A narrow QRS complex Tachycardia with an apparently concentric retrograde atrial activation sequence

Abstract

The retrograde atrial activation sequence constitutes an initial important clue to elucidate the tachycardia mechanism during diagnostic electrophysiological testing in patients with supraventricular tachycardia. However, in some cases its correct analysis is challenging.

Keywords: Supraventricular tachycardia; catheter ablation; mitral isthmus.

Figure 1

Shown from top to bottom are tracings from leads II, V1, V5, high right atrium (HRA), proximal (1-2) and distal (3-4) His Bundle (HBE), proximal (9-10) to distal (1-2) coronary sinus (CS) and right ventricular apex (RVA). A: Short RP supraventricular tachycardia with concentric atrial activation is seen. B: Response to RVA overdrive pacing at 340 ms. The tachycardia returns with V-A-V pattern and the post pacing interval following ventricular overdrive entrainment pacing is 442 ms (Post pacing interval - tachycardia cycle length = 78 ms). ABL=Ablation catheter.

Figure 2

A: Surface electrocardiogram and intracardiac electrograms during tachycardia including recordings from a 5 Fr decapolar catheter placed in the CS with distal bipole at the anterolateral site of the AV groove. The earliest atrial activation is recorded at the CS poles 3-4 with these poles being positioned at the lateral region of the AV groove (3:30 h in left anterior oblique projection). B: Ablation catheter positioned at the lateral mitral annulus where the accessory pathway was successfully ablated being in close relationship with CS poles 3-4. The shortest VA during tachycardia is seen at this site.

Figure 3

Schematic representation of the retrograde atrial activation during orthodromic atrioventricular reentrant tachycardia using a left lateral accessory pathway with concomitant presence of conduction block through the mitral isthmus. A: Explains tracings recorded when a quadripolar catheter was placed in the proximal third of the CS; and B: when a decapolar one was advanced more distally (distal bipole at anterolateral position). Atrial activation wavefront proceeds from the atrial insertion of the accessory pathway along the superior mitral annulus to the His region and then spread to right atrium and proximal to distal CS. Two possibilities might explain why CS bipoles 5-6 to 9-10 are activated from distal (5-6) to proximal (9-10), in panel B: 1-. existence of conduction delay (not complete block) through the mitral isthmus; 2-. activation front through the lateral aspect of the blocked isthmus turned around the left-sided pulmonary veins and then activates the posterolateral to posteroseptal aspect of the CS. MI = mitral isthmus; AP = accessory pathway.