Mapping strategies in focal atrial tachycardias demonstrating early septal activation: distinguishing left from right

Abstract

Determining the chamber of origin of focal atrial tachycardias (FATs) arising at or close to the septum might require biatrial mapping. This review focuses on the available tools and methods used to distinguish right atrial from left atrial origin before left atrial access is obtained. These include analysis of P wave morphology, assessing the timing of right atrial septal activation, the sequence of right atrial and/or biatrial activation and analysis of earliest electrogram morphology. The electroanatomical properties of the interatrial septum and coronary sinus that provide the basis for the above mentioned tools have also been briefly described.

Fig. (1)

Evidence of discordant electrical activation of the septum at the His bundle region. Panels A and B. Left anterior oblique (45°) fluoroscopic projection showing the position of the catheters during paraseptal pacing. HBE – catheter positioned at the His bundle region; LA – catheter positioned at the left atrial septum adjacent to the His bundle region; and TA – catheter positioned at the anterosuperior tricuspid annulus. The two circles represent the presumed location of the tricuspid and mitral annulus. Pacing site during tricuspid (panel A) and mitral annular pacing (panel B) is also shown. Panels C and D. Surface electrocardiogram leads I and V1 and intracardiac recordings from the anterosuperior left atrial septum (LA), distal and proximal His bundle region (HBEd and HBEp), and the anterosuperior tricuspid annulus (TA). Panel C. Double HBE electrogram with higher amplitude and higher-frequency component (arrow) and a lower frequency, loweramplitude (arrowhead) component during right atrial paraseptal pacing. Note that the timing of the lower-amplitude, lower-frequency component on the HBE coincides with the local activation at the left atrial septum. Panel D. In the same patient the sequence is reversed during left atrial paraseptal pacing. Paper speed 300 mm/s. Modified and reproduced from [24] with permission from Oxford University Press.

Fig. (2)

Representative examples of intracardiac recordings as presented for analysis to the observers showing single beats of FATs successfully ablated in the RA (panels A and B) and in the LA (panels C and D). Panel A. Earliest activation at the HBE with the near-field component preceding the far-field one (N-F sequence). Panel B. Earliest activation at CS 9–10 with N–F sequence. Panel C. Earliest activation at the HBE with the far-field component preceding the near-field one (F-N sequence). (D) Earliest activation at CS 5–6 demonstrating F–N sequence. CS 9–10 is positioned at the ostium. CS - coronary sinus. The other abbreviations are the same as in Figure 2. Arrows and arrowheads denote near-field and far-field EGM components, respectively. Paper speed 300 mm/s. Reproduced from [24] with permission from Oxford University Press.

Fig. (3)

Schematic representation of the anatomical distribution of the foci included in the studied series. The two atria are presented as viewed from the atrioventricular annuli. Foci that were correctly identified by both observers are presented by the filled circles, those that were misclassified are denoted by the open circles, and half-filled circles represent the foci that were misclassified by only one of the observers. Reproduced from [24] with permission from Oxford University Press.