Entrainment of idiopathic ventricular tachycardia of left ventricular origin with evidence for reentry with an area of slow conduction and effect of verapamil

Upper turnaround point in a reentry circuit of the idiopathic left posterior fascicular ventricular tachycardia

BACKGROUND

The anatomic extent of the reentry circuit in idiopathic left posterior fascicular ventricular tachycardia (LPF-VT) is yet to be fully elucidated. We hypothesized that entrainment mapping could be used to delineate the reentry circuit of an LPF-VT, especially including the upper turnaround point.

METHODS

Twenty-three consecutive LPF-VT patients (mean age, 29 ± 9 years, 18 males) were included. We performed overdrive pacing with entrainment attempts at the left bundle branch (LBB) and the left His bundle (HB) region.

RESULTS

Overdrive pacing from the LBB region showed concealed fusion in all 23 patients (post-pacing interval [PPI], 322.1 ± 64.3 ms; tachycardia cycle length [TCL], 319.0 ± 61.6 ms; PPI-TCL, 3.1 ± 4.6 ms) with a long stimulus-to-QRS interval (287.9 ± 58.0 ms, approximately 90% of the TCL). Pacing from the same LBB region at a slightly faster pacing rate showed manifest fusion with antidromic conduction to the LBB and minimal in-and-out time to the LBB potential (PPI-TCL, 21.3 ± 13.7 ms). Overdrive pacing from the left HB region showed manifest fusion with a long PPI-TCL (53.9 ± 22.5 ms).

CONCLUSIONS

Our pacing study results suggest that the upper turnaround point in a reentry circuit of the LPF-VT may extend to the proximal His-Purkinje conduction system near the LBB region but below the left HB region. The LPF may constitute the retrograde limb of the reentry circuit.

Fascicular Ventricular Tachycardias: Potential Role of the Septal Fascicle

Ventricular tachycardias involving the fascicular system are amongst the most challenging and intriguing arrhythmias for cardiac electrophysiologists. Although some of the more common forms have been recognized clinically for decades, other variants continue to be characterized. Moreover, considerable uncertainty persists to date with regards to the mechanisms underpinning these arrhythmias. In this state-of-the-art review, we discuss the seminal historical and contemporary observations that have collectively advanced our understanding of fascicular ventricular tachycardias. From this base, we canvas the basic and clinical evidence supporting a potential role for the septal fascicular network and propose a new schema hypothesizing involvement of this fascicle. Although we focus primarily on the most common left posterior fascicular ventricular tachycardia, our discussion and proposal have mechanistic and therapeutic implications for the spectrum of fascicular arrhythmias.

Diagnosis and Management of Complex Reentrant Arrhythmias Involving the His-Purkinje System

The His-Purkinje system is a network of bundles and fibres comprised of specialised cells that allow for coordinated, synchronous activation of the ventricles. Although the histology and physiology of the His-Purkinje system have been studied for more than a century, its role in ventricular arrhythmias has recently been discovered with the ongoing elucidation of the mechanisms leading to both benign and life-threatening arrhythmias. Studies of Purkinje-cell electrophysiology show multiple mechanisms responsible for ventricular arrhythmias, including enhanced automaticity, triggered activity and reentry. The variation in functional properties of Purkinje cells in different areas of the His-Purkinje system underlie the propensity for reentry within Purkinje fibres in structurally normal and abnormal hearts. Catheter ablation is an effective therapy in nearly all forms of reentrant arrhythmias involving Purkinje tissue. However, identifying those at risk of developing fascicular arrhythmias is not yet possible. Future research is needed to understand the precise molecular and functional changes resulting in these arrhythmias.

The change of cardiac axis deviation in catheter ablation of verapamil-sensitive idiopathic left ventricular tachycardia

BACKGROUND

The underlying mechanism of verapamil-sensitive idiopathic left ventricular tachycardia (ILVT) has been postulated to be reentrant activation in the Purkinje fiber network of the left posterior fascicle or the left anterior fascicle (LAF). However, changing of cardiac axis deviation in sinus rhythm (SR) or during ILVT after radiofrequency catheter ablation (RFCA) has been rarely analyzed.

