Electrophysiology of ventricular tachycardia: an historical perspective

Ripple mapping in ventricular tachycardia substrate mapping and ablation of nonischemic ventricular tachycardia

INTRODUCTION

Substrate-based ablation for ventricular tachycardia (VT) using Ripple map (RM) is an effective treatment strategy for patients with ischemic cardiomyopathy but has yet to be evaluated in patients with nonischemic cardiomyopathy (NICMO). The aim of this study is to determine the feasibility and effectiveness of an RM-based ablation for NICMO patients.

METHODS AND RESULTS

This was a single-center, retrospective study including all NICMO patients undergoing VT ablation at St Vincent Hospital between January 1, 2018 and January 12, 2019. Retrospective RM analysis was performed on those that had a substrate-based ablation to identify the location and number of Ripple channels as well as their proximity to ablation lesions. Thirty-three patients met the inclusion criteria and had a median age of 65 (58, 73.5) with 15.2% of the population being female, and were followed for a median duration of 451 (217.5, 586.5) days. Of these patients, 23 (69.7%) had a substrate-based ablation with a median procedural duration of 196.4 (186.8, 339) min, 1946 (517, 2750) points collected per map, and 277 (141, 554) points were within the scar. Two (8.6%) procedural complications occurred, and 7 (30.4%) patients had VT recurrence during follow-up. RM analysis revealed an average of two Ripple channels and the patients without VT recurrence had ablation performed closer to the Ripple channels: 0 (0, 4.7) versus 14.3 (0, 23.5) cm; p = .02.

CONCLUSION

An RM-based substrate ablation can be performed in NICMO patients and ablation within Ripple channels is a predictor of VT freedom.

Correlation of spatial patterns of endocardial pace mapping to underlying scar topography in patients with scar-related ventricular tachycardia

INTRODUCTION

Endocardial pace mapping (PM) can identify conducting channels for ventricular tachycardia (VT) circuits in patients with structural heart disease (SHD). Recent findings show the temporal and spatial pattern of PM may aid identification of the surface harboring VT isthmii. The specific correlation of PM patterns to scar topography has not been examined.

OBJECTIVE

To correlate the pattern of endocardial PMs to underlying scar topography in SHD patients with VT.

METHODS

Data from patients undergoing VT ablation from August 2018 to February 2022 were reviewed.

RESULTS

Sixty-three patients with SHD-related VT (mean age 65 ± 14 years) with 83 endocardial PM correlation maps were analysed. Two main correlation patterns were identified, an "abrupt-change correlation pattern (AC-pattern)" and "centrifugal-attenuation correlation pattern (CA-pattern)." AC-pattern had lower scar ratio (unipolar/bipolar % scar area; 1.1 vs. 1.5, p < .001), had longer maximal stimulus-QRS intervals (97.5 vs. 68 ms, p = .002), and higher likelihood of endocardial dominant scar (11/21 [52%] vs. 3/38 [8%], p < .001) than CA-pattern seen on intracardiac echocardiography (ICE). In contrast, CA-pattern was more likely to have epicardial dominant scar or mid-intramural scar on ICE (epicardial dominant scar; CA-pattern: 12/38 [32%] vs. AC-pattern: 1/21 [5%], p = .02, mid-intramural scar; CA-pattern: 15/38 [39%] vs. AC-pattern: 1/21 [5%], p = .005).

CONCLUSIONS

The spatial pattern of endocardial PM in SHD-related VT directly correlates with scar topography. AC-pattern is associated with endocardial dominant scar on ICE with lower scar ratio and longer stimulus-QRS intervals, whereas CA-pattern is strongly associated with epicardial dominant or mid-intramural scar with higher scar ratio and shorter stimulus-QRS intervals.

Contemporary Management of Complex Ventricular Arrhythmias

Percutaneous catheter ablation is an effective and safe therapy that can eliminate ventricular tachycardia, reducing the risks of both recurrent arrhythmia and shock therapies from a defibrillator. Successful ablation requires accurate identification of arrhythmic substrate and the effective delivery of energy to the targeted tissue. A thorough pre-procedural assessment is needed before considered 3D electroanatomical mapping can be performed. In contemporary practice, this must combine traditional electrophysiological techniques, such as activation and entrainment mapping, with more novel physiological mapping techniques for which there is an ever-increasing evidence base. Novel techniques to maximise energy delivery to the tissue must also be considered and balanced against their associated risks of complication. This review provides a comprehensive appraisal of contemporary practice and the evidence base that supports recent developments in mapping and ablation, while also considering potential future developments in the field.

