Exploring postinfarction reentrant ventricular tachycardia with entrainment mapping

Stabilization of collapsing scroll waves in systems with random heterogeneities

In three-dimensional reaction-diffusion systems, excitation waves may form and rotate around a one-dimensional phase singularity called the filament. If the filament forms a closed curve, it will shrink over time and eventually collapse. However, filaments may pin to non-reactive objects present in the medium, reducing their rate of collapse or even allowing them to persist indefinitely. We use numerical simulations to study how different arrangements of non-reactive spheres affect the dynamics of circular filaments. As the filament contracts, it gets closer to and eventually touches and pins to objects in its path. This causes two possible behaviors. The filament can detach from the spheres in its path, slowing down the rate of contraction, or it can remain pinned to a collection of spheres. In general, more or larger spheres increase the chance that the filament remains pinned, but there are exceptions. It is possible for a small number of small spheres to support the filament and possible for the filament to pass through a large number of large spheres. Our work yields insights into the pinning of scroll waves in excitable tissue such as cardiac muscle, where scar tissue acts in a way similar to the non-reactive domains.

Varieties of reentrant dynamics

Experiments were carried out in monolayer tissue cultures of embryonic chick heart cells imaged using a calcium sensitive fluorescent dye. The cells were grown in annular geometries and in annular geometries with an isthmus connecting antipodal region of the annulus. We observed a large number of spatially different patterns of propagation consisting of one or more circulating waves. As well, we also observed rhythms in which rotors embedded in the annuli generated propagating pulses. These results demonstrate that many different patterns of excitation can be present in cardiac tissue with simple geometries.

Entrainment Mapping

Mapping during ventricular tachycardia (VT) aims to elucidate mechanism, describe myocardial propagation, and identify the origin and critical regions of VT that can be targeted for ablation, most commonly with radiofrequency ablation. Most VTs in structural heart disease are due to macro-reentry in and around scar. A combination of mapping techniques, including mapping to identify the arrhythmia substrate, activation sequence mapping, pace-mapping, and entrainment mapping, may be used to identify putative ablation targets. This review describes the principles of entrainment mapping as it pertains to catheter ablation of scar-related VT.

Pace Mapping to Localize the Critical Isthmus of Ventricular Tachycardia

Most postinfarct ventricular tachycardias (VT) are sustained by a reentrant mechanism. The "protected isthmus" of the reentrant circuit is critical for the maintenance of VTs and the target for catheter ablation. In this article, the authors describe the technique of pace-mapping during sinus rhythm to unmask postinfarct VT isthmuses. A pace-mapping map should be considered as the surrogate of an activation map during VT, in both patients with a normal heart and patients with a structural heart disease. Pace mapping is useful to unmask VT isthmuses in patients with postinfarct reentrant VTs.

Sympathetic modulation of electrical activation in normal and infarcted myocardium: implications for arrhythmogenesis

The influence of cardiac sympathetic innervation on electrical activation in normal and chronically infarcted ventricular myocardium is not understood. Yorkshire pigs with normal hearts (NL, n = 12) or anterior myocardial infarction (MI, n = 9) underwent high-resolution mapping of the anteroapical left ventricle at baseline and during left and right stellate ganglion stimulation (LSGS and RSGS, respectively). Conduction velocity (CV), activation times (ATs), and directionality of propagation were measured. Myocardial fiber orientation was determined using diffusion tensor imaging and histology. Longitudinal CV (CV_L) was increased by RSGS (0.98 ± 0.11 vs. 1.2 ± 0.14m/s, P < 0.001) but not transverse CV (CV_T). This increase was abrogated by β-adrenergic receptor and gap junction (GJ) blockade. Neither CV_L nor CV_T was increased by LSGS. In the peri-infarct region, both RSGS and LSGS shortened ARIs in sinus rhythm (423 ± 37 vs. 322 ± 30 ms, P < 0.001, and 423 ± 36 vs. 398 ± 36 ms, P = 0.035, respectively) and altered activation patterns in all animals. CV, as estimated by mean ATs, increased in a directionally dependent manner by RSGS (14.6 ± 1.2 vs. 17.3 ± 1.6 ms, P = 0.015), associated with GJ lateralization. RSGS and LSGS inhomogeneously modulated AT and induced relative or absolute functional activation delay in parts of the mapped regions in 75 and 67%, respectively, in MI animals, and in 0 and 15%, respectively, in control animals (P < 0.001 for both). In conclusion, sympathoexcitation increases CV in normal myocardium and modulates activation propagation in peri-infarcted ventricular myocardium. These data demonstrate functional control of arrhythmogenic peri-infarct substrates by sympathetic nerves and in part explain the temporal nature of arrhythmogenesis.NEW & NOTEWORTHY This study demonstrates regional control of conduction velocity in normal hearts by sympathetic nerves. In infarcted hearts, however, not only is modulation of propagation heterogeneous, some regions showed paradoxical conduction slowing. Sympathoexcitation altered propagation in all infarcted hearts studied, and we describe the temporal arrhythmogenic potential of these findings.Listen to this article's corresponding podcast at http://ajpheart.podbean.com/e/sympathetic-nerves-and-cardiac-propagation/.

