Sustained atrial tachycardia in adult patients. Electrophysiological characteristics, pharmacological response, possible mechanisms, and effects of radiofrequency ablation

Supraventricular Tachyarrhythmia

The main treatment modalities for supraventricular tachycardia are medications and catheter ablation. Ablation is appropriate therapy for paroxysmal supraventricular tachycardia in patients who have a preference for ablation over medications, symptoms that are refractory to medications, severe symptoms, Wolff-Parkinson-White syndrome, or incessant tachycardia. Ablation also is reasonable as first-line therapy in patients with recurrent typical atrial flutter.

Atrial tachycardias originating from the atrial septum: electrophysiologic characteristics and radiofrequency ablation

INTRODUCTION

The characteristics of atrial tachycardia (AT) have varied widely among different reports. The anatomic locations of ATs may bias the results. We propose that septal ATs and free-wall ATs have different characteristics.

METHODS AND RESULTS

One hundred forty-one patients with AT underwent electropharmacologic study, endocardial mapping, and radiofrequency ablation. Forty-nine (34.7%) patients had septal AT originating from the anteroseptal, mid-septal, and posteroseptal areas. Tachycardia cycle length was similar between septal AT and free-wall AT (367 +/- 46 msec vs 366 +/- 58 msec, P > 0.05). More patients with septal AT required isoproterenol to facilitate induction (44.9% vs 31.5%, P <.0.05). Septal AT was more sensitive to adenosine than free-wall AT (84.4% vs 67.8%, P < 0.05). Only posteroseptal AT showed a positive P wave in lead V1 and negative P wave in all the inferior leads (II, III, aVF). Radiofrequency catheter ablation had a comparable success rate for septal AT and free-wall AT (96% vs 95%) without impairment of AV conduction. During follow-up of 49 +/- 13 months (range 17 to 85), the recurrence rate was similar for septal AT and free-wall AT (3.2% vs 4.6%, P = 0.08).

CONCLUSION

Septal AT has electrophysiologic characteristics that are distinct from those of free-wall AT. Catheter ablation of the septal AT is safe and effective.

Temperature-sensitive focal atrial tachycardia in the left atrium

Temperature sensitivity has not been reported in focal atrial tachycardia. We describe a patient with a left atrial tachycardia whose tachycardia rate was affected by hot and cold drinks. The effects were still evident after autonomic blockade. The arrhythmia focus was located at the entrance of the left upper pulmonary vein. Radiofrequency ablation was carried out, which proved to be difficult, but it was successful after several applications of energy, suggesting an epicardial location of the arrhythmia focus. Sensitivity of atrial tachycardia rate to the temperature of food or drink ingested suggests a left atrial focus with a posterior and possibly epicardial location.

Computer-assisted animation of atrial tachyarrhythmias recorded with a 64-electrode basket catheter

OBJECTIVES

The aim of this study was to assess the value of a new mapping technique based on computer-assisted animation of multielectrode basket catheter (BC) recordings in patients with atrial arrhythmias.

BACKGROUND

The three-dimensional activation patterns of cardiac arrhythmias are not completely understood owing to limitations of conventional mapping techniques.

METHODS

The study included 32 patients with atrial tachycardia (AT) and 38 patients with atrial flutter (AFL). A software program was developed to analyze the activation patterns based on 56 bipolar electrograms recorded with a 64-electrode BC deployed in the right atrium (RA).

RESULTS

The total time needed for the animation of activation patterns of atrial arrhythmias was 5 +/- 0.8 min. In 22 patients with right AT, the animated maps revealed that arrhythmia was unifocal in 15 patients, multifocal in 2 patients, polymorphic in 4 patients and reentrant in 1 patient. In 10 patients with left AT, breakthroughs on the right side of the septum (2 in 8 patients and 1 in 2 patients) and a left-to-right activation of the RA were demonstrated. In patients with typical AF, the reentrant excitation was a broad activation front with preferential propagation around the tricuspid annulus. In patients with atypical AFL, the reentry circuit involved one of the venae cavae and a line of block located in the posterior wall.

CONCLUSIONS

The computer-assisted animation of multiple electrograms recorded with a BC is a valuable mapping tool that delineates the three-dimensional activation patterns of various atrial arrhythmias. The technique is appropriate for complex, short-lived or unstable arrhythmias.

Computer-controlled heart rate increase by isoproterenol infusion: mathematical modeling of the system

The purpose of this study was mathematical modeling of the heart rate (HR) response to isoproterenol (Iso) infusion. We developed a computerized system for the controlled increase of HR by Iso, based on a modified proportional-integral controller. HR was measured in conscious, freely moving rats. We found that the steady-state HR can be described as a hyperbolic power function of the steady-state Iso flow rate. This dependence was coupled with a first-order difference equation to form a pharmacodynamic model that reliably describes the relationship between HR and Iso flow for any arbitrary form of Iso flow function. In simulation studies, we showed that the model continued to follow the HR curve from real-time experiments far beyond the initial "learning interval" from which its parameters were calculated. Our results suggest that the predictive ability and the simplicity of calculating the parameters render this pharmacodynamic model appropriate for use within future advanced, model-based, adaptive control systems and as a part of larger cardiovascular models.

Atrial Tachycardia

The available therapies for atrial tachycardia include the use of antiarrhythmic drugs, radiofrequency catheter ablation, and antiarrhythmic surgery. The growing realization that catheter ablation cures atrial tachycardia with high efficacy and safety has contributed to the increasing popularity of the procedure and makes it the therapy of choice in symptomatic patients. Antiarrhythmic drugs are thought to be effective acutely in 40% to 60% of patients, but their long-term efficacy remains poorly defined. Infrequently, atrioventricular nodal catheter ablation combined with pacing may be needed in patients whose arrhythmias are refractory to antiarrhythmic drugs and curative radiofrequency ablation. Antiarrhythmic surgery has a limited role as a therapy of last resort.

Change of atrial refractory period after short duration of rapid atrial pacing: regional differences and possible mechanisms

It is unknown whether there are regional differences in the change of atrial effective refractory period (ERP) after a short duration of rapid atrial pacing. Furthermore, the effects of calcium channel and potassium channel on this phenomenon have not been extensively investigated. In opened-chest dogs, the endocardial monophasic action potential duration at 90% repolarization (APD90) from the right atrial appendage, and ERP from seven atrial sites were measured before and after rapid atrial pacing at 800 beats/min for 30 minutes. Both atrial ERP and APD90 significantly shortened after rapid atrial pacing. The postpacing atrial ERP and APD90 shortening persisted for 119 +/- 3 and 123 +/- 4 seconds after cessation of pacing, respectively. There was no significant difference in the magnitude or recovery course of atrial ERP shortening after pacing among the seven atrial sites. Pretreatment with nicorandil and d-sotalol had no effects on the magnitude or recovery course of atrial ERP shortening after pacing. However, the degree of ERP and APD90 shortening after pacing was significantly attenuated in the verapamil and ryanodine groups; furthermore, the recovery of ERP and APD90 after cessation of pacing was faster in the two groups. In conclusion, shortening of atrial ERP induced by short-duration rapid atrial pacing was uniform in both atria. Both the adenosine triphosphatase (ATP) dependent potassium current and rapid component of the delayed rectifier did not significantly influence this phenomenon, but both the verapamil and ryanodine could significantly attenuate the degree of atrial ERP and APD90 shortening.

