Relationship of slow conduction detected by pace-mapping to ventricular tachycardia re-entry circuit sites after infarction

Substrate-based approaches in ventricular tachycardia ablation

Catheter ablation for ventricular tachycardia (VT) in patients with structural heart disease is now part of standard care. Mapping and ablation of the clinical VT is often limited when the VT is noninducible, nonsustained or not haemodynamically tolerated. Substrate-based ablation strategies have been developed in an aim to treat VT in this setting and, subsequently, have been shown to improve outcomes in VT ablation when compared to focused ablation of mapped VTs. Since the initial description of linear ablation lines targeting ventricular scar, many different approaches to substrate-based VT ablation have been developed. Strategies can broadly be divided into three categories: 1) targeting abnormal electrograms, 2) anatomical targeting of conduction channels between areas of myocardial scar, and 3) targeting areas of slow and/or decremental conduction, identified with “functional” substrate mapping techniques. This review summarises contemporary substrate-based ablation strategies, along with their strengths and weaknesses.

Epicardial and Endocardial Ablation Based on Channel Mapping in Patients With Ventricular Tachycardia and Chronic Chagasic Cardiomyopathy: Importance of Late Potential Mapping During Sinus Rhythm to Recognize the Critical Substrate

Background

Ventricular tachycardia (VT) in patients with chronic chagasic cardiomyopathy (CCC) is associated with considerable morbidity and mortality. Catheter ablation of VT in patients with CCC is very complex and challenging. The main goal of this work was to assess the efficacy of VT catheter ablation guided by late potentials (LPs) in patients with CCC.

Methods and Results

Seventeen consecutive patients with refractory VT and CCC were prospectively included in the study. Combined endo‐epicardial voltage and late activation mapping were obtained during baseline rhythm to define scarred and LP areas, respectively. The end point of the ablation procedure was the elimination of all identified LPs. Epicardial and endocardial dense scars (<0.5 mV) were detected in 17/17 and 15/17 patients, respectively. LPs were detected in the epicardial scars of 16/17 patients and in the endocardial scars of 14/15 patients. A total of 63 VTs were induced in 17 patients; 22/63 (33%) were stable and entrained, presenting LPs recorded in the isthmus sites. The end point of ablation was achieved in 15 of 17 patients. Ablation was not completed in 2 patients because of cardiac tamponade or vicinity of the phrenic nerve and circumflex artery. Three patients (2 with unsuccessful ablation) had VT recurrence during follow‐up (39 months).

Conclusions

Endo‐epicardial LP mapping allows us to identify the putative isthmuses of different VTs and effectively perform catheter ablation in patients with CCC and drug‐refractory VTs.

A novel algorithm for 3-D visualization of electrogram duration for substrate-mapping in patients with ischemic heart disease and ventricular tachycardia

BACKGROUND

Myocardial slow conduction is a cornerstone of ventricular tachycardia (VT). Prolonged electrogram (EGM) duration is a useful surrogate parameter and manual annotation of EGM characteristics are widely used during catheter-based ablation of the arrhythmogenic substrate. However, this remains time-consuming and prone to inter-operator variability. We aimed to develop an algorithm for 3-D visualization of EGM duration relative to the 17-segment American Heart Association model.

METHODS

To calculate and visualize EGM duration, in sinus rhythm acquired high-density maps of patients with ischemic cardiomyopathy undergoing substrate-based VT ablation using a 64-mini polar basket-catheter with low noise of 0.01 mV were analyzed. Using a custom developed algorithm based on standard deviation and threshold, the relationship between EGM duration, endocardial voltage and ablation areas was studied by creating 17-segment 3-D models and 2-D polar plots.

RESULTS

140,508 EGMs from 272 segments (n = 16 patients, 94% male, age: 66±2.4, ejection fraction: 31±2%) were studied and 3-D visualization of EGM duration was performed. Analysis of signal processing parameters revealed that a 40 ms sliding SD-window, 15% SD-threshold and >70 ms EGM duration cutoff was chosen based on diagnostic odds ratio of 12.77 to visualize rapidly prolonged EGM durations. EGMs > 70 ms matched to 99% of areas within dense scar (<0.2 mV), in 95% of zones within scar border zone (0.2-1.0 mV) and detected ablated areas having resulted in non-inducibility at the end of the procedure. Ablation targets were identified with a sensitivity of 65.6% and a specificity of 94.6% avoiding false positive labeling of prolonged EGMs in segments with healthy myocardium.

CONCLUSION

The novel algorithm allows rapid visualization of prolonged EGM durations. This may facilitate more objective characterization of arrhythmogenic substrate in patients with ischemic cardiomyopathy.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

Accurate Conduction Velocity Maps and Their Association With Scar Distribution on Magnetic Resonance Imaging in Patients With Postinfarction Ventricular Tachycardias

BACKGROUND

Characterizing myocardial conduction velocity (CV) in patients with ischemic cardiomyopathy (ICM) and ventricular tachycardia (VT) is important for understanding the patient-specific proarrhythmic substrate of VTs and therapeutic planning. The objective of this study is to accurately assess the relation between CV and myocardial fibrosis density on late gadolinium-enhanced cardiac magnetic resonance imaging (LGE-CMR) in patients with ICM.

