Surgical treatment of supraventricular tachycardia in infants and children

The technique, indications and results of surgical division of accessory atrioventricular connections in 10 infants and children with drug-resistant Supraventricular tachycardia are described. The patients ranged in age from 6 months to 15 years. Four patients had associated congenital heart disease. Division of accessory connections were performed on free wall pathways in nine patients (seven right atrial, two left atrial) and on a septal pathway in one patient. Four patients had both anterograde and retrograde conduction over the accessory connection (manifest Wolff-Parkinson-White conduction) whereas six had only retrograde conduction (concealed Wolff-Parkinson-White conduction). The manifest Wolff-Parkinson-White conduction was abolished by surgical division in all four patients. In 8 of the 10 patients the procedure stopped the attacks of paroxysmal supraventricular tachycardia for follow-up periods ranging from 9 months to 3 $\text{1}\text{2}$ years; no patient receives medication to date.     

Coexistent Mahaim and Kent accessory connections: diagnostic and therapeutic implications

Six patients with coexistent Mahaim and Kent accessory connections are described. Two had left nodoventricular Mahaim connections, the first reported cases demonstrating these findings. In neither were the left-sided Mahaim connections components of a tachycardia and their presence was incidental. In two of four with nodoventricular connections, associated atrioventricular (AV) node conduction and coexistent posteroseptal accessory pathways were found. One of these had the unusual finding of a right-sided Mahaim connection arising from a "fast" AV node pathway. In only one patient did the tachycardia incorporate the Mahaim connection. In this patient, anterograde conduction during tachycardia occurred over a right nodoventricular connection whereas retrograde conduction occurred through a concealed right free wall Kent connection. Two patients had fasciculoventricular connections that were associated with either septal (one patient) or left free wall (one patient) Kent connections. The latter also had evidence of enhanced AV node conduction. This report is unique in that it describes in detail two patients with left nodoventricular connections (Mahaim) inserting in or near the left posterior fascicle. Combined Kent and Mahaim connections, present in the six patients, appear to occur in approximately 5% of patients with the Wolff-Parkinson-White syndrome. Precise identification of bypass connections critical for reentrant circuits is essential for intelligent application of treatment options.     

Electrocardiographic body surface potential mapping in the Wolff-Parkinson-White syndrome. Noninvasive determination of the ventricular insertion sites of accessory atrioventricular connections

BACKGROUND. A reliable, noninvasive procedure to determine the location of accessory atrioventricular connections in patients with Wolff-Parkinson-White syndrome would add an important diagnostic tool to the clinical armamentarium. METHODS AND RESULTS. Body surface potential mapping (BSPM) using 180 electrodes in various-sized vests and displayed as a calibrated color map was used to determine the ventricular insertion site of the accessory atrioventricular (AV) connections in 34 patients with Wolff-Parkinson-White syndrome. Attempts were made to determine the 17 ventricular insertion sites described by Guiraudon et al. All 34 patients had an electrophysiologic study (EPS) at cardiac catheterization, and 18 had surgery so the ventricular insertion sites could be accurately located using EPS at surgery. A number of physiologic observations were also made with BSPM. CONCLUSIONS. The following conclusions were drawn: 1) BSPM using QRS analysis accurately predicts the ventricular insertion site of accessory AV connections in the presence of a delta wave in the electrocardiogram; 2) the ventricular insertion sites of accessory AV connections determined by BSPM and by EPS at surgery were identical or within one mapping site (1.5 cm or less) in all but four of 18 cases; three of the four exceptions had more than one accessory AV connection, and the other had a very broad ventricular insertion; 3) BSPM and EPS locations of the accessory AV connections correlated very well in the 34 cases despite the fact that BSPM determines the ventricular insertion site and EPS determines the atrial insertion site of the accessory AV connection; 4) as suggested by the three cases of multiple accessory AV connections, EPS and BSPM may be complementary since BSPM identified one pathway and EPS identified the other (in the case with a broad ventricular insertion, BSPM and EPS demonstrated different proportions of that insertion); 5) BSPM using ST-T analysis is very much less accurate in predicting the ventricular insertion site of accessory AV connections unless there is marked preexcitation; 6) standard electrocardiography using the Gallagher grid methodology (but with no attempt at stimulating maximal preexcitation) was not as accurate as QRS analysis of BSPM in predicting the ventricular insertion site of the accessory AV connection; however, exact comparison is hampered by the different number and size of the Gallagher and Guiraudon insertion sites; 7) BSPM using QRS analysis appears to be very accurate in predicting right ventricular versus left ventricular posteroseptal accessory AV connections; 8) typical epicardial right ventricular breakthrough, indicative of conduction via the specialized AV conduction system, occurs in all patients with left ventricular free wall accessory AV connections; 9) epicardial right ventricular breakthrough was not observed in cases with right ventricular free wall or anteroseptal accessory AV connections; 10) epicardial right ventricular breakthrough can occur in the presence of posteroseptal accessory AV connections, whether right or left ventricular; and 11) the delay in epicardial right ventricular breakthrough in cases with left ventricular insertion may provide a marker to estimate the degree of ventricular preexcitation.     