Differential effects of adenosine on focal and macroreentrant atrial tachycardia

INTRODUCTION

The effects of adenosine on atrial tachycardia (AT) remain controversial, and the mechanistic implications of adenosine termination have not been fully established. The purpose of this study was to elucidate the differential effects of adenosine on focal and macroreentrant AT and describe the characteristics of adenosine-sensitive AT.

METHODS AND RESULTS

Thirty patients received adenosine during AT. Tachycardia origins were identified as focal or macroreentrant during invasive electrophysiologic studies. Responses to adenosine were analyzed and characterized as tachycardia termination, transient suppression, or no effect. Electrophysiologic studies demonstrated a focal origin of tachycardia in 17 patients. Adenosine terminated focal tachycardias in 14 patients (dose 7.3 +/- 4.0 mg) and transiently suppressed the arrhythmias in three others (dose 10.0 +/- 6.9 mg). A macroreentrant mechanism was demonstrated in 13 patients; adenosine terminated only one of these tachycardias and had no effect on the remaining 12 patients (dose 10.2 +/- 2.9 mg). Four classes of adenosine-sensitive AT were identified. Class I consisted of nine patients with tachycardia arising from the crista terminalis; these tachycardias also terminated with verapamil (4/4). Class II consisted of four patients with repetitive monomorphic AT arising from diverse sites in the right atrium; these either slowed or terminated in response to verapamil (2/2). Class III consisted of the three patients with transient suppression and demonstrated electropharmacologic characteristics consistent with an automatic mechanism, including insensitivity to verapamil (2/2). In the one patient with macroreentrant AT that was comprised of decremental atrial tissue, adenosine terminated tachycardia in a zone of decremental slow conduction (Class IV); this tachycardia slowed with verapamil.

CONCLUSIONS

Adenosine-sensitive AT is usually focal in origin and arises either from the region of the crista terminalis (inclusive of the sinus node) or from diverse atrial sites with an incessant nonsustained repetitive pattern. Although most forms of macroreentrant AT are insensitive to adenosine, rarely macroreentrant AT with zones of decremental slow conduction can demonstrate adenosine sensitivity.

Right atrial focal atrial fibrillation: electrophysiologic characteristics and radiofrequency catheter ablation

INTRODUCTION

Information about focal atrial fibrillation (AF) originating from the right atrium has not been well described. The purposes of this study were to demonstrate the electrophysiologic characteristics and radiofrequency catheter ablation in patients who had right atrial focal AF.

METHODS AND RESULTS

From January 1996 to September 1998, 172 patients with clinically documented attacks of paroxysmal AF were referred to this institution for electrophysiologic study and/or radiofrequency catheter ablation. Anterior free wall, crista terminalis, and right and left superior pulmonary veins were mapped simultaneously. Eight patients (4.7%) had right atrial focal AF, consistent activation sequence, irregular fibrillation interval (mean fibrillation interval: 164 +/- 11 msec), and episodes of exit block from the initiating foci observed. The presumed ablation site was chosen on the basis of the earliest bipolar activity relative to an atrial electrogram reference during the initiation of AF. After application of 2 +/- 1 radiofrequency pulses, AF was eliminated without recurrence during the follow-up period (mean: 14 +/- 8 months; range: 3 to 25). Twenty-four-hour Holter monitoring showed that the number of atrial premature beats decreased significantly at the 3-month follow-up (4,216 +/- 411 vs 135 +/- 14 beats/day).

CONCLUSION

Right atrial focal AF is one subgroup of focal AF, and it can be cured by radiofrequency catheter ablation.

Double multielectrode mapping catheters facilitate radiofrequency catheter ablation of focal atrial fibrillation originating from pulmonary veins

INTRODUCTION

Several reports have demonstrated that focal atrial fibrillation (AF) may arise from pulmonary veins (PVs). The purpose of this study was to investigate the safety and efficacy of using double multielectrode mapping catheters in ablation of focal AF.

METHODS AND RESULTS

Forty-two patients (30 men, 12 women, age 65+/-14 years) with frequent attacks of paroxysmal AF were referred for catheter ablation. After atrial transseptal procedure, two long sheaths were put into the left atrium. Two decapolar catheters were put into the right superior PV (RSPV) and left superior PV (LSPV), or inferior PVs if necessary, guided by pulmonary venography. All the patients had spontaneous initiation of AF either during baseline (2 patients), after isoproterenol infusion (8 patients) or high-dose adenosine (2 patients), after short duration burst pacing under isoproterenol (14 patients), or after cardioversion of pacing-induced AF (16 patients). The trigger points of AF were from the LSPV (12 patients), RSPV (8 patients), and both superior PVs (19 patients). The trigger points from PVs (total 61 points) were 18 (30%) in the ostium of PVs and 43 inside the PVs (9 to 40 mm). After 6+/-3 applications of radiofrequency energy, 57 of 61 triggers were completely eliminated, and the other 4 triggers were partially eliminated. During a follow-up period of 8+/-2 months, 37 patients (88%) were free of symptomatic AF without any antiarrhythmic drugs. Twenty patients received a transesophageal echocardiogram, and 19 showed small atrial septal defects (2.8+/-1.2 mm) with trivial shunt. Fifteen defects closed spontaneously 1 month later.

CONCLUSION

The technique using double multielectrode mapping catheters is a relatively safe and highly effective method for mapping and ablation of focal AF originating from PVs.

Bezold-Jarisch-like reflex during radiofrequency ablation of the pulmonary vein tissues in patients with paroxysmal focal atrial fibrillation

INTRODUCTION

Information is lacking about the occurrence of ablation-related proarrhythmic events during application of radiofrequency (RF) energy at the pulmonary veins in patients with paroxysmal focal atrial fibrillation. The purpose of this study was to assess the theoretical risk of reflex bradycardia and hypotension response during RF ablation of these regions rich in endocardial nerve terminals.

