ECG Characteristics of Post-Ablation Atrial Tachycardia
Does the electrocardiogram (ECG) of post-ablation atrial tachycardia (AT) contain clues that might guide mapping and ablation?
Electrocardiograms of AT (n = 227) that occurred during or after catheter ablation of persistent atrial fibrillation (AF) in 142 patients (mean age 59 years, 80% men, mean ejection fraction 58%, mean left atrial diameter 4.6 cm) were reviewed. Atrial activity was characterized with respect to morphology of the P wave, and the presence or absence of electrical activity between successive P waves. Mechanism of AT was characterized broadly as macro-reentry (i.e., atrial flutter) or centrifugal activity (small reentrant circuits or focal). ECGs during which the P waves were obscured or could not be characterized because of low voltage were excluded (n = 31).
A total of 196 ECGs from among 127 patients were analyzed. The mechanism was macro-reentry in 57% and centrifugal activity in 43% of cases. Among the former, reentry utilizing the left atrial roof and mitral isthmus was the most common. An isoelectric interval of >80 ms between P waves in all 12 leads was more prevalent in centrifugal versus macro-reentrant tachycardias (47% vs. 24%; positive predictive value, 60%). However, the absence of such an interval was more helpful in distinguishing large versus small circuits/focal activity (78% vs. 22%). Negative P waves in the inferior leads, although present in only 15% of cases, were consistent with counterclockwise (CCW) typical atrial flutter. However, only 27% of such ECGs demonstrated classic saw-tooth activity. A gradual transition across the precordium (positive to negative) was compatible with CCW typical atrial flutter (sensitivity, 59%), as opposed to an abrupt transition, which was consistent with a reentry around the mitral annulus (sensitivity, 30%). Subtle, negative notching at the onset of an upright P wave in the inferior leads pointed toward reentry around the mitral annulus in a CW manner (sensitivity, 25%).
The authors concluded that the ECG during post-AF AT frequently lacks localizing information that might guide the ablation procedure.
Unlike in patients with paroxysmal AF, one frequently encounters ATs following catheter ablation of persistent AF. Most of these tachycardias arise from the left atrium, and may be due to large (“atrial flutter”) or small circuits. These arrhythmias are challenging to map owing to the presence of scar, multiplicity, anatomic constraints, and our incomplete mechanistic understanding. Further, left atrial ablation modifies the substrate such that activation patterns are altered or obscured, making it difficult to interpret the ECG and determine pathognomonic associations. Nonetheless, the few clues identified herein remain relevant in the mapping and ablation of these challenging arrhythmias.
Keywords: Arrhythmias, Cardiac, Atrial Fibrillation, Atrial Flutter, Catheter Ablation, Electrocardiography, Heart Atria, Stroke Volume, Tachycardia
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