Wolff-Parkinson-White syndrome in children: electrophysiologic and pharmacologic characteristics.

Intracardiac electrophysiologic studies were performed on 28 infants and children, ages 1 month to 18 years, with the Wolff-Parkinson-White syndrome to try to determine 1) the electrophysiologic characteristics of the accessory connection and 2) the mechanisms of associated supraventricular dysrhythmias. Although the antegrade refractory periods of the normal conduction system were shorter than those found in adults, those of the accessory connection were slightly longer. Reciprocating supraventricular tachycardia (SVT), which had been a clinical problem in 26 of 28, could be induced in the laboratory in all 26 subjects. The mechanism involved reentry with antegrade conduction through the atrioventricular (AV) node and retrograde through the accessory connection in 22. Eleven of these 22 had a wide QRS during tachycardia due to a bundle branch block. Three other subjects had wide QRS tachycardia, but the mechanism involved antegrade conduction through the accessory connection and retrograde through the AV node. The other patient had AV node reentry tachycardia. Two patients did not have clinical SVT, and in these two, SVT could not be induced. Neither patient had retrograde conduction through the accessory connection. The site of the accessory connection could be identified in 26 subjects by the sequence of retrograde activation of the atrium during SVT or ventricular pacing. Digitalis shortened the refractory period of the accessory connection in five of the eight patients studied.     

Usefulness of combined propranolol and verapamil for evaluation of surgical ablation of accessory atrioventricular connections in patients without structural heart disease

Successful surgical ablation of atrioventricular (AV) accessory connections may be confirmed during postoperative electrophysiologic testing by the absence of accessory connection conduction in both the anterograde and retrograde directions. Whereas the former may be readily apparent by examination of the surface electrocardiogram during sinus rhythm or atrial pacing, assessment of the latter may be complicated by the frequent presence of enhanced retrograde AV nodal conduction in the postoperative period. Consequently, availability of interventions that selectively affect AV nodal conduction and refractoriness without concomitant effects on accessory connections may be helpful for assessing the success of the surgical procedure. In this study the effects of combined propranolol and verapamil administration on electrophysiologic properties of the AV node and the accessory AV connection were assessed both pre- and postoperatively in 17 patients (12 men and 5 women, mean age 33 years) undergoing surgical ablation of accessory connections. Preoperatively, electrophysiologic characteristics of all but 1 of the accessory AV connections were unaffected by propranolol and verapamil administration. Postoperatively, on the other hand, propranolol and verapamil significantly prolonged both the retrograde AV node effective refractory period (baseline: 272 +/- 34 ms vs after drugs: 384 +/- 70 ms [p less than 0.0001]) and the shortest cycle length maintaining 1:1 ventriculoatrial conduction (baseline: 357 +/- 99 ms vs after drugs: 485 +/- 64 ms [p less than 0.0001]). Late postoperative electrophysiologic evaluation (7 +/- 3 weeks) revealed no evidence of residual accessory AV connection conduction, and all patients remain asymptomatic at 21 +/- 10 months follow-up.(ABSTRACT TRUNCATED AT 250 WORDS)     

