Activation times in and adjacent to reentry circuits during entrainment: implications for mapping ventricular tachycardia

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.

Mapping and ablation procedures for the treatment of ventricular tachycardia

INTRODUCTION

Ventricular tachycardia (VT) may occur in the presence or absence of structural heart disease. Given that the management of VT hinges on the presence of symptoms and risk of sudden cardiac death (SCD), the main treatment goals are elimination of symptoms (including frequent implantable cardioverter defibrillator [ICD] therapies) and prevention of SCD. Unfortunately, medical management is suboptimal in a significant proportion of patients. As such, ablative therapy plays a prominent role in the treatment of ventricular tachycardia.

AREAS COVERED

In this review, we will discuss various VT disorders that are encountered in patients with and without structural heart disease. Further, we will highlight salient features regarding mapping and ablation of the various VT syndromes. Finally, we will discuss what lies on the horizon for VT ablation. Expert commentary: Meticulous mapping should aim to find the region that is most likely to be successful and least likely to result in a complication. Although recognition of the various mechanisms of VT, familiarity with different methods to mapping and ablation, and awareness of potential limitations of current approaches is critical, a thorough understanding of the fundamental principles and nuances of each facet within EP is required to ensure optimal outcomes for our patients.

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

OBJECTIVES

The goal of this study was to assess entrainment for distinguishing far-field potentials (FFP) due to depolarization of tissue at a distance from the mapping catheter from the local potential (LP) due to depolarization of tissue at the catheter electrode during mapping of ventricular tachycardia (VT).

BACKGROUND

Electrograms with multiple peaks commonly complicate mapping and identification of catheter ablation targets in infarcts.

METHODS

Retrospective analysis of catheter mapping data from eight patients with prior infarction was performed to evaluate multipotential electrograms at sites where pacing entrained VT. Potentials that were visible and not altered during pacing were defined as FFP. Potentials obscured by the pacing stimulus were designated possible LPs. The criteria for FFP were then assessed in a second cohort of five patients.

RESULTS

At 32 of 39 (82%) sites with multiple potentials, entrainment identified one of the potentials as an FFP. Radiofrequency ablation, assessed at 15 sites, reduced the amplitude of LPs by 62%, without significant effect on FFP amplitude. At 56% of sites with multiple potentials, measuring the postpacing interval to an FFP would lead to erroneous classification of the site location relative to the reentry circuit. In prospective evaluation, double potentials were identified at 77 sites in infarcts; entrainment demonstrated an FFP at 66 (86%) sites.

CONCLUSIONS

Far-field potentials are common during mapping in infarcts. Many can be distinguished from local potentials by entrainment, improving the accuracy of mapping.

Estimation of entrainment response using electrograms from remote sites: validation in animal and computer models of reentrant tachycardia

INTRODUCTION

Studies suggest that entrainment response (ER) of reentrant tachycardia to overdrive pacing can be estimated using signals from sites other than the paced site.

METHODS AND RESULTS

A formula for estimation of ER using remote sites against the difference between the postpacing interval (PPI) and tachycardia cycle length (TCL) determined solely from the paced site signal was validated in experimental data and using a simple two-dimensional cellular automata model of reentry. The model also was used to study the behavior and features of entrained surfaces, including the resetting of tachycardia phase by single premature paced stimuli. Experimental results from 1,484 remote sites in 115 pacing sequences showed the average of the median ER estimate error at each pacing site was -2 +/- 5 msec, and the median ER estimate was within 10 msec of PPI-TCL for 94% of pacing sites. From simulation results, ER at the paced site was accurately estimated from >99.8% of 20,764 remote sites during pacing at 24 sites and three paced cycle lengths. Intervals measured from remote electrograms revealed whether the site was activated orthodromically or nonorthodromically during pacing, and results of simulations illustrated that the portion of the surface activated nonorthodromically during pacing increased with distance from the pacing site to the circuit. The phenomenon of nonorthodromic activation of reentrant circuits predicted by modeling was discernible in measurements taken from the animal model of reentrant tachycardia. Results also showed that, for single premature stimuli that penetrated the tachycardia circuit, phase reset of the tachycardia was linearly related to distance between the central obstacle and the paced site.

CONCLUSION

The ER is a complex but predictable perturbation of the global activation sequence of reentrant tachycardias. This predictability allows calculations of the response from anywhere on the perturbed surface. These findings suggest new techniques for measurement of the ER, which may lend themselves to computer-based methods for accurate and rapid mapping of reentrant circuits.

Exploring postinfarction reentrant ventricular tachycardia with entrainment mapping

Ventricular tachycardia late after myocardial infarction is usually due to reentry in the infarct region. These reentry circuits can be large, complex and difficult to define, impeding study in the electrophysiology laboratory and making catheter ablation difficult. Pacing through the electrodes of the mapping catheter provides a new approach to mapping. When pacing stimuli capture the effects on the tachycardia depend on the location of the pacing site relative to the reentry circuit. The effects observed allow identification of various portions of the reentry circuit, without the need for locating the entire circuit. Isthmuses where relatively small lesions produced by radiofrequency catheter ablation can interrupt reentry can often be identified. A classification that divides reentry circuits into one or more functional components helps to conceptualize the reentry circuit and predicts the likelihood that heating with radiofrequency current will terminate tachycardia. These methods are helping to define human reentry circuits.

