Comparison of novel ventricular pacing strategies using an electro-mechanical simulation platform

Abstract

Aims: Focus of pacemaker therapy is shifting from right ventricular (RV) apex pacing (RVAP) and biventricular pacing (BiVP) to conduction system pacing. Direct comparison between the different pacing modalities and their consequences to cardiac pump function is difficult, due to the practical implications and confounding variables. Computational modelling and simulation provide the opportunity to compare electrical, mechanical, and haemodynamic consequences in the same virtual heart.

Methods and results: Using the same single cardiac geometry, electrical activation maps following the different pacing strategies were calculated using an Eikonal model on a three-dimensional geometry, which were then used as input for a lumped mechanical and haemodynamic model (CircAdapt). We then compared simulated strain, regional myocardial work, and haemodynamic function for each pacing strategy. Selective His-bundle pacing (HBP) best replicated physiological electrical activation and led to the most homogeneous mechanical behaviour. Selective left bundle branch (LBB) pacing led to good left ventricular (LV) function but significantly increased RV load. RV activation times were reduced in non-selective LBB pacing (nsLBBP), reducing RV load but increasing heterogeneity in LV contraction. LV septal pacing led to a slower LV and more heterogeneous LV activation than nsLBBP, while RV activation was similar. BiVP led to a synchronous LV-RV, but resulted in a heterogeneous contraction. RVAP led to the slowest and most heterogeneous contraction. Haemodynamic differences were small compared to differences in local wall behaviour.

Conclusion: Using a computational modelling framework, we investigated the mechanical and haemodynamic outcome of the prevailing pacing strategies in hearts with normal electrical and mechanical function. For this class of patients, nsLBBP was the best compromise between LV and RV function if HBP is not possible.

Keywords: Computational modelling; Conduction system pacing; Haemodynamics; Mechanics.

Graphical abstract

Figure 1

(A) biventricular mesh generated from the end-diastolic mean shape of 100 healthy patients. A cross-section is defined for viewing purposes. (B) Fractal tree based Purkinje network, which is connected via Purkinje-Myocardial Junctions. Both upper and lower row are endocardial views. (C) Fibre field generated using a rule-based algorithm, viewed from the endocardium. (D) Fibre field, viewed from the epicardium.

Figure 2

Left bundle branch area pacing modes. The Purkinje fibres generated via the fractal tree are represented in white, while myocardium is blue. All points within 2 mm of the pacing lead location are considered the activation site and are colored red. Bottom, Left—LVSP, only myocardium is part of the activation site. Middle—non-selective LBBP, where both the LBB and surrounding myocardium are activated. Right—selective LBBP.

Figure 3

Workflow of simulated eikonal model to CircAdapt. First, the moment of activation for each point in the 3D mesh is determined using the Eikonal model, and represented as an activation map. Then, the cardiac mesh is divided into 12, 6, and 12 segments for the RV free wall, IVS, and LV free wall, respectively, and mean activation times are calculated. These are then used as input for the moment of activation for the corresponding patches in the lumped parameter model to calculate resulting mechanics and haemodynamics.

Figure 4

Three-dimensional activation maps following each pacing strategy and their corresponding segmental activation time in bullseye form. Note the difference between capture of only myocardium (top row) and inclusion of LBB capture (bottom row). These values are used as input for the mechanical/haemodynamic model.

Figure 5

Mean activation time and the time it takes to activate 95% of the myocardial mass (AT-95). The RVfw, IVS, and LVfw are represented in dark green, red, and green, respectively. All data are computed using the entire ventricular wall (endo- to epicardium).

Figure 6

Strain waveforms after each pacing. Lines indicate the mean strain for each ventricular wall, while the colored area represents the distribution of strain for each wall. Only the lateral segments of the RVfw and LVfw are taken into account, in line with clinical data acquisition using ultrasound strain imaging. The RVfw, IVS, and LVFw are represented in light blue, pink, and light green, respectively. Time t₀ is chosen to be mitral valve closure. Light blue segments indicate ejection.

Figure 7

Segmental work density vs. activation time after each pacing strategy, determined using the area of the stress-strain loop for each ventricular segment.

Figure 8

Haemodynamic parameters for each ventricle. The LV and RV are shown in dark green and red, respectively. Since absolute differences between pacing strategies are relatively small, data are normalized with respect to RVAP, as it is the current standard of care for bradycardia patients.