Recurrence and Late Block of Accessory Pathway Conduction Following Radiofrequency Catheter Ablation

Recurrence After RF Ablation of AP. Introduction: Many issues regarding the recurrence of accessory pathway conduction and the long-term outcome of late block of accessory pathway conduction are still unknown or controversial. Methods and Results: Data from 217 patients who underwent an initially successful radiofrequency ablation of accessory pathways and 7 patients with late block of accessory pathway conduction following an initially unsuccessful ablation were analyzed. During a mean follow-up of 19 ± 11 months, accessory pathway conduction resumed in 21 (10%) of 217 patients following an initially successful ablation and in 6 (86%) of 7 patients with late block of accessory pathway conduction (P < 0.01). After initially successful ablations, the recurrence rates of accessory pathway conduction at 1, 3, and 6 months were 5.9%, 7.4%, and 11.3%, respectively. A late electrophysiologic study at 6 months uncovered recurrence in only 1 of 124 asymptomatic patients, but failed to detect the late recurrence in 2 patients in whom the accessory pathway conduction resumed after more than 6 months. Multivariate analysis revealed that independent predictors for recurrence of accessory pathway conduction were concealed accessory pathway, presence of transient effect of radiofrequency pulse, and more than 5 pulses required for initial cure. Accessory pathway location, length of the tip electrode of the ablation catheter, and repeat radiofrequency pulses (“safety pulses”) after effective pulses did not predict resumption of accessory pathway conduction. Conclusions: After initially successful ablation, the recurrence rates of accessory pathway conduction at 1, 3, and 6 months were 5.9%, 7.4%, and 11.3%, respectively. Late electrophysiologic testing had little prognostic value in asymptomatic patients following successful ablation. Application of “safety pulses” did not prevent recurrence. Late block of accessory pathway conduction did not predict long-term efficacy.     

Recurrence of Accessory Pathway Conduction After Successful Radiofrequency Ablation: Histological Findings

The histological findings from a patient with Wolff-Parkinson-White syndrome (right superior paraseptal accessory pathway) who underwent successful radiofrequency ablation and had recurrence of tachycardia one month later in the absence of overt pre-excitation are reported. Histology revealed three small, oval to circular shaped, whitish, smooth areas on the right endocardial surface, the one being situated at the atrial free wall, and the other two being at the ventricular aspect. A very small hole was present in the interventricular component of the membranus septum. The accessory pathway band passed to either side of the small hole albeit disrupted by fibrous tissue in places.These findings indicate that multiple applications may cause penetration of the myocardium, and to achieve success, complete disruption of the pathway at some point along its course is required. Recurrence of retrograde accessory pathway conduction can be explained with the impedance mismatch hypothesis.     

Radiofrequency Catheter Ablation of Accessory Pathways:

RF Catheter Ablation of APs. Catheter ablation techniques are now advocated as the first line of therapy for arrhythmias caused by accessory pathways (APs). The most common energy source is radiofrequency current, but technical characteristics vary. Several parameters can be used to determine the optimal target site: AP potential, AV time, atrial or ventricular insertion site, or unipolar morphology. Specific considerations are needed depending on AP location. Despite the different approaches described, there is no significant difference in the reported success rate, which is over 90%. However, the number of radiofrequency applications needed to achieve ablation appears to differ significantly, with median values from 3 to 8 reported. A combination of criteria related to both timing and direction of the activation wave-front or use of subthreshold stimulation could improve the accuracy of mapping. In patients with "resistant" APs, different changes in ablation technique must be considered during the procedure to achieve elimination of AP conduction. The incidence of complications in multi-center reports is close to 4%, with a recurrence rate of 8%. The long-term safety of catheter ablation requires further study.     

