Fig 1.
Electrode configuration for nsPEF ablation.
A: Electrode geometry: Two parallel 250 μm tungsten needles uninsulated at the tip (yellow segment). B: Electrode placement in the tissue. A slab of cardiac tissue (pink) is penetrated by two needle electrodes. Upon shock delivery, an area between and around the electrodes is ablated (yellow). C: Electrode placement in a rabbit heart. Electrodes were inserted from the epicardium, penetrating all the way through the myocardial wall.
Fig 2.
Electric pulse generation and shape.
A: Pulse generation with a transmission line generator. Rcharge is the charging resistor, Ztl is the impedance of the transmission line, Ztissue is the impedance of the tissue, and Zm is the additional impedance added in parallel to the tissue in order to match the impedance of the load to that of the transmission line. VBD is the breakdown voltage of the spark gap, adjustable by changing its width and L is the length of the transmission line. B: Theoretical pulse shape, for the diagram in Panel A, where v is the speed of light in the transmission line. Pulse duration is proportional to the length of the transmission line in Panel A. C: Experimentally measured pulse shape.
Fig 3.
Propagation of excitation before and after nsPEF application.
A: Photograph of the cardiac surface before ablation. The stimulation electrode (marked “SE”) is used to initiate electrical activation. B: Photograph of the cardiac surface after ablation. The electrode insertion points are marked by black dots. C: Action potential amplitude map before shock application. Black corresponds to zero action potential amplitude, white to maximal action potential amplitude. D: Action potential amplitude map after shock application. E: Activation map before shock application. Colors code the time after stimulus application at which a surface element is activated. Black areas are activated first, white areas last (see scale). Small red “x” marks the stimulation site, arrow indicate the direction of propagation. F: Activation map after shock application. Activation is blocked at the site of shock application (small red dots indicate shock electrode positions.
Fig 4.
Success Rate of nsPEF ablation for different field strengths.
The threshold field strength (T) was 2.3 kV for 2.3 mm electrode separation and 4 kV for 4 mm electrode separation. The bars show combined results for both field strengths, relative to the thresholds.
Fig 5.
Ablated volume varies with shock amplitude.
Black dots indicate the positions of the ablation electrodes, surface fluorescence of propidium iodide (red) shows which part of the tissue has been ablated. Ablation electrodes are 4 mm apart. A: Shock amplitude 1 kV, B: Shock amplitude 2 kV. C: Computed field distribution (|E|) for a 1 kV shock. D: Computed field distribution for a 2 kV shock.
Fig 6.
Evaluation of nsPEF lesion (compare Fig 3 for details).
A: Photograph of the cardiac surface after ablation. The pairs of black dots mark the locations of the (successive) positions of the ablation electrodes, the black diagonal line in the upper right is the stimulation electrode. B: Action potential amplitude map after ablation. C: Activation map after ablation.
Fig 7.
For shocks of 2.3 kV over 2.3 mm, we evaluated lesion width in some hearts with TTC staining and in other hearts with PI staining. For shock of 4 kV over 4 mm, we evaluated lesion width in all hearts with TTC staining. Bar heights show averages, error bars indicate standard deviations.
Fig 8.
3D reconstruction of the geometry of the ablated volume.
A: A stack of TTC-stained sections of the lesion. White and red areas identify dead and live tissues, respectively. Sections are 300 μm thick. B: Three-dimensional rendering of the lesion geometry, obtained from the sections in Panel A. The red bars indicate the successive positions of the ablation electrodes. C: Zoom into one of the TTC-stained sections at the boundary of the ablated volume.