Cellular mechanisms of ventricular bipolar electrograms showing double and fractionated potentials

Catheter Ablation of Ventricular Tachycardia in Patients With Arrhythmogenic Right Ventricular Cardiomyopathy/Dysplasia: A Sequential Approach

Background

It has been suggested that endocardial and epicardial ablation of ventricular tachycardia (VT) improves outcome in arrhythmogenic right ventricular cardiomyopathy/dysplasia. We investigated our sequential approach for VT ablation in patients with arrhythmogenic right ventricular cardiomyopathy/dysplasia in a single center.

Methods and Results

We included 47 patients (44±16 years) with definite (81%) or borderline (19%) arrhythmogenic right ventricular cardiomyopathy/dysplasia between 1998 and 2016. Our ablation strategy was to target the endocardial substrate. Epicardial ablation was performed in case of acute ablation failure or lack of an endocardial substrate. Single and multiple procedural 1‐ and 5‐year outcome data for the first occurrence of the study end points (sustained VT/ventricular fibrillation, heart transplant, and death after the index procedure, and sustained VT/ventricular fibrillation for multiple procedures) are reported. Eighty‐one radiofrequency ablation procedures were performed (mean 1.7 per patient, range 1–4). Forty‐five (56%) ablation procedures were performed via an endocardial, 11 (13%) via an epicardial, and 25 (31%) via a combined endo‐ and epicardial approach. Complete acute success was achieved in 65 (80%) procedures, and partial success in 13 (16%). After a median follow‐up of 50.8 (interquartile range, [18.6; 99.2]) months after the index procedure, 17 (36%) patients were free from the primary end point. After multiple procedures, freedom from sustained VT/ventricular fibrillation was 63% (95% CI, 52–75) at 1 year, and 45% (95% CI, 34–61) at 5 years, with 36% of patients receiving only endocardial radiofrequency ablation. A trend (log rank P=0.058) towards an improved outcome using a combined endo‐/epicardial approach was observed after multiple procedures.

Conclusion

Endocardial ablation can be effective in a considerable number of arrhythmogenic right ventricular cardiomyopathy/dysplasia patients with VT, potentially obviating the need for an epicardial approach.

Antiarrhythmic and antioxidant activity of novel pyrrolidin-2-one derivatives with adrenolytic properties

A series of novel pyrrolidin-2-one derivatives (17 compounds) with adrenolytic properties was evaluated for antiarrhythmic, electrocardiographic and antioxidant activity. Some of them displayed antiarrhythmic activity in barium chloride-induced arrhythmia and in the rat coronary artery ligation-reperfusion model, and slightly decreased the heart rate, prolonged P-Q, Q-T intervals and QRS complex. Among them, compound EP-40 (1-[2-hydroxy-3-[4-[(2-hydroxyphenyl)piperazin-1-yl]propyl]pyrrolidin-2-one showed excellent antiarrhythmic activity. This compound had significantly antioxidant effect, too. The present results suggest that the antiarrhythmic effect of compound EP-40 is related to their adrenolytic and antioxidant properties. A biological activity prediction using the PASS software shows that compound EP-35 and EP-40 can be characterized by antiischemic activity; whereas, compound EP-68, EP-70, EP-71 could be good tachycardia agents.

Modeling cardiac electrical activity at the cell and tissue levels

Significant tissue structures exist in cardiac ventricular tissue, which are of supracellular dimension. It is hypothesized that these tissue structures contribute to the discontinuous spread of electrical activation, may contribute to arrhythmogenesis, and also provide a substrate for effective cardioversion. However, the influences of these mesoscale tissue structures in intact ventricular tissue are difficult to understand solely on the basis of experimental measurement. Current measurement technology is able to record at both the macroscale tissue level and the microscale cellular or subcellular level, but to date it has not been possible to obtain large volume, direct measurements at the mesoscales. To bridge this scale gap in experimental measurements, we use tissue-specific structure and mathematical modeling. Our models, which can incorporate ion channel models at the cell level into the reaction-diffusion equations at the tissue level, have enabled us to consider key hypotheses regarding discontinuous activation.

