Recognition of far-field electrograms during entrainment mapping of ventricular tachycardia

State of the Art: Mapping Strategies to Guide Ablation in Ischemic Heart Disease

Catheter ablation to prevent ventricular tachycardia (VT) that emerges late after a myocardial infarction aims to interrupt the re-entry substrate. Interruption of potential channels and regions of slow conduction that can be identified during stable sinus or paced rhythm is often effective and a number of substrate markers for guiding this approach have been described. While there is substantial agreement with different markers in some patients, the different markers select different regions for ablation in others. Mapping during VT to identify critical re-entry circuit isthmuses is likely more specific, and most useful when VT is incessant or frequent during the procedure or when sinus rhythm substrate ablation fails. Both approaches are often combined. These methods for identifying and characterizing post-infarct-related arrhythmia substrate and the re-entry circuits are reviewed.

Peak frequency mapping of atypical atrial flutter

INTRODUCTION

Peak frequency (PF) mapping is a novel method that may identify critical portions of myocardial substrate supporting reentry. The aim of this study was to describe and evaluate PF mapping combined with omnipolar voltage mapping in the identification of critical isthmuses of left atrial (LA) atypical flutters.

METHODS AND RESULTS

LA omnipolar voltage and PF maps were generated in flutter using the Advisor HD-Grid catheter (Abbott) and EnSite Precision Mapping System (Abbott) in 12 patients. Normal voltage was defined as ≥0.5 mV, low-voltage as 0.1-0.5 mV, and scar as <0.1 mV. PF distributions were compared with ANOVA and post hoc Tukey analyses. The 1 cm radius from arrhythmia termination was compared to global myocardium with unpaired t-testing. The mean age was 65.8 ± 9.7 years and 50% of patients were female. Overall, 34 312 points were analyzed. Atypical flutters most frequently involved the mitral isthmus (58%) or anterior wall (25%). Mean PF varied significantly by myocardial voltage: normal (335.5 ± 115.0 Hz), low (274.6 ± 144.0 Hz), and scar (71.6 ± 140.5 Hz) (p < .0001 for all pairwise comparisons). All termination sites resided in low-voltage regions containing intermediate or high PF. Overall, mean voltage in the 1 cm radius from termination was significantly lower than the remaining myocardium (0.58 vs. 0.95 mV, p < .0001) and PF was significantly higher (326.4 vs. 245.1 Hz, p < .0001).

CONCLUSION

Low-voltage, high-PF areas may be critical targets during catheter ablation of atypical atrial flutter.

Simultaneous Entrainment Response Assessment at Multiple Sites

BACKGROUND

The entrainment response, defined as the difference between the postpacing interval and the tachycardia cycle length (TCL) recorded from a mapping catheter, allows to track down the components of the tachycardia loop.

OBJECTIVES

The aim of this study was to evaluate if the postpacing interval measured simultaneously from multiple sites that are remote from the pacing site (PPIR) could be clinically useful in mapping re-entrant circuits.

METHODS

Ninety-two episodes of entrainment response in 29 patients with different macro-re-entrant tachycardias were evaluated using a standardized entrainment protocol. The spatial distribution of different values of PPIR-TCL in a simulation and a computational model of an entrained re-entrant tachycardia was also analyzed.

RESULTS

The PPIR exceeded TCL by more than 20 milliseconds only if both pacing and recording sites were outside the tachycardia circuit. The PPIR-TCL at in-circuit sites was always ≤20 milliseconds. Sites with negative PPIR-TCL values were found either outside or inside the tachycardia circuit.

CONCLUSIONS

Assessment of entrainment response from catheters remote from the pacing site may enhance spatial mapping of the tachycardia circuit. The PPIR-TCL above 20 milliseconds has an excellent positive predictive value in identifying sites outside the tachycardia circuit.

Successful Application of Stereotactic Body Radiation Therapy for Ventricular Tachycardia Substrate in a Patient With Nonischemic Cardiomyopathy

Cardiac stereotactic body radiotherapy (SBRT) has been gaining attention as a potential treatment for patients with ventricular tachycardia (VT). Here, we describe a nonischemic patient with severe heart failure and VTs originating from the deep anteroseptal substrate that was refractory to standard and bipolar catheter ablations, and was successfully managed with SBRT. In conclusion, anteroseptal VTs resistant to catheter ablation in severe nonischemic heart failure might be an indication for cardiac SBRT as palliative therapy.

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.

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.

First clinical use of novel ablation catheter incorporating local impedance data

INTRODUCTION

Successful catheter ablation is limited by both poor spatial resolution of abnormal local signals and inability to deliver an effective lesion due to poor tissue contact. We report first worldwide use of the Intellanav MiFi OI catheter (Boston Scientific), providing ultra-high density mapping and incorporating a "DirectSense" algorithm to measure local tissue impedance (LI).

