Discrete potentials guided radiofrequency ablation for idiopathic outflow tract ventricular arrhythmias

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1 Europace (2015) 17, doi: /europace/euu184 CLINICAL RESEARCH Cardiac electrophysiology Discrete potentials guided radiofrequency ablation for idiopathic outflow tract ventricular arrhythmias Enzhao Liu, Gang Xu*, Tong Liu, Lan Ye, Qitong Zhang, Yanshu Zhao, and Guangping Li Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University, Tianjin , People s Republic of China Received 18 March 2014; accepted after revision 10 June 2014; online publish-ahead-of-print 1 September 2014 Aims Discrete potentials (DPs) have been recorded and targeted as the site of ablation of the outflow tract arrhythmias. The aim of the present study was to investigate the significance of DPs with respect to mapping and ablation for idiopathic outflow tract premature ventricular contractions (PVCs) or ventricular tachycardias (VTs).... Methods Seventeen consecutive patients with idiopathic right or left ventricular outflow tract PVCs/VTs who underwent radiofrequency catheter ablation were included. Intracardiac electrograms during the mapping and ablation were analysed. and results During sinus rhythm, sharp high-frequency DPs that displayed double or multiple components were recorded following or buried in the local ventricular electrograms in all of the 17 patients, peak amplitude mv. The same potential was recorded prior to the local ventricular potential of the PVCs/VTs. Spontaneous reversal of the relationship of the DPs to the local ventricular electrogram during the arrhythmias was noted. The DPs were related to a region of low voltage showed by intracardiac high-density contact mapping. At the sites with DPs, lower unipolar and bipolar ventricular voltage of sinus beats were noted compared with the adjacent regions without DPs (unipolar: vs mv, P, 0.05; bipolar: vs mv, P, 0.05). The targeted DPs were still present in 12 patients after successful elimination of the ectopies. Discrete potentials were not present in seven controls.... Conclusion Discrete potentials and related low-voltage regions were common in idiopathic outflow tract ventricular arrhythmias. Discrete potential- and substrate-guided ablation strategy will help to reduce the recurrence of idiopathic outflow tract arrhythmias Keywords Ventricular arrhythmia Outflow tract Discrete potentials Local voltage Introduction The majority of idiopathic premature ventricular contractions (PVCs) or ventricular tachycardias (VTs) have a right ventricular outflow tract (RVOT) or left ventricular inferoseptal origin. 1,2 In addition, a small number of cases with idiopathic PVCs/VTs have been reported to originate from the pulmonary artery (PA) or the aortic sinus cusp (ASC) and can be ablated successfully. 3 9 Clinically, discrete and fragmented local potentials have been documented in electrograms recorded at ablation site during sinus rhythm or the arrhythmia in patients undergoing radiofrequency ablation for arrhythmias originating in the outflow tract or PA. 5,10,11 In a recent study, catheter ablation targeting sites with local abnormal ventricular activities during stable sinus or paced rhythm offers a substrate ablation strategy of VTs in the setting of structural heart disease. 12 However, a better understanding of the correlation between the discrete potentials (DPs) and the origin of the outflow tract arrhythmia is needed. The aim of the present study was to investigate the characteristics and significance of the DPs with respect to idiopathic outflow tract arrhythmia ablation. * Corresponding author. Tel: ; fax: address: xugang_163com@163.com Published on behalf of the European Society of Cardiology. All rights reserved. & The Author For permissions please journals.permissions@oup.com.