Cardiac electrophysiology and tissue structure: bridging the scale gap with a joint measurement and modelling paradigm

Significant tissue structures exist in cardiac ventricular tissue that are of supracellular dimension. It is hypothesized that these tissue structures contribute to the discontinuous spread of electrical activation, may contribute to arrhymogenesis and also provide a substrate for effective cardioversion. However, the influences of these mesoscale tissue structures in intact ventricular tissue are difficult to understand solely on the basis of experimental measurement. Current measurement technology is able to record at both the macroscale tissue level and the microscale cellular or subcellular level, but to date it has not been possible to obtain large volume, direct measurements at the mesoscales. To bridge this scale gap in experimental measurements, we use tissue-specific structure and mathematical modelling. Our models have enabled us to consider key hypotheses regarding discontinuous activation. We also consider the future developments of our intact tissue experimental programme.

Multichannel data acquisition system for mapping the electrical activity of the heart

BACKGROUND

Details of the electrical conduction pattern of the heart are revealed to the electrophysiologist when multichannel data are used for activation mapping. Commercial electronic systems are available for simultaneous acquisition of many surface electrograms; however, the cost of these systems may be prohibitive and they can be mostly inflexible for adaptation to other research projects. Furthermore, the hardware and software design is often proprietary. In this article we describe the in-house design and implementation of a 320-multichannel acquisition system for animal electrophysiologic research.

METHOD AND RESULTS

Several modules comprise this system. The multichannel data are first preprocessed by amplification, filtering, and analog multiplexing. An algorithm for automatic adjustment of signal gains is implemented to maximize the voltage resolution and minimize noise pickup. Signals are then digitized, and sequenced to order the multichannel data and to add markers required for analysis. The digital data are streamed to archival storage media. Additionally, the electrocardiogram (ECG), blood pressure, and stimulus channel signals are stored simultaneously. Selected signals are then displayed in real-time for measurement and analysis and as a check of the system integrity. Examples of multielectrode arrays and surface recordings are provided. Costs for building such a system are estimated.

CONCLUSIONS

Multichannel data acquisition systems that are designed and constructed in-house have several advantages over turnkey commercial systems, including the potential for considerable cost savings, flexibility in acquiring data, and the ability to subsequently add additional components.

Vector Mapping in Localizing the Transverse Conduction Site of the Crista Terminalis in Patients with Typical Atrial Flutter

BACKGROUND

The difference in the conduction properties of the crista terminalis (CT) along its course, has not been fully clarified. Using the vector mapping method, we localized the transverse conduction (TC) site of the CT and elucidated its conduction capabilities in patients with typical atrial flutter (AF).

METHODS

The TC site of the CT was localized by the analysis of the polarity reversal of the double potentials recorded at 10 sites along the CT using a 20-pole deflectable catheter in 17 patients. The conduction capabilities of the TC site were analyzed during incremental pacing delivered from 100 beats/min to 2-to-1 local capture at the low anterior (LARA) and posterior (LPRA) right atrium.

RESULTS

At a pacing rate of 100 beats/min, TC at a single site was observed in 15 patients during LARA pacing and 7 patients during LPRA pacing, respectively. TC sites were distributed from superior to middle third of the CT in all patients. TC was bidirectional in 4 sites, but was unidirectional in the remaining 14 sites. Following an increase in the pacing rate, TC was blocked in all 7 sites during LPRA pacing and 11 of 15 sites during LARA pacing. Shift in the location of the TC site was not observed in any of the patients before TC block. The conduction block rate during pacing from LARA was significantly higher than that from LPRA (211 +/- 59 beats/min vs 145 +/- 66 beats/min, P < 0.01).

CONCLUSIONS

The superior to middle third of the CT provides TC capabilities. The TC across the CT was caused by a preferential conduction site and most of these TC were unidirectional, and stable in location irrespective of the change in the conduction rate.

Synthesis and evaluation of in vivo activity of diphenylhydantoin basic derivatives

During the search for antiarrhythmic agents among amide derivatives of phenytoin, compound 7 {3-ethyl-1-[2-hydroxy-3-(4-phenyl-piperazin-1-yl)-propyl]-2,4-dioxo-5,5-diphenyl-imidazolidine} was selected as it showed antiarrhythmic as well as antihypertensive activity. Treating this compound as a lead, new derivatives 8-19 were synthesised, differing in piperazine phenyl ring substitution (2-, 3-, 4-Cl, 2-CH3O) as well as in hydantoin N3 alkyl chain (ethyl, ethyl acetate or ethyl 2-propionate). The obtained compounds in form of hydrochlorides 7a-19a were examined for prophylactic antiarrhythmic and antihypertensive properties. Compounds containing ethyl 2-propionate moiety (17a, 18a) exhibited the highest antihypertensive properties. Water-soluble compounds, containing 2-methoxyphenylpiperazine group (11a, 19a), showed strong antiarrhythmic properties in adrenaline-induced arrhythmia; compound 9a {1-[3-(4-(3-chloro-phenyl)-piperazin-1-yl)- 2-hydroxy-propyl]- 3-ethyl-2,4-dioxo-5,5-diphenyl-imidazolidine hydrochloride} exhibited the highest antiarrhythmic activity in barium chloride arrhythmia model.

