Development and Validation of an ECG Algorithm for Identifying the Optimal Ablation Site for Idiopathic Ventricular Outflow Tract Tachycardia

A quantitative and qualitative analysis of the virtual unipolar electrograms from non-contact mapping of right or left-sided outflow tract premature ventricular contractions/ventricular tachycardia origins

OBJECTIVE

This study was conducted to examine the virtual unipolar electrogram configuration of right/left outflow tract (OT) premature ventricular contraction (PVC)/ventricular tachycardia (VT) origins obtained from a non-contact mapping system (NCMS).

METHODS

The subjects consisted of 30 patients with OT-PVCs/VT who underwent NCMS-guided ablation. We evaluated the virtual unipolar electrograms of the origin on 3D right ventricular (RV)-OT isochronal maps.

RESULTS

Successful ablation was achieved from the RV in 20 patients (RVOT group), and it failed in 10 (non-RVOT group: including left-sided/pulmonary artery/deep RVOT foci). On the virtual unipolar electrograms, the earliest activation (EA) preceded the QRS onset by 11.2 ± 2.6 ms in the RVOT group and by 7.4 ± 10.5 ms in the non-RVOT group (P = 0.138). The negative slope of the electrogram at the EA site (EA slope(5)), quantified by the virtual unipolar voltage amplitude 5 ms after the EA onset, was significantly steeper in the RVOT group than in the non-RVOT group (0.66 ± 0.52 mV vs. 0.14 ± 0.17 mV, P = 0.005). Cutoff values for the EA-to-QRS onset time and EA slope(5) of ≥ 8 ms and >0.3 mV, respectively, completely differentiated the RVOT group from the non-RVOT group. A lesser EA slope(5) was associated with a greater radiofrequency energy delivery required to terminate RVOT-PVCs/VT.

CONCLUSIONS

These demonstrate the importance of the virtual unipolar electrograms from OT-PVC/VT origins obtained with the NCMS. The virtual EA predicts both successful and potentially difficult ablation sites from the RV side.

Utility of distinctive local electrogram pattern and aortographic anatomical position in catheter manipulation at coronary cusps

BACKGROUND

The coronary cusps have recently become target sites for radiofrequency catheter ablation of both outflow tract ventricular arrhythmias originating near the coronary cusps (CC-VA) and atrial tachyarrhythmias such as focal atrial tachycardia originating near the noncoronary cusp (NCC-AT). However, the relation between local electrograms recorded at each CC during sinus rhythm and their anatomical position as assessed by aortography has not yet been systematically described.

METHODS AND RESULTS

In 28 patients undergoing RFCA for CC-VA or NCC-AT, amplitudes of the atrial and ventricular potentials at the CCs were measured during sinus rhythm, and the atrial/ventricular (A/V) potential ratio was computed. Relative positions of the CCs were assessed by aortography in 2 X-ray projections. In the right (RCC) and left coronary cusps (LCC), amplitudes of the ventricular potential were larger than those of the atrial potential, leading to an A/V ratio <1 in all patients (0.08 ± 0.10, 0.32 ± 0.21, respectively). In contrast, in the NCC, the amplitude of the atrial potential was larger than the ventricular potential, leading to a higher A/V ratio relative to the CCs (5.7 ± 2.6, P < 0.0001). Aortography demonstrated the rightward and anterior location of the RCC, the leftward and superior location of the LCC, and the inferior and posterior location of the NCC.

CONCLUSIONS

Awareness of the distinctive local electrogram pattern of each CC and their positions on aortography should lead to safer and more effective catheter ablation at the CCs.

Novel transitional zone index allows more accurate differentiation between idiopathic right ventricular outflow tract and aortic sinus cusp ventricular arrhythmias

BACKGROUND

Although several ECG algorithms have been proposed for differentiating the origins of outflow tract ventricular arrhythmia (OT-VA), their accuracy still is limited in cases with cardiac rotation.

OBJECTIVE

The purpose of this study was to assess whether a novel "cardiac rotation-corrected" transitional zone (TZ) index would be a useful marker for differentiating right ventricular outflow tract (RVOT) origin from aortic sinus cusp (ASC) origin.

METHODS

Surface ECGs of OT-VAs with left bundle branch block morphology and inferior axis in 112 patients who were successfully ablated in the RVOT (n = 87) or the ASC (n = 25) were analyzed. The TZ index was defined according to the site of R-wave transition of sinus beats and OT-VAs.