Long-term results of catheter ablation of a posteroseptal accessory atrioventricular connection in 48 patients

Forty-eight patients with a posteroseptal accessory atrioventricular (AV) connection underwent catheter ablation of the accessory AV connection with 200-400 J shocks delivered by a standard defibrillator. Cathodal shocks were delivered through the proximal pair of electrodes of a 6F quadripolar electrode catheter positioned in the coronary sinus such that the proximal electrodes straddled the ostium (12 patients) or the third electrode from the tip was at the ostium (36 patients). A 16-cm patch electrode positioned on the back or anterior chest served as the anode. Two to 4 shocks were delivered (total, 635 +/- 198 J, mean +/- SD). The cathether ablation procedure was clinically successful in eliminating symptomatic tachycardias in in 32 of 48 patients (67%) during a mean follow-up of 26 +/- 19 months. A long-term follow-up electrophysiology study was performed in 27 of the 32 patients who had a successful clinical outcome, and this showed that conduction through the accessory AV connection was completely absent in 25 patients and present but impaired in two patients. The success rate was significantly higher in patients with a concealed accessory AV connection (13 of 13, 100%) than in patients with manifest preexcitation (19 of 35, 54%; p less than 0.001). Among the 12 patients in whom the proximal electrodes of the ablation catheter straddled the ostium of the coronary sinus, one patient developed cardiac tamponade requiring needle pericardiocentesis; there were no instances of cardiac tamponade among the 36 patients in whom the third electrode from the tip was at the ostium of the coronary sinus. Other complications were AV block requiring a permanent pacemaker and transient atrial tachycardia in one patient each and an asymptomatic pericardial effusion in three patients. In conclusion, with the catheter ablation technique described in this study, a successful clinical outcome may be achieved in approximately two thirds of patients who have a posteroseptal accessory AV connection, and the risk of serious complications is low. This technique is particularly well suited to patients with a concealed posteroseptal accessory AV connection, in whom the success rate is higher than in patients with manifest preexcitation.     

Incessant atrioventricular tachycardia involving an accessory pathway: preoperative and intraoperative electrophysiologic studies and surgical correction.

In three patients with incessant supraventricular tachycardia, the anatomic substrate was a left-sided atrioventricular (A-V) accessory pathway. In two patients there was no expression of anterograde conduction through this pathway during spontaneous or induced atrial rhythms. The three patients had had increasingly frequent palpitations for more than 10 years despite adequate antiarrhythmic drug therapy.Preoperative intracardiac studies indicated that a left lateral accessory pathway was utilized in the retrograde limb of supraventricular tachycardia in all three patients. The spontaneous initiation of supraventricular tachycardia was due to (1) frequent spontaneous ventricular premature beats in two patients, (2) increase in sinus rate in two patients, and (3) ventriculoatrial reentry without preceding changes in sinus rate or intracardiac conduction intervals in one patient.At operation the accessory pathway was located in two patients with epicardial and endocardial electrographic mapping and cryothermal mapping. In one patient the His bundle was located with electrographic and cryothermal mapping. The accessory pathway (two patients) or the His bundle (one patient) were cryoablated by freezing over the area of the conducting tissue for 120 seconds at a temperature of ?65 ° C. Attempts to reinitiate supraventricular tachycardia after this procedure were unsuccessful. The operation was without significant morbidity. During follow-up for 3 to 10 months, no patient has experienced any further attacks of supraventricular tachycardia or required antiarrhythmic drugs.These observations confirm that an A-V accessory pathway may be the anatomic substrate for incessant or persistently repetitive tachycardias that may be resistant to medical and pacing therapy. Surgical interruption or cryothermal ablation of part of the reentrant circuit may abolish tachycardia, thus providing proof of the underlying mechanism.     

Deceptive surgical results in three siblings with familial Wolff-Parkinson-White syndrome

Three siblings with familial Wolff-Parkinson-White syndrome and two instances of sudden death are described. In all of them, multiple accessory pathways with a very short anterograde refractory period and rapid ventricular responses during atrial fibrillation had been documented, thus surgical ablation of the bypass tracts had been performed. Although abolition of the accessory pathway conduction had been demonstrated post-operatively, an electrophysiologic evaluation performed after 2-8 years showed resumption of conduction over the anomalous connections, with life-threatening arrhythmias during induced fast atrial rhythms. This report demonstrates that apparent success of surgery for pre-excitation syndrome, judged during the postoperative course, may be illusory in some patients, and return of accessory pathway conduction can occur later on.     