Life-Threatening Ventricular Arrhythmias: Current Role of Imaging in Diagnosis and Risk Assessment

Sudden cardiac arrest continues to be a major cause of death from cardiovascular disease but our ability to predict patients at the highest risk of developing lethal ventricular arrhythmias remains limited. Left ventricular ejection fraction is inversely related to the risk of sudden death but has a low sensitivity and specificity for the population at risk. Nevertheless, it continues to be the main variable considered in identifying patients most likely to benefit from implantable defibrillators to prevent sudden death. Imaging myocardial sympathetic innervation with PET and SPECT as well as imaging characteristics of myocardial infarcts using gadolinium-enhanced cardiac magnetic resonance are emerging as imaging modalities that may further refine patient selection beyond ejection fraction. This review will primarily focus on employing advanced imaging approaches to identify patients with left ventricular dysfunction that are most likely to develop lethal arrhythmias and benefit from inserting a primary prevention implantable cardiac defibrillator. While not yet tested in prospective studies, we will review risk prediction models incorporating quantitative imaging and biomarkers that have been developed that appear promising to identify those at highest risk of sudden death.

Mathematical model of the atrioventricular nodal double response tachycardia and double-fire pathology

A proposed model consisting of two coupled models (Hodgkin-Huxley and Yanagihara-Noma-Irisawa model) is considered as a description of the heart's action potential. System of ordinary differential equations is used to recreate pathological behaviour in the conducting heart's system such as double fire and the most common tachycardia: atrioventricular nodal reentrant tachycardia (AVNRT). Part of the population has an abnormal accessory pathways: fast and slow (Fujiki, 2008). These pathways in the atrioventricular node (AV node) are anatomical and functional contributions of supraventricular tachycardia. However, the appearance of two pathways in the AV node may be a contribution of arrhythmia, which is caused by coexistent conduction by two pathways (called double fire). The difference in the conduction time between these pathways is the most important factor. This is the reason to introduce three types of couplings and delay to our system in order to reproduce various types of the AVNRT. In our research, introducing the feedback loops and couplings entails the creation of waves which can correspond to the re-entry waves occurring in the AVNRT. Our main aim is to study solutions of the given equations and take into consideration the influence of feedback and delays which occur in these pathological modes. We also present stability analysis for both components, that is Hodgkin-Huxley and Yanagihara-Noma-Irisawa models, as well as for the final double-fire model.

Anesthetic Management in Radiofrequency Catheter Ablation of Ventricular Tachycardia

Radiofrequency catheter ablation is increasingly being used to treat patients who have ventricular tachycardia, and anesthesiologists frequently manage their perioperative care. This narrative review is intended to familiarize anesthesiologists with preprocedural, intraprocedural, and postprocedural implications of this ablation. Ventricular tachycardia typically arises from structural heart disease, most often from scar tissue after myocardial infarction. Many patients thus affected will benefit from radiofrequency catheter ablation in the electrophysiology laboratory to ablate the foci of arrhythmogenesis. The pathophysiology of ventricular tachycardia is complex, as are the technical aspects of mapping and ablating these arrhythmias. Patients often have substantial comorbidities and tenuous hemodynamic status, necessitating pharmacologic and mechanical cardiopulmonary support. General anesthesia and monitored anesthesia care, when used for sedation during ablation, can lead to drug interactions and side effects in the presence of ventricular tachycardia, so anesthesiologists should also be aware of potential perioperative complications. We discuss variables that can help anesthesiologists safely guide patients through the challenges of radiofrequency catheter ablation of ventricular tachycardia.

Ablation of ischemic ventricular tachycardia: evidence, techniques, results, and future directions

PURPOSE OF REVIEW

This article summarizes current understanding of the arrhythmia substrate and effect of catheter ablation for infarct-related ventricular tachycardia, focusing on recent findings.

RECENT FINDINGS

Clinical studies support the use of catheter ablation earlier in the course of ischemic disease with moderate success in reducing arrhythmia recurrence and shocks from implantable defibrillators, although mortality remains unchanged. Ablation can be lifesaving for patients presenting with electrical storm. Advanced mapping systems with image integration facilitate identification of potential substrate, and several different approaches to manage hemodynamically unstable ventricular tachycardia have emerged. Novel ablation techniques that allow deeper lesion formation are in development.

SUMMARY

Catheter ablation is an important therapeutic option for preventing or reducing episodes of ventricular tachycardia in patients with ischemic cardiomyopathy. Present technologies allow successful ablation in the majority of patients, even when the arrhythmia is hemodynamically unstable. Failure of the procedure is often because of anatomic challenges that will hopefully be addressed with technological progress.

Incessant tachycardia in a patient with advanced heart failure and left ventricular assist device: What is the mechanism?

We present a case of incessant wide-complex tachycardia in a patient with left-ventricular assist device, and discuss the differential diagnosis with an in-depth analysis of the intracardiac tracings during the invasive electrophysiologic study, including interpretation of the relative timing of the fascicular signals during tachycardia and in sinus rhythm, and interpretation of pacing and entrainment maneuvers.

Multicenter Experience With Catheter Ablation for Ventricular Tachycardia in Lamin A/C Cardiomyopathy

Background—

Lamin A/C ( LMNA ) cardiomyopathy is a genetic disease with a proclivity for ventricular arrhythmias. We describe the multicenter experience with percutaneous catheter ablation of sustained monomorphic ventricular tachycardia (VT) in LMNA cardiomyopathy.

Methods and Results—

Twenty-five consecutive LMNA mutation patients from 4 centers were included (mean age, 55±9 years; ejection fraction, 34±12%; VT storm in 36%). Complete atrioventricular block was present in 11 patients; 3 patients were on mechanical circulatory support for severe heart failure. A median of 3 VTs were inducible per patient; in 82%, mapping was consistent with origin from scar in the basal left ventricle, particularly the septum, but also basal inferior wall and subaortic mitral continuity. After multiple procedures (median 2/patient; transcoronary alcohol in 6 and surgical cryoablation in 2 patients), acute success (noninducibility of any VT) was achieved in only 25% of patients. Partial success (inducibility of a nonclinical VT only: 50%) and failure (persistent inducibility of clinical VT: 12.5%) was attributed to intramural septal substrate in 13 of 18 patients (72%). Complications occurred in 25% of patients. After a median follow-up of 7 months after the last procedure, 91% experienced ≥1 VT recurrence, 44% received or were awaiting mechanical circulatory support or transplant for end-stage heart failure, and 26% died.

