for instituting trials of medical therapy. Future studies will hopefully result in a more exact definition of the anatomic substrates of preexcitation and their relationship to the pathophysiology of the associated syndromes. New antiarrhythmic agents must also be developed to add to the relatively small number of available drugs. Important questions still remain. Should asymptomatic patients with preexcitation be studied? If found to demonstrate potential for malignant arrhythmias, should they be treated prophylactically? The answers to these questions will require study and long-term follow-up of nonhospital referral patients. Surgery offers a feasible therapeutic alternative for patients with life-threatening or disabling arrhythmias but demands a team equipped to perform precise preoperative and intraoperative mapping studies to define the type and location of underlying anatomic substrates.

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.

Preexcitation

Recent increase in our knowledge of the basic features involved in ventricular preexcitation has moved it from being a somewhat rare curiosity for which there was no cure to an important medical condition requiring careful therapeutic planning. This review summarizes a body of information concerning mechanisms, various forms of preexcitation, embryologic features, electrophysiology and special testing maneuvers, treatment, prognosis and aviation plus insurance aspects of the syndrome. A new classification of the locations of the Kent bundles in the Wolff-Parkinson-White form of preexcitation is also offered.

Relationship between the electrical (electrocardiographic) and mechanical (echocardiographic) events in Wolff-Parkinson-White syndrome

Studies using epicardial mapping on patients with Wolff-Parkinson-White syndrome have demonstrated that the delta vector of the electrocardiogram is a detector of the location of at least one bypass tract. In order to relate the electrical activities (preexcitation) with the mechanical activity (septal and ventricular wall motion), echocardiographic strip-chart recordings were obtained in 22 patients with Wolff-Parkinson-White syndrome. Our studies indicated that in the majority of patients with Wolff-Parkinson-White syndrome, left ventricular and septal contraction is normal, suggesting that normal activation predominates and that the determinants of abnormal septal wall motion are (1) the location (right ventricular free lateral wall or septrum) and (2) the degree (duration of the QRS complex greater than 130 msec) of ventricular preexicitation.

Mechanisms of atrioventricular junctional tachycardia. Role of reentry and concealed accessory bypass tracts

Electrophysiologic investigations with programmed stimulation of the human heart have clearly established the participation of the atrioventricular (A-V) junction in three different types of junctional reciprocating tachycardia: (1) paroxysmal supraventricular tachycardia in the Wolff-Parkinson-White syndrome: (2) the vast proportion of "paroxysmal atrial tachycardia" without evidence of preexcitation during sinus rhythm with antegrade conduction; and (3) the permanent or almost permanent (chronic relapsing) form of supraventricular tachycardia with its characteristic rate-dependent initiating mechanism. The obvious presence of the Wolff-Parkinson-White syndrome during sinus rhythm does not necessarily imply that the accessory pathway will be utilized during supraventricular tachycardia. Conversely, in the absence of preexcitation, the mechanism of A-V junctional reciprocating tachycardia has been traditionally attributed to pure intranodal dissociation, often without definite direct proof. Concealed accessory pathways (with unidirectional block) may be more frequent than realized and should be carefully searched for. Proof that supraventricular tachycardia utilizes an accessory pathway for retrograde conduction to the atrium often requires meticulous electrophysiologic studies- Conslucions based on the absence of various findings may be misleading. Emphasis must be placed on positive viagnostic features. One or more of the following observations may prove or disprove participation of a Kent bundle during supraventricular tachycardia: (1) induction of A-V block during tachycardia: (2) influence of electrically induced ventricular premature beats upon tachycardia; (3) patterns of retrograde atrial activation during tachycardia; or (4) influence of functional bundle branch block on the rate of the tachycardia. Analysis of events at the onset of rather than during the tachycardia is probably less important but may also provide suggestive clues about the mechanism of reentry. Observation of the following variables may be helpful: (1) behavior of antegrade conduction at the onset of tachycardia; (2) relation of atrial and ventricular activation at the onset of tachycardia; (3) presence of retrograde ventriculoatrial (V-A) conduction; (4) prolongation of the H-V interval at the onset of tachycardia; and (5) atrial stimulation at various sites. Precise understanding of the pathophysiology of supraventricular tachycardia is important because specific therapy (pharmacologic, pacemaker or surgical) may ultimately depend on accurate knowledge of the underlying mechanisms.

Intermittent AV conduction disturbances in patients with AV nodal bypass tracts. Possible mechanisms of unusual variant of tachycardia-bradycardia syndrome

His bundle recordings were performed in 2 patients in whom AV nodal bypass tracts coexisted with intermittent AV conduction disturbances occurring below the site from which the His bundle deflection was recorded. Case 1 had: (a) tachycardia dependent right bundle-branch block, (b) persistent HV prolongation, and (c) bradycardia dependent AV block. Case 2 showed: (a) intra-atrial conduction delay, (b) tachcardia dependent left bundle-branch block with HV prolongation, (c) bradycardia dependent HV conduction disturbance, (d) tachycardia-bradycardia syndrome of an unusual type; the latter presumably resulted, during atrial flutter, from the alternation of rapid AH conduction through the bypass tract with intermittent (complete) distal His bundle block or bilateral bundle-branch block.

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.