Apparent Bidirectional Conduction Block Following Radiofrequency Catheter Ablation of Typical Atrial Flutter

Objective: The purpose of this study is to determine the reliability of activation sequence mapping in assessing the presence of bidirectional conduction block (BCB) in typical atrial flutter (AFL) ablation. Introduction: Radiofrequency ablation (RFA) can cure typical AFL by creating BCB across the right atrial isthmus. Effective conduction block across this region can prevent AFL recurrence, but accurate assessment of isthmus conduction may be flawed. Methods: BCB was measured before and after RFA by pacing at multiple rates on both sides of the isthmus during sinus rhythm. Pacing was performed from a low lateral tricuspid annulus site (proximal to the isthmus) and a coronary sinus Os site (distal to the isthmus), while recording simultaneously from 8–10 right atrial sites bordering the isthmus (4–5 free wall sites; 4–5 septal sites) as well as from an isthmus site. After ablation reinduction of atrial flutter was attempted from both sides of the block with rapid atrial pacing after BCB was established in all patients. In some patients lines of conduction block were evident at the isthmus (using the ablation catheter to map). Results: Of 65 patients undergoing RFA of AFL, 59 had typical AFL. In all 59 patients, BCB was demonstrated at all pacing cycle lengths 30[emsp4 ]min after RFA applications. In 6 of these 59, AFL was inducible with atrial pacing despite apparent BCB. Further RFA resulted in non inducibility in all 6 patients. In the remaining 53/59 patients, BCB was associated with noninducibility at 30[emsp4 ]min. A total of 8 recurrences were seen during a mean 19.3[emsp4 ]±[emsp4 ]8.3 (SD) month follow-up. Conclusion: Apparent BCB as determined by activation sequence mapping outside of the isthmus is an excellent marker, but, as measured, may be a misleading method of assessing the presence or absence of conduction through the isthmus. It is necessary to attempt reinduction of AFL after apparent success. Elimination of typical AFL does not preclude other AFLs.     

Temperature-Controlled Irrigated Tip Radiofrequency Catheter Ablation:

Temperature-Controlled Irrigated Tip Ablation. Introduction : In patients with ventricular tachycardias due to structural heart disease, catheter ablation cures < 60% partly due to the limited lesion size after conventional radiofrequency ablation. Irrigated tip radiofrequency ablation using power control and high infusion rates enlarges lesion size, hut has increased risk of cratering. The present study explores irrigated tip catheter ablation in temperature- controlled mode, target temperature 60°C, using an irrigation rate of 1 mL/min, comparing this to conventional catheter technique, target temperature 80°C.
Methods and Results : In vivo anesthetized pigs were ablated in the left ventricle. In vitro strips of porcine left ventricular myocardium were ablated in a tissue bath. Lesion volume was significantly larger after irrigated tip ablation both in vivo (544 ± 218 vs 325 ± 194 mm³, P < 0.01) and in vitro (286 ± 113 vs 179 ± 23 mm³, P < 0.01). The incidence of cratering was not significantly different between the two groups. In vivo, no coagulum formation on part of the catheter tip was seen after irrigated tip ablation as opposed to 52% of the applications with conventional ablation (P < 0.05).
Conclusion : We conclude that temperature-controlled radiofrequency ablation with irrigated tip catheters using low target temperature and low infusion rate enlarges lesion size without increasing the incidence of cratering and reduces coagulum formation of the tip.     

Nonuniform Heating Patterns of Commercial Electrodes for Radiofrequency Catheter Ablation

Heating Patterns of Ablation Electrodes. Introduction : Previous investigations of the biophysics of myocardial ablation using radiofrequency energy have focused mainly on the electrode-myocardial interface. Relatively little has been written about the overall function of commercial electrodes used for ablation. The purpose of this study was to evaluate the heating patterns of several commercial electrodes used for myocardial ablation.
Methods and Results : The specific absorption rate, a unit of measure proportional to the initial rate of rise of the temperature at the electrode-tissue interface and reflecting the energy deposition from the electrode, was measured during radiofrequency energy application at multiple points around each electrode. These measurements were combined to form a specific absorption rate pattern, which reflected the spatial pattern of energy deposition from the electrode. There was significant nonuniformity of the specific absorption rate pattern of each electrode evaluated. The proximal edge of the electrode and the curvature of the distal portion of the electrode were two sites of accentuated heating relative to the remaining portions of the electrode. The magnitude of this nonuniformity was similar between the 4-mni length electrodes of different manufacturers, but increased progressively in larger (5- and 8-mm length) electrodes.
Conclusions : The heating patterns of commercial electrodes used for myocardial ablation are nonuniform. These data have implications for electrode design and utilization.     

