Mapping Of Ventricular Tachycardia Research Articles

Decrement Evoked Potential Mapping: Basis of a Mechanistic Strategy for Ventricular Tachycardia Ablation.

Substrate-based mapping for ventricular tachycardia (VT) ablation is hampered by its inability to determine critical sites of the VT circuit. We hypothesized that those potentials, which delay with a decremental extrastimulus (decrement evoked potentials or DEEPs), are more likely to colocalize with the diastolic pathways of VT circuits. DEEPs were identified in intraoperative left ventricular maps from 6 patients with ischemic cardiomyopathy (total 9 VTs) and were compared with late potential (LP) and activation maps of the diastolic pathway for each VT. Mathematical modeling was also used to further validate and elucidate the mechanisms of DEEP mapping. All patients demonstrated regions of DEEPs and LPs. The mean endocardial surface area of these potentials was 18±4% and 21±6%, respectively (P=0.13). The mean sensitivity for identifying the diastolic pathway in VT was 50±23% for DEEPs and 36±32% for LPs (P=0.31). The mean specificity was 43±23% versus 20±8% for DEEP and LP mapping, respectively (P=0.031). The electrograms that displayed the greatest decrement in each case had a sensitivity and specificity for the VT isthmus of 29±10% and 95±1%, respectively. Mathematical modeling studies recapitulated DEEPs at the VT isthmus and demonstrated their role in VT initiation with a critical degree of decrement. In this preliminary study, DEEP mapping was more specific than LP mapping for identifying the critical targets of VT ablation. The mechanism of DEEPs relates to conduction velocity restitution magnified by zigzag conduction within scar channels.

VALIDATION OF NOVEL ALGORITHM TO AUTOMATE DETECTION OF FRACTIONATED ELECTROGRAMS DURING VENTRICULAR TACHYCARDIA (VT) ABLATION

INTRODUCTION: Ablation of ventricular tachycardia (VT) substrate in patient at risk for VT in the setting of ischemic heart disease is a technically challenging procedure. We thought to evaluate a novel algorithm used to automatically identify target electrograms. METHODS: 16 consecutive patients (70 10 years of age, 90% male, 34 18% LV EF) had 20 ablations for ischemic VT using CARTO 3 mapping system over 2 years. Left ventricular (LV) substrate was mapped during right ventricular (RV) apical stimulation. Navistar Thermocool 3.5 mm irrigated tip catheters were used in all patients. A novel algorithm counting the number of electrogram deflections (NOD) crossing the 0.05mV noise threshold and duration of time from first to last such deflection during the window of interest (total fractionation time, TFT) was applied to all acquired maps after ablation was complete. Snapshots of 200 electrograms representing the high and low end of TFT and NOD values were presented to a group of 8 electrophysiologists experienced in VT ablation who were asked to select electrograms they would target for substrate ablation. The diagnostic accuracy of TFT and NOD values was then analyzed. RESULTS: Across the range of TFT values (0.0-281.0 ms), a cut-off value of 49.0 ms (81.6% sensitivity, 57% specificity) was established as an optimal indicator of an ablation target. Area under the curve for TFT was 0.675 (95% CI: 0.59-0.75, p1⁄40.001). For NOD values (0.0-70.0 deflections), a cut off of 4.5 deflections (88.0% Sensitivity, 57 % specificity) was established as an optimal indicator of an ablation target. The area under the curve for NOD yielded an area of 0.75 (95% CI: 0.68-0.82, P1⁄40.001). For TFT-NOD product as a variable, a cut-off value of 64 (91.0% Sensitivity, 52.4 % specificity) was an optimal indicator of an ablation target. The Area under the curve for NOD and TFT multiple was 0.72 (95% CI: 0.65-0.80, P1⁄40.001). CONCLUSION: A novel algorithm may be able to automatically classify LV substrate during mapping and ablation of ischemic VT with high sensitivity and acceptable specificity.

