Catheter Ablation of Ventricular Tachycardia After Myocardial Infarction: Relation of Endocardial Sinus Rhythm Late Potentials to the Reentry Circuit

Objectives. We sought to determine whether endocardial late potentials during sinus rhythm are associated with reentry circuit sites during ventricular tachycardia (VT).Background. During sinus rhythm, slow conduction through an old infarct region may depolarize tissue after the end of the QRS complex. Such slow conduction regions can cause reentry.Methods. Endocardial catheter mapping and radiofrequency ablation were performed in 24 patients with VT late after myocardial infarction. We selected for analysis a total of 103 sites where the electrogram was recorded during sinus rhythm and, without moving the catheter, VT was initiated and radiofrequency current applied in an attempt to terminate VT.Results. Late potentials were present at 34 sites (33%). During pace mapping, the stimulus-QRS complex was longer at late potential sites, consistent with slow conduction, than at sites without late potentials (p < 0.0001). Late potentials were present at 15 (71%) of 21 sites classified as central or proximal in the reentry circuit based on entrainment, but also occurred frequently at bystander sites (13 [33%] of 39) and were often absent at the reentry circuit exit (3 [23%] of 13). Late potentials were present at 20 (54%) of 37 sites where ablation terminated VT, compared with 14 (21%) of 66 sites where ablation did not terminate VT (p = 0.004). Ablation decreased the amplitude of the late potentials present at sites where ablation terminated VT.Conclusions. Although sites with sinus rhythm late potentials often participate in VT reentry circuits, many reentry circuit sites do not have late potentials. Late potentials can also arise from bystander regions. Late potentials may help identify abnormal regions in sinus rhythm but cannot replace mapping during induced VT to guide ablation.     

Entrainment mapping and radiofrequency catheter ablation of ventricular tachycardia in right ventricular dysplasia

Objectives. The purpose of this study was to determine if entrainment mapping techniques and predictors of successful ablation sites previously tested in coronary artery disease can be applied to ventricular tachycardia (VT) in arrhythmogenic right ventricular dysplasia (ARVD).Background. VT in ARVD has not been well characterized. Reentry circuits in areas of abnormal myocardium are the likely cause, but these circuits have not been well defined.Methods. Mapping of 19 VTs in 5 patients with ARVD was performed. At 58 sites pacing entrained VT and radiofrequency current (RF) was applied to assess acute termination of VT.Results. Sites classified as exits, central/proximal, inner loop, outer loop, remote bystander and adjacent bystander were identified by entrainment criteria. The reentrant circuit sites were clustered predominantly around the tricuspid annulus and in the right ventricular outflow tract (RVOT). RF ablation acutely terminated VT at 13 sites or 22% of the applications. Of the 19 VTs, eight were rendered noninducible and three were modified to a longer cycle length. In 2 patients ablation at a single site abolished two VTs.Conclusion. VT in ARVD shows many of the characteristics of VT due to myocardial infarction. Entrainment mapping techniques can be used to characterize reentry circuits in ARVD. The use of entrainment mapping to guide ablation is feasible.     

Relative Timing of Isolated Potentials During Postinfarction Ventricular Tachycardia and Sinus Rhythm

BACKGROUND: In postinfarction patients, isolated potentials separated by an isoelectric segment from the ventricular electrogram indicate areas of block. Isolated potentials can be recorded during both sinus rhythm and ventricular tachycardia (VT). In an attempt to differentiate bystander pathways from critical sites within a reentry circuit, we compared the relative timing of isolated potentials during VT and sinus rhythm. METHODS: In 19 patients (mean age 68 +/- 6 years) with postinfarction VT who were referred for VT ablation, mapping was performed in the presence and absence of VT. Forty-three sites at which there was concealed entrainment during 35 VT's (mean cycle length 469 +/- 74 ms) displayed an isolated potential separated from the main portion of the ventricular electrogram by an isoelectric segment of >/=30 msec in the presence and absence of VT. The interval between the ventricular electrogram and the isolated potential was measured during VT and baseline rhythm, and the absolute difference (DeltaIPI) was calculated. The DeltaIPI was significantly greater at effective ablation sites (119 +/- 69 ms) than at ineffective ablation sites (30 +/- 28 ms, p < 0.001). The positive predictive value of a DeltaIPI > 85 ms for an effective ablation site was 100%. CONCLUSION: At sites of concealed entrainment, an absolute difference >85 ms between the isolated potential intervals during sinus rhythm and VT is highly specific for a critical area of the VT reentry circuit in post-infarction patients.     