METHODS

Of the 232 patients with sustained ILVT induced and surface electrocardiogram (ECG) in SR recorded before and after RFCA, the changes of ECG morphology in SR and during ILVT were analyzed.

RESULTS

The surface ECG in SR changed in 114 (49.1%) patients after RFCA. ILVT could still be induced in 27 (23.7%) patients. In comparison with the original ILVT, three forms of ECG morphology were observed. In eight patients, the ILVT morphology was unchanged. In the 13 patients with ILVT axis deviation conversion after ablation, the successful target was more proximal. In the six patients with ILVT morphology change but without axis deviation conversion after ablation, the successful ablation site was more distal. Among 15 patients with recurrent ILVT during follow-up, seven patients had previous axis deviation changes in SR after RFCA, the changes maintained in four patients and recovered in three patients.

CONCLUSIONS

The morphology changes on surface ECG in SR after RFCA would not be a necessary prerequisite or a good endpoint for ILVT ablation. To analyze ILVT morphology changes after ablation would help to further clarify an appropriate approach for catheter ablation of ILVT.

Mapping and Ablation of Fascicular Tachycardias (Reentrant and Nonreentrant)

Fascicular ventricular tachycardia (FVT) usually involves the left fascicular system; namely the left posterior fascicle, anterior fascicle, and rarely the upper septal fascicle. It may also involve the right Purkinje arborization. This tachycardia can be seen in normal heart or in the setting of structural heart diseases. Monomorphic FVT can be reentrant or nonreentrant and verapamil-sensitive left FVT is the second most common type of idiopathic ventricular tachycardia (VT) after right ventricular outflow tract VT. This article focuses on the practical approach for both reentrant and nonreentrant FVT, explaining the mechanism, electrocardiographic features, and electrophysiologic features of FVT.

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.

Evaluation of left ventricular false tendons in children with idiopathic left ventricular tachycardia

BACKGROUND

Left ventricular false tendons (FT) traverse the ventricular cavity and are thought to have some association with idiopathic left ventricular tachycardia (ILVT). However, reported prevalence of FT varies widely, making correlation difficult. Superior echocardiographic windows of pediatric patients may permit better analysis of FT in ILVT. Our study describes the relationship between FT and ILVT in young patients.

METHODS

Retrospective case-control study of 30 ILVT patients with 98 controls compared for FT. Diagnosis of ILVT was made by electrocardiogram and clinical history, and for 25 patients was further confirmed by electrophysiology study (EPS). Presence of FT was identified by one blinded observer and verified by a second blinded observer. Presence of FT was then compared between ILVT patients and controls using Fisher's exact test.

RESULTS

Presence of FT did not differ significantly between patients and controls (53% vs 43%, P  =  0.40). Twelve FT patients (19%) had multiple FTs detected, though the incidence of ILVT was no higher in the setting of multiple FTs. A total of 25 patients with ILVT underwent EPS for intended ablation therapy, with ultimate success in 22/25 (88%) after one or more ablation sessions. Of the 25 EPS patients, FTs were present in 11, but precise correlation between successful ablation location and FT location was not possible since intraprocedural echocardiography was not performed in this patient group.

CONCLUSIONS

Presence of FTs did not differ between ILVT patients and controls. While FTs are not absolutely required for ILVT, they may still play a role in some cases.

Belhassen anterior fascicular ventricular tachycardia: a case in a black African

Belhassen ventricular tachycardia can be characterized by a complete right branch block and a right axial deviation. This type, although rare, must be recognized to properly treat the patient, as verapamil treatment is effective.

Change in QRS morphology as a marker of spontaneous elimination in verapamil-sensitive idiopathic left ventricular tachycardia

BACKGROUND

Verapamil-sensitive idiopathic left ventricular tachycardia (verapamil-ILVT) is thought to be due to a reentry within the LV fascicular system. Radiofrequency catheter ablation (RFCA) is effective for elimination of the VT; however, a long-term prognosis of patients with verapamil-ILVT is still unclear.