USING TIMING RELATIONSHIPS OF SINGLE DIASTOLIC ELECTROGRAMS DURING RAPID ACTIVATION MAPPING TO DETERMINE CRITICAL SITE DURING VENTRICULAR TACHYCARDIA ABLATION

USING TIMING RELATIONSHIPS OF SINGLE DIASTOLIC ELECTROGRAMS DURING RAPID ACTIVATION MAPPING TO DETERMINE CRITICAL SITE DURING VENTRICULAR TACHYCARDIA ABLATION

Temporal-component analysis of diastolic electrograms in ventricular tachycardia differentiates nonvulnerable regions of the circuit.

Successful activation mapping of ventricular tachycardia (VT) is dependent on the identification of a region of diastolic conduction by use of point-by-point sequential mapping. It is important to identify the site of transition from diastolic conduction to systolic activation of healthy myocardium (exit site) and differentiate this from nonvulnerable regions of the circuit. We sought to determine the temporal and component characteristics of exit-site electrograms using simultaneous multielectrode endocardial mapping and to differentiate them from bystander sites during activation mapping. Sixteen VTs induced in 12 patients with ischemic cardiomyopathy who underwent multielectrode mapping during VT performed with a custom-made 112-bipolar-electrode endocardial array were analyzed retrospectively. The activation sequence in systole and diastole was annotated, and the timing at exit and bystander sites of the near-field component was characterized in relation to surface electrocardiogram activation and to the far-field component. Spectral content of bipolar electrograms recorded at these sites was additionally analyzed to identify the near-field to far-field interval. The mean activation time at exit sites was 60.0 ± 31.5 ms (range 21-113 ms) ahead of surface QRS but was not significantly different from bystander sites (72.0 ± 55.0 ms, P = .63). However, the time delay from local to far-field activity was significantly lower at exit sites than at bystander sites (24.9 ± 15.6 vs. 86.6 ± 92.0 ms, P = .003), which was confirmed by spectral analysis (10.0 ± 13.1 vs. 89.0 ± 64.5 ms, P = .003). Our analysis suggests that temporal-component analysis of diastolic electrograms during activation mapping of VT provides a practical method to differentiate nonvulnerable sites from the exit site without the need for pacing maneuvers.

Ventricular tachycardia ablation: a comprehensive review for anesthesiologists.

Percutaneous catheter ablation is being increasingly performed in patients with recurrent ventricular tachycardia (VT) unresponsive to medical treatment. Optimal management of patients requires careful consideration of the severity of the underlying cardiac disease, the anesthetic drug interactions, and the procedural technique during VT mapping and ablation. The goal is to choose an anesthetic technique that has the least effect on arrhythmogenicity, allowing reproducibility of the VT in the electrophysiology laboratory. Anesthetics can alter action potential and ventricular depolarization directly through their effects on ion channels and gap junctions, as well as indirectly via their effects on the autonomic nervous system. Furthermore, maintaining hemodynamic stability and monitoring for adequate end-organ perfusion are additional challenges. In this review, we provide a comprehensive update on the currently performed VT ablation procedures and their anesthetic considerations.

Outcomes and ventricular tachycardia recurrence characteristics after epicardial ablation of ventricular tachycardia in arrhythmogenic right ventricular dysplasia/cardiomyopathy.

