Spatial orientation of the reentrant circuit of idiopathic left ventricular tachycardia

Idiopathic Left Ventricular Tachycardia Originating in the Left Posterior Fascicle

Ventricular tachycardias originating from the Purkinje system are the most common type of idiopathic left ventricular tachycardia. The majority if not all of the reentrant circuit involved in this type of tachycardia is formed by the Purkinje fibres of the left bundle branch, particularly the left posterior fascicle. In general, slowly conducting Purkinje fibres (P1) form the antegrade limb, and normally conducting Purkinje fibres (P2) form the retrograde limb of the reentrant circuit of the ventricular tachycardia originating from the left posterior fascicle. Elimination of the critical Purkinje elements in the reentrant circuit is the route to successful ablation. While the reentrant circuit identified by activation mapping provides the roadmap to ablation targets, comparing the difference in the His-ventricular interval during sinus rhythm and tachycardia also helps to identify the critical site in the reentrant circuit.

Cellular Physiology and Clinical Manifestations of Fascicular Arrhythmias in Normal Hearts

Fascicular ventricular arrhythmias represent a spectrum of ventricular tachycardias dependent on the specialized conduction system. Although they are more common in structurally abnormal hearts, there is an increasing body of literature describing their role in normal hearts. In this review, the authors present data from both basic and clinical research that explore the current understanding of idiopathic fascicular ventricular arrhythmias. Evaluation of the cellular electrophysiology of the Purkinje cells shows clear evidence of enhanced automaticity and triggered activity as potential mechanisms of arrhythmias. Perhaps more importantly, heterogeneity in conduction system velocity and refractoriness of the left ventricular conduction system in animal models are in line with clinical descriptions of re-entrant fascicular arrhythmias in humans. Further advances in our understanding of the conduction system will help bridge the current gap between basic science and clinical fascicular arrhythmias.

Identification of the slow conduction zone in a macroreentry circuit of verapamil-sensitive idiopathic left ventricular tachycardia using electroanatomic mapping

BACKGROUND

Although idiopathic left ventricular tachycardia (ILVT) has been shown to possess a slow conduction zone (SCZ), the details of the electrophysiological and anatomic aspects are still not well understood.

OBJECTIVE

We hypothesized that the SCZ can be identified using a 3-dimensional electroanatomic (EA) mapping system.

METHODS

Ten patients with ILVT were mapped using a 3-dimensional electroanatomic (EA) mapping system. After a 3-dimensional endocardial geometry of the left ventricular was created, the conduction system with left Purkinje potential (PP) and the SCZ with diastolic potential (DP) in LV were mapped during sinus rhythm (SR) and ventricular tachycardia (VT) and were tagged as special landmarks in the geometry. The electrophysiological and anatomic aspects of it were investigated.

RESULTS

EA mapping during SR and VT was successfully performed in 7 patients, during VT in 3 patients. The SCZ with DPs located at the inferoposterior septum was found in 7 patients during SR and all patients during VT. The length of the SCZ was 25.2 ± 2.3 mm with conduction velocity 0.08 ± 0.01 m/s. No differences in these parameters were found between patients during SR and VT (P > 0.05). An area with PP was found within the posterior septum. A crossover junction area with DP and PP was found in 7 patients during SR and VT. This area with DP and PP during SR coincided or were in proximity to such area during VT and radiofrequency ablation targeting the site within the area abolished VT in all patients.

CONCLUSION

The ILVT substrate within the junction area of the SCZ and the posterior fascicular can be identified and can be used to guide the ablation of ILVT.

The significance of repetitive ventricular responses induced by radiofrequency energy application for idiopathic left ventricular tachycardia

In radiofrequency (RF) ablation for idiopathic left ventricular tachycardia (ILVT), the termination of tachycardia during RF ablation is considered a hallmark of success. However, in cases of patients with difficulty of induction of ventricular tachycardia (VT), the evaluation of procedural success can be problematic. We have observed thermal responses reflected as ventricular rhythm change to RF energy delivered on sinus rhythm for ILVT. We therefore describe the significance of repetitive ventricular responses. The study subjects were 11 ILVT patients for whom RF energy was delivered during sinus rhythm because of difficulty in re-induction of tachycardia. During each energy delivery, we focused on the occurrence of repetitive ventricular responses especially exhibiting a similar morphology to clinical VT. The repetitive ventricular responses were noted in 10 of 11 patients. Two patients received a second procedure due to the recurrence of ILVT. The mean follow-up period was 36.2+/-12.8 months. The clinical course of the remaining patients was favorable and without recurrence of ILVT. Based on the favorable clinical outcomes, ablation-induced repetitive ventricular responses with similar QRS morphology to clinical ILVT are useful markers for selecting an ablation site and could be used as an additional mapping method, termed as "thermal mapping".