Effect of recording site on postpacing interval measurement during catheter mapping and entrainment of postinfarction ventricular tachycardia

INTRODUCTION

During entrainment of reentrant ventricular tachycardia (VT), the difference between the postpacing interval (PPI) and the VT cycle length (VTCL) measured at the pacing site is an indication of the conduction time from the pacing site to the reentry circuit. The difference is usually < or = 30 msec at successful ablation sites. However, electrical noise during pacing sometimes obscures the electrograms recorded directly from the pacing site. The objective of this study is to determine if the PPI-VTCL difference measured at the mapping catheter electrodes proximal to the stimulating electrode accurately predicts the PPI-VTCL difference at the stimulating electrode.

METHODS AND RESULTS

Endocardial catheter mapping was performed in 26 patients with infarct-related VT. At 191 sites during 56 VTs, unipolar pacing from the distal electrode entrained VT and electrograms recorded from the mapping catheter were discernable following pacing in both the bipolar recordings from the distal electrode pair (BI 1-2) and the electrode pair 6 mm proximal to the distal electrode (BI 3-4). The PPI-VTCL difference at BI 1-2 correlated well with that measured at BI 3-4 (r = 0.88, P = 0.001). A PPI-VTCL difference at BI 3-4 < or = 30 msec predicted a PPI-VTCL difference at BI 1-2 < or = 30 msec with a sensitivity of 95%, specificity of 87 %, and predictive accuracy of 91%.

CONCLUSIONS

Measurement of the PPI from electrodes proximal to the stimulating electrode is a reasonable alternative when the PPI cannot be assessed from the pacing electrode.

Current role and future perspectives for radiofrequency catheter ablation of postmyocardial infarction ventricular tachycardia

The most common substrate for ventricular tachycardia (VT) is a postmyocardial infarction (MI) scar. Radiofrequency catheter ablation (RFCA) in post-MI VT faces clinical, electrophysiologic, anatomic, and methodologic difficulties not found in many other human tachycardias. The pathophysiologic understanding of post-MI VT is incomplete; this influences the process of selecting RFCA target sites, which is time consuming, demands catheter stability, and has low sensitivity and predictive value for VT interruption by RF current. Improving and simplifying the methodology of RFCA in post-MI VT is badly needed. We review the pathophysiology of post-MI VT from the data reported on endocardial, epicardial, and intramural ventricular mapping obtained either intraoperatively or in a Langendorff perfused set-up in hearts from transplanted patients. From these studies we conclude that (1) some post-MI VT cases are not amenable to RFCA (reentry around the scar, VT having a subepicardial or deep intramural substrate, or a wide, extensive, subendocardial intrascar area of slow conduction); and (2) searching for the endocardial exit is advantageous for selecting the RFCA targets. We also comment on a new self-reference mapping catheter that allows the recording of high gain, noise-free, unfiltered and filtered unipolar signals as well as unipolar pacing. Among the unresolved issues in these patients is the meaning of fast nonclinical VT induced after successful RFCA of the clinical VT, which may explain why a substantial number of these patients still receive an implantable cardioverter-defibrillator.

Catheter ablation of clinical intraatrial reentrant tachycardias resulting from previous atrial surgery: localizing and transecting the critical isthmus

OBJECTIVES

We sought to evaluate the efficacy of anatomically based radiofrequency catheter ablation for the treatment of intraatrial reentrant tachycardia in patients with previous atrial surgery.

BACKGROUND

Intraatrial reentrant tachycardias, a common late complication of atrial surgery, are often refractory to standard medical management. Data from experimental animals and from humans indicate that anatomic barriers resulting from residual atrial scars provide a substrate for intraatrial reentry. We speculated that these tachycardias require a narrow isthmus of tissue between surgical scars and native nonconductive boundaries and that transection of this isthmus with radiofrequency ablation would therefore constitute an effective treatment.

METHODS

Fourteen patients with a history of atrial surgery and clinical intraatrial reentrant tachycardia underwent electrophysiologic testing. From activation mapping, putative surgical scars and patches that served as boundaries of reentrant circuits were identified. Radiofrequency lesions were then placed to transect the narrowest isthmus of conducting tissue between a surgical scar and an anatomic barrier. Catheter ablation was attempted only for tachycardias consistent with the patient's clinical arrhythmias.

RESULTS

Radiofrequency catheter ablation was attempted for 17 (55%) of 31 tachycardias identified; it successfully terminated tachycardias in 13 (93%) of 14 patients (95% confidence interval [CI] 79% to 99%). There were clinical recurrences in six patients (46%, 95% CI 19% to 73%), each of whom underwent a repeat ablation that was successful. Twelve (86%) of 14 patients (95% CI 67% to 99%) have remained free of intraatrial reentrant tachycardia for a mean of 7.5 +/- 5.3 months.

CONCLUSIONS

Anatomically guided radiofrequency catheter ablation is an effective technique for definitive management of intraatrial reentrant tachycardia in patients with previous atrial surgery.

Entrainment techniques for mapping atrial and ventricular tachycardias

Many atrial tachycardias, atrial flutter, and postmyocardial infarction ventricular tachycardias are due to reentry through large "macroreentrant" circuits. These circuits can be difficult to define by catheter mapping of the activation sequence. Entrainment techniques allow the relation of a mapping site to the reentrant circuit to be assessed on a site-by-site basis during catheter mapping. Regions of abnormal conduction that are in the reentrant circuit can be distinguished from bystander sites outside the circuit. A mapping site classification to guide catheter ablation is reviewed.