METHODS AND RESULTS

Among the 40 consecutive patients (29 men, 11 women; mean age 65+/-12 years) with clinically documented frequent attacks of paroxysmal atrial fibrillation who underwent superior pulmonary vein ablation for left focal atrial fibrillation, 6 patients (15%) developed bradycardia-hypotension syndrome during energy delivery. A single atrial fibrillation trigger focus in the left or right superior pulmonary vein was found in 3 and 1 patients, respectively. Two patients had two trigger foci originating from the orifice or proximal part of both superior pulmonary veins. After RF current was applied for a period of 14+/-10 seconds, 2 patients developed junctional rhythm and sinus bradycardia, another 2 patients had profound sinus bradycardia, 1 patient had two episodes of sudden onset of complete AV block with resultant 9.5-second asystole, and 1 patient showed profound sinus bradycardia, transient AV block, and an 8-second asystole due to sinus arrest. Blood pressure fell when any substantial bradyarrhythmias occurred. All 6 patients were free of rhythm disturbances during the postablation follow-up period (mean 8+/-2 months).

CONCLUSION

RF catheter ablation of the pulmonary vein tissues could evoke a variety of profound bradycardia-hypotension responses. The Bezold-Jarisch-like reflex might be the underlying mechanism.

Radiofrequency current application on immature porcine atrial myocardium: no evidence of areas of slow conduction after 12-month follow-up

INTRODUCTION

Radiofrequency current (RFC) application is a widely used procedure for treatment of supraventricular arrhythmias. The purpose of this study was to investigate late electrophysiologic sequelae of RFC lesions at immature atrial myocardium in pigs, as they have not yet been systematically investigated in vitro.

METHODS AND RESULTS

RFC application (temperature guided) was performed in seven piglets (mean age 6 weeks) by a steerable 6-French electrode catheter positioned at the lateral aspect of the tricuspid valve annulus. After 12 months, hearts were removed, and lesions with surrounding tissue were isolated. The viable tissue at the border of the specimen was paced with a cycle length of 500 and 600 msec. One hundred fifty impalements were performed on each specimen using capillary microelectrodes to record action potential characteristics from the lesion's surface and the surrounding tissue. In all seven specimens, no transmembrane action potentials from the fibrotic surface of each of the lesions could be recorded. The surrounding viable tissue was sharply demarcated electrically. No areas of slow conduction were detected. Action potential characteristics as mean maximum diastolic transmembrane potential, mean action potential duration at 90% repolarization, and upstroke velocity of phase 0 of the action potential were all normal.

CONCLUSION

No evidence of areas of slow conduction 12 months after RFC application at immature atrial myocardium suggests that this technique is safe regarding occurrence of late atrial tachyarrhythmias after the procedure.

Simple electrocardiographic criteria for identifying the site of origin of focal right atrial tachycardia

To construct an algorithm for identifying the precise site of origin of focal right atrial tachycardia (RAT), we analyzed the P wave configuration in 32 patients with RAT who underwent successful radiofrequency catheter ablation. The RA was divided into three areas in the left anterior oblique view: superolateral, inferolateral, and inferomedial. There were 17 RATs arising from the crista terminalis (CT-AT), 12 from the tricuspid annulus (TA-AT), and 3 from the septum away from the TA (Sep-AT). A negative P wave in lead aVR identified CT-AT with a sensitivity (sens) of 100% and a specificity (spec) of 93%. In CT-ATs, positive P waves in the inferior leads differentiated superolateral AT from inferolateral AT with a sens of 86% and a spec of 100%. In any type of AT with inferomedial or inferolateral foci, the P wave deflections in at least one of the inferior leads was negative, and negative P waves in leads V5 and V6 identified inferomedial AT with a sens of 92% and a spec of 100%. In ATs near the apex of Koch's triangle, the P wave duration in the inferior leads was shorter than during sinus rhythm.

CONCLUSIONS

(1) the P wave configuration in lead aVR can easily differentiate CT-AT from TA-AT and Sep-AT; (2) the P wave configuration in the inferior leads helps to determine a superior versus inferior origin in any type of AT; (3) in inferior AT, the P wave polarity in leads V5 and V6 is useful in determining a lateral versus medial origin; (4) this algorithm can predict accurately the origin of AT.

Electrophysiologic characteristics of different ectopic rhythms during slow pathway ablation in patients with atrioventricular nodal reentrant tachycardia

The presence of ectopic rhythm has been considered to be the most important marker for successful slow pathway ablation, but the details of different ectopic rhythms have not been well described. This study included 83 consecutive patients with typical AV node reentrant tachycardia who underwent slow pathway ablation. The interval between the atrial signals of the His bundle electrogram and the distal ablation catheter [A(H)-A(Ab)], and the interval between the atrial components of the distal ablation catheter and the ostium of coronary sinus catheter [A(Ab)-A(CSos)] were measured. One hundred episodes of ectopic rhythm occurred with 81 (81%) successful applications. There are two different origins and three activation sequences of ectopic rhythms, including HIS rhythm (78 applications, the earliest atrial activation in the His bundle electrogram), CSos rhythm (6 applications, the earliest atrial signal in the coronary sinus ostium electrogram) and CSos preceding HIS (CSos-->HIS) rhythm (16 applications, the atrial activation sequences changing from CSos to HIS rhythm). The CSos rhythm had a shorter mean cycle length (445 +/- 81 vs. 511 +/- 132 vs. 579 +/- 140 ms, p < 0.05), a shorter [A(Ab)-A(CSos)] interval (-2.5 +/- 9.8 vs. 14.1 +/- 11.2 vs. 12.8 +/- 8.4 ms, p < 0.05) and a lower success rate (33% vs. 84% vs. 94% p < 0.05) than HIS rhythm and CSos-->HIS rhythm. Otherwise, the mean cycle length of ectopic rhythm was significant shorter in successful than in failed ablation (506 +/- 135 vs. 559 +/- 118 ms, p = 0.04). In conclusion, we found two different origins and three activation sequences of ectopic rhythms. CSos rhythm had a lower success rate in ablation of slow pathway, thus it was a poor marker for successful ablation.

Focal atrial tachycardia: reanalysis of the clinical and electrophysiologic characteristics and prediction of successful radiofrequency ablation

INTRODUCTION

Reports about the clinical and electrophysiologic characteristics of focal atrial tachycardia vary widely. Furthermore, the impact of age, gender, associated cardiac diseases, mechanism, location of atrial tachycardia, and the prediction of results of radiofrequency catheter ablation was not clear. The purpose of this study was to further understand the clinical and electrophysiologic characteristics of focal atrial tachycardia and the prediction of results of radiofrequency ablation.

METHODS AND RESULTS

We searched the literature published between January 1969 and July 1997 using the key word "atrial tachycardia" from the MEDLINE and National Library of Medicine systems. The items analyzed were age, sex, cardiac disease, mechanism, attack pattern, cycle length, location, number of atrial tachycardias, results of ablation, and recurrence after ablation. Multivariate analysis showed that age and paroxysmal type of tachycardia were independent predictors of nonautomatic mechanism; age and presence of other cardiac diseases were independent predictors of multiple atrial tachycardias, and age also was the independent predictor of right-sided atrial tachycardia. Atrial tachycardia located in the right atrium was the only significant predictor of successful radiofrequency catheter ablation. Other cardiac diseases and multiple atrial tachycardias were the significant predictors of recurrence after initial successful radiofrequency catheter ablation.

