Electrical and mechanical ventricular activation during left bundle branch block and resynchronization

Abstract

Cardiac resynchronization therapy (CRT) aims to treat selected heart failure patients suffering from conduction abnormalities with left bundle branch block (LBBB) as the culprit disease. LBBB remained largely underinvestigated until it became apparent that the amount of response to CRT was heterogeneous and that the therapy and underlying pathology were thus incompletely understood. In this review, current knowledge concerning activation in LBBB and during biventricular pacing will be explored and applied to current CRT practice, highlighting novel ways to better measure and treat the electrical substrate.

Fig. 1

Typical examples of 3D electrical activation in canine hearts during normal conduction (left panel) and after creation of left bundle branch block (right panel). Each electrical activation map is reconstructed using a single-beat recording of simultaneous epicardial and endocardial electrical mapping. Epicardial potentials were derived using electrode bands placed around the heart, containing over 100 contact electrodes while the LV endocardium was mapped using custom-made plunge electrodes [63]. Early activated regions are indicated by a red color (close to 0 ms) and late activation regions are indicated by a dark blue color (over 100 ms), see color bar. Reproduced with permission [8]

Fig. 2

Timing of electrical activation (depolarization) wavefronts in normal conduction and during LBBB shown in sagittal view. For reference, two QRS-T waveforms are shown in their anatomic locations (V3 on the chest and aVF inferiorly). Electrical activation starts at the small arrows and spreads in a wavefront with each colored line representing successive 10 ms. In normal conduction, activation begins within both the LV and RV endocardium. In LBBB, activation only begins in the RV and must proceed through the septum before reaching the LV endocardium. Reproduced with permission [64]

Fig. 3

Epicardial isochrone maps during native rhythm in a patient with LBBB. Left anterior escending (LAD) coronary artery is shown and the approximate valve region is covered by gray. Earliest and latest ventricular activation times (in milliseconds) are indicated by framed numbers. Activation times are given with respect to QRS onset. QRSd QRS duration. Reproduced with permission [10]

Fig. 4

3D reconstruction of electrical activation times of the LV and the RV during intrinsic conduction (LBBB) and BiV pacing (at the RV apex and basal-lateral LV wall) in representative hearts with LBBB (left), LBBB with LAD infarction (middle), and LBBB with LCX infarction (right). Reproduced with permission [65]

Fig. 5

Typical examples of 3D electrical activation in canine hearts with chronic LBBB and transmural myocardial infarction during CRT with epicardial LV pacing (left panel) and endocardial LV pacing (right panel). Reproduced with permission [1]