Radiofrequency catheter ablation of both atrial ventricular nodal reentrant and atrial ventricular reentrant tachycardia in a single session

Radiofrequency catheter ablation is a new therapeutic approach to treat patients with symptomatic drug-resistant paroxysmal supraventricular tachycardia. Ablation of two accessory atrioventricular pathways in a single session has been frequently described previously. However, ablation in a single session of both the fast pathway, involved in atrial ventricular nodal reentrant tachycardia, and a concealed atrioventricular accessory pathway involved in a circus movement tachycardia has rarely been reported. A 57-year-old man with a grade III aortic incompetence had the infrequent association of atrial ventricular nodal reentrant tachycardia and orthodromic circus movement tachycardia due to a concealed accessory pathway. He presented with drug-resistant reentrant supraventricular tachycardia and, in a single session, underwent a successful radiofrequency catheter ablation of the fast atrial ventricular nodal pathway and a concealed posteroseptal accessory pathway. During a 10-month follow-up he was free of palpitations without any antiarrhythmic therapy and underwent elective aortic valve replacement.     

Quadruple atrioventricular nodal pathways: involved in orthodromic atrioventricular reentrant tachycardia

Supraventricular tachycardia can be caused by multiple atrioventricular nodal pathways or atrioventricular accessory pathways. Herein, we report the case of a patient who was diagnosed with an orthodromic atrioventricular reentrant tachycardia that was caused by an unusual combination of quadruple atrioventricular nodal pathways and an atrioventricular accessory pathway. Radiofrequency catheter ablation of the accessory pathway successfully eliminated the arrhythmias and the patient's symptoms. Careful analysis of complete electrophysiologic studies can help in the diagnosis of such rare clinical presentations.     

Radiofrequency ablation in a patient with atrioventricular reentrant tachycardia and atrioventricular nodal reentrant tachycardia with 2:1 atrioventricular block.

The authors report the case of 15-year-old girl with a history of palpitations and shortness of breath during exercise. The electrocardiogram showed ventricular preexcitation suggesting a Wolff-Parkinson-White syndrome with a posteroseptal accessory pathway. During the electrophysiological study a left posterospetal accessory pathway was identified and an orthodromic atrioventricular reentry tachycardia was reproducibly induced (cycle length 400 ms). After disappearance of the ventricular pre-excitation with radiofrequency ablation, a dual physiology of atrioventricular node condution was documented and a slow-fast atrioventricular nodal reentrant tachycardia was repeatedly induced. Upon induction, this tachycardia presented a proximal atrioventricular block with 2:1 condution converted to 1:1 condution with overdrive pacing from the proximal coronary sinus (cycle length 270 ms). Radiofrequency ablation of the slow pathway was performed with success. We discuss the need to suspect and seek different arrhythmogenic substracts of tachycardia in a single patient, the electrophysiologic conditions that could explain the inducibility of different arrhythmias in this case, and the controversy regarding ablation of more than one reentry circuit in a single procedure.     

Concomitant reentrant tachycardias from concealed accessory atrioventricular bypass tract and atrioventricular nodal reentry in a patient with Williams syndrome.

Williams syndrome is characterized by a constellation of features including mental retardation and supravalvular aortic stenosis. Other cardiovascular abnormalities including arrhythmias contributing to sudden death have been described in these patients. In this report we describe a case of a 49-year-old female with Williams syndrome who presented with severe symptomatic supraventricular tachycardia. Cardiac electrophysiology study identified a left posteroseptal concealed accessory bypass tract responsible for atrioventricular reentrant tachycardia and a concomitant typical atrioventricular nodal tachycardia. Such unusual association of combination of two different types of supraventricular tachycardia and Williams syndrome has not been previously reported. Radiofrequency ablation was successfully performed to cure these arrhythmias.     

Entrainment phenomenon of atrioventricular nodal reentrant and atrioventricular reentrant tachycardias]

Atrioventricular nodal reentrant tachycardia (AVNRT) and atrioventricular reentrant tachycardia (AVRT) were induced by esophageal pacing and their entrainment zones were examined in 20 patients. The results showed that the entrainment phenomenon, which was a common electrophysiological phenomenon in reentrant tachycardia, occurred during overdrive pacing in 19 cases (19/20). The entrainment zone was 10-70 (30.50 +/- 20.85, mean +/- s) ms. The tachycardias could not be interrupted by pacing within the entrainment zone, but they were terminated by burst pacing, with starting pacing cycle length shorter than the shortest entrainment cycle length.     

