Localized reentry as a novel type of the proarrhythmic effects of linear ablation in the left atrium

Background: There is a consistent understanding that the proarrhythmic effect of linear ablation in the left atrium body for atrial fibrillation (AF) always manifests as the macroreentry tachycardia. However, its genesis of localized reentry has been underestimated. Methods: Among 90 persistent AF patients who had accepted linear ablation in the left atrium body, a total of 11 patients (12%) presented with a localized reentry (six men, mean age 59 ± 11 years) associated with previous ablation lines. Among the 11 patients, four were encountered during the index procedure for AF ablation and the remaining seven during the redo procedure for atrial tachycardias (ATs). Results: The ATs were all located at previously ablated lesion sites and manifested a centrifugal mode in both the activation mapping and pattern of the postpacing interval response. The mean tachycardia cycle length (TCL) of the localized reentrant ATs was 306 ± 73 ms. The target sites demonstrated low amplitude (0.17 ± 0.09 mV) continuous complex electrograms or long double potentials, covering 142 ± 57 ms (46 ± 12 % of the TCL). The localized reentrant tachycardias were all successfully eliminated by catheter ablation. Conclusions: A novel type of the proarrhythmic effects of linear ablation in the left atrium for AF may manifest as localized reentrant ATs, as evidenced by the association of the site of origin with the prior lesions. (PACE 2011; 34:919–926)     

Catheter Ablation of Scar‐Related Ventricular Tachycardia in Patients with Electrical Storm Using Remote Magnetic Catheter Navigation

Background: A remote magnetic navigation system (MNS) has been used for ablation of ventricular arrhythmias. However, irrigated tip catheter has not been evaluated in large series of patients. Objective: To evaluate acute and long‐term efficiency of the newly available irrigated tip magnetic catheter for radiofrequency (RF) ablation of scar‐related ventricular tachycardia (VT) in patients with ischemic heart disease. Methods: Between January 2008 and October 2009, a total of 30 consecutive patients with ischemic heart disease (26 men, age 70.1 ± 8.7 years, left ventricular ejection fraction: 30 ± 9%) and electrical storm due to monomorphic VT underwent RF ablation using a remote MNS and a magnetic irrigated tip catheter. Results: Acute success was defined as noninducibility of any monomorphic VT during programmed right and left ventricular stimulation, and obtained in 24 (80%) patients. A total of 1–6 VTs (mean 2.3 ± 1.2, 394 ± 108 ms, 210–660 ms) were inducible during each procedure. The duration of RF energy application was 41.2 ± 23.3 minutes, with total procedure and fluoroscopy times of 158 ± 47 minutes and 9.8 ± 5.3 minutes, respectively. No acute complications were observed during the procedures. During mean follow‐up of 7.8 months, 21 patients (70%) had no recurrence of VT and received no implantable cardioverter defibrillator therapy. Among patients who were noninducible during programmed right ventricular stimulation (n = 25), ≥1 monomorphic VT was inducible during programmed left ventricular stimulation in four (16%) that was ablated successfully in three of them. Conclusions: Irrigated ablation of scar‐related VT using remote MNS is an effective modality for management of the monomorphic VT in patients with ischemic cardiomyopathy with minimal radiation exposure. Programmed left (in addition to right) ventricular stimulation might be necessary to assess acute outcome of the ablation procedure. (PACE 2010; 1312–1318)     

Catheter Ablation of Idiopathic Left Ventricular Tachycardia

ZARDINI, M., etal .: Catheter Ablation of Idiopathic Left Ventricular Tachycardia . Idiopathic left ventricular tachycardia (ILVT) characterized by right bundle branch block, left axis morphology, response to verapamil and inducibility from the atrium in patients without structural heart disease may represent a distinct clinical entity. We report our experience with catheter ablation of this uncommon arrhythmia using radiofrequency energy (RF) and/or direct current (DC) shocks. Six men and 2 women, aged 16–50 years (mean ± SD, 32 ± 13), had recurrent VT for 16 ± 16 years with a mean frequency of 4 ± 3 episodes/ year. Three patients had syncope during VT. None had identifiable structural heart disease. Catheter ablation was guided by earliest endocardial activation, presence of a high frequency presystolic potential and/or pacemapping of the left ventricle. The left ventricle was accessed via a retrograde aortic approach in 6 patients, a transeptal approach in 1 patient, and a combined approach in the remaining patient. All patients had inducible right bundle branch block morphology, left axis VT with a mean cycle length (CL) of 361 ± 61 ms. A presystolic potential preceding ventricular activation and the His potential during VT was identified in 4 patients. All ablation sites were identified in a relatively uniform location, in the inferoapical left ventricle. Noninducibility of VT was obtained with RF in 3 patients and with DC in 5 patients. In 1 patient, DC delivery after unsuccessful RF prevented further inducibility. Similarly, RF was successful in 1 patient in whom an initial DC attempt was ineffective. Mean total procedure time was 282 ± 51 minutes and mean total fluoroscopy time was 40 ± 15 minutes. There were no complications. One patient treated with DC shock had recurrence of VT during treadmill test the day after ablation and refused repeat ablation. During a mean follow-up of 17 ± 13 months, no VT recurrences or other cardiovascular events occurred. In conclusion, catheter ablation in the inferoapical left ventricle is an effective treatment for this type of ILVT. RF energy can be safely complemented by low energy DC shocks when the former is ineffective.     