RESULTS

The TZ index was significantly lower in the ASC origin than in the RVOT origin (-1.2 ± 0.9 vs 0.3 ± 0.7, P <.0001). A cutoff value of the TZ index <0 predicted the ASC origin with 88% sensitivity and 82% specificity. The previously reported R-wave duration index ≥ 50% had a high specificity of 85% but a low sensitivity of 44%, and R/S-wave amplitude index ≥ 30% had 68% sensitivity and 79% specificity. The area under the curve by receiver operating characteristic curve analysis was 0.90 for the TZ index, which was significantly higher than the R-wave duration index and R/S-wave amplitude index of 0.74 and 0.76, respectively.

CONCLUSION

This novel TZ index can be a more useful marker for differentiating RVOT origin from ASC origin.

Is single-view fluoroscopy sufficient in guiding cardiac ablation procedures?

The CARTO XP ablation system provides real-time data on 3D, color-coded maps of the electrical activity of the heart; however, it is expensive and can only use a dedicated costly magnetic catheter per patient intervention. The purpose of our study is to shorten the duration of the radiofrequency ablation procedure and increase its efficacy by developing an affordable prototype catheter navigation system that simulates the CARTO system. To obtain 3D geometrical data from catheter locations inside the heart chamber, we acquired only single-view images using an Integris Allura fluoroscope and estimated the depth of the mapping electrode using pattern recognition techniques. Validation was performed in ideal and clinical conditions. For phantom experiment, when using a 7-French catheter, the average recovered depth error was 2.05 +/- 1.46 mm using a single image. However, when using the 8-French catheter, the average recovered depth error was 1.54 +/- 1.29 mm. In clinical experimentation, the standard error of estimate for the estimated depth was about 13.1 mm and 10.1 mm, respectively, for the posterior and lateral views. In conclusion, this paper describes our achievements and shortfalls in developing an affordable fluoroscopic navigation system to guide RF catheter ablation of cardiac arrhythmias.

Epicardial Ablation of Idiopathic Ventricular Tachycardia

Epicardial ventricular tachycardia (VT) is an increasingly recognized arrhythmia in clinical practice. Electrocardiographic algorithms to identify epicardial VT should be used with the understanding that they are an initial guide to localization and do not exclude an epicardial origin of VT, particularly when endocardial approaches are unsuccessful. Ablation using a transvenous approach or direct epicardial access may produce favorable results, although care must be taken to avoid coronary artery or phrenic nerve injury. A subset of patients require a combined endocardial and epicardial approach to eliminate VT. Although these ablation strategies are generally well tolerated, they should be limited to patients with highly symptomatic arrhythmias or those in whom myocardial depression is thought to be related to prolonged tachycardia or repetitive ventricular ectopy.

Electrocardiographic Recognition of Epicardial Arrhythmias

The great majority of arrhythmias can be ablated with current techniques using an endocardial approach. However, an epicardial approach may be required in some cases. ECG-based criteria have been developed to aid recognition of arrhythmias with an epicardial origin, which allows for a planned epicardial ablation procedure. This article summarizes the current ECG-based criteria to recognize these epicardial arrhythmias.

Use of a circular mapping and ablation catheter for ablation of atypical right ventricular outflow tract arrhythmia

A new technique for ablation of persistent ectopic activity with atypical electrocardiographic characteristics at the vicinity of the right ventricular outflow tract is described. A new circular mapping and ablation catheter initially designed for pulmonary vein ablation was used. Abolition of ectopic activity was achieved with minimal fluoroscopy and ablation times.

Imaging modalities in cardiac electrophysiology

Cardiac imaging, both noninvasive and invasive, has become a crucial part of evaluating patients during the electrophysiology procedure experience. These anatomical data allow electrophysiologists to not only assess who is an appropriate candidate for each procedure, but also to determine the rate of success from these procedures. This article incorporates a review of the various cardiac imaging techniques available today, with a focus on atrial arrhythmias, ventricular arrhythmias and device therapy.

Electrocardiographic algorithm to identify the optimal target ablation site for idiopathic right ventricular outflow tract ventricular premature contraction

AIMS

Several electrocardiographic (ECG) algorithms have been developed to identify the site of origin of ventricular premature contractions (VPCs) from right ventricular outflow tract (RVOT) based on pacemapping; however, their accuracy remains unclear.