Sympathetic predominance of cardiac autonomic regulation in patients with left free wall accessory pathway and orthodromic atrioventricular reentrant tachycardia

AIMS: The aim of this study was to compare cardiac autonomic regulationin patients with a history of paroxysmal supraventricular tachyarrhythmias,such as atrioventricular nodal reentrant tachycardia and atrioventricularreentrant tachycardia, and healthy controls. METHODS AND RESULTS: Seventeen patients with paroxysmal atrioventricular nodal reentranttachycardia (atrioventricular nodal reentrant tachycardia group),14 patients with overt preexcitation and paroxysmal atrioventricularreentrant tachycardia caused by a left free wall accessory pathway(atrioventricular reentrant tachycardia group) and 14 healthycontrol subjects, were studied. The patients and the controlswere age and gender matched. Cardiac autonomic regulation wasassessed by means of frequency domain analysis of heart ratevariability at rest, during head-up tilt, active standing, treadmillexercise and after exercise. The high frequency component (0·15–0·5 Hz)of heart rate variability tended to be lower and the low frequencycomponent (0·04–0·15 Hz) tended to be higheramong the atrioventricular reentrant tachycardia patients thanin atrioventricular nodal reentrant tachycardia patients andcontrols. The difference reached statistical significance atrest (P<0·05) and during standing (P<0·05atrioventricular reentrant tachycardia vs atrioventricular nodalreentrant tachycardia and P<0·01 atrioventricularreentrant tachycardia vs controls). Accordingly, the low-to-highfrequency ratio — the marker of cardiac sympathetic regulation— was higher in atrioventricular reentrant tachycardiapatients than in atrioventricular nodal reentrant tachycardiapatients (P<0·05 at rest and during standing) andcontrols (P<0·01 during standing). CONCLUSION: The cardiac autonomic status in atrioventricular reentrant tachycardiapatients was suggestive of a higher sympathetic tone than inatrioventricular nodal reentrant tachycardia patients or healthycontrols. This may be related to inhomogeneous ventricular activationin the presence of antegrade conduction via the accessory atrioventricularpathway.     

Risk of development of delayed atrioventricular block after slow pathway modification in patients with atrioventricular nodal reentrant tachycardia and a pre-existing prolonged PR interval.

AIMS: The objective of this prospective study was to assess risk factors for the development of atrioventricular block following slow pathway modification in patients with atrioventricular nodal reentrant tachycardia and a pre-existing prolonged PR interval. METHODS AND RESULTS: Of 346 consecutive patients with atrioventricular nodal reentrant tachycardia undergoing slow pathway modification, 18 patients (62 +/- 7 years; five females) were found to have a prolonged PR interval prior to ablation. Total elimination of the functional slow pathway was assumed if the antegrade effective refractory period following slow pathway modification was longer than the cycle length of atrioventricular nodal reentrant tachycardia. To detect atrioventricular node conduction disturbances, 24-h Holter recordings were performed 1 day prior to slow pathway modification, and 1 day, 1 week, 1, 3 and 6 months after the procedure. Six patients developed late atrioventricular block. The incidence of delayed atrioventricular block following successful slow pathway modification was higher in patients with, compared to patients without, prolonged PR interval at baseline (6/18 vs 0/328, P < .001). In the former group, the antegrade effective refractory period was longer in patients with, compared to those without, a delayed atrioventricular block (492 +/- 150 ms vs 332 +/- 101 ms, P < 0.05). The incidence of delayed atrioventricular block was higher in patients with total elimination of the slow pathway compared to patients without (5/7 vs 1/11, P < 0.01). CONCLUSIONS: Slow pathway modification in patients with atrioventricular nodal reentrant tachycardia and a prolonged PR interval is highly effective. However, there is a significant risk of development of delayed atrioventricular block, particularly when the procedure results in total elimination of the slow pathway.     