Fulguration of Ventricular Tachycardia Using High Cumulative Energy: Results in Thirty-one Patients with a Mean Follow-Up of Twenty-seven Months

Catheter electrical ablation of ventricular tachycardia (VT) was attempted in 31 patients (57 ± 15 years) who had refractory recurrent VT. Fifteen patients had coronary artery disease, seven had arrhythmogenic right ventricular dysplasia, four had cardiomyopathy and five had no structural heart disease. Ten patients were NYHA class III-IV. Ten patients experienced cardiac arrest or syncope during VT. Twenty-two patients had only one documented morphologic type of spontaneous VT. Whereas nine patients had more than one: the VT was incessant or daily in 17 patients. One to 16 shocks (mean 5.6) of 160 to 240 joules each (1162 ± 1060 joules) were delivered to the endocardial exit site of VT—as identified by endocardial activation mapping (29 patients) and pacemapping (31 patients)—during one (22 patients) or more than one session (nine patients). Cumulative delivered energy was 840 ± 558 joules for right ventricular VT (11 patients) and 1362 ± 1240 joules for left ventricular VT (20 patients). Reversible side effects occurring immediately after shocks included: nonclinical VT (two patients), ventricular fibrillation (two patients), AV block (three patients). Mean CK—MB fraction 6 hours after shocks was 93 ± 46 IU/1. An electrophysiology study performed 7 to 10 days later demonstrated that the original clinical VT was inducible in seven patients, nonclinical monomorphic VT was inducible in eight patients and no VT was inducible in 13 patients. The procedure was successful in 25/29 patients (86%) who had no recurrence of the original VT (or sudden death) either on no antiarrhythmic therapy (16 patients) or on the same regimen that was ineffective before ablation (nine patients) over a follow-up period of 27 ± 11 months. A nonclinical VT occurred in two patients. The ablation result was not interpretable in two patients and unsuccessful in four patients: the endocardial activation time at site of shocks was –5 ± 5 ms in the failures versus ?43 ± 29 ms in the successes (P < 0.05).     

Ventricular tachyarrhythmias in patients receiving an implantable cardioverter-defibrillator for primary versus secondary prophylaxis indications

Introduction: Data on the mechanisms of sudden cardiac death are limited and may be biased by delays in rhythm recording and selection bias in survivors. As a result, the relative contributions of monomorphic ventricular tachycardia (VT) (cycle length [CL] > 260 ms), monomorphic fast VT (FVT) (CL ≤ 260 ms), and polymorphic VT (PMVT)/ventricular fibrillation (VF) have not been well characterized nor compared in patients with and without prior arrhythmic events. Methods: A retrospective cohort study of implantable cardioverter‐defibrillator (ICD) recipients with primary or secondary implant indications was used to evaluate intracardiac electrograms (EGMs) for the first spontaneous VT/VF resulting in appropriate ICD therapy. EGMs were categorized into VT, FVT, and PMVT/VF based on CL and morphologic criteria. Results: Of 616 implants, 145 patients (58 [40%] primary indications) received appropriate ICD therapy for VT/VF over mean follow‐up of 3.8 ± 3.2 years. Primary implants had more diabetes (28% vs 12%; P = 0.02) and less antiarrhythmic use (15% vs 33%; P = 0.02). In those patients with spontaneous arrhythmia, PMVT/VF occurred in 20.7% of primary versus 21.8% of secondary implants, FVT in 19.0% versus 21.8%, and VT in 60.3% versus 56.4%, respectively (P = 0.88). Spontaneous VT CL was similar regardless of implant indication (284 ± 56 [primary] vs 286 ± 67 ms [secondary]; P = 0.92). Conclusions: Monomorphic VT is the most common cause of appropriate ICD therapy regardless of implant indication. These results provide insight into the mechanisms of sudden cardiac death and have implications for the use of interventions designed to limit ICD shocks. (PACE 2011; 34:571–576)     

