Chapter 75 Clinical Features and Treatment of Fascicular Ventricular Tachycardia

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1 Chapter 75 Clinical Features and Treatment of Fascicular Ventricular Tachycardia RAMPRAKASH BALASUNDARAM INTRODUCTION Fascicular ventricular tachycardia (VT) was first reported by Zipes et al. in ; they described a VT of right bundle branch block (RBBB) morphology with left-axis deviation in structurally normal heart with a relatively narrow QRS width. Later, Belhassen et al. 2 in 1981, observed that the VT was sensitive to intravenous administration of verapamil which significantly reduced the rate and termination of this VT and prevented its re-induction during electrophysiological study. CLINICAL FEATURES Presently, fascicular VT is well characterized as exerciserelated VT, occurring in paroxysms, in the age group of years with male predominance (60% 80%). It occurs in patients with structurally normal hearts. Tachycardiomyopathy may occur rarely in case of incessant arrhythmia 3. Calcium channel blockers are very effective in termination of the tachycardia, whereas catheter ablation is very effective in long-term management with cure of this tachycardia. The mechanism, electrophysiologic properties and various method of catheter ablation of this tachycardia will be discussed in this chapter. ELECTROCARDIOGRAPHIC FEATURES The baseline electrocardiogram (ECG) is normal; however, T-wave inversion immediately after tachycardia termination may be seen due to cardiac memory. The ECG shows a relatively narrow QRS complex of QRS duration less than ms with sharp initial deflection (RS interval of ms). Sometimes, this mistakenly leads to a diagnosis of aberrant supraventricular tachycardia. Depending on the site of origin, three types of fascicular VT are described 4 : 1. Posterior fascicular VT: It is characterized by RBBB morphology and left-axis deviation. The tachycardia circuit is located in the inferoposterior septum. It is the commonest subtype and accounts for the 90% 95% of cases 5 ( Fig ). 2. Anterior fascicular VT: It is characterized by RBBB morphology and right-axis deviation. The tachycardia circuit is located in the anterolateral wall of the left ventricle (LV). 3. Upper septal fascicular VT: It is characterized by a QRS duration of less than 120 ms with RBBB or normal QRS morphology. This type is the rarest. CLINICAL DIFFERENTIAL DIAGNOSIS Due to its occurrence in young patients without structural heart disease, sensitivity to verapamil and relatively narrow QRS morphology fascicular VT can be confused with paroxysmal supraventricular tachycardia conducted with aberrancy. The presence of ventriculoatrial dissociation in the ECG or during the electrophysiological study may clarify the diagnosis. Fascicular VT requires exclusion of structural heart disease. It is therefore recommended to perform echocardiography and coronary angiography or cardiac MRI to exclude ischaemic and infiltrative aetiologies which can have narrow QRS VT related to intramyocardial re-entry close to the conduction system with early invasion of the His Purkinje system. The presence of RS interval less than 80 ms in all the precordial leads favours the diagnosis of idiopathic fascicular VT as opposed to that from an organic ethology

2 632 SECTION VIII Cardiac Electrophysiology Abnormal ECG I avr V1 V4 II avi V2 V5 III avf V3 V6 Figure lead ECG in a patient with posterior fascicular VT showing right bundle branch block morphology with left-axis deviation. The arrows show P waves which are dissociated from the ventricular complexes. LONG-TERM MANAGEMENT Verapamil is very effective in acute termination of the tachycardia but not as effective in long-term management to prevent recurrence. Long-term management with beta blockers or verapamil may be tried in patients with mild symptoms, whereas catheter ablation is recommended in patients with frequent recurrence on drugs and when pharmacologic treatment is not effective or poorly tolerated7,8. The results of catheter ablation are quite encouraging with success rates of 85% and 95%, especially in those with posterior fascicular VT. Recurrence rates are low, with reported recurrence varying between 5% and 12.5%. Complications during ablation are rare. The most common complication is the development of atrioventricular block and left bundle branch block. ANATOMIC CORRELATION: ROLE OF FALSE TENDON Anatomically, the substrate for this tachycardia might involve a false tendon or fibromuscular band extending from the posteroinferior LV to the basal septum. Physiologically, these structures are found to be electrically active with conduction properties of Purkinje fibres. The electrical properties of these fibres in the false tendon may vary with the change in tension and length of the false tendon9 11. ELECTROPHYSIOLOGICAL CHARACTERISTICS Fascicular tachycardia is a unique VT because it can be induced by programmed stimulation from both atrium and ventricle. Antiarrhythmic drugs need to be stopped for a period of three half-lives before the commencement of study. Isoprenaline infusion may be needed for induction of tachycardia in some cases. Sometimes, the tachyarrhythmia may be noninducible in a significant number of patients. Gopi et al. have proposed a step wise approach to the induction of this tachycardia in such cases12. About 10% 25% of patients with idiopathic fascicular tachycardia have an associated supraventricular tachycardia inducible during programmed stimulation13.

