The Role of Ultra-high-frequency ECG in the Localization of Left Ventricular Conduction Disorders and Prediction of Response to Resynchronization Therapy

Since the introduction of cardiac resynchronization therapy (CRT), a way to better define the patients who will benefit from it most has been sought. Their selection based on the duration of the QRS complex or its morphology fails in some of them. Current data demonstrate that CRT done by pacing the conduction system below the site of the left bundle branch block may be a better therapy than biventricular pacing. A prerequisite for a better effect of conduction system pacing is to perform it in patients in whom a conduction block is present in the left bundle branch block ("true" LBBB) and not in the patients with a more distal left ventricular conduction problem (IVCD). The criteria derived from the surface standard ECG are insufficient to differentiate "true" LBBB from IVCD, and thus it is not possible to determine the optimal treatment in some patients. The sequence of ventricular activation can be visualized within a few minutes using ultra-highfrequency ECG (UHF-ECG) in virtually all patients. It is a non-invasive method that shows ventricular dyssynchrony as a time difference between the activation of the ventricles or their individual segments. Pilot data show that patients with "true" LBBB are likely to have greater ventricular dyssynchrony and a different pattern of ventricular depolarization than patients with IVCD. The aim of this project is to test the hypothesis that UHF-ECG can distinguish "true" LBBB from IVCD in patients with heart failure and left ventricular conduction disturbance better than using standard criteria assessing QRS duration and morphology. Other aim is to demonstrate that in patients with trueLBBB resynchronization using conduction system pacing will lead to better echocardiographic and clinical outcomes than biventricular pacing. Finally, the echocardiographic and clinical response of IVCD patients will depend on the reduction of UHF-ECG ventricular dyssynchrony after CRT.