"Nodoventricular" accessory pathway: evidence for a distinct accessory atrioventricular pathway with atrioventricular node-like properties

Two patients are described with recurrent pre-excited tachycardia and electrophysiologic characteristics typically ascribed to a nodoventricular accessory connection. The accessory pathway in each case demonstrated rate-dependent prolongation of conduction time and a low right ventricular insertion site; it was associated with a left bundle branch block configuration during pre-excitation. Intraoperatively, the pathway was demonstrated to originate at the anterior right atrioventricular (AV) anulus and not at the AV node. These data suggest that a "typical" nodoventricular pathway, by electrophysiologic criteria, may in fact be an AV pathway with AV node-like conduction properties and a distal right ventricular insertion site.     

Electrophysiological effects and clinical efficacy of propafenone in children with recurrent paroxysmal supraventricular tachycardia

Twenty-four patients aged 10.1 +/- 4.5 (mean +/- SD) years with recurrent paroxysmal supraventricular tachycardia underwent an electrophysiological study. Eleven patients had an overt and seven had a concealed accessory connection; six patients had no accessory connection. An orthodromic reciprocating tachycardia was inducible in 17 of 18 patients with an accessory connection, and an atrioventricular nodal reentrant tachycardia was inducible in four of six patients without accessory connection. After administration of propafenone, the sinus cycle length decreased. Intra-arterial, intranodal, and His-ventricle intervals and QRS duration increased. The atrial and ventricular effective refractory periods and anterograde and retrograde effective refractory periods of the atrioventricular node increased. The cycle length at which nodal second-degree block occurred increased. Of 18 patients with accessory connection, propafenone prolonged retrograde conduction in all, blocked anterograde conduction in five, and prolonged it in six. The drug terminated the orthodromic reciprocating tachycardia in all 17 patients and the atrioventricular nodal reentrant tachycardia in three of four patients. In three of four patients with atrioventricular nodal reentrant tachycardia and in 15 of 17 patients with orthodromic reciprocating tachycardia, the tachycardia was no longer inducible or nonsustained after propafenone. A follow-up of 26 +/- 10 months revealed that the drug when orally administered to all patients prevented recurrences of tachycardia in 15 of 18 patients with and in four of six patients without accessory connection. The results of short-term drug testing with propafenone predict the response to long-term oral therapy with this drug.     

Transcatheter ablative techniques for treatment of the permanent form of junctional reciprocating tachycardia in young patients

Five patients with medically refractory incessant supraventricular tachycardia due to a posterior septal, slowly conducting accessory connection underwent transcatheter closed chest ablative treatment. The tachycardia characteristics were consistent with the permanent form of junctional reciprocating tachycardia. In each patient the ablative attempts resulted in independent interruption of either the anterograde limb (atrioventricular node-His bundle conduction) or the retrograde limb (accessory connection) of the tachycardia circuit. Permanent retrograde pathway ablation was achieved in only one patient and followed separate permanent transcatheter His bundle ablation. In three of the other four patients the ablation attempt caused temporary interruption of retrograde conduction. Each patient had improved control of tachycardia related to the ablation attempt. Of the five patients, four required pacemaker implantation. With further refinements, selective ablation of the retrograde limb of the tachycardia circuit may be possible. This experience confirms the anatomic independence of the anterograde and retrograde limbs of the tachycardia circuit.     