3 Chapter 75 Clinical Features and Treatment of Fascicular Ventricular Tachycardia 633 TACHYCARDIA CIRCUIT The tachycardia circuit is localized to the posterior septal area of the LV and thought to involve distal left bundle, posterior fascicle, Purkinje arborization in that area, local myocardium and specialized structure like the false tendon. The precise circuit and the participation of the above anatomic structures in the re-entrant circuits is a matter of debate. Intracardiac recording during tachycardia shows two distinct potentials before the ventricular electrogram, namely the Purkinje potential (PP or P2) and pre-purkinje potential (Pre-PP or P1) ( Fig ) 14, 15. The Purkinje potential (PP or P2) is due to the activation of the left posterior fascicle or the Purkinje fibre near the left posterior fascicle. The relative activation time of PP to the onset of QRS complex vary between 5 and 25 ms. It is characterized by a brief, sharp, high-frequency potential preceding the onset of QRS during tachycardia 16 ( Figs 75-2 and 75-3 ). The pre-purkinje potential (Pre-PP or P1) is due to excitation at the entrance to the specialized verapamilsensitive zone in the ventricular septum, which has decremental properties. The pre-pp is a dull, lowfrequency potential preceding the PP during tachycardia. During tachycardia, this area is captured antidromically and the pre-pp precedes the PP. During sinus rhythm, this area is captured orthodromically and the pre-pp follows the ventricular complex 17 ( Figs 75-2 and 75-3 ). With the background of these anatomic and electrophysiologic observations, different circuits for re-entry have been proposed. In the first speculation, the antegrade activation occurs from the basal to the apical aspect of the left ventricular septum through the verapamil-sensitive zone which might be a false tendon and gives rise to the pre-pp. As a result, pre-pp occurs earliest in the basal septum and latest activation in the apical aspect at the lower turnaround region of the tachycardia circuit. Here, the impulse captures the Purkinje fibres with propagation of the retrograde limb of the tachycardia in the opposite direction from apical to basal septum. This gives rise to the PP with earliest activation in apical septum and latest activation in basal septum. Therefore, the presumed lower turnaround point for this tachycardia is identified where there is closest pre-pp and PP. From the lower turnaround, antegrade activation occurs down the posterior fascicle fibres to break through in the posterior septal myocardium. The re-entrant circuit of fascicular tachycardia is completed by a zone of slow conduction between PP and pre-pp areas in the basal interventricular septum near the main left bundle where there is maximum separation of pre-pp and PP ( Fig ). Itsuro et al. postulated that posterior fascicle as a bystander and the myocardium in the vicinity of the posterior septum are thought to complete the re-entrant circuit s retrograde limb. Qiang et al. further refined this hypothesis and proposed that the antegrade limb of the circuit proceeds through the verapamil-sensitive slow-conducting zone from Figure Surface and intracardiac recording during sinus rhythm with the ablation catheter in the left ventricle against the apical septum The Purkinje potential (PP: short arrow) is sharp, high frequency potential, preceding the onset of QRS. The pre-purkinje potential (pre-pp: long arrow) is a comparatively dull, lower frequency potential, following the ventricular complex.