2 454 E. Liu et al. What s new? Local low-voltage region correlated with discrete potentials (DPs) was recorded during voltage mapping in successful ablation site for idiopathic outflow tract ventricular arrhythmias. We supposed that idiopathic outflow tract ventricular arrhythmia was substrate-related arrhythmia. In most cases of this series, no isoelectric interval between the DPs and local ventricular electrogram was observed. We supposed that the overlap of the DPs with the local ventricular potentials indicates the interlock distribution of a low-voltage zone with relatively normal myocardium. Discrete potentials-guided substrate mapping and ablation for idiopathic outflow tract ventricular arrhythmias in this series achieved good clinical results. Methods Study population The study population consisted of 17 out of 24 consecutive patients who underwent radiofrequency catheter ablation of symptomatic idiopathic outflow tract PVCs between September 2012 and December 2013 at the Second Hospital of Tianjin Medical University. The selection criteria for catheter ablation included severe symptoms that were clearly related to frequent ventricular arrhythmias, inability of the patient to tolerate treatment, or unsuccessful treatment with at least two antiarrhythmic drugs. Patients with arrhythmogenic right ventricular cardiomyopathy/ dysplasia (ARVC/D, 2010 Task Force Criteria 13 ) and who had undergone failed ablation procedures previously were excluded. All patients had a normal electrocardiogram (ECG) during sinus rhythm, no structural abnormalities were apparent on echocardiography and cardiac magnetic resonance. SPECT was performed in five patients. No myocarditis was suspected in this series. The average age was years (range: years), and 12 (70.6%) were women. The average ejection fraction was (range: ). On 24 h Holter recordings, the mean percentage of PVCs was % (range: %). Four of the 17 patients had non-sustained VT (NSVT) lasted for,30 s. None patient had sustained VT. The other 13 patients had symptomatic PVCs. The patients symptoms, clinical history, and arrhythmia characterization are summarized in Table 1. The study was approved by the hospital Ethics Committee. Twelve-lead surface ECG, procedure notes, intracardiac unipolar and bipolar electrograms, and electroanatomical data were reviewed. The characteristics of the local potentials at successful ablation sites during either sinus rhythm or PVCs were further analysed. Electrophysiological study and mapping procedure After obtaining informed consent, electrophysiological evaluation and radiofrequency catheter ablation were performed. All antiarrhythmic drugs were withdrawn for at least five half-lives. Under local anaesthesia, one 6F quadripolar catheter was introduced into the right ventricular apex or the His bundle region via the femoral veins. Also, a 6F decapolar catheter was advanced within the coronary sinus via the right jugular vein. All 12 surface ECG leads and the intracardiac electrograms were recorded and stored by EP-Mate system (St Jude Medical). Electrograms were bandpass filtered from 30 to 500 Hz for bipolar and 1 to 240 Hz for unipolar recordings. After the baseline study, a deflectable 7F quadripolar open-irrigated catheter with 4 mm distal electrode ( mm interelectrode spacing, Therapy TM Cool Path TM Duo, St Jude Medical) used for mapping Table 1 Clinical characteristics of the patients Case Gender Age Symptoms Symptom Clinical PVCs Echo Coronary Previous (years) Duration arrhythmia per day LVEF angiography ablation (n,%) (%) attempts... 1 F 37 Palpitations, syncope 1 year PVC/NSVT 8303, 7.4% 62 ND No 2 M 45 Palpitations, short of breath 5 months PVC , 24.4% 67 ND No 3 F 47 Chest discomfort 1 year PVC , 22.6% 59 Normal No 4 F 66 Chest discomfort 1 month PVC 7439, 7.3% 64 Normal No 5 F 65 Palpitations 8 years PVC/NSVT 8034, 6.8% 70 ND No 6 F 54 Palpitations, chest discomfort 5 months PVC , 16.3% 70 ND No 7 F 55 Palpitations 1 year PVC , 15.2% 70 Normal No 8 F 59 Palpitations 30 years PVC 6057, 5.7% 69 ND No 9 M 71 Palpitations 4 years PVC , 9.5% 55 Normal No 10 F 57 Palpitations 5 years PVC 8903, 7.8% 64 ND No 11 M 65 Syncope 30 years PVC/NSVT 1323, 1.2% 61 Normal No 12 F 57 Palpitation 5 years PVC 7866, 6.9% 58 Normal No 13 M 45 Palpitation 2 years PVC , 21.8% 68 Normal No 14 M 44 Palpitation 3 months PVC 9835, 8.3% 64 ND No 15 F 63 Palpitation, short of breath 1 year PVC , 10.2% 58 Normal No 16 F 58 Palpitation 2 years PVC/NSVT 7685, 5.9% 60 Normal No 17 F 49 Palpitation 7 months PVC , 8.9% 65 ND No F, female; M, male; LVEF, left ventricular ejection fraction; ND, not done; PVC, premature ventricular contractions; NSVT, non-sustained ventricular tachycardia.