Effects of intravenous adenosine on antegrade refractoriness of accessory atrioventricular connections

BACKGROUND. Several groups have suggested the use of intravenous adenosine or adenosine triphosphate in the diagnosis of regular broad complex tachycardias. However, the short half-life of these agents has precluded assessment of their effects on refractoriness of accessory connections, and their safety in preexcited arrhythmias has not been demonstrated. METHODS AND RESULTS. We examined the effects of intravenous adenosine on accessory atrioventricular (AV) connections in 30 patients with the Wolff-Parkinson-White syndrome. Intravenous adenosine (12 mg, rapid bolus) was administered to 14 patients (group 1) during continuous atrial pacing at a cycle length 20 msec below that required to cause 2:1 conduction block in the accessory connection (mean pacing cycle length 261 +/- 41 msec). After adenosine, transient 1:1 conduction occurred via the accessory connection in 12 of 14 patients, indicating a shortening of antegrade refractoriness. In three of seven patients, this effect was abolished after intravenous propranolol (0.2 mg/kg). Nineteen patients (group 2) received adenosine (0.17 +/- 0.04 mg/kg) during induced, preexcited atrial arrhythmias. The minimum RR interval during preexcited atrial fibrillation transiently decreased (252 +/- 44 msec to 224 +/- 35 msec, p less than 0.01) after adenosine, but no change in average RR interval was observed (360 +/- 59 msec to 357 +/- 60 msec, NS). The preexcited ventricular response to atrial flutter was transiently accelerated in five of eight patients (415 +/- 21 msec to 360 +/- 49 msec, p less than 0.05) due to shortening of flutter cycle length (207 +/- 10 msec to 180 +/- 24 msec, p less than 0.05). However, 2:1 accessory connection conduction was maintained in all eight patients. All effects were short lived, with the decrease in RR interval during atrial fibrillation occurring for a maximum of two RR intervals only. No patient suffered ventricular arrhythmias or hemodynamic deterioration. CONCLUSIONS. Adenosine shortens antegrade refractoriness of accessory AV connections, and in some patients this action is mediated by beta-adrenergic stimulation. Adenosine may cause acceleration of preexcited atrial arrhythmias, but these effects are transient and should not discourage the use of adenosine as a diagnostic agent in broad complex, regular tachycardias of uncertain origin.     

Indications for modification of coexisting dual atrioventricular node pathways in patients undergoing surgical ablation of accessory atrioventricular connections

Concomitant susceptibility to atrioventricular (AV) node reentrant tachycardia has been demonstrated in certain patients having reentrant tachycardia utilizing accessory AV connections. For those patients undergoing accessory connection ablation, AV node surgical modification may be warranted during the same operative procedure. To assess indications for a combined operative procedure, this study evaluated potential predictors of subsequent spontaneous AV node reentrant tachycardia in patients undergoing ablation of accessory AV connections. Among 62 consecutive patients undergoing surgical ablation of an accessory AV connection, 13 (21%) manifested dual AV node pathways. The latter were identified preoperatively in five patients (four with concealed and one with bidirectional accessory connections) and postoperatively in seven (all seven with bidirectional accessory connections). In one patient with a bidirectional accessory connection, dual AV node pathways could not be demonstrated preoperatively, but AV node reentrant tachycardia was induced. Operative ablation of an accessory connection was successful in all patients. However, postoperatively, 2 of the 13 patients had inducible AV node reentrant tachycardia, 5 had AV node "echo" beats and 6 had no inducible arrhythmia. During 26 +/- 7 months of follow-up study, the two patients with inducible AV node reentrant tachycardia postoperatively had symptomatic AV node reentrant tachycardia. In addition, the one patient with inducible AV node reentrant tachycardia preoperatively had recurrence of this tachycardia 4 months after attempted surgical modification of the AV node. Consequently, although dual AV node pathways appear to be common in patients undergoing surgical ablation of an accessory AV connection (21%), only a small group (3 of 13) of these patients are at risk for subsequent clinical AV node reentrant tachycardia.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of multiple pathways in the Wolff-Parkinson-White syndrome. Diagnostic problems and therapeutic implications

With advanced electrophysiological methods evaluation of functional properties and location of accessory pathways has become possible. Multiple pathways may, however, be difficult to outline with regard to localization and electrophysiological properties due to differences in refractoriness and/or fusion of conduction between the pathways. The investigational procedures in patients with multiple accessory pathways are described and discussed in connection with an illustrative patient with three accessory pathways, two of which are Kent's bundles and one most probably a Mahaim's bundle.     

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.     