METHODS AND RESULTS

We evaluated the accuracy of these algorithms in 52 consecutive patients (31 female, mean age 42.6+/-14.6 years) with successful radiofrequency ablation of RVOT-VPC as guided by 3D electroanatomical non-contact mapping (Ensite, St Jude Medical, USA) and compared with a newly proposed ECG algorithm. As guided by 3D electroanatomical mapping, the successful ablation sites of RVOT-VPC were RVOT septum (n=31), RVOT free wall (n=19), and His region (n=2). Retrospective evaluation in the initial 39 patients shows that the overall positive prediction value to identify a successful ablation site of this newly proposed ECG algorithm is 77.3% and is higher than the 73.3% by Ito et al., 73.3% by Joshi et al., and 53.8% by Dixit et al. (P>0.05). Prospective evaluation in the subsequent 13 patients also demonstrate similar high overall sensitivity (79.0%), specificity (92.7%), and positive prediction value (88.2%) to identify a successful ablation site with this newly proposed ECG algorithm.

CONCLUSION

On the basis of detail 3D electroanatomical mapping of successful ablation sites, a newly proposed ECG algorithm was developed to improve the sensitivity, specificity, and positive prediction value in identification of targeted ablation sites for RVOT-VPC.

Idiopathic premature ventricular contractions exhibiting preferential conduction within the aortic root

A 65-year-old man with frequent premature ventricular contractions (PVCs) underwent electrophysiological testing. Although an excellent pace map was obtained from the right coronary cusp (RCC), radiofrequency ablation at that site interrupted the PVCs transiently. Successful ablation was achieved in the left coronary cusp with earlier local ventricular activation during the PVCs than that in the RCC. These findings suggest that preferential conduction within the aortic root may exist and cause ventricular arrhythmias (VAs) arising from this region to exhibit variable electrocardiographic features, thereby limiting the reliability of electrocardiographic algorithms and pace mapping to predict the site of the VA origin.

Vagal reflex provoked by radiofrequency catheter ablation in the right aortic sinus cusp: a Bezold-Jarisch-like phenomenon

A 66-year-old woman with idiopathic premature ventricular contractions with a left bundle branch block QRS morphology and left inferior axis underwent electrophysiologic testing. Successful radiofrequency ablation was achieved in the right coronary cusp (RCC). However, radiofrequency ablation at sites adjacent to the successful ablation site provoked sinus bradycardia followed by atrioventricular conduction block. That phenomenon might be explained by a vagal reflex through stimulation of vagal pathways or receptors in the anterior epicardial fat pads neighboring to the RCC. A vagal reflex should be kept in mind as a complication during catheter ablation of ventricular arrhythmias originating from the RCC.

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.

Successful radiofrequency catheter ablation of ventricular tachycardia originating from underneath the mechanical prosthetic aortic valve

A 67-year-old man who developed sustained ventricular tachycardia (VT) 4 years after a prosthetic aortic valve replacement, underwent electrophysiologic testing and catheter ablation. The mechanism of the VT was suggested to be triggered activity because the VT could be induced by programmed ventricular stimulation, and burst ventricular pacing demonstrated overdrive suppression without a transient entrainment. Successful catheter ablation using a transseptal approach was achieved underneath the mechanical prosthetic aortic valve on the blind side for that approach. This case demonstrated that catheter mapping and ablation of the entire LV using a transseptal approach might be possible.

Non-pharmacological management of ventricular tachycardia

Ventricular tachyarrhythmias (VTA), a major cause of sudden cardiac death, require meticulous management in order to prevent recurrent episodes. Recently, non-pharmacological interventions, including radiofrequency catheter ablation and implantable cardioverter defibrillators (ICD), have become important treatments of VTA. Catheter ablation is curative in a relatively high percentage of patients presenting with idiopathic monomorphic ventricular tachycardia (VT). For VT associated with structural heart disease, however, the efficacy of catheter ablation remains limited, and ICD is the first-line therapy. In a subset of patients presenting with recurrent episodes of ventricular fibrillation (VF), catheter ablation is a therapeutic option when the VF is triggered by specific premature ventricular complexes. In Japan, unlike in the United States and Europe, ICD have not yet been accepted as first-line prevention of sudden cardiac death caused by VTA. The efficacy of ICD is occasionally limited by intolerable complications, such as electrical storm, inappropriate shock delivery and infection. Catheter ablation and ICD therapy might need to be combined for problematic cases.

Premature ventricular contractions with a right bundle branch block and inferior QRS axis morphology: where is the site of the origin?