Conclusions—

Catheter ablation of VT associated with LMNA cardiomyopathy is associated with poor outcomes including high rate of arrhythmia recurrence, progression to end-stage heart failure, and high mortality. Basal septal scar and intramural VT origin makes VT ablation challenging in this population.

Ablating Premature Ventricular Complexes: Justification, Techniques, and Outcomes

We reviewed the underlying principles that allow for safe and effective ablation for premature ventricular complexes. Clinical scenarios that necessitate consideration for ablation, the underlying anatomy, and the unique consideration to maximize energy delivery without compromising safety are sequentially examined.

Long Postpacing Interval After Entrainment of Tachycardia Including a Slow Conduction Zone Within the Circuit

BACKGROUNDS

Postpacing interval (PPI) measured after entrainment pacing describes the distance between pacing site and reentrant circuit. However, the influential features to PPI remain to be elucidated.

METHODS AND RESULTS

This study included 22 cases with slow/fast atrioventricular (AV) nodal reentrant tachycardia (AVNRT), 14 orthodromic AV reciprocating tachycardia (AVRT) using an accessary pathway, 22 typical atrial flutter (AFL), and 18 other macroreentrant atrial tachycardia (atypical AFL). Rapid pacing at a pacing cycle length (PCL) 5% shorter than tachycardia cycle length (TCL) was done from a site on or close to the reentry circuit. Pacing sites included the coronary sinus ostium in AVNRT, earliest atrial activation site in AVRT, and cavotricuspid isthmus in typical AFL. In atypical AFL, tachycardia circuit was determined on the basis of CARTO mapping, and then the pacing site was. TCL was significantly longer in AVNRT and AVRT than in typical AFL and atypical AFL (both P < 0.05). PCL minus TCL value was similar among the 4 groups. PPI minus TCL value (milliseconds) was significantly longer in AVNRT (median, 40 [IQR, 29-60.8]) and AVRT (34 [20-47]) than in typical AFL (0 [0-4]) and atypical AFL (3.5 [0-8]) (both P < 0.05). Furthermore, PPI minus TCL was prolonged with shortening of PCL in AVNRT and AVRT (both P < 0.05), whereas it was unchanged in typical AFL (P = 0.50).

CONCLUSION

PPI after concealed entrainment is prolonged compared with TCL when the reentry circuit involves a slow conduction zone with a decremental conduction property such as the AV node.

ICD discrimination of SVT versus VT with 1:1 V-A conduction: A review of the literature

Inappropriate ICD shocks are associated with increased mortality. They also impair patients' quality of life, increase hospitalizations, and raise health-care costs. Nearly 80% of inappropriate ICD shocks are caused by supraventricular tachycardia. Here we report the case of a patient who received a single-lead dual-chamber sensing ICD for primary prevention of sudden cardiac death and experienced inappropriate ICD shocks. V-A time, electrogram morphology, and response to antitachycardia pacing suggested atrioventricular nodal reentry tachycardia, which was confirmed in an electrophysiology study. Inspired by this case, we performed a literature review to discuss mechanisms for discrimination of supraventricular tachycardia with 1:1 A:V relationship from ventricular tachycardia with 1:1 retrograde conduction.

Simultaneous Amplitude Frequency Electrogram Transformation (SAFE-T) Mapping to Identify Ventricular Tachycardia Arrhythmogenic Potentials in Sinus Rhythm

OBJECTIVES

This study sought to develop a novel automated technique, simultaneous amplitude frequency electrogram transformation (SAFE-T), to identify ventricular tachycardia (VT) isthmuses by analysis of sinus rhythm arrhythmogenic potentials (AP).

BACKGROUND

Substrate ablation is useful for patients with scar-related hemodynamically unstable VT; however, the accuracy of different approaches remains inadequate, varying from targeting late potentials to full scar homogenization.

METHODS

High-density ventricular mapping was performed in 3 groups: 1) 18 normal heart control subjects; 2) 10 ischemic patients; and 3) 8 nonischemic VT patients. In VT patients, isthmus sites were characterized using entrainment responses. Sinus rhythm right ventricle/left ventricle endocardial and epicardial electrograms underwent Hilbert-Huang spectral analysis and were displayed as 3-dimensional SAFE-T maps. AP and their relation to the VT isthmus sites were studied.

RESULTS

AP were defined by a cutoff value of 3.08 Hz mV using normal heart control subjects. Receiver-operating characteristics showed that VT isthmus sites were best identified using SAFE-T mapping (p < 0.001) as compared with bipolar and unipolar scar and late potential mapping with an optimal cutoff value of 3.09 Hz mV, allowing identification of 100% of the 34 mapped VT isthmuses, compared with 68% using late potentials. There was no significant difference between sinus rhythm and paced SAFE-T values. Abnormal SAFE-T areas involved about one-quarter of the scar total area.

CONCLUSIONS

Automated electrogram analysis using 3-dimensional SAFE-T mapping allows rapid and objective identification of AP that reliably detect VT isthmuses. The results suggest that SAFE-T mapping is good alternative strategy to late potential mapping in identifying VT isthmuses and allows reduced ablation as compared to scar homogenization.

