Circulatory support without surgery for heart failure patients

A team of life science entrepreneurs in Houston, Texas, has developed the first catheter-deployed circulatory assist device intended for long-term use in the treatment of chronic heart failure. Procyrion, Inc.'s Aortix provides a minimally invasive treatment option for the more than two million chronic heart failure patients who are too sick for medication. This pre-clinical cardiologist tool reduces risks associated with circulatory support devices and enables treatment of younger, healthier patients before progressive damage occurs.

Assisting the natural function of the heart, the intra-aortic pump has been thoughtfully designed with integrated technologies as an alternative to large, cumbersome surgical devices currently providing full circulatory support. Aortix accelerates a portion of the body's native blood flow within the pump and pushes it through fluid entrainment ports directed downstream. The jets entrain native aortic flow, transferring energy to the cardiovascular system and increasing blood flow to vital organs such as the kidneys. In addition, in a model of chronic heart failure, Aortix decreased energy consumption of the heart by 39 per cent, allowing the heart to operate more efficiently, encouraging cardiac rehabilitation and recovery.

Unlike other circulatory assist devices, which must be surgically implanted, Aortix's small size and design provide minimal procedural risk. Measuring approximately 6mm in diameter and 6.5cm long, a cardiologist can deliver Aortix via catheter in the femoral artery to the descending thoracic aorta. Once the catheter sheath is retracted, the self-expanding nickel-titanium anchors deploy to affix the pump to the aortic wall.

The location of Aortix eliminates the risk of damage to the heart or valves, and simplifies deployment. Moreover, placement of Aortix downstream of the carotid arteries effectively eliminates the risk of thrombotic stroke, which affects approximately 11 per cent of patients using surgical ventricular assist devices.

Because traditional assist devices replace heart function rather than support it, device failure can be fatal. With Aortix, a partial support device which does not obstruct native blood flow, failure is not life threatening. Should the pump fail, the device can easily be retrieved and replaced in another minimally invasive, catheter-based procedure.

Each Aortix device consists of a small, continuous flow pump mounted within a self-expanding anchoring system. The anchored pump attaches to a flexible power lead, which can be tunnelled to a desired transdermal exit site or to a Transcutaneous Energy Transfer (TET) system for subcutaneous implantation without an indwelling power lead.

Durable and biocompatible

Procyrion has been working with Maxon for almost 2 years to develop a custom motor for this demanding application. The basis for the Aortix device is a Maxon EC6 motor with some customisation including the electrical lead, shaft length and bearing assemblies - all designed to make the pump durable and biocompatible. Maxon also designed a high-efficiency motor core for this application, which extends battery life and produces less heat so it does not adversely affect the circulating blood.

In addition, Maxon is working closely with Procyrion to implement a magnetic torque drive, so the motor could be mounted inside a hermetically sealed chamber with the magnetically coupled impeller suspended between two bearing surfaces. This configuration eliminates the possibility of blood entering the motor core. This magnetically coupled pump arrangement is a method sometimes used for giant pumps in the oil field, but because of Maxon's breadth of experience across multiple industries, the company was able to help the Procyrion team successfully transfer this technology to a miniature-scale medical application based on their motors' wide industrial uses.

Jet pumping, or fluid entrainment, is used extensively in mining, refrigeration, inline mixing and other industrial applications to promote efficient mixing and flow. However, it has not previously been used in a medical application. Procyrion's Aortix harnesses fluid entrainment with its small diameter axial flow pump in a jet pump configuration inside the aorta. The Aortix device augments native blood flow by accelerating blood and increasing cardiac output, thus reducing the workload of the heart, so it can heal. The pump drives an impeller at speeds of up to 30,000rpm, which generates high levels of torque. For this reason, the high-efficiency motor was developed to decrease heat output and increase battery life at the higher required torque.

Presently, the device can operate for over 8 hours on a single battery pack. The external battery pack and control unit have been designed to be "hot swappable', meaning the battery can be changed without needing to stop the device. A variety of charging devices can be used. As previously mentioned, the Procyrion team has also built a TET charging system that enables the battery to be charged wirelessly, without the need for an electrical power lead that crosses the skin. This design has the potential to significantly reduce the risk of infection, common with other implantable heart pumps.

Procyrion's intra-aortic pump supports the natural function of the heart while reducing the risks associated with circulatory support, ultimately providing a means to rest and heal the failing heart.

To learn more about miniature brushless DC motors, please visit www.maxonmotor.co.uk.