Temperature Monitoring in Radiofrequency Catheter Ablation of Atrial Flutter Using the Linear Ablation Technique

Temperature Monitoring of Ablation. Introduction: Information about temperature and impedance monitoring during radiofrequency catheter linear ablation of atrial flutter bas not been reported. We proposed that a radiofrequency catheter ablation system using a closed-loop temperature control model could decrease the incidence of coagulum formation and shorten the radiation exposure and procedure times compared with those found in a power control model.
Methods and Results: Forty patients (8 women and 32 men; mean age 64 ± 7 years) with atrial flutter were referred for radiofrequency ablation. The patients were randomized into two groups: group I patients underwent radiofrequency catheter linear ablation of atrial flutter using a power control of energy output model; and group II patients underwent the closed-loop temperature control model with a target electrode temperature of 70°C. As compared with group II, group I patients bad a higher incidence of coagulum formation (12% vs 2%, P < 0.05), temperature shutdown (11% vs 0%, P < 0.01), and impedance shutdown (16% vs 3%, P < 0.01), more radiofrequency applications (7 ± 3 vs 4 ± 2, P < 0.01), and longer procedure time (100 ± 25 vs 75 ± 23 minutes, P < 0.05) and radiation exposure time (31 ± 10 vs 20 ± 7 minutes, P < 0.05) required for successful ablation. Larger deviations of temperature (9.0°± 2.4°C vs 5.0°± 1.2°C, P < 0.0001) and impedance (9.2 ± 2.6 ω vs 5.3 ± 1.6 ω, P < 0.0001) were also found in group I patients compared with those in group II.
Conclusions : This study demonstrated that a closed-loop temperature control model could facilitate the effects of radiofrequency catheter ablation of the atrial flutter circuit by decreasing coagulum formation, temperature and impedance shutdown, and procedure and radiation exposure times.     

射频导管消融治疗室性早搏的研究进展

室性早搏的治疗,以往学者不主张对其进行药物处理,只是出现较明确的临床症状、患者精神上受较大的影响、且药物效果不好或不愿用药的情况,才推荐导管消融治疗。随着科技进步和人对高水平生活的追求,导管消融治疗室性早搏的适应证也相应调整了,现将在回顾文献的基础上,对经射频导管消融治疗室性早搏的现况作一概述。     

Neonatal Radiofrequency Catheter Ablation of Junctional Tachycardias

Junctional tachycardias comprise several arrhythmia types with differing mechanisms, principally involving the region of the atrioventricular (A-V) junction. Neonatal radiofrequency catheter ablation has typically been reserved for life-threatening, drug-refractory cases due to the unique concerns regarding patient size and development. We performed radiofrequency catheter ablation on two neonates with incessant, rapid junctional tachycardias and hemodynamic compromise after failing conventional medical therapy. This report describes 2 neonates who underwent emergent radiofrequency catheter ablation, and compares these two patients to a larger pediatric catheter ablation patient cohort. Both neonates had an acutely successful outcome and were able to be discharged within a week of the ablation procedure. Fluoroscopy time and total procedure time were shorter in these two patients than in the course of the average pediatric catheter ablation. Though long-term developmental consequences of neonatal catheter ablation are yet unknown, in unique extreme situations, radiofrequency catheter ablation can be performed in neonates, as in older children and adults, without excessive acute morbidity.     

Electrogram-Guided Radiofrequency Catheter Ablation of Atrial Tissue Comparison with Thermometry-Guide Ablation

Objectives: To characterize a new method for radiofrequency energy titration during ablation of atrial tissue based on reduction in electrogram amplitude. To compare this method with energy titration using electrode thermometry. Background: Complications associated with anatomy-based atrial endocardial radiofrequency ablation for suppression of atrial fibrillation may be due to flawed methods of energy titration. Methods: The effect of radiofrequency ablation on electrogram amplitude was characterized in a porcine model. A method for energy titration guided by electrogram amplitude reduction (electrogram-guided) was developed and validated prospectively. Focal (smooth and trabeculated endocardial areas) and linear (smooth endocardial areas) ablation was performed comparing energy titration guided by amplitude reduction with electrode thermometry. Results: Amplitude reduction during radiofrequency application was not necessarily equal among unipolar and bipolar electrograms in the ablation region; specific patterns of reduction could be discerned, based on factors such as catheter-endocardial orientation. A criterion of >90% reduction of unipolar and/or bipolar amplitude best predicted pathologic lesion success. Electrogram-guided focal and linear lesions in smooth areas were free of lesion complications such as endocardial charring, barotrauma, or damage to contiguous extraatrial structures. However, there was a significant incidence of insufficient lesion size, principally non-transmurality, probably due to undertitration of energy. Thermometry-guided focal and linear lesions in smooth areas were uniformly transmural but frequently evidenced complications, due to overtitration of energy. Electrogram-guided focal lesions in trabeculated areas could usually not be achieved, probably due to insufficient contact of the ablation electrode with adjacent pectinate muscles. Thermometry-guided focal lesions in trabeculated areas were smaller than electrogram-guided lesions and did not evidence complications. Conclusions: Electrogram-guided lesions in smooth endocardial areas were uncomplicated but had a significant incidence of non-transmurality. Thermometry-guided lesions were uniformly transmural but were frequently complicated.     