3 DPs for idiopathic outflow tract PVCs or VTs 455 and ablation was introduced to RVOT via the femoral vein or left ventricle via the femoral artery. If the clinical arrhythmia did not appear spontaneously, programmed ventricular stimulation and incremental burst pacing or intravenous isoproterenol infusion (1 3 mg/min) was administered to provoke the arrhythmia. Detailed high-density voltage mapping during sinus rhythm and activation mapping during clinical PVCs with EnSite Velocity TM (St Jude Medical) were started in the right or left ventricular outflow tract (determined by QRS morphology of the PVCs on the surface ECG). The activation times were assigned on the basis of the onset of the local bipolar electrograms using a surface ECG lead as a reference and displayed as colour gradients on a three-dimensional activation map. Electroanatomical points that were clearly internal to the three-dimensional surface were excluded. When a PA or ASC arrhythmia origin was suspected, arteriography of the PA or aortic roots in the right and left anterior oblique projections was performed to determine the position of the semilunar valves. In the region of earliest activation determined by activation mapping, detailed local potential mapping was performed to record DPs. Discrete potentials were defined as sharp high-frequency potentials occurring after or during the local ventricular electrogram in sinus rhythm or preceding the local ventricular electrogram during PVCs that sometimes displayed double or multiple components. During both sinus rhythm and the ectopies, the peak-to-peak amplitude of DPs and local ventricular potentials were measured. After the DPs were analysed, local ventricular potentials of the adjacent region within outflow tract where the mapping catheter just lost the discrete signals were analysed to compare with the local voltage at the sites with DPs. Pace mapping at the sites with DPs was attempted in all patients with a stimulus pulse width of 2 ms at twice the diastolic threshold, although this was sometimes limited by non-capture even at high output (20 ma). The pacing morphology was compared with that of the clinical arrhythmias. Ablation procedure The primary target for ablation was selected based on the earliest local activation with DPs, which wasclearly associated with the clinical arrhythmia and confirmed by pace mapping that exhibited 11 of 12 matches between the paced and spontaneous QRS complexes during PVCs. If no such potential was associated with the clinical arrhythmia or the pace mapping was limited by non-capture, the ablation was targeted to the earliest endocardial activation sites during PVCs. Radiofrequency energy was delivered with a preset temperature of 438C and a power limit of 20 W for 30 s when the catheter was positioned in the root of PA or aorta and 30 W when the catheter was positioned in the ventricular outflow tract below semilunar valves. Successful ablation for the arrhythmia met three criteria: (i) the absence of spontaneous or induced clinical PVCs or VTs (both in the absence and presence of isoproterenol) during at least 30 min after ablation; (ii) the absence of any clinical arrhythmias during 48 h ECG monitoring in the absence of antiarrhythmic drugs; and (iii) no recurrence of symptomatic arrhythmias recorded by 24 h Holter monitoring in the absence of any antiarrhythmic drugs during at least 3-month follow-up. Seven consecutive patients (structural heart disease were excluded) without PVCs undergoing radiofrequency ablation because of typical atrial flutter or paroxysmal atrial fibrillation served as controls. The ablation catheter was placed in RVOT below the pulmonary valve. After three-dimensional voltage mapping during sinus rhythm was completed, RVOT pacing was performed at different sites. The local electrograms recorded during sinus rhythm and pacing were compared with the same filter settings and amplification used in the patients with PVCs ablation. Statistical analysis Continuous data are expressed as mean + SD. The mean values were compared using the Student s unpaired t-test. A value of P, 0.05 was considered statistically significant. Results Table 2 summarizes