Ablation of Ventricular Tachycardia in Patients with Ischemic Cardiomyopathy

Ventricular tachycardias (VTs) occurring after prior myocardial infarction are usually caused by reentrant circuits formed by surviving myocardial bundles. Although part of the reentrant circuits may be located in the midmyocardium or epicardium, most of the VTs can be safely and successfully ablated by endocardial ablation targeting the late potentials/local abnormal ventricular activation, which are surrogates for the surviving myocardial bundles. A combination of activation, substrate, pace, and entrainment mapping, as well as the use of contact force catheters, further improves ablation success and safety.

Therapy for ventricular arrhythmias in structural heart disease: a multifaceted challenge

The unpredictable nature and potentially catastrophic consequences of ventricular arrhythmias (VAs) have obligated physicians to search for therapies to prevent sudden cardiac death (SCD). At present, a low left ventricular ejection fraction (LVEF) has been used as a risk factor to predict SCD in patients with structural heart disease and has been consistently adopted as the predominant, and sometimes sole, indication for implantable cardioverter defibrillator (ICD) therapy. Although the ICD remains the mainstay life-saving therapy for SCD, it does not modify the underlying arrhythmic substrate and may be associated with adverse effects from perioperative and long-term complications. Preventative pharmacological therapy has been associated with limited benefits, but anti-arrhythmic medications have significant side effects profiles. Catheter ablation of VAs has greatly evolved over the last few decades. Substrate mapping in sinus rhythm has allowed haemodynamically unstable VAs to be successfully treated. Both LVEF as an indication for ICD therapy and electro-anatomical mapping for substrate modification identify static components of underlying myocardial arrhythmogenicity. They do not take into account dynamic factors, such as the mechanisms of arrhythmia initiation and development of new anatomical or functional lines of block, leading to the initiation and maintenance of VAs. Dynamic factors are difficult to evaluate and consequently are not routinely used in clinical practice to guide treatment. However, progress in the treatment of VAs should consider and integrate dynamic factors with static components to fully characterize the myocardial arrhythmic substrate.

Visualization of the Critical Isthmus by Tracking Delayed Potential in Edited Windows for Scar-Related Ventricular Tachycardia

Background and Objectives

Identifying the critical isthmus of slow conduction is crucial for successful treatment of scar-related ventricular tachycardia. Current 3D mapping is not designed for tracking the critical isthmus and may lead to a risk of extensive ablation. We edited the algorithm to track the delayed potential in order to visualize the isthmus and compared the edited map with a conventional map.

Subjects and Methods

We marked every point that showed delayed potential with blue color. After substrate mapping, we edited to reset the annotation from true ventricular potential to delayed potential and then changed the window of interest from the conventional zone (early, 50-60%; late, 40-50% from peak of QRS) to the edited zone (early, 80-90%; late, 10-20%) for every blue point. Finally, we compared the propagation maps before and after editing.

Results

We analyzed five scar-related ventricular tachycardia cases. In the propagation maps, the resetting map showed the critical isthmus and entrance and exit sites of tachycardia that showed figure 8 reentry. However, conventional maps only showed the earliest ventricular activation sites and searched for focal tachycardia. All of the tachycardia cases were terminated by ablating the area around the isthmus.

Conclusion

Identifying the channel and direction of the critical isthmus by a new editing method to track delayed potential is essential in scar-related tachycardia.

Usefulness of combined CARTO electroanatomical mapping and manifest entrainment in ablating adenosine triphosphate-sensitive atrial tachycardia originating from the atrioventricular node vicinity

Background

By using a noncontact mapping system, adenosine triphosphate (ATP)-sensitive atrial tachycardia (ATP-AT) originating from the atrioventricular (AV) node vicinity was successfully ablated at the entrance to the slow conduction zone indicated by the manifest entrainment technique. We aimed to prospectively validate the efficacy of the combination of CARTO electroanatomical mapping and manifest entrainment in ablating this ATP-AT.

Methods

Of the 27 AT patients from January 2013 to March 2014, 6 patients with sustained ATP-AT were studied (age, 67±13 years; tachycardia cycle length, 350±95 ms). We first created the CARTO map during AT, and performed rapid pacing from the anterior right atrial wall (ARAW) and cavotricuspid isthmus (CTI) approximately 30 mm remote from the earliest activation site (EAS). We identified the site where manifest entrainment, defined as the orthodromic capture of the EAS with a long conduction time, was observed, and ablated the site approximately 20 mm remote from the EAS, between the pacing site and the EAS.

Results

Manifest entrainment was demonstrated in all patients paced from the ARAW (four patients) and from the CTI (two patients). Ablation at the prespecified site terminated AT in 6±3 s, and AT became no longer inducible in all patients. At the successful ablation sites, discrete atrial electrograms were recorded; however, low-amplitude, fractionated electrograms suggestive of slow conduction were not observed in all patients. The atrio-His interval during sinus rhythm remained unchanged (from 96±12 to 89±7 ms, p=NS). During 11±6 months, no patients showed AT recurrence and AV conduction abnormality.

Conclusion

CARTO mapping- and manifest entrainment-guided ablation strategy is effective and safe in the treatment of ATP-AT.

The precise timing of tachycardia entrainment is determined by the postpacing interval, the tachycardia cycle length, and the pacing rate: Theoretical insights and practical applications

BACKGROUND

Previous observations have reported that the number of pacing stimuli required to entrain a tachycardia varies on the basis of arrhythmia type and location, but a quantitative formulation of the number needed to entrain (NNE) that unifies these observations has not been characterized.

OBJECTIVE

We sought to investigate the relationship between the number of pacing stimulations, the tachycardia cycle length (TCL), the overdrive pacing cycle length (PCL), and the postpacing interval (PPI) to accurately estimate the timing of tachycardia entrainment.