Effect of Amiodarone on Electric Induction, Morphology, and Rate of Ventricular Tachycardia and its Relation to Clinical Efficacy

Using His bundle electrograms and programmed ventricular stimulation, the effects of chronic amiodarone treatment on induction, morphology, and the rate of ventricular tachycardia (VT) were studied in 17 consecutive patients treated with amiodarone for control of recurrent sustained VT or ventricular fibrilation. Studies were done before and after treatment with amiodarone for an average duration of 5.3 (range 2 to 18) months. During the control study, sustained VT could be induced in 16 patients. VT was initiated by single or double right ventricular (RV) extrastimuli in 14 patients, by double left ventricular (LV) extrastimuli in 1 patient, and by RV burst pacing in 1 patient. Only one pattern (morphology) of VT similar to that of spontaneous VT was induced in 12 patients and two patterns of VT in 4 patients. The average cycle length (CL) (mean ± SD) of induced VT was 325.8 ± 61.2 ms. After amiodarone, VT could be induced in 7 of 17 patients and was initiated by single RV extrastimuli in 5 patients, double RV extrastimuli in 1 patient, and RV burst pacing in 1 patient. In 3 of 5 patients in whom VT could be initiated by single RV extrastimuli, initiation of VT required double RV or double LV extrastimuli in the control study; in 1 of 5 patients VT could not be induced in the control study. Amiodarone induced nonclinical, polymorphic VT in 4 patients in whom only clinical VT could be induced during the control study. Compared to control, the CL of induced VT was significantly longer (322 ± 65.7 vs 416 ± 41.5 ms; P < 0.001). During a follow-up period ranging from 4 to 53 (mean ± SD; 18.6 ± 11.4) months, VT did not recur in 8 patients with no inducible VT and in 6 patients with persistence of inducible VT. One patient without inducible VT died suddenly; VT recurred in 2 patients, one without inducible VT and one with inducible VT. The results show that programmed stimulation studies late in the course of treatment do not accurately reflect the clinical efficacy of amiodarone in VT.     

Ranolazine reduces ventricular tachycardia burden and ICD shocks in patients with drug-refractory ICD shocks

Background: There are limited options for patients who present with antiarrhythmic‐drug (AAD)‐refractory ventricular tachycardia (VT) with recurrent implantable cardioverter defibrillator (ICD) shocks. Ranolazine is a drug that exerts antianginal and antiischemic effects and also acts as an antiarrhythmic in isolation and in combination with other class III medications. Ranolazine may be an option for recurrent AAD‐refractory ICD shocks secondary to VT, but its efficacy, outcomes, and tolerance are unknown. Methods and Results: Twelve patients (age 65 ± 9.7 years) were treated with ranolazine. Eleven (92%) were male, and 10 (83%) had ischemic heart disease with an average ejection fraction of 0.34 ± 0.13. All patients were on a class III AAD (11 amiodarone, one sotalol), with six (50%) receiving mexilitene or lidocaine. Five patients had a prior ablation and two were referred for a VT ablation at the index presentation. The QRS increased nonsignificantly from 128 ± 31 ms to 133 ± 31 ms, and the QTc increased nonsignificantly from 486 ± 32 ms to 495 ± 31 ms after ranolazine initiation. Over a follow‐up of 6 ± 6 months, 11 (92%) patients had a significant reduction in VT and no ICD shocks were observed. VT ablation was not required in those referred. In two patients, gastrointestinal side effects limited long‐term use. Of these two patients, one died due to progressive heart failure. In one patient, severe hypoglycemia limited dosing to 500 mg daily, but this was sufficient for VT control. Conclusion: Ranolazine proved effective in reducing VT burden and ICD shocks in patients with AAD‐refractory VT. Ranolazine should be further tested for this indication and considered for clinical application when other options have proven ineffective. (PACE 2011; 34:1600–1606)     

Local Activation Time Derived from Stored EGM is Associated with Failure of Antitachycardia Pacing in Patients with Implantable Defibrillator

Background : Antitachycardia pacing (ATP) is an effective treatment of ventricular tachycardia (VT). However, persistent failure of ATP in some patients is well recognized. Methods : A method of deriving the local activation time from stored intracardiac electrograms in implantable cardioverter defibrillators is described. Using a case‐control design, the local activation times were compared between patients with persistent unsuccessful ATP with comparable controls with successful ATP. Results : The local activation times during VT in patients with failed ATP were longer at 120–180 ms compared with corresponding control patients with successful ATP (60–80 ms). The local activation time expressed as a proportion of VT cycle length in patients with failed ATP compared with patients with successful ATP were 0.40 ± 0.08 versus 0.19 ± 0.08 (P = 0.012). Conclusion : A novel method of deriving local activation time is described, and delayed local activation time may explain failure of ATP in terminating VT in some patients. (PACE 2010; 549–552)     