the electrocardiographic characteristics of the ventricular ectopies and electrophysiological parameters during the mapping and ablation. Electrocardiographic and electrophysiological characteristics before ablation The clinical PVCs occurred spontaneously in 13 patients. Four of the 17 arrhythmias were induced during isoproterenol administration or burst ventricular pacing. During the clinical arrhythmia, surface ECG revealed a single QRS morphology in all patients. The four patients with clinically documented NSVT also had PVCs with the same QRS morphology as the VTs. The QRS width of the PVCs and cycle length of the four clinically documented VTs were ms ( ms) and ms ( ms), respectively. In 13 of the 15 patients with PVCs showed a left bundle branch block (LBBB) pattern, the frontal QRS axis was normal. Inferior axis was shown in two patients with PVCs of LBBB pattern and two patients with PVCs of right bundle branch block (RBBB) pattern. Mapping and ablation procedure In the 17 patients treated by radiofrequency ablation, the ablation sites were located in RVOT in 11 patients, in left ventricular outflow tract (LVOT) in 2 patients, in right coronary cusp in 1 patient, and in PA in 3 patients (Table 2). In all of the 17 patients, DPs were recorded at the final ablation sites. For voltage and activation mapping, the mapping density was points/cm 2 and points/map. Characteristics of the local signals at final ablation sites were summarized in Table 3. Sharp high-frequency potentials were shown in all of the 17 patients. The bipolar electrograms displayed a DP following or buried in the local ventricular electrogram during sinus rhythm (V sinus ). Spontaneous reversal of the relationship of DPs to local ventricular electrograms during PVCs was noted in all of the 17 patients (Figures 1 and 2). At the sites where the unipolar and bipolar electrograms were optimal with regard to ablation, DPs were recorded with a DPs QRS of ms (median 33 ms) during the PVCs. Patients who experienced VTs during the procedure also showed the same DPs preceding each QRS complex of the VTs. The mean peak amplitude of the DPs during sinus rhythm was mv. During the PVCs, the amplitude ( mv) of the DPs showed no difference to sinus rhythm (P. 0.05). At the sites with DPs, lower unipolar and bipolar ventricular voltage of sinus beats were noted compared with the adjacent region without DPs (unipolar: vs mv, P, 0.05; bipolar: vs mv, P, 0.05; Figure 2). Very low-amplitude signals or an isoelectric interval between DPs and local ventricular electrograms presented only in Case 3 with the PVCs originating in the PA. The duration of DPs could not be

4 456 E. Liu et al. Table 2 Electrocardiographic characteristics of the arrhythmias and electrophysiological parameters during the mapping and ablation Case PVC/VT morphology QRS width VT cycle PVC/VT induction Pace map Successful and the frontal QRS axis (ms) length (ms) (QRS P /QRS PVC ) ablation site... 1 LBBB, normal axis Burst pacing N/A RVOT 2 LBBB, normal axis 170 N/A N/A RVOT 3 LBBB, inferior axis 200 N/A 11/12 PA 4 LBBB, normal axis 160 N/A 12/12 RVOT 5 LBBB, normal axis /12 RVOT 6 LBBB, normal axis 140 N/A 12/12 PA 7 LBBB, normal axis 160 N/A Isoproterenol 12/12 RVOT 8 RBBB, inferior axis 180 N/A Isoproterenol 12/12 LVOT 9 RBBB, inferior axis 160 N/A 11/12 LVOT 10 LBBB, normal axis 160 N/A 12/12 RVOT 11 LBBB, normal axis /12 RVOT 12 LBBB, normal axis 180 N/A 12/12 RVOT 13 LBBB, normal axis 130 N/A 12/12 RVOT 14 LBBB, normal axis 145 N/A 12/12 RVOT 15 LBBB, inferior axis 150 N/A N/A RCC 16 LBBB, normal axis Isoproterenol 12/12 RVOT 17 LBBB, normal axis 130 N/A N/A PA LBBB, left bundlebranchblock; RBBB, rightbundle branchblock; RVOT, rightventricularoutflowtract; PA, pulmonaryartery; LVOT, leftventricularoutflow tract; RCC, right coronary cusp. Table 3 Characteristics of intracardiac local potentials during mapping and ablation Case Sinus... PVC/VT... DP sinus V sinus UNI sinus V n UNI n DP PVC DP PVC QRS amplitude amplitude amplitude amplitude amplitude amplitude (ms) (mv) (mv) (mv) (mv) (mv) (mv) Mean + SD DP sinus, discrete potential of a sinus beat recorded at ablation site; V sinus, local bipolar ventricular electrogram of a sinus beat at ablation site; UNI sinus, local unipolar voltage of a sinus beat at ablationsite; V n, local bipolar ventricularpotential of a sinusbeatat a siteadjacent to the regionwith DPs recorded; UNI n, localunipolarvoltageof a sinus beat ata siteadjacentto the region with DPs recorded; DP PVC, discrete potential recorded during the ectopy at ablation site; DP PVC QRS, interval between the DP PVC to the earliest onset of surface QRS of the PVC.