METHODS

First, we detailed a mathematical derivation unifying electrophysiological parameters with empirical confirmation in 2 patients undergoing catheter ablation of typical atrial flutter. Second, we validated our formula in 44 patients who underwent various catheter ablation procedures. For accuracy, we corrected for rate-related changes in conduction velocity.

RESULTS

We derived the equations NNE = |(PPI - TCL)/(TCL - PCL)| + 1 and Tachycardia advancement = (NNE - 1) × (TCL - PCL) - (PPI - TCL), which state that the NNE and the amount of tachycardia advancement on the first resetting stimulation are determined using regularly measured intracardiac parameters. In the retrospective cohort, the observed PPI - TCL highly correlated with the predicted PPI - TCL (mean difference 5.8 ms; r = 0.97; P < .001), calculated as PPI - TCL = (NNE - 1) × (TCL - PCL) - tachycardia advancement.

CONCLUSION

The number of pacing stimulations required to entrain a reentrant tachycardia is predictable at any PCL after correcting for cycle length-dependent changes in conduction velocity. This relationship unifies established empirically derived diagnostic and mapping criteria for supraventricular tachycardia and ventricular tachycardia. This relationship may help elucidate when antitachycardia pacing episodes are ineffective or proarrhythmic and could potentially serve as a theoretical basis to customize antitachycardia pacing settings for improved safety and effectiveness.

Epicardial Radiofrequency Ablation Failure During Ablation Procedures for Ventricular Arrhythmias

Background—

Radiofrequency ablation (RFA) from the epicardial space for ventricular arrhythmias is limited or impossible in some cases. Reasons for epicardial ablation failure and the effect on outcome have not been systematically analyzed.

Methods and Results—

We assessed reasons for epicardial RFA failure relative to the anatomic target area and the type of heart disease and assessed the effect of failed epicardial RFA on outcome after ablation procedures for ventricular arrhythmias in a large single-center cohort. Epicardial access was attempted during 309 ablation procedures in 277 patients and was achieved in 291 procedures (94%). Unlimited ablation in an identified target region could be performed in 181 cases (59%), limited ablation was possible in 22 cases (7%), and epicardial ablation was deemed not feasible in 88 cases (28%). Reasons for failed or limited ablation were unsuccessful epicardial access (6%), failure to identify an epicardial target (15%), proximity to a coronary artery (13%), proximity to the phrenic nerve (6%), and complications (<1%). Epicardial RFA was impeded in the majority of cases targeting the left ventricular summit region. Acute complications occurred in 9%. The risk for acute ablation failure was 8.3× higher (4.5–15.0; P <0.001) after no or limited epicardial RFA compared with unlimited RFA, and patients with unlimited epicardial RFA had better recurrence-free survival rates ( P <0.001).

Conclusions—

Epicardial RFA for ventricular arrhythmias is often limited even when pericardial access is successful. Variability of success is dependent on the target area, and the presence of factors limiting ablation is associated with worse outcomes.

Determining the Site of Accessory Pathways in Orthodromic Reciprocating Tachycardia by Using the Response to Right Ventricular Pacing

BACKGROUND

Postpacing interval (PPI) after right ventricular (RV) pacing entrainment minus tachycardia cycle length (TCL) with a correction for atrioventricular (AV) node delay (corrected PPI-TCL) was useful to differentiate atrioventricular node reentrant tachycardia (AVNRT) from orthodromic reciprocating tachycardia (ORT). However, the value of corrected PPI-TCL in determining the site of the accessory pathway (AP) in ORT has not been investigated. The purpose of this study was to assess whether the corrected PPI-TCL is useful in differentiating ORT using a left-sided AP from a right-sided AP.

METHODS

We studied 52 patients with ORT using a left-sided AP and 13 patients with a right-sided AP. The PPI was measured upon cessation of the RV pacing at a cycle length 10-40 ms shorter than the TCL. The corrected PPI-TCL was calculated from the subtraction of the increment in AV nodal conduction time of the first PPI from the PPI-TCL.

RESULTS

The mean corrected PPI-TCL was 83 ± 20 ms in patients with ORT using a left-sided AP and 27 ± 19 ms in patients with a right-sided AP (P ≤ 0.001). All patients with ORT using a left-sided AP except three patients with left septal AP and none of the patients with ORT using a right-sided AP had a corrected PPI-TCL > 55 ms.

CONCLUSIONS

The corrected PPI-TCL after the RV pacing entrainment is useful to guide differentiating ORT using a left-sided AP from a right-sided AP.

Substrate Mapping for Ventricular Tachycardia: Assumptions and Misconceptions

Substrate mapping was developed to treat poorly tolerated infarct-related ventricular tachycardias (VTs). This concept was based on 30-year-old data derived from surgical and percutaneous mapping during sinus rhythm and VT that demonstrated specific electrograms (EGMs) that characterized the "arrhythmogenic substrate" of VT. Electrogram characteristics of the arrhythmogenic VT substrate during sinus rhythm included low-voltage, fractionation, long duration, split signals, and isolated late potentials as well as EGMs demonstrating adjacent early and late activation. Introduction of electroanatomical mapping (EAM) systems during the mid-1990s has allowed investigators to record electrograms in 3 dimensions and to identify sites assumed to represent the central common pathway ("isthmus") during re-entrant VTs. However, several important assumptions and misconceptions make currently used "substrate mapping" techniques inaccurate. These include: 1) re-entrant circuits are produced by fixed barriers of immutable "inexcitable" scar; 2) low voltage amplitude (≤0.5 mV) implies dense "inexcitable" scar; 3) isthmuses identified in patients with tolerated VTs using entrainment mapping are both valid and provide an accurate depiction of isthmuses in less hemodynamically tolerated VTs; and 4) current mapping tools and methods can delineate specific electrophysiologic features that will determine the barriers forming channels during re-entrant VTs. None of these assumptions has been validated and recent experimental and human data using higher resolution mapping with very small electrodes cast doubt on their validity. These data call for re-evaluation of substrate-mapping techniques to characterize the arrhythmogenic substrate of post-infarction VT. Standardization of recording techniques including electrode size, interelectrode spacing, tissue contact, catheter orientation, and wavefront activation must be taken into consideration.