METHODS

We enrolled 6 patients with ICM undergoing VT ablation and 5 with structurally normal left ventricles (controls) undergoing premature ventricular contraction or VT ablation. All patients underwent LGE-CMR and electroanatomic mapping (EAM) in sinus rhythm (2960 electroanatomic mapping points analyzed). We estimated CV from electroanatomic mapping local activation time using the triangulation method that provides an accurate estimate of CV as it accounts for the direction of wavefront propagation. We evaluated the association between LGE-CMR intensity and CV with multilevel linear mixed models.

RESULTS

Median CV in patients with ICM and controls was 0.41 m/s and 0.65 m/s, respectively. In patients with ICM, CV in areas with no visible fibrosis was 0.81 m/s (95% CI, 0.59-1.12 m/s). For each 25% increase in normalized LGE intensity, CV decreased by 1.34-fold (95% CI, 1.25-1.43). Dense scar areas have, on average, 1.97- to 2.66-fold slower CV compared with areas without dense scar. Ablation lesions that terminated VTs were localized in areas of slow conduction on CV maps.

CONCLUSIONS

CV is inversely associated with LGE-CMR fibrosis density in patients with ICM. Noninvasive derivation of CV maps from LGE-CMR is feasible. Integration of noninvasive CV maps with electroanatomic mapping during substrate mapping has the potential to improve procedural planning and outcomes. Visual Overview: A visual overview is available for this article.

Clinical, procedural and long-term outcome of ischemic VT ablation in patients with previous anterior versus inferior myocardial infarction

Background

Outcome of ischemic VT ablation may differ between patients with previous myocardial infarction (MI) in relation to infarct localization.

Methods

We analyzed procedural data, acute and long-term outcomes of 152 consecutive patients (139 men, mean age 67 ± 9 years) with previous anterior or inferior MI who underwent ischemic VT ablation at our institution between January 2010 and October 2015.

Results

More patients had a history of inferior MI (58%). Mean ejection fraction was significantly lower in anterior MI patients (28 ± 10% vs. 34 ± 10%, p < 0.001). NYHA class and presence of comorbidities were not different between the groups. Indication for the procedure was electrical storm in 43% of patients, and frequent implantable cardioverter defibrillator (ICD) therapies in 57%, and did not differ significantly between anterior and inferior MI patients. A mean of 3 ± 2 VT morphologies were inducible, with a trend towards more VT in the anterior MI group (3.1 ± 2.2 vs. 2.6 ± 1.9, p = 0.18). Procedural parameters and acute success did not differ between the groups. During a mean follow-up of 3 ± 2 years, more anterior MI patients had undergone a re-ablation (49% vs. 33%, p = 0.09, Chi-square test). There was a trend towards more ICD shocks in patients with previous anterior MI (46% vs. 34%). After adjusting for risk factors and ejection fraction, multivariable Cox regression analyses showed no significant difference in mortality (p = 0.78) and cardiovascular mortality between infarct localizations (p = 0.6).

Conclusion

Clinical characteristics of patients with anterior and inferior MI are similar except for ejection fraction. Patients with inferior MI appear to have better outcome regarding survival, ICD shocks and re-ablation, but this appears to be related to better ejection fraction when compared with anterior MI.

An efficient algorithm based on electrograms characteristics to identify ventricular tachycardia isthmus entrance in post-infarct patients

AIMS

Our study assesses the value of electrograms (EGMs) characteristics to identify a ventricular tachycardia (VT) isthmus entrance in patients with post-infarct VT. Post-infarct VTs are mostly due to a re-entrant circuit. A pacemapping (PM) approach is able to localize the VT isthmus during sinus rhythm. Limited data are available about the role of local EGMs in defining VT isthmus location.

METHODS AND RESULTS

Twenty consecutive patients (70% male) referred for post-infarct VT catheter ablation were included in the present study. The VT isthmus was defined according to the PM method. At each recording site, 10 characteristics of the local EGM were assessed to predict the location of the VT isthmus entrance. In total, 924 EGMs were acquired, of which 127 were located in the VT isthmus entrance. Logistic regression analysis showed that bipolar voltage, number of EGM positive peaks, and sQRS interval were independently associated with VT isthmus entrance location. The ROC curve best fitted the model at the cut-off 0.1641 (sensitivity 72%, specificity 75.2%, positive predictive value 31.3%, negative predictive value 94.4%, area under the curve 0.78, P < 0.001). Based upon these results, we developed an algorithm implemented in an automatic calculator to determine the likelihood that an EGM is located at a VT isthmus entrance.

CONCLUSION

Our study suggests that three EGM characteristics: bipolar voltage, number of positive peaks, and sQRS interval can successfully identify a VT isthmus entrance in post-infarct patients.