Idiopathic Left Ventricular Tachycardia: New Insights, into Electrophysiological Characteristics and Radiofrequency Catheter Ablation

KOTTKAMP, H., et.al .: Idiopathic Left Ventricular Tachycardia: New Insights into Electrophysiological Characteristics and Radiofrequency Catheter Ablation . Objectives: This study was performed to investigate the electrophysiological characteristics of idiopathic left ventricular tachycardia and to determine the feasibility of radiofrequency catheter ablation for nonpharmacological cure. Background: The underlying electrophysiological mechanism of idiopathic left ventricular tachycardia with right bundle branch block morphology and left-axis deviation is presently not known. Additionally, only limited data describing the results of radiofrequency catheter ablation for treatment of idiopathic left ventricular tachycardia so far exist. Methods: Electrophysiological studies and radiofrequency catheter ablation were performed in 5 patients (3 male and 2 female, mean age 31 ± 10 years) with idiopathic left ventricular tachycardia (cycle length 376 ± 72 msec). The patients had a history of recurrent palpitations of 4 ± 1 years and had been treated unsuccessfully with 2 ± 1 antiarrhythmic drugs. Sustained ventricular tachycardia with right bundle branch block morphology and left- or right-axis deviation was documented in all patients. Results: Inducibility with critically timed ventricular extrastimuli, inverse relationships of the coupling interval of the initiating extrastimulus and the interval to the first beat of the tachycardia, continuous diastolic or mid-diastolic electrical activity during ventricular tachycardia, and fragmented late potentials during sinus rhythm suggested reentrant activation as the underlying mechanism in three patients. On the other hand, induction dependent on isoproterenol infusion and rapid ventricular pacing and exercise inducibility indicated different electrophysiological characteristics in the remaining two patients. During electrophysiological study, intravenous verapamil terminated ventricular tachycardia in all patients, whereas ventricular tachycardia did not respond to intravenous adenosine, autonomic maneuvers, or intravenous β-blocking agent esmolol. Catheter mapping revealed earliest endocardial activation during ventricular tachycardia in different areas of the left ventricular septum being distributed from the base to the midapical portion of the septum in all patients. In 4 of 5 patients, radiofrequency catheter ablation (median number of pulses 4, range 1–9) resulted in complete abolition of idiopathic left ventricular tachycardia during a follow-up of 4–43 months (median 10) without antiarrhythmic drugs. Successful target sites for catheter ablation included continuous diastolic or mid-diastolic electrical activity during ventricular tachycardia and late potentials during sinus rhythm (2 patients), polyphasic fragmented presystolic potentials during ventricular tachycardia (1 patient), and pace mapping with identical QRS morphology compared to the ventricular tachycardia and “earliest” detectable activity during tachycardia (1 patient). No procedure related complications occurred. Conclusions: Two different patterns of electrophysiological properties of idiopathic left ventricular tachycardia were observed, indicating that this arrhythmia entity does not represent a homogeneous group. The “origin” of the tachycardias as identified by successful radiofrequency catheter ablation was located in different areas of the left ventricular septum and was distributed from the base to the mid-apical region. Radiofrequency catheter ablation was an effective and safe treatment modality in most of these patients. Distinct target site characteristics for successful catheter ablation including polyphasic diastolic activity during tachycardia and fragmented late potentials during sinus rhythm could be identified.     

Reinitiation of ventricular macroreentry within the His-Purkinje system by back-up ventricular pacing - a mechanism of ventricular tachycardia storm

BACKGROUND: We describe immediate reinitiation of macroreentry ventricular tachycardia (VT) involving the His-Purkinje system by ventricular pacing from the electrode of an implantable cardioverter defibrillator (ICD) as a mechanism of VT storm refractory to ICD therapy. METHODS AND RESULTS: Repetitive reinitiation of bundle branch reentry tachycardia (BBRT), interfascicular tachycardia, or both VTs by ventricular pacing was identified in four ICD patients presenting with VT storm or incessant VT. All patients had a pre-existing prolonged HV interval (75 +/- 9 ms) and left bundle branch block (LBBB) or bifascicular block during sinus rhythm. The VTs included BBRT with LBBB in three patients and interfascicular tachycardia with right bundle branch block (RBBB) and left anterior or left posterior fascicular block in two patients. The paced beats from the ICD electrode exhibited a LBBB pattern of depolarization in two patients and a RBBB contour in V1 and V2 with left axis deviation in two patients. The QRS complex during pacing from the ICD electrode closely resembled that of the recurrent VT in all four patients suggesting that the pacing site of the ICD electrode was in proximity to the myocardial exit site of the bundle fascicle used for antegrade conduction during the reinitiated VT. Ventricular pacing from the ICD electrode after termination of the VT apparently encountered the retrograde refractoriness of this bundle fascicle and allowed immediate re-propagation of the wavefront orthodromically along the VT circuit. BBRT was eliminated by ablation of the right bundle branch. Successful ablation of the interfascicular tachycardias was achieved by targeting (1) an abnormal potential of the distal left posterior Purkinje network or (2) a diastolic potential during VT in the midinferior left ventricular (LV) septum. CONCLUSIONS: Repetitive reinitiation of BBRT and interfascicular tachycardia by ventricular pacing from the ICD electrode should be considered as a mechanism of VT storm refractory to ICD therapy in patients with a pre-existing conduction delay within the His-Purkinje system.     