METHODS AND RESULTS

Eighty consecutive verapamil-ILVT patients (62 men, 31 ± 12 years of age, LVEF: 65 ± 4%) were enrolled. Seventy-six (95%) cases of VT involved right bundle branch block and left axis deviation. We retrospectively analyzed changes in the QRS duration (ΔQRS-d) and QRS axis (ΔQRS-axis) during follow-up and compared them with recurrence of VT. During a mean follow-up period of 10 years (2-32 years), no sudden death or heart failure occurred. Fifty-one (64%) patients underwent RFCA, and 46 (90%) of them had no VT without any medication after RFCA. The ΔQRS-d (16 ± 2 vs. 8 ± 1 ms, P = 0.24) and ΔQRS-axis (20 ± 4 vs. 4 ± 3 degrees, P = 0.23) were not different in patients with no VT (VT[-]) and those with recurrence of VT (VT[+]). However, in the remaining 29 patients without RFCA, VT was spontaneously eliminated in 16 patients. The ΔQRS-d (30 ± 6 vs. 6 ± 1 ms, P = 0.002) and ΔQRS-axis (23 ± 4 vs. 5 ± 2 degrees, P = 0.001) were significantly larger in VT(-) patients compared to VT(+) patients during follow-up.

CONCLUSIONS

Some verapamil-ILVT patients who show QRS morphology changes over the follow-up period may become free from VT without any invasive or pharmacological treatments, suggesting that further altered LV fascicular conduction might eliminate the reentry of verapamil-ILVT.

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.

Spectrum of Fascicular Arrhythmias

Fascicular arrhythmias encompass a wide spectrum of ventricular arrhythmias that depend on the specialized conduction system of the right and left ventricles. These arrhythmias include premature ventricular complexes, monomorphic ventricular tachycardia, polymorphic ventricular tachycardia, and ventricular fibrillation. These arrhythmias may be organized by mechanism, including intrafascicular reentry, interfascicular reentry, and focal. Mapping and ablation of the fascicular system can result in high cure rates of debilitating and potentially life-threatening arrhythmias. When approaching these arrhythmias, careful consideration of the structure of the His Purkinje system as well as their electrophysiologic properties may help guide even the most complex of 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.

Electroanatomical characteristics of idiopathic left ventricular tachycardia and optimal ablation target during sinus rhythm: significance of preferential conduction through Purkinje fibers

PURPOSE

We hypothesized that Purkinje potential and their preferential conduction to the left ventricle (LV) posteroseptum during sinus rhythm (SR) are part of reentrant circuits of idiopathic left ventricular tachycardia (ILVT) and reentry anchors to papillary muscle.

MATERIALS AND METHODS

In 14 patients with ILVT (11 men, mean age 31.5±11.1 years), we compared Purkinje potential and preferential conduction during SR with VT by non-contact mapping (NCM). If clear Purkinje potential(SR) was observed in the LV posteroseptum and the earliest activation site (EA) of preferential conduction at SR (EA(SR)) was well matched with that of VT (EA(VT)), EA(SR) was targeted for radiofrequency catheter ablation (RFCA). Also, the anatomical locations of successful ablation sites were evaluated by echocardiography in five additional patients.

RESULTS

1) All induced VTs exhibited clear Purkinje potential(VT) and preferential conduction in the LV posteroseptum. The Purkinje potential(VT) and EA(VT) was within 5.8±8.2 mm of EA(SR). However, the breakout sites of VT were separated by 30.2±12.6 mm from EA(VT) to the apical side. 2) Purkinje potential(SR) demonstrated a reversed polarity to Purkinje potential(VT), and the interval of Purkinje potential(SR)-QRS was longer than the interval of Purkinje potential(VT)-QRS (p<0.02) 3) RFCA targeting EA(SR) eliminated VT in all patients without recurrence within 23.3±7.5 months, and the successful ablation site was discovered at the base of papillary muscle in the five additional (100%) patients.

CONCLUSION

NCM-guided localization of EA(SR) with Purkinje potential(SR) matches well with EA(VT) with Purkinje potential(VT) and provides an effective target for RFCA, potentially at the base of papillary muscle in patients with ILVT.

The characteristics of verapamil-sensitive idiopathic left ventricular tachycardia combined with a left accessory pathway and the effect of radiofrequency catheter ablation

AIMS

Verapamil-sensitive idiopathic left ventricular tachycardia (ILVT) combined with a left accessory pathway (AP) is a relatively rare condition. This study examines the characteristics of patients with this condition and the effect of radiofrequency catheter ablation (RFCA).