Prophylactic Catheter Ablation of Ventricular Tachycardia in Ischemic Cardiomyopathy: a systematic review and meta-analysis of randomized controlled trials Electrophysiology Collaborative Consortium for Metaanalysis - ELECTRAM Investigators

Aims

Catheter ablation is an effective strategy for drug-refractory ventricular tachycardia (VT) in ischemic cardiomyopathy. We aimed to perform a systematic review and meta-analysis of outcomes of prophylactic catheter ablation (PCA) of Ventricular Tachycardia (VT) in ischemic cardiomyopathy patients.

Methods

We performed a comprehensive literature search through February 10, 2020, for all eligible randomized controlled trials that compared "PCA" versus "No PCA" for VT. Primary efficacy outcomes included - appropriate ICD therapy (composite of anti-tachycardia pacing and ICD shock), appropriate ICD shocks, electrical storm, cardiac mortality, and all-cause mortality. The primary safety outcome was any adverse events.

Results

Four randomized controlled trials (N = 505) met inclusion criteria. Prophylactic catheter ablation was associated significant reduction in appropriate ICD therapies (RR 0.70; 95% CI 0.55 - 0.89, p = 0.004), appropriate ICD shocks (RR 0.57 95% CI 0.40 - 0.80, p = 0.001) with a trend towards reduced risk of electrical storm (RR 0.64; CI 0.39 - 1.05; p = 0.075) compared to "No PCA". There was no significant difference in cardiac mortality (RR 0.66, 95% CI 0.31 - 1.43, p = 0.29) and all-cause mortality (RR 0.98, 95% CI 0.52 - 1.82, p = 0.94) with similar adverse events (RR 1.46, 95% CI 0.73 - 2.95, p = 0.29) between two groups.

Conclusions

Prophylactic catheter ablation in ischemic cardiomyopathy patients was associated with a lower risk of ICD therapies, including ICD shocks and VT storm with no difference in cardiac and all-cause mortality.

Impact of Spacing and Orientation on the Scar Threshold With a High-Density Grid Catheter

BACKGROUND

Multipolar catheters are increasingly used for high-density mapping. However, the threshold to define scar areas has not been well described for each configuration. We sought to elucidate the impact of bipolar spacing and orientation on the optimal threshold to match magnetic resonance imaging-defined scar.

METHOD

The HD-Grid catheter uniquely allows for different spatially stable bipolar configurations to be tested. We analyzed the electrograms with settings of HD-16 (3 mm spacing in both along and across bipoles) and HD-32 (1 mm spacing in along bipoles and 3 mm spacing in across bipoles) and determined the optimal cutoff for scar detection in 6 infarcted sheep.

RESULTS

From 456 total acquisition sites (mean 76±12 per case), 14 750 points with the HD-16 and 32286 points with the HD-32 configuration for bipolar electrograms were analyzed. For bipolar voltages, the optimal cutoff value to detect the magnetic resonance imaging-defined scar based on the Youden's Index, and the area under the receiver operating characteristic curve (AUROC) differed depending on the spacing and orientation of bipoles; across 0.84 mV (AUROC, 0.920; 95% CI, 0.911-0.928), along 0.76 mV (AUROC, 0.903; 95% CI, 0.893-0.912), north-east direction 0.95 mV (AUROC, 0.923; 95% CI, 0.913-0.932), and south-east direction, 0.87 mV (AUROC, 0.906; 95% CI, 0.895-0.917) in HD-16; and across 0.83 mV (AUROC, 0.917; 95% CI, 0.911-0.924), along 0.46 mV (AUROC, 0.890; 95% CI, 0.883-0.897), north-east direction 0.89 mV (AUROC, 0.923; 95% CI, 0.917-0.929), and south-east direction 0.83 mV (AUROC, 0.913; 95% CI, 0.906-0.920) in HD-32. Significant differences in AUROC were seen between HD-16 along versus across (P=0.002), HD-16 north-east direction versus south-east direction (P=0.01), HD-32 north-east direction versus south-east direction (P<0.0001), and HD-16 along versus HD-32 along (P=0.006). The AUROC was significantly larger (P<0.01) when only the best points on each given site were selected for analysis, compared with when all points were used.