Identification of unusual reentry circuit sites of nonischemic ventricular outflow tract tachycardia

Identification of Ventricular Outflow Tract Tachycardia. Background: Reentrant ventricular outflow tract (OT) tachycardia is rare in patients with nonischemic heart disease. The mechanism of ventricular tachycardia (VT) arising from the region of the aortic sinus of Valsalva (ASOV) is usually focal, rather than reentrant. Consequently, less is known about reentrant circuits in the OT and the aortic sinuses. The purpose of this study was to evaluate existence of reentry circuits in these areas using entrainment mapping techniques. Methods: We performed electrophysiological study in 51 consecutive patients with idiopathic or nonischemic symptomatic VT arising from the OT. Six of these patients were found to have VT of reentrant mechanism with 8 VT morphologies. Entrainment mapping, electroanatomical mapping (in 2 patients), and radiofrequency catheter ablation were performed. Results: Pacing entrained the VT at 93 sites, 52 of which were determined to be in the reentry circuit based on matching of the postpacing interval and VT cycle length. Of the reentry circuit sites, 6 were in the aortic sinus, 43 were below the aortic valve, and 3 were in the right OT below the pulmonary valve. Classification of reentry circuit sites identified 7 as exit, 1 as central‐proximal, 19 as inner loop, and 25 as outer loop sites. Catheter ablation terminated VT at 4 of the 6 aortic sinus sites and 4 of the 46 OT sites (P = 0.0006). Conclusions: We definitively demonstrated involvement of the ASOV in OT reentrant tachycardia using entrainment mapping. It may be useful for successful VT ablation to identify reentry circuit localization. (J Cardiovasc Electrophysiol, Vol. 23, pp. 179‐187, February 2012)     

Reentrant ventricular tachycardia originating in the right ventricular outflow tract: slow conduction identified by right coronary artery ostium pacing.

A case of reentrant ventricular tachycardia (VT) originating from the right ventricular outflow tract (RVOT) is described. An electrophysiological study revealed that programmed stimulation from the right ventricle apex induced 2 types of VT with similar left bundle branch block configuration and inferior axis. Yet, VT cycle length (CL) was different; one was stable, sustained VT with a CL of 360 ms and the other was hemodynamically intolerable VT with a CL of 330 ms. Similarly for both VTs, perfect pace mapping was obtained at the anterior septum beneath the pulmonary valve in the RVOT, and exits of both VTs were very close. Entrainment mapping during stable VT was performed and the anterior septum RVOT was designated as the exit for the stable VT. Intriguingly, entrainment pacing from the ostium of the right coronary artery showed that the post-pacing interval was identical to VTCL. The stimulus to QRS interval was very long (340 ms) during entrainment with concealed fusion, and the right coronary artery ostium was therefore consistent with the VT reentry circuit inner loop or the upper portion of the VT reentry circuit exit. These findings suggest that the stable VT reentry circuit had a slow conduction zone from the ostium of the right coronary artery to the exit in the anterior septum RVOT. When radiofrequency catheter ablation was performed at the 2 exits of the anterior septum RVOT, both VTs then could not be induced.     