METHODS AND RESULTS

Catheter ablation was performed on 140 ILVT patients at a single centre from January 2004 to December 2009. A concealed left AP was found in seven patients (5%), all of whom were male, with an average age of 21 ± 9 years. Sustained ILVT and orthodromic atrioventricular reentrant tachycardia (AVRT) were induced in all seven patients. Retrograde activation through a bystander AP occurred concomitantly with ILVT, with an average tachycardia length of 346 ± 29 ms (range 310-400 ms). The location of the APs in four patients was left posterior, two of which showed a slow and decremental property, while in three it was left lateral. Ablation via a retrograde transaortic approach was performed in the seven patients. The left AP was ablated first in six patients, but ILVT was no longer induced in one and became non-sustained in another. In the seventh patient, ILVT was ablated first and this proved successful.

CONCLUSIONS

Among patients with IVLT, 5% had a concomitant left AP, most of who were young men. The location of the left AP was mainly posterior and lateral, with 30% showing a slow and decremental property. Idiopathic left ventricular tachycardia and AP should be ablated simultaneously.

Ablation of idiopathic ventricular tachycardia

Idiopathic ventricular arrhythmias occur in patients without structural heart disease. They can arise from a variety of specific areas within both ventricles and in the supravalvular regions of the great arteries. Two main groups need to be differentiated: arrhythmias from the outflow tract (OT) region and idiopathic left ventricular, so-called fascicular, tachycardias (ILVTs). OT tachycardia typically originates in the right ventricular OT, but may also occur in the left ventricular OT, particularly in the sinuses of Valsalva or the anterior epicardium or the great cardiac vein. Activation mapping or pace mapping for the OT regions and mapping of diastolic potentials in ILVTs are the mapping techniques that are typically used. The ablation of idiopathic ventricular arrhythmias is highly successful, associated with only rare complications. Newly recognized entities of idiopathic ventricular tachycardias are those originating in the papillary muscles and in the atrioventricular annular regions.

Pilsicainide-Induced Verapamil Sensitive Idiopathic Left Ventricular Tachycardia

A 20-year-old man was admitted to our hospital for treatment of verapamil sensitive idiopathic left ventricular tachycardia (ILVT). During the electrophysiologic study (EPS), no sustained ventricular tachycardia (VT) could be induced both at baseline and after infusion of isoproterenol. However, sustained clinical VT could be easily induced with single ventricular extrastimulation following intravenous administration of pilsicainide, a class Ic sodium channel blocker. The arrhythmia was ablated with radiofrequency catheter ablation.

Is the Fascicle of Left Bundle Branch Involved in the Reentrant Circuit of Verapamil-Sensitive Idiopathic Left Ventricular Tachycardia?

The exact reentrant circuit of the verapamil-sensitive idiopathic left VT with a RBBB configuration remains unclear. Furthermore, if the fascicle of left bundle branch is involved in the reentrant circuit has not been well studied. Forty-nine patients with verapamil-sensitive idiopathic left VT underwent electrophysiological study and RF catheter ablation. Group I included 11 patients (10 men, 1 woman; mean age 25 +/- 8 years) with left anterior fascicular block (4 patients), or left posterior fascicular block (7 patients) during sinus rhythm. Group II included 38 patients (29 men, 9 women; mean age 35 +/- 16 years) without fascicular block during sinus rhythm. Duration of QRS complex during sinus rhythm before RF catheter ablation in group I patients was significant longer than that of group II patients (104 +/- 12 vs 95 +/- 11 ms, respectively, P=0.02). Duration of QRS complex during VT was similar between group I and group II patients (141 +/- 13 vs 140 +/- 14 ms, respectively, P=0.78). Transitional zones of QRS complexes in the precordial leads during VT were similar between group I and group II patients. After ablation, the QRS duration did not prolong in group I or group II patients (104 +/- 11 vs 95 +/- 10 ms, P=0.02); fascicular block did not occur in group II patients. Duration and transitional zone of QRS complex during VT were similar between the two groups, and new fascicular block did not occur after ablation. These findings suggest the fascicle of left bundle branch may be not involved in the antegrade limb of reentry circuit in idiopathic left VT.

