A miniaturized cooling system for trans-esophageal echocardiographic probes may improve patients safety in minimally invasive cardiac surgery or trans-catheter percutaneous interventions
Authors: Parrotta F , Faoro G , Tognarelli S , Menciassi A , Giannoni A 
Published: January 2025

Abstract

Introduction
The recent development of real-time three-dimensional trans-esophageal echocardiography (RT-3D TEE) has favoured a wider transition from open-heart to minimally invasive surgery (MIS) or various trans-catheter percutaneous interventions, minimizing surgical risks and allowing faster post-operative and procedural discharge [1]. However, recent studies have highlighted the potential risk of oesophageal lesions partly related to thermal injury caused by the heat of the TEE probe during cardiac interventions [2].

Purpose
This work aims to design a cooling system for trans-esophageal echocardiographic probes to be used during MIS or trans-catheter procedures. Currently during those interventions, fluoroscopic and RT-3D TEE images are simultaneously used, since commercial TEE probes automatically switch off at a temperature threshold of approximately 42.5°C [3], to avoid potential thermal oesophageal lesions. Additionally, ultrasound (US) image quality tends to decrease as temperature increases. The creation of a cooling device for TEE probes would therefore increase the reliability of US images in the intraoperative context, also considering their complete harmlessness to the patient.

Methods
The proposed cooling system design is a silicone cap – thus potentially sterilisable and reusable - into which the probe is inserted. The cap has an inner tube in which water flows at 25°C, constituting the cooling fluid. Heat exchange was studied through thermo-fluid dynamic simulations to analyse the cooling phenomenon. The hydraulic flow is controlled by a pumping device that activates when the probe temperature reaches a specific threshold deemed to be critical, also for image quality. Temperature trends are constantly monitored by means of two thermistors.

Results
The cooling system was extensively tested (5 repetitions for each experimental condition: Probe alone, Passive silicone and Active cooling system) on a probe produced by GE Healthcare, setting 38°C as the activation temperature threshold for the pump. Considering the duration of MIS or transcatheter interventions (about two hours) [2], it was experimentally observed that by using the cooling system the probe never exceeded the temperature of 39°C. From experimental tests, it is possible to state that the insulating properties of silicone result in a dual effect: a) silicone passively hinders heat dispersion produced by the probe due to the Joule effect - Passive silicone condition ; b) once the system is activated the cooling effect is maintained by the precence of water inside the cap - Active cooling system condition.

Conclusions
In conclusion, based on numerical simulations and experimental results, this novel tool seems promising, increasing the safety and potentially also the reliability of US images in the intraoperative and intraprocedural scenario.
Cooling system design Experimental results