Pacemakers and Antiarrhythmia Devices by liaoqinmei


									                New Generation Pacemakers in the Operating Room
                                      William A. Shapiro, M.D.

Pacemaker prevalence
    For all cardiac surgical procedures performed in the operating room, most, if not all, include
placement of temporary pacing wires before the patient leaves the operating room. The number of
permanent pacemakers implanted to treat signs or symptoms of bradycardia continues to grow.
More than one million people have pacemakers for this indication, and over 200,000 new devices
are implanted each year for this indication alone.1 Starting in the 1980s, implantable cardioverter
defibrillators (ICD) have been inserted to treat symptomatic ventricular tachycardia or ventricular
fibrillation.2 Approximately 150,000 such devices are implanted in Americans every year.
Biventricular pacing, known as cardiac resynchronization, introduced in the late 1990s, has rapidly
gained favor as a treatment option for patients in CHF with a widened QRS complex.3,4 In addition,
a variety of electrical devices exist for treatment of atrial fibrillation.5 Given the number of patients
in the US alone with atrial fibrillation, over 2 million, future developments in this area will
skyrocket the number of electrical devices used just to manage this condition alone. It is challenging
to get accurate information regarding the numbers of pacemakers and ICDs inserted each year, you
can easily imagine that cardiac electrical devices will continue to increase6 and we will see these
patients in the OR more frequently than ever before.

                                 Anesthetic Considerations
    The number of different electrical devices currently used to diagnose,7 treat or prevent cardiac
arrhythmias, guarantees that most, if not all, anesthesiologists will manage patients with such
devices over the course of their clinical practice.

Reasonable goals and expectations for anesthesiologists
   By the early 1980’s, it was clear that permanent pacemakers used to treat bradycardia had
become complex enough that it was difficult, if not impossible, for every anesthesiologist to know
everything about each and every pacemaker. The trend toward increasing complexity continues as
companies produce new pacemakers, ICDs, and resynchronization therapy devices with proprietary
features that incorporate numerous additional complex-programming modes. Without industry-wide
standardization of the relevant technology, it is unrealistic to expect competent working knowledge
of every pacing device currently used. Are we fighting a losing battle? I hope not.
    My goal is to review the common features currently available in the majority of implantable
pacemakers, to highlight important features for their perioperative management, and to address
recent recommendations regarding intraoperative placement of a magnet over the pacemaker
generator. I will also review perioperative considerations for the ICDs, and discuss some possible
New Generation Pacemakers in the Operating Room                                                      2

intraoperative pacemaker emergencies. In a later section, there is a brief review of the basic concepts
of pacemaker components and the pacemaker coding system.
   For detailed discussion of the pacemaker coding system and the indications for pacemaker
implantation, there are numerous anesthesia8 and cardiology texts to which the reader can refer.
Indications for placement of ICD devices and studies documenting their efficacy are readily found in
the cardiology literature.

Recent updates
   Here are some key changes in pacemaker models that warrant our maintaining an awareness of
both the old and new technology.

In June 2005, the FDA issued a safety alert for a Guidant ICD: In December 2005, Guidant recalled
109, 000 devices. Guidant company internal documents show that they were aware of the problem
in 2002, but did not share this information with the doctors until forced to in May 2005. The FDA
said that they learned in March 2005 that a college student died after receiving a flawed Guidant
ICD. Since that first death, at least 6 other patients died when their Guidant ICD failed to work
properly. A front-page article in the New York Times on September 12, 2005 documents that the
FDA actually had information about these flawed devices as early as 2003. In spite of knowing
about the FDA alert and the Guidant recall, Boston Scientific, in December 2005, announced plans
to purchase Guidant. The deal closed in April 2006. In June 2006, Boston Scientific announced the
recall of an additional 27,000 ICDs, and stated that it would be likely that additional recalls would
be made. On July 13, 2007, Boston Scientific said that it agreed to pay $195 million to settle claims
by ‘thousands of patients’ who received potentially flawed Guidant defibrillators. This settlement,
announced 2 weeks before the start of the first trial, is not the end. Possible criminal charges are still
being considered by the Justice Department. We will provide anesthesia for these patients who
choose to exchange their ICD, based on these recalls, and possibly to patients who still have
defective ICD devices.

Saturday, March 14, 2009, New York Times: Medtronic Links Device For Heart to 13 Deaths: Yet
another almost unbelievable story showing that the company, Medtronic, knew as early as 2004, that
there were complaints about fractures in a cable, known as the Sprint Fidelis, that connects the ICD
to the heart. In spite of the concern first raised in 2004, more than ‘tens of thousands’ of additional
patients received this device before Medtronic recalled the Sprint Fidelis cable from the market in
October 2007. Only after the FDA got involved did Medtronic agree to the withdrawal.