Clinical Value of the Postpacing Interval for Mapping of Ventricular Tachycardia in Patients with Prior Myocardial Infarction

Postpacing Interval. Introduction: The postpacing interval (PPI) has been used to discriminate bystander sites from critical sites within a ventricular tachycardia (VT) reentry circuit, with a PPI that is similar to the VT cycle length (CL) being indicative of a site within the reentry circuit. The purpose of this study was to assess the clinical value of the PPI for identifying effective target sites for ablation of VT at sites of concealed entrainment in patients with prior myocardial infarction.
Methods and Results: In 24 patients with coronary artery disease and a past history of myocardial infarction, 36 VTs with a mean CL of 483 ± 80 msec (± SD) were mapped and targeted for radiofrequency (RF) ablation. The only criterion used to select target sites for ablation was concealed entrainment. In a post hoc analysis, the PPI was measured at 47ineffective and 26 effective ablation sites. The mean PPI-VTCL difference at the 26 effective sites(114 ± 137 msec) did not differ significantly from the mean at the 47 ineffective sites (177 ± 161msec; P = 0.1). The sensitivity of a PPI-VTCL difference ≤ 30 msec for identifying an effective ablation site was 46%, the specificity 64%, the positive predictive value 41%, and the negative predictive value 68%.
Conclusion: The PPI-VTCL difference is not useful for discriminating between sites of concealed entrainment that are within or outside of a VT reentry circuit in patients with prior infarction. Therefore, in patients with prior infarction, the PPI is not clinically useful for identifying sites of concealed entrainment at which RF ablation should or should not beat tempted.     

Demonstration of diastolic and presystolic Purkinje potentials as critical potentials in a macroreentry circuit of verapamil-sensitive idiopathic left ventricular tachycardia

OBJECTIVES: The purpose of this study was to determine the relation of diastolic and presystolic potentials recorded during verapamil-sensitive idiopathic left ventricular tachycardia (ILVT) to reentry circuit. BACKGROUND: Successful ablation of verapamil-sensitive ILVT at the zone of slow conduction from which the diastolic potential is recorded has been reported. However, the relationship between the diastolic potential and the reentrant circuit remains a matter of debate. METHODS: Radiofrequency (RF) ablation was performed in 20 patients with verapamil-sensitive ILVT. After identifying the ventricular tachycardia (VT) exit site, we searched for the mid-diastolic potential (P1) during VT. Entrainment followed by RF current application was performed. If the mid-diastolic potential could not be detected, RF current was applied at the VT exit site showing the earliest ventricular activation with a single fused presystolic Purkinje potential (P2). RESULTS: In 15 of 20 patients, both P1 and P2 were recorded during VT from midseptal region. Entrainment pacing captured P1 orthodromically and reset the VT. The interval from stimulus to P1 was prolonged as the pacing rate was increased. Radiofrequency ablation was successfully performed at this site in all 15 patients. After successful ablation, P1 appeared after the QRS complex during sinus rhythm with the identical sequence to that during VT. In the remaining five patients, the diastolic potential could not be detected, and a single fused P2 was recorded only at the VT exit site. Successful ablation was performed at this site in all five patients. CONCLUSIONS: This study demonstrates that P1 and P2 are critical potentials in a circuit of verapamil-sensitive ILVT and suggests the presence of a macroreentry circuit involving the normal Purkinje system and the abnormal Purkinje tissue with decremental property and verapamil-sensitivity.     

Preferential Locations for Critical Reentry Circuit Sites Causing Ventricular Tachycardia After Inferior Wall Myocardial Infarction