Temperature Monitoring During Radiofrequency Ablation

Temperature Monitoring During RF Ablation. Thermal injury is the primary mechanism of lesion formation during radiofrequency catheter ablation procedures. Irreversible tissue injury requires heating to approximately 50°C. Temperatures above 100°C result in coagulum formation. Because of this importance of temperature during radiofrequency catheter ablation procedures, temperature monitoring has been proposed as a tool to facilitate catheter ablation procedures. The results of recent clinical studies demonstrate that electrode temperatures do not differ at successful and failed ablation sites, electrode temperature does not predict or eliminate the possibility of arrhythmia recurrence, and closed-loop temperature control decreases but does not eliminate the development of coagulum nor guarantees that target temperatures will be achieved. These observations are due in large part to the important distinctions between electrode temperature, the temperature at the electrode-tissue interface, and the temperature at the ablation target. Nonetheless, temperature monitoring and temperature control are valuable tools during radiofrequency ablation procedures as they provide important information regarding the adequacy of tissue heating, minimize the development of coagulum, and maximize lesion size.     

Catheter Ablation of Canine Ventricular Myocardium Utilizing Radiofrequency Current

To determine if catheter-delivered radiofrequency current (RFC) could safely destroy ventricular myocardium, 6P quadripolar catheters were inserted into the right ventricular and left ventricular endocardium of 11 heparinized, closed-chest dogs. RFC (continuous wave, 625 kHz) was delivered via a commercially available eiectrosurgical unit for 10–20 sec between the catheter tip and a surface electrode (unipolar configuration). Voltage delivered was 42 ± 8 volts with a current of 0.23 ± 0.07 amperes and an impedance of 182 ± 32 ohms. An average power of 9.8 ± 4.4 watts resulted in a delivered energy of 112 ± 60 joules. The catheters were repositioned in the right and left ventricular apices and RFC was delivered between the two tip electrodes for 10–20 sec (bipolar configuration). Voltage delivered was 44 ± 7 watts with a current of 0.20 ± 0.07 amperes and an impedance of 241 ± 49ohms. An averageof 8.5 ± 4.3 watts of power resulted on delivered energy of 106 ± 29 joules.
At necropsy, lesions were identified in 5/11 right and 9/11 left ventricular free-wall sites and 7/11 right and 11/11 left ventricular apical sites. Lesion size ranged from 4–8 mm in depth and 3–9 mm in diameter and the size did not correlate with energy delivered. The endocardial surface was grossly intact in all. No hemodynamic compromise, electrode pitting, or changes in postshock catheter resistance were noted. However, one dog had spontaneous ventricular fibrillation after a transseptal pulse. Although no large thrombi were noted, a thin layer of endocardial thrombus formation was usually present. We conclude that catheter-delivered RFC can selectively damage myocardial tissue with minimal complications.     

Radiofrequency Catheter Ablation of Idiopathic Left Ventricular Tachycardia:

Idiopathic Left Ventricular Tachycardia. Introduction: Idiopathic left ventricular tachycardia with a QRS pattern of right bundle branch block and left-axis deviation constitutes a rare but electrophysiologically distinct arrhythmia entity. The underlying mechanism of this tachycardia, however, is still a matter of controversy. This report describes findings in a 42-year-old man who underwent successful radiofrequency catheter ablation of idiopathic left ventricular tachycardia.
Methods and Results: On electrophysiologic study, the tachycardia was reproducibly induced and terminated with double ventricular extrastimuli. Intravenous verapamil terminated the tachycardia whereas adenosine did not. Detailed left ventricular catheter mapping during sinus rhythm revealed a fragmented delayed potential at the mid-apical region of the inferior site near the posterior fascicle of the left bundle branch. At the same site, continuous electrical activity throughout the entire cardiac cycle was recorded during ventricular tachycardia. Repeated spontaneous termination of this continuous electrical activity in late diastole was followed immediately by termination of the tachycardia. Single application of radiofrequency current for 20 seconds at this site completely abolished inducibility of the tachycardia. After catheter ablation, at the identical site of preablation recording of the fractionated potential during sinus rhythm, no fragmented delayed activity could be recorded. There was no complication from the ablation procedure.
Conclusion: The preablation recordings of fragmented delayed potentials during sinus rhythm and continuous diastolic electrical activity during tachycardia, together with ablation characteristics and previously reported electrophysiologic properties of this arrhythmia, may further support microreentry as the underlying mechanism in idiopathic left ventricular tachycardia.     

Catheter Ablation in the Canine Coronary Sinus Using Radiofrequency Energy

This study was performed to evaluate the effects of radiofrequency catheter ablation in the coronary sinus as a potential means of eliminating conduction over left-sided accessory pathways in humans. Radiofrequency current at a frequency of 500 kHz was delivered by electrode catheter to two sites in the coronary sinus of each often dogs. Left coronary arteriography with venous phase visualization of the coronary sinus was performed before, immediately after, and 2 weeks following ablation. Unipolar electrograms from the ablating electrode were recorded before and immediately after ablation. Coronary arteriography revealed no evidence of damage to the adjacent left circumflex coronary artery or its branches as a result of ablation. Contrast visualization of the coronary sinus showed persistent contrast staining following ablation at two of the ablated sites. Angiographically apparent stenosis of the coronary sinus was seen both acutely and chronically in two cases. Unipolar electrogram recordings from the ablating electrode showed an increase in atrial repolarization voltage (atrial current of injury) of 1.53 ± 1.03 mV (P = 0.00004), and an increase in ventricular repolarization voltage of 0.73 ± 0.84 mV (P = 0.005). There was a 23% decrease in amplitude of atrial electrograms (P = 0.006) and a 7% decrease in amplitude of ventricular electrograms (P = 0.02) recorded from the ablating electrode following ablation. Lesions could be identified grossly and microscopically at 16 of the 20 ablated sites. Perforation of the coronary sinus did not occur. Microscopical observation showed normal healing with granulation tissue and fat necrosis extending outward from the coronary sinus involving the atrial epicardium in 13 lesions, the ventricular epicardium in 5 lesions, and the adventitia of the left circumflex coronary artery in 5 lesions. No medial or intimal involvement of the coronary artery was seen. The coronary sinus itself showed luminal organized thrombus in 4 lesions, with near occlusion of the lumen in 1 case. Radiofrequency ablation in the coronary sinus thus results in lesions of a size and extent that would be expected to successfully ablate some left-sided accessory pathways if delivered in humans. Monitoring of the unipolar electrogram provides insight into the extent of injury during ablation. In some cases, thrombosis of the coronary sinus occurs, the long-term effects of which are not known.     

Effects of Radiofrequency Catheter Ablation on Patients with Permanent Pacemakers

The objective of this study was to assess the effects ofradiofrequency energy application on implanted pacemaker functions.Radiofrequency (RF) catheter ablation may cause pacemaker dysfunction dueto electromagnetic interferences. The effects of RF on pacemaker behaviorwere studied in a series of 38 pacemakers, implanted 18 ± 26 monthsprior to a RF procedure using either a right ventricular approach (AV nodeablation, n = 35) or a left ventricular approach (left concealedaccessory pathway ablation, n = 1; VT ablation, n = 2). The38 patients (mean age 65 ± 9 years) included 20 men and 18 women.Before energy applications, the 23 different pacemaker models wereprogrammed to the VVI mode at the lowest available rate. The continuoussurface ECG was recorded throughout the procedure. Thorough testing of thedevices was performed before and after each RF delivery. Unusual pacemakerresponses occurred in 20 of the 38 cases studied (53%). The impactof RF delivery was unpredictable, and variable dysfunctions were observedat different times for a given patient or could vary for a given model.Unusual pacemaker responses included pacemaker inhibition (n = 8), untoggled backup mode (n = 3), electromagnetic interference noisemode (n = 3), temporary RF-induced pacemaker tachycardia (n =2), erratic behavior (n = 1), oversensing of RF onset and offset (n= 8), and transient loss of ventricular capture, (n = 1).Postablation, most devices automatically toggled back to fullfunctionality. The three devices in the untoggled backup mode had to bereprogrammed to obtain normal operations. At the end of the procedure,pacing thresholds remained unchanged in all but one patient, in whom theincrease in ventricular threshold was due to a nicked lead. In conclusion,implanted pacemakers frequently exhibit transient, unpredictable responsesto RF energy application. Although all pacemaker functions were restored postablation, some devices had to be reset manually. The anomalies observedduring the RF application argue for the simultaneous use of an externalpacemaker in pacing-dependent patients.     