CONCLUSION

Patient age is closely related to the clinical and electrophysiologic characteristics of atrial tachycardia based on our reanalysis, which found that patient age is an independent predictor of nonautomatic mechanism, right atrial location, existence of multiple atrial tachycardias, and recurrence of atrial tachycardia after initial successful ablation.

"Cristal tachycardias": origin of right atrial tachycardias from the crista terminalis identified by intracardiac echocardiography

OBJECTIVES

We sought to use intracardiac echocardiography (ICE) to identify the anatomic origin of focal right atrial tachycardias and to define their relation with the crista terminalis (CT).

BACKGROUND

Previous studies using ICE during mapping of atrial flutter and inappropriate sinus tachycardia have demonstrated an important relation between endocardial anatomy and electrophysiologic events. Recent studies have suggested that right atrial tachycardias may also have a characteristic anatomic distribution.

METHODS

Twenty-three consecutive patients with 27 right atrial tachycardias were included in the study. ICE was used to facilitate activation mapping in relation to endocardial structures. A 20-pole catheter was positioned along the CT under ICE guidance. ICE was also used to assist in guiding detailed mapping with the ablation catheter in the right atrium.

RESULTS

Of 27 focal right atrial tachycardias, 18 (67%, 95% confidence interval [CI] 46% to 83%) were on the CT (2 high medial, 8 high lateral, 6 mid and 2 low). ICE identified the location of the tip of the ablation catheter in immediate relation to the CT in all 18 cases. The 20-pole mapping catheter together with echocardiographic visualization of the CT provided a guide to the site of tachycardia origin along this structure. Radiofrequency ablation was successful in 26 (96%) of 27 (95% CI 81% to 100%) right atrial tachycardias.

CONCLUSIONS

This study demonstrates that approximately two thirds of focal right atrial tachycardias occurring in the absence of structural heart disease will arise along the CT. Recognition of this common distribution may potentially facilitate mapping and ablation of these tachycardias.

Recognition and Management of Cardiac Arrhythmias: Part I. General Principles and Supraventricular Tachyarrhythmias

Management of cardiac arrhythmias has undergone major changes in the last few years. In the first part of this review, general principles of arrhythmia diagnosis are discussed. New techniques such as event recording and signal-averaged electrocardiography have a significant role in the clinical management of arrhythmias. Many new antiarrhythmic drugs are now available. Suppression of premature ventricular contractions to prevent malignant ventricular arrhythmias has been demonstrated to be an ineffective strategy. Implantable defibrillators and radio frequency ablation have revolutionized the treatment of arrhythmias. Differentiation of various supraventricular tachycardias has become very important since some these arrhythmias may be cured by radiofrequency ablation. Diagnosis and treatment of common supraventricular arrhythmias are discussed.

Role of the surface electrocardiogram in the diagnosis of patients with supraventricular tachycardia

In this era of interventional electrophysiology, the accuracy of the electrocardiogram in diagnosis of supraventricular tachycardia could be improved by detailed endocardial mapping and confirmed by results of radiofrequency catheter ablation. This article describes the electrocardiographic characteristics for different types of supraventricular tachycardia: atrial fibrillation, atrial flutter, atrial tachycardia, atrioventricular reciprocating tachycardia using an accessory pathway, and atrioventricular node reentrant tachycardia. Several limitations, including the identification of P wave morphologies and polarities and separation between the terminal part of T wave and P wave during tachycardia, should be resolved before an accurate algorithm of the 12-lead surface electrocardiogram is developed for the diagnosis of supraventricular tachycardia.

Catheter ablation for patients with atrial tachycardia

Although atrial tachycardias are relatively rare, their poor response to standard therapies, the suboptimal hemodynamic results of complete atrioventricular node ablation and pacer implantation, and their potential for serious hemodynamic effects make management difficult. Although their mechanisms are complex and divergent, catheter ablation has proven to be highly effective in management of atrial tachycardias. This article discusses arrhythmia mechanisms and therapeutic approaches by catheter ablation.

[Arrhythmias and pregnancy]

Although arrhythmias are one of the most frequent consultations during pregnancy, fortunately the majority are benign. Usually, they are well tolerated assuming they occur in patients with structurally normal hearts. However, pregnancy adds a new aspect to the so called "arrhythmia tolerance", because arrhythmia and therapy may jeopardize the fetus. For acute treatment of narrow and wide tachycardias, with few exceptions, antiarrhythmic medications appear to be safe. In addition to the relative security of drugs such as adenosine, digoxin, propranolol, procainamide and flecainide, we could use direct current countershock with no evidence of significant complications. Because no drug is absolutely safe, chronic pharmacologic therapy is best avoided during pregnancy. Finally, radiofrequency ablation could be recommended as an alternative in women with previous tachycardias who would like to become pregnant.

Ablation therapy for cardiac arrhythmias

Ablation has become an important and, in some cases, the first-line therapy for a number of tachyarrhythmias. The feasibility of treating arrhythmias with ablation was initially demonstrated with surgical ablation techniques. Recently, catheter ablation techniques have replaced the surgical approach in nearly all cases. Catheter ablation is highly effective for the Wolff-Parkinson-White syndrome, atrioventricular nodal reentry, and atrial ectopic tachycardia. It is effective for atrial flutter, although approximately one quarter of patients treated with catheter ablation continue to require therapy for concomitant atrial fibrillation. The surgical maze procedure has proved to be feasible for preventing atrial fibrillation. The risks and long-term efficacy of catheter ablation maze procedures for atrial fibrillation need to be defined. The efficacy of ablation for ventricular tachycardia varies with the type of tachycardia. Catheter ablation is very effective for the rare idiopathic ventricular tachycardias that occur in structurally normal hearts and for bundle-branch reentry ventricular tachycardia, which occurs most frequently in patients with dilated cardiomyopathy. When performed at an experienced center, surgical ablation is an excellent option for selected patients with ventricular tachycardia due to prior myocardial infarction who have a discrete aneurysm but otherwise well-preserved ventricular function. Catheter ablation shows promise for this arrhythmia, but it can be offered only to those patients who have relatively slow tachycardias that allow catheter mapping. Substantial advances in mapping and ablation technology will continue to occur, allowing nonpharmacologic control of cardiac arrhythmias to be achieved in an ever greater number of patients.