Reentrant VT Post MI. Introduction : For relatively slow monomorphic ventricular tachycardia (VT) after myocardial infarction, entrainment can be used to identify reentry circuit "isthmus sites" (exit sites and sites proximal to the exit) where radioifrequency (RF) catheter ablation has the greatest likelihood of interrupting reentry. Similarities in coronary and ventricular anatomy may cause such sites to form in preferential locations. The objective of this study is to determine if there are preferential locations for reentry circuit isthmus regions in chronic inferior wall infarctions causing VT.
Methods and Results : Catheter mapping and RF catheter ablation was performed in 21 patients with an old inferior wall myocardial infarction and VT. The inferior wall was divided into 9 anatomic regions: 3 apical, 3 mid, and 3 basal segments. Of 46 different VTs, an endocardial isthmus site was identified in one or more zones in 28 (61%), with 10 VTs having isthmus sites in two or more adjacent regions. Isthmus zones were found in a basal region of the left ventricle in 24 (86%) of 28 VTs, in a mid segment in 9 (32%) VTs, and in an apical segment in 1 (4%) (P = 0.002). Of 30 RF current applications that terminated VT, 21 (70%) were at basal isthmus sites.
Conclusion : The high prevalence of endocardial isthmus zones near the base of the left ventricle suggests that the mitral annulus often plays a role in defining the margins of reentry circuits that cau.se relatively slow VTs after inferior wall myocardial infarction.     

Identifying sites for catheter ablation of ventricular tachycardia.

The approach to localizing sites for catheter ablation of ventricular tachycardia foci depends on the type of tachycardia. In large reentry circuits such as those arising from infarct scars, areas of slow conduction in and around the scar should be targeted. During sinus rhythm, these can be suspected from the presence of fractionated electrograms and, at some sites, long stimulus to QRS delays during pacing. Slow conduction areas can be classified as: 1. central slow conduction zone sites, 2. exits from the slow conduction zone, 3. entrances to the slow conduction zone, and 4. bystander areas which are not involved in the tachycardia circuit. In the central slow conduction zone stimulation entrains or resets tachycardia with a long stimulus to QRS (S-QRS) delay (40 to greater than 300 ms) without altering the QRS morphology (entrainment with concealed fusion). At slow conduction zone exits, presystolic electrograms are recorded during VT, the pacemap matches the VT QRS morphology, and with pacing during VT the S-QRS interval is relatively short and VT may or may not be entrained. At entrances to the slow conduction zone electrogram timing is variable but early diastolic electrograms are expected and the pace-map QRS may differ from the VT QRS morphology. Relatively late stimuli or slow trains of stimuli entrain VT with concealed fusion with a relatively longer S-QRS interval than observed in the central slow conduction zone. Early stimuli may entrain VT while altering the QRS morphology due to propagation of the stimulated antidromic wavefront out of the scar from a site other than the tachycardia exit. At bystander sites electrogram timing, pace-mapping, and the effects of programmed stimulation are variable but may occasionally mimic reentry circuit sites. Relatively late stimuli are likely to capture the site without altering the VT. If discrete electrograms are present, analysis of these during pacing may provide further evidence that the site is not in the reentry circuit. Catheter ablation will probably be most effective at central slow conduction zone sites. When VT originates from a small focus surrounded by normal myocardium, such as is likely for idiopathic RV outflow tract and some idiopathic left ventricular tachycardias, presystolic electrical activity and pacemapping are likely to identify the tachycardia focus. For macroreentry involving the bundle branches, the right bundle branch can be easily targeted.     

Mechanism of Ventricular Tachycardia Termination by Pacing at Left Ventricular Sites in Patients with Coronary Artery Disease

Objective: The mechanism by which pacing terminates ventricular tachycardia (VT) may depend on the location of the pacing site relative to the reentry circuit. The purpose of this study was to compare the mechanisms by which pacing terminates VT at left ventricular (LV) sites with and without concealed entrainment (CE) in patients with prior myocardial infarction. Methods and Results: LV mapping was performed in 29 patients (26 men, 3 women, mean age 67±11 years, ejection fraction 0.28±0.11) with 55 hemodynamically-tolerated VTs (mean cycle length 478±92 msec). A total of 408 pacing trains were delivered at 102 sites with CE. Radiofrequency catheter ablation was successful in 41 of 55 VT's. At sites with concealed entrainment, VT was terminated by pacing at 17/41 (41%) successful and at 4/61 (7%) unsuccessful ablation sites (p<0.01). Termination without global ventricular capture was the most frequent termination mode (10/21), followed by termination with orthodromic (4/21) and non-orthodromic capture (7/21). Conclusion: In patients with prior myocardial infarction, pacing at sites of CE during VT usually terminates VT either without global capture or by orthodromic capture. Termination of VT by pacing without global capture or with orthodromic capture at sites of CE suggests that the site is within a critical area of the reentry circuit.     