Ventricular tachycardia in structurally normal hearts

This review focuses on four distinct syndromes of ventricular tachycardia that occur in the structurally normal heart. Recent advances in the fields of molecular biology and genetics, along with intracardiac mapping techniques, have led to a greater understanding of the underlying mechanisms of and therapeutic options for these syndromes. The cyclic AMP-mediated triggered activity tachycardias, including exercise-induced right ventricular outflow track tachycardia and repetitive monomorphic ventricular tachycardia, are the most common of these syndromes. Idiopathic left ventricular tachycardia, for which there is significant evidence for re-entry within the Purkinje network, is largely curable with catheter ablation. The long QT syndrome comprises a heterogeneous group of ion channel defects leading to prolongation of myocyte repolarization and Torsade de Pointes ventricular tachycardia. Brugada syndrome, a familial disorder of transmembrane ion transport, is felt to be the result of a group of sodium channel defects leading to characteristic electrocardiographic abnormalities, and syncope and sudden death. Primary focus is given to recent advances in our understanding of the underlying mechanism and current therapeutic approaches.

Electroanatomic substrate of idiopathic left ventricular tachycardia: unidirectional block and macroreentry within the purkinje network

BACKGROUND

An abnormal potential (retroPP) from the left posterior Purkinje network has been demonstrated during sinus rhythm (SR) in some patients with idiopathic left ventricular tachycardia (ILVT). We hypothesized that this potential can specifically be identified and be a critical substrate for ILVT.

METHODS AND RESULTS

In 9 patients with ILVT and 6 control patients who underwent mapping of the left ventricle during SR using 3-dimensional electroanatomic mapping, an area with retroPP was found within the posterior Purkinje fiber network only in patients with ILVT. The earliest and latest retroPP was 185.4+/-57.4 and 465.2+/-37.3 ms after Purkinje potential; in the other patient with ILVT, an entire left ventricle mapping demonstrated a slow conduction area and passive retrograde activation along the posterior fascicle during ILVT. ILVT was noninducible in 3 patients after SR mapping. Diastolic potentials critical for ILVT during ILVT coincided with the earliest retroPP during SR in 7 patients. Mechanical termination of ILVT occurred in 5 patients. A single radiofrequency pulse was applied at the site with mechanical translation in 5 patients and the site with diastolic potential in 2 patients, and 3 radiofrequency pulses were delivered to the site with the earliest retroPP in the other 3 patients without inducible ILVT after SR mapping. No ILVT was inducible during control stimulation, and none recurred during follow-up of 9.1+/-5.1 months.

CONCLUSION

In patients with ILVT, abnormal retroPP within the posterior Purkinje fiber network is a common finding. The earliest retroPP critical for ILVT substrate can be used for guiding successful ablation.

Clinical characteristics and catheter ablation of left ventricular outflow tract tachycardia

Left ventricular outflow tract (LVOT) tachycardia is an uncommon form of idiopathic ventricular tachycardia (IVT). The underlying mechanism of this arrhythmia appears to be cyclic AMP-medicated triggered activity. The tachycardia occurs in the absence of structural heart disease and is generally benign, presenting commonly as palpitations and presyncope. It can manifest either a right or left bundle branch block morphology with an inferior axis. Subtle variations in the QRS morphology in leads I, V1, and V2 can help in localizing the anatomic site of origin (SOO). The arrhythmia is typically responsive to a variety of pharmacologic agents (beta-blockers, calcium channel blockers, Class I and II agents). Radiofrequency catheter ablation of LVOT tachycardia SOO as determined by pace mapping is quite efficacious (success rates of 90%). Magnetic electroanatomic mapping augments this by permitting three-dimensional catheter mapping and reproducible localization of the SOO. Catheter ablation should be considered relatively early in patients who experience severe symptoms with their arrhythmia and have failed, or are reluctant to take medications for the disorder.

