New design for an endoesophageal sector- based array for the treatment of atrial fibrillation: a parametric simulation study

Atrial fibrillation (AF) is the most frequent and sustained cardiac arrhythmia affecting humans. The electrical isolation by ablation of the pulmonary veins (PV) in the left atrium (LA) of the heart has proved to be an effective cure for the AF. The ablation consists mainly of the formation of a localized circumferential thermal coagulation of the cardiac tissue surrounding the PVs. In this article, a parametric study was carried out to establish an optimal configuration of endesophageal ultrasound phased arrays intended to treat the AF. The devices are spherical-surface sections truncated at 15 mm, with a depth of 4 mm, and they are cut in concentric-rings, each composed of independently driven sectors. The number of independent elements (N_e) was minimized for different values of ratio of pressure amplitude of the secondary lobe over the main lobe (n) of 0.35, 0.4, 0.45, and 0.5 inside a volume of interest (VOI). After assuming a Cartesian system with the origin in the center of the device, the VOI was defined as the prism enclosed by the coordinates (-12, 10, -9) mm and (12, 37, 9) mm. The VOI has its center at (0, 23.5, 0) mm and is large enough to contain all the targets identified in the Visible Human Project Male specimen. Operating at 1 MHz, n and N_e were calculated in function of the element size and focal length (F). Four devices for each value of n were found. After keeping values of F and normalized dimensions of the independent elements in terms of wavelength, higher frequencies were considered: 1.25 MHz, 1.5 MHz, and 2 MHz. In total, 16 device configurations were obtained. Realistic modeling of lesion formation in the heart chamber showed that the 16 configurations were able to produce the typical lesion used to treat the AF while preserving surrounding structures. At higher frequencies, lower power was required, and a greater number of array elements was required. For an exposure of 5 s and a maximum temperature of 70degC, the av- rage (plusmns.d.) acoustical intensity at transducer surface varied from 22.3(plusmn5.8) W/cm² for a device with F = 98 mm at 1 MHz to 5.8(plusmn1.2) W/cm² for a device with F = 186 mm at 2 MHz, while requiring 319 and 2093 elements, respectively, and achieving values of n of 0.5 and 0.41, respectively. For the intended application, the selected devices implied a better focusing when compared with more traditional planar 2-D arrays, while requiring less power and fewer independent elements.