CONCLUSIONS

Spacing and orientation of bipoles impacts the accuracy of scar detection. Optimal threshold specific to each bipolar configuration should be determined. Selecting one best voltage point among multiple points projected on the same surface is also critical on the Ensite-system to increase the accuracy of scar-mapping.

Effect of bipolar electrode orientation on local electrogram properties

BACKGROUND

The direct effect of bipolar orientation on electrograms (EGMs) remains unknown.

OBJECTIVE

The purpose of this study was to examine the variation of EGMs with diagonally orthogonal bipoles.

METHODS

The HD-32 Grid catheter (Abbott, Minneapolis, MN) can assess the effect of bipolar orientation while keeping the interelectrode distance and center unchanged. Seven sheep with anterior myocardial infarction were analyzed using diagonally orthogonal electrode pairs across splines by comparing local EGMs from each pair of opposing electrodes {eg. A1-B3 (southeast direction [SE]) vs A3-B1 (northeast direction [NE])}.

RESULTS

A total of 4084 EGMs (1 in each direction) were analyzed for 2042 sites (544 in the infarcted area, 488 in the border area, and 1010 in the normal area). The higher and lower voltages measured using each pair of opposing electrodes significantly differed (1.10 mV [0.43-2.56 mV] vs 0.69 mV [0.28-1.58 mV]; P < .0001), and the median variation was 0.28 mV (0.11-0.80 mV) (31.7% [16.0%-48.9%]). The voltage variation was maximized to 48.7% (37.7%-61.6%) (P < .0001) on sites where the activation wavefront was perpendicular to the one bipolar direction and parallel to the other. A total of 594 of 719 (82.6%) sites with the voltage <0.5 mV and 539 of 699 (77.1%) sites with the voltage >1.5 mV in NE stayed in the same voltage range as those in SE. However, only 348 of 624 (55.8%) sites with the voltage 0.5-1.5 mV in NE stayed in the same range as those in SE. Local ventricular abnormal activities (LAVAs) were detected in 592 of 2042 (29.0%) sites in total, frequently distributed in the border area. A total of 177 (29.9%) LAVAs were missed in one direction and 180 (30.4%) in the other. When 415 (70.1%) LAVAs detected in NE are defined as the reference, 235 of 415 (56.6%) matched with those detected in SE.

CONCLUSION

The bipolar voltage and distribution of LAVAs may differ significantly between diagonally orthogonal bipolar pairs at any given site.

Directional Influences of Ventricular Activation on Myocardial Scar Characterization: Voltage Mapping With Multiple Wavefronts During Ventricular Tachycardia Ablation

BACKGROUND

The effects of varying the wavefront of activation on ventricular scar characterization has not been systematically assessed.

METHODS AND RESULTS

Patients referred for ablation of scar-related ventricular tachycardia underwent voltage maps during a minimum of 2 wavefronts of activation. The bipolar and unipolar low-voltage areas were compared, and direct electrogram analysis was performed in regions where discrepancies were seen. Concordance between wavefronts was measured by calculating percentage of overlap between maps. Sixty endocardial voltage maps (360±147 points) were performed in 29 patients during 2 distinct wavefronts, with 3 wavefronts in 7 patients. With median bipolar and unipolar low-voltage areas of 37 and 116 cm(2), respectively, 22% and 14% variability in median scar area was observed with a different activation wavefront. Concordance between wavefronts was lower in patients with mixed scar compared to those with dense scar (52% [interquartile range, 29%-70%] versus 84% [interquartile range, 71%-87%]), with septal scars exhibiting the lowest concordance [(27% (interquartile range, 21%-56%)]. Among 16 critical sites for ventricular tachycardia, 3 (18%) were in a discordant region of scar, with one of the wavefronts showing voltage >1.5 mV.

CONCLUSIONS

Significant differences in bipolar and unipolar low-voltage characterization of scar were observed with different ventricular activation wavefronts, particularly in septal locations and in patients without dense scar. In patients with a paucity of dense, low-voltage regions identified during substrate mapping, an alternate activation wavefront may increase the sensitivity to detect arrhythmogenic substrate and critical sites for ventricular tachycardia.