慢传导带传导阻滞作为心房扑动消融终点的意义（附Halo导管应用一例报告）

应用Ｈａｌｏ导管标测技术，结合冠状静脉窦与希氏束电图识别心房扑动折返环的慢传导带，在下腔静脉口到三尖瓣环峡部作射频线性消融，并以慢传导带出现双向阻滞作为心房扑动消融成功的标志，治疗了１例Ｉ型心房扑动患者。随访１个月心动过速未发。由于Ｈａｌｏ导管能在右房内全面记录右房激动顺序，便于了解峡部的传导情况，在心房扑动消融中有助于明确其诱发与终止的机制，并为慢传导带传导阻滞作为成功消融终点提供了可靠的手段。     

Parahisian Radiofrequency Catheter Ablation in Dogs: Comparison of the above-valve and below-valve approaches

In patients with an accessory pathway close to the His bundle, radiofrequency catheter ablation (RFCA) requires additional care to avoid damage to the normal conduction system. To assess differences between approaches from above or below the tricuspid valve (TV), we performed RFCA in 20 dogs (from above, group A, n=10; from below, group B, n=10). RF energy with temperature control at 60° 60 seconds was administered at the site where a small His potential was recorded from the ablation catheter guided by fluoroscopy and transesophageal echocardiography (TEE) (in the latter six dogs). Before and after RFCA, electrophysiological testing was performed and histological findings were compared. An ablated lesion was created in 7 of 10 (2 of 2 guided by TEE) dogs in group A and 5 of 10 (3 of 4 TEE) dogs in group B. In group A, an ablated lesion involved the atrium and ventricle in the anterior site of His bundle, but the lesion was only in the ventricle in group B. An atrioventricular block (AVB) and severe damage to the penetrating bundle was observed in one dog of group A. A large hematoma on the TV was made in 2 dogs and the complete right bundle branch block (CRBBB) occurred in 3 dogs of group B. The approach from below the TV was safer than that from above the TV in parahisian RFCA, because it did not create an AVB, although it has a high incidence of CRBBB and associated technical difficulties.     

射频消融治疗恶性室性心律失常现状

包括持续性室性心动过速、心室颤动在内的恶性室性心律失常是导致患者心脏性猝死的主要原因,近年来研究证明射频消融可有效治疗恶性室性心律失常,并避免了其它治疗手段的风险和不良反应。现讨论射频消融治疗恶性室性心律失常的现状与进展。     

Radiofrequency Catheter Ablation of Atrial Flutter After Orthotopic Heart Transplantation

Ablation of Atrial Flutter After Heart Transplantation. Introduction : Antiarrhythmic drug refractory recurrent atrial flutter occurred in a 39-year-old man who had undergone successful orthotopic heart transplantation 3 months ago.
Methods and Results : At electrophysiologic study, the transplanted right atrium showed type I atrial flutter. The recipient right atrium was in sinus rhythm with complete atrioatrial dissociation of electrical activity. Mapping demonstrated double-spike electrograms in the low posterior region of the donor right atrium. During radiofrequency current application near this site, the double potentials were dissociated progressively and atrial flutter was terminated immediately. Thereafter, both the recipient and the transplanted atria were in sinus rhythm of different cycle lengths with continued electrical dissociation.
Conclusion : This is the first report of successful radiofrequency catheter ablation of atrial flutter in a transplanted heart. Although mapping of the arrhythmia is more difficult due to the large circumference of the right atrium, which consists of parts of the recipient right atrium and the transplanted atrium, ablation should be considered in those patients with drug refractory supraventricular tachyarrhythmias.