Evaluation of a real-time magnetic resonance imaging-guided electrophysiology system for structural and electrophysiological ventricular tachycardia substrate assessment

Aims

Potential advantages of real-time magnetic resonance imaging (MRI)-guided electrophysiology (MR-EP) include contemporaneous three-dimensional substrate assessment at the time of intervention, improved procedural guidance, and ablation lesion assessment. We evaluated a novel real-time MR-EP system to perform endocardial voltage mapping and assessment of delayed conduction in a porcine ischaemia–reperfusion model.

Methods and results

Sites of low voltage and slow conduction identified using the system were registered and compared to regions of late gadolinium enhancement (LGE) on MRI. The Sorensen–Dice similarity coefficient (DSC) between LGE scar maps and voltage maps was computed on a nodal basis. A total of 445 electrograms were recorded in sinus rhythm (range: 30–186) using the MR-EP system including 138 electrograms from LGE regions. Pacing captured at 103 sites; 47 (45.6%) sites had a stimulus-to-QRS (S-QRS) delay of ≥40 ms. Using conventional (0.5–1.5 mV) bipolar voltage thresholds, the sensitivity and specificity of voltage mapping using the MR-EP system to identify MR-derived LGE was 57% and 96%, respectively. Voltage mapping had a better predictive ability in detecting LGE compared to S-QRS measurements using this system (area under curve: 0.907 vs. 0.840). Using an electrical threshold of 1.5 mV to define abnormal myocardium, the total DSC, scar DSC, and normal myocardium DSC between voltage maps and LGE scar maps was 79.0 ± 6.0%, 35.0 ± 10.1%, and 90.4 ± 8.6%, respectively.

Conclusion

Low-voltage zones and regions of delayed conduction determined using a real-time MR-EP system are moderately associated with LGE areas identified on MRI.

Massive Accumulation of Myofibroblasts in the Critical Isthmus Is Associated With Ventricular Tachycardia Inducibility in Post-Infarct Swine Heart

Objectives

In this study the authors determined the extent of cellular infiltration and dispersion, and regional vascularization in electrophysiologically (EP) defined zones in post–myocardial infarction (MI) swine ventricle.

Background

The critical isthmus (CI) in post-MI re-entrant ventricular tachycardia (VT) is a target for catheter ablation. In vitro evidence suggests that myofibroblasts (MFB) within the scar border zone (BZ) may increase the susceptibility to slow conduction and VT, but whether this occurs in vivo remains unproven.

Methods

Six weeks after mid–left anterior descending coronary artery occlusion, EP catheter-based mapping was used to assess susceptibility to VT induction. EP data were correlated with detailed cellular profiling of ventricular zones using immunohistochemistry and spatial distribution analysis of cardiomyocytes, fibroblasts, MFB, and vascularization.

Results

In pigs with induced sustained monomorphic VT (mean cycle length: 353 ± 89 ms; n = 6) the area of scar that consisted of the BZ (i.e., between the normal and the low-voltage area identified by substrate mapping) was greater in VT-inducible hearts (iVT) than in noninducible hearts (non-VT) (p < 0.05). Scar in iVT hearts was characterized by MFB accumulation in the CI (>100 times that in normal myocardium and >5 times higher than that in the BZ in non-VT hearts) and by a 1.7-fold increase in blood vessel density within the dense scar region extending towards the CI. Sites of local abnormal ventricular activity potentials exhibited cellularity and vascularization that were intermediate to the CI in iVT and BZ in non-VT hearts.

Conclusions

The authors reported the first cellular analysis of the VT CI following an EP-based zonal analysis of iVT and non-VT hearts in pigs post-MI. The data suggested that VT susceptibility was defined by a remarkable number of MFB in the VT CI, which appeared to bridge the few remaining dispersed clusters of cardiomyocytes. These findings define the cellular substrate for the proarrhythmic slow conduction pathway.

2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias

Ventricular arrhythmias are an important cause of morbidity and mortality and come in a variety of forms, from single premature ventricular complexes to sustained ventricular tachycardia and fibrillation. Rapid developments have taken place over the past decade in our understanding of these arrhythmias and in our ability to diagnose and treat them. The field of catheter ablation has progressed with the development of new methods and tools, and with the publication of large clinical trials. Therefore, global cardiac electrophysiology professional societies undertook to outline recommendations and best practices for these procedures in a document that will update and replace the 2009 EHRA/HRS Expert Consensus on Catheter Ablation of Ventricular Arrhythmias. An expert writing group, after reviewing and discussing the literature, including a systematic review and meta-analysis published in conjunction with this document, and drawing on their own experience, drafted and voted on recommendations and summarized current knowledge and practice in the field. Each recommendation is presented in knowledge byte format and is accompanied by supportive text and references. Further sections provide a practical synopsis of the various techniques and of the specific ventricular arrhythmia sites and substrates encountered in the electrophysiology lab. The purpose of this document is to help electrophysiologists around the world to appropriately select patients for catheter ablation, to perform procedures in a safe and efficacious manner, and to provide follow-up and adjunctive care in order to obtain the best possible outcomes for patients with ventricular arrhythmias.