Surgical Division of Right and Left Free Wall Accessory Atrioventricular Electrical Connections in a Child with Incessant Supraventricular Tachycardia

Abstract: Surgical division of right and left free wall accessory atrioventricular electrical connections in a child with incessant supraventricular tachycardia. D. Richards, A. Denniss, P. Russell, D. Johnson, N. Buchanan, C. Whight, A. Chong and J. Uther, Aust. N.Z. J. Med., 1982, 12 , pp. 52–55.
A child with Wolff-Parkinson-White syndrome developed incessant supraventricular tachycardia refractory to medical therapy and countershocks. Supraventricular tachycardias incorporating both right and left free wall accessory atrioventricular electrical connections were demonstrated. The more frequent, broad complex tachycardia utilised both the accessory connections and was independent of the atrioventricular node. The less frequent, narrow complex tachycardia utilised the atrioventricular node for anterograde conduction and the left sided accessory connection for retrograde conduction. Surgical division of the accessory connections restored normal sinus rhythm and eliminated supraventricular tachycardia.     

Radiofrequency ablation of accessory pathways guided by the location of the ligament of Marshall

INTRODUCTION: In humans, complex muscle connections are present near the junction between the coronary sinus (CS) and the ligament of Marshall. We hypothesize that these complex muscle connections participate in accessory pathway conduction. METHODS AND RESULTS: Electrophysiologic studies and radiofrequency ablation were performed in four patients with refractory AV reciprocating tachycardia. Case 1 was a 19-year-old male. Marshall bundle potentials were recorded by a catheter in the vein of Marshall. Radiofrequency energy application from that catheter resulted in successful ablation. Case 2 was a 43-year-old male who had undergone two unsuccessful radiofrequency ablation procedures of a left free-wall accessory pathway by conventional techniques. Coronary sinus electrography during tachycardia and ventricular pacing showed a long V-A interval. Radiofrequency energy application directed toward the ligament of Marshall eliminated the pathway conduction. Case 3 was a 17-year-old male who had undergone three unsuccessful ablation procedures. Radiofrequency energy application directed toward the stump of the vein of Marshall successfully eliminated the pathway conduction. Case 4 was a 20-year-old female who underwent one unsuccessful ablation procedure. Successful ablation was achieved in the left atrial free wall, approximately 1 cm above the AV annulus, at a location near the ligament of Marshall. CONCLUSION: We report four patients in whom successful accessory pathway ablation was achieved by targeting the ligament of Marshall. These findings suggest that the complex muscle connections among the coronary sinus, ligament of Marshall, and left atrium is important in accessory pathway conduction and maintenance of circus movement tachycardia in these patients.     

Radiofrequency catheter ablation of Mahaim tachycardia by targeting Mahaim potentials at the tricuspid annulus.

BACKGROUND--Reentrant tachycardias associated with Mahaim pathways are rare but potentially troublesome. Various electrophysiological substrates have been postulated and catheter ablation at several sites has been described. OBJECTIVE--To assess the efficacy and feasibility of targeting discrete Mahaim potentials recorded on the tricuspid annulus for the delivery of radiofrequency energy in the treatment of Mahaim tachycardia. PATIENTS--21 patients out of a consecutive series of 579 patients referred to one of three tertiary centres for catheter ablation of accessory pathways causing tachycardia. All had symptoms and presented with tachycardia of left bundle branch block configuration or had this induced at electrophysiological study. In all cases, the tachycardia was antidromic with anterograde conduction over a Mahaim pathway. RESULTS--6 patients had additional tachycardia substrates (4 had accessory atrioventricular connections and 2 had dual atrioventricular nodal pathways and atrioventricular nodal reentry). After ablation of the additional pathways, Mahaim potentials were identified in 16 (76%) associated with early activation of the distal right bundle branch and radiofrequency energy at this site on the tricuspid annulus abolished Mahaim conduction in all 16 cases. In 2 patients there was early ventricular activation at the annulus without a Mahaim potential but radiofrequency energy abolished pre-excitation. In the remaining patients no potential could be found (1 patient), no tachycardia could be induced after ablation of an additional pathway (1 patient), or no Mahaim conduction was evident during the study (1 patient). During follow up (1-29 months (median 9 months)) all but 1 patient remained symptom free without medication. CONCLUSIONS--Additional accessory pathways seem to be common in patients with Mahaim tachycardias. The identification of Mahaim potentials at the tricuspid annulus confirms that most of these pathways are in the right free wall and permits their successful ablation and the abolition of associated tachycardia.     

