Current Role of Electrocardiographic Imaging in Patient Selection for Cardiac Resynchronization Therapy

Figure 1. Representation of the left ventricular myocardial work in LBBB. During LBBB, the septal wall contracts in a low-pressure cavity without encountering any resistance; the myocardial work is therefore wasted. The lateral wall undergoes an initial stretch in response to the contraction of the septal wall, and then, through the Frank–Starling effect, develops a greater contractile force/work than in the absence of electrical asynchrony.

Figure 2. Impact of the electromechanical asynchronism on systolic dysfunction. Electrical dyssynchrony increases end-diastolic volumes and dilates the ventricular cavity, shifting the pressure–volume loop to the right. The latest wall activated develops a greater myocardial workload, resulting in the activation of hypertrophy pathways associated with electrophysiological remodeling and action potential lengthening. These structural changes favor longer electrical impulse propagations and aggravate electromechanical dyssynchrony.

Figure 3. Typical 3D activation map of LBBB and RVAP. Averaged activation map per segment of 16 patients with normal axis LBBB (left top panel) and of 13 RVAP patients (left bottom panel). Three-dimensional activation maps of a typical LBBB (right top panel) and RVAP (right bottom panel). LBBB: left bundle branch block; RVAP: right ventricular apical pacing.

Figure 4. Role of ECGi and ECG belt in patient selection/optimization for CRT. Both the ECGi and ECG belt are validated tools to identify interventricular dyssynchrony, which is the main driver for CRT response. ECGi is a validated tool to improve understanding of biventricular activation during CRT. Both tools are inefficient to optimize CRT response; further study regarding whether ECGi can improve LV lead placement is warranted. ECGi: electrocardiographic imaging; CRT: cardiac resynchronization therapy.

Figure 5. Theoretical multiparametric approach using a biophysical model (Circadapt Model) to predict response to cardiac resynchronization. For all patients undergoing CRT: measurement of VEU, SSI, fibrosis and RV function. Simulated flow variation values are obtained by considering one or more variables and obtaining an AUC for each simulation level. AUC values are given as examples. AUC: area under the curve; CRT: cardiac resynchronization therapy; RV: right ventricular; SSI: systolic stretch index; VEU: ventricular electrical uncoupling.