Use of intracardiac echocardiography in interventional electrophysiology

Intracardiac echocardiography is emerging as a potentially useful tool during RF ablation procedures. There are a number of potential benefits of direct endocardial visualization during RF ablation including: (1) precise anatomical localization of the ablation catheter tip in relation to important endocardial structures, which cannot be visualized with fluoroscopy; (2) reduction in fluoroscopy time; (3) evaluation of catheter tip tissue contact; (4) confirmation of lesion formation and identification of lesion size and continuity; (5) immediate identification of complications; and (6) as a research tool to help in understanding the critical role played by specific endocardial structures in arrhythmogenesis. This article will review existing data and speculate as to possible future roles for intracardiac echocardiography in interventional electrophysiology.

Adenosine-sensitive atrial reentrant tachycardia originating from the atrioventricular nodal transitional area

INTRODUCTION

Atrial tachycardia shows wide variations in its electrophysiologic properties and sites of origin. We report an atrial tachycardia with ECG manifestations and electrophysiologic characteristics similar to an atypical form of AV nodal reentrant tachycardia (AVNRT).

METHODS AND RESULTS

This supraventricular tachycardia was observed in 11 patients. It was initiated by atrial extrastimulation with an inverse relationship between the coupling interval of an extrastimulus and the postextrastimulus interval. Its induction was not related to a jump in the AH interval, and its perpetuation was independent of conduction block in AV node. Ventricular pacing during tachycardia demonstrated AV dissociation without affecting the atrial cycle length. A very small dose of adenosine triphosphate (mean 3.9 +/- 1.2 mg) could terminate the tachycardia. The earliest atrial activation during tachycardia was recorded at the low anteroseptal right atrium with a different intra-atrial activation sequence from that recorded during ventricular pacing, where the tachycardia was successfully ablated in 9 of 10 attempted patients. Bidirectional AV nodal conduction remained unaffected after successful ablation.

CONCLUSION

There may be an entity of adenosine-sensitive atrial tachycardia probably due to focal reentry within the AV node or its transitional tissues without involvement of the AV nodal pathways. This tachycardia can be ablated without disturbing AV nodal conduction from the right atrial septum.

Influence of beta-adrenergic and vagal activity on the effect of exogenous adenosine on supraventricular tachycardia termination

Adenosine, which binds to cell surface receptors and couples with guanosine triphosphate-binding inhibitory proteins (G(i)), is potent in terminating supraventricular tachycardia (SVT). However, whether the differences in autonomic tone will influence this effect remains unknown. This study was designed to investigate the role of beta-adrenergic and vagal activity on the action of adenosine. Forty patients with clinically documented SVT (22 with atrioventricular node reentrant tachycardia and 18 with atrioventricular reciprocating tachycardia) were divided into 4 groups with 10 patients in each group. In groups 1 and 2, adenosine was intravenously injected during the baseline state and during infusion of isoproterenol (2 and 4 microg/min, respectively). Group 2 patients received atropine (0.04 mg/kg) injection before isoproterenol infusion. In groups 3 and 4, intravenous injection of adenosine was given during the baseline state and after injection of atropine (0.02 and 0.04 mg/kg, respectively). Group 4 patients received propranolol (0.2 mg/kg) before atropine injection. The minimal dose of adenosine to terminate tachycardia during isoproterenol infusion of 2 microg/min was greater than that during the baseline state in both groups 1 and 2. The minimal dose of adenosine during isoproterenol infusion with 4 microg/min was higher than that with 2 microg/min in group 2, but not in group 1 patients. In both groups 3 and 4, the minimal dose of adenosine required to terminate tachycardia during atropine injection with 0.02 mg/kg was greater than that during the baseline state. The minimal effective dose of adenosine during atropine injection with 0.04 mg/kg was higher than that with 0.02 mg/kg in group 4, but not in group 3 patients. In conclusion, either limb of the autonomic nervous system may modulate the adenosine dosage required for termination of SVT. Patients taking drugs such as beta blockers or vagolytic agents may need alterations in the dose of adenosine for therapy.

Results of radiofrequency ablation in patients with clinically documented, but noninducible, atrioventricular node reentrant tachycardia and orthodromic atrioventricular reciprocating tachycardia

Among 1,281 patients with symptomatic supraventricular tachycardia, 34 patients (2.7%) with presumed diagnosis of atrioventricular node reentrant tachycardia and orthodromic atrioventricular reciprocating tachycardia did not have inducible tachycardia in the electrophysiologic laboratory. Application of radiofrequency energy to the presumed arrhythmogenic sites could achieve a high success rate, with a low recurrence rate in these patients.

Ventricular tachycardia: pathophysiology and radiofrequency catheter ablation

Limitations of pharmacological therapy for VT have led to great interest in alternative nonpharmacological therapies. The appeal of a curative therapy for VT initially led to the search for operative techniques to identify and destroy the underlying substrate, and more recently, has resulted in the development of catheter techniques to achieve the same goal in the electrophysiology laboratory. Investigations into the pathophysiology of VT have resulted in the recognition that this arrhythmia reflects a mechanistically and anatomically heterogeneous set of disorders. Recent growth in our understanding of these distinctions has both led to, and resulted from, simultaneous advances in catheter ablation techniques. The clinical electrophysiology laboratory has served as a testing ground for theories derived from in vitro and animal experiments while also providing its own set of human experimental data regarding the pathophysiology and treatment of VT. As a result of this process, several distinct forms of VT that are amenable to catheter ablation have been characterized. This article will summarize current knowledge of the pathophysiology of various VT subtypes and of techniques for catheter mapping and ablation.

A new electrocardiographic algorithm using retrograde P waves for differentiating atrioventricular node reentrant tachycardia from atrioventricular reciprocating tachycardia mediated by concealed accessory pathway

OBJECTIVES

The purpose of this study was to use an electrocardiographic (ECG) algorithm, derived from the results of radiofrequency ablation, to discriminate atrioventricular node reentrant tachycardia (AVNRT) from atrioventricular reciprocating tachycardia (AVRT) and to localize a concealed accessory pathway, prospectively.

BACKGROUND

Information about ECG criteria for differentiating AVNRT from AVRT is limited and has not been confirmed by surgical or catheter ablation.

METHODS

Four hundred six ECGs (obtained from 406 different patients) that demonstrated narrow QRS complex (< 0.12 s) supraventricular tachycardia with an RP' interval less than the P'R interval or pseudo r' wave in lead V1 or pseudo S wave in inferior leads, or both, were examined, and the results were confirmed by radiofrequency catheter ablation. The initial 226 ECGs were analyzed to develop a stepwise algorithm, and the subsequent 180 ECGs were prospectively evaluated by the new algorithm.

