Catheter Ablation for Scar-related Ventricular Tachycardias

Potential Application of Pulsed Field Ablation in Ventricular Arrhythmias

Pulsed field ablation (PFA) is a new ablative method for the therapy of arrhythmia. Recent preclinical and clinical studies have already demonstrated the feasibility and safety of PFA for the treatment of atrial fibrillation (AF). However, the application of PFA may not be limited to the above fields. There are some data on the application of PFA on ventricular arrhythmias (VAs), such as ventricular fibrillation (VF) and ventricular tachycardia (VT). Further, a case report about PFA has been published recently, in which PFA was successfully applied to the ablation of premature ventricular contractions (PVCs) from the right ventricular outflow tract. Thus, we aimed to review recent research findings of PFA in ventricular ablation and evaluate the possibility of its application in VAs.

Role of spatial dispersion of repolarization in reentry around a functional core versus reentry around a fixed anatomical core

INTRODUCTION

Successful initiation of spiral wave reentry in the neonatal rat ventricular myocyte (NRVM) monolayer implicitly assumes the presence of spatial dispersion of repolarization (DR), which is difficult to quantify. We recently introduced a NRVM monolayer that utilizes anthopleurin-A to impart a prolonged plateau to the NRVM action potential. This was associated with a significant degree of spatial DR that lends itself to accurate quantification.

METHODS AND RESULTS

We utilized the monolayer and fluorescence optical mapping of intracellular calcium transients (F_Cai ) to systematically study and compare the contribution of spatial dispersion of the duration of F_Cai (as a surrogate of DR) to induction of spiral wave reentry around a functional core versus reentry around a fixed anatomical obstacle. We show that functional reentry could be initiated by a premature stimulus acting on a substrate of spatial DR resulting in a functional line of propagation block. Subsequent wave fronts circulated around a central core of functional obstacle created by sustained depolarization from the circulating wave front. Both initiation and termination of spiral wave reentry around an anatomical obstacle consistently required participation of a region of functional propagation block. This region was similarly based on spatial DR. Spontaneous termination of spiral wave reentry also resulted from block in the functional component of the circuit obstacle, usually preceded by beat-to-beat slowing of propagation.

CONCLUSIONS

The study demonstrates the critical contribution of DR to spiral wave reentry around a purely functional core as well as reentry around a fixed anatomical core.

[Current strategies in the treatment of ventricular tachycardia by catheter ablation : A review]

The treatment of ventricular tachycardia has recently undergone relevant changes as certain interventional treatment options, such as radiofrequency catheter ablation, have gained in importance. Numerous current publications have demonstrated the advantages of catheter ablation compared to conventional therapy with antiarrhythmic drugs in terms of effectiveness and morbidity. Improving the ablation technique and identifying those patient collectives who are most likely to benefit from ablation are still the objectives of current research. The treatment of ventricular tachycardia in the setting of different cardiac and non-cardiac conditions can be challenging and requires understanding of the current procedures and the recommendations for catheter ablation of ventricular tachycardia. This review succinctly summarizes the current research in this evolving field of interventional cardiology.

Sudden Cardiac Death Substrate Imaged by Magnetic Resonance Imaging: From Investigational Tool to Clinical Applications

Sudden cardiac death (SCD) is a devastating event afflicting 350 000 Americans annually despite the availability of life-saving preventive therapy, the implantable cardioverter defibrillator. SCD prevention strategies are hampered by over-reliance on global left ventricular ejection fraction <35% as the most important criterion to determine implantable cardioverter defibrillator candidacy. Annually in the United States alone, this results in ≈130 000 implantable cardioverter defibrillator placements at a cost of >$3 billion but only a 5% incidence per year of appropriate firings. This approach further fails to identify individuals who experience the majority, as many as 80%, of SCD events, which occur in the setting of more preserved left ventricular ejection fraction. Better risk stratification is needed to improve care and should be guided by direct pathophysiologic markers of arrhythmic substrate, such as specific left ventricular structural abnormalities. There is an increasing body of literature to support the prognostic value of cardiac magnetic resonance imaging with late gadolinium enhancement in phenotyping the left ventricular to identify those at highest risk for SCD. Cardiac magnetic resonance has unparalleled tissue characterization ability and provides exquisite detail about myocardial structure and composition, abnormalities of which form the direct, pathophysiologic substrate for SCD. Here, we review the evolution and the current state of cardiac magnetic resonance for imaging the arrhythmic substrate, both as a research tool and for clinical applications.

