Chapter 35
- Implantable Cardiac Pulse Generators: Pacemakers and Cardioverter-Defibrillators
- Marc A. Rozner
Battery operated pacing devices were introduced by CW Lillehei
(a cardiothoracic surgeon) and Earl Bakken (an electrical technician) in 1958, just
four years after the invention of the transistor. A few years later, Wilson Greatbatch,
a cardiologist in Buffalo, NY, created the first implantable battery powered device
in his barn.[1]
Advances in electronic miniaturization
as well as improvements in battery technology have led to the development of very
small (10-mL volume), but electronically complicated, programmable pacing devices.
The natural progression of pacemaker developments led to the invention
of the implanted cardioverter-defibrillator
*
(ICD) around 1980 by Michael Mirowski (Baltimore, MD). First approved by the U.S.
Food and Drug Administration (FDA) in 1985, implantation of these devices required
a thoracotomy, a significant operation for the patient with poor heart function.
However, four technologic advances (transvenous lead placement,
*The
terms antibradycardia and antitachycardia will be used throughout this chapter.
Antibradycardia refers to pacing to maintain a minimum rate. Conventional pacemakers
are antibradycardia devices. Antitachycardia refers to therapy delivered in the
setting of a tachycardia, and it is designed to reduce the underlying heart rate.
antitachycardia
*
pacing capability, miniaturization permitting pectoral pocket placement, and dual
chamber, rate responsive antibradycardia pacing) have led to increases in implantations.
These changes in ICD implantation and indication have two important
results for health care providers. First, a pectoral (rather than abdominal) pocket
ICD with pacing capability might be mistaken, by virtue of pacing "spikes" on the
surface electrocardiogram, for a (non-ICD) pacemaker. At many centers, electrocardiograms
are collected from patients with "pacemakers" using a magnet. Since some ICDs from
Guidant Medical and Cardiac Pacemakers, Inc. (CPI) can undergo permanent deactivation
of antitachycardia therapy with magnet placement, this mistake could leave a patient
unprotected.[2]
Second, pacing functions in an
ICD often respond to external stimuli (magnet placement, electromagnetic interference)
differently than a pacemaker. These issues will be addressed in the text below.
The complexity of pacemakers and ICDs, as well as the multitude
of programmable parameters, limits the number of generalizations that can be made
about the perioperative care of the patient with an implanted pulse generator. Population
aging, continued enhancements in implantable technology, and new indications for
implantation of cardiac devices will lead to growing numbers of patients with these
devices in the new millennium. The American College of Cardiology (ACC) has taken
note of these issues, and guidelines (hereafter the ACC Guidelines) have been published
regarding the care of the perioperative patient with a device.[3]
The ACC is not alone in this endeavor; recently, Pinski and Trohman also reviewed
this subject and published similar recommendations.[4]
[5]
Because ICDs now also perform permanent cardiac
pacing, some ICD issues related primarily to pacing will be discussed further on.
Patients with an implanted cardiac pulse generator (PG) often
have significant comorbid diseases in addition to their cardiac rhythm disturbances.
Our ability to care for these patients requires attention to their medical and psychological
problems. We also need an understanding of the pulse generator, its functions, and
its probable idiosyncrasies in the operating or procedure room.
Not all electronic generators implanted in the chest are cardiac
devices, and devices resembling cardiac pulse generators are being implanted at increasing
rates for indications unrelated to cardiac issues. When implanted in the pectoral
position (the usual place for current cardiac generators), these devices can be mistakenly
identified as cardiac generators.[6]
Pulse generator
implantation has been approved by the FDA for pain control, thalamic stimulation
to control Parkinson's disease, phrenic nerve stimulation to stimulate the diaphragm
in paralyzed patients, and vagus nerve stimulation to control epilepsy. When evaluating
a patient with any pulse generator, one must now determine whether the PG will be
pacing the heart, stimulating the central nervous system, stimulating the spinal
cord, or stimulating the vagus nerve. Adding to this confusion, Cyberonics Corporation
(Houston, TX) has a patent on a vagus nerve stimulator for heart failure, although,
at this time, there have been no clinical trials to evaluate vagus nerve stimulation
in the setting of heart failure.
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