Variable success rates have been reported after epicardial radiofrequency catheter ablation (RFA) in arrhythmogenic right ventricular dysplasia/cardiomyopathy (ARVD/C). The details of the electroanatomic substrate are limited to a few studies, and the characteristics of the recurrent ventricular tachycardia (VT) in ARVD/C remain largely unknown. The purpose of this study was to report procedural strategy, safety, and efficacy of epicardial RFA at a tertiary single center with a focus on the characteristics of the substrate and recurrent VT. We included 30 ARVD/C patients (mean age 33.1 ± 11.1 years, 53% male) who underwent endocardial/epicardial mapping and epicardial catheter ablation of VT at the Johns Hopkins Hospital. Implantable cardioverter-defibrillator interrogations were evaluated for VT recurrence. The majority of critical VT circuits (69%) were on the epicardial surface, mostly in the subtricuspid region. Eight patients (27%) experienced VT recurrence after epicardial RFA, and the VT-free survival was 83%, 76%, and 70% at 6,12, and 24, months respectively. A significant reduction of VT burden was observed (P <.001), even among those with VT recurrence. No complications occurred except for acute pericarditis in 1 patient. The majority of VT recurrences occurred during the first year after RFA, during exercise, had fast cycle lengths, and required implantable cardioverter-defibrillator shock for termination. The vast majority of critical VT circuits were epicardial, mostly in the subtricuspid region. Epicardial RFA of VT appears to be both safe and effective in achieving arrhythmia control in ARVD/C. The features of the recurrent VT suggest a possible catecholamine-mediated mechanism with an origin in a region not targeted for ablation.

Utility of high-resolution electroanatomic mapping of the left ventricle using a multispline basket catheter in a swine model of chronic myocardial infarction.

Standard electroanatomic mapping systems use a single catheter to perform left ventricular substrate mapping. A new mapping system uses a 64-electrode mini-basket catheter to perform rapid automated acquisition of chamber geometry, voltage, and activation. The aim of this study was to compare the accuracy of electroanatomic mapping using the basket catheter with that of mapping using a standard linear catheter in a swine model of chronic myocardial infarction. Ten swine underwent left anterior descending coronary artery occlusion to create an anteroseptal myocardial infarction. Animals underwent delayed-enhancement magnetic resonance imaging (MRI) and then detailed left ventricular voltage mapping with both the basket and the linear catheter. Map characteristics and scar area were compared between the basket catheter, linear catheter, and MRI. Induced ventricular tachycardia (VT) was mapped with the basket catheter. More points were acquired with the basket catheter than with the standard catheter (8762 ± 3164 vs 1712 ± 551; P < .001). The fifth percentile of normal bipolar voltage distribution with the basket catheter was 1.54 mV. Using a bipolar voltage cutoff of 1.5 mV, the total infarct areas measured using the basket catheter, linear catheter, and MRI were similar (17.8 cm(2) vs 20.9 cm(2) vs 17.5 cm(2); P = .69); however, the correlation between MRI and catheter scar area measurement was best for the basket catheter (basket vs linear: r = .76 vs r = .71). In 3 animals, sustained poorly tolerated VT was initiated and the circuit mapped successfully with the basket catheter in <5 minutes. Rapid substrate and activation mapping using a 64-electrode mini-basket catheter allows detailed voltage and activation mapping in postinfarction cardiomyopathy. This system may be useful for substrate and VT mapping in human postinfarction cardiomyopathy.

Procedural and clinical outcomes after catheter ablation of unstable ventricular tachycardia supported by a percutaneous left ventricular assist device

