Local Ventricular Electrogram Research Articles

Procedural Adaptations to Avoid Haemodynamic Instability During Catheter Ablation of Scar-related Ventricular Tachycardia.

Classically, catheter ablation for scar-related ventricular tachycardia (VT) relied upon activation and entrainment mapping of induced VT. Advances in post-MI therapies have led to VTs that are faster and haemodynamically less stable, because of more heterogeneous myocardial fibrosis patterns. The PAINESD score is one means of identifying patients at highest risk for haemodynamic decompensation during attempted VT induction, who may, therefore, benefit from alternative ablation strategies. One strategy is to use temporary mechanical circulatory support, although this warrants formal assessment of cost-effectiveness. A second strategy is to minimise or avoid VT induction altogether by employing a family of 'substrate'-based approaches aimed at identifying VT isthmuses during sinus or paced rhythm. Substrate mapping techniques are diverse, and focus on the timing, morphology and amplitude of local ventricular electrograms - sometimes aided by advanced non-invasive cardiac imaging modalities. In this review, the evolution of VT ablation over time is discussed, with an emphasis on procedural adaptations to the challenge of haemodynamic instability.

Reverse-Type Left Posterior Fascicular Ventricular Tachycardia: A New Electrocardiographic Entity.

This study sought to demonstrate a new type of verapamil-sensitive fascicular ventricular tachycardia (VT) with a reverse circuit. Left posterior fascicular ventricular tachycardia (LPFVT) is the most common form of verapamil-sensitive fascicular VT. Reverse-type LPFVT has not been reported. We searched for a reverse-type LPFVT among 242 patients with verapamil-sensitive VT from February 2006 to September2019. Three patients had a reverse-type LPFVT (cycle lengths: 340, 360, and 340ms). QRS configuration during VT was narrow (140, 150, and 140ms) and exhibited rSr' morphology in V1 with an early precordial transition and inferior axis. Two of 3 patients had common-type LPFVT. During reverse-type LPFVT, the earliest ventricular activation was the left superior middle septum. Fragmented Purkinje potentials (P1) buried within the local ventricular electrogram were recorded with an activation sequence from the apex to the base and were linked to the subsequent left ventricular septal activation. After radiofrequency catheter ablation at P1 during LPFVT, the reverse-type LPFVT also became noninducible. In 1 patient with only the reverse-type LPFVT, radiofrequency catheter ablation at the earliest LV activation site suppressed VT. These findings suggest that this new type of verapamil-sensitive fascicular VT shares a re-entrant circuit with a reverse direction of common LPFVT with an intramural exit site at the superior middle septum. Reverse-type LPFVT can occur. If common LPFVT exists, diastolic P1 during LPFVT can be a common target of ablation. If only reverse-LPFVT is inducible, the earliest ventricular activation site can be a target.

Pseudo normalization of H–V interval due to intra-His block in a patient with fasciculoventricular accessory pathway

A 57-year-old male suffering from cardiogenic syncope was found to have preexcited QRS on surface ECG at admission. A dual-chamber ICD was implanted after discovering intermittent high degree A–V block and ventricular tachycardia during hospitalization. An EP study was performed 2 days later. Fasciculoventricular accessory pathway was diagnosed based on the fixed H–V interval with different A–H interval when atrial activation conducted to ventricle. However, the H–V interval was normal, which can be explained by intra-His block based on the findings of two split His potentials, the second of which was closely followed by local ventricular electrogram. The conduction delay in His bundle led to pseudo normalization of H–V interval.

Ultra-high resolution mapping and ablation of accessory pathway conduction.