Antegrade conduction and AV node function in patients with unidirectional retrograde accessory pathways

In 26 patients with unidirectional retrograde accessory pathways (URAP), antegrade conduction properties were evaluated. During electrophysiologic study the interval from the low septal right atrial potential to the His bundle potential (LSRA-H) in sinus rhythm (SR) was found to be less than 60 msec in 7 out of the 18 patients with left-sided URAP and in one out of two patients with septal URAP. Each of the six patients with right-sided URAP had an LSRA-H equal to or greater than 70 msec. During atrial extrastimulus testing, LSRA-H failed to prolong more than 100 msec (LSRA-H increment equal to or less than 100 msec) in four of six patients with left-sided URAP and LSRA-H of less than 60 msec in SR as well as in the one of two patients with septal URAP in whom the LSRA-H in SR was less than 60 msec. During rapid atrial pacing, we found 1:1 AV node conduction at a pacing rate of more than 200 bpm in the one patient with septal URAP and in 7 out of 14 patients with left-sided URAP who could be assessed. Three of these patients had progression from 1:1 AV conduction to 2:1 AV block without intervening Wenckebach. In conclusion, accelerated AV node conduction in SR and reduced AV node function during rapid atrial pacing or extrastimulus testing was found in 44% of our patients with left-sided or septal URAP. Since these patients are at higher risk for faster ventricular response to atrial flutter and fibrillation and for high frequency during supraventricular tachycardia, these findings were of clinical relevance.(ABSTRACT TRUNCATED AT 250 WORDS)     

Electrogram criteria for identification of appropriate target sites for radiofrequency catheter ablation of accessory atrioventricular connections.

BACKGROUND. Catheter ablation of accessory atrioventricular (AV) connections using radiofrequency current has been demonstrated to be effective in the majority of patients with the Wolff-Parkinson-White syndrome or paroxysmal supraventricular tachycardia involving a concealed accessory AV connection. However, electrogram criteria have not been established to guide attempts at radiofrequency catheter ablation. METHODS AND RESULTS. The characteristics of local electrograms recorded at successful and unsuccessful sites of radiofrequency catheter ablation were determined in 132 patients. Electrograms recorded at a total of 438 sites were analyzed: 338 recorded during ablation of 90 manifest accessory AV connections and 100 recorded during ablation of 44 concealed accessory AV connections. During ablation of manifest accessory AV connections, the independent predictors of outcome were electrogram stability (p less than 0.001), the interval between activation of the ventricular electrogram and onset of the QRS complex (p less than 0.001), and the presence of an accessory AV connection potential (p less than 0.001). Radiofrequency energy delivery at sites demonstrating stable electrograms, a probable or possible accessory AV connection potential, and activation of the local ventrical electrogram before the onset of the QRS complex had a 57% probability of success compared with a 3% probability of success at sites without these features. During ablation of concealed accessory AV connections, the independent predictors of outcome were electrogram stability (p = 0.02), the presence of an accessory AV connection potential (p = 0.05), and the presence of retrograde continuous electrical activity (p = 0.04). Sites demonstrating a stable local electrogram, an accessory AV connection potential, and retrograde continuous electrical activity had an 82% probability of success compared with only a 5% probability of success at sites demonstrating none of these features. CONCLUSIONS. The local electrogram parameters of greatest importance in predicting the success or failure of radiofrequency catheter ablation of accessory AV connections are electrogram stability, the presence of an accessory AV connection potential, and the timing of ventricular activation relative to the QRS complex (for manifest accessory AV connections) or retrograde continuous electrical activity (for concealed accessory AV connections). Awareness of these variables during attempts at radiofrequency catheter ablation of accessory AV connections may minimize the number of unnecessary applications of radiofrequency energy.