Virtual electrophysiological study as a tool for evaluating efficacy of MRI techniques in predicting adverse arrhythmic events in ischemic patients

Myocardial infarct (MI) related indices determined by late gadolinium enhancement (LGE) MRI have been widely investigated in determining patients suitable for implantable cardiovascular-defibrillator (ICD) therapy to complement left ventricular ejection fraction (LV EF). In comparison to LGE-MRI using inversion-recovery fast-gradient-echo (IR-FGRE), T1 mapping techniques, such as multi contrast late enhancement (MCLE), have been shown to provide more quantitative and reproducible estimates of infarct regions. The objective of this study is to use individualized heart computer models in determining the efficacy of IR-FGRE and MCLE techniques in predicting the occurrence of post-MI ventricular tachycardia (VT). Twenty-seven patients with MI underwent LGE-MRI using IR-FGRE and MCLE prior to ICD implantation and were followed up for 6-46 months. Individualized image-based computational models were built separately for each imaging technique; simulations of propensity to VT were conducted with each model. The imaging methods were evaluated by comparing simulated inducibility of VT to clinical outcome (appropriate ICD therapy) in patients. Twelve patients had at least one appropriate ICD therapy for VT at follow-up. For both MCLE and IR-FGRE, the outcomes of the simulations of VT were significantly associated with the events of appropriate ICD therapy. This indicates that, as compared to conventional measurements such as LV EF, the simulations of VT corresponding to both MCLE and IR-FGRE were more sensitive in predicting appropriate ICD therapy in post-MI patients.

Catheter Ablation of Post-Infarct VT: Mechanisms, Strategies and Outcomes

Ventricular arrhythmias are one of the leading causes of death in patients with a prior myocardial infarction. Implantable cardioverter-defibrillators (ICDs) are very effective in the prevention of sudden cardiac death but the risk of recurrence remains an issue since defibrillation does not alter the underlying substrate. Recurrent ICD shocks are distressing and are associated with an increase in mortality. Catheter ablation is an effective treatment for recurrent ventricular tachycardia in these patients, particularly when antiarrhythmic therapy produces side effects or is ineffective. This paper reviews the underlying mechanisms of VT in patients with a prior myocardial infarction, and the indications, strategies and outcomes of catheter ablation.

Determinants of slowed conduction in premature ventricular beats induced during programmed stimulations in perfused guinea-pig heart

NEW FINDINGS

What is the central question of this study? Is the slowed conduction upon premature ventricular activations during clinical electrophysiological testing attributable to the prolonged activation latency, or increased impulse propagation time, or both? What is the main finding and its importance? Prolonged activation latency at the stimulation site is the critical determinant of conduction slowing and associated changes in the ventricular response intervals in premature beats initiated during phase 3 repolarization in perfused guinea-pig heart. These relations are likely to have an effect on arrhythmia induction and termination independently of the presence of ventricular conduction defects or the proximity of the stimulation site to the re-entrant circuit.

ABSTRACT

During cardiac electrophysiological testing, slowed conduction upon premature ventricular activation can limit the delivery of the closely coupled impulses from the stimulation site to the region of tachycardia origin. In order to examine the contributing factors, in this study, cardiac conduction intervals and refractory periods were determined from left ventricular (LV) and the right ventricular (RV) monophasic action potential recordings obtained in perfused guinea-pig hearts. A premature activation induced immediately after the termination of the refractory period was associated with conduction slowing. The latter was primarily accounted for by the markedly increased (+54%) activation latency at the LV stimulation site, with only negligible changes (+12%) noted in the LV-to-RV delay. The prolonged activation latency was acting to limit the shortest interval at which two successive action potentials can be induced in the LV and RV chambers. The prolongation of the activation latency in premature beats was accentuated upon an increase in the stimulating current intensity, or during hypokalaemia. This change was related to the reduced ratio of the refractory period to the action potential duration, which allowed extrastimulus capture to occur earlier during phase 3 repolarization. Flecainide, a Na⁺ channel blocker, prolonged both the activation latency and the LV-to-RV delay, without changing their relative contributions to conduction slowing. In summary, these findings suggest that the activation latency is the critical determinant of conduction slowing and associated changes in the ventricular response intervals upon extrastimulus application during phase 3 of the action potential.

Catheter Ablation of Ventricular Tachycardia in Structural Heart Disease: Indications, Strategies, and Outcomes-Part II

In contrast to ventricular tachycardia (VT) that occurs in the setting of a structurally normal heart, VT that occurs in patients with structural heart disease carries an elevated risk for sudden cardiac death (SCD), and implantable cardioverter-defibrillators (ICDs) are the mainstay of therapy. In these individuals, catheter ablation may be used as adjunctive therapy to treat or prevent repetitive ICD therapies when antiarrhythmic drugs are ineffective or not desired. However, certain patients with frequent premature ventricular contractions (PVCs) or VT and tachycardiomyopathy should be considered for ablation before ICD implantation because left ventricular function may improve, consequently decreasing the risk of SCD and obviating the need for an ICD. The goal of this paper is to review the pathophysiology, mechanism, and management of VT in the setting of structural heart disease and discuss the evolving role of catheter ablation in decreasing ventricular arrhythmia recurrence.

