Fig 1.
Shock Wave Catheter Ablation (SWCA) System and Catheter Position in Animal Study.
The spherical SW was generated in a water-filled semi-elliptical reflector attached to the catheter tip by irradiation of Q-switched Holmium (Ho):yttrium aluminum garnet (YAG) laser beam through quartz optical fiber. The SW was then reflected by the reflector and was converged onto the outer focus. The RF-induced lesion started from the contact area and decreased proportionally with the distance, resulting in a risk of thrombus formation and the inability to reach deep arrhythmic origins (A). The SW catheter was 14-Fr size in diameter and equipped with two polar electrodes at the tip (B). The SW catheter was located vertically to the ventricular myocardium under direct vision in the epicardial ablation study (C). The SW catheter was located as vertically as possible to the right ventricular wall under fluoroscopic vision in the endocardial ablation study (D).
Fig 2.
Characteristics of Focused SW Generated by the SWCA System.
The shadowgraphs of SW under water taken by high-speed camera showed the converging time course from the reflector onto the focus (0.4, 0.8 and 1.2 μsec). Cavitation bubbles were observed in the third frame (1.2 μsec) (A). The representative pressure waveform of SW at the focus showed a typical time history with instantaneous high positive pressure followed by negative pressure. Max overpressures along the longitudinal axis had a peak at each focal length set by two different reflectors (2.0 and 3.0 mm) (left panel in C), and those across the short axis at the focal level (2.0 mm) were steeply decreased 500 μm in width (right panel in C).
Fig 3.
Histopathological Findings of Epicardial Lesions in the Acute Phase.
The RF lesions were semi-circular in shape (A) with severe superficial tissue damages including the thinning of adventitial membrane (B; enlarged view of the black square in E). The SW-induced lesions were spheroidal in shape toward the focus (the blue dash line in C) with mild superficial tissue damage (D), disruptions of myocardial fibers and interstitial hemorrhage beyond the focus (E; enlarged view of the black square in C), and the strongest myocardial tissue degeneration including contraction band necrosis at the focus (F; enlarged view of the black square in C). The histological grading scores of epicardial injury were significantly different between the RF- and SW-induced lesions (G). The specimens were stained with hematoxylin—eosin. Scale bars: 1.0 mm (A and E), 200 μm (B and F), and 50 μm (C and D). The results are expressed as mean ± standard deviation (SD). The Mann—Whitney’s U test was used to compare the histological grading score between the SW and RF lesions.
Fig 4.
Time-course of Histopathological Findings of Epicardial Lesions.
The SW-induced lesion at Day 1 (A, E, I, and M), Day 2 (B, F, J, and N), and Day 7 (C, G, K, and O) showed the sphenoidal lesions in each phase. The magnified images at the SW focus site showed the infiltration of inflammatory cells around the degenerated myocardium at Day 1 (E) and more at Day 2 (F). The SW-induced lesion showed homogeneous fibrotic changes at Day 7 (K and O). The RF lesion showed central residual necrotic tissue (D) and a border zone with fibrosis (L and P) and chronic infiltration of inflammatory cells (H) at Day 7. The specimens were stained with hematoxylin—eosin (HE) (A–H) and Masson’s trichrome (MT) (I–P). Scale bars: 1.0 mm (A–D and I–L), and 50 μm (E–H and M–P).
Fig 5.
Time course of Depth, Width and Area of the SW-induced Lesions.
The lesion depth and width were measured as indicated by the arrows, and the area was measured as indicated by the dashed line (A). The lesion depth was maximal at 1 h after the procedure and decreased over time with the depth equivalent to the SW focal length (2.0 mm; the red dashed line) at Day 7 (B). The lesion width was equivalent to the opening diameter of the SW reflector (3.6 mm) (C). The lesion area was also maximal at 1 h and decreased over time (D). Results are expressed as mean ± SD. One-way analysis of variance was used to compare data for statistically significant differences, followed by the Tukey’s honestly significant difference (HSD) to elucidate any interactions among the lesion depth, width, and area at each time course. *P < 0.05 vs. 1 h.
Fig 6.
AV Node Ablation by the SWCA System.
The SW catheter was inserted through the jugular vein approach (A) and located at the target site where the His-bundle potential (arrow) was recognized (B). A junctional escape rhythm was observed immediately after starting the SW application (C), followed by a complete AV block (D). Blue and red arrows show the atrial and ventricular potentials, respectively.
Fig 7.
Persistent Electrophysiological Effect of SWCA.
Representative ECGs with AV dissociation in a SW-treated animal (A) and the percentage of animals presenting with complete AV block (B) or any AV conduction disturbance including complete AVB in panel B (C) immediately after procedure, and at Day 1, Day 3, and at the end of the follow-up period. The data from Day 1 and Day 3 were obtained from the Holter electrocardiogram with pacing (VVI 80 beats/min). The AV conduction disturbance in both RFCA and SWCA were sustained during each follow-up period. The number on the top of the bar graphs show the animals with complete AV block (B) and those with AV conduction disturbance (C) to the total animal numbers (Sham, n = 3; RFCA, n = 3; SWCA, n = 9).
Fig 8.
Histopathological Examination of the AV Node after Ablation.
In the sham operated group (A–D), no morphological change of AV nodal cells (black arrows in C) was noted except for slight interstitial fibrosis (D). In the RFCA group (E–H), the thermal degeneration of AV nodal cells (black arrows in G) in the acute phase and fibrotic lesions with residual central necrosis in the chronic phase (H, day 14) were noted. Massive endothelial damage was also noted (E). In the SWCA group (I–L), the degeneration of AV nodal cells, including cell body atrophy (black arrows in K) in the acute phase and homogenous fibrotic lesions in the chronic phase (L, day 14), were noted.The specimens were stained with hematoxylin—eosin (A–C, E–G and I–K) and Masson’s trichrome (D, H and L). Scale bars: 1.0 mm (panels D, H, and L), 500 μm (B, F, and J), 100 μm (A, E, and I), and 50 μm (C, G, and K).