MRI compatible pacemaker: In 2009, Medtronic reported at the European Society of Cardiology on
a study of 245 patients with a new type of cardiac pacemaker that is safe for patients undergoing an
MRI examination. It is estimated that between 50%-75% of all patients with pacemakers will, in
their lifetime, need at least one MRI exam. Medtronic stated that their goal is to develop an MRI-
safe ICD, and an MRI-safe cardiac resynchronization device.
New Generation Pacemakers in the Operating Room                                                   3

Pacesetter® “Vario” magnet mode: Normally, every pacemaker manufacturer builds their
permanent pacemaker to respond to a magnet placed over the pacemaker generator by changing the
pacing mode to asynchronous or fixed rate pacing. The “Vario” mode is a threshold-testing mode
that is activated when the magnet is placed over the pacemaker generator. In this mode, the magnet
initiates a 16-beat sequence of decreasing energy to identify the threshold energy required to
“capture” or pace the heart. The pacemaker now has two “magnet mode” options available but the
one programmed into the pacemaker cannot be identified until the magnet is applied or the
pacemaker generator is interrogated. Threshold testing remains the “magnet” mode until the Vario
mode is deactivated. Models with the “Vario” threshold-testing magnet mode are still manufactured
and patients with pacemakers containing this option will present for surgery. Therefore, it is
important to verify preoperatively what the magnet does when it is placed over the pacemaker
generator.9,10 If the “Vario” mode is the magnet mode, then the magnet mode should be
reprogrammed to become a fixed rate mode during the operative procedure. St. Jude Medical now
owns Pacesetter®.

Electromagnetic interference and pacing devices: There is increasing concern about cellular phones,
hand-held computers, and other devices that send or transmit electrical signals, particularly if these
devices are used in close proximity to the pacemaker generator.11-13 The introduction of new
wireless, as well as wired, technology will require careful evaluation to ensure that proximity of
these technologies does not affect pacemaker function.14,15 For example, one patient with a rate-
adaptive permanent pacemaker (see "Pacemaker Basics") developed a supraventricular tachycardia
when attached to a Datex® respiratory rate monitor after surgery.16 Guidelines to prevent potential
pacemaker complications due to the new technologies do not yet exist.

Preoperative cardiovascular evaluation of the patient with a pacemaker
   Most, if not all, patients who have a cardiac pacemaker have some degree of myocardial
dysfunction or have just undergone cardiac surgery. Those with an ICD also are often being
managed for significantly depressed cardiac function, characterized by little or no cardiac reserve.

Preoperative evaluation of the pacemaker
    All patients with a permanent pacemaker or ICD are given a pacemaker “card” with information
about the pacemaker generator and lead serial numbers, and the name of a physician who can
provide answers to clinical questions when the patient cannot. The back of the card provides a
technical support telephone number for the manufacturer. The phone numbers are answered 24-
hours a day by a real person, and they can be quite helpful.
    Evaluating a preoperative ECG in a patient with a pacemaker can be difficult, particularly when
the rate-adaptive feature has been activated. For example, paced rates will vary as metabolic rate
changes (as in patients who are nervous when the ECG is obtained), or the chamber paced may
change, suggesting that the pacemaker is not functioning correctly. To verify proper pacemaker
function and/or change the pacing mode (if necessary), it may be useful to consult a cardiologist.
New Generation Pacemakers in the Operating Room                                                   4

Pacemaker function, chemical abnormalities, and anti-arrhythmic agents
   Electrolyte or acid/base abnormalities are rarely, if ever, the primary cause of pacing failure,
particularly if the pacemaker was tested preoperatively and found to be functioning correctly.
Hypoxia, acidosis, hyperkalemia, hypokalemia, or any other electrolyte abnormality severe enough
to cause pacemaker failure will first cause the patient to fail; necessitating systemic treatment to
avoid an effect on pacemaker function. Although some anti-arrhythmic medications can affect the
pacing threshold, this effect should not produce clinically relevant problems under anesthesia.

Anesthetic choices
      All anesthetic agents have been used safely in patients with pacemakers, and both regional and
general anesthesia can be administered without detrimental effects on the device or its function. Thus,
the presence of a pacing device should not alter any planned anesthetic technique. Nevertheless,
pacemakers programmed in the demand mode may interpret shivering or other movement (such as
fasciculations) as intrinsic cardiac activity and become temporarily inhibited.

Intraoperative monitoring of pacemaker function
   Monitoring pacemaker function in the operating room is made difficult by the electrical milieu.
The ECG and pulse oximeter monitors provide all the information necessary to evaluate pacemaker
function during and after surgery. Some intