A team of life science entrepreneurs in Houston, TX, has developed the first catheter-deployed circulatory assist device intended for long-term use to treat chronic heart failure. The 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 from Procyrion, Inc., reduces the risks associated with circulatory support devices and enables younger, healthier patients to be treated before progressive damage occurs.
Designed to assist the natural function of the heart, the intra-aortic pump uses 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. Additionally, in a model of chronic heart failure, the device decreased energy consumption of the heart by 39 percent, allowing the heart to operate more efficiently, encouraging cardiac rehabilitation and recovery. (See Figure 1)
Unlike other circulatory assist devices, which must be surgically implanted, Aortix’s small size and unique design provide minimal procedural risk. Measuring approximately 6 mm in diameter and 6.5 cm long, a cardiologist can deliver the device via catheter in the femoral artery to the descending thoracic aorta. (See Figure 2) Once the catheter sheath is retracted, the self-expanding nickel-titanium anchors deploy to affix the pump to the aortic wall.
Its location eliminates the risk of damage to the heart or valves, and greatly simplifies deployment. Moreover, placement of Aortix downstream of the carotid arteries effectively eliminates the risk of thrombotic stroke, which affects approximately eleven percent of patients using surgical ventricular assist devices.
Because traditional assist devices replace heart function rather than support it, device failure can be fatal. With a partial support device, which doesn’t 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.
Pump and Motor Technology
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 tunneled to a desired transdermal exit site or to a Transcutaneous Energy Transfer (TET) system for subcutaneous implantation without an indwelling power lead.
Procyrion worked with maxon precision motors for nearly two years to develop a custom motor for this unique and demanding application. The basis for the Aortix device is a standard motor with some customization including the electrical lead, shaft length, and bearing assemblies, all designed to make the pump durable and biocompatible. A specialized high efficiency motor core was designed for this application to extend battery life and produce less heat so it doesn’t adversely affect the circulating blood. (See Figure 3)
In addition, maxon worked 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 that can be used for giant pumps in the oil field. However, since its motors can be used across multiple industries, the technology was successfully transferred to a miniature-scale medical application.
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 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 30,000 rpm, 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 more than eight hours on a single battery pack. Its 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. 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.
This article was written by Mark Dwyer, Engineer, maxon precision motors, inc., Fall River, MA. For more information on maxon precision motors, visit http://info.hotims.com/49748-165. For more information on Procyrion, Houston, TX, visit http://info.hotims.com/49748-164.