Catheter ablation of idiopathic left ventricular tachycardia with multiple breakthrough sites guided by an electroanatomical mapping system

Idiopathic ventricular tachycardia (VT) has been considered to be amenable to radiofrequency catheter ablation guided by Purkinje potentials. However, there appear to be various types of reentrant circuits associated with this VT deduced from the results of the successful radiofrequency catheter ablation cases. We describe in this report a patient with idiopathic left ventricular tachycardia which was electrically inducible and verapamil sensitive. Multiple earliest ventricular activation sites during tachycardia were detected with electroanatomical mapping using the CARTO system. Multiple applications at these sites failed to eliminate the VT. The earliest Purkinje potential was recorded at least 1.5 cm away from the earliest ventricular activation sites, and the radiofrequency current application at this site resulted in the complete abolition of this VT. The reentrant circuit of this tachycardia seemed to have multiple breakthrough sites to the ventricular myocardium, which were distant from the requisite part of the reentrant circuit of this VT involving the Purkinje fiber network conduction system.

Effects of verapamil and lidocaine on two components of the re-entry circuit of verapamil-senstitive idiopathic left ventricular tachycardia

OBJECTIVES

We characterized pharmacologically the slow conduction zone of verapamil-sensitive idiopathic left ventricular tachycardia (ILVT) with regard to the late diastolic potential (LDP).

BACKGROUND

We showed that the slow conduction zone of ILVT could be divided into two components by LDP; that is, the distal component with a tachycardia-dependent conduction delay property and the proximal one without it.

METHODS

Electrophysiologic studies were performed in eight consecutive patients. The LDP was recorded during left ventricular (LV) mapping during ILVT. Entrainment was performed from the right ventricular outflow tract while recording LDP. The effects of lidocaine (1 mg/kg body weight) and verapamil (0.5 or 1.0 mg) were examined during entrainment.

RESULTS

The LDPs preceding the Purkinje potential (PP) were serially recorded from the upper third to the middle of the LV septum along the narrow longitudinal line. The ventricular tachycardia (VT) cycle length increased after lidocaine (p < 0.05), and further after verapamil (p < 0.05). The increments in the VT cycle length after administration of the drugs strongly correlated with those in LDP-PP (r > 0.9 for both drugs). The interval from the ventricular potential to LDP was unchanged after administration of the drugs. In one patient, verapamil terminated VT by local conduction block between LDP and PP. The LDP-PP measured during entrainment increased after lidocaine, and further after verapamil, whereas the interval from the stimulus to LDP remained unchanged.

CONCLUSIONS

The component distal to LDP is mainly calcium channel-dependent and partly depressed sodium channel-dependent. The proximal component is considered to be sodium channel-dependent (normal).

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.

Management of ventricular tachycardia in patients with clinically normal hearts

The majority of patients who present with ventricular tachycardia have underlying structural heart disease. However, there has been increasing appreciation of the existence of multiple forms of idiopathic ventricular tachycardia with distinct features and unique mechanisms. The most common form of idiopathic ventricular tachycardia originates from the right ventricular outflow tract, is characterized by sensitivity to adenosine, and appears to be due to cyclic AMP-mediated triggered activity. Other forms of idiopathic ventricular tachycardia include intrafascicular left ventricular tachycardia, due to reentry, which is sensitive to verapamil, and automatic, propranolol-sensitive ventricular tachycardia.

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.

Ablation of noninducible idiopathic left ventricular tachycardia using a noncontact map acquired from a premature complex with tachycardia morphology

We describe use of a novel noncontact system to permit mapping in a noninducible patient from a single premature ventricular complex with tachycardia morphology, thus guiding successful ablation after two previously failed conventional efforts. The instantaneous global electroanatomic map demonstrated fascicular macroreentry. Subsequent to ablation at an inferolateral site, there has been no clinical recurrence despite difficult arrhythmia control preprocedure. This case demonstrated that noncontact mapping can be used to create a potential map to guide successful ablation from a single premature ventricular complex in a patient with idiopathic left ventricular tachycardia that became noninducible at electrophysiological study.

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.

Significance of late diastolic potential preceding Purkinje potential in verapamil-sensitive idiopathic left ventricular tachycardia

BACKGROUND

Verapamil-sensitive idiopathic left ventricular tachycardia (VT) is due to reentry with an excitable gap. A late diastolic potential (LDP) is recorded during endocardial mapping of this VT, but its relation to the reentry circuit and significance in radiofrequency (RF) ablation remain to be elucidated.