Ablation of postinfarction ventricular tachycardia guided by isolated diastolic potentials.

Frequent recurrences of ventricular tachycardia (VT) despite implantable cardioverter-defibrillator (ICD) and antiarrhythmic drug therapy are a typical indication for catheter ablation. We performed endocardial mapping of an haemodynamically tolerated VT in a 67-year-old male patient. Isolated diastolic potentials (IDPs) of similar morphology were recorded during atrial paced rhythm at baseline and during monomorphic VT. The isolated potentials were required for initiation and maintenance of ventricular arrhythmia. These diastolic electrograms were considered to be part of the reentry circuit, as they remained constantly associated with VT during oscillations of cycle length and resetting. Validation of the ablation target was not performed by exact entrainment pacing in order to test the predictive value of the observed diagnostic phenomena. Radiofrequency (RF) energy applications were successful at the site where IDPs were recorded during atrial paced rhythm and VT. Ablation decreased the need for ICD therapies effectively in a patient with scar-related, slow VT.     

Insights into the mechanism of sustained ventricular tachycardia after myocardial infarction in a closed chest porcine model using a multielectrode "basket" catheter

INTRODUCTION: Accurate analysis of the arrhythmia substrate is important for successful radiofrequency ablation of sustained ventricular tachycardia (VT) after myocardial infarction (MI). METHODS AND RESULTS: A multielectrode "basket" catheter capable of endocardial recording and pacing was inserted percutaneously into the left ventricle of post-MI swine for analysis of the mechanism of sustained VT. Sustained VT was induced in 42 of 61 pigs that survived an acute MI produced by percutaneous transluminal coronary angioplasty balloon occlusion of the left anterior descending coronary artery and injection of agarose gel beads. A multielectrode "basket" catheter (Constellation) with 64 electrodes was inserted in 35 of these animals for analysis of the VT. Induced VT had a cycle length of 179 +/- 25 msec at control and 230 +/- 43 msec after administration of intravenous procainamide. Presystolic electrical activity was recorded from at least 1 of 32 bipolar pairs of electrodes at a mean 40.7 +/- 23.6 msec prior to QRS onset. Isolated mid-diastolic potentials were recorded in 26 of 35 animals. In 22 animals, there were multiple isolated potentials recorded from adjacent electrode pairs. Isochronal maps demonstrated that these potentials returned to the systolic site of origin. Resetting of sustained VT by single premature ventricular stimuli was observed in 6 of 12 animals. Entrainment with overdrive pacing was seen in 19 of 26 animals with induced VT. Concealed entrainment was observed in ten animals. The mean stimulus to QRS interval was 45 +/- 28 msec. Concealed entrainment was observed from adjacent electrode pairs with different stimulus to QRS intervals. CONCLUSION: These data suggest that sustained VT in this model is due to reentry with an excitable gap. A multielectrode "basket" catheter is useful for analyzing the zone of slow conduction participating in the tachycardia circuit. Such analysis may provide useful information to guide successful catheter ablation of sustained VT after MI.     