Sudden cardiac death risk stratification

Arrhythmic sudden cardiac death (SCD) may be caused by ventricular tachycardia/fibrillation or pulseless electric activity/asystole. Effective risk stratification to identify patients at risk of arrhythmic SCD is essential for targeting our healthcare and research resources to tackle this important public health issue. Although our understanding of SCD because of pulseless electric activity/asystole is growing, the overwhelming majority of research in risk stratification has focused on SCD-ventricular tachycardia/ventricular fibrillation. This review focuses on existing and novel risk stratification tools for SCD-ventricular tachycardia/ventricular fibrillation. For patients with left ventricular dysfunction or myocardial infarction, advances in imaging, measures of cardiac autonomic function, and measures of repolarization have shown considerable promise in refining risk. Yet the majority of SCD-ventricular tachycardia/ventricular fibrillation occurs in patients without known cardiac disease. Biomarkers and novel imaging techniques may provide further risk stratification in the general population beyond traditional risk stratification for coronary artery disease alone. Despite these advances, significant challenges in risk stratification remain that must be overcome before a meaningful impact on SCD can be realized.

Freedom from recurrent ventricular tachycardia after catheter ablation is associated with improved survival in patients with structural heart disease: An International VT Ablation Center Collaborative Group study

BACKGROUND

The impact of catheter ablation of ventricular tachycardia (VT) on all-cause mortality remains unknown.

OBJECTIVE

The purpose of this study was to examine the association between VT recurrence after ablation and survival in patients with scar-related VT.

METHODS

Analysis of 2061 patients with structural heart disease referred for catheter ablation of scar-related VT from 12 international centers was performed. Data on clinical and procedural variables, VT recurrence, and mortality were analyzed. Kaplan-Meier analysis was used to estimate freedom from recurrent VT, transplant, and death. Cox proportional hazards frailty models were used to analyze the effect of risk factors on VT recurrence and mortality.

RESULTS

One-year freedom from VT recurrence was 70% (72% in ischemic and 68% in nonischemic cardiomyopathy). Fifty-seven patients (3%) underwent cardiac transplantation, and 216 (10%) died during follow-up. At 1 year, the estimated rate of transplant and/or mortality was 15% (same for ischemic and nonischemic cardiomyopathy). Transplant-free survival was significantly higher in patients without VT recurrence than in those with recurrence (90% vs 71%, P<.001). In multivariable analysis, recurrence of VT after ablation showed the highest risk for transplant and/or mortality [hazard ratio 6.9 (95% CI 5.3-9.0), P<.001]. In patients with ejection fraction <30% and across all New York Heart Association functional classes, improved transplant-free survival was seen in those without VT recurrence.

CONCLUSION

Catheter ablation of VT in patients with structural heart disease results in 70% freedom from VT recurrence, with an overall transplant and/or mortality rate of 15% at 1 year. Freedom from VT recurrence is associated with improved transplant-free survival, independent of heart failure severity.

Core Isolation of Critical Arrhythmia Elements for Treatment of Multiple Scar-Based Ventricular Tachycardias

Background—

Radiofrequency ablation of multiple or unmappable ventricular tachycardias (VTs) remains a challenge with unclear end points. We present our experience with a new strategy isolating core elements of VT circuits.

Methods and Results—

Patients with structural heart disease presenting for VT radiofrequency ablation at 2 centers were included. Strategy involved entrainment/activation mapping if VT was hemodynamically stable, and voltage mapping with electrogram analysis and pacemapping. Core isolation (CI) was performed incorporating putative isthmus and early exit site(s) based on standard criteria. If VT was noninducible, the dense scar (<0.5 mV) region was isolated. Successful CI was defined by exit block (20 mA at 2 ms) within the isolated region. VT inducibility was also assessed. Forty-four patients were included (mean age, 63; 95% male; 73% ischemic cardiomyopathy; mean left ventricular ejection fraction, 31%; 68% with multiple unstable VTs [mean, 3+2]). CI area was 11+12 versus 55+40 cm 2 total scar area. Additional substrate modification was performed in 27 (61%), and epicardial radiofrequency ablation was performed in 4 (9%) patients. CI was achieved in 37 (84%) and led to better VT-free survival (log rank P =0.013).

Conclusions—

CI is a novel strategy with a discrete and measurable end point beyond VT inducibility to treat patients with multiple or unmappable VTs. The CI region can be selected based on standard characterization of suspected VT isthmus surrogates thus limiting ablation target size. Exit block within the isolated area is achievable in most and may further improve long-term success.

Relationship between sinus rhythm late activation zones and critical sites for scar-related ventricular tachycardia: systematic analysis of isochronal late activation mapping

BACKGROUND

It is not known whether the most delayed late potentials are functionally most specific for scar-related ventricular tachycardia (VT) circuits.

METHODS AND RESULTS

Isochronal late activation maps were constructed to display ventricular activation during sinus rhythm over 8 isochrones. Analysis was performed at successful VT termination sites and prospectively tested. Thirty-three patients with 47 scar-related VTs where a critical site was demonstrated by termination of VT during ablation were retrospectively analyzed. In those who underwent mapping of multiple surfaces, 90% of critical sites were on the surface that contained the latest late potential. However, only 11% of critical sites were localized to the latest isochrone (87.5%-100%) of ventricular activation. The median percentage of latest activation at critical sites was 78% at a distance from the latest isochrone of 18 mm. Sites critical to reentry were harbored in regions with slow conduction velocity, where 3 isochrones were present within a 1-cm radius. Ten consecutive patients underwent ablation prospectively guided by isochronal late activation maps, targeting concentric isochrones outside of the latest isochrone. Elimination of the targeted VT was achieved in 90%. Termination of VT was achieved in 6 patients at a mean ventricular activation percentage of 78%, with only 1 requiring ablation in the latest isochrone.

