Tech Briefs

Heart Pump with Behind-the-Ear Power Connector

One-third of patients with heart pumps develop infection at abdominal connection.

Cardiac surgeons and cardiologists at the University of Maryland Heart Center are part of a multi-center clinical trial evaluating the efficacy of powering heart pumps through a skull-based connector behind the ear. The pumps, called left ventricular assist devices (LVADs), support the heart’s main pumping chamber, the left ventricle. LVADs are implanted in the chest and powered with external batteries. Typically, these devices, which are used for patients with severe heart failure, are powered through an electrical cord connected at the abdomen, where potentially deadly infections can develop.

“Over time, nearly one-third of our patients surviving with the assistance of an implanted blood pump develop an infection at the site where the power cord exits the skin. This complication may be lethal but, if not, it is always a difficult problem,” says the University of Maryland’s principal investigator, Bartley P. Griffith, MD, the Thomas E. and Alice Marie Hales Distinguished Professor of Surgery at the University of Maryland School of Medicine, and a senior cardiac surgeon at the University of Maryland Medical Center.

The study, named RELIVE (Randomized Evaluation of Long-term Intraventricular VAD Effectiveness), compares two similar LVADs, which provide long-term support to patients with endstage heart failure who, for a variety of reasons at the time of implant, are ineligible for a heart transplant.

Two Different Methods of Connection

The major difference is in the way electrical power from the battery pack gets to each pump implanted in the chest. In one case, the internal power cord is routed through a traditional opening, or pump pocket, in the abdominal wall. In the other, the internal power cable is tunneled through the neck to the head. The internal cable is connected to a socket or pedestal placed behind the ear in the skull, in the same area used to pass cochlear implant electrode wires into the body. On the outside of the skull, a waterproof cable running from the battery pack is plugged into the socket. (See Figures 1a and b)

Patients in the study were randomly assigned to one of two groups. One group received a Jarvik 2000 LVAD equipped with an investigational behind-the-ear connector from Jarvik Heart, Inc., the funder of the study. The other group of patients were given Thoratec Corporation’s HeartMate II Left Ventricular Assist System, which is the most widely used FDA-approved LVAD for destination therapy. The Thoractec unit employs an abdominal connector.

One of the problems with the abdominal approach relates to the softness and flexibility of the abdomen. According to Griffith, even micro-movements of the power cable at the abdominal entrance can set the stage for infection. The investigators theorize that the stability of the bone-mounted terminal coupled with the vast blood supply in the scalp can reduce the chance of infection. And, locating the connector in the head allows patients to shower or swim.

Since the Jarvik implantation involves the head and neck, the cardiac team has formed an unusual collaboration with another surgical department at the School of Medicine. Ronna P. Hertzano, MD, PhD, assistant professor of Otorhino laryngology-Head and Neck Surgery at the University of Maryland School of Medicine, extends the internal Jarvik power cord through the neck and places the socket in the skull. Hertzano, whose specialty includes hearing restoration and diseases of the ear and lateral skull base, works alongside the cardiac surgical team at the time of the procedure to correctly place the wire and skull connector.

In the early days of heart pump technology, infection was less of an issue compared with device failure, bleeding, clotting, and limited patient survival. But, with today's more durable units and with patients using them for extended periods of time, infection protection has taken on a new importance. Today’s improved pump designs producing continuous, minimally pulsatile blood flow make it possible for LVADs to run for years, even supporting the patient for the remainder of his or her life.

The Jarvik skull model has already been approved for use in Europe. The clinical comparison in the United States opened for patients this year. The study will follow 350 patients for up to three years.