A 63-year-old woman with symptomatic premature ventricular contractions (PVCs) underwent electrophysiologic testing. The PVCs were suggested to originate from the infra-aortic valvular left ventricular outflow tract because the PVCs had S-waves in leads I, V5, and V6, and an R/S ratio >1 in lead V(1). However, during some PVCs without S-waves, the ST segment had negative retrograde P-waves with a longer ventricularatrial (VA) interval. A Radiofrequency (RF) application in the left coronary cusp completely eliminated the PVCs, suggesting that negative retrograde P-waves might have been observed as pseudo S-waves during the PVCs.

Preferential Conduction Across the Ventricular Outflow Septum in Ventricular Arrhythmias Originating From the Aortic Sinus Cusp

OBJECTIVES

The purpose of this study was to examine the relationship between the origin and breakout site of idiopathic ventricular tachycardia (VT) or premature ventricular contractions (PVCs) originating from the myocardium around the ventricular outflow tract.

BACKGROUND

The myocardial network around the ventricular outflow tract is not well known.

METHODS

We studied 70 patients with idiopathic VT (n = 23) or PVCs (n = 47) with a left bundle branch block and inferior QRS axis morphology. Electroanatomical mapping was performed in both the right ventricular outflow tract (RVOT) and aortic sinus cusp (ASC) during VT or PVCs.

RESULTS

The earliest ventricular activation (EVA) was recorded in the RVOT in 55 patients (group R) and in the ASC in 15 (group A). In all group R patients, the closest pace map and successful ablation were achieved at the EVA site. Although a successful ablation was achieved at the EVA site in all group A patients, the closest pace map was obtained at the EVA site in 8 and RVOT in 7 (with an excellent pace map in 4). The stimulus to QRS interval was 0 ms during pacing from the RVOT and 36 +/- 8 ms from the ASC. The distance between the EVA and perfect pace map sites in those 4 patients was 11.9 +/- 3.0 mm.

CONCLUSIONS

Ventricular arrhythmias originating from the ASC often show preferential conduction to the RVOT, which may render pace mapping or some algorithms using the electrocardiographic characteristics less reliable. In some of those cases, an insulated myocardial fiber across the ventricular outflow septum may exist.

Using the Initial Vector from Surface Electrocardiogram to Distinguish the Site of Outflow Tract Tachycardia

BACKGROUND

The purpose of this study is to determine whether initial vector force might best distinguish tachycardias arising from the right ventricular (RV) outflow tract (OT) versus aortic sinus cusps (ASCs).

METHODS

Among 45 patients with OT tachycardia, we measured the time from the earliest QRS onset in any lead to local onset and to the first QRS peak/nadir in each surface leads during VT. We compared the earliest phase differences among patients with foci in RVOT (n = 32) and in ASCs (n = 13) (determined by ablation), using unpaired t-tests. We determined the optimum cut-points by analyzing the receiver-operator characteristics curves, and derived an algorithm to discriminate ASC from RVOT foci.

RESULTS

Compared with an RVOT focus, origin in the ASC was associated with lower likelihood that the earliest lead of QRS activation was V2 (4/13 [12%] vs 29/32 [88%], P = 0.0001), later initial peak/nadir in III (110 +/- 19 vs 93 +/- 16 ms, P = 0.0026) and V2 (75 +/- 26 vs 42 +/- 19 ms, P < 0.0001). After determining the optimum cut-points for each, we found that the presence of any one of these findings discriminated well between RVOT and ASC foci (sensitivity 92%, specificity 88%, positive predictive value 75%, and negative predictive value 97%). The sensitivity and specificity using standard ECG criteria were inferior to the vector approach.

CONCLUSIONS

The ECG phase differences during VT can distinguish the origin of OT-VT. Earliest onset or first peak/nadir in V2 and early initial peak/nadir in the inferior leads suggest a RVOT focus.

Demonstration of Ventricular Myocardial Extensions into the Pulmonary Artery and Aorta Beyond the Ventriculo-Arterial Junction

BACKGROUND

A subgroup of outflow tract (OT) ventricular tachycardias (VT) originate from the aortic sinuses or the main stem of the pulmonary artery. The anatomic substrate for these tachycardias is unknown. The aim of this study was to investigate the presence of ventricular myocardial extensions (VME) into the pulmonary artery (PA) and aorta (Ao) beyond the ventriculo-arterial junction (VAJ) and determine the anatomical and histological characteristics of these muscle extensions.