Anterior Mitral Valve Length is Associated with Ventricular Tachycardia in Patients with Classical Mitral Valve Prolapse

Background: The aim of this study was to investigate the electrocardiographic and echocardiographic predictors of ventricular tachycardia (VT) in patients with classical mitral valve prolapse (MVP). Methods: Thirty patients (nine men and 21 women; mean age, 41.5 ± 15 years) in sinus rhythm with mitral valve prolapse who had VT in 24‐hour Holter analysis and 30 patients with MVP without VT (eight men and 22 women; mean age, 43 ± 16 years) were included in this study. Transthoracic echocardiography, QT analyses from 12‐lead electrocardiography, and 24‐hour Holter electrocardiogram recordings were performed. Results: Mitral posterior leaflet thickness (0.48 ± 0.03 cm vs 0.43 ± 0,08 cm, P = 0.025), mitral anterior leaflet length (3.2 ± 0.24 cm vs 2.9 ± 0.36, P < 0.001), mitral posterior leaflet length (2.2 ± 0.3 cm vs 1.9 ± 0.35 cm, P = 0.01), left atrium anteroposterior diameter (4.2 ± 0.8 cm vs 3.5 ± 0.5 cm, P = 0.001), and mitral annulus circumference (15.7 ± 1.3 cm vs 14.6 ± 1.6 cm, P = 0.004) were increased significantly in MVP cases with VT. No significant difference was found between the cases with and without VT in terms of frequency‐ and time‐domain analysis. QT dispersion (72 ± 18 ms vs 55 ± 15 ms, P = 0.0002) and corrected QT dispersion (QTcD) (76 ± 18 ms vs 55 ± 15 ms, P = 0.0002) were significantly increased in cases with VT compared with those without VT. Based on logistic regression analysis for MVP cases, in the case of VT, an enhancement in QTcD (P = 0.01) and the mitral anterior leaflet length (P = 0.003) were the independent predictors of VT. Conclusion: Mitral anterior leaflet length and enhanced QTcD are closely related with VT in patients with classical MVP. (PACE 2010; 33:1224–1230)     

Superior type of atypical AV nodal reentrant tachycardia: incidence, characteristics, and effect of slow pathway ablation

Background: Atypical atrioventricular (AV) nodal reentrant tachycardias (AVNRT) usually exhibit the earliest retrograde atrial activation (ERAA) at the right inferoseptum (Rt-IS) or proximal coronary sinus (PCS). The purpose of this study was to characterize atypical AVNRT with the ERAA at the right superoseptum (Rt-SS).
Methods: Seventy-three atypical AVNRTs induced in 63 cases were classified into the superior type with the ERAA at the Rt-SS and inferior type with the ERAA at the Rt-IS or PCS.
Results: There were nine superior (12%) and 64 inferior types of atypical AVNRT (88%) in seven and 56 cases, respectively. The superior type exhibited a short atrial-His interval during the tachycardia (166 ± 41 ms), long His-atrial interval during the tachycardia (H-At:156 ± 38 ms), and ventricular pacing at the tachycardia cycle length (TCL) (H-Ap:201 ± 36 ms), and evidence for a lower common pathway, including second-degree AV block (four tachycardias) and an H-Ap being longer than the H-At (nine tachycardias). The TCL was shorter in the superior type than in the inferior type (322 ± 35 vs 404 ± 110 ms; P < 0.02). In the inferior type, all tachycardias were eliminated after the ablation at the Rt-IS (44 tachycardias) or PCS (20 tachycardias) where an ERAA was recorded. In the superior type, ablation at the Rt-IS was ineffective; however, ablation at the right midseptum eliminated seven (78%) of the nine tachycardias.
Conclusions: The tachycardia circuit of the superior type might have deviated to a more superior part of Koch's triangle than that of the inferior type.     