Unusual induction of slow-fast atrioventricular nodal reentrant tachycardia. Report of two cases

INTRODUCTION: Generally, the induction of typical atrioventricular nodal reentrant tachycardia (AVNRT) occurs with a premature atrial stimulus that blocks in the fast pathway and proceeds down the slow pathway slowly enough to allow the refractory fast pathway time to recover. We describe two cases in which a typical AVNRT was induced in an unusual fashion. RESULTS: The first case is a 41-year-old man with paroxysmal supraventricular tachycardia. During the electrophysiology study, the atrial extrastimulus inducing the typical AVNRT was conducted simultaneously over the fast (AH) and the slow pathway (AH'). A successful ablation of the slow pathway was performed. During the follow-up no recurrence was noted. The second case is a 52-year-old woman with a Wolff-Parkinson-White syndrome due to a left posterior accessory pathway. After 5 minutes of atrioventricular reentrant tachycardia (AVRT) induced by a ventricular extrastimulus, a variability of the antegrade conduction was noted in presence of the same VA conduction. In fact, a short AH interval (fast pathway) alternated with a more prolonged AH intervals (slow pathway) that progressively lengthened until a typical AVNRT was induced. The ablation of the accessory pathway eliminated both tachycardias. DISCUSSION: A rare manifestation of dual atrioventricular nodal pathways is a double ventricular response to an atrial impulse that may cause a tachycardia with an atrioventricular conduction of 1:2. In our first case, an atrial extrastimulus was simultaneously conducted over the fast and the slow pathway inducing an AVNRT. This nodal reentry implies two different mechanisms: 1) a retrograde block on the slow pathway impeding the activation of the slow pathway from the impulse coming down the fast pathway, and 2) a critical slowing of conduction in the slow pathway to allow the recovery of excitability of the fast pathway. Interestingly, in the second case, during an AVRT the atrial impulse suddenly proceeded alternately over the fast and the slow pathway. The progressive slowing of conduction over the slow pathway until a certain point which allows the recovery of excitability of the fast pathway determines the AVNRT. This is a case of "tachycardia-induced tachycardia" as confirmed by the fact that the ablation of the accessory pathway eliminated both tachycardias.     

Fast-slow and slow-slow form of atrioventricular nodal reentrant tachycardia sustained by the same reentrant circuit: a case report.

It has been suggested that a reentrant circuit confined to the posterior extensions of the atrioventricular node underlies both fast-slow and slow-slow types of atrioventricular nodal reentrant tachycardia (AVNRT). According to this hypothesis the fast-slow reentrant circuit would be formed by two slow pathways, located in the rightward and leftward posterior extension of the atrioventricular node. Thus, the fast pathway would act as a bystander with respect to the reentrant circuit. We describe the case of a 40-year-old woman with several episodes of palpitations unresponsive to antiarrhythmic drugs. The ECG during symptoms showed a narrow QRS tachycardia with a long ventriculo-atrial interval and a negative P wave in the inferior leads. Electrophysiological study showed the inducibility of a slow-slow AVNRT which rapidly shifted to a fast-slow AVNRT without any change in the duration of the tachycardia cycle. Our observation is in agreement with the hypothesis that the fast-slow reentrant circuit consists of two slow pathways with the fast pathway acting as a bystander.     

Ablation of Atrioventricular nodal “slow pathway” for simultaneous treatment of coexisting atrioventricular and nodal reciprocating tachycardias

Introduction We report the case of a 49-year-old male patient with recurrent palpitations and two different supraventricular reciprocating tachycardias due to atrioventricular (AV) nodal reentry and orthodromic AV reentry sustained by a left-sided, concealed AV accessory pathway (AP). Methods and results During the baseline electrophysiological study, dual AV nodal conduction (90 ms jump) and non-decremental, eccentric, ventriculo-atrial conduction due to a left-sided, unidirectional, postero-septal AP were documented. Both typical AV nodal reentrant and orthodromic AV reentrant tachycardias were induced by programmed electrical stimulation. In both cases, shift and sustained conduction over the AV “slow pathway” were required for tachycardia induction and maintenance, respectively. Accordingly, catheter ablation was performed by targeting the AV nodal “slow pathway” first with radiofrequency current applications delivered at the inferior portion of the Koch’s triangle. Irritative, slow-rate junctional rhythm was observed during ablation. Afterward, programmed electrical stimulation demonstrated a continuous AV nodal conduction curve, persistent conduction over the AP, and only single orthodromic AV echo beat inducible under baseline condition and pharmacological stress (atropine 0.02 mg/kg i.v. bolus and continuous isoprenaline i.v. administration). Sustained reentrant tachycardias were not inducible any more. For these reasons, the procedure was stopped without any attempt to ablate the AP. After a 4 years follow-up the patient is still asymptomatic without antiarrhythmic drug usage. Conclusion AV nodal “slow pathway” ablation may abolish both typical AV nodal reentry tachycardia and orthodromic AV reentry tachycardia induction when the latter arrhythmia is dependent from AV nodal “slow pathway” conduction for induction and maintenance. This ablation strategy could be considered, under some instances (e.g. right antero-septal accessory pathways, older patients, etc), in order to reduce the procedure risks due to multiple arrhythmia substrate ablations.     