METHODS

Ninety-five consecutive human hearts obtained at autopsy were studied. Longitudinal strips of tissue containing each cusp, aortic, and pulmonary artery walls and left and right ventricular outflow tracts were excised and histologically analyzed. Anatomical measurements, including length and thickness of VMEs, obtained at autopsy, were made.

RESULTS

VMEs beyond the VAJ were found in 21 of 95 (22%) patients studied. VMEs were found in 16 of 95 PAs (17%) and 7 of 95 Aos (7%) were examined. VMEs were located within the adventitia in 23 (88%) and on the epicardial surface in three (12%). The majority of VMEs were in continuity with the underlying ventricular OT muscle tissue. Myocellular hypertrophy and fibrosis were present in 19 (73%) and fatty tissue between the layers of VME in 18 (69%). Clinical data were available in 14 of 21 patients with positive VME. None of the patients (clinical data available group) had history of cardiac disease or signs or symptoms (palpitations or syncope) of cardiac disease.

CONCLUSIONS

VMEs into the PA and Ao beyond the VAJ are relatively common. It seems that their mere presence does not predispose to OT VTs. There are probably intrinsic arrhythmogenic properties in tissues specific to these regions in those patients who develop OT VTs.

[Ventricular tachycardia. Diagnostic spectrum and therapeutic measures]

The origin of ventricular tachycardia lies in the ventricular tissue and includes a variety of symptoms such as monomorphic and polymorphic ventricular tachyarrhythmia (VT), ventricular flutter and ventricular fibrillation. Due to transitions of one form of VT to another, any form of VT incurs in principal the risk of cardiac failure. Apart from different electrophysiologic mechanisms such as reentry or triggered activity, any occurrence of VT has to be considered in an individual context: VT can be caused by structural heart disease such as coronary artery disease or dilative cardiomyopathy, or primary electrical disease such as long or short QT syndromes or can even occur without any detectable cause (idiopathic VT). Correct identification of the underlying cause of the arrhythmia is essential for the prognosis, differential therapy and long-term treatment of patients.

Idiopathic ventricular arrhythmias originating from the tricuspid annulus: Prevalence, electrocardiographic characteristics, and results of radiofrequency catheter ablation

BACKGROUND

Idiopathic ventricular tachycardias (VTs) and premature ventricular contractions (PVCs) arising from the tricuspid annulus have been reported.

OBJECTIVE

The purpose of this study was to clarify the prevalence and characteristics of VT/PVCs originating from the tricuspid annulus.

METHODS

The ECG characteristics and results of radiofrequency (RF) catheter ablation were analyzed in 454 patients with idiopathic VT/PVCs.

RESULTS

Thirty-eight (8%) patients had VT/PVCs arising from the tricuspid annulus: 28 VT/PVCs (74%) originated from the septal portion of the tricuspid annulus and the remaining 10 (26%) from the free wall of the tricuspid annulus. QRS duration and Q-wave amplitude in each of leads V1-V3 were greater in VT/PVCs arising from the free wall of the tricuspid annulus than those from the septum of the tricuspid annulus (all P < .01). "Notching" of the QRS complex was observed more often in VT/PVCs arising from the free wall of the tricuspid annulus than those from the septum of the tricuspid annulus (P < .01). A Q wave in lead V1 was observed more often in VT/PVCs arising from the septum of the tricuspid annulus than those from the free wall of the tricuspid annulus (P < .005). R-wave transition occurred beyond lead V3 more often in VT/PVCs arising from the free wall of the tricuspid annulus than those from the septum of the tricuspid annulus (P < .005). RF catheter ablation eliminated 90% of the VT/PVCs arising from the free wall of the tricuspid annulus but only 57% of the VT/PVCs arising from septum of the tricuspid annulus.

CONCLUSION

Idiopathic VT/PVCs arising from tricuspid annulus are not rare, and the detailed origin can be determined by ECG analysis. The preferential site of origin was the septum but also could be the free wall of the tricuspid annulus.

Idiopathic Ventricular Tachycardia: Diagnosis and Management

Idiopathic ventricular tachycardia (VT) is an uncommon form of VT that is seen in patients without structural heart disease. It is commonly seen in young patients and usually has a benign course. Recent studies have delineated the mechanisms and anatomical locations of this form of VT. Recognition of various forms of idiopathic VT based on characteristic QRS morphology from the 12-lead electrocardiogram (ECG) has important prognostic and therapeutic implications. The understanding of the mechanisms of idiopathic VT has led to the use of specific antiarrhythmic drugs targeting particular arrhythmias. Recent technological advances in the field of mapping and catheter ablation have led to a suitable alternative to drug therapy with a very high cure rate. This review describes the clinical features, ECG recognition, and management of idiopathic monomorphic VT.