Electroanatomic mapping of endocardial right ventricular activation as a guide for catheter ablation in patients with arrhythmogenic right ventricular dysplasia

Arrhythmogenic right ventricular dysplasia is a structural heart disease characterized by fibrofatty degeneration of right ventricular myocardium and arrhythmias of right ventricular origin. The aim of this study was to characterize endocardial right ventricular activation by electroanatomic mapping as a guide for catheter ablation in patients with arrhythmogenic right ventricular dysplasia. Electroanatomic mapping and entrainment procedures were performed in 5 patients with arrhythmogenic right ventricular dysplasia. Endocardial mapping during ventricular tachycardia demonstrated a focal activation pattern with radial spreading of activation from a site of earliest ventricular activation in all directions. Right ventricular activation time (127 +/- 34 ms) was markedly shorter than tachycardia cycle length (415 +/- 92 ms). The site of earliest ventricular activation was found in an aneurysmal outflow tract (n = 2), at the border of aneurysms near the tricuspid annulus (n = 2), and at the apex of the right ventricle (n = 1). Entrainment mapping criteria of these areas of earliest endocardial activity were consistent with exit sites of a reentrant circuit in an area of abnormal myocardium. Fractionated potentials were found 61 +/- 29 ms before the onset of the QRS complex at these sites. Catheter ablation rendered the "clinical" ventricular tachycardia noninducible in four patients but "nonclinical" faster ventricular tachycardias were inducible in three patients. During the follow-up of 7 +/- 3 months after ablation, the frequency of therapies in 4 patients with an implantable cardioverter defibrillator decreased from 49 +/- 61 episodes per month before ablation, to 0.3 +/- 0.5 episodes per month after ablation (P < 0.05). Electroanatomic mapping during ventricular tachycardia facilitates localization of exit sites in relation to aneurysms in diseased right ventricle and may guide catheter ablation in patients with arrhythmogenic right ventricular dysplasia.     

Analysis during Sinus Rhythm and Ventricular Pacing of Reentry Circuit Isthmus Sites in Right Ventricular Cardiomyopathy

Background: The entrainment mapping algorithm is used for ablation of ventricular tachycardia (VT) in right ventricular (RV) cardiomyopathy, but ablation at endocardial isthmus sites has only a moderate success rate. This study was performed to identify additional local electrogram characteristics associated with successful ablation. Patients and Methods: Using entrainment mapping, 45 reentry circuit isthmus sites were detected in 11 patients with RV cardiomyopathy presenting with 13 monomorphic VTs. Local bipolar electrograms were retrospectively analyzed at reentry circuit isthmus sites during VT, sinus rhythm, and programmed stimulation from the right ventricular apex (RVA), and compared between successful and unsuccessful ablation sites. Results: Ablation was successful at 10 reentry circuit isthmus sites and unsuccessful at 35 isthmus sites. During VT, a longer endocardial activation time relative to QRS onset, an increased electrogram‐QRS interval as a percentage of VT cycle length, and a longer electrogram duration were found at successful in comparison to unsuccessful ablation sites. The presence of isolated diastolic potentials during sinus rhythm at reentry circuit isthmus sites, consistent with slow conduction or unidirectional conduction block, was associated with successful catheter ablation. Prolongation of the duration of the local multipotential electrogram by >100 ms during programmed RVA pacing at reentry circuit exit sites, indicating functional conduction disorder was also a marker of successful ablation. Conclusions: The demonstration of multipotential electrogram characteristics indicating fixed or functional conduction block may increase the likelihood of successful VT ablation at exit and central isthmus sites of reentry circuits in RV cardiomyopathy.     

Atrial Sensing to Augment Ventricular Tachycardia Detection by the Automatic Implantable Cardioverter Defibrillator: A Utility Study

The triggering of automatic implantable cardioverter defibrillator (AICD) discharges by supraventricular tachycardias, despite the presence of a probability density function algorithm, remains a limitation of an otherwise highly effective device. We systematically investigated the diagnostic utility which theroretically could derive form the addition of atrial sensing capability to the AICD in 25 patients with 30 inducible sustained monomorphic ventricular tachycardias (VTs) at clinically relevant rates (greater than or equal to 150 beats/min). Patients were included only if they were not taking medication capable of depressing ventriculoatrial (VA) conduction for at least 5 half-lives prior to electrophysiological testing. We tested the simple criterion for VT that ventricular cycle length (CL) be shorter than the atrial CL (not met in sinus or most other supraventricular tachycardias). Mean VT CL was 283 +/- 47 ms (range 210 to 370). In 25 (83%) VTs, the VT criterion was consistently satisfied. Of the five cases in which the criterion was not met, 1:1 VA conduction during VT was present in four, three of which initially manifested 2:1 VA conduction lasting from 14 to 28 s and therefore would have transiently fulfilled the VT criterion. The remaining patient who failed to satisfy the VT criterion had ongoing atrial flutter during a relatively slower sustained VT, but this circumstance could be recognized because of the varying AV interval. The absence of 1:1 VA conduction at CLS less than or equal to 400 ms during ventricular pacing accurately predicted the absence of 1:1 VA conduction during VT in 95% of patients.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationship between Cycle Length of Typical Atrial Flutter and Double Potential Interval after Achievement of Complete Isthmus Block