Detailed mapping studies of accessory pathway (AP) conduction have not been previously performed using ultra-high resolution mapping systems. We sought to evaluate the clinical utility of ultra-high resolution mapping systems and the novel "Lumipoint" algorithm in AP ablation. This study included 17 patients who underwent AP mapping using minielectrode basket catheters and Rhythmia systems. Ablation was performed with 4-mm irrigated-tip catheters. Antegrade and retrograde AP conduction was observed in 6 and 16 patients. Atrial activation map was obtained during orthodromic tachycardia and ventricular pacing in 13 (76.5%) and 14 (82.3%) patients, and the earliest activation area was identical. Ventricular activation maps were created during atrial pacing in 3 patients. All maps showed focal activation patterns on global activation histograms, and the valley on the histogram highlighted the earliest activation area. "Complex activation" features further highlighted limited areas with continuous electrical activity during the time period in the majority. APs were located at the mitral and tricuspid annuli in 15 and 2 patients, and all were successfully eliminated with 3.4 ± 0.6s applications. No patients had recurrences during a median follow-up of 15 [10.5-22.5] months. At successful ablation sites, the local atrial and ventricular electrogram amplitudes and ratio tended to be greater, and fusion or continuous electrical activity between the atrial and ventricular components was more frequently observed on the minielectrode than ablation catheter (17/17 vs. 12/17, p = 0.005). Ultra-high resolution activation mapping and a novel algorithm facilitated the AP localization. The local electrogram characteristics differed between the minielectrode and ablation catheters.

New Substrate-Guided Method of Predicting Slow Conducting Isthmuses of Ventricular Tachycardia: Preliminary Analysis to the Combined Use of Voltage Limit Adjustment and Fast-Fourier Transform Analysis.

Several conducting channels of ventricular tachycardia (VT) can be identified using voltage limit adjustment (VLA) of substrate mapping. However, the sensitivity or specificity to predict a VT isthmus is not high by using VLA alone. This study aimed to evaluate the efficacy of the combined use of VLA and fast-Fourier transform analysis to predict VT isthmuses. VLA and fast-Fourier transform analyses of local ventricular bipolar electrograms during sinus rhythm were performed in 9 postinfarction patients who underwent catheter ablation for a total of 13 monomorphic VTs. Relatively higher voltage areas on an electroanatomical map were defined as high voltage channels (HVCs), and relatively higher fast-Fourier transform areas were defined as high-frequency channels (HFCs). HVCs were classified into full or partial HVCs (the entire or >30% of HVC can be detectable, respectively). Twelve full HVCs were identified in 7 of 9 patients. HFCs were located on 7 of 12 full HVCs. Five VT isthmuses (71%) were included in the 7 full HVC+/HFC+ sites, whereas no VT isthmus was found in the 5 full HVC+/HFC- sites. HFCs were identical to 9 of 16 partial HVCs. Eight VT isthmuses (89%) were included in the 9 partial HVC+/HFC+ sites, whereas no VT isthmus was found in the 7 partial HVC+/HFC- sites. All HVC+/HFC+ sites predicted VT isthmus with a sensitivity of 100% and a specificity of 80%. Combined use of VLA and fast-Fourier transform analysis may be a useful method to detect VT isthmuses.

Usefulness of Intracardiac Local Ventricular Electrogram to Predict Responders in Patients Undergoing Cardiac Resynchronization Therapy

Usefulness of Intracardiac Local Ventricular Electrogram to Predict Responders in Patients Undergoing Cardiac Resynchronization Therapy

Ventriculoatrial Intervals ≤70 ms in Orthodromic Atrioventricular Reciprocating Tachycardia.

Although a ventriculoatrial interval (VAI) of ≤70 ms is used to distinguish atrioventricular nodal reentrant tachycardia from orthodromic atrioventricular reciprocating tachycardia (AVRT), a VAI of ≤70 ms is sometimes observed in cases of AVRT. The study aimed to evaluate the short VAI that is seen in AVRT and to understand its underlying mechanism. Electrophysiologic studies of 46 consecutive patients with AVRT involving an accessory pathway (AP) were examined retrospectively. AP was right sided in seven patients and left sided in 39. A VAI (interval from QRS onset to the earliest intracardiac atrial electrogram recorded by any mapping catheter during AVRT) ≤70 ms during AVRT (short VAI) was observed in eight patients: six with a left lateral AP and two with a left posteroseptal AP. During AVRT involving a left-sided AP, the QRS-V interval (from the earliest QRS onset to the local ventricular electrogram at a site which showed earliest atrial electrogram recorded from the coronary sinus catheter) was significantly shorter (37 ± 7 ms vs 54 ± 13 ms, P = 0.001) and supernormal conduction (QRS duration or the QRS-V interval shortening by ≥10 ms during AVRT) was more frequently seen (63% vs 6%, P = 0.02) in the short VAI group than in the normal VAI group. Furthermore, these parameters were shown to be determinants for short VAI. A short VAI is sometimes observed during AVRT involving a left-sided AP. The short VAI may be caused by rapid propagation or supernormal conduction between the proximal Purkinje-muscle junction and basal left ventricular myocardium.

