The development of a new, simple electrocardiographic method for the estimation of the latest activated left ventricular site

Abstract

Abstract Background Current cardiac resynchronization therapy (CRT) works by pacing the latest activated left ventricular (LV) site. The estimation of the location of the latest activated LV site (LALVS) may be important to determine the optimal position of the LV electrode during CRT or to predict the patient response to the current CRT technique devised to pace the LALVS usually present in patients with left bundle branch block (LBBB) pattern. Methods We used a modified 12-lead ECG algorithm originally devised and used by other authors* for a different purpose, to identify the segment of origin of ventricular tachycardia in the 16-segment American Heart Association LV model by analyzing the QRS axis in the limb and chest leads. We hypothesized that modifying this ECG algorithm by using the secondary ST vector axis instead of the QRS axis in the limb and chest leads, we can apply this ECG method to estimate the LALVS instead of the site of origin of the ventricular tachycardia. The resultant secondary ST vector is directed 180o away from the LALVS. Using this ECG method we determined the LALVS in 22 patients with LBBB and 20 patients with nonspecific intraventricular conduction disturbance (NICD) patterns and heart failure. To validate the ECG method, we also estimated the LALVS by echocardiography using 3D parametric imaging and 2D speckle tracking. Results The LALVS determined by the electrocardiographic method and echocardiogrpahy in the 16-segment model matched (was in the same or adjacent segment) in 38/42 (90.5%) patients and among these patients complete matching (the LALVSs were in the same segment) was found in 16/38 (42%) and partial matching (the LALVSs were in adjacent segments) in 22/38 (58%) patients. When the LBBB and NICD groups were separated to patients with ≥150 ms and <150 ms QRS duration subgroups, the LALVSs of the ≥150 ms subgroup were almost exclusively in the anterolateral (or anterior) or inferolateral areas and those of the <150 ms subgroup were in the above mentioned areas or sometimes at other sites located remote from these areas. Conclusions The novel, simple surface electrocardiographic method could as reliably estimate the approximate location of LALVS as echocardiography. The possible explanation for the effectivity of CRT in patients with sinus rhythm with intraventricular conduction disturbance and ≥150 ms QRS duration is that their LALVS is at the same most distant areas (anterolateral, anterior, inferolateral) from the initial septal activation site where the LV electrodes are positioned during application of the current CRT technique. Funding Acknowledgement Type of funding sources: None.