Effects of Preexcitation Syndrome on Terminal QRS Vector Observed in Spatial Vector

Abstract

Background: Preexcitation syndrome could affect terminal QRS vector, which is not emphasized in clinic. In this study, we made a comparison between vectorcardiogram (VCG) before and after ablation to observe the change of terminal QRS vector. Furthermore, the relationship between the change of terminal QRS vector and accessory pathway (AP) as well as the change of initial QRS vector (delta vector) was analyzed.

Methods: Thirty patients who were proved to have a single AP by ablation were included. All patients were divided into seven groups based on the AP location. Comparison between VCG before and after ablation was made to observe the change of terminal and delta vector. The relationship between the change of terminal QRS vector and AP location as well as delta vector was analyzed.

Results: (1) All 30 patients had a change in terminal QRS vector (elevation and/or azimuth) in comparison to postablation VCG. (2) The change of terminal QRS vector was related to delta vector and AP location. The agreement and consistency between the change of terminal QRS vector and delta vector were 91.65% and 0.856 (P < 0.01), respectively.

Conclusions: (1) Both initial and terminal QRS vector are affected by the antegrade conduction of AP. The change of terminal QRS vector is related to the AP location and delta vector. (2) The effect of preexcitation syndrome on QRS terminal vector is shown as more intuitive and easy in spatial vector by comparison with electrocardiogram, which is helpful for the diagnosis of atypical preexcitation and localization of AP.

Keywords: QRS terminal vector; cardiology; catheter ablation; preexcitation syndrome; vectorcardiography.

Figure 1

Measurements of the elevation and azimuth. (A) Elevation = the angle between the vector and the axis (Y‐axis) perpendicular to the transverse plane, defined as zero when pointing downwards and 180° when pointing in the cranial direction. (B) Azimuth = the angle of the projection of the vector in the transverse plane (X–Z plane), defined as zero when the vector is pointing to the left. Forward vector directions are designated 0∼ +180° and backward vector directions 0∼ −180°).

Figure 2

The delineation of the mechanism of preexcitation syndrome with overt bypass. (A) The activation prematurely depolarizes the ventricle via accessory pathway forming the delta wave (the shortened extent of PR interval is equal to the duration of delta wave). (B) The onset of the normal conduction is the termination of delta wave, but the bypass conduction is continuous (masked in ECG). (C) The activation conducts through the bypass and normal conduction system fuses into the monophyletic ventricular fusion, with delta wave in its initiation and the deformation in its termination.

Figure 3

The ECG before and after ablation of a 46‐year‐old female patient (right posteroseptal accessory pathway). (A) Limb lead. (B) Chest leads. Top panel shows the ECG before ablation; Bottom panel shows the ECG after ablation. ↑ and ↓ show the leads with an obvious change in terminal QRS vector.

Figure 4

QRS‐T vector loops of the patient in Figure 3. (A) The vectorcardiogram before ablation. (B) The vectorcardiogram after ablation. ↗ shows terminal QRS vector direction. The antegrade conduction of accessory pathway not only affects the initial QRS vector, but also changes the terminal QRS vector.