Radiofrequency ablation of posteroseptal accessory pathways associated with coronary sinus diverticula.

Posteroseptal accessory pathways may be associated with a coronary sinus (CS) diverticulum. Our purpose was to describe the clinical characteristics, mapping and ablation of these pathways. This was a retrospective study of all patients who underwent ablation of posteroseptal accessory pathways in a single centre. Patients with a diverticulum of the CS or one of its tributaries were included in group I, while the other patients formed group II. Clinical presentation, ablation procedure and outcome were compared between the two groups. A total of 51 patients were included, 16 in group I and 35 in group II. There were no significant differences in age or sex distribution. Atrial fibrillation (AF) and previous unsuccessful ablation were more common in group I. A negative delta wave in lead II was the ECG finding with best sensitivity and specificity for the presence of a diverticulum. A pathway potential was common at the successful site in group I, and the interval between local ventricular electrogram and delta wave onset was shorter (19.5 ± 8 vs 33.1 ± 7.6ms, p < 0.001). There was a trend toward lower procedural success rate and higher recurrence rate in group I, although this was not significant. CS diverticula should be suspected in patients with manifest posteroseptal accessory pathways who have a previous failed ablation, documented AF or typical electrocardiographic signs. A discrete potential is frequently seen at the successful site, but the local ventricular electrogram is not as early as in other accessory pathways.

Recruitment of bundle branches with permanent His bundle pacing in a patient with advanced conduction system disease: What is the mechanism?

The patient was a 69-year-old man with coronary artery disease who presented with syncope. His electrocardiogram showed sinus rhythm with a first-degree atrioventricular block, right bundle branch block (RBBB), and left anterior fascicular block (LAFB), and he was referred for an electrophysiology (EP) study. Baseline electrograms suggested intra-Hisian conduction disease, with split His potentials, H′ and H, and an intra-Hisian interval of 78 ms (Figure 1A). It was difficult to maintain His catheter stability during the EP study, and only the distal His signal (H) was consistent, with an His-ventricular (HV) interval of 70 ms (Figure 1A). Decremental atrial pacing demonstrated progressive rate-related HV prolongation up to 280 ms, beyond which HV Wenckebach block occurred (Figure 1B). No arrhythmias were induced with programmed atrial or ventricular stimulation. Given the evidence of infranodal AV conduction disease with probable intra-Hisian disease, we decided to implant a pacemaker. Pacing from the proximal His bundle (HB) position with the His catheter resulted in a wide QRS complex (duration 164 ms) with RBBB/LAFB and a long stimulus-QRS interval, whereas pacing at the distal HB resulted in a narrower QRS using a pacing output of 5 mA at 2 ms (threshold). Given narrowing of the QRS with distal HB pacing, we decided to implant the ventricular lead in the HB region. Unipolar recordings from the tip electrode of a 3830 pace-sense lead (3830, Medtronic Inc., Minneapolis, MN) were used to map the HB region. As seen in Figure 2, recordings from the proximal HB reveal a large A with an HV interval of 64 ms, while recordings from the distal HB reveal a far-field atrial electrogram (A) with a shorter HV interval of 46 ms. Pacing at the distal HB (distal to the site of block/delay resulting in RBBB/LAFB) resulted in para-Hisian (nonselective HB) capture (His + V), evidenced by a narrow QRS of duration 124 ms and presence of a slurred upstroke indicating local myocardial capture. The threshold of para-Hisian capture was 0.5 V at 0.5 ms. The lead was implanted in the distal HB location. What is the mechanism of narrowing of the QRS complex by permanent HB pacing in this patient with conduction disease characterized by RBBB and LAFB? Figure 2Proximal and distal His bundle (HB) recordings (paper speed 50 mm/s) and paced QRS morphology using permanent His bundle lead (3830, Medtronic). A = atrial electrogram; H = His electrogram; V = local ventricular electrogram. View Large Image Figure Viewer Download Hi-res image

