Design and evaluation of a transesophageal HIFU probe for ultrasound-guided cardiac ablation: simulation of a HIFU mini-maze procedure and preliminary ex vivo trials

Abstract

Atrial fibrillation (AF) is the most frequent cardiac arrhythmia. Left atrial catheter ablation is currently performed to treat this disease. Several energy sources are used, such as radio-frequency or cryotherapy. The main target of this procedure is to isolate the pulmonary veins. However, significant complications caused by the invasive procedure are described, such as stroke, tamponade, and atrioesophageal fistula, and a second intervention is often needed to avoid atrial fibrillation recurrence. For these reasons, a minimally-invasive device allowing performance of more complex treatments is still needed. High-intensity focused ultrasound (HIFU) can cause deep tissue lesions without damaging intervening tissues. Left atrial ultrasound-guided transesophageal HIFU ablation could have the potential to become a new ablation technique. The goal of this study was to design and test a minimally-invasive ultrasound-guided transesophageal HIFU probe under realistic treatment conditions. First, numerical simulations were conducted to determine the probe geometry, and to validate the feasibility of performing an AF treatment using a HIFU mini-maze (HIFUMM) procedure. Then, a prototype was manufactured and characterized. The 18-mm-diameter probe head housing contained a 3-MHz spherical truncated HIFU transducer divided into 8 rings, with a 5-MHz commercial transesophageal echocardiography (TEE) transducer integrated in the center. Finally, ex vivo experiments were performed to test the impact of the esophagus layer between the probe and the tissue to treat, and also the influence of the lungs and the vascularization on lesion formation. First results show that this prototype successfully created ex vivo transmural myocardial lesions under ultrasound guidance, while preserving intervening tissues (such as the esophagus). Ultrasound-guided transesophageal HIFU can be a good candidate for treatment of AF in the future.

Image-guided ultrasound phased arrays are a disruptive technology for non-invasive therapy

“…Phased arrays may offer a less invasive approach via the trans-esophageal route routinely used for cardiac imaging. Simulation studies [289] have demonstrated the feasibility of this approach, and the practical development of such arrays has been promising [290, 291], however, fully electronically-steerable arrays for this purpose have not yet been realized.…”

Extra-pericardial tamponade following Wolf Mini-Maze procedure: a case report

“…As such, this case appears to be the first to report cardiac tamponade in absence of CABG with the MINI procedure. Current literature references cardiac tamponade with MINI procedures only once in a simulation study related to catheter ablation and Maze procedures, not an association of adverse effects reported following Maze procedures [11]. A search for extra-pericardial tamponade produced few results.…”

Catheter-based ultrasound technology for image-guided thermal therapy: Current technology and applications

“…Simulation and preliminary studies have been reported for phased array devices for such applicators [67-72]. Some of these designs also have integrated MR imaging coils [60, 61] or ultrasound imaging probes [62, 63]. …”

“…Further, transesophageal devices have been designed for targeted ablation of the left atrium for treatment of atrial fibrillation (Figure 2d). Some recent studies include in vivo swine models with atrial and ventricular myocardial ablations [72], ex vivo pig hearts [63, 64, 86], and simulation and device design [68-70]. …”