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.

Biophysical parameters during radiofrequency catheter ablation of scar-mediated ventricular tachycardia: epicardial and endocardial applications via manual and magnetic navigation

BACKGROUND

There is a paucity of data on biophysical parameters during radiofrequency ablation of scar-mediated ventricular tachycardia (VT).

METHODS AND RESULTS

Data were collected from consecutive patients undergoing VT ablation with open-irrigation. Complete data were available for 372 lesions in 21 patients. The frequency of biophysical parameter changes were: >10Ω reduction (80%), bipolar EGM reduction (69%), while loss of capture was uncommon (32%). Unipolar injury current was seen in 72% of radiofrequency applications. Both EGM reduction and impedance drop were seen in 57% and a change in all 3 parameters was seen in only 20% of lesions. Late potentials were eliminated in 33%, reduced/modified in 56%, and remained after ablation in 11%. Epicardial lesions exhibited an impedance drop (90% vs. 76%, P = 0.002) and loss of capture (46% vs. 27%, P < 0.001) more frequently than endocardial lesions. Lesions delivered manually exhibited a >10Ω impedance drop (83% vs. 71%, P = 0.02) and an EGM reduction (71% vs. 40%, P < 0.001) more frequently than lesions applied using magnetic navigation, although loss of capture, elimination of LPs, and a change in all 3 parameters were similarly observed.

CONCLUSIONS

VT ablation is inefficient as the majority of radiofrequency lesions do not achieve more than one targeted biophysical parameter. Only one-third of RF applications targeted at LPs result in complete elimination. Epicardial ablation within scar may be more effective than endocardial lesions, and lesions applied manually may be more effective than lesions applied using magnetic navigation. New technologies directed at identifying and optimizing ablation effectiveness in scar are clinically warranted.

Functional pace-mapping responses for identification of targets for catheter ablation of scar-mediated ventricular tachycardia

BACKGROUND

Myocardial scars harbor areas of slow conduction and display abnormal electrograms. Pace-mapping at these sites can generate a 12-lead ECG morphological match to a targeted ventricular tachycardia (VT), and in some instances, multiple exit morphologies can result. At times, this can also result in the initiation of VT, termed pace-mapped induction (PMI). We hypothesized that in patients undergoing catheter ablation of VT, scar substrates with multiple exit sites (MES) identified during pace-mapping have improved freedom from recurrent VT, and PMI of VT predicts successful sites of termination during ablation.

METHODS AND RESULTS

High-density mapping was performed in all subjects to delineate scar (0.5-1.5 mV). Sites with abnormal electrograms were tagged, stimulated (bipolar 10 mA at 2 ms), and targeted for ablation. MES was defined as >1 QRS morphology from a single pacing site. PMI was defined as initiation of VT during pace-mapping (400-600 ms). In a 2-year period, 44 consecutive patients with scar-mediated VT underwent mapping and ablation. MES were observed during pace-mapping in 25 patients (57%). At 9 months, 74% of patients who exhibited MES during pace-mapping had no recurrence of VT compared with 42% of those without MES observed (P=0.024), with an overall freedom from VT of 61%. Thirteen patients (30%) demonstrated PMI, and termination of VT was seen in 95% (18/19) of sites where ablation was performed.

CONCLUSIONS

During pace-mapping, electrograms that exhibit MES and PMI may be specific for sites critical to reentry. These functional responses hold promise for identifying important sites for catheter ablation of VT.

Catheter ablation for ventricular tachycardia

Sudden cardiac death due to ventricular arrhythmias remains the most common cause of death in developed nations. Implantable cardioverter defibrillators have been shown to improve mortality in high-risk groups for ventricular tachyarrhythmias, but they are not curative, with the risk of arrhythmia recurrence remaining unaltered. It is also important to remember that ventricular tachycardia (VT) in the setting of a structurally normal heart is often not associated with an increased risk of sudden death and catheter ablation is a potentially curative procedure in this cohort. Recent advances in catheter ablation for VT have increased the efficacy in creating adequate lesions, accurate three-dimensional maps and mapping haemodynamically unstable VT, all of which have increased the utility of this modality in the treatment of ventricular arrhythmias. In this article, we review the recent advances that have fuelled renewed interest in catheter ablation of VT, its clinical utility and who should be referred.