Extracorporeal Membrane Oxygenation for Hemodynamic Support of Ventricular Tachycardia Ablation

Background—

We report the experience in a cohort of consecutive patients receiving extracorporeal membrane oxygenation during catheter ablation of unstable ventricular tachycardia (VT) at our center.

Methods and Results—

From 2010 to 2015, extracorporeal membrane oxygenation was initiated in 64 patients (average age: 63±15 years; left ventricular ejection fraction in 27±9%; cardiogenic shock in 23%, and electrical storm in 62% of patients) undergoing 74 unstable VT catheter ablation procedures. At least one VT was terminated in 81% of procedures with baseline inducible VT, and VT noninducibility was achieved in 69%. Acute heart failure occurred in 5 patients: 3 underwent emergency heart transplantation, 1 had left ventricular assist device (LVAD) implantation, and 1 patient eventually died because of subsequent mesenteric ischemia. All other patients were discharged alive. After a median follow-up of 21 months (13–28 months), VT recurrence was 33%; overall survival was 56 out of 64 patients (88%). Extracorporeal membrane oxygenation–supported ablation was the bridge to LVAD in 6.9% and to heart transplantation in 3.5% of patients. VT recurrence was related to ablation success (after 180 days of follow up: 19% when VT was noninducible, 42% if nonclinical VT was inducible, 75% when clinical VT was inducible, and 75% in untested patients, P <0.001). Incidence of all-cause death, heart transplantation, and LVAD was independently related to ablation outcome (at 180 days of follow-up: 9% when noninducibility was achieved, 50% in case of inducible VT, and 75% in untested patients, P <0.001). At multivariable analyses, noninducibility (hazard ratio 0.198; P =0.001) and left ventricular ejection fraction (hazard ratio 0.916; P =0.008) correlated with all-cause death, LVAD, and heart transplantation.

Conclusions—

Ablation of unstable VTs can be safely supported by extracorporeal membrane oxygenation, which allows rhythm stabilization with low procedure mortality, bridging decompensated patients to permanent LVAD or heart transplantation. Successful ablation is associated with better outcomes than unsuccessful ablation.

Nonsustained Ventricular Tachycardia in the Normal Heart: Risk Stratification and Management

Nonsustained ventricular tachycardia (NSVT) may trigger concern, particularly in patients with known congestive heart failure, structural heart disease, or prolonged QT interval. When NSVT occurs in patients with normal hearts, it usually has a benign prognosis. Therefore, establishing the presence or absence of structural or inherited heart disease is a critical step in each patient's evaluation. It is important to approach a wide-complex tachycardia in a systematic manner, to ensure correct diagnosis and treatment. When NSVT occurs in a patient with a normal heart, treatment is targeted toward symptoms and may consist of observation, medical therapy, or catheter ablation.

Cardiac magnetic resonance for prediction of arrhythmogenic areas

Catheter ablation has been widely used to manage recurrent atrial and ventricular arrhythmias. It has been established that contrast-enhanced magnetic resonance can accurately characterize the myocardium. In this review, we summarize the role of cardiac magnetic resonance in identification of arrhythmogenic substrates, and the potential utility of cardiac magnetic resonance for catheter ablation of complex atrial and ventricular arrhythmias.

Impact of general anesthesia on initiation and stability of VT during catheter ablation

BACKGROUND

Radiofrequency ablation of ventricular tachycardia (VT) may be performed with general anesthesia (GA) or conscious sedation; however, comparative data are limited.

OBJECTIVE

The purpose of the study was to assess the effects of GA on VT inducibility and stability.

METHODS

A retrospective comparison of 226 patients undergoing radiofrequency ablation for scar-related VT under GA or intravenous conscious sedation was performed. Data were then prospectively collected in 73 patients undergoing noninvasive programmed stimulation (NIPS) while awake, followed by GA and invasive programmed stimulation for VT induction.