RESULTS

The presence of a pseudo r' wave in lead V1 or a pseudo S wave in leads II, III, aVF indicated anterior-type AVNRT with an accuracy of 100%. With the difference of RP' intervals in leads V1 and III > 20 ms, posterior-type AVNRT could be differentiated from AVRT utilizing a posteroseptal pathway with a sensitivity of 71% (95% confidence interval [CI] 55% to 89%), a specificity of 87% (95% CI 67% to 97%) and a positive predictive value of 75% (95% CI 56% to 91%). According to the polarity of retrograde P waves in leads V1, II, III, aVF and I during AVRT, the concealed accessory pathway could be localized to one of the nine regions on the atrioventricular annuli with an accuracy of 75% (for a right midseptal pathway) to 93.8% (for a left posterior pathway). Overall, the new algorithm had an accuracy of 97.8% in discriminating AVNRT from AVRT and 88.1% in localizing a concealed accessory pathway, prospectively. Prediction was incorrect in only 15 patients (9.1%).

CONCLUSIONS

The new ECG algorithm derived from the analysis of retrograde P waves during tachycardia could provide a criterion for differential diagnosis between AVNRT and AVRT and for predicting the location of concealed accessory pathways.

Electrophysiologic characteristics and radiofrequency catheter ablation in patients with clockwise atrial flutter

INTRODUCTION

Although the mechanism and radiofrequency catheter ablation of counterclockwise (typical) atrial flutter have been studied extensively, information about the electrocardiographic and electrophysiologic characteristics and effects of radiofrequency ablation in patients with clockwise atrial flutter is limited.

METHODS AND RESULTS

Thirty consecutive patients with clinically documented paroxysmal clockwise atrial flutter were studied. Endocardial recordings and entrainment study using a "halo" catheter with 10 electrode pairs in the right atrium were performed. Radiofrequency energy was applied to the inferior vena cava-tricuspid annulus (IVC-TA) and/or coronary sinus ostium-tricuspid annulus (CSO-TA) isthmus to evaluate the effects of linear catheter ablation. Eighteen patients had both counterclockwise and clockwise atrial flutters, and 12 patients had only clockwise atrial flutter. Both forms of atrial flutter had similar flutter cycle lengths (232 +/- 30 vs 226 +/- 25 msec, P = 0.526) but reverse activation sequences. Right atrial pacing at a cycle length 20 msec shorter than the flutter cycle length from the CSO-TA isthmus, IVC-TA isthmus, and the area between the two isthmuses revealed concealed entrainment with stimulus-to-P wave intervals of 32 +/- 19, 95 +/- 14, and 50 +/- 17 msec (P = 0.022) in the counterclockwise form, and 110 +/- 12, 40 +/- 20, and 60 +/- 15 msec (P = 0.018) in the clockwise form. In clockwise atrial flutter, 20 patients with biphasic P waves in the inferior leads had the presumed exit site of slow conduction area located at the low posterolateral right atrium; 10 patients with positive P waves in the inferior leads had the presumed exit site located at the mid-high posterolateral right atrium. Among the 18 patients with both forms of atrial flutter, linear ablation lesions directed at the IVC-TA isthmus eliminated both forms of atrial flutter in 14 patients; in the remaining 4 patients, CSO-TA linear lesions eliminated the counterclockwise form and IVC-TA lesions eliminated the clockwise form. Among the 12 patients with the clockwise form only, CSO-TA linear lesions eliminated flutter in 2 and IVC-TA linear lesions eliminated flutter in 10 patients. Successful ablation was confirmed by creation of bidirectional conduction block in the IVC-TA and/or CSO-TA isthmus during pacing from the proximal coronary sinus and right posterolateral atrium sandwiching the linear lesions. During the follow-up period of 17 +/- 8 months, 2 patients had recurrence of clockwise atrial flutter, 1 patient had new onset of atypical atrial flutter, and 2 patients had new onset of atrial fibrillation.

CONCLUSIONS

Counterclockwise and clockwise atrial flutters may have overlapping slow conduction areas with different exit sites. Radiofrequency catheter ablation using the linear method directed at the IVC-TA and CSO-TA isthmuses was feasible and effective in treating both forms of atrial flutter.

Effects of isoproterenol in facilitating induction of slow-fast atrioventricular nodal reentrant tachycardia

This study demonstrates that patients with poorer conduction properties of the anterograde slow and retrograde fast pathways usually need isoproterenol to facilitate induction of atrioventricular nodal reentrant tachycardia. Isoproterenol infusion usually facilitates induction of tachycardia by enhancing the retrograde ventriculoatrial conduction.

Electrophysiologic characteristics and anatomical complexities of accessory atrioventricular pathways with successful ablation of anterograde and retrograde conduction at different sites

INTRODUCTION

Catheter ablation may eliminate anterograde and retrograde accessory pathway conduction at closely adjacent but anatomically discrete sites. However, the mechanisms of this discrepancy, the electrophysiologic and anatomical characteristics, and information about systematic study from a large patient population are not available. The purpose of this study was to investigate the electrophysiologic characteristics and anatomical complexities of the accessory pathway in which anterograde and retrograde conduction was successfully ablated at different sites.

METHODS AND RESULTS

Thirty-eight (10.9%) patients (19 men and 19 women; mean age 37 +/- 2.4 years) fulfilling the criteria of having separate ablation sites for anterograde and retrograde conduction were designated as group I, and the other 310 patients (215 men and 95 women; mean age 47 +/- 0.6 years) were designated as group II. The patients with right-sided free-wall pathways had the highest incidence (18.6%) of separate ablation sites. The anatomical distance between anterograde and retrograde directions (left anterior oblique view, 13 +/- 0.6 vs 8 +/- 0.9 mm, P < 0.01; right anterior oblique view, 17 +/- 0.6 vs 5 +/- 0.7 mm, P < 0.01), and incidence of conduction impairment in one direction after successful ablation of another direction (15% vs 78%, P < 0.05) differed significantly between left and right free-wall pathways. The mean distances obtained from left (7 +/- 0.4 vs 14 +/- 0.4 mm, P < 0.05) and right (7 +/- 1.1 vs 15 +/- 0.9 mm, P < 0.05) anterior oblique views were shorter in patients who had impairment of conduction properties than those in patients without impaired conduction after successful ablation of one direction.

CONCLUSIONS

This study showed that anatomical and functional dissociation of the accessory pathway into anterograde and retrograde components was possible. Further study on the relation between electrophysiologic and pathologic characteristics would be helpful to confirm these findings.

Catheter ablation of clinical intraatrial reentrant tachycardias resulting from previous atrial surgery: localizing and transecting the critical isthmus

OBJECTIVES

We sought to evaluate the efficacy of anatomically based radiofrequency catheter ablation for the treatment of intraatrial reentrant tachycardia in patients with previous atrial surgery.

