Elsevier

Heart Rhythm

Volume 8, Issue 8, August 2011, Pages 1245-1253
Heart Rhythm

Clinical
General
Electrophysiologic properties of para-Hisian atrial tachycardia

https://doi.org/10.1016/j.hrthm.2011.03.011Get rights and content

Background

Focal atrial tachycardia (AT) originates from preferential sites, including the tricuspid and mitral annuli. AT arising from the atrioventricular annuli is initiated and terminated with programmed stimulation and is, in general, adenosine and verapamil sensitive. Para-Hisian AT arising from the apex of the triangle of Koch has been considered to be a distinct entity, characterized by unique electrophysiological properties.

Objective

We sought to more fully delineate the electrophysiological and electrocardiographic properties of para-Hisian AT in a large series of patients.

Methods

The study population consisted of 38 patients (63 ± 15 years; 23 female) with AT from the para-Hisian region. The ATs were focal and originated from the anteroseptal tricuspid annulus, in close proximity to the His bundle recording. Proximity to the His bundle was confirmed by electrogram recordings, fluoroscopy, and centrifugal activation during three-dimensional mapping.

Results

The mean AT cycle length was 421 ± 69 ms. AT was associated with a distinct P-wave morphology that was significantly narrower than the P wave during sinus rhythm. Adenosine (5.0 ± 1.5 mg) terminated AT in 34/35 patients. Intravenous verapamil terminated AT in three of three patients. Catheter ablation was attempted in 30 patients and was successful in 26 (87%).

Conclusion

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. The electropharmacologic findings in para-Hisian AT are mechanistically consistent with cyclic AMP-mediated triggered activity.

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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    The first two authors contributed equally to this paper.

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