Atrial Tachycardia



Atrial Tachycardia








12-LEAD ECG

The P-wave morphology during AT is determined by its anatomic site of origin and, therefore, valuable for localization.2,3,4,5 It is best visualized during periods of atrio-ventricular (AV) block when not obscured by QRS complexes or T waves. (A burst of rapid ventricular pacing during tachycardia can dissociate P waves from QRS complexes/T waves.)


RIGHT VERSUS LEFT

The most helpful leads to differentiate right from left ATs are V1 and aVL.6 In general, because the right atrium is anterior relative to the left atrium (LA), right ATs generate posterior (V1: negative or biphasic [positive-negative]) and leftward (aVL: positive) P-wave axes.2,6 In contrast, left ATs generate anterior (V1: positive or biphasic [negative-positive]) and rightward (aVL: negative or isoelectric) P-wave axes, (except for origin from the right superior pulmonary vein [RSPV] where P waves can be positive in aVL.)


SUPERIOR VERSUS INFERIOR

Superior foci (e.g., high crista terminalis, superior pulmonary veins, atrial appendages) generate positive P wave in the inferior leads. As the tachycardia origin shifts downward (low crista terminalis, inferior pulmonary veins, CS os, inferior annuli), P-wave amplitudes decrease and even become negative in the inferior leads.


SEPTAL VERSUS FREE WALL

Tachycardia P waves closer to the septum (e.g., right-sided pulmonary veins) tend to be narrower than those originating farther from the septum (e.g., left-sided pulmonary veins).


SPECIFIC P-WAVE MORPHOLOGIES


Sinus-Like Morphology

The crista terminalis is the most common site for right ATs. Because it is close to the sinus node, it generates sinus-like P waves (biphasic [positive-negative] in V1, inferior axis and negative in aVR) (Fig. 13-1).7 Occasionally, a crista tachycardia shows a positive P wave in V1 in which case, the P wave is also positive in V1 during normal sinus rhythm (NSR) (due to the anatomic position of the heart relative to V1). This can be differentiated from the RSPV tachycardia, which shows the normal biphasic (positive-negative) P wave in V1 during NSR.2 Right atrial appendage and superior tricuspid annular tachycardias demonstrate a negative P wave in V1 with variable precordial progression and an inferior axis, which can be difficult to differentiate from each other because of their close anatomic proximity.8,9


Atypical AVNRT-Like Morphology

Because the slow pathway (SP) of the AV node lies near the CS os, tachycardias originating from the CS os produce a similar characteristic morphology (isoelectric and then positive
or biphasic [negative-positive] P waves in V1 and inverted P waves inferiorly) (Fig. 13-1).10 CS tachycardias show precordial P-wave regression. Transition from positive to negative occurs earlier with tachycardia origin at CS os (V2) than in the body of the CS (V4).11






FIGURE 13-1 A 12-lead ECG of AT arising from the crista terminalis (top) and CS os (bottom). P waves of “crista tachycardias” resemble sinus tachycardia because of their close proximity to the SA node. P waves of CS tachycardias resemble atypical AVNRT because the SP lies near the ostium of the CS.


Biphasic (Negative-Positive) Morphology

The unusual narrow, biphasic (negative-positive) P-wave morphology in lead V1 and/or the inferior leads should raise suspicion of a septal origin: noncoronary cusp (NCC), aorto-mitral continuity (superior mitral annulus), perinodal, or interatrial septum (Fig. 13-2).5,12,13,14,15,16


Concordance

P waves inverted in the inferior leads and negatively concordant across the precordium are characteristic of origin from the inferior tricuspid annulus (the most anterior structure of the atrium) (Fig. 13-3).9 Conversely, positive precordial P-wave concordance suggests origin from the pulmonary veins (the most posterior structure of the atrium and most common site for left ATs) (Fig. 13-3).17 AT arising from the left-sided pulmonary veins are wider and more commonly notched than right-sided pulmonary veins. Because of their close anatomic proximity, differentiating the left superior
pulmonary vein (LSPV) from LA appendage tachycardias can be difficult. LA appendage tachycardias might show deeper negative P waves in aVL (because of its more leftward location) and less positive concordant (because of its more anterior location).






FIGURE 13-2 A 12-lead ECG of AT arising from the NCC of the aortic valve. 1:1 (top) and 2:1 (bottom) AV conduction. P waves show a characteristic biphasic (negative-positive) morphology in the inferior leads.


ELECTROPHYSIOLOGIC FEATURES

Intracardiac atrial activation patterns allow further localization of AT, particularly when P waves are difficult to identify on the 12-lead ECG. Certain features help differentiate AT from atrio-ventricular nodal reentrant tachycardia (AVNRT) and orthodromic reciprocating tachycardia (ORT).


AV RELATIONSHIP

AV block is common during AT. In contrast, AV block is uncommon and usually transient during AVNRT and never occurs with ORT.


BUNDLE BRANCH BLOCK

In contrast to ORT, AT is not dependent on the His-Purkinje system and is therefore unaffected by development of bundle branch block.







FIGURE 13-3 A 12-lead ECG of AT arising from the inferior tricuspid annulus (TA) (top) and LSPV (bottom) showing negative and positive precordial concordance, respectively. The LSPV tachycardia shows intermittent 4:2 exit Wenckebach block from the pulmonary vein causing relative bradycardia and QT prolongation.


ZONES OF TRANSITION

Gradual acceleration of tachycardia (warm-up phenomenon) occurs with automatic ATs. The morphology and atrial activation pattern of the first and subsequent P waves are identical because they are all driven by the same ectopic focus. Abrupt initiation by spontaneous atrial premature depolarizations occurs with triggered activity or reentry, in which case the first (initiating) and subsequent P waves can differ. Gradual deceleration of tachycardia (cool-down phenomenon) occurs with automatic ATs, while abrupt termination is observed with triggered activity and reentry. Because AT is not dependent on the AV node, a narrow complex tachycardia that repeatedly terminates spontaneously with AV block excludes AT.


PACING MANEUVERS FROM THE



VENTRICLE (“AAV” RESPONSE)

While the response of AVNRT and ORT to entrainment from the ventricle is “AV” (or “AH”), it is “AAV” (“AAH”) for AT (see Fig. 5-23).18,19 Rarely, a macroreentrant AT can generate an “AV” response if 1) the AT circuit time > AVJ refractory period and 2) the recording atrial site is orthodromically captured during entrainment. (An antidromically captured site generates an “AAV” response.20)



PACING MANEUVERS FROM THE ATRIUM (ABSENCE OF VA LINKING)

While both AVNRT and ORT show ventriculoatrial (VA) linking (ΔVA <10 ms) one beat after differential atrial overdrive pacing, AT does not (ΔVA >10 ms) (see Fig. 5-27).21,22 Apparent VA linking, however, might occur if atrial overdrive pacing terminates AT, which is then reinitiated by typical AV nodal echoes (not by pacing per se) (Fig. 13-4).


MAPPING AND ABLATION


FOCAL ATRIAL TACHYCARDIA

The focal site of origin of AT can be identified by 1) activation mapping, 2) pacemapping, and 3) atrial overdrive pacing.23,24,25,26,27 Creating three-dimensional electro-anatomic reconstructions of the atrium facilitates mapping within the atrial cavity and overcomes limitations of two-dimensional fluoroscopy.

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Oct 13, 2019 | Posted by in CARDIOLOGY | Comments Off on Atrial Tachycardia
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