METHODS AND RESULTS

31 patients (65±6 years, 20 male) underwent ablation. LI from the catheter, generator impedance (GI) and maximum electrogram amplitude were recorded in the blood pool, and in regions from healthy to dense scar before, during and after ablation. The catheter demonstrated clear nearfield signal where standard bipolar recordings included farfield signal. LI was lower in dense scar than either healthy tissue or blood pool, and demonstrated an exponential relationship with maximum electrogram amplitude. Maximum LI drop on ablation linearly correlated with initial LI. The median LI drop for successful lesions, resulting in lack of local tissue capture, was 16.0Ω (12.1-19.8 Ω) for LV and 14.6 Ω (10.0-18.3 Ω) for LA, which was larger than for unsuccessful lesions (LV: 9.4 Ω [5.4-15.6 Ω] P = 0.001; LA: 6.8 Ω [4.7-13.0 Ω], P = 0.049). LI percentage drop was also significantly larger for successful than unsuccessful lesions (LV: 17.1 Ω [14.0-19.6 Ω] vs. 10.6 Ω (7.1-16.5 Ω) P = 0.002; LA: 14.2 Ω [10.8-19.5 Ω] vs. 7.5Ω [5.1-11.0 Ω], P = 0.005).

CONCLUSION

This novel catheter gives reproducible recordings of local impedance, which are dependent on scar level. Absolute LI drop, and also percentage drop, on ablation may give an indication of tissue contact and subsequent effective lesion formation.

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.

Effect of the restitution properties of cardiac tissue on the repeatability of entrainment mapping response

BACKGROUND

The difference between the postpacing interval (PPI) and the tachycardia cycle length (TCL; PPI-TCL) is a useful tool in mapping macro-reentrant tachycardias. However, entrainment pacing causes some perturbation of the conduction velocity within the tachycardia circuit, which may affect the repeatability and consequently the accuracy of the measurement of PPI-TCL. The aim of this study was to assess PPI-TCL repeatability both in vivo and in silico.

METHODS AND RESULTS

In the experimental part, entrainment pacing was performed twice at each of the 124 tested sites for 30 patients undergoing radiofrequency ablation of atrial and ventricular re-entrant arrhythmias. A similar protocol was used in a simplified computer model of the cardiac tachycardia circuit in a 2-dimensional tissue strip using a Fenton-Karma model of cardiac tissue. In vivo, in the case of fast tachycardias (<350 ms), PPI-TCL variability observed was doubled compared with slow tachycardias (>350 ms; 95% Limits of Agreement ranged from -21.4 to 21.6 ms for TCL<350 ms and from -10.8 to 11.5 ms for TCL>350 ms). Simulations show that this increase of variability may be because of the oscillations of the conduction velocity inside the tachycardia circuits. The effect of the restitution properties of cardiac tissue on the outcome of entrainment pacing is discussed.

CONCLUSIONS

PPI-TCL is characterized by a high repeatability with the differences between the results for individual stimulations of ≤20 ms. The variability of this parameter is significantly lower in the case of slow tachycardias.

Number needed to entrain: a new criterion for entrainment mapping in patients with intra-atrial reentrant tachycardia

BACKGROUND

Measuring postpacing intervals (PPIs) is the standard maneuver for localizing reentrant tachycardia circuits. However, changes or termination of the tachycardia during entrainment pacing, or difficulties in defining the correct local activity, limit the use of PPIs.

METHODS AND RESULTS

We hypothesized that the number of pacing stimuli needed to entrain (NNE) was useful for mapping intra-atrial reentrant tachycardias. First, 10 patients with typical atrial flutter were studied to characterize the NNE. Next, 317 entrainment attempts in 30 patients with 76 intra-atrial reentrant tachycardias were analyzed to determine the efficacy of the NNE. The NNE was small at sites within the reentrant circuit (median 2) and large at remote sites during typical atrial flutter. The NNE depended on the pacing cycle length and coupling interval of the initial paced beat, where the NNE became smaller at shorter pacing cycle lengths and coupling intervals. The NNE highly correlated with the difference between the PPI and tachycardia cycle length (r = 0.906; P<0.001). When the pacing cycle length and coupling interval were 16 to 30 ms below the tachycardia cycle length, a NNE ≤2 and >3 predicted a PPI-tachycardia cycle length ≤20 and >20 ms, respectively, with 100% accuracy. Thirty-six (11%) entrainment attempts changed or terminated intra-atrial reentrant tachycardia. Importantly, the NNE remained valid in those cases. Furthermore, the NNE provided additional information in cases with some difficulties with PPI measurements.

