Resetting and Entrainment of Reentrant Arrhythmias: Part II: Informative Content and Practical Use of These Responses

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.

Incremental benefit of a novel signal recording system during mapping and ablation

AIMS

Current electrophysiology signal recording and mapping systems have limited dynamic range (DR) and bandwidth, which causes loss of valuable information during acquisition of cardiac signals. We evaluated a novel advanced signal processing platform with the objective to obtain and assess additional information of clinical importance.

METHODS AND RESULTS

Over 10 canines, we compared intracardiac recordings within all cardiac chambers, in various rhythms, in pacing and during radiofrequency (RF) ablation across two platforms; a conventional system and the PURE EP™ [(PEP); Bio Sig Technologies, Inc., Los Angeles, CA, USA]. Recording cardiac signals with varying amplitudes were consistently and reproducibly observed, without loss of detail or introduction of artefact. Further the amplitude of current of injury (COI) on the unipolar signals correlated with the instantaneous contact force (CF) recorded on the sensing catheter in all the animals (r2 = 0.94 in ventricle). The maximum change in the unipolar COI correlated with the change in local electrogram amplitude during non-irrigated RF ablation (r2 = 0.61 in atrium). Reduction in artefact attributable to pacing (20 sites) and noise during ablation (48 sites) was present on the PEP system. Within the PEP system, simultaneous display of identical signals, filtered differently, aided the visualization of discrete conduction tissue signals.

CONCLUSION

Compared to current system, the PEP system provided incremental information including identifying conduction tissue signals, estimates of CF and a surrogate for lesion formation. This novel signal processing platform with increased DR and minimal front-end filtering may be useful in clinical practice.

Left posterior fascicular ventricular tachycardia in a young infant with a structurally normal heart: Clinical course and caveats to electrocardiographic diagnosis

In this illustrative case report, we describe a rare case of left posterior fascicular ventricular tachycardia (LPFVT) in a 2 month-old infant with emphasis on electrocardiographic caveats to diagnosis. The clinical course, treatment, and eventual resolution of the VT over a 2 year follow-up is comprehensively compared and contrasted to a modicum of individual such case reports of infants. The corpus of each such case of infantile LPVT is systematically reviewed and succinctly summarized in a tabular compendium. The collective knowledge compiled here should allow for a refined approach to diagnosis and management of this unusual arrhythmia.

A constant postpacing interval in response to overdrive pacing with variable number of beats: An aid in the identification of entrainment for a particular pacing train during macroreentrant atrial tachycardias

BACKGROUND

When pacing trains with a constant cycle length (CL) but increasing number of beats are introduced during a macroreentrant atrial tachycardia (MAT), the postpacing interval (PPI) is expected to increase if entrainment does not occur but could be stable if entrainment occurs. We tested the ability of PPI analysis to detect entrainment.

METHODS

Synchronized pacing trains with increasing number of beats (1-20) were delivered from the coronary sinus (CS) and lateral right atrium (RA) at a CL 20 ms shorter than the MAT CL. Pacing trains were grouped in pairs differing by one-paced beat, and the ∆PPI measured.

RESULTS

In an initial prospective cohort of 21 patients (48% had left atrial flutter) the mean ∆PPI was 21.3 ± 5.6 ms for pairs of pacing trains in which neither entrained the MAT and 2.8 ± 1.4 ms for those in which both entrained the MAT (P < .0001). Results were similar for common vs atypical flutter, PPI-TCL ≤30 ms vs PPI-TCL >30 ms, presence vs absence of antiarrhythmic drugs and faster vs slower MAT. When an index pacing train was compared to one with two-paced beats less, a PPI difference of <19 ms identified entrainment with 95% sensitivity and 98% specificity. In a validation cohort of 16 patients, this cut-off value resulted in sensitivity and specificity of 90% and 94%.

CONCLUSIONS

A relatively constant ∆PPI in response to overdrive pacing with identical CL but different number of beats allows accurate discrimination between trains that entrained vs those which did not entrain a MAT.

Focal atrial tachycardia ablation: Highly successful with conventional mapping

BACKGROUND/OBJECTIVE

Radiofrequency catheter ablation (RFCA) of focal atrial tachycardia (FAT) traditionally is guided by conventional endocardial mapping of earliest atrial activation; however, more recently electro-anatomical mapping is heralded as a more effective, albeit more expensive, tool to guide ablation. Herein we present the results of conventional mapping-guided RFCA. Apropos, we conducted a literature search of studies reporting > 10 FAT patients submitted to RFCA.