CONCLUSIONS

Late potentials identified in the latest isochrone of activation during sinus rhythm are infrequently correlated with successful ablation sites for VT. The targeting of slow conduction regions propagating into the latest zone of activation may be a novel and promising strategy for substrate modification.

Successful Ablation of Single Reentrant Ventricular Tachycardia Arising from Peri-Aortic Scar in a Patient with an Apparently Normal Heart

Peri-aortic region is one of the arrhythmogenic foci associated not only with idiopathic ventricular tachycardia (VT), but also scar-related VT in patients with an apparently normal heart.[1-3] A recent study reported that the patients with scar-related VT were significantly older, had a frequent history of hypertension, and inducibility of multiple monomorphic VTs compared to the patients with idiopathic VT.[2] However, whether these clinical features are the causes of the peri-aortic scar or innocent by-standers, remain uncertain. Here, we present a relatively young normotensive patient with a peri-aortic scar and emphasize the importance of cardiac MRI to detect latent arrhthmogenic substrates.

Application of ripple mapping to visualize slow conduction channels within the infarct-related left ventricular scar

BACKGROUND

Ripple mapping (RM) displays each electrogram at its 3-dimensional coordinate as a bar changing in length according to its voltage-time relationship with a fiduciary reference. We applied RM to left ventricular ischemic scar for evidence of slow-conducting channels that may act as ventricular tachycardia (VT) substrate.

METHODS AND RESULTS

CARTO-3© (Biosense Webster Inc, Diamond Bar, CA) maps in patient undergoing VT ablation were analyzed on an offline MatLab RM system. Scar was assessed for sequential movement of ripple bars, during sinus rhythm or pacing, which were distinct from surrounding tissue and termed RM conduction channels (RMCC). Conduction velocity was measured within RMCCs and compared with the healthy myocardium (>1.5 mV). In 21 maps, 77 RMCCs were identified. Conduction velocity in RMCCs was slower when compared with normal left ventricular myocardium (median, 54 [interquartile range, 40-86] versus 150 [interquartile range, 120-160] cm/s; P<0.001). All 7 sites meeting conventional criteria for diastolic pathways coincided with an RMCC. Seven patients had ablation colocating to all identified RMCCs with no VT recurrence during follow-up (median, 480 [interquartile range, 438-841] days). Fourteen patients had ≥1 RMCC with no ablation lesions. Five had recurrence during follow-up (median, 466 [interquartile range, 395-694] days). One of the 2 patients with no RMCC locations ablated had VT recurrence at 605 days post procedure. RMCCs were sensitive (100%; negative predictive value, 100%) for VT recurrence but the specificity (43%; positive predictive value, 35.7%) may be limited by blind alleys channels.

CONCLUSIONS

RM identifies slow conduction channels within ischemic scar and needs further prospective investigation to understand the role of RMCCs in determining the VT substrate.

Ventricular tachycardia in cardiac sarcoidosis: characterization of ventricular substrate and outcomes of catheter ablation

BACKGROUND

Cardiac sarcoid-related ventricular tachycardia (VT) is a rare disorder; the underlying substrate and response to ablation are poorly understood. We sought to examine the ventricular substrate and outcomes of catheter ablation in this population.

METHODS AND RESULTS

Of 435 patients with nonischemic cardiomyopathy referred for VT ablation, 21 patients (5%) had cardiac sarcoidosis. Multiple inducible VTs were observed with mechanism consistent with scar-mediated re-entry in all VTs. Voltage maps showed widespread and confluent right ventricular scarring. Left ventricular scarring was patchy with a predilection for the basal septum, anterior wall, and perivalvular regions. Epicardial right ventricular scar overlay and exceeded the region of corresponding endocardial scar. After ≥1 procedures, ablation abolished ≥1 inducible VT in 90% and eliminated VT storm in 78% of patients; however, multiple residual VTs remained inducible. Failure to abolish all inducible VTs was because of septal intramural circuits or extensive right ventricular scarring. Multiple procedure VT-free survival was 37% at 1 year, but VT control was achievable in the majority of patients with fewer antiarrhythmic drugs compared with preablation (2.1±0.8 versus 1.1±0.8; P<0.001).

CONCLUSIONS

Patients with cardiac sarcoidosis and VT exhibit ventricular substrate characterized by confluent right ventricular scarring and patchy left ventricular scarring capable of sustaining a large number of re-entrant circuits. Catheter ablation is effective in terminating VT storm and eliminating ≥1 inducible VT in the majority of patients, but recurrences are common. Ablation in conjunction with antiarrhythmic drugs can help palliate VT in this high-risk population.

Molecular imaging to predict ventricular arrhythmia in heart failure

Ventricular tachycardia (VT) is a major cause of sudden cardiac death (SCD) in patients with heart failure (HF). Left ventricular ejection fraction (LVEF) and heart failure class according to the New York Heart association (NYHA) are in most common use to identify patients that may benefit from implantable cardioverter defibrillator (ICD) therapy. But during 3 years of follow up only 35% of patients receive appropriate ICD action. Therefore, there is a continued need for refinement of selection criteria for ICD implantation. In this regard, molecular imaging of the autonomic nervous system, which plays a central role in HF progression and cardiac electro-mechanical regulation, can make a substantial contribution. This article reviews the currently available literature concerning the value of molecular neuronal cardiac imaging for prediction of ventricular arrhythmias in HF patients.