Electrophysiologic features of protected channels in late postinfarction patients with and without spontaneous ventricular tachycardia

PURPOSE

Protected channels of surviving myocytes in late postinfarction ventricular scar predispose to ventricular tachycardia (VT). However, only a few patients develop VT spontaneously. We studied differences in electric remodeling and protected channels in late postinfarction patients with and without spontaneous VT.

METHODS

Patients with ischemic cardiomyopathy (ICM) with recurrent sustained monomorphic VT (n = 22) were compared with stable ICM patients without spontaneous VT (control group; n = 5). Left ventricular mapping was performed with a 20-pole catheter. Detailed pace mapping was used to identify channels of protected conduction, and confirmed, when feasible, by entrainment. Anatomical and electrophysiological properties of VT channels and non-VT channels in VT patients and channels in controls were evaluated.

RESULTS

Seventy-three (median 3) VTs were inducible in VT patients compared to two (median 0) in controls. The VT channels in VT patients (n = 57, 3 ± 1 per patient) were lengthier (mean ± SEM 53 ± 5 vs. 33 ± 4 vs. 24 ± 8 mm), had longer S-QRS (73 ± 4 vs. 63 ± 3 vs. 44 ± 8 ms), longer conduction time (103 ± 13 vs. 33 ± 4 vs. 24 ± 8 ms), and slower conduction velocity (CV) (0.85 ± 0.21 vs. 1.39 ± 0.20 vs. 1.31 ± 0.41 m/s) than non-VT channels in VT patients (n = 183, 8 ± 6 per patient) (p ≤ 0.01) and channels in controls (n = 46, 9 ± 8 per patient) (p ≤ 0.01). Additionally, non-VT channels in VT patients had longer S-QRS (p = 0.02); however, they were similar in length, conduction time, and CV compared to channels in controls.

CONCLUSIONS

Channels supporting VT are lengthier, with longer conduction times and slower CV compared to channels in patients without spontaneous VT. These observations may explain why some ICM patients have spontaneous VT and others do not.

Development of Time- and Voltage-Domain Mapping (V-T-Mapping) to Localize Ventricular Tachycardia Channels During Sinus Rhythm

BACKGROUND

In ventricular scar, impulse spread is slow because it traverses split and zigzag channels of surviving muscle. We aimed to evaluate scar electrograms to determine their local delay (activation time) and inequality in voltage splitting (entropy), and their relationship to channels. We reasoned that unlike innocuous channels, which are often short with multiple side branches, ventricular tachycardia (VT) supporting channels have very slow impulse spread and possess low entropy because of their longer protected length and relative lack of side-branching.

METHODS AND RESULTS

Patients with ischemic cardiomyopathy and multiple VT were studied. In initial mapping stage (16 patients and 58 VTs), left ventricular endocardial mapping was performed in sinus rhythm. Detailed pace mapping was used to identify VT channels and confirmed, when feasible, by entrainment. Scar electrograms were analyzed in time and voltage domains to determine mean activation time, dispersion in activation time, and entropy. Predictive performances of these properties to detect VT channels were tested. In the application stage (7 patients and 20 VTs), these properties were prospectively tested to guide catheter ablation. A mean number of 763±203 sampling points were taken. From 1770 pace maps, 47 channels corresponded to VTs. A combination of scar electrograms with the latest mean activation time and minimum entropy, in a high activation dispersion region, accurately recognized regions containing VT channels (κ=0.89, sensitivity=86%, specificity=100%, positive predictive value=93%, and negative predictive value=100%). Finally, focused ablation within 5-mm rim of the prospective channel regions eliminated 18 of 20 inducible VTs.

CONCLUSIONS

Activation time and entropy mapping in the scar accurately identify VT channels during sinus rhythm. The method integrates principles of reentry formation to recognize VT channels without pace mapping or mapping during VT.

Relationship Between Distance and Change in Surface ECG Morphology During Pacemapping as a Guide to Ablation of Ventricular Arrhythmias

Background—

Pacemapping is used to localize the exit site of ventricular arrhythmia. Although the relationship between distance and change in QRS morphology is its basis, this relationship has not been systematically quantified.