METHODS AND RESULTS

Sixteen consecutive patients with this specific VT were studied (12 men and 4 women; mean age, 32 years). In all patients, sustained VT was induced and during left ventricular endocardial mapping, LDP preceding Purkinje potential (PP) was recorded at the basal (11 patients), middle (3 patients), or apical septum (2 patients). The area with LDP recording was confined to a small region (0.5 to 1.0 cm2) in each patient and was included in the area where PP was recorded (2 to 3 cm2). The relative activation times of LDP, PP, and local ventricular potential (V) at the LDP recording site to the onset of QRS complex were -50.4+/-18.9, -15.2+/-9.6, and 3.0+/-13.3 ms, respectively. The earliest ventricular activation site during VT was identified at the posteroapical septum and was more apical in the septum than the region with LDP in every patient. In 9 patients, VT entrainment was done by pacing from the right ventricular outflow tract while recording LDP. During entrainment, LDP was orthodromically captured, and as the pacing rate was increased, the LDP-to-PP interval was prolonged, whereas stimulus-to-LDP and PP-to-V interval were constant. In 3 patients, the pressure applied to the catheter tip at the LDP region resulted in conduction block between LDP and PP and in VT termination. RF energy application at the LDP recording site successfully eliminated VT.

CONCLUSIONS

LDP was suggested to represent the excitation at the entrance to the specialized area with a conduction delay in response to the increase in the rate within the critical slow conduction zone participating in the reentry circuit of this VT. LDP can be a useful marker for successful RF ablation for this VT.

Idiopathic ventricular tachycardia

Most ventricular tachycardias encountered in clinical practice occur in patients who have structural heart disease. Idiopathic ventricular tachycardia refers to those arrhythmias that occur in patients without structural heart disease, metabolic/electrolyte abnormalities, or the long QT syndrome. Three commonly recognized forms of idiopathic ventricular tachycardia include: (a) ventricular tachycardia associated with mitral valve prolapse, (b) ventricular tachycardia originating from the right ventricular outflow tract, and (c) ventricular tachycardia originating from the left ventricle. Recently, a fourth type of idiopathic ventricular tachycardia, termed the Brugada syndrome, has been identified as responsible for some cases of cardiac arrest in persons without apparent structural heart disease. Each form of ventricular tachycardia may be considered a discrete syndrome based on its electrocardiographic characteristics, mechanisms, responses to pharmacologic intervention, and prognosis (good in most cases). Ventricular tachycardias range from the common to the exotic, but all represent syndromes with which the internist and general cardiologist should be familiar.

Mid-diastolic potential is related to the reentrant circuit in a patient with verapamil-sensitive idiopathic left ventricular tachycardia

We report a case of verapamil-sensitive idiopathic ventricular tachycardia in which a mid-diastolic potential (MDP) 45 msec preceding the Purkinje potential (P potential) was recorded. Pacing during the tachycardia caused concealed entrainment, and the stimulus-QRS interval was equal to the P potential-QRS interval. The interval between the last pacing stimulus and the next P potential (postpacing interval) was longer than the ventricular tachycardia cycle length, but the MDP was orthodromically activated. These findings suggest that the MDP was on the reentrant circuit and the P potential was not on the reentrant circuit, but a bystander.

Idiopathic left ventricular tachycardia with block between purkinje potential and ventricular myocardium

We performed radiofrequency current catheter ablation in a patient with idiopathic LV. While mapping the inferoapical LV septum during tachycardia, spontaneous termination of tachycardia was observed with block between Purkinje (P) potential and ventricular electrogram (P-V block). The cycle length of the tachycardia was associated with prolongation of P-P interval and P-V interval. P potential recording at this site was earliest and at very low amplitude during tachycardia. The radiofrequency current at this site was successful. These findings indicated that Purkinje fiber was a critical part of the tachycardia circuit. Ablation was successful at a site where both an earliest and low amplitude P potential was recorded during tachycardia, and where P-V block that was induced by catheter manipulation was observed during tachycardia.