5 DPs for idiopathic outflow tract PVCs or VTs 457 I II III avr avl avf V1 V2 V3 V4 V5 V6 ABLd ABLp HIS UNI 100 ms Figure 1 Representative intracardiac electrogram at a successful ablation site in PA. ABLd exhibited a discrete sharp potential (arrow head) following the local ventricular potential during sinus rhythm and had a reversed sequence during the PVC (arrow). PA, pulmonary artery; PVC, premature ventricular contraction. measured accurately because the DPs always overlap with local ventricular electrograms in most of the cases. Pace mapping at the sites with DPs could be performed successfully in 13 of 17 patients, because it was limited by non-capture even at high output (20 ma) in 4 patients. At optimal ablation sites, pace mapping demonstrated concordance in at least 11 of 12 ECG leads in the 13 patients. Neither low-voltage region nor DP was present in any of the seven controls. Response to ablation and procedural outcome Radiofrequency ablation was successful in all of the 17 patients, with an average of ablation attempts (range: 3 10) for s (range: s). The mean temperature achieved was C (range C). The targeted DPs were still present during sinus rhythm after radiofrequency ablation in 12 of the 17 patients in whom ablation was successful. It was noted that the DPs in the late phase of local ventricular electrograms were delayed gradually before complete elimination was achieved in the patients whose DPs were abolished completely, and in the patients with DPs still present after successful radiofrequency ablation, decrement of the interval between ventricular potential and the DPs was observed in sinus beats. In all cases, the clinical arrhythmia did not recur spontaneously and was non-inducible by burst pacing or intravenous isoproterenol infusion after ablation. No procedure-related acute complications occurred in any patient. Follow-up All patients were discharged without any medications and were free from arrhythmias and symptoms during follow-up of months (range 3 14 months). No chronic complications occurred during the follow-up period. Discussion Major findings Previous studies using catheter ablation to treat idiopathic outflow tract arrhythmias reported excellent outcomes, 14 but the substrate of the idiopathic outflow tract arrhythmias was not systematically studied. In the present study, idiopathic outflow tract PVCs/VTs were ablated successfully by targeting the region with DPs. These DPs indicated the presence of a region of low voltage. Therefore, we speculated that idiopathic outflow tract PVCs/VTs are substrate-related arrhythmias. Characteristics of the local electrograms and the possible mechanism of the outflow tract arrhythmias Some significant characteristics were observed in the local electrograms at the successful ablation sites in the present study. On intracardiac electrograms, sharp high-frequency DPs at the successful ablation sites were shown in all of the cases (Figures 1 and 2). Because the ventricular myocardium in the semilunar region of the aorta and PA is thinner with intervening fibrous tissue, the local voltage in the relatively normal outflow tract region of this series ( mv) could be lower than other part of the ventricle. Although no ARVC/D was suspected in this series, Corrado et al. 15 demonstrated fragmented low-voltage regions in 7 out of 27 patients with RVOT tachycardia and suggested that these patients represented early and minor forms of ARVC/D. In addition, DPs and lowvoltage region were also recorded in LVOT in our series. The lower local voltage in the successful ablation regions compared with the relatively normal regions within the outflow tract (Figure 2) supported the hypothesis that the