MILLIONS of people around the world benefit from having artificial pacemakers implanted into their chests, to help restore a normal heartbeat. Yet pacemakers are not without problems. The bulk of the device—which contains its battery and electronic control systems—usually sits just under the wearer's skin. From this box thin, flexible leads are threaded through a vein and into the appropriate part of the heart. These leads detect the heart's electrical activity (which controls when it contracts, and is regulated by a cluster of specialised muscle cells that act as a natural pacemaker), transmit that information to the artificial pacemaker's electronics for analysis and, if the natural activity is deemed irregular, deliver an electrical charge from the artificial pacemaker's batteries that causes the cardiac muscle to contract, pacing the pumping of the heart.
Fitting the body of an artificial pacemaker is fairly easy. Fitting the leads, though, can be tricky; impossible, even, in some patients. And if the leads fail, removing them may require major surgery. They also bring risk of infection.
But not, perhaps, for much longer. Pacemakers are going wireless. Cambridge Consultants, a technology-development company based in Cambridge, England, and EBR Systems, a Californian firm set up specifically to make leadless cardiac pacemakers, have been collaborating on what they call a Wireless Cardiac Stimulation system (or WiCS, as they abbreviate it). On November 14th the two companies announced that WiCS had become the first device of its kind to have successfully completed a series of clinical trials. These trials, which involved 100 patients, some of whom were suffering problems with pacing leads, were carried out at a number of hospitals across Europe.
Pacemakers used to have but a single lead, going to one of the heart's four chambers. These days, many use two or three leads, each ending in a different place (see videographic below) These additional leads provide what is known as cardiac-resynchronisation therapy. This involves stimulating both the left and right sides of the heart, in order to synchronise their contraction. That, in turn, improves the pumping action. Inserting leads into the left side of the heart, however, can be particularly difficult, since the best route involves going through the right side of the heart first.
Instead of leads, WiCS uses a tiny wireless electrode which, at about 3mm by 13mm, is no bigger than a long grain of rice. This is inserted, as a normal electrode would be, using a catheter (a small flexible tube). The lack of a trailing wire, however, makes the procedure much easier than it otherwise would be. The trick is getting power to the electrode.
That is done using ultrasound, which is generated by a box called a pulse-generator that is similar in size to a pacemaker box, but is inserted lower down in the chest (see illustration). When the pulse-generator sends an ultrasonic pulse to the wireless electrode, the sonic energy causes a receiver in the electrode to vibrate. This mechanical vibration is then converted into the electrical energy required to stimulate the heart.
At present, WiCS is used only on the difficult-to-reach left hand side of the heart. It works, in other words, in conjunction with a conventional pacemaker that has a lead into the right hand chambers. When the conventional pacemaker generates a pulse to pace the right hand side of the heart, this is detected by the pulse-generator and a pulse is sent to stimulate the left hand side of the heart.
The next step is to combine the conventional pacemaker and pulse generator into one, implantable unit. That, according to Andrew Diston, the head of Cambridge Consultants' Global Medical Technology, will both give cardiologists more freedom in placing electrodes to treat different conditions, and boost the reliability of their procedures. Eventually, Mr Diston believes, the system may be able to do away with leads altogether, for totally wireless heart control. That would really set a new pace for medical science.