Discrete potentials guided ablation for idiopathic outflow tract ventricular arrhythmias

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). Seventeen out of 24 consecutive patients with idiopathic right or left ventricular outflow tract PVCs/VTs who underwent radiofrequency catheter ablation between September 2012 and December 2013 in our department were included. Intracardiac electrograms during the mapping and ablation were analyzed. 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 was (0.51 ± 0.21) 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 was noted during the arrhythmias. The DPs were related to a region of low voltage showed by intracardiac high-density contact mapping. At the sites with DPs, unipolar and bipolar ventricular voltage of sinus beats were lower compared with the adjacent regions without DPs (unipolar: (6.1 ± 1.8) mV vs. (8.3 ± 2.3) mV, P < 0.05; bipolar: (0.62 ± 0.45) mV vs. (1.03 ± 0.60) 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. Discrete potentials and related low-voltage regions were common in idiopathic outflow tract ventricular arrhythmias. Discrete potential- and substrate-guided ablation strategy could help to reduce the recurrence of idiopathic outflow tract arrhythmias.

Discrete potentials guided radiofrequency ablation for idiopathic outflow tract ventricular arrhythmias.

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). 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. 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 0.51 ± 0.21 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: 6.1 ± 1.8 vs. 8.3 ± 2.3 mV, P < 0.05; bipolar: 0.62 ± 0.45 vs. 1.03 ± 0.60 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. 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.

Two distinct electrocardiographic forms of idiopathic ventricular arrhythmia originating in the vicinity of the His bundle

The objective is to assess electrocardiographic characteristics predicting the precise location of ventricular arrhythmia (VA) origin within the right ventricle (RV) close to the His bundle (HB) region. Twenty-five patients (14 men, age 65 ± 14 years) underwent successful catheter ablation of para-Hisian VA. Ventricular arrhythmias were considered to arise in the vicinity of the HB region based on the criteria that mapping exhibited the earliest RV activation before QRS onset in the HB region. Surface 12-lead electrocardiogram during the para-Hisian VAs was analysed. Of the 25 patients, 8 originated from the RV antero-septum just above the HB region, and 17 arose from the RV mid-septum just below the HB region. There was no significant difference in precedence of the local ventricular electrogram of the HB region from the onset of surface QRS during VAs. Surface electrocardiographic findings were characterized according to R-wave amplitude in lead I (0.43 ± 0.18 vs. 0.67 ± 0.19 mV, P = 0.005), mean R-wave amplitude in inferior leads (1.12 ± 0.32 vs. 0.71 ± 0.24 mV, P = 0.002), R-wave amplitude ratio of leads III/II (0.77 ± 0.10 vs. 0.50 ± 0.23, P = 0.005), incidence of S-wave in lead III [1/8 (13%) vs. 16/17 (94%), P < 0.001], and QS morphology in lead V1 [3/8 (38%) vs. 17/17 (100%), P = 0.001]. Despite their adjacent locations, para-Hisian VAs could be classified into two subgroups with distinctive electrocardiographic characteristics according to origin either above or below the HB region. The present findings can be helpful for planning catheter ablation of para-Hisian VAs, and can reduce the risk of inadvertent atrioventricular block.

Successful Transseptal Catheter Ablation of Premature Ventricular Contractions Arising from the Mitral Annulus: A Case with a Pure Annular Origin

A 74-year-old man with symptomatic premature ventricular contractions (PVCs) with a right bundle branch block and right inferior axis QRS morphology underwent electrophysiologic testing. During the PVCs, coronary sinus mapping revealed ventricular prepotentials with the earliest activation in the distal great cardiac vein (GCV) where the local ventricular electrograms were smaller in amplitude than the atrial electrograms. The transaortic approach could not reach the earliest activation site within the GCV, but the transseptal catheter ablation successfully eliminated the PVCs on the mitral valve. With catheter ablation of ventricular arrhythmias with pure mitral annular origins, a transseptal approach may be necessary.