Pleomorphic Ventricular Tachycardia: An Uncommon Presentation in Idiopathic Left Ventricular Tachycardia

Idiopathic left ventricular tachycardia (ILVT) is a distinct entity that arises in the left ventricle, may have reentrant mechanism and is verapamil-sensitive. Pleomorphism as defined by multiple ventricular tachycardia morphologies is usually associated with either coronary artery disease or cardiomyopathy but very rare in cases of ILVT. In this case report, we describe an unusual case of ILVT with two ECG morphologies of the opposite axis that were successfully eliminated with radiofrequency ablation. The successful ablation sites were closely located to each other in the left lower ventricular septum.

Idiopathic sustained left ventricular tachycardia in pediatric patients

BACKGROUND

Idiopathic sustained ventricular tachycardia originating from the left ventricle (ILVT) has been an indication for catheter ablation. The present study evaluated the clinical features, long-term prognosis and indications for treatment in pediatric patients with ILVT.

METHODS

The subjects of the present study were eight patients (four males and four females) with a mean age at onset of 11.0 years (range 3-15 years). The mean follow-up period was 7.7 years (range 2.1-11.3 years).

RESULTS

In electrophysiologic studies, intravenously administered verapamil was effective for the termination of tachycardia in all six patients who received this treatment and for the prevention of tachycardia in four of five patients. Oral administration of verapamil was effective in five of seven patients. Propranolol or flecainide was added to the treatment protocol for two patients who did not respond to verapamil alone. Tachycardia disappeared without drugs in four patients during the follow-up period and became non-sustained in another patient. Two of three patients with persistent tachycardia underwent catheter ablation. Pharmacologic treatment was very effective for ILVT among these patients.

CONCLUSIONS

Pharmacologic therapy, such as with verapamil, is still the treatment of choice for ILVT because of a good long-term prognosis and potential risks and complications by manipulation of catheter ablation.

Radiofrequency ablation of idiopathic left ventricular tachycardia at the site of earliest activation as determined by noncontact mapping

INTRODUCTION

The most effective method for guiding radiofrequency (RF) ablation of idiopathic left ventricular tachycardia (ILVT) has yet to be determined. We investigated the use of noncontact mapping in five patients with this condition.

METHODS AND RESULTS

The multielectrode array was positioned in the left ventricular apex via the retrograde approach. Isopotential color maps of ILVT were examined to determine the site of earliest endocardial activation. The ablation catheter was steered to the target site using the locator signal. Pace mapping was performed and contact electrograms examined for diastolic potentials. RF energy was applied to the target site. Sustained ventricular tachycardia was induced in 2 patients and nonsustained ventricular tachycardia in 3. The site of earliest activation was at the apical septum in 3, the inferior apex in 1, and the base of the inferior wall in 1. Mean timing was 21 +/- 10 msec before onset of the surface QRS. Diastolic activity was visualized with noncontact mapping at the base of the septum in 1 patient. A Purkinje potential was seen at the ablation site in only 1 patient. No diastolic activity was seen in the remaining 3 patients. Tachycardia was successfully terminated in all 5 patients with a median of four RF applications. No patient suffered a recurrence after 9.6 +/- 4.7 months of follow-up.

CONCLUSION

By identifying the precise site of earliest activation during ILVT, noncontact mapping has been shown to be an effective and safe method for guiding RF ablation.

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.

Ventricular arrhythmias in normal hearts

Idiopathic ventricular tachycardia (VT) is characterized by two predominant forms. The most common form originates from the right ventricular outflow tract and presents as repetitive monomorphic VT or exercise-induced VT. The tachycardia is adenosine sensitive and is thought to be because of cAMP-mediated triggered activity. The other major form of idiopathic VT is owing to verapamil-sensitive intrafascicular re-entrant tachycardia, which most often originates in the region of the left posterior fascicle. Both forms of idiopathic VT can be readily treated with radiofrequency catheter ablation.