Significance and Utility of Plasma Brain Natriuretic Peptide Concentrations in Patients with Idiopathic Ventricular Arrhythmias

BACKGROUND

Secretion of B-type natriuretic peptide (BNP) appears to be regulated mainly by wall tension, and an increase in the plasma BNP concentration is considered to reflect ventricular structural and functional abnormalities. The aim of this study was to clarify the significance and utility of the measurement of the plasma BNP in the setting of idiopathic ventricular arrhythmias (I-VT/PVCs).

METHODS

This study included 135 patients with symptomatic, monomorphic I-VT/PVCs (73 women; 53 +/- 17 years; 50 ventricular tachycardias [VTs], 85 premature ventricular contractions) who underwent radiofrequency catheter ablation. None had structural heart disease or renal dysfunction.

RESULTS

The plasma BNP concentration exceeded the normal range (>18.4 pg/mL; high BNP concentration) in 79 patients (56%). The high BNP concentration was found more often in I-VT/PVCs originating from the left ventricle (LV; 74%) than the right ventricle (RV; 49%; P < 0.01). The plasma BNP concentration correlated with the age (P = 0.0001) and frequency of premature ventricular contractions (P < 0.0001), and left-sided I-VT/PVCs and the presence of controlled hypertension were independent predictors of a high BNP concentration (both P < 0.05). In patients with a successful ablation and high BNP concentration before the ablation, the BNP concentration decreased to the normal range in 61% of patients after ablation. In patients with a failed ablation, the BNP concentration did not decrease to the normal range after ablation in any of the patients (P < 0.0005).

CONCLUSIONS

The plasma BNP concentration was elevated in about 60% of the patients with symptomatic I-VT/PVCs. Normalization of the high BNP concentration after ablation may indicate a successful ablation.

Idiopathic Epicardial Left Ventricular Tachycardia Originating Remote From the Sinus of Valsalva

Background— Despite the success of catheter ablation for treatment of idiopathic ventricular tachycardia (VT), occasional patients have been reported in whom VT could not be ablated from the right or left ventricular endocardium or from the aortic sinus of Valsalva (ASOV).

Methods and Results— In 12 of 138 patients (9%) with idiopathic VT referred for ablation, an epicardial left ventricular site of origin was identified >10 mm from the ASOV. Coronary venous mapping demonstrated epicardial preceding endocardial activation by >10 ms (41±7 versus 15±11 ms before QRS onset; P <0.001). VT induction was facilitated by catecholamines and terminated by adenosine. Ablation through the coronary veins or via percutaneous transpericardial catheterization was successful in 9 patients; 2 required direct surgical ablation as a result of anatomic constraints. No ECG pattern was specific for epicardial VT. However, slowed initial precordial QRS activation, as quantified by a novel metric, the maximum deflection index, was more useful. A delayed precordial maximum deflection index ≥0.55 identified epicardial VT remote from the ASOV with a sensitivity of 100% and a specificity of 98.7% relative to all other sites of origin ( P <0.001).

Conclusions— Although clinically underrecognized, idiopathic VT may originate from the perivascular sites on the left ventricular epicardium. The mechanism is consistent with triggered activity. It is amenable to ablation by transvenous or transpericardial approaches, although technical challenges remain. Recognition of a prolonged precordial maximum deflection index and early use of transvenous epicardial mapping are critical to avoid protracted and unsuccessful ablation elsewhere in the ventricles.

Epicardial Idiopathic Ventricular Tachycardia Originating Within the Left Main Coronary Artery Ostium Area: Identification Using the LocaLisa Nonfluoroscopic Catheter Navigation System

Idiopathic ventricular tachycardia (IVT) in patients without structural heart disease commonly arises from the right or left outflow tracts, but there remain arrhythmias that can only be ablated by an epicardial approach. We report a case of an epicardial ventricular tachycardia originating within the left main coronary artery ostium area, as identified using the LocaLisa nonfluoroscopic catheter navigation system. Due to the high risk of coronary artery thrombosis, ventricular tachycardia was successfully ablated by a transthoracic surgical approach using cryoenergy. Ventricular ectopy disappeared and ventricular tachycardia did not recur during long-term follow-up.