Background: There is some disagreement concerning the minimal value of the interval between components of double potentials (DPs interval) that allows distinguishing complete and incomplete block in the cavotricuspid isthmus (CTI). Objectives: To assess clinical utility of the relationship between atrial flutter cycle length (AFL CL) and the DPs interval. Methods: Ablation of the CTI was performed in 87 patients during AFL (245 ± 40 ms). Subsequently, DPs were recorded during proximal coronary sinus pacing at sites close to a gap in the ablation line and after achievement of complete isthmus block. Results: We noted strong correlation between AFL CL and the DPs interval after achievement of isthmus block (r = 0.73). The mean DPs interval was 95.3 ± 18.3 ms (range 60–136 ms) and 123.3 ± 24.3 ms (range 87–211 ms) during incomplete and complete isthmus block, respectively (P < 0.001). When expressed as a percentage of AFL CL, this interval was 35.7 ± 3.5% AFL CL (range 28–40.2%) and 50.4 ± 6.9% AFL CL (range 39–72%) during incomplete and complete isthmus block, respectively (P < 0.001). A cutoff value of 40% of AFL CL identified CTI block with 96.7% sensitivity and 100% specificity. Conclusions: The interval between DPs after achievement of block in the CTI correlates with AFL CL. The DPs interval expressed as a percentage of AFL CL allows better distinguishing between complete and incomplete isthmus block compared to standard method based on milliseconds. The DPs interval below 40% of AFL CL indicates sites close to a gap in the ablation line. (PACE 2010; 33:1518–1527)     

The Effect of an Entrainment Protocol on Ouabain-Induced Ventricular Tachycardia

Overdrive stimulation of reentrant ventricular tachycardias (VT) may result in entrainment and/or termination of these arrhythmias. We investigated whether surface ECG criteria of entrainment can also be observed in nonreentrant VT. For this purpose ouabain-induced tachycardias were used that are considered to be based on delayed afterdepolarizations. In nine conscious dogs, having surgically induced complete AV block, pacing was performed using trains of 20 stimuli from a site distant to the origin of the VT. The pacing intervals were shortened in steps of 5-10 msec, until complete capture from the pacing site or termination of the VT was obtained. During stimulation variable fusion was seen and complete capture of the ventricles from the pacing site occurred just after a slight decrease in pacing cycle length (20 +/- 10 msec). Overdrive stimulation resulted only in 1 out of 58 stimulation trains in termination of VT. Following stimulation it was observed that: (1) The length of the first postpacing interval was significantly longer (P less than 0.001) than both the mean prepacing VT cycle length and interstimulus interval; (2) A change in QRS configuration occurred after 57% of the stimulation trains; (3) The VT accelerated slightly in comparison to the prepacing rate (P less than 0.05); and (4) The length of the first postpacing interval and the mean R-R interval of the VT postpacing were directly related to the interstimulus interval (r = 0.82 and 0.97, respectively). In conclusion, overdrive stimulation of ouabain-induced arrhythmias did not result in entrainment or in termination of the tachycardia. Instead, other responses were seen that may be of help in differentiating between arrhythmias caused by delayed afterdepolarizations and reentry.     

Clinical Observations and Outcome of Ventricular Tachycardia Ablation in Patients with Left Ventricular Assist Devices

Background: Ablation of ventricular tachycardia (VT) in patients with left ventricular assist devices (LVAD) is challenging and not well documented. This report describes our experience with endocardial VT ablation in six patients with an LVAD. Methods: We retrospectively reviewed the clinical records of LVAD patients who underwent an ablation procedure for refractory VT. Results: A total of eight ablation procedures were performed in six patients who, during the last 2 weeks before the ablation procedure, received a total of 101 appropriate shocks for VT. A closed aortic valve (n = 2) or aortic atheroma (n = 1) required a transseptal catheterization in three of six patients. The apical LVAD cannula served as a VT substrate in two of six patients. VT was eliminated in four patients and markedly reduced in two others. The latter two patients experienced a total of only four implantable cardioverter defibrillator (ICD) shocks during a follow‐up of 130 and 493 days. Intravenous antiarrhythmic medications used in five of six patients before ablation were discontinued in all. The ablation procedures permitted hospital discharge in four of six patients. Five patients died during follow‐up (228 ± 207 days after the procedure). The cause of death was unrelated to cardiac arrhythmias. One patient is still alive 1,205 days after the procedure. Conclusion: Ablation of VT in LVAD patients is feasible and can result in a markedly decreased VT burden with a reduction of ICD shocks. The subsequent discontinuation of intravenous antiarrhythmic medications may facilitate hospital discharge. (PACE 2012; 35:1377–1383)     

