Unifying mechanism of sustained idiopathic atrial and ventricular annular tachycardia

Ripple map delineation of the reentrant circuit in a tricuspid annular atrial tachycardia mimicking focal activity

A 70-year-old man with hypertensive heart disease underwent catheter ablation of persistent atrial fibrillation. After completing the pulmonary vein isolation, atrial burst pacing induced an annular atrial tachycardia (AT). Overdrive pacing exhibited constant fusion, indicating a macroreentrant mechanism of the AT. However, the CARTO3 activation map created using the Octaray catheter (both Biosense Webster, Irvine, CA) exhibited a centrifugal spread with the earliest activation site at the 4 o'clock position of the tricuspid annulus. In contrast, the Ripple map revealed a clear reentrant circuit with its isthmus located at the 4-6 o'clock position of the tricuspid annulus. The local electrograms in these areas recorded systolic and diastolic potentials simultaneously, and the misannotation of the large far-field potentials caused this discrepant result. Handling low-amplitude complex fractionated electrograms remains a challenge in creating a precise activation mapping. The Ripple map, especially when combined with the Octaray catheter, was effective in dynamically visualizing all these electrograms and accurately delineating the reentrant circuit.

Ventricular Tachycardia Due to Triggered Activity: Role of Early and Delayed Afterdepolarizations

Most forms of sustained ventricular tachycardia (VT) are caused by re-entry, resulting from altered myocardial conduction and refractoriness secondary to underlying structural heart disease. In contrast, VT caused by triggered activity (TA) is unrelated to an abnormal structural substrate and is often caused by molecular defects affecting ion channel function or regulation of intracellular calcium cycling. This review summarizes the cellular and molecular bases underlying TA and exemplifies their clinical relevance with selective representative scenarios. The underlying basis of TA caused by delayed afterdepolarizations is related to sarcoplasmic reticulum calcium overload, calcium waves, and diastolic sarcoplasmic reticulum calcium leak. Clinical examples of TA caused by delayed afterdepolarizations include sustained right and left ventricular outflow tract tachycardia and catecholaminergic polymorphic VT. The other form of afterpotentials, early afterdepolarizations, are systolic events and inscribe early afterdepolarizations during phase 2 or phase 3 of the action potential. The fundamental defect is a decrease in repolarization reserve with associated increases in late plateau inward currents. Malignant ventricular arrhythmias in the long QT syndromes are initiated by early afterdepolarization-mediated TA. An understanding of the molecular and cellular bases of these arrhythmias has resulted in generally effective pharmacologic-based therapies, but these are nonspecific agents that have off-target effects. Therapeutic efficacy may need to be augmented with an implantable defibrillator. Next-generation therapies will include novel agents that rescue arrhythmogenic abnormalities in cellular signaling pathways and gene therapy approaches that transfer or edit pathogenic gene variants or silence mutant messenger ribonucleic acid.

Unipolar and bipolar electrograms to predict successful ablation site of premature ventricular contractions originating from the free wall of the tricuspid annulus

INTRODUCTION

This study aimed to identify the characteristics of unipolar and bipolar electrogram (UniEGM and BiEGM) in guiding successful ablation of premature ventricular contractions (PVCs) originating from the free wall of the ventricular aspect of the tricuspid annulus (TA). We hypothesized that the negative concordance pattern (NCP) on the onset of UniEGM and BiEGM, together with the least value of the difference between the earliest BiEGM and UniEGM dV/dTmax, might improve the accuracy of conventional mapping.

METHODS AND RESULTS

Thirty consecutive patients who underwent successful catheter ablation from February 2018 to July 2021 were retrospectively analyzed. The BiEGM and UniEGM for successful ablation sites were compared with those for non-successful ablation sites. Among the 30 patients, 30 successful and 26 nonsuccessful ablation sites were compared. The earliest activation time of the BiEGM (BiEGMoneset-QRS) was 25 ± 6 ms for the successful ablation sites and 21 ± 6 ms for the nonsuccessful ablation sites (p = .47). The value of the difference in the earliest BiEGM and UniEGM dV/dTmax differed between successful and nonsuccessful ablation sites (6.4 ± 3.6 ms vs. 10.4 ± 6.8 ms). NCP was observed at 90.0% and 42.3% of the successful and nonsuccessful ablation sites, respectively. Alignment of NCP and BiEGMonset-UniEGM ≤6 ms was applied as the mapping criterion for successful PVC suppression (73.1% sensitivity and 87.7% specificity). The area under the receiver-operating characteristic curve for this cutoff was 0.85.

CONCLUSION

Mapping based on an NCP at the onset of the BiEGM and UniEGM and the least difference value of the earliest BiEGM and UniEGM dV/dTmax had an excellent predictive value for successful ablation. These strategies may reduce the number of radiofrequency catheter ablation (RFCA) applications for free-wall tricuspid annular PVCs.