Methods and Results—

Patients (n=68) undergoing ventricular arrhythmia ablation between March 2012 and July 2013 were recruited. Pacemapping was targeted to areas of voltage >0.5 mV. Linear mixed-effects models were constructed of distance against morphology difference measured by the root mean square error sum across all 12 ECG leads (E12). Forty of 68 (58%) patients had structural heart disease, and 21/40 (53%) patients were ischemic. Nine hundred thirty-five pacing points were collected, generating 6219 pacing site pair combinations (3087 [50%] ventricular bodies, 756 [12%] outflow tract, and 162 [3%] epicardial). In multivariable analysis, increase in E12 was predicted by increasing distance (0.07 per mm; 95% confidence interval 0.07–0.08; P <0.001). Compared with the left ventricle, E12 values were lower in the right ventricle ( P =0.037) and left ventricular outflow tract ( P <0.001) and higher in left ventricle–right ventricle pairs ( P =0.021) and left ventricular epicardium ( P =0.08). There was no difference in E12 in the right ventricular outflow tract compared with the right–left ventricular outflow tract ( P =0.75) pairs. Structural heart disease or inadvertent pacing in scar was not associated with changes in E12; however, the presence of latency and split potentials were associated with higher and lower E12 values, respectively ( P <0.001).

Conclusions—

A robust positive relationship exists between distance and QRS morphological change when restricting pacing points to areas of voltage >0.5 mV. Significant differences in the spatial resolution of pacemapping exist within the heart.

Beyond the Storm: Comparison of Clinical Factors, Arrhythmogenic Substrate, and Catheter Ablation Outcomes in Structural Heart Disease Patients With versus Those Without a History of Ventricular Tachycardia Storm

AIMS

Catheter ablation can be lifesaving in ventricular tachycardia (VT) storm, but the underlying substrate in patients with storm is not well characterized. We sought to compare the clinical factors, substrate, and outcomes differences in patients with sustained monomorphic VT who present for catheter ablation with VT storm versus those with a nonstorm presentation.

METHODS

Consecutive ischemic (ICM; n = 554) or nonischemic cardiomyopathy patients (NICM; n = 369) with a storm versus nonstorm presentation were studied (ICM storm 186; NICM storm 101).

RESULTS

In ICM, storm compared with nonstorm patients had significantly lower left ventricular (LV) ejection fraction (EF), greater number of antiarrhythmic drug (AAD) failures, slower VTs, greater number of scarred LV segments, higher incidence of anterior, septal, and apical endocardial LV scar (all P < 0.05). However, outcomes in follow-up were similar (12-month ventricular arrhythmia [VA]-free survival: 51% vs. 52%, P = 0.6; survival free of death/transplant 75% vs. 87%, P = 0.7). In addition to the above differences, NICM storm patients were also older; however, the extent and distribution of scar was similar except for a higher incidence of lateral endocardial scar in storm patients (P = 0.05). VA-free survival (36% vs. 47%, P = 0.004) and survival free of death/transplant, however, were worse in NICM storm than nonstorm patients (72% vs. 88%, P = 0.001). NICM storm patients had worse VA-free survival than ICM storm patients.

CONCLUSION

There are differences in clinical factors and scar patterns in patients undergoing VT ablation who present with VT storm versus those with a nonstorm presentation. Clinical outcomes are worse in NICM storm patients.

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.

A Historical Perspective on the Role of Functional Lines of Block in the Re-entrant Circuit of Ventricular Tachycardia

The ablation strategy for ventricular tachycardia (VT) rapidly evolved from an entrainment mapping approach for identification of the critical isthmus of the re-entrant circuit during monomorphic VT, toward a substrate-based approach aiming to ablate surrogate markers of the circuit during sinus rhythm in hemodynamically nontolerated and polymorphic VT. The latter approach implies an assumption that the circuits responsible for the arrhythmia are anatomical or fixed, and present during sinus rhythm. Accordingly, the lines of block delimiting the channels of the circuits are often considered fixed, although there is evidence that they are functional or more frequently a combination of fixed and functional. The electroanatomical substrate-based approach to VT ablation performed during sinus rhythm is increasingly adopted in clinical practice and often described as scar homogenization, scar dechanneling, or core isolation. However, whether the surrogate markers of the VT circuit during sinus rhythm match the circuit during arrhythmias remains to be fully demonstrated. The myocardial scar is a heterogeneous electrophysiological milieu with complex arrhythmogenic mechanisms that potentially coexist simultaneously. Moreover, the scar consists of different areas of diverse refractoriness and conduction. It can be misleading to limit the arrhythmogenic perspective of the myocardial scar to fixed or anatomical barriers held responsible for the re-entry circuit. Greater understanding of the role of functional lines of block in VT and the validity of the surrogate targets being ablated is necessary to further improve the technique and outcome of VT ablation.

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.

High-density mapping of ventricular scar: a comparison of ventricular tachycardia (VT) supporting channels with channels that do not support VT

BACKGROUND

Surviving myocytes within scar may form channels that support ventricular tachycardia (VT) circuits. There are little data on the properties of channels that comprise VT circuits and those that are non-VT supporting channels.