BACKGROUND

Intraatrial reentrant tachycardias, a common late complication of atrial surgery, are often refractory to standard medical management. Data from experimental animals and from humans indicate that anatomic barriers resulting from residual atrial scars provide a substrate for intraatrial reentry. We speculated that these tachycardias require a narrow isthmus of tissue between surgical scars and native nonconductive boundaries and that transection of this isthmus with radiofrequency ablation would therefore constitute an effective treatment.

METHODS

Fourteen patients with a history of atrial surgery and clinical intraatrial reentrant tachycardia underwent electrophysiologic testing. From activation mapping, putative surgical scars and patches that served as boundaries of reentrant circuits were identified. Radiofrequency lesions were then placed to transect the narrowest isthmus of conducting tissue between a surgical scar and an anatomic barrier. Catheter ablation was attempted only for tachycardias consistent with the patient's clinical arrhythmias.

RESULTS

Radiofrequency catheter ablation was attempted for 17 (55%) of 31 tachycardias identified; it successfully terminated tachycardias in 13 (93%) of 14 patients (95% confidence interval [CI] 79% to 99%). There were clinical recurrences in six patients (46%, 95% CI 19% to 73%), each of whom underwent a repeat ablation that was successful. Twelve (86%) of 14 patients (95% CI 67% to 99%) have remained free of intraatrial reentrant tachycardia for a mean of 7.5 +/- 5.3 months.

CONCLUSIONS

Anatomically guided radiofrequency catheter ablation is an effective technique for definitive management of intraatrial reentrant tachycardia in patients with previous atrial surgery.

Co-existence of atrial tachycardia and common atrial flutter: electrophysiological characteristics and radiofrequency catheter ablation

Four patients, who had no prior atrial surgery, underwent radiofrequency ablation for clinically documented typical atrial flutter. In addition to typical atrial flutter re-entrant atrial tachycardia was initiated during electrophysiological study in these four patients. We used earliest atrial endocardial activation and concealed entrainment pace mapping with short stimulus-P interval (< 40 ms) to identify the exit site of slow conduction are of atrial flutter were located at the posteromedial right atrium between the coronary ostium and the tricuspid annulus and those of slow conduction area of atrial tachycardia were located at high lateral right atrium in all four patients. Radiofrequency energy applied to these exit sites successfully eliminated both atrial flutter and atrial tachycardia in these four patients. Typical atrial flutter and re-entrant atrial tachycardia with two distinct re-entrant circuits concomitantly occurring in patients without prior atrial surgery are rare. Radiofrequency ablation can abolish both atrial tachyarrhythmias in the same ablation session.

To fumble flutter or tackle "tach"? Toward updated classifiers for atrial tachyarrhythmias

Aristotle proposed in his short work, The Categories, that a definition is a statement of a thing's essential nature, and the essence of a thing are those of its properties that cannot change without losing its identity. But Aristotle was not faced with the flux of new information that confronts modern medicine. Nowadays, the argot of a discipline arises organically at the intersection of a given state of empiric knowledge and the exigencies of present scientific discourse. Thus, when the only treatment for a regular, narrow QRS complex tachycardia was digitalis glycosides or vasopressor infusion, the term "PAT" ("paroxysmal atrial tachycardia") seemed adequate, at least to distinguish it from ventricular tachycardia. We now prefer the term "PSVT" (paroxysmal supraventricular tachycardia) because we understand that most such tachycardias are not in truth "atrial" but involve the AV node and/or an accessory AV connection, and because we wish to report on the results of treatment specific to each of the subcategories of "PSVT." Similarly, as our knowledge of atrial arrhythmias has grown and especially as we need to describe the outcome of new interventional approaches to therapy, it may be prudent to use a nomenclature for atrial tachyarrhythmias that is based on the geometry of the tachycardia substrate, the relationship of that substrate to atrial anatomy, and the type of atrial lesions required to abolish that substrate.

Role of catheter-induced mechanical trauma in localization of target sites of radiofrequency ablation in automatic atrial tachycardia

OBJECTIVES

We compared the efficacy of two different mapping techniques in identifying the ablation site for atrial tachycardia. Moreover, we evaluated the additive positive predictive value of mechanical interruption of atrial tachycardia to reduce the number of ineffective radiofrequency applications.

BACKGROUND

Radiofrequency catheter ablation has been suggested as a highly effective technique to treat drug-resistant atrial tachycardia. However, irrespective of the mapping technique utilized, success was most often achieved with a large number of radiofrequency applications.

METHODS

Forty-five patients with atrial tachycardia underwent radiofrequency catheter ablation. Mapping techniques included identification of earliest atrial activation and pace-mapping concordant sequence.

RESULTS

Atrial tachycardia was successfully treated in 42 (93.3%) of 45 patients with a mean of 3.9 radiofrequency pulses/patient. An interval between the onset of the intracavitary atrial deflection and the onset of the P wave during atrial tachycardia (AP interval) > or = 30 ms (p < 0.001) and pace-mapping concordant sequence (p = 0.01) were all significant predictors of outcome. An AP interval > or = 30 ms and a pace-mapping concordant sequence were highly sensitive (92.8%, 95% confidence interval [CI] 80.5% to 98.5%; 85.7%, 95% CI 71.5% to 94.6%, respectively) but less specific (47.8%, 95% CI 37.9% to 58.2%, 36.8%, 95% CI 27.6% to 47.2%, respectively) in identifying the site of ablation. By using atrial tachycardia mechanical interruption combined with the AP interval >30 ms or the pace-mapping concordant sequence, we obtained a specifically of 76.5% (95% CI 66.4% to 84.0%) and 73.5% (95% CI 63.2% to 81.4%), respectively, and a positive predictive value of 49.2% and 44.6%, respectively.

CONCLUSIONS

An AP interval > or = 30 ms and a pace-mapping concordant sequence were reliable mapping features for predicting the outcome of the ablation procedure. Mechanical interruption of atrial tachycardia improved the specificity and positive predictive value of these two mapping techniques.

Radiofrequency catheter ablation of common atrial flutter: comparison of electrophysiologically guided focal ablation technique and linear ablation technique

OBJECTIVES

The purpose of this study was to study electrophysiologic characteristics and compare the electrophysiologically guided focal ablation technique and linear ablation technique in patients with common atrial flutter in a prospective randomized fashion. Background. Catheter ablation of the common atrial flutter circuit can be performed with different techniques. To date, these two techniques have not been compared prospectively in a randomized study.

METHODS

Sixty patients with drug-refractory common atrial flutter were randomly assigned to undergo radiofrequency catheter ablation performed with the electrophysiologically guided focal ablation (Group I) or linear ablation technique (Group II). In Group I, radiofrequency energy was delivered to the site characterized by concealed entrainment with a short stimulus-P wave interval (<40 ms) and a postpacing interval equal to the atrial flutter cycle length. In Group II, continuous migratory application of radiofrequency energy was used to create two linear lesions in or around the inferior vena cava-tricuspid ring isthmus. Serial 24-h ambulatory electrocardiographic (Holter) and follow-up electrophysiologic studies were performed to assess recurrence of tachycardia and possible atrial arrhythmogenic effects.