Prophylactic catheter ablation for the prevention of defibrillator therapy

BACKGROUND

For patients who have a ventricular tachyarrhythmic event, implantable cardioverter-defibrillators (ICDs) are a mainstay of therapy to prevent sudden death. However, ICD shocks are painful, can result in clinical depression, and do not offer complete protection against death from arrhythmia. We designed this randomized trial to examine whether prophylactic radiofrequency catheter ablation of arrhythmogenic ventricular tissue would reduce the incidence of ICD therapy.

METHODS

Eligible patients with a history of a myocardial infarction underwent defibrillator implantation for spontaneous ventricular tachycardia or fibrillation. The patients did not receive antiarrhythmic drugs. Patients were randomly assigned to defibrillator implantation alone or defibrillator implantation with adjunctive catheter ablation (64 patients in each group). Ablation was performed with the use of a substrate-based approach in which the myocardial scar is mapped and ablated while the heart remains predominantly in sinus rhythm. The primary end point was survival free from any appropriate ICD therapy.

RESULTS

The mortality rate 30 days after ablation was zero, and there were no significant changes in ventricular function or functional class during the mean (+/-SD) follow-up period of 22.5+/-5.5 months. Twenty-one patients assigned to defibrillator implantation alone (33%) and eight patients assigned to defibrillator implantation plus ablation (12%) received appropriate ICD therapy (antitachycardia pacing or shocks) (hazard ratio in the ablation group, 0.35; 95% confidence interval, 0.15 to 0.78, P=0.007). Among these patients, 20 in the control group (31%) and 6 in the ablation group (9%) received shocks (P=0.003). Mortality was not increased in the group assigned to ablation as compared with the control group (9% vs. 17%, P=0.29).

CONCLUSIONS

In this randomized trial, prophylactic substrate-based catheter ablation reduced the incidence of ICD therapy in patients with a history of myocardial infarction who received ICDs for the secondary prevention of sudden death. (Current Controlled Trials number, ISRCTN62488166 [controlled-trials.com].).

Triggers of sustained monomorphic ventricular tachycardia differ among patients with varying etiologies of left ventricular dysfunction

BACKGROUND

The mechanisms underlying the initiation of sustained ventricular tachycardia (VT) have not been fully elucidated. The extent to which reentry, abnormal automaticity, and triggered activity play a role in VT differs depending on the etiology of left ventricular dysfunction. By analyzing electrograms from implantable cardioverter defibrillator (ICD), we sought to determine whether there were differences in VT initiation patterns between patients with ischemic and nonischemic cardiomyopathy.

METHODS

We analyzed ICD electrograms in patients with ejection fractions < 40% who had sustained VT over a 27-month period. The trigger for VT onset was classified as a ventricular premature beat (VPB), supraventricular tachycardia, or of "sudden onset." The baseline cycle length, VT cycle length, coupling interval, and prematurity ratio were recorded for each event. The prematurity ratio was calculated as the coupling interval of the VT initiator divided by the baseline cycle length.

RESULTS

Sixty-three VT events in 14 patients met the inclusion criteria. A VPB initiated the VT in 58 episodes (92%), 1 episode (2%) was initiated by a supraventricular tachycardia, and 4 episodes (6%) were sudden onset. The prematurity ratio was significantly higher (P < 0.05) in patients with ischemic cardiomyopathy (0.751 +/- 0.068) as compared to patients with nonischemic cardiomyopathy (0.604 +/- 0.139).

CONCLUSION

VPBs initiated most sustained VT episodes. A significantly higher prematurity ratio was observed in the ischemic heart disease group. This may represent different mechanisms of VT initiation in patients with ischemic versus nonischemic heart disease.

The pathology of sudden cardiac death in patients with ischemic heart disease—arrhythmology for anatomic pathologists

The goal of this review is to help anatomic pathologists interpret the significance of pathologic changes in the hearts of patients with coronary artery disease who died suddenly of spontaneous ventricular arrhythmias. Attention is focused on dynamic interactions between triggering events, such as acute ischemia, and stable anatomic substrates of arrhythmias, such as healed myocardial infarcts. A basic knowledge of arrhythmia mechanisms is necessary to understand the role of pathologic anatomy in the pathophysiology of sudden death.