Focal left atrial tachycardias not associated with prior catheter ablation for atrial fibrillation: clinical and electrophysiological characteristics

Background: The clinical features and electrophysiological characteristics of patients with focal left atrial tachycardias (LATs) are not well characterized. This study reports the experience of a single center in catheter mapping and radiofrequency ablation of focal LAT not associated with prior atrial fibrillation (AF) ablation, including in cardiac sarcoidosis and transplant patients. Methods: Patients with focal LAT without a history of AF ablation were included in this retrospective analysis. Results: A total of 24 focal LATs were documented in 20 patients. Two patients were subsequently diagnosed with cardiac sarcoidosis. Two patients were status post a thoracic transplant. The mean initial cycle length of the focal LATs was 347.4 ± 96.2 ms (range 190–510 ms). Patients with a pulmonary vein (PV) ostium focus (n = 6) demonstrated a shorter cycle length than patients with other LA foci (259.2 ± 56.4 ms vs 371.9 ± 91.1 ms, P = 0.02), as well as a trend for a history of AF (67% vs 21%, P = NS). Catheter ablation was immediately successful for 19 of 22 focal LATs. Conclusions: Focal LATs not associated with prior AF ablation can originate in a variety of LA locations and clinical settings. Focal LAT arising in the PV ostia is associated with a history of AF and demonstrates a faster tachycardia rate. We also report focal LAT in cardiac sarcoidosis patients and in the donor heart of an orthotopic heart transplant recipient. Radiofrequency ablation is a successful treatment for focal LAT not associated with prior ablation, including those refractory to medical therapy. (PACE 2012; 35:17–27)     

Catheter-ablation of ventricular tachycardia in patients with coronary artery disease: influence of the endocardial substrate size on clinical outcome

Ablation of symptomatic ventricular tachycardia (VT) in patients with coronary artery disease is frequently performed using the three dimensional mapping system CARTO. In the amplitude map, bipolar potentials of <1.5 mV are considered abnormal and represent damaged myocardium due to previous infarction. This pathological electrical area can be arrhythmogenic, serving as the substrate for reentrant VT. The purpose of this study was to correlate the size of the endocardial substrate with the success of VT catheter ablation. Included in this retrospective analysis were 69 consecutive patients with coronary artery disease who underwent ablation for symptomatic clinical VT using CARTO. The voltage maps were analyzed and the area with abnormal bipolar electrograms (<1.5 mV) was determined using geometric approximation models. The area of abnormal electrograms was divided into three sizes: small (≤15 cm²; 11 patients), medium (16–99 cm²; 50 patients), and large (≥100 cm²; 8 patients). Patient characteristics were not different between the three substrate groups in regard to age, tachycardia cycle length, or number of radiofrequency applications, however differed significantly between the small, medium and large group in regard to left ventricular ejection fraction (44 ± 12% vs. 32 ± 9% vs. 21 ± 7%, respectively; P = 0.001). Overall, there was a significant correlation between myocardial infarction locations and endocardial substrate sizes (P = 0.031), such that 73% of small substrates were found after inferior myocardial infarctions, and 100% of large substrates after anterior and multiple myocardial infarctions (P = 0.003). After ablation, inducibility of ventricular arrhythmias was more rare in patients with small substrates compared to patients with medium or large substrates (small substrates: 9%, medium and large substrates: 43%, P = 0.043). Although during follow-up of 25 ± 17 months (1 day to 72 months) there was no significant difference between endocardial substrate sizes in regard to recurrence rates (small: 27%, medium: 38%, large: 50%, P = 0.588), patients with a small substrate did not have fast VT or ventricular fibrillation (VF), in contrast to 30% and 38% of patients with medium and large substrates, respectively. We conclude that in patients with coronary artery disease a small area of low amplitude bipolar potentials (≤15 cm²) was seen more often after inferior myocardial infarction than after anterior and multiple infarctions. After ablation, patients with small substrates were rarely inducible and showed a more benign course during follow-up (trend towards fewer arrhythmia recurrences and no fast VT or VF). As a result smaller arrhythmogenic substrates appear to be better amenable to catheter ablation than larger substrates.