Fast pathway ablation in patients with common atrioventricular nodal reentrant tachycardia and prolonged PR interval during sinus rhythm

Aims This study aimed to clarify the safety and efficacy of selectivefast pathway ablation in patients with atrio-ventricular nodalreentrant tachycardia and a prolonged PR interval during sinusrhythm. Such patients have been reported to have an increasedincidence of complete atrioventricular block. Methods and Results In this study, the earliest retrograde atrial activation duringatrioventricular nodal reentrant tachycardia and right ventricularstimulation was localized. Fast pathway ablation was then performedin five patients with the common form of atrioventricular nodalreentrant tachycardia and a prolonged PR interval. Three ofthe five patients had almost incessant atrioventricular nodalre-entrant tachycardia. Radiofrequency catheter ablation induceda complete ventriculo-atrial block during right ventricularstimulation in four patients and a marked prolongation of ventriculo-atrialconduction during right ventricular stimulation in one. Non-inducibilityof common atrioventricular nodal reentrant tachycardia withand without isoproterenol was achieved in all five patients.The PR interval increased from 254±53ms to 276±48msand the atrio-His interval from 172±46ms to 192±45ms.Second- or third-degree atrioventricular block did not occurduring the ablation procedure. During the follow-up of 19±20months none of the patients developed symptoms suggestive ofatrioventricular nodal reentrant tachycardia or evidence ofsecond- or third-degree atrioventricular block. Conclusion These data suggest that atrioventricular node (retrograde) fastpathway ablation can apparently be safely performed in patientswith common atrioventricular nodal reentrant tachycardia anda prolonged PR interval during sinus rhythm.     

Differentiating atrioventricular nodal reentrant tachycardia from tachycardia via concealed accessory pathway

Studies analyzing the diagnostic value of 12-lead electrocardiographic criteria differentiating slow-fast atrioventricular nodal reentrant tachycardia (AVNRT) from atrioventricular reentrant tachycardia (AVRT) due to concealed accessory pathway have shown inconsistent results. In 97 patients (50 with AVNRT, 47 with AVRT) 12-lead electrocardiograms (ECGs) were recorded during sinus rhythm and tachycardia (QRS <120 ms). The ECGs were blinded for diagnosis and patient and analyzed independently by 2 electrophysiologists. The studied criteria differentiating AVNRT from AVRT included pseudo-r'/S, the presence of a retrograde P wave, RP interval, ST-segment depression >/=2 mm with the number and location of the affected leads, QRS amplitude, and cycle length alternans.     

Electrophysiologic effects and clinical efficacy of flecainide in children with recurrent paroxysmal supraventricular tachycardia

The electrophysiologic effects of intravenous flecainide were evaluated in 16 patients aged 9 +/- 4 years: 15 with recurrent paroxysmal supraventricular tachycardia (SVT) and 1 with overt accessory pathway and history of syncope. Eleven patients had an accessory pathway; it was concealed in 2, overt in 9 and in 10 of these patients an orthodromic atrioventricular reentrant tachycardia was induced. Five patients without accessory pathway had an atrioventricular nodal reentrant tachycardia. After intravenous flecainide (1.5 mg/kg) the effective refractory period of the atrium and ventricle increased significantly; the anterograde and retrograde effective refractory periods of the atrioventricular node did not. Flecainide blocked retrograde conduction in the accessory pathway in 4 patients (effective refractory period 245 +/- 41 ms) and anterograde conduction in 8 of 9 patients (effective refractory period 284 +/- 57 ms). The mean cycle length of orthodromic reciprocating tachycardia and atrioventricular nodal reentrant tachycardia increased significantly. After flecainide tachycardia was noninducible in 6 patients with orthodromic reciprocating tachycardia and in 1 with atrioventricular nodal reentrant tachycardia. It was inducible but nonsustained (less than or equal to 30 seconds) in 1 patient with orthodromic reciprocating tachycardia and in 3 with atrioventricular nodal reentrant tachycardia. Fifteen patients continued oral flecainide treatment for 19 +/- 11 months.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical and electrophysiological characteristics in patients with atrioventricular reentrant and atrioventricular nodal reentrant tachycardia.