METHODS AND RESULTS

In 22 patients with ischemic cardiomyopathy and VT, high-density mapping was performed with the PentaRay catheter and Ensite NavX system during sinus rhythm. A channel was defined as a series of matching pace-maps with a stimulus (S) to QRS time of ≥40 ms. Sites were determined to be part of a VT channel if there were matching pace-maps to the VT morphology. This was confirmed with entrainment mapping when possible. Of the 238 channels identified, 57 channels corresponded to an inducible VT. Channels that were part of a VT circuit were more commonly located within dense scar than non-VT channels (97% versus 82%; P=0.036). VT supporting channels were of greater length (mean±SEM, 53±5 versus 33±4 mm), had higher longest S-QRS (130±12 versus 82±12 ms), longer conduction time (103±14 versus 43±13 ms), and slower conduction velocity (0.87±0.23 versus 1.39±0.21 m/s) than non-VT channels (P<0.001). Of all the fractionated, late, and very late potentials located in scar, only 21%, 26%, and 29%, respectively, were recorded within VT channels.

CONCLUSIONS

High-density mapping shows substantial differences among channels in ventricular scar. Channels supporting VT are more commonly located in dense scar, longer than non-VT channels, and have slower conduction velocity. Only a minority of scar-related potentials participate in the VT supporting channels.

Impact of nonischemic scar features on local ventricular electrograms and scar-related ventricular tachycardia circuits in patients with nonischemic cardiomyopathy

BACKGROUND

The association of local electrogram features with scar morphology and distribution in nonischemic cardiomyopathy has not been investigated. We aimed to quantify the association of scar on late gadolinium-enhanced cardiac magnetic resonance with local electrograms and ventricular tachycardia circuit sites in patients with nonischemic cardiomyopathy.

METHODS AND RESULTS

Fifteen patients with nonischemic cardiomyopathy underwent late gadolinium-enhanced cardiac magnetic resonance before ventricular tachycardia ablation. The transmural extent and intramural types (endocardial, midwall, epicardial, patchy, transmural) of scar were measured in late gadolinium-enhanced cardiac magnetic resonance short-axis planes. Electroanatomic map points were registered to late gadolinium-enhanced cardiac magnetic resonance images. Myocardial wall thickness, scar transmurality, and intramural scar types were independently associated with electrogram amplitude, duration, and deflections in linear mixed-effects multivariable models, clustered by patient. Fractionated and isolated potentials were more likely to be observed in regions with higher scar transmurality (P<0.0001 by ANOVA) and in regions with patchy scar (versus endocardial, midwall, epicardial scar; P<0.05 by ANOVA). Most ventricular tachycardia circuit sites were located in scar with >25% scar transmurality.

CONCLUSIONS

Electrogram features are associated with scar morphology and distribution in patients with nonischemic cardiomyopathy. Previous knowledge of electrogram image associations may optimize procedural strategies including the decision to obtain epicardial access.

Catheter Ablation for Ventricular Arrhythmias

Catheter ablation has emerged as an important and effective treatment option for many recurrent ventricular arrhythmias. The approach to ablation and the risks and outcomes are largely determined by the nature of the severity and type of underlying heart disease. In patients with structural heart disease, catheter ablation can effectively reduce ventricular tachycardia (VT) episodes and implantable cardioverter defibrillator (ICD) shocks. For VT and symptomatic premature ventricular beats that occur in the absence of structural heart disease, catheter ablation is often effective as the sole therapy. Advances in catheter technology, imaging and mapping techniques have improved success rates for ablation. This review discusses current approaches to mapping and ablation for ventricular arrhythmias.

Radiofrequency catheter ablation for ventricular tachycardia

The management of ventricular tachycardia (VT) has evolved considerably in recent times. The majority of patients with VT have structural heart disease and often implantable defibrillators. Implantable defibrillators can terminate ventricular arrhythmias and prevent sudden death but do not prevent these arrhythmias from occurring. Ventricular tachycardia may also occur in patients without structural heart disease and although these patients generally have a benign prognosis, the symptoms can be significant. Radiofrequency catheter ablation has a definite role as an alternative to anti-arrhythmic therapy in both groups of patients. This review outlines the indications, techniques and outcomes of catheter ablation in the management of patients with ventricular tachycardia.

The origin of epicardial ventricular tachycardia revealed by entrainment from a permanent epicardial left ventricular pacing lead

Entrainment From Left Ventricular Pacing Lead. Recognizing ventricular tachycardias (VTs) that require epicardial ablation is desirable, but challenging when prior surgery prevents percutaneous epicardial mapping. This patient had cardiomyopathy, prior cardiac surgery, and VT that failed endocardial ablation. Observing that the Bi-V implantable cardioverter defibrillator (ICD), left ventricular (LV) lead was epicardial to the area of infarct scar, it was used to pace during VT. Entrainment with concealed fusion with long stimulus to QRS interval, consistent with an epicardial VT circuit, was observed. Surgical cryoablation targeting the area around the LV lead eliminated VT. Thus pacing maneuvers from permanent epicardial leads can occasionally help identify an epicardial VT origin.