RESULTS

In the retrospective study, groups did not differ in VT inducibility, complications, or abolition of clinical VT. Intravenous hemodynamic support was used more often in the GA group. In the prospective group, 12 patients (16%) were noninducible with NIPS. Of the 61 patients with inducible VT with NIPS, 5 (8%) were noninducible with GA, 25 (41%) were inducible with more aggressive simulation, and 31 (51%) were inducible with the same or less aggressive stimulation. Of the 56 patients who were inducible with NIPS and under GA, 28 (50%) had the same induced VTs and 28 (50%) had different induced VTs. In 23 of 56 patients, the clinical VT morphology was known. The clinical VT was reproduced with NIPS in 17 of 23 patients (74%) and under GA in 13 of 23 patients (59%). Under GA, nonclinical VTs were more often induced in patients with a lower ejection fraction and nonischemic cardiomyopathy.

CONCLUSION

GA does not prevent inducible VT in the majority of patients. GA is associated with an increased use of hemodynamic support, but this did not adversely affect VT stability or procedure outcomes.

Multi-Stencil Streamline Fast Marching: A General 3-D Framework to Determine Myocardial Thickness and Transmurality in Late Enhancement Images

We propose a fully 3-D methodology for the computation of myocardial nonviable tissue transmurality in contrast enhanced magnetic resonance images. The outcome is a continuous map defined within the myocardium where not only current state-of-the-art measures of transmurality can be calculated, but also information on the location of nonviable tissue is preserved. The computation is done by means of a partial differential equation framework we have called multi-stencil streamline fast marching. Using it, the myocardial and scarred tissue thickness is simultaneously computed. Experimental results show that the proposed 3-D method allows for the computation of transmurality in myocardial regions where current 2-D methods are not able to as conceived, and it also provides more robust and accurate results in situations where the assumptions on which current 2-D methods are based-i.e., there is a visible endocardial contour and its corresponding epicardial points lie on the same slice-, are not met.

Electrophysiological mapping and radiofrequency catheter ablation for ventricular tachycardia in a patient with peripartum cardiomyopathy

A 38-year-old female with prior failed endocardial ablation for ventricular tachycardia (VT) was referred for further treatment. She had been diagnosed with peripartum cardiomyopathy 7 years before and had persistent left ventricular dysfunction with an ejection fraction of 20%. Epicardial voltage mapping showed extensive epicardial scar despite absence of endocardial scar. Five distinct VT morphologies were induced. Ablation was aided by electrogram characteristics, pace mapping, entrainment mapping, and establishing electrical inexcitability along areas of epicardial scar. After epicardial ablation no sustained VT was induced. She had been doing well without VT occurrence but died 1 year later unexpectedly at home.

Acute failure of catheter ablation for ventricular tachycardia due to structural heart disease: causes and significance

BACKGROUND

Acute end points of catheter ablation for ventricular tachycardia (VT) remain incompletely defined. The aim of this study is to identify causes for failure in patients with structural heart disease and to assess the relation of this acute outcome to longer-term management and outcomes.

METHODS AND RESULTS

From 2002 to 2010, 518 consecutive patients (84% male, 62 ± 14 years) with structural heart disease underwent a first ablation procedure for sustained VT at our institution. Acute ablation failure was defined as persistent inducibility of a clinical VT. Acute ablation failure was seen in 52 (10%) patients. Causes for failure were: intramural free wall VT in 13 (25%), deep septal VT in 9 (17%), decision not to ablate due to proximity to the bundle of His, left phrenic nerve, or a coronary artery in 3 (6%), and endocardial ablation failure with inability or decision not to attempt to access the epicardium in 27 (52%) patients. In multivariable analysis, ablation failure was an independent predictor of mortality (hazard ratio 2.010, 95% CI 1.147 to 3.239, P=0.004) and VT recurrence (hazard ratio 2.385, 95% CI 1.642 to 3.466, P<0.001).

CONCLUSIONS

With endocardial or epicardial ablation, or both, acute ablation failure was seen in 10% of patients, largely due to anatomic factors. Persistence of a clinical VT is associated with recurrence and comparatively higher mortality.