4 634 SECTION VIII Cardiac Electrophysiology NCS LBB Area of slow conduction/myocardium Anterior fascicle Earliest pre-pp Posterior fascicle Pre-PP PP V Earliest PP Myocardial exit point Figure Diagrammatic representation of the tachycardia circuit in fascicular VT. The antegrade limb of the circuit proceeds through the verapamil-sensitive zone (curved line) from basal to apical left ventricular septum giving rise to the pre-pp as seen in the accompanying electrogram. The lower turnaround site of the re-entrant circuit occurs in the lower third of the septum with the capture of the fast conduction Purkinje fibres along the posterior fascicle. From here, antegrade activation occurs down the septum to break through septal myocardium below, and retrograde activation occurs over the posterior fascicle from apical to basal septum forming the retrograde limb of the tachycardia. The re-entrant circuit is completed by a zone of slow conduction at the upper turnaround point of the circuit located close to the main trunk of the left bundle branch. ( Source: Ramprakash, B., Jaishankar, S., Rao, H. B., & Narasimhan, C. (2008). Catheter ablation of fascicular ventricular tachycardia. Indian Pacing and Electrophysiology Journal, 8(3), ) basal septal myocardium to proximal P1 fibres which could have an anatomical correlate like a false tendon, which in turn connects with the left posterior fascicle and proceeds antegradely into Purkinje fibres locally giving rise to P1 or PP and exits into the myocardium. The retrograde limb of the tachycardia is posterior septal myocardium with the impulse propagating apical to basal into the slow-conduction zone which connects to the P1 area, thus completing the re-entrant circuit. The part of the left posterior fascicle before the connection of P1 fibres acts as a bystander and conducts the impulse retrogradely 18, 19 ( Fig ). ELECTROPHYSIOLOGICAL DIFFERENTIAL DIAGNOSIS Fascicular VT is frequently misdiagnosed as supraventricular tachycardia with aberrancy on account robust VA conduction which may result in 1:1 VA association. During EP study, induction and entrainment is possible by atrial stimulation leading to mistaken diagnosis of SVT. However, VA dissociation can occur spontaneously or by rapid atrial pacing ( Fig ). Rarely, interfascicular VT, a type of bundle branch re-entrant VT may mimic fascicular VT, as it has a typical RBBB morphology and left or right-axis deviation. However, interfascicular VT is seen in patients with anterior myocardial infarction and left anterior or posterior hemifascicular block. During EP study, the ventricular depolarization is preceded by His bundle depolarization in interfascicular VT which is not seen in fascicular VT 20. Idiopathic mitral annulus VT mimics anterior fascicular VT, as both have RBBB morphology with right-axis deviation of the frontal QRS vector. Tada et al. 21 described presystolic potential preceding QRS complex during arrhythmia in one-third of their patients with mitral annulus VT.

5 Chapter 75 Clinical Features and Treatment of Fascicular Ventricular Tachycardia 635 AVN AVN AVN His LAF His LAF His LAF RB RB RB LPF P1 LPF P1 LPF P1 A B C Figure Diagrammatic representation of the tachycardia circuit in fascicular VT. The antegrade limb of the circuit proceeds through the verapamil-sensitive slow-conducting zone from basal septal myocardium to proximal P1 or pre-pp which could have an anatomical correlate like a false tendon, which in turn connects with the left posterior fascicle at various distance between the His bundle and Purkinje arborization (A, B and C) and proceeds antegradely into Purkinje fibres locally giving rise to P2 or PP and exits into the myocardium. The retrograde limb of the tachycardia is posterior septal myocardium with the impulse propagating apical to basal into the slow-conduction zone which connects to the P1 area, thus completing the re-entrant circuit. The part of the left posterior fascicle before the connection of P1 fibres acts as a bystander and conducts the impulse retrogradely. (From: Circulation: Arrhythmia and Electrophysiology, (2016), 9, e DOI: /CIRCEP ) MEDICAL MANAGEMENT ACUTE MANAGEMENT In haemodynamically unstable patients, electrical cardioversion is recommended. In stable patients, first-line treatment is verapamil for acute conversion to sinus rhythm. The risk of haemodynamic collapse in cases of wrong diagnosis makes it advisable to only administrate verapamil in stable patients with an established diagnosis. Fascicular VT does not respond to vagal manoeuvres, adenosine or beta blockers. RADIOFREQUENCY ABLATION In 1987, Fontaine et al. 22 first reported successful ablation of fascicular VT by application of a high-energy DC shock in the inferoseptal area. Subsequently, Klein et a1. 23 reported radiofrequency ablation in one patient with idiopathic left VT. Thereafter, various methods of mapping and ablation have been described during VT and during sinus rhythm. ABLATION DURING TACHYCARDIA Mapping and ablation is performed during tachycardia as definition of electrophysiological targets is clear and termination of tachycardia during ablation can be a useful end point. Various investigators have used different targets for ablation during tachycardia. Ablation at Purkinje Potential Site The anatomical landmark for localizing the PP is an area over 2 3 cm 2 in the posterior half of the left ventricular septum, one-quarter to one-third of the distance from apex to base. Here, mapping during tachycardia leads to identification of the PP preceding the onset of QRS. The site recording the earliest PP, where it fuses with the latest pre-pp is considered to be the lower turnaround point of the re-entrant circuit. From the lower turnaround point, antegrade activation occurs down the posterior fascicle fibres to break through in the posterior septal myocardium where the earliest ventricular activation is seen. This is not an ideal target for ablation and therefore activation mapping is not useful in this tachycardia. The interval between PP at the site of successful ablation and the onset of the QRS complex during VT was 18 6 ms (6 3% of VT cycle length). During tachycardia, entrainment can be performed from the target site. Entrainment with concealed fusion, postpacing interval minus VT cycle length difference within 30 ms and a stimulus to QRS interval same as PP to QRS interval during VT predicts success during ablation. Termination of the tachycardia and noninduciblity after ablation were considered as valid end points However, a recurrence of 10% was noted in this approach. Vikas et al. targeted the same area but described an additional end point of dissociation