Hemodynamic support using percutaneous left ventricular assist devices (pLVADs) during catheter mapping and ablation of unstable ventricular tachycardia (VT) can provide effective end-organ perfusion. However, its effect on procedural and clinical outcomes remains unclear. To retrospectively evaluate the procedural and clinical outcomes after the catheter ablation of unstable VT with and without pLVAD support. Sixty-eight consecutive unstable, scar-mediated endocardial and/or epicardial VT ablation procedures performed in 63 patients were evaluated. During VT mapping and ablation, hemodynamic support was provided by intravenous inotropes with a pLVAD (n = 34) or without a pLVAD (control; n = 34). Baseline patient characteristics were similar. VT was sustained longer with a pLVAD (27.4 ± 18.7 minutes) than without a pLVAD (5.3 ± 3.6 minutes) (P < .001). A higher number of VTs were terminated during ablation with a pLVAD (1.2 ± 0.9 per procedure) than without a pLVAD (0.4 ± 0.6 per procedure) (P < .001). Total radiofrequency ablation time was shorter with a pLVAD (53 ± 30 minutes) than without a pLVAD (68 ± 33 minutes) (P = .022), but with similar procedural success rates (71% for both pLVAD and control groups; P = 1.000). Although during 19 ± 12 months of follow-up VT recurrence did not differ between pLVAD (26%) and control (41%) groups (P = .305), the composite end point of 30-day rehospitalization, redo-VT ablation, recurrent implantable cardioverter-defibrillator therapies, and 3-month mortality was lower with a pLVAD (12%) than without a pLVAD (35%) (P = .043). In this nonrandomized retrospective study, catheter ablation of unstable VT supported by a pLVAD was associated with shorter ablation times and reduced hospital length of stay. While pLVAD support did not affect VT recurrence, it was associated with a lower composite end point of 30-day rehospitalization, redo-VT ablation, recurrent implantable cardioverter-defibrillator therapies, and 3-month mortality.

Percutaneous Left Ventricular Assist Devices in Ventricular Tachycardia Ablation

Background— Data on relative safety, efficacy, and role of different percutaneous left ventricular assist devices for hemodynamic support during the ventricular tachycardia (VT) ablation procedure are limited. Methods and Results— We performed a multicenter, observational study from a prospective registry including all consecutive patients (N=66) undergoing VT ablation with a percutaneous left ventricular assist devices in 6 centers in the United States. Patients with intra-aortic balloon pump (IABP group; N=22) were compared with patients with either an Impella or a TandemHeart device (non-IABP group; N=44). There were no significant differences in the baseline characteristics between both the groups. In non-IABP group (1) more patients could undergo entrainment/activation mapping (82% versus 59%; P =0.046), (2) more number of unstable VTs could be mapped and ablated per patient (1.05±0.78 versus 0.32±0.48; P &lt;0.001), (3) more number of VTs could be terminated by ablation (1.59±1.0 versus 0.91±0.81; P =0.007), and (4) fewer VTs were terminated with rescue shocks (1.9±2.2 versus 3.0±1.5; P =0.049) when compared with IABP group. Complications of the procedure trended to be more in the non-IABP group when compared with those in the IABP group (32% versus 14%; P =0.143). Intermediate term outcomes (mortality and VT recurrence) during 12±5-month follow-up were not different between both groups. Left ventricular ejection fraction ≤15% was a strong and independent predictor of in-hospital mortality (53% versus 4%; P &lt;0.001). Conclusions— Impella and TandemHeart use in VT ablation facilitates extensive activation mapping of several unstable VTs and requires fewer rescue shocks during the procedure when compared with using IABP.

Catheter ablation of ventricular tachycardia in patients with post-infarction cardiomyopathy.

Monomorphic ventricular tachycardia (VT) in patients with post-infarction cardiomyopathy (CMP) is caused by reentry through slowly conducting tissue with in areas of myocardial scar. The use of implantable cardioverter-defibrillators (ICDs) has helped to decrease the risk of arrhythmic death in patients with post-infarction CMP, but the symptomatic and psychological burden of ICD shocks remains significant. Experience with catheter ablation has progressed substantially in the past 20 years, and is now routinely used to treat patients with post-infarction CMP who experience VT or receive ICD therapy. Depending on the hemodynamic tolerance of VT, a variety of mapping techniques may be used to identify sites for catheter ablation, including activation and entrainment mapping for mappable VTs, or substrate mapping for unmappable VTs. In this review, we discuss the pathophysiology of VT in post-infarction CMP patients, and the contemporary practice of catheter ablation.