Ablation of Polymorphic Ventricular Tachycardias in Patients with Structural Heart Disease

Monomorphic ventricular premature beats (VPB) originating from the Purkinje network can induce polymorphic ventricular tachycardia (PMVT) and ventricular fibrillation (VF) storm. We hereby report the results of targeted ablation to treat PMVT/VF storms initiated by monomorphic VPB in seven patients with structural heart disease and left ventricular (LV)-dysfunction (n=4 withcoronary artery disease (CAD), n=2 with chronic and remote myocarditis, n=1 after aortic valve replacement). Pace-mapping and activation mapping was used to identify optimal ablation targets. Earliest activation during mapping was found midseptal of LV in three patients, midinferoseptal of LV in two patients. One patient with myocarditis showed earliest activation at free wall of right ventricle, the other one basal midseptal of LV. Local ventricular electrograms at the successful ablation sites were preceded by short, high frequency, low amplitude potentials by 22-90 ms (median 35 ms). The same local potentials were seen in sinus rhythm. Cycle lengths of VT ranged between 200 and 360 ms (median 245 ms). A median of nine radiofrequency (RF)-ablations (range 3-19) were necessary to abolish all local Purkinje potentials at the site of earliest activation. Two patients with CAD died due to refractory heart failure. The other five patients had no recurrence of PMVT and VF during follow up (median 10 months, range 1-27 months). The distal Purkinje network plays an important role in triggering PMVT/VF in patients with structural heart disease. Ablation of the triggering VPB originating from the Purkinje arborization is feasible; prevents recurrence in a long-term follow up; and is potentially life saving in patients with severe LV-dysfunction after myocardial infarction, in patients after aortic valve replacement, or in patients with myocarditis particularly when medical treatment, including antiarrhythmic drugs, failed to suppress electrical storms.

Successful catheter ablation of a ventricular tachycardia storm originating from the left ventricular posterior papillary muscle involved with a remote myocardial infarction

A 61-year-old man with a remote posterior myocardial infarction underwent electrophysiological testing for a ventricular tachycardia (VT) storm. Repeated cardioversions terminated the VT with immediate resumption after one sinus beat. Pacing neither terminated the VT nor demonstrated transient entrainment. Echocardiographically guided electroanatomic mapping revealed a centrifugal activation from the septal mid-apical region of the left ventricle on the septal portion of the posterior papillary muscle where a high frequency potential was observed within the local ventricular electrogram. Irrigated radiofrequency current at this site eliminated the VT. This case suggested that papillary muscles may be a target for catheter ablation of electrical storms after myocardial infarctions.

Successful catheter ablation of premature ventricular contractions originating from the tricuspid annulus using a Halo-type catheter

A 31-year-old woman with idiopathic premature ventricular contractions originating from the tricuspid annulus (TA) underwent electrophysiological testing. Activation mapping with a 20-pole bipolar Halo-type catheter positioned along the TA revealed the earliest ventricular activation at a site between 7 and 8 o'clock along the TA. A reversal in the polarity of the local ventricular electrograms was observed between the two neighbouring electrode pairs of the TA catheter. Successful catheter ablation was achieved at the ventricular site between those electrode pairs. A Halo-type catheter may be effective for mapping and catheter ablation of ventricular arrhythmias originating from the TA.

Is the activation potential of Mahaim pathway always a fast potential? Implication for radiofrequency catheter ablation