Electrophysiologic substrate underlying postinfarction ventricular tachycardia: characterization and role in catheter ablation

The electrophysiologic substrate underlying the development of ventricular tachycardia (VT) in patients with prior infarction has been studied in depth. An increased understanding of its composition and role in the maintenance of reentrant VT has led to the development of substrate modification approaches to ablation of unmappable VT. The area of low bipolar voltage that corresponds to the subendocardial projection of the scar as well as specific potential targets within it have been defined. These targets are selected because they may be involved in forming, or are in close proximity to, critical diastolic isthmuses during VT. The targets include sites of good pacemaps in the border zone, corridors of relatively preserved voltage within dense scar, regions between electrically unexcitable scar, isolated potentials, very late potentials, and regions with good pacemaps which display long stimulus to QRS delays. Ablation strategies have been designed based on these targets, mostly incorporating linear lesions to transect putative isthmus sites. This review examines the role that the electrophysiologic substrate plays in the mechanism of scar-related VT and how this substrate is mapped, defined, and ablated.

Non-pharmacological management of ventricular tachycardia

Ventricular tachyarrhythmias (VTA), a major cause of sudden cardiac death, require meticulous management in order to prevent recurrent episodes. Recently, non-pharmacological interventions, including radiofrequency catheter ablation and implantable cardioverter defibrillators (ICD), have become important treatments of VTA. Catheter ablation is curative in a relatively high percentage of patients presenting with idiopathic monomorphic ventricular tachycardia (VT). For VT associated with structural heart disease, however, the efficacy of catheter ablation remains limited, and ICD is the first-line therapy. In a subset of patients presenting with recurrent episodes of ventricular fibrillation (VF), catheter ablation is a therapeutic option when the VF is triggered by specific premature ventricular complexes. In Japan, unlike in the United States and Europe, ICD have not yet been accepted as first-line prevention of sudden cardiac death caused by VTA. The efficacy of ICD is occasionally limited by intolerable complications, such as electrical storm, inappropriate shock delivery and infection. Catheter ablation and ICD therapy might need to be combined for problematic cases.

Relationship Between Successful Ablation Sites and the Scar Border Zone Defined by Substrate Mapping for Ventricular Tachycardia Post-Myocardial Infarction

INTRODUCTION

It is unknown if identification of scar border zones by electroanatomical mapping correlates with successful ablation sites determined from mapping during ventricular tachycardia (VT) post-myocardial infarction (MI). We sought to assess the relationship between successful ablation sites of hemodynamically stable post-MI VTs determined by mapping during VT with the scar border zone defined in sinus rhythm.

METHODS AND RESULTS

Forty-six patients presenting with hemodynamically stable, mappable monomorphic VT post-MI and who had at least one such VT successfully ablated were prospectively included in the study. In each patient, VT was ablated by targeting regions during VT that exhibited early activation, +/- isolated mid-diastolic potentials, and concealed entrainment suggesting a critical isthmus site. Prior to ablation, a detailed sinus-rhythm CARTO voltage map of the left ventricle was obtained. A voltage <0.5 mV defined dense scar. Successful VT ablation sites were registered on the sinus voltage map to assess their relationship to the scar border zone. Of the 86 VTs, 68% were successfully ablated at sites in the endocardial border zone. The remaining VTs had ablation sites within the scar in (18%), in normal myocardium (4%), and on the epicardial surface (10%). There were no significant differences in VT recurrence amongst the different groups.

CONCLUSION

Successful ablation sites of hemodynamically stable, monomorphic VTs post-MI are often located in the scar border zone as defined by substrate voltage mapping. However, in a sizable minority, ablation sites are located within endocardial scar, epicardially, and even in normal myocardium.

Sinus Rhythm Electrogram Shape Measurements are Predictive of the Origins and Characteristics of Multiple Reentrant Ventricular Tachycardia Morphologies

INTRODUCTION

During clinical electrophysiologic study, multiple clinical tachycardia morphologies often can be induced in the infarct border zone, and all morphologies must be targeted for ablation therapy to be successful. Analysis of sinus rhythm electrogram shape for localizing figure-of-eight reentrant circuits in cases of multiple morphologies is proposed.

METHODS AND RESULTS

Sinus rhythm activation maps were constructed from bipolar electrograms acquired at 196 to 312 sites in the epicardial border zone in 10 postinfarction canine hearts. In each heart, at least two distinct figure-of-eight reentrant ventricular tachycardia morphologies were inducible by premature electrical stimulation, as determined by activation maps of sustained tachycardias. Sinus rhythm maps were used to predict the location of the isthmus (central common pathway [CCP]), which is the protected region of the circuit bounded by arcs of block (mean accuracy 76.7 +/- 4%). Although reentrant circuits differed, the positions of the entrance point of each CCP were common. The location of the line that would span the CCP at its narrowest width also was estimated (mean accuracy 91.3 +/- 5%). Ablation at this line is expected to prevent reentry recurrence. In one test experiment, ablation prevented recurrence of both sustained reentrant tachycardia morphologies.

CONCLUSION

Sinus rhythm electrogram analyses are useful for (1) localizing multiple reentrant circuits with differences in morphology that are inducible by premature stimulation in the infarct border zone, and (2) locating and orienting the position of a linear lesion for preventing recurrence of all morphologies with minimal damage to the heart.