CONCLUSIONS

The NNE is a simple and reliable criterion, which facilitates mapping intra-atrial reentrant tachycardia.

CLINICAL TRIAL REGISTRATION URL

http://www.clinicaltrials.gov. Unique identifier: NCT001747.

Characterization of Trans-septal Activation During Septal Pacing

Background—

Identification of intramural basal-septal ventricular tachycardia (VT) substrate is challenging in nonischemic cardiomyopathy. We sought to (1) characterize normal/abnormal trans-septal right ventricular (RV) to left ventricular activation; (2) assess the effect of opposite RV pacing on left ventricular septal bipolar electrograms (EGMs); and (3) establish criteria for the identification of intramural septal VT substrate.

Methods and Results—

Endocardial activation mapping and local EGM assessment of the left interventricular septum was performed during RV basal septal pacing in 40 patients undergoing VT ablation with no evidence of septal scar (group 1, n=14) and with septal scar (group 2, n=26) defined by low septal unipolar voltage (<8.3 mV) and delayed enhancement on cardiac MRI with/without abnormal bipolar voltage (<1.5 mV) in sinus rhythm. Left ventricular trans-septal activation time was prolonged in Group 2 compared with Group 1 (55.3±33.0 versus 25.7±8.8 ms; P =0.003). In 6 group 2 patients, left ventricular septal breakthrough was displaced to the scar border. During RV pacing, group 2 had fractionated (8.8%), late (2.8%), and split (5.7%) EGMs not seen in group 1. Trans-septal activation >40 ms (sensitivity 60%, specificity 100%; P <0.001) and EGM duration >95 ms during pacing (sensitivity 22%, specificity 91%; P <0.001) identified septal scar (13/26 pts).

Conclusions—

In patients with nonischemic cardiomyopathy, VT and septal scar, delayed transmural conduction time (>40 ms) and fractionated, late, split, and wide (>95 ms) bipolar EGMs during RV basal pacing identify intramural VT substrate. In select cases, the basal septum appears compartmentalized as the stimulated wavefront is rerouted to the scar border.

Pseudo-postpacing interval of diastolic potential after entrainment pacing of remote bystander pathway in reentrant ventricular tachycardia

After entrainment pacing, the postpacing interval of a diastolic potential may be misinterpreted if the distal tip of the ablation catheter captures a remote bystander pathway adjacent to the critical isthmus of a complex reentrant circuit in a structurally diseased heart. We discuss this possible pitfall of entrainment mapping of reentrant ventricular tachycardia, observed after a healed myocardial infarction.

Influence of left ventricular hypertrophy on scar identification during bipolar voltage mapping

PURPOSE

Bipolar endocardial signal amplitude (BESA) <1.5 mV defines scar in the left ventricle (LV). It is not known if LV hypertrophy (LVH) increases overall bipolar signal amplitude and if scar identification with LVH requires a higher voltage cutoff.

METHODS

We compared the LV BESA of four patients with moderate LVH on echo (≥1.6 cm) to that of ten consecutive patients with no LVH with both groups having normal systolic function and no scar. Additionally, in 12 patients with ischemic scar (ICM) and moderate LVH (≥1.6 cm), we assessed scar area and percent abnormal electrograms (width >80 ms and/or split/fractionated) using 1.5 and 2.5 mV defined border zone cutoff values and compared results to those from 12 ICM patients with no LVH matched for age, sex, scar distribution, and LV ejection fraction.

RESULTS

Average BESA in the setting of normal systolic function/no scar was comparable in patients with (4.7 ± 3.0 mV, 95% signals >1.58 mV) and those without LVH (4.9 ± 1.6 mV, 95% signals >1.62 mV). In patients with ICM and LVH versus without LVH, there was a smaller area of dense scar <0.5 mV/total scar (15% versus 23%, p = 0.03) but no significant difference in the size of the border zone, or percentage of abnormal electrograms identified within border zones defined by either the 0.5-1.5 mV or 0.5-2.5 mV cutoff values.

CONCLUSIONS

Patients with and without LVH with normal systolic function show similar LV endocardial bipolar signal characteristics. Modifying the bipolar amplitude cutoff at the infarct border zone did not increase overall scar size in patients with versus those without LVH. A 1.5 mV-bipolar voltage cutoff used for scar definition seems appropriate even in patients with marked LVH.

How to troubleshoot the electroanatomic map

An electroanatomical mapping system is a useful tool for complex arrhythmia ablation. The system reconstructs the precise 3-dimensional chamber of interest with electrical and anatomical information. There are several technical aspects that physicians should be aware of to maximize its efficacy. This review provides relevant information on troubleshooting of the mapping system.