器质性心脏病室性心动过速导管消融治疗进展

器质性心脏病瘢痕相关性室性心动过速（室速）的发生主要是折返机制,目前多采用心脏三维标测系统指引下对耐受性好、血流动力学稳定的室速激动标测消融,对于血流动力学不稳定的室速,窦性心律下基质标测、电压图判断室速的解剖基质,结合起搏标测和拖带标测技术识别室速的折返环,盐水灌注导管消融治疗;近年来不断积累有关临床循证证据、适应证进一步拓展、新的标测消融和辅助技术临床上应用,取得了新的进展。     

Recognition of far-field electrograms during entrainment mapping of ventricular tachycardia

OBJECTIVES: The goal of this study was to assess entrainment for distinguishing far-field potentials (FFP) due to depolarization of tissue at a distance from the mapping catheter from the local potential (LP) due to depolarization of tissue at the catheter electrode during mapping of ventricular tachycardia (VT). BACKGROUND: Electrograms with multiple peaks commonly complicate mapping and identification of catheter ablation targets in infarcts. METHODS: Retrospective analysis of catheter mapping data from eight patients with prior infarction was performed to evaluate multipotential electrograms at sites where pacing entrained VT. Potentials that were visible and not altered during pacing were defined as FFP. Potentials obscured by the pacing stimulus were designated possible LPs. The criteria for FFP were then assessed in a second cohort of five patients. RESULTS: At 32 of 39 (82%) sites with multiple potentials, entrainment identified one of the potentials as an FFP. Radiofrequency ablation, assessed at 15 sites, reduced the amplitude of LPs by 62%, without significant effect on FFP amplitude. At 56% of sites with multiple potentials, measuring the postpacing interval to an FFP would lead to erroneous classification of the site location relative to the reentry circuit. In prospective evaluation, double potentials were identified at 77 sites in infarcts; entrainment demonstrated an FFP at 66 (86%) sites. CONCLUSIONS: Far-field potentials are common during mapping in infarcts. Many can be distinguished from local potentials by entrainment, improving the accuracy of mapping.     

Case Report: Alternating Exit Sites in Reentry Circuit of Ventricular Tachycardia with Nonischemic Cardiomyopathy – Relationship between Ablation Site and Inner Loop

We present a patient with nonischemic cardiomyopathy who had ventricular tachycardia (VT) with QRS morphology alternans. VTs of two QRS morphologies (VT1 and VT2) exhibiting a right bundle branch block pattern with inferior axis was induced by ventricular pacing. The morphology of the QRS complex during VT1 exhibited more distinctively inferior axis than those during VT2. Induced VTs had similar morphologies to clinically the documented VTs. Pacemapping at anterolateral site of the left ventricle during sinus rhythm produced the same QRS complex of VT1 in a surface 12-lead electrocardiogram. A mapping study was performed with an electrode catheter located at the same site of LV during sustained VT1. The analysis of the local electrograms and postpacing interval during concealed entrainment at the catheter mapping revealed this pacing site was at the inner loop of the reentry circuit. Radiofrequency catheter ablation was performed at this site. The morphology of VT1 changed to different QRS morphology (VT2) during the first delivery of radiofrequency energy and was terminated after 20 seconds of the application. Then VT with alternans of QRS morphology and cycle length of VT1 and VT2 was induced by ventricular pacing, and was abolished by the second application of radiofrequency energy at this same site, suggesting that this site was located in the exit site close to inner loop of the reentry circuit and the alternans of QRS morphology was linked to the change of exit site.     

Electrophysiology of Postinfarction Ventricular Tachycardia:

Sustained monomorphic ventricular tachycardia (VT) is a paradigm of a stable reentrant rhythm. The hallmark of stable reentry is the presence of an excitable gap, which in reentrant VT composes 15% to 45% of the tachycardia cycle length. Resetting allows definition of the extent and pattern of the excitable gap. Site-specific resetting responses suggest that the VT circuit has both functionally and anatomically derived characteristics. Entrainment provides information regarding the effects of overdrive pacing on properties of the tissue composing the circuit rather than on properties of the tachycardia itself. These data help us to understand the mechanisms of pharmacologic agents and to direct ablation of reentrant VT.     