Initial Human Feasibility of Infusion Needle Catheter Ablation for Refractory Ventricular Tachycardia

Ablation of ventricular tachycardia (VT) is sometimes unsuccessful when ablation lesions are of insufficient depth to reach arrhythmogenic substrate. We report the initial experience with the use of a catheter with an extendable/retractable irrigated needle at the tip capable of intramyocardial mapping and ablation. Sequential consenting patients with recurrent VT underwent ablation with the use of a needle-tipped catheter. At target sites, the needle was advanced 7 to 9 mm into the myocardium, permitting pacing and recording. Infusion of saline/iodinated contrast mixture excluded perforation and ensured intramyocardial deployment. Further infusion was delivered before and during temperature-controlled radiofrequency energy delivery through the needle. All 8 patients included (6 male; mean age, 54) with a mean left ventricular ejection fraction of 29% were refractory to multiple antiarrhythmic drugs, and 1 to 4 previous catheter ablation attempts (epicardial in 4) had failed. Patients had 1 to 7 (median, 2) VTs present or inducible; 2 were incessant. Some intramyocardial VT mapping was possible in 7 patients. A mean of 22 (limits, 3-48) needle ablation lesions were applied in 8 patients. All patients had at least 1 VT terminated or rendered noninducible. During a median of 12 months follow-up, 4 patients were free of recurrent VT, and 3 patients were improved, but had new VTs occur at some point during follow-up. Two died of the progression of preexisting heart failure without recurrent VT. Complications included tamponade in 1 patient and heart block in 2 patients. Intramyocardial infusion-needle catheter ablation is feasible and permits control of some VTs that have been refractory to conventional catheter ablation therapy, warranting further study.

Feasibility of remote magnetic navigation for epicardial ablation

Percutaneous epicardial mapping and ablation is an emerging method to treat ventricular tachycardias (VT), premature ventricular complexes (PVC), and accessory pathways. The use of a remote magnetic navigation system (MNS) could enhance precision and maintain safety. This multiple case history demonstrates the feasibility and safety of the MNS-guided epicardial approach in mapping and ablation of ischaemic VT, outflow tract PVCs, and a left-sided accessory pathway. All patients had previously undergone endocardial mapping for the same arrhythmia. MNS could present an advantage from more precise navigation for mapping and maintaining catheter stability during energy application.

Open Chest Epicardial Ablation of Ventricular Tachycardia Early after Left Ventricular Assist Device Implantation

Purpose Patients with advanced heart failure who require left ventricular assist device (LVAD) implant are also susceptible to ventricular tachycardia (VT). Recurrent VT can compromise the hemodynamic support provided with LVADs and if not managed can cause RV failure and ultimately refractory shock. Methods and Materials Between March of 2009 and June of 2012, 5 patients underwent open chest hybrid epicardial mapping and ablation of recurrent VT early after placement of an LVAD. Patients had the VT ablation at the time of mediastinal washout or chest closure (median post-op day #3, range day #1-12). Results Five patients (4 males, median age 57, range 52-73, 3 ischemic cardiomyopathy) had received LVAD. Two patients had HeartMate II, one patient had HeartMate XVE, one patient had HeartMate XVE and right ventricular assist device (RVAD) and one patient had Levitronix for post-cardiotomy shock following coronary bypass surgery requiring placement of an ECMO. All patients had failed medical therapy for VT with at least 1 (median 3) antiarrhythmic agents. Two patients had had endocardial ablation of VT prior to LVAD. Four patients had acute success with VT ablation. The termination of VT allowed removal of the RVAD in one patient. In all patients, VT was either eliminated or significantly reduced with epicardial ablation. No procedure-related complications occurred. Three patients died in the index hospitalization due to other causes (intracranial hemorrhage, sepsis or refractory cardiogenic shock). Conclusions Open-chest hybrid epicardial ablation for recurrent or incessant VT is feasible in selected patients early after LVAD implant although the overall prognosis remains guarded.