Identification of the slow conduction zone in idiopathic left ventricular tachycardia

The mechanism of verapamil sensitive idiopathic left ventricular tachycardia (ILVT) is considered to be reentry. However, the nature of the reentry circuit, including the location of the slow conduction zone, is unclear. We sought the local electrical activity that would reflect slow conduction by precise mapping around the tachycardia exit (TE) in nine patients with ILVT (mean age, 28 +/- 10 years) undergoing radiofrequency catheter ablation (RFCA). The TE was defined as the earliest discrete spiky potential (SP) recorded during the tachycardia, or as a complete configuration-matched pacemap 12-lead electrocardiogram (ECG). In all patients, the TE was located at the mid or inferior distal portion of the septum. The SP at the TE preceded the surface QRS by 20 +/- 9 ms. The pacemap score at the TE was 11.4 +/- 0.6 points. In three patients, fractionated potentials (FP) were recorded during the tachycardia. The onset of the FP preceded the surface QRS by 47 +/- 8 ms and was earlier than the SP at the TE (P < 0.01). The sites where an FP was detectable were restricted to a small area, and were at a distance of 14 +/- 4 mm from the TE. The direction of the FP site from the TE was more basal in two patients and inferior in one. Pacemap ECGs at the sites with an FP showed poor matching (9 +/- 1 points), presumably because of predominant capture of the local ventricular muscle rather than an electrically isolated reentry circuit. Successful RFCA was achieved at the site of the FP in all three patients in which one was recorded, and at the TE in the other six patients. The FP, which has been shown to reflect the slow conduction of the ventricular tachycardia circuit in structural heart disease, was also detected in ILVT in the present study, and it is likely to reflect electrical excitation of the distal rim of the slow conduction zone.

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.

Diastolic potentials observed in idiopathic left ventricular tachycardia

Radiofrequency catheter ablation (RF-CA) has demonstrated a high success rate in eliminating idiopathic left ventricular tachycardia (ILVT), and the target site is determined by the score of pace mapping or the Purkinje potential (PP) preceding the onset of the ventricular activation, which is considered to indicate the exit site of the reentrant circuit. However, only a few reports have described the potential obtained from the slow conduction zone. RF-CA was successfully performed in 8 patients with ILVT. Careful mapping of the left ventricle during tachycardia was carried out to find the diastolic potential (DP). A DP was obtained in 4 patients (group 1), but not in 4 others (group 2). The local electrogram was recorded from the distal tip of the ablation catheter during the RF current application in order to investigate the pattern of termination of ILVT. A DP was recorded at the point where the catheter was slightly pulled back to a site proximal to the exit site of the reentrant circuit at the left interventricular basal septum. In group 1, conduction block between the DP and PP eliminated ILVT in 3 out of 4 cases, and 1 case showed conduction block between the DP and ventricular potential. In 2 out of 4 patients in group 2, the local electrogram showed conduction block between PP and the ventricular potential when VT terminated. The ablation site in group 1 was located relatively more basal than that in group 2 in anatomy. A DP was obtained in a half of the cases with ILVT and RF-CA at this site could eliminate ILVT. A DP was obtained at a site relatively basal to the exit of the reentrant circuit and it is considered that this is a useful marker in terms of the successful ablation of ILVT.

Demonstration of Purkinje potential during idiopathic left ventricular tachycardia: a marker for ablation site by transient entrainment

During VT of QRS morphology with right bundle branch block and left axis deviation in a patient without obvious structural heart disease, entrainment by pacing from the right ventricular outflow tract and high right atrium was demonstrated. During entrainment of VT, a Purkinje potential preceding the QRS and recorded at the left ventricular mid-septum was activated by orthodromic impulses in the reentry circuit. The interval between the Purkinje potential and the earliest left ventricular activation was decrementally prolonged with shortening of pacing cycle length. Radiofrequency energy was applied to this site, resulting in successful elimination of VT. Therefore, the Purkinje potential represented activation by an orthodromic wavefront in the reentry circuit, while the orthodromically distal site to this potential showed an area of slow conduction with decremental property.

Adenosine-sensitive ventricular tachycardia from the anterobasal left ventricle

OBJECTIVES

This study demonstrates that exercise-provocable tachycardia resembling right ventricular outflow tract tachycardia may originate from the anterobasal left ventricle.

BACKGROUND

Reentry is the operative mechanism of idiopathic left ventricular tachycardia, with a QRS complex of right bundle branch block and superior axis that is responsive to verapamil but not adenosine. Whether some mechanism other than reentry is operative in some idiopathic left ventricular tachycardias is unclear.

METHODS

In 4 of 53 consecutive patients with idiopathic left ventricular tachycardia, the tachycardia was sensitive to adenosine. These four patients were women 63, 61, 61 and 31 years old and were the subjects of the present study.