METHODS AND RESULTS

Conventional mapping-guided RFCA, performed in 63 FAT patients (aged 42.4 + 17.3 years; 14 with incessant tachycardia and 12 with tachycardiomyopathy (TCM)), was successful in 61 (96.8%) patients, applied for single foci in 59 (93.7%) and two foci in 4 patients, right (n = 46) or left sided (n = 17). The earliest atrial activation time at the ablation site was 41.3 ± 16.2 ms. Fluoroscopy time averaged 27.3 + 18.7 min, and procedure lasted 2.6 + 1.7 h. Complications occurred in two patients (sinus pauses in one needing a pacemaker and a large inguinal hematoma in one). Over 29.0 + 22.9 months, four patients (6.5%) had recurrences, of whom three were successfully re-ablated. All patients with TCM showed gradual improvement to normalization over 4-6 months. Literature search showed that RFCA success is equally high when guided with either conventional (88.5%) or electro-anatomical mapping (90%) with similar recurrences (9.6% vs. 9.5%).

CONCLUSION

Conventional mapping-guided RFCA of FAT had high success (96.8%) with low complication (3.2%) and recurrence rates (6.5%). TCM was fully reversible. These results are comparable to those achieved with the more expensive electro-anatomical mapping, which may be reserved for more complex cases or for those failing the conventional approach.

Unifying Algorithm for Mechanistic Diagnosis of Atrial Tachycardia

BACKGROUND

No existing criteria unequivocally differentiate focal atrial tachycardia (AT) caused by microreentry, triggered activity, or enhanced automaticity. Although macroreentrant AT is readily diagnosed based on entrainment criteria, the smaller circuit dimension associated with microreentrant AT makes it challenging to validate the presence of reset with fusion. An algorithm was, therefore, developed that is independent of entrainment but which reliably identifies specific mechanisms of focal AT.

METHODS AND RESULTS

Fifty-nine patients with AT underwent adenosine testing after mapping of tacycardia. Ten ATs had nonfocal activation, with ≥90% of tachycardia cycle length identified with electroanatomical mapping, findings consistent with macroreenty. All ATs were insensitive to adenosine. Forty-nine patients had focal AT with centrifugal activation. In 32/49 (67%) ATs, electrograms were nonfractionated, and <50% of tachycardia cycle length could be mapped. Based on programmed stimulation, 26/32 (81%) of these ATs were classified as due to triggered activity and 6/32 (19%) as due to enhanced automaticity. Adenosine terminated 100% of triggered ATs and transiently slowed or suppressed 100% of automatic ATs. The remaining 17 focal ATs had localized fractionated electrograms (≥35% of tachycardia cycle length) at the site of successful ablation and were classified as microreentrant. Adenosine had no effect in these ATs. The response to adenosine accurately differentiated all subtypes of focal AT, P<0.05.

CONCLUSIONS

Adenosine-sensitivity (termination or transient slowing/suppression) in response to adenosine was 100% sensitive and specific for identifying focal AT mechanisms due to triggered activity or automaticity, respectively. Absence of adenosine effect on focal AT identifies tachycardia due to microreentry.

The pioneering work of George Mines on cardiac arrhythmias: groundbreaking ideas that remain influential in contemporary cardiac electrophysiology

George Mines was a pioneering physiologist who, despite an extremely short period of professional activity and only primitive experimental methodology, succeeded in formulating concepts that continue to be of great influence today. Here, we review some of his most important discoveries and their impact on contemporary concepts and clinical practice. Mines' greatest contribution was his conceptualization and characterization of circus movement reentry. His observations and ideas about the basis for cardiac reentrant activity underlie how we understand and manage a wide range of important clinical rhythm disturbances today. The notions he introduced regarding the influence of premature extrastimuli on reentry (termination, resetting and entrainment) are central to contemporary assessment of arrhythmia mechanisms in clinical electrophysiology laboratories and modern device therapy of cardiac tachyarrhythmias. Refinements of his model of reentry have led to sophisticated biophysical theories of the mechanisms underlying cardiac fibrillation. His seminal observations on the influence of electrolyte derangements and autonomic tone on the heart are relevant to our understanding of the physiology and pharmacology of arrhythmias caused by cardiac pathology. In this era of advanced technology, it is important to appreciate that ideas of lasting impact come from great minds and do not necessarily require great tools.