AIM: To compare clinical, electrophysiological characteristics and transcatheter ablation results between two groups of patients, one with atrioventricular reentrant tachycardia (AVRT) and the other with atrioventricular nodal reentrant tachycardia (AVNRT). METHODS: The study population consisted of 94 consecutive patients who underwent endocavitary electrophysiological study and radiofrequency (RF) ablation: 46 patients had AVRT due to an accessory pathway with only retrograde conduction while 48 patients had AVNRT. RESULTS: In relation to general and clinical characteristics, differences between the two groups emerged regarding the age of symptom onset (25+/-16 vs 37+/-17 years, p=0.001), the prevalence of heart disease (8 vs 31%, p=0.001) and the correct diagnosis on surface ECG (50 vs 79%, p=0.001). Clinical presentation was quite similar apart from a higher prevalence of fatigue and sweating in the AVNRT group. Transcatheter RF ablation therapy results were similar. CONCLUSIONS: Patients with AVRT have a lower mean age at arrhythmia symptom onset compared with those with AVNRT and have fewer associated cardiac abnormalities. Clinical presentation is quite similar as well as their outcome after ablation. A correct diagnosis by standard ECG is more frequent in AVNRT.     

Observations on spontaneous termination of atrioventricular nodal reentrant tachycardia

Unusual mechanisms of spontaneous termination of atrioventricular (A-V) nodal reentrant tachycardia were observed in two patients during programmed electrical stimulation of the heart. In both patients the mechanism of termination was based on the use of another reentrant pathway than the one used during tachycardia. This pathway was located extranodally in one patient and intranodally in the other. The Observations illustrate some of the complexities of reentry in the human heart and how they can play a role in spontaneous termination of A-V nodal tachycardia.     

Double ventricular responses during extrastimulation of atrioventricular nodal reentrant tachycardia

In patients with dual atrioventricular (AV) nodal pathways,double ventricular responses to a single atrial depolarizationhave been shown to occur, but virtually only during a trialpacing in sinus rhythm. We report on a patient with a slow-fastform of AV nodal reentrant tachycardia who exhibited doubleventricular responses following extrastimulation during AV nodalreentrant tachycardia. The phenomenon of double ventricularresponses during the tachycardia was demonstrated by ex trastimulationfrom the proximal coronary sinus. Retrograde unidirectionalblock in the slow pathway, and an anterograde effective refractoryperiod that was shorter in the fast pathway than that in theslow pathway, are suggested.     

Twin atrioventricular node associated with interruption of the inferior vena cava and atrioventricular nodal reentrant tachycardia

We report the case of a patient exhibiting symptomatic junctional bigeminy associated with twin atrioventricular (AV) node and an anomaly in the inferior vena cava. The patient evidenced twin AV node and complete interruption of the inferior vena cava, with azygos continuation. The catheters for mapping of the AV junctional area and ablation were accessed via jugular and subclavian venous approaches, and azygos venous approach via the femoral vein. Twin AV node was diagnosed by (1) the existence of 2 discrete non-preexcited QRS morphologies of junctional bigeminy, (2) decremental anterograde and retrograde conduction, and (3) inducible AV nodal reentrant tachycardia. Atrioventricular nodal reentrant tachycardia and bigeminal rhythm were eliminated by ablation of the retrograde pathway. The postablation rhythm was a regular junctional rhythm, without tachycardia.     

Targeting the slow pathway for atrioventricular nodal reentrant tachycardia: initial results and long-term follow-up in 379 consecutive patients.