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Epicardial ventricular tachycardia

In ventricular tachycardia (VT) arising in the myocardial tissue, the site of origin may be the endocardium, mid-myocardium or epicardium. The incidence of epicardial origin varies with the underlying heart disease, and is probably not more than 20% in ischemic heart disease and higher in non-ischemic cardiomyopathies. Percutaneous subxiphoid access to the pericardial space has enabled a non-surgical approach to catheter mapping and ablation of epicardial VT. Several algorithms are available for electrocardiographic recognition of epicardial origin. Idiopathic epicardial VTs are rare but may be curable by catheter ablation. The electrophysiologic principles guiding the mapping and ablation of epicardial VTs are similar to those used for endocardial VTs, but the biophysics of energy delivery may be different. Complications of the epicardial approach are also different from those of endocardial ablation, and specific precautions have to be taken to protect the coronary arteries and phrenic nerves and to avoid pericardial tamponade.

Abstract 19432: Exit Site of Ischemic Ventricular Tachycardia: Lessons from Simultaneous Multi-Electrode Mapping Era Applied to Sequential Mapping Era

Background: Ventricular tachycardia mapping in the sequential era is dependent on determining the exit site using entrainment mapping and or activation mapping. During entrainment mapping, VT has the potential of degenerating into ventricular fibrillation, requiring cardioversion that may distort the electroanatomic map. In addition entrainment may change the activation sequences and initiate another VT. Thus it is of importance to identify the exit site based on temporal characteristics of the activation map and characterize the exit site. In the era of point by point sequential mapping it is unclear how much time ahead of surface activation is the activation at the exit site. We sought to determine the temporal characteristics of the exit site where successful ablation was performed in relation to the surface activation. Methods and Results: Twelve patients with ischemic VT who had multi-electrode simultaneous endocardial mapping during ventricular tachycardia were retrospectively reviewed. 16 VTs induced in these twelve patients were analyzed and the activation sequence in systole, diastole, and the presystolic period was annotated. Activation time in relation to surface activation was characterized at the exit site where ablation was performed. Mapping was performed with a custom-made system consisting of a 112 electrode endocardial array with simultaneous uni and bipolar recording. Filter settings for uni was 0.1 - 200 Hz, bipolar 28 - 700Hz, sampling rate was 1 kHz for uni and 2 kHz for bipolar electrograms.The mean activation time at the exit site was 60 +/- 24 msec ahead of surface VT activation. The range of the timing of the activation at the exit site preceding surface activation was was 18 - 114 ms. The unipolar characteristic at the site was not useful in identifying timing on a consistent basis. Conclusion: The exit site of an ischemic ventricular tachycardia is on average 60 ms ahead of surface activation. This presytolic timing is earlier than what is generally believed in the current sequential mapping era of VT ablation. Our analysis suggests that catheter position at shorter activation times would indicate a location in the post exit site and unlikely to produce a useful outcome.

Abstract 19384: Catheter Ablation of Scar-Based Ventricular Tachycardia: Impact of Procedural Duration on Outcomes

Background: The relationship of procedural duration with efficacy and complication rate in ventricular tachycardia (VT) ablation has not been well studied. The aim of this report is to examine the relationship between procedural duration and VT ablation outcomes. Methods: All patients referred for VT ablation between 6/04-6/11 were included in the present study. Procedural duration was defined as the time from the insertion of catheter sheaths through the femoral vein to the time of their withdrawal. Variables that were recorded and analyzed for relationship to procedural duration included: number of induced VTs, in-hospital mortality, and 6-month outcomes. Results: 148 patients with scar-mediated VT were available for analysis. The mean procedural duration for cases with endocardial, epicardial, and combined epicardial-endocardial VT mapping were: 5.1 ± 1.7, 5.0 ± 1.6, and 6.4 ± 1.7 hours, respectively. Longer procedural duration was associated with a greater number of VT morphologies induced (range 1.5- 3.7 mean VTs induced). The six month freedom from VT for the overall cohort was 53% (ICM=66% (49/74), NICM=39% (27/69)). The duration of the procedure did not impact success rates. An increase in in-hospital mortality was observed for procedures longer than eight hours. Conclusion: While longer procedural duration was associated with comparable 6 month freedom from VT recurrence, an escalating risk for in-hospital mortality was seen in patients who underwent procedures longer than eight hours.