Accessory pathways (AP) exhibiting Mahaim physiology are amenable to radiofrequency (RF) catheter ablation. The recording of an AP potential is an excellent guide for selection of ablation site. The purpose of this study is to determine whether the pathway potential is always a fast potential. Ten patients (six females, mean age, 30 +/- 12 years) with preexcited tachycardias involving a Mahaim pathway underwent electrophysiological study and subsequent attempts at RF ablation. Mahaim potentials (M-potential) recorded at the site of successful ablation were reviewed and classified by at least two reviewers. In all patients, Mahaim pathways were characterized as atriofascicular types. The M-potential was fast in seven patients (group one), and slow in the remaining patients (group two). All group two patients had a history of prior failed ablation. Atrial electrograms were recorded closer to the QRS onset in group one. Atrium to fast M-potential (42 +/- 15 ms) was shorter than atrium to slow M-potential (83 +/- 12 ms, P = 0.03) but M-potentials were recorded with similar distance before local ventricular electrogram (P = NS). Ablation was successful in all patients with mean of 2.9 +/- 1.4 RF applications per patient. Ablation data were similar between the two groups (P = NS). No complications occurred. During 12 months of follow-up, no recurrence was observed. Our results illustrated that the activation potential of Mahaim pathways is not always a fast potential. One-third of Mahaim pathways can be mapped and ablated when the slow type of M-potential was used as a target for ablation. We also confirmed high efficacy of catheter ablation of Mahaim pathways guided by activation potentials.

Coronary sinus mapping to differentiate left versus right ventricular outflow tract tachycardias

Outflow tract ventricular tachycardia (OT-VT) can originate from several different segments of the outflow tract. Various ECG criteria have been proposed for localization of OT-VTs. We present two patients, one with left and one with right OT-VT. We used local ventricular electrograms in the coronary sinus to localize the focus of the OT-VT. Mapping of local ventricular electrograms in the coronary sinus may be a simple and effective method for differentiating right versus left ventricular outflow tract tachycardias. However, the diagnostic value and precision of this method should be evaluated in a series of patients before its implementation in the OT-VT ablation decision algorithm.

Electrocardiographic Characteristics of Repetitive Monomorphic Right Ventricular Tachycardia Originating Near the His‐Bundle

Most idiopathic nonreentrant ventricular tachycardia (VT) and ventricular premature contractions (VPCs) arise from the right or left ventricular outflow tract (OT). However, some right ventricular (RV) VT/VPCs originate near the His-bundle region. The aim of this study was to investigate ECG characteristics of VT/VPCs originating near the His-bundle in comparison with right ventricular outflow tract (RVOT)-VT/VPCs. Ninety RV-VT/VPC patients underwent catheter mapping and radiofrequency ablation. ECG variables were compared between VT/VPCs originating from the RVOT and near the His-bundle. Ten patients had foci near the His-bundle (HIS group), with the His-bundle local ventricular electrogram preceding the QRS onset by 15-35 msec (mean: 22 msec) and His-bundle pacing produced a nearly identical ECG to clinical VT/VPCs. The HIS group R wave amplitude in the inferior leads (lead III: 1.0 +/- 0.6 mV) was significantly lower than that of the RVOT group (1.7 +/- 0.4 mV, P < 0.05). An R wave in aVL was present in 6 of 10 HIS group patients, while almost all RVOT group patients had a QS pattern in aVL. Lead I in HIS group exhibited significantly taller R wave amplitudes than RVOT group. HIS group QRS duration in the inferior leads was shorter than that of the RVOT group. Eight of 10 HIS group patients exhibited a QS pattern in lead V1 compared to 14 of 81 RVOT group patients. HIS group had larger R wave amplitudes in leads V5 and V6 than RVOT group. VT/VPCs originating near the His-bundle have distinctive ECG characteristics. Knowledge of the characteristic QRS morphology may facilitate catheter mapping and successful ablation.

Structure of the reentrant circuit of isiopathic left ventricular tachycardia: New insights into the role of the purkinje network

In idiopathic left ventricular tachycardia (ILVT), the reentrant circuit is considered to involve the Purkinje system, and the Purkinje potential (P-potential) appears to be a marker for successful ablation. However, the characteristics of the reentrant circuit in ILVT have not yet been defined. In 2 cases of ILVT, we performed detailed mapping along the left ventricular septum during VT and sinus rhythm. ILVTs were successfully ablated at the posteroapical area of the left ventricular septum where the high frequency P-potential was recorded and this portion was considered to be the exit site of the reentrant circuit. A small P-potential was also recorded at the portion proximal to the exit site, and it preceded the P-potential at the exit site. However, the local ventricular electrogram at the exit site preceded that at the proximal site during VT. Moreover, the small P-potential was orthodromically entrained by ventricular pacing from the proximal site. These findings suggest that the reentry circuit of ILVT appeared to have considerable size.