Entrainment mapping for rapid distinction of left and right atrial tachycardias

BACKGROUND

Distinguishing left from right atrial tachycardia is a critical step for guiding ablation.

OBJECTIVES

The purpose of this study was to develop and validate a simple algorithm predicting the location of macroreentrant atrial tachycardia (AT) circuits from limited entrainment mapping in right atrium (RA) and coronary sinus (CS).

METHODS

In 180 patients with organized reentrant AT, entrainment was performed at the high RA, proximal CS, and distal CS. The difference between the postpacing interval (PPI) and tachycardia cycle length (TCL) was calculated at each site. The location of the AT reentrant circuit was determined by mapping and ablation. An algorithm predicting AT regions was developed from 104 ATs in the first 90 patients (group I) and prospectively evaluated in a validation cohort of 106 ATs in the second 90 patients (group II).

RESULTS

In group I, PPI-TCL difference <50 or >50 ms at the high RA distinguished RA from LA reentrant circuits. For RA tachycardias, PPI-TCL difference at the proximal CS distinguished common flutter from lateral RA circuits. For LA circuits, PPI-TCL difference at the proximal and distal CS distinguished perimitral reentry from reentry involving the right pulmonary veins and septum. In group II, an algorithm based on PPI-TCL difference >50 or <50 ms at the high RA, proximal CS, or distal CS had sensitivity of 94%, specificity of 88%, and predictive accuracy of 93% for predicting the successful ablation region.

CONCLUSION

Limited entrainment from sites accessible from the RA can expeditiously suggest the AT location to guide more detailed mapping and potentially avoid unnecessary transseptal punctures in some patients.

Comparison of mapping criteria for hemodynamically tolerated, postinfarction ventricular tachycardia

BACKGROUND

Mapping criteria for hemodynamically tolerated, postinfarction ventricular tachycardia (VT) have been evaluated in only small series of patients.

OBJECTIVES

The purpose of this study was to evaluate the utility of various mapping criteria for identifying a critical VT circuit isthmus in a post hoc analysis.

METHODS

Ninety VTs (cycle length 491 +/- 84 ms) were mapped in 48 patients with a prior myocardial infarction. The mapping catheter was positioned within a protected area of the reentrant circuit of the targeted VTs at 176 sites. All sites showed concealed entrainment. The predictive values of the following mapping criteria for a successful ablation site were compared: discrete isolated potential during VT, inability to dissociate the isolated potential from the VT, endocardial activation time >70 ms, matching electrogram-QRS and stimulus-QRS intervals, VT termination without global capture during pacing, stimulus-QRS/VT cycle length ratio <or=0.7, and postpacing interval. For each criterion, the receiver operating characteristic curve was constructed, and the area under the curve was calculated to assess the discriminatory value of the criterion.

RESULTS

Seventy-eight of 90 VTs (87%) were successfully ablated. The area under the receiver operating characteristic curve was largest (0.89) for matching stimulus-QRS and electrogram-QRS intervals. In combination with an isolated potential that could not be dissociated from the VT, the area under the receiver operating characteristic curve increased to 0.93.

CONCLUSION

At sites with concealed entrainment, matching stimulus-QRS and electrogram-QRS intervals were superior to other criteria in differentiating a critical isthmus from bystander or noncritical sites in postinfarction VT.

Recording Techniques for Clinical Electrophysiology

The precise techniques employed in the electrophysiology laboratory influence the nature of the electrograms that are recorded during mapping procedures. Unipolar recordings that are minimally filtered can be useful for mapping focal arrhythmia sources, but have substantial far-field signal that can obscure low-amplitude signals of interest in abnormal regions. Bipolar recordings are standard in most laboratories because rejection of far-field signal facilitates identification of local potentials in abnormal areas, but the signal of interest can be beneath either recording electrode and far-field signals do occur. Simultaneously obtained unipolar recordings are a useful adjunct to bipolar recordings in some situations. High pass filtering and digital sampling also influence electrogram characteristics. High pass filtering of unipolar recordings can be useful to reduce far-field components, but limits inferences from electrogram morphology.

Novel use of postpacing interval mapping to guide radiofrequency ablation of focal atrial tachycardia with long intra-atrial conduction time

If the intra-atrial conduction time of a focal tachycardia is prolonged and exceeds the tachycardia cycle length, isochronal electroanatomical maps may be confusing by not showing the classical centrifugal pattern of focal activation. In addressing the hypothesis that by mapping post pacing intervals (PPI), the shortest PPI (ideally identical to tachycardia cycle length) would clearly display the site of origin of a focal tachycardia; this technique was used successfully to identify the origin and ablate the atrial tachycardia of a patient with previously corrected Tetralogy of Fallot.