An unusual location of the origin of an adenosine-sensitive atrial tachycardia: The lateral mitral annulus

A 56-year-old woman underwent an electrophysiological study and radiofrequency catheter ablation of a narrow QRS tachycardia. Programmed atrial extrastimulation reproducibly induced the tachycardia. During the tachycardia, differential atrial overdrive pacing exhibited no ventriculoatrial (VA) linking, and ventricular overdrive pacing exhibited VA dissociation. Entrainment of the tachycardia with atrial overdrive pacing was not demonstrable because the tachycardia cycle length varied from 262 to 320 ms. An intravenous bolus of 5 mg of adenosine reproducibly terminated the tachycardia without atrioventricular (AV) block. Based on these findings, the clinical tachycardia was diagnosed as an adenosine-sensitive atrial tachycardia (AT). Activation mapping during the AT using the EnSite Precision system and Advisor HD Grid mapping catheter (Abbott, Minneapolis, MN, USA) exhibited a centrifugal pattern with the earliest activation along the lateral mitral annulus. A radiofrequency application at the earliest activation during the AT successfully terminated the AT. Adenosine-sensitive ATs generally originate from the vicinity of the AV node and tricuspid annulus. We present a case with an unusual location of the origin of an adenosine-sensitive AT, which was successfully ablated at the lateral mitral annulus. Since the AT was sensitive to adenosine, the AT substrate appeared to have been calcium channel-dependent tissue along the mitral annulus. <Learning objective: Adenosine-sensitive atrial tachycardias (ATs) generally originate from the right-sided atrioventricular (AV) annulus and are eliminated by ablation at the vicinity of the AV node, tricuspid annulus, proximal coronary sinus, and non-coronary sinus of Valsalva. This case report described a rare type of an adenosine-sensitive AT originating from the lateral mitral annulus. A radiofrequency application targeting the earliest activation on the activation map during the AT terminated the AT.>.

Adenosine-A drug with myriad utility in the diagnosis and treatment of arrhythmias

Adenosine has been used in the emergency treatment of arrhythmia for more than nine decades. However, cardiologists are often unfamiliar about its basic mechanism and various diagnostic and therapeutic uses, considering it mainly as a therapeutic drug for supraventricular tachycardia. This article discusses the role of adenosine relevant to emergency physicians, cardiologists, and electrophysiologists. Understanding of the mechanisms of adenosine and its electrophysiological effects is discussed first, followed by dosing, side effects, diagnostic, and therapeutic uses. Finally, the role of adenosine in the electrophysiology laboratory is discussed.

Atrial Tachycardias and Atypical Atrial Flutters: Mechanisms and Approaches to Ablation

Atrial tachycardias (ATs) may be classified into three broad categories: focal ATs, macroreentry and localised reentry – also known as ‘microreentry’. Features that distinguish these AT mechanisms include electrogram characteristics, responses to entrainment and pharmacological sensitivities. Focal ATs may occur in structurally normal hearts but can also occur in patients with structural heart disease. These typically arise from preferential sites such as the valve annuli, crista terminalis and pulmonary veins. Macro-reentrant ATs occur in the setting of atrial fibrosis, often after prior catheter ablation or post atriotomy, but also de novo in patients with atrial myopathy. High-resolution mapping techniques have defined details of macro-reentrant circuits, including zones of conduction block, scar and slow conduction. Localised reentry occurs in the setting of diseased atrial myocardium that supports very slow conduction. A characteristic feature of localised reentry is highly fractionated, low-amplitude electrograms that encompass most of the tachycardia cycle length over a small diameter. Advances in understanding the mechanisms of ATs and their signature electrogram characteristics have improved the efficacy and efficiency of catheter ablation.

Termination of a long RP supraventricular tachycardia by carotid sinus massage

Carotid sinus massage is a useful diagnostic and therapeutic maneuver in patients with supraventricular tachycardia. Abrupt tachycardia termination with carotid sinus massage typically indicates a mechanism dependent on the atrioventricular node. Here, we present the case of a 79-year-old patient presenting with a long-RP supraventricular tachycardia terminated with carotid sinus massage that was proven invasively to be due to a focal atrial tachycardia. We discuss mechanistic explanations for this unusual phenomenon and review the literature.

Should the Aortic Root Be the Preferred Route for Ablation of Focal Atrial Tachycardia Around the AV Node?: Support From Intracardiac Echocardiography

OBJECTIVES

The purpose of this study was to determine the optimal approach to focal atrial tachycardia originating from around the atrioventricular node.

BACKGROUND

Focal atrial tachycardia (FAT) demonstrating earliest activation around the atrioventricular (AV) node during right atrial (RA) mapping has been eliminated by ablation at the RA para-Hisian region, from the left atrium (LA) or the noncoronary aortic cusp (NCC). However the optimal approach has not been determined.

METHODS

We conducted a retrospective analysis of a consecutive series of 148 patients undergoing catheter ablation for FAT between 2006 and 2014 in our institution.

RESULTS

Earliest activation was recorded in the peri-AV nodal region during RA mapping in 34 patients (23%). Of these, 7 patients (20.5%) had successful ablation at the RA septum, using either radiofrequency (n = 4) or cryoenergy (n = 3). Seven FATs (20.5%) were ablated from the LA at the region of the aortomitral continuity, and 20 patients (59%) had successful ablation in the NCC, including 1 patient with a recurrence after a temporarily successful cryoablation from the RA. The proportion of the 3 approaches in this series showed a significant temporal evolution and overall frequency favoring ablation in the NCC (p = 0.011 for time trend and 0.013 for actual vs. expected frequencies). Intracardiac echocardiography proved superior catheter stability with the NCC approach. There were 2 cases of atrioventricular block and 1 recurrence after RA ablation versus no complications or recurrent FAT with NCC and LA approaches.

CONCLUSIONS

Most peri-AV nodal FATs can be safely and effectively ablated from the NCC. The strategy of preferential NCC approach avoids RA para-Hisian ablation with the accompanying risk of AV block.