Left ventricular endocardial pacing is less arrhythmogenic than conventional epicardial pacing when pacing in proximity to scar

Figure 1. Pacing locations. Endocardial pacing locations are in red and epicardial pacing locations in black. Distances from the scar surface are indicated by the white point cloud. Epicardial (epi) and endocardial (endo) surfaces and the transmural action potential duration (APD) gradient are indicated by the black arrow.A: Patient-specific model. Locations were chosen at (from right to left) 0.2, 0.5, 1.5, 2.5, and 3.5 cm from the scar surface. B: Idealized model. Locations were chosen at 0.2 and 3.5 cm from the scar surface.

Figure 2. A: Example of a 1-mm-thick layer of fast endocardial conduction (FEC) over scar (black), border zone (BZ) (blue), and healthy tissue (gray).B: Multiplying factor of the slow rectifying potassium current conductance (gKs) across the ventricular wall. Shown are examples of the physiological (right) and inverted (left) transmural gradient.

Figure 3. Control case with fast endocardial conduction and physiological transmural action potential duration gradient. A, B: High repolarization gradients (HRGs) within 1 cm around the scar (blue) for endocardial (A) and epicardial (B) pacing. Endocardial lead locations are shown by red circles and epicardial lead locations by black circles. Regions of interest are highlighted by yellow circles.C: HRG volume for endocardial (red) and epicardial (black) pacing at 0.2–3.5 cm from a scar. Dashed lines indicate a significant difference (P <.05).

Figure 4. No transmural action potential duration (APD)gradient case. A, B: High repolarization gradients (HRGs) within 1 cm around the scar (blue) for endocardial (A) and epicardial (B) pacing. Endocardial lead locations are shown by red circles and epicardial lead locations by black circles. Regions of interest are highlighted by yellow circles.C: HRG volume for endocardial (red) and epicardial (black) pacing at 0.2–3.5 cm from a scar. Dashed lines indicate a significant difference (P<.05).

Figure 5. Inverted transmural action potential duration (APD) gradient case. A, B: High repolarization gradients (HRGs) within 1 cm around the scar (blue) for endocardial (A) and epicardial (B) pacing. Endocardial lead locations are shown by red circles and epicardial lead locations by black circles. Regions of interest are highlighted by yellow circles.C: HRG volume for endocardial (red) and epicardial (black) pacing at 0.2–3.5 cm from a scar. Dashed lines indicate a significant difference (P <.05).

Figure 6. Idealized models. High repolarization gradients (blue) for endocardial (A, C) and epicardial (B, D) pacing. Shown are epicardial and endocardial views when pacing 0.2 and 3.5 cm from scar. Endocardial lead locations are shown by red spheres and epicardial lead locations by black spheres. Region 1 cm around the scar is highlighted by yellow circles. Orange arrows indicate the direction of the action potential duration (APD) gradient across the wall.

Figure 7. Repolarization times in the transmural direction across the ventricular wall of the idealized models when pacing at endocardial (red) and epicardial (black) surfaces. Shown are results with (C, D) and without (A, B) a transmural action potential duration (APD) gradient when pacing 0.2 cm (A, C) and 3.5 cm (B, D) from the scar. Dashed lines indicate the maximum and minimum repolarization times. The direction of activation during endocardial and epicardial pacing as well as the direction of the transmural APD gradient (blue) are indicated at the top.