ClinicalGeneralElectrophysiologic properties of para-Hisian atrial tachycardia
Introduction
Recently, a classification system categorizing atrial tachycardias (ATs) as being either “focal” or “macroreentrant” has been proposed.1 The rationale of this classification is based on electrophysiological mechanism, as defined by entrainment and three-dimensional mapping, and has important implications regarding the strategy for ablation.
The underlying mechanism of focal AT can be difficult to ascertain clinically but can be inferred from the mode of initiation and termination, response to entrainment, and specific pharmacological sensitivity. Focal ATs arise from preferential sites in the atria and most commonly originate from the crista terminalis, atrioventricular (AV) annuli, pulmonary vein ostia, and coronary sinus ostium/musculature.2, 3, 4, 5, 6, 7, 8 Less frequently, the atrial appendages and superior vena cava are identified as sites of AT origin.9, 10 Three-dimensional mapping systems may help in determining a reentrant mechanism by registration of electrical activity that spans 90%–100% of the tachycardia cycle length (TCL; head meets tail). In contrast, a focal origin of AT shows a centrifugal pattern of activation. The apex of the triangle of Koch, that is, the para-Hisian region, has been reported to be another distinct site of origin of AT, although its underlying arrhythmia mechanism has yet to be identified.11, 12 The boundaries of the triangle of Koch include the tendon of Todaro, the septal leaflet of the tricuspid annulus, and the His bundle. It is unclear whether tachycardias from the apex of this region (i.e., near the His bundle) should be considered a separate entity given its signature origin or as part of the broader category of tachycardias arising from the AV annuli, which share identical electrophysiological properties. To clarify this distinction, we sought to fully characterize the pharmacological and electrophysiological properties of para-Hisian ATs.
We have previously proposed that the effects of adenosine on AT can differentiate between focal and macroreentrant ATs.3, 13 That is, in general, adenosine has no effect on macroreentrant circuits but can terminate or suppress focal ATs, depending on their underlying mechanism. In addition to its tissue-specific effects on supraventicular tissue mediated by IKACh,Ado, adenosine also has antiadrenergic effects, decreasing intracellular cyclic adenosine monophosphate (AMP).14 This results in inhibition of the L-type calcium current (ICa(L)) as well as the transient inward current (ITi).15 These effects are consistent with adenosine-mediated termination of tachycardia due to cyclic AMP-dependent triggered activity.
Section snippets
Patient characteristics
Thirty-eight consecutive patients (62 ± 15 years; 23 females) who presented for invasive electrophysiological evaluation and catheter ablation of AT arising from the para-Hisian region comprise this series. This study was approved by the participating institutional review boards.
Noninvasive evaluation
Patients underwent evaluation of cardiac structure, function, and ectopy burden. When possible, this included 24-hour Holter monitoring and/or inpatient telemetry. Presence of coronary artery disease was assessed as
Patient characteristics
The baseline characteristics of the patients are listed in Table 1. The mean age was 62 ± 15 years. Twenty-three of the 38 patients were female (60%). Structural heart disease was present in six (22%) patients. All six had ischemic heart disease; five had a history of coronary artery bypass surgery. Thirty-four (89%) patients were taking antiarrhythmic agents or AV nodal blocking agents at the time of the procedure. These included β-blockers (n = 25), calcium channel blockers (n = 13), and
Discussion
The principal findings in this study are that (1) the para-Hisian region is a source of focal AT, with properties consistent with AT arising circumferentially along the tricuspid and mitral annuli, and should be considered a subset of this broader group of “annular” ATs; (2) ECG findings suggestive of a para-Hisian AT include narrowing of the P wave during AT and biphasic P waves in V1, with the dominant component having a polarity opposite to that observed in the inferior leads; and (3) the
Limitations
Although this is the largest series of patients with para-Hisian AT, this study only included those patients in whom sustained tachycardia or long runs of nonsustained tachycardia could be consistently induced and anatomic localization could be confirmed. Patients with brief nonsustained AT or isolated atrial ectopy were not included, and thus it is possible that mechanisms other than triggered activity could also be responsible for arrhythmias arising from the para-Hisian region.
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Cited by (38)
Epicardial ablation of a focal atrial tachycardia adjacent to the sinoatrial node: A case report
2022, HeartRhythm Case ReportsCitation Excerpt :We report a case of an epicardial right atrial tachycardia that was adjacent to the epicardial sinoatrial node area. Origins of right atrial tachycardia include crista terminalis,1 tricuspid annulus,2 the para-His region,3 coronary sinus ostium,4 and, less frequently, the RAA.5 Almost all the focal atrial tachycardias can be ablated from the endocardial side of the RA.
Ablation of Focal Atrial Tachycardias
2019, Catheter Ablation of Cardiac ArrhythmiasCatheter ablation of atrial tachycardia on the non-coronary aortic cusp during pregnancy without fluoroscopy
2018, HeartRhythm Case ReportsAtrial Tachycardia
2018, Cardiac Electrophysiology: From Cell to Bedside: Seventh EditionComparison of strategies for catheter ablation of focal atrial tachycardia originating near the His bundle region
2017, Heart RhythmCitation Excerpt :Radiofrequency catheter ablation (RFCA) of para-Hisian atrial tachycardia (AT) represents a challenging task due to their anatomical proximity to the conduction system and the consequent risk of complete atrioventricular (AV) block.1,2 Several studies have suggested that para-Hisian ATs can be successfully ablated from the right atrium (RA), left atrium (LA), or noncoronary cusp (NCC) in the aorta.3–17 Currently, there are little and incomplete data comparing these different approaches for the treatment of para-Hisian ATs.3,7,8,12–16
The first two authors contributed equally to this paper.