Negative participation of the left posterior fascicle in the reentry circuit of verapamil-sensitive idiopathic left ventricular tachycardia

Left posterior fascicle and idiopathic Left VT. The left posterior fascicle may be a bystander of the circuit of verapamil-sensitive idiopathic left ventricular tachycardia. During ventricular tachycardia (VT), 3 sequences of potentials were seen at the left posterior septum: diastolic Purkinje potentials propagating from base to apex and presystolic left posterior fascicular potentials and systolic left ventricular (LV) myocardial potentials propagating in the reverse direction. Selective capture of the left posterior fascicle by the sinus beat did not affect the VT cycle length. Entrainment pacing revealed that the retrograde limb of the circuit was not the left posterior fascicle, but the LV myocardium.     

Analysis During Sinus Rhythm of Critical Sites in Reentry Circuits of Postinfarction Ventricular Tachycardia

Background: Critical sites within reentry circuits of postinfarction ventricular tachycardia (VT) were identified during sinus rhythm (SR) and VT to determine whether electrogram characteristics during SR may be helpful in identifying successful ablation sites. Methods: In 33 patients (mean age 67 ± 11 yrs) with prior infarction, mapping and radiofrequency (RF) catheter ablation of 57 hemodynamically-tolerated VT's (cycle length 478 ± 96) were performed. The morphologies of electrograms (EGM) at sites of concealed entrainment (CE) were compared during SR and VT. RF energy was delivered at 94 sites (51 successful and 43 unsuccessful ablation sites). Results: During SR, isolated potentials (IP), but not late potentials (LP) recorded via the mapping catheter, were associated with successful ablation. At 29/39 sites with an IP during sinus rhythm, an isolated diastolic potential (IDP) also was present during VT, whereas at 4 sites IP's were present only during SR (p < 0.001). At 11/29 sites where isolated potentials were present during SR and VT, the morphology of the isolated potential during VT and SR was similar; and all but one of these sites were successful ablation sites (p = 0.01). The EGM amplitude during VT correlated with the amplitude during SR (R = 0.9, p < 0.001). An identical pacemap was present during SR at 33/94 sites; this was not associated with successful ablation. Conclusion: SR mapping may be helpful in identifying critical sites of reentry in postinfarction VT. At sites within the reentry circuit, characteristics of sinus rhythm EGM's that are associated with successful ablation include the presence of IP's, but not the presence of LP's.     

Catheter ablation guided by termination of postinfarction ventricular tachycardia by pacing with nonglobal capture.

OBJECTIVES: We prospectively investigated the prevalence and value of this criterion for identifying a target site for ablation in patients with postinfarction ventricular tachycardia (VT). BACKGROUND: Termination of postinfarction VT by pacing with nonglobal capture identifies a critical component of the reentrant circuit. METHODS: In a consecutive series of 34 patients with prior infarction (age 67 +/- 10 years, ejection fraction 0.26 +/- 0.1) referred for radiofrequency catheter ablation, mapping was performed in the left ventricle. At sites with abnormal electrograms, pacing was performed during VT. If VT terminated with nonglobal capture during the pacing train, radiofrequency energy was delivered. RESULTS: Sixty-two VTs (cycle length 450 +/- 84 ms) were mapped and targeted for radiofrequency ablation. Concealed entrainment was present at 101 endocardial sites. Among the 101 sites, VT terminated by pacing with nonglobal capture at 5 sites (5%). At 10 additional sites in 10 patients, VT terminated by pacing with nonglobal capture, and concealed entrainment could not be documented at these sites because of reproducible termination of the VT. An application of radiofrequency energy resulted in VT termination at all 15 sites where nonglobal capture was documented and the targeted VTs were no longer inducible after ablation. CONCLUSIONS: Termination of VT by pacing with nonglobal capture can be demonstrated in approximately one third of patients with postinfarction VT and is a specific criterion for identifying a critical component of the reentrant circuit, whether or not concealed entrainment can be documented at that site.     

Structure of the reentrant circuit of idiopathic 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.