Development of an ultrasound thrombolysis system for artificial hearts

Abstract

Thrombus formation in artificial hearts remains a key risk factor in the death of patients. Anticoagulant therapy is essential in patients with artificial hearts. However, thrombogenesis can also occur under anticoagulant therapy. Once thrombogenesis has begun, anticoagulant therapy cannot recover the thrombus-free state. Therefore, in order to prevent thrombogenesis in the artificial heart, we developed a prototype ultrasound thrombolysis system. The system is assumed to work continuously, dissolving micro thrombi before they can grow, thereby preventing the thrombogenesis. As a method of preventing thrombogenesis, we focused on the thrombolytic effect of ultrasound. We herein assume that three phenomena, namely, cavitation, acceleration, and acoustic streaming, can dissolve micro thrombi. Considering the specifications required for applying ultrasound thrombolysis in the artificial heart, the prototype ultrasound thrombolysis system consists primarily of piezoelectric vibrators for generating ultrasound and a driver unit. Two types of vibrator were prepared for two different ultrasound frequencies (23 and 220 kHz). Thrombolysis by cavitation was expected to occur at 23 kHz, and thrombolysis by acceleration was expected to occur at 220 kHz. The driver unit is composed of a switching circuit, an output transformer, and a matching circuit. In order to confirm thrombolysis using the developed system, a thrombolysis test was carried out in vitro. The thrombus was formed from human whole blood (Hematocrit: 46%) and was divided into three parts. These were placed into three disposable optical cells (samples A, B, and C) with saline. Two continuous ultrasound waves (Frequency: 23 and 220 kHz, Common Ultrasound Intensity: 1.2 W/cm2) were radiated for 30 minutes to samples A and B, respectively. For comparison, sample C was prepared without ultrasound. As a result, thrombolysis was observed visually in samples A and B. In conclusion, the developed ultrasound thrombolysis system was confirmed to provide two mechanisms for preventing thrombogenesis in the artificial heart.