RESULTS

Successful elimination of the flutter circuit was achieved in 28 of 30 patients in Group I and 29 of 30 patients in Group II. More atrial premature beats and episodes of short run atrial tachyarrhythmias in the early period (within 2 weeks) after ablation were found in Group II. Recurrence rate (2 of 28 vs. 3 of 29) and incidence of new sustained atrial tachyarrhythmias (3 of 28 vs. 3 of 29) was similar in the two groups. Occurrence of recurrent atrial flutter and new sustained atrial tachyarrhythmias was related to associated cardiovascular disease and atrial enlargement in both groups. However, in Group II, the procedure time (104 +/- 17 vs. 181 +/- 29 min, p<0.01) were significantly shorter than those in Group I.

CONCLUSIONS

Radiofrequency ablation of the common atrial flutter circuit was safe and effective with either the electrophysiologically guided focal ablation or linear ablation technique. However, the linear ablation technique was time-saving.

Electrocardiographic and electrophysiologic characteristics of anteroseptal, midseptal, and para-Hisian accessory pathways. Implication for radiofrequency catheter ablation

STUDY OBJECTIVE

To investigate the ECG characteristics, the electrophysiologic properties, and an effective radiofrequency catheter ablation technique in patients with septal accessory pathways.

PATIENTS

Forty-six consecutive subjects with septal accessory pathways located in the anteroseptal, midseptal, and para-Hisian areas.

DESIGN AND INTERVENTIONS

ECGs obtained during sinus rhythm and orthodromic tachycardia, conduction properties obtained from electrophysiologic study, and results of two different ablation techniques were analyzed.

MEASUREMENTS AND RESULTS

(1) Twenty-four (52.2%) had manifest preexcitation and 15 (32.6%) had multiple accessory pathways; (2) midseptal pathways could be differentiated from anteroseptal and para-Hisian pathways by a negative delta wave in lead III and a biphasic delta wave in lead aVF during sinus rhythm, and a negative retrograde P wave in two inferior leads during orthodromic tachycardia; (2) midseptal pathways had better antegrade conduction properties and a significantly higher incidence (61.5%) of inducible atrial fibrillation; (4) radiofrequency catheter ablation using lower energy (20+/-6 W) had a comparable effect to ablation using higher energy (36+/-5 W), but without impairment of atrioventricular (AV) node conduction or development of AV block; and (5) during the follow-up period of 26+/-14 months (range, 5 to 54 months), three (6.5%) patients had recurrence.

CONCLUSIONS

Midseptal accessory pathways had ECG and electrophysiologic characteristics that were distinctive from those of anteroseptal and para-Hisian pathways. Catheter ablation of these septal pathways using low radiofrequency energy was safe and effective.

Electrophysiologic characteristics and radiofrequency catheter ablation in patients with multiple atrioventricular nodal reentry tachycardias

Information about the mechanism and radiofrequency catheter ablation of multiple atrioventricular (AV) nodal reentry tachycardias is limited. Among the 550 consecutive patients with AV nodal reentry tachycardia, 36 with multiple forms of AV nodal reentry tachycardia were included in this study. Electrophysiologic characteristics, as well as the efficacy and safety of radiofrequency ablation, were evaluated. Results showed that anterograde dual pathways were seen in 32 patients and triple pathways in 2, and retrograde dual pathways were seen in 23 patients and triple pathways in 11. Twenty-two patients had 2 types, 7 had 3 types, 5 had 4 types, and 2 had 5 types of AV nodal reentry tachycardia and echoes. After delivering radiofrequency energy to the target sites, 32 patients had no induction of AV nodal reentry tachycardia and only 4 had induction of 1 echo. Furthermore, 22 patients (61%) had simultaneous elimination or modification of the slow and/or intermediate pathways in the anterograde and retrograde direction. During the follow-up period of 19 +/- 14 months, 2 patients had recurrence of tachycardia. Thus, multiple anterograde and retrograde AV nodal pathways were present in the human AV node and they constituted the substrates of reentry circuits. Radiofrequency catheter ablation was safe and effective in eliminating the slow and intermediate pathways for maintenance of multiple AV nodal reentry tachycardias.

Involvement of nitric oxide, but not prostaglandins, in the vascular sympathoinhibitory effects of losartan in the pithed spontaneously hypertensive rat

1. The aim of this study was to investigate whether nitric oxide (NO) and/or vasodilator prostaglandins (PGs) are involved in the sympathoinhibitory effects exerted by losartan versus the vascular responses elicited by spinal cord electrical stimulation (SCS) in pithed spontaneously hypertensive rats (SHRs). 2. SHRs were given orally and for 8 days either losartan (10 mg kg-1 daily) or distilled water (controls). After pithing, blood pressure, heart rate, cardiac output, renal and muscular blood flows (pulsed Doppler technique) and the corresponding vascular resistance values were measured or calculated at baseline. Then, animals from both groups were given i.v. either saline, or NG-nitro-L-arginine methyl ester (L-NAME, 1 mg kg-1), or diclofenac (4 mg kg-1). Thereafter, haemodynamic parameters were determined in the six subgroups of animals in response (a) to SCS at increasing frequencies, and (b) to a noradrenaline bolus injection. 3. Losartan significantly decreased mean arterial pressure as well as renal and total peripheral resistances. In addition, losartan exhibited strong vascular sympathoinhibitory effects, significantly decreasing the systemic pressor and regional vasoconstrictor responses to SCS, but did not affect those to exogenous noradrenaline. In contrast, SCS-induced tachycardia was not modified by losartan. 4. L-NAME significantly increased total peripheral and regional vascular resistances but did not affect blood pressure and heart rate basal values. L-NAME potentiated the haemodynamic responses to SCS in control and, to a larger extent, in losartan-treated SHRs so that, with the exception of the renal vascular bed, the sympathoinhibitory effects of losartan were attenuated in all vascular beds studied. L-Arginine (300 mg kg-1) caused reversal of L-NAME effects in both control and losartan-treated SHRs. 5. Diclofenac did not affect the basal values of haemodynamic parameters in control and losartan-treated SHRs. Diclofenac potentiated the pressor and vasoconstrictor responses to SCS and to a similar extent, in both control and losartan-treated SHRs, so that the sympathoinhibitory effects of losartan were fully maintained. 6. These results demonstrate that in pithed SHRs: (a) NO but not PGs contribute to the basal vasomotor tone, (b) both NO and PGs attenuate the pressor and vasoconstrictor responses to SCS, (c) NO plays a major role in the vascular sympathoinhibitory effects of losartan, except at the renal level, and (d) endogenous PGs are not involved in these sympathoinhibitory effects.