Ventricular Tachycardia Ablation - The Right Approach for the Right Patient

Scar-related reentry is the most common mechanism of monomorphic ventricular tachycardia (VT) in patients with structural heart disease. Catheter ablation has assumed an increasingly important role in the management of VT in this setting, and has been shown to reduce VT recurrence and implantable cardioverter defibrillator (ICD) shocks. The approach to mapping and ablation will depend on the underlying heart disease etiology, VT inducibility and haemodynamic stability. This review explores pre-procedural planning, approach to ablation of both mappable and unmappable VT, and post-procedural testing. Future developments in techniques and technology that may improve outcomes are discussed.

Left-Sided Ablation of Ventricular Tachycardia in Adults With Repaired Tetralogy of Fallot

Background—

Radiofrequency catheter ablation (RFCA) of ventricular tachycardia (VT) in repaired Tetralogy of Fallot focuses on isthmuses in the right ventricle but may be hampered by hypertrophied myocardium or prosthetic material. These patients may benefit from ablation at the left side of the ventricular septum.

Methods and Results—

Records from 28 consecutive repaired Tetralogy of Fallot patients from 2 centers who underwent VT ablation were reviewed. Ablation targeted anatomic isthmuses containing VT re-entry circuits, which were identified by 3-dimensional substrate, pace, and entrainment mapping. A left-sided approach was considered beneficial if (1) right-sided RFCA failed, (2) part of the circuit was mapped to the left side, and (3) left-sided RFCA resulted in isthmus transection and prevention of VT induction. In 4 of 28 patients (52±13 years; 75% men), inducible for 1.5 (quartiles, 1.0 – 2.0) VTs (335±58 ms), left-sided RFCA was performed. In 3 patients, RFCA at aortic sites terminated VT related to a septal isthmus and prevented reinduction. In 1 patient, with prior biventricular implantable cardioverter-defibrillator, diastolic activity was recorded at the left side of the septum in proximity to the His-bundle. RFCA prevented VT reinduction with anticipated complete atrioventricular block. The left-sided approach resulted in complete procedural success (transection of anatomic isthmus and noninducibility) and freedom of VT recurrence during follow-up (20±15 months) in all patients. Right-sided RFCA failure was likely because of septal hypertrophy in 2, overlying pulmonary homograft in 1, and overlying ventricular septal defect patch in 1.

Conclusions—

Left-sided RFCA for VTs dependent on septal anatomic isthmuses improves ablation outcome in repaired Tetralogy of Fallot.

I-123 mIBG and Tc-99m myocardial SPECT imaging to predict inducibility of ventricular arrhythmia on electrophysiology testing: a retrospective analysis

OBJECTIVES

The purpose of this study is to assess mIBG uptake in scar border zone and its relation with ventricular arrhythmia (VA) inducibility on electrophysiology (EP) testing using I-123 mIBG SPECT and resting Tc-99m SPECT myocardial perfusion imaging (MPI).

METHODS

Forty-seven patients from a previous clinical trial were retrospectively analyzed. These patients underwent I-123 mIBG and resting Tc-99m tetrofosmin SPECT, and EP testing. Twenty-eight patients were positive (EP+) and 19 patients were negative (EP-) for inducibility of sustained (>30 seconds) VA on EP testing. MPI scar extent, border zone extent, and mIBG uptake in border zone were used to predict VA inducibility on EP testing, respectively.

RESULTS

There was no significant difference in scar extent between the EP+ and EP- groups. The EP+ group had significantly larger border zone and lower mIBG uptake ratio in the border zone than the EP- group. Receiver operating characteristic (ROC) curve analysis showed that the prediction accuracy for border zone extent (area under ROC = 0.75) was better than scar extent (area under ROC = 0.66). The prediction accuracy was further improved (area under ROC = 0.78), when assessing mIBG uptake in the border zone.

CONCLUSION

A new tool has been developed to measure scar and border zone and to assess mIBG uptake in scar and border zone from combined I-123 MIBG SPECT and resting Tc-99m SPECT MPI. The mIBG uptake in the border zone predicted VA inducibility on EP testing with a promising accuracy.

Computational model of erratic arrhythmias in a cardiac cell network: the role of gap junctions

Cardiac morbidity and mortality increases with the population age. To investigate the underlying pathological mechanisms, and suggest new ways to reduce clinical risks, computational approaches complementing experimental and clinical investigations are becoming more and more important. Here we explore the possible processes leading to the occasional onset and termination of the (usually) non-fatal arrhythmias widely observed in the heart. Using a computational model of a two-dimensional network of cardiac cells, we tested the hypothesis that an ischemia alters the properties of the gap junctions inside the ischemic area. In particular, in agreement with experimental findings, we assumed that an ischemic episode can alter the gap junctions of the affected cells by reducing their average conductance. We extended these changes to include random fluctuations with time, and modifications in the gap junction rectifying conductive properties of cells along the edges of the ischemic area. The results demonstrate how these alterations can qualitatively give an account of all the main types of non-fatal arrhythmia observed experimentally, and suggest how premature beats can be eliminated in three different ways: a) with a relatively small surgical procedure, b) with a pharmacological reduction of the rectifying conductive properties of the gap-junctions, and c) by pharmacologically decreasing the gap junction conductance. In conclusion, our model strongly supports the hypothesis that non-fatal arrhythmias can develop from post-ischemic alteration of the electrical connectivity in a relatively small area of the cardiac cell network, and suggests experimentally testable predictions on their possible treatments.