OBJECTIVES: This study is designed to examine the immediate and short-term outcomes of patients who have undergone slow pathway ablation/modification for atrioventricular nodal reentrant tachycardia. BACKGROUND: Targeting the slow pathway has emerged as the superior form of treatment for atrioventricular nodal reentrant tachycardia. This technique has been found effective and is associated with a low complication rate. However, little is known of the long-term outcome of patients undergoing this procedure. METHODS: Over a 40-month period the slow pathway was targeted in 379 consecutive patients with proven atrioventricular nodal reentrant tachycardia. The case records of all patients were examined. Accurate follow-up data is available in 96% of patients a mean of 20.6 months after the procedure. RESULTS: The initial success rate was 97%. The incidence of complete heart block was 0.8% and the mean fluoroscopy duration was 27.3 min. The recurrence rate was 6.9%. Age, number of pulses and fluoroscopy time were positively associated with either initial failure or recurrence. A total of 11.3% of patients were still taking antiarrhythmic medication at follow-up. CONCLUSIONS: Targeting the slow pathway is an effective form of treatment for atrioventricular nodal reentrant tachycardia. The technique has a high initial success rate, a low complication rate and a low recurrence rate at long-term follow-up. Slow pathway modification is associated with similar success rates and recurrence rates as slow pathway ablation and may confer theoretical long-term benefits.     

希氏束旁起搏鉴别间隔部隐匿性AVRT与AVNRT的临床价值

目的：探讨希氏束旁起搏鉴别间隔部隐匿性房室旁道与慢一快型房室结折返性心动过速（AVNRT）的临床价值。方法：采用希氏束逆传不应期心室早搏刺激法将61例患者分别诊断为37例慢一快AVNRT和24例间隔部房室折返性心动过速（AVRT）；再对61例患者采用希氏束旁起搏方法进一步检测。结果：采用希氏束旁起搏法检测37例AVNRT患者中有6例未检测成功，其余31例均为逆传房室结图形；24例AVRT患者中4例未检测成功，15例呈逆传旁道／旁道图形，5例呈非逆传旁道／旁道图形。如以逆传旁道／旁道图形为标准，鉴别间隔快旁路引起的AVRT与慢一快型房室结折返性心动过速，敏感性75％，特异性可达1009／6。结论：希氏束旁刺激法对鉴别诊断AVRT与AVNRT有较高的特异性。     

Electrophysiologic and antiarrhythmic actions of bepridil : Comparison with verapamil and ajmaline for atrioventricular reentrant tachycardia

Bepridil (2 mg/kg intravenously) was given to 20 patients with atrioventricular (AV) reentrant tachycardia and its effects were compared with those of verapamil (0.15 mg/kg intravenously) in 8 patients and ajmaline (0.75 mg/kg intravenously) in 12. After baseline electrophysiologic measurements, the drugs were given during sustained AV reentrant tachycardia (8 patients had dual AV nodal pathways and 12 had an accessory AV pathway). Verapamil terminated AV reentrant tachycardia in 7 patients and bepridil terminated it in 6. In 8 of the patients who received ajmaline, AV reentrant tachycardia was terminated and in 6 of this group bepridil did so. Bepridil was more successful in terminating AV reentrant tachycardia in those with dual AV nodal pathways than in those with an accessory AV pathway. Bepridil slowed sinus rate by 10% (p <0.0001), whereas verapamil did not change it significantly. Both verapamil and bepridil administration prolonged AV nodal conduction (39% and 44%, respectively), lengthened AV nodal effective refractory period (18% and 17% respectively) and increased the Wenckebach cycle length of the AV node (24% and 25%, respectively) to a significant degree (p <0.05). Bepridil also lengthened atrial and ventricular effective refractory periods (p <0.01) and QT interval (p <0.0001) in the group as a whole; in those receiving ajmaline and bepridil only atrial refractoriness was significantly altered (p <0.05). After treatment for 3 to 5 days with oral bepridil, 19 patients underwent repeat study. There was further slowing in sinus rate and prolongation in both atrial effective refractory period and QT interval; the AV Wenckebach cycle length had returned toward the control level, but was still significantly increased (p <0.01). In the 17 cases in whom reinducibility of AV reentry tachycardla was tested, 7 had no inducible arrhythmia, 6 had non-sustained AV reentrant tachycardia and 4 had sustained but slower tachycardia. Thus, bepridil has both AV nodal and myocardial electrophysiologic actions which suggest a useful role in the treatment and prophylaxis of supraventricular arrhythmias.