6 636 SECTION VIII Cardiac Electrophysiology Figure Surface ECG (white) intracardia ventricular recording in RV (blue and yellow) and CS recording (green) during induction of tachycardia by ventricular burst pacing. Top panel shows 1:1 VA association with retrograde conduction through AV node suggesting a diagnosis of AVNRT with aberrancy. However, in the bottom panel, the tachycardia continues with the same rate but VA conduction weakens and shows Wenckebach VA block, thus making the diagnosis of fascicular VT clear. of the fascicular Purkinje potential from the myocardial potential to achieve a local distal fascicular myocardial conduction block an additional end point with no observed recurrence during follow-up24. Ablation at Pre-Purkinje Potential Site It is a less frequently used target. The pre-pp is recorded only in 75% of the patients during VT. Performance of ablation at this site carries the risk of causing atrioventricular block or left bundle branch block. However, fewer applications were needed in those targeted to pre-pp recording site than those targeted to PP site ( vs , P.05)14,15,19,25. ABLATION DURING SINUS RHYTHM Not infrequently, the tachycardia may be bumped during entry or manipulation of the catheter in LV and the tachycardia may be rendered noninducible. Sometimes, the tachycardia may be ill-sustained during the study. In these situations, mapping and ablation during tachycardia is not possible and various methods of mapping

7 Chapter 75 Clinical Features and Treatment of Fascicular Ventricular Tachycardia 637 and ablation during sinus rhythm have been described. Pace Mapping Conceptually, pace mapping is useful in mapping focal tachycardias, whereas it is not preferred in reentrant tachycardias and results of ablation are less favourable 26, 27. In patients with fascicular VT, pace mapping may lead to capture of adjacent myocardium and pathways within the Purkinje network that are not included in the tachycardia circuit. In a study by Nogami et al. 15, pacing from successful ablation site did not show a perfect match with VT morphology in the surface ECG ( of the 12 ECG leads only). Electroanatomic Mapping Electroanatomic mapping system is used for construction of geometry of the LV and the conduction system in the LV during sinus rhythm are superimposed on it. The electrophysiological targets are identified on this map and lesions are created to interrupt the circuit of fascicular VT. Electroanatomical mapping can be used for anatomical localization and tagging areas having pre-pp, and ablation during sinus rhythm at these sites 11. Likewise, linear lesions can be created perpendicular to the wave front propagation direction of the left posterior fascicle at various levels with Purkinje potentials as an additional guide 10, 28 ( Fig ). CONCLUSION Fascicular VT is a re-entrant arrhythmia involving the ventricular conduction system and the ventricular myocardium. Acute management with verapamil is very effective but for long-term management catheter ablation is the preferred. Most of the patients with fascicular VT can be ablated during tachycardia, using conventional mapping techniques by targeting the Purkinje potential. Electroanatomical mapping and sinus rhythm ablation are to be reserved for patients with noninducible or ill-sustained tachycardia. Figure ENSITE 3D map of the left ventricle during sinus rhythm in a patient with fascicular VT. The conduction system is mapped and tagged from the His bundle to the peripheral insertion of the fascicles. Ablation points are marked in brown mid-way between the left bundle and the ventricular breakthrough area of the tachycardia.

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9 Chapter 75 Clinical Features and Treatment of Fascicular Ventricular Tachycardia Calkins, H., Kalbfleisch, S., El-Atassi, R., Langberg, J. J., & Morady, F. ( 1993 ). Relation between efficacy of radiofrequency catheter ablation and site of origin of idiopathic ventricular tachycardia. American Journal of Cardiology, 71, Morady, F., Harvey, M., Kalbfleisch, S. J., el-atassi, R., Calkins, H., & Langberg, J. J. ( 1993 ). Radiofrequency catheter ablation of ventricular tachycardia in patients with coronary artery disease. Circulation, 87, Chen, M., Yang, B., Zou, J., Shan, Q., Chen, C., Xu, D., et al. ( 2005 ). Non-contact mapping and linear ablation of the left posterior fascicle during sinus rhythm in the treatment of idiopathic left ventricular tachycardia. Europace, 7,

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