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Inverse Solution Mapping of Epicardial Potentials

Background— Catheter ablation of ventricular tachycardia (VT) is still one of the most challenging procedures in cardiac electrophysiology, limited, in part, by unmappable arrhythmias that are nonsustained or poorly tolerated. Calculation of the inverse solution from body surface potential mapping (sometimes known as ECG imaging) has shown tremendous promise and can rapidly map these arrhythmias, but we lack quantitative assessment of its accuracy in humans. We compared inverse solution mapping with computed tomography–registered electroanatomic epicardial contact catheter mapping to study the resolution of this technique, the influence of myocardial scar, and the ability to map VT. Methods and Results— For 4 patients undergoing epicardial catheter mapping and ablation of VT, 120-lead body surface potential mappings were obtained during implantable defibrillator pacing, catheter pacing from 79 epicardial sites, and induced VT. Inverse epicardial electrograms computed using individualized torso/epicardial surface geometries extracted from computed tomography images were compared with registered electroanatomic contact maps. The distance between estimated and actual epicardial pacing sites was 13±9 mm over normal myocardium with no stimulus-QRS delay but increased significantly over scar ( P =0.013) or was close to scar ( P =0.014). Contact maps during right ventricular pacing correlated closely to inverse solution isochrones. Maps of inverse epicardial potentials during 6 different induced VTs indicated areas of earliest activation, which correlated closely with clinically identified VT exit sites for 2 epicardial VTs. Conclusions— Inverse solution maps can identify sites of epicardial pacing with good accuracy, which diminishes over myocardial scar or over slowly conducting tissue. This approach can also identify epicardial VT exit sites and ventricular activation sequences.

734 Exit Site of Ischemic Ventricular Tachycardia: Lessons From Simultaneous Multi-Electrode Mapping Era Applied to Sequential Mapping Era

Ventricular tachycardia mapping in the sequential era is dependent on determining the exit site using entrainment mapping and or activation mapping. During entrainment mapping, VT has the potential of degenerating into ventricular fibrillation, requiring cardioversion that may distort the electroanatomic map. In addition entrainment may change the activation sequences and initiate another VT. Thus it is of importance to identify the exit site based on temporal characteristics of the activation map and characterize the exit site. In the era of point by point sequential mapping it is unclear how much time ahead of surface activation is the activation at the exit site. We sought to determine the temporal characteristics of the exit site where successful ablation was performed in relation to the surface activation. Twelve patients with ischemic VT who had multi-electrode simultaneous endocardial mapping during ventricular tachycardia were retrospectively reviewed. 16 VTs induced in these twelve patients were analyzed and the activation sequence in systole, diastole, and the presystolic period was annotated. Activation time in relation to surface activation was characterized at the exit site where ablation was performed. Mapping was performed with a custom-made system consisting of a 112 electrode endocardial array with simultaneous uni and bipolar recording. Filter settings for uni was 0.1 - 200 Hz, bipolar 28 - 700Hz, sampling rate was 1 kHz for uni and 2 kHz for bipolar electrograms.The mean activation time at the exit site was 60 +/− 24 msec ahead of surface VT activation. The range of the timing of the activation at the exit site preceding surface activation was was 18 - 114 ms. The unipolar characteristic at the site was not useful in identifying timing on a consistent basis. The exit site of an ischemic ventricular tachycardia is on average 60 ms ahead of surface activation. This presytolic timing is earlier than what is generally believed in the current sequential mapping era of VT ablation. Our analysis suggests that catheter position at shorter activation times would indicate a location in the post exit site and unlikely to produce a useful outcome.