A theoretical model of the high-frequency arrhythmogenic depolarization signal following myocardial infarction

Theoretical body-surface potentials were computed from single, branching and tortuous strands of Luo-Rudy dynamic model cells, representing different areas of an infarct scar. When action potential (AP) propagation either in longitudinal or transverse direction was slow (3-12 cm/s), the depolarization signals contained high-frequency (100-300 Hz) oscillations. The frequencies were related to macroscopic propagation velocity and strand architecture by simple formulas. Next, we extended a mathematical model of the QRS-complex presented in our earlier work to simulate unstable activation wavefront. It combines signals from different strands with small timing fluctuations relative to a large repetitive QRS-like waveform and can account for dynamic changes of real arrhythmogenic micropotentials. Variance spectrum of wavelet coefficients calculated from the composite QRS-complex contained the high frequencies of the individual abnormal signals. We conclude that slow AP propagation through fibrotic regions after myocardial infarction is a source of high-frequency arrhythmogenic components that increase beat-to-beat variability of the QRS, and wavelet variance parameters can be used for ventricular tachycardia risk assessment.

"Double" potentials define linear lesion conduction block using a novel mapping/linear lesion ablation catheter

INTRODUCTION

A novel mapping/ablation catheter using a coaxially ablation electrode (E) that is moveable between distal and proximal ring electrodes along its shaft was used to create a linear lesion over the cavotricuspid isthmus (CTI) and bidirectional block in 32 patients (21 men; age 38-79 years) undergoing ablation for counterclockwise atrial flutter.

METHODS AND RESULTS

Two bipolar electrograms (E1 and E2) were recorded: between E and the distal ring electrode and between E and the proximal ring electrode. Interpole distance varied for both as the E traversed the slide shaft. Given the catheter's concept, these bipoles are orientated exactly along the line of lesion creation. Prior to ablation, unitary bipolar electrograms were recorded along the catheter slide shaft position. As the CTI lesion was created (E moved along the catheter slide shaft in 2-mm steps with radiofrequency energy delivered to achieve 65 degrees C for 60 sec at each), double potentials (DP) were observed. Interpotential distance became maximal with completion of the linear lesion and bidirectional block. DPs were noted in all these procedures. With pacing from the low septal right atrium at bidirectional block creation, interpotential timing was 140.9 +/- 15 msec and from the low right atrial free wall was 145.13 +/- 18 msec. In sinus rhythm, DP interpotential timing was less (35.13 +/- 9 msec) as activation fronts arrived from both septal and anterior atrial aspects.

CONCLUSION

Bipolar recordings from the coaxially moveable electrode catheter provide unique electrogram data. DPs recorded during and after linear lesion creation can define conduction block across that lesion without the need for additional mapping catheters or complex mapping technology.

Current concepts of ventricular defibrillation

The aim of this article is to review the current concepts of ventricular defibrillation. We studied the interaction between strong electrical stimulus and cardiac responses in both animal models and in humans. We found that a premature stimulus (S2) of appropriate strength results in figure-eight reentry in vitro by inducing propagated graded responses. The same stimulation protocol induces figure-eight reentry and ventricular fibrillation (VF) in vivo. When the S2 strength and the magnitude of graded responses increase beyond a critical level, the increase in refractoriness at the site of the stimulus becomes so long that the unidirectional block becomes bidirectional block, preventing the formation of reentry (upper limit of vulnerability [ULV]). In other studies, we found that the effects of an electrical stimulation on reentry is in part determined by the timing of the stimulus. A protective zone is present after the induction of VF and after an unsuccessful defibrillation shock during which an electrical stimulus can terminate reentry and protect the heart from VF. These results indicate that the effects of a defibrillation shock is dependent on both the strength and the timing of the shock. Timing is not important in areas where the shock field strength is > or = ULV because the shock terminates all reentry but cannot reinitiate new ones. However, in areas where shock field strength is < ULV, the effects of the shock are determined by the timing of the shock relative to local VF activations. This ULV hypothesis of defibrillation explains the probabilistic nature of ventricular defibrillation. It also indicates that, to achieve a high probability of successful defibrillation, a shock must result in a shock field strength of > or = ULV throughout the ventricles.