Biomedical Engineering Reference
In-Depth Information
In 1968, Mirowski began developing the implantable cardioverter defibril-
lator (ICD) to stop heart fibrillation (irregular beating) by delivering a high
voltage and high energy shock (Efimov et al., 2008). It took several years to
develop the circuitry, battery, and capacitor suitable for an implantable device.
The first device was implanted in 1980. The transvenous defibrillation lead
system was approved in the 1990s, allowing patients to avoid the more invasive
thoracotomy procedure. Later, tiered therapy was added to the ICD so the device
could provide various therapies at an escalating energy scale for defibrillation.
While the use of electrical stimulation of excitable tissue for therapeutic
purposes began with the heart, expansion of this technology to new therapy
modalities involving other specialized tissues such as the brain and nervous
tissues was forthcoming. Many different therapeutic applications have been
explored with this technology throughout the years. While it is impractical to
review all of them here, a few therapies that have gained relatively widespread
commercial use are representative of the broader field of these applications and
are relevant for review in this chapter.
One such therapeutic application, neurostimulation (as it has broadly become
known), involves technology that spun off from pacing technology. This therapy
has been developed from an understanding of the nervous system `wiring
diagram' for a particular body function. The advent of Melzack and Wall's Gate
Control Theory of Pain in the latter half of the 1960s, proposing endogenous
neural circuits capable of inhibiting pain perception, led to several approaches to
stimulate these neurological circuits (Melzack and Wall, 1965). Norm Shealy,
working with Mortimer, developed a neurostimulator designed to stimulate the
dorsal columns of the spinal cord (Shealy et al., 1967). The dorsal columns
function to convey somatosensory information from the periphery and are part
of the pain inhibition circuitry. Initially, they performed a laminectomy and
opened the dura to place a flat electrode with its stimulating surface directly
against the spinal cord.
As with pacemakers, these techniques have evolved. Modern techniques
employ a Tuohy needle to insert a cylindrical lead into the epidural space
between the dura and dorsal aspect of the spinal column. Alternatively, a paddle-
shaped lead is inserted through a laminotomy to lie over the dorsal columns.
These various techniques, specifically referred to as spinal cord stimulation
(SCS), are in widespread commercial use as a pain treatment modality used
primarily for neurogenic pain, or pain caused by damage to the nervous system
itself.
Further understanding of endogenous pain suppression circuitry within the
brain led to techniques to activate opioid responsive nerve cells deep inside the
brain. Hosobuchi and Adams implanted electrical stimulation leads into the
periventricular gray to treat pain. The cylindrical leads were inserted through a
small burr hole in the skull using stereotaxic surgery (Hosobuchi et al., 1977).
While this particular therapy is employed infrequently today, the technology of