Cardiac MRI visualization for ventricular tachycardia ablation

OBJECTIVE

The integrated visualization of cardiac MRI during a ventricular tachycardia (VT) mapping and ablation procedure would provide improved catheter guidance and tissue assessment. We developed a system for and explored the added value of simultaneous visualization of intracardiac voltage measurements and MRI-derived myocardial scar information during VT ablation procedures.

METHOD

We propose the use of a synchronized 3D and 2D view. In 3D, the catheter will be guided optimally by assessing 3D scar characteristics and its relation to the ventricular anatomy. In 2D, a detailed assessment of the tissue can be made. We developed several 3D visualization techniques, including volume rendering of the scar and myocardial surfaces colored according to the voltage measurements. We also visualized context structures in the heart. For the 2D view, we proposed showing three adjacent slices simultaneously. To link the 3D with the 2D view, we added a linking plane and linking contours; the slice level shown in the 2D view is indicated in the 3D view.

RESULTS

We evaluated our method via a case study during which we simulated the visual environment of an ablation procedure. The MRI-based volume rendering of scar tissue and the linking between the 3D and 2D views were both positively received. However, the visualization of the voltage measurements was found to be hard to interpret, partly due to the perceptually suitable but non-standard colormap.

CONCLUSIONS

Based on this study, we can conclude that our approach of displaying MRI data and integrating it with voltage measurements has potential to improve VT ablation procedures.

Results of recent studies in catheter ablation of ventricular tachycardias: in whom to abandon the ICD?

The implantable cardioverter defibrillator (ICD) has emerged as an accepted therapy for prevention of sudden cardiac death due to ventricular arrhythmias in selected groups of high-risk patients, however, it cannot prevent the ventricular arrhythmias. ICD shocks are painful, reduce the quality of life, and spontaneous episodes of ventricular tachycardia (VT) despite effective treatment by the ICD are associated with increased mortality. The recently published studies have shown the important role of catheter ablation in patients with structural heart disease and ICD who experienced appropriate ICD therapy due to recurrent VT. Successful catheter ablation in these patients prevents or reduces the number of VT recurrences (and ICD shocks) which will improve the quality of life and probably the long-term mortality. This review summarizes the results of recent important clinical studies in the field of catheter ablation of ventricular arrhythmias in patients with structural heart disease and ICD.

Inactivation of human glutamate dehydrogenase by aluminum

Aluminum inactivated glutamate dehydrogenase (GDH) by a pseudo-first-order reaction at micromolar concentrations. A double-reciprocal plot gave a straight line with a k(inact) of 2.7 min(-1) and indicated the presence of a binding step prior to inactivation. The inactivation was strictly pH dependent and a marked increase in sensitivity to aluminum was observed as the pH decreased. At a pH higher than 8.5, no inactivation was observed. The completely inactivated GDH contained 2 mol of aluminum per mole of enzyme subunit monomer. When preincubated with enzyme, several chelators such as citrate, NaF, N-(2-hydroxyethyl) ethylenediaminetriacetic acid or ethylenediaminetriacetic acid efficiently protected the enzyme against the aluminum inactivation. In a related experiment, only citrate and NaF released the aluminum from the completely inactivated aluminum-enzyme complex and fully recovered the enzyme activity. Ferritin, NADP+, or nerve growth factor did not show any effects on the recovery of the aluminum-inactivated GDH activity. The dissociation constant for the aluminum-enzyme complex was calculated to be 5.3 microM. Although aluminum has been known to form a complex with nucleotides, no such effects were observed in the inactivation of GDH by aluminum as determined using GDHs mutated at the ADP-binding site, NAD+-binding site or GTP-binding site. Circular dichroism studies showed that the binding of aluminum to the enzyme induced a decrease in alpha helices and beta sheets and an increase in random coil. Therefore, inactivation of GDH by aluminum is suggested to be due to the conformational change induced by aluminum binding. These results suggest a possibility that aluminum-induced alterations in enzymes of the glutamate system may be one of the causes of aluminum-induced neurotoxicity.