RESULTS

In all four patients, spontaneous tachycardia was related to exercise or emotional stress. The tachycardia displayed atypical left (one patient) or right (three patients) bundle branch block with an inferior axis and marked variation in cycle length. An intravenous bolus of adenosine triphosphate (10 to 20 mg) terminated tachycardia in all four patients. Tachycardia was terminated or prevented in three patients given intravenous or oral verapamil. Atrial or ventricular incremental or extrastimulus testing induced tachycardia in all four patients (three with, one without isoproterenol infusion). Electrically induced tachycardia also demonstrated marked variation in cycle length, which ranged from 230 to 390 ms. Entrainment was not demonstrable with overdrive pacing from multiple sites. Endocardial mapping during tachycardia revealed that the earliest activations were registered 25, 40, 35 and 50 ms before onset of the QRS complex, respectively, from the anterior aspect of the left ventricle just below the mitral annulus, adjacent to the left ventricular outflow tract. High frequency Purkinje spikes were not recorded at this site. Radiofrequency current delivered to this site successfully ablated the tachycardia in three of the four patients.

CONCLUSIONS

Exercise-provocable, catecholamine-mediated, verapamil-responsive, adenosine-sensitive ventricular tachycardia may arise from the anterobasal left ventricle adjacent to the outflow tract.

Successful radiofrequency ablation of idiopathic left ventricular tachycardia at a site away from the tachycardia exit

OBJECTIVES

This study sought to assess the possibility of ablating verapamil-responsive idiopathic left ventricular tachycardia at a site distant from the tachycardia exit and thus to define the tachycardia circuit.

BACKGROUND

The nature of the reentry circuit in idiopathic left ventricular tachycardia is unclear. If the circuit is of considerable size, then it should be possible to ablate the tachycardia at a site distant from the exit site.

METHODS

Electrophysiologic studies and radiofrequency ablation were performed in 27 consecutive patients with verapamil-responsive idiopathic left ventricular tachycardia. In all 27 patients, the tachycardia exit site was defined as the site where the earliest Purkinje potential was recorded > or = 25 ms before the onset of the QRS complex during the tachycardia and where the pace map QRS complex resembled that during the tachycardia. A potential ablation site other than the exit site was then sought around the midseptum, proximal to the exit site. At such sites the tachycardia could be terminated transiently by pressure applied to the catheter tip, without induction of ventricular ectopic beats.

RESULTS

The potential ablation site, other than the tachycardia exit site, was identified in seven male patients (mean [+/-SD] age 31 +/- 12 years, range 13 to 52). Application of the radiofrequency current at this site resulted in termination of the tachycardia within 1 to 5 s (mean 2.9 +/- 1.6), and successful ablation of the tachycardia was achieved in all seven patients (success rate 100%, 95% exact confidence interval 0.5898 to 1). The mean distance between the ablation site and the tachycardia exit site was 3.1 +/- 0.7 cm (range 2.0 to 4.0). A presystolic Purkinje spike was recorded 14 +/- 5 ms (range 8 to 20) before the onset of the QRS complex during the tachycardia. During the follow-up period of 24 +/- 11 months (range 12 to 39), there was no recurrence of tachycardia in these seven patients.

CONCLUSIONS

Successful ablation of idiopathic left ventricular tachycardia can be achieved at sites away from the tachycardia exit site in some patients. This finding suggests that the reentry circuit is likely to be of considerable size, encompassing the middle, inferior and lower aspects of the left interventricular septum.

Mechanisms of idiopathic left ventricular tachycardia

Idiopathic left ventricular tachycardia (ILVT) differs from idiopathic right ventricular outflow tract (RVOT) tachycardia with respect to mechanism and pharmacologic sensitivity. ILVT can be categorized into three subgroups. The most prevalent form, verapamil-sensitive intrafascicular tachycardia, originates in the region of left posterior fascicle of the left bundle. This tachycardia is adenosine insensitive, demonstrates entrainment, and is thought to be due to reentry. The tachycardia is most often ablated in the region of the posteroinferior interventricular septum. A second type of ILVT is a form analogous to adenosine-sensitive RVOT tachycardia. This tachycardia appears to originate from deep within the interventricular septum and exits from the left side of the septum. This form of VT also responds to verapamil and is thought to be due to cAMP-mediated triggered activity. A third form of ILVT is propranolol sensitive. It is neither or initiated or terminated by programmed stimulation, does not terminate with verapamil, and is transiently suppressed by adenosine, responses consistent with an automatic mechanism. Recognition of the heterogeneity of ILVT and its unique characteristics should facilitate appropriate diagnosis and therapy in this group of patients.