idiopathic outflow tract PVCs/VTs were substrate-related arrhythmias. Careful mapping and recognizing of discrete and/or multi-component potentials and low-voltage region during sinus rhythm are important so as not to overlook any arrhythmia substrate. The presence of DPs always related to a region with low voltage and indicated the target for ablation. In our study, the DPs recorded in the patients with idiopathic outflow tract ventricular ectopies seem to be a prerequisite for the arrhythmias. A recent study revealed that in the patients with ventricular arrhythmias ablated within the PA, a spiky potential recorded above the pulmonary valve reflects the near-field activation of the myocardial extension into the PA, and a dull potential reflects the far-field ventricular activation. When the successful ablation sites

6 458 E. Liu et al. A 10 mv C I II III avr avl avf V1 V2 5 mv 0 mv V3 V4 V5 V6 CS5,6 B CS ABL CS ABLd ABLp UNI Figure 2 A representative case of PVC ablated successfully within RVOT below the pulmonary valve. Arrhythmogenic right ventricular cardiomyopathy/dysplasiawas ruled out. (A) Voltage mapping (EnSite Velocity TM ) during sinus rhythm showed a zone with voltage below0.5 mv in the high anterior interventricular septum. The black line indicated the pulmonary valve position. The arrow indicated the area of low voltage. (B) The LAO view of the radiogram showed the ablation catheter position in the septum of RVOT. (C) The intracardiac electrogram on the mapping catheter (ABLd) revealed a discrete electrogram (arrow) during both sinus rhythm and premature beat at the success site. PVC, premature ventricular contraction; RVOT, right ventricular outflow tract; LAO, left anterior oblique projection. were located at more distant sites from the pulmonary valve, the two components were more separated. 16 However, no isoelectric interval was observed in most of our cases. The duration of the DPs could not be measured accurately in this study because of overlapping with the local ventricular potentials in some of the cases, which indicated the interlock distribution of the fragmented low-voltage regions with relatively normal myocardium. In the present study, the delay of DPs during ablation and its complete elimination when successful ablation of the PVCs was achieved in some cases suggested that DPs were correlated with the arrhythmia rather than a bystander. On the other hand, we performed high-density mapping in this study. The recording of DPs was restricted within the region of low voltage where the ablation was effective in each patient. When the catheter was moved to the adjacent area with normal voltage, no DP was recorded. We did not detect a bystander low-voltage area in any patient. Recording of discrete potentials as the target for ablation of outflow tract arrhythmias In the past, several investigators have demonstrated similar potentials in patients in whom the site of origin was above the semilunar valves. Mapping and direct ablation of the potential were useful to eliminate the ventricular arrhythmias. 17 Srivathsan et al. 18 described discrete arterial potentials in 12 patients with outflow tract ventricular arrhythmias originating above the semilunar valves. They also provided electrophysiological evidence to support the notion that the potentials are involved in the ventricular arrhythmia substrate. The potentials were considered to be an arrhythmogenic source for the patient s clinical arrhythmia, and targeting these potentials was effective. Timmermans et al. 5 recorded sharp local potentials similar to the DPs in five out of six patients with arrhythmias originating in the root of the PA and the sharp potential was considered to be the activation of the myocardial connection from this site to the RVOT. Tada et al. 10 found similar sharp local potentials during sinus rhythm as well as during PVCs/VTs before ablation in 12 patients with ectopy originating above the pulmonary valve. Their results with the recording of this potential at the final ablation site within the PA during sinus rhythm after a successful ablation in some patients may support the idea that the sharp potential represents activation of the discrete myocardial extension connecting the arrhythmia focus and right ventricular myocardium rather than activation of the focus itself. Ouyang et al. 7 described that a low-amplitude, high-frequency potential preceded the onset of the QRS complex in patients with VTs originating from the ASC and suggested that the potential might be a slow conduction area between the ventricle and aortic sinus. In a recent report, Bloch Thomsen et al. 19 recorded fragmented local potential below the semilunar valves in patients with outflow tract ectopy and demonstrated that this potential does not represent pacemaker activity but rather slow conduction of the impulse after exiting the focus. Using the earliest surface QRS as reference, the DPs were very early in some of the cases we ablated (Table 3). As

7 DPs for idiopathic outflow tract PVCs or VTs 459 demonstrated in recent studies, 5,7,11,19 DPs might represent a critical slow conduction zone or some impaired connections between the arrhythmia focus and relatively normal tissue. Therefore, we postulated that the early DPs in our study may represent a longer conducting distance from the arrhythmia focus (endocardial or epicardial) to the ablation site. As we anticipated, the arrhythmias with epicardial origin also have the chance to be eliminated by ablating the endocardial exit. In other words, we ablated the critical slow conduction zone instead of the arrhythmia focus in this series. Ablation in the slow conduction zone may block the exit of the impulse from the ectopic pacemaker rather than eliminate the ectopic focus. We speculate that the persistence of DPs after ablation represents some remnant part of the slow conduction tissue. We do not exclude the possibility that the early DPs indicate epicardial origin of the ectopies. An endocardial unipolar amplitude of,4.4 mv in the right ventricule was considered the optimal cutoff predicting epicardial scar. 20 In fact, the unipolar voltage recorded at the site with DPs in some cases was,4.4 mv. Therefore, epicardial focus was possible in some patients. Our results supported the hypothesis that the region with fragmented low voltage characterized by the presence of DPs represents a critical slow conduction zone or some zone of impaired conductivity within the outflow tract. Based on the results of this study, we proposed the ablation strategy of outflow tract ectopies guided by mapping DPs and low-voltageregion, especiallyin patients withhaemodynamic unstable VTs or few ectopies are found during procedure. Limitations First, the duration of DPs could not be measured accurately because of overlapping with the local ventricular electrograms in some of the cases especially during sinus rhythm. But on the other hand, the overlap of DPs with local ventricular electrograms may indicate the interlock distribution of the low-voltage region with relatively normal myocardium. Secondly, substrate mapping was carried out with a quadripolar catheter without contact force sensors, which could affect the meaning of low-voltage substrate and diseased tissue. However, the mapping and ablation catheter was operated by experienced operators and the contact between the catheter and tissue was relatively stable. The electroanatomical points that were clearly internal to the three-dimensional surface were excluded, and.300 points were included in each map. Thirdly, de Bakker et al. 21 demonstrated an increase in the delay in local activation time in the infarcted human heart by performing incremental pacing. But no decremental property was observed during incremental atrial and ventricular pacing in the study of Bloch Thomsen et al. 19 Since the DPs were not validated systematically in this retrospective study, it could not be certain that the DP recorded during sinus rhythm is the DP during PVCs. However, DPs were recorded in all of the 17 patients at the successful ablation site during both sinus and ectopic beats. In the patients with DPs still present after successful radiofrequency ablation, decrement of the interval between ventricular potentials and the DPs was observed in sinus beats. Finally, this study was retrospective and the total number of patients included was small, but the presence of DPs in all of the cases will indicate the significance of the DPs with respect to the mapping and ablation of idiopathic outflow tract arrhythmias. A prospective study including more patients and a control group to validate the role of DPs in guiding outflow tract PVC ablation is needed. Conclusions Discrete potentials were more common in idiopathic outflow tract ventricular arrhythmias than previously recognized. The presence of DPs and related low-voltage regions indicated that the outflow tract ventricular arrhythmias are substrate-related arrhythmias. Detailed DP and substrate mapping should be performed in the ablation of idiopathic outflow tract arrhythmias to reduce the recurrence of PVCs/VTs. Conflict of interest: none declared. References 1. Ito S, Tada H, Naito S, Kurosaki K, Ueda M, Hoshizaki H et al. Development and validation of an ECG algorithm for identifying the optimal ablation site for idiopathic ventricular outflow tract tachycardia. J Cardiovasc Electrophysiol 2003;14: Ohe T, Aihara N, Kamakura S, Kurita T, Shimizu W, Shimomura K. Long-term outcome of verapamil-sensitive sustained left ventricular tachycardia in patients without structural heart disease. 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8 460 E. Liu et al. 18. SrivathsanKS, Bunch TJ, AsirvathamSJ, EdwardsWD, FriedmanPA, Munger TM et al. Mechanisms and utility of discrete great arterial potentials in the ablation of outflow tract ventricular arrhythmias. Circ Arrhythmia Electrophysiol 2008;1: Bloch Thomsen PE, Johannessen A, Jons C, Hansen TF, Kanters JK, Haarbo J et al. The role of local voltage potentials in outflow tract ectopy. Europace 2010;12: Tokuda M, Tedrow UB, Inada K, Reichlin T, Michaud GF, John RM et al. Direct comparison of adjacent endocardial and epicardial electrograms: implications for substrate mapping. J Am Heart Assoc 2013;2:e de Bakker JM, van Capelle FJ, Janse MJ, Tasseron S, Vermeulen JT, de Jonge N et al. Slow conduction in the infarcted human heart. Zigzag course of activation. Circulation 1993;88: EP CASE EXPRESS doi: /europace/euu363 Online publish-ahead-of-print 23 December Hybrid atrial fibrillation ablation via direct right atrial approach: first-ever case Eugene H. Chung 1 *, Mark Joseph 2, and Andy C. Kiser 2 1 Division of Cardiology, The University of North Carolina at Chapel Hill, School of Medicine, 160 Dental Circle CB 7075, Chapel Hill, NC 27599, USA and 2 Department of Surgery, Division of Cardiothoracic Surgery, The University of North Carolina at Chapel Hill, 160 Dental Circle CB 7065, Chapel Hill, NC 27599, USA * Corresponding author. Tel: ; fax: address: ehchung@med.unc.edu A 60-year-old female with persistent atrial fibrillation (AF) and flutter was referred for hybrid AF ablation. She had an occluded inferior vena cava filter from a history of deep vein thrombosis and pulmonary embolism. Via a right mini-thoracotomy, the pericardium was accessed and unipolar/bipolar radiofrequency lesions were placed around the pulmonary veins (PV) and on the roof of the right atrium (RA). Her flutter terminated. With fluoroscopy and TEE, the RA free wall was punctured with a Tuhoy needle and the interatrial septum was crossed. Left atrial (LA) access was maintained with glidewires over which 12 fr sheaths were positioned in the RA and secured with Rummel tourniquets. After a second transseptal puncture, long steerable sheaths were placed in the LA. Signal was still present in the low posterior wall and the anterior aspect of the right superior PV so additional lesions were placed. Assessment of the PVs confirmed entrance and exit block. Neither AF nor flutter could be induced. The long sheaths were withdrawn and the ablation catheter was inserted into one of the 12 fr sheaths to create a cavotricuspid-isthmus line. This direct RA approach could be a viable option for patients with challenging venous access or anatomy. The full-length version of this report can be viewed at: Documents/Hybrid-atrial-fibrillation.pdf. Published on behalf of the European Society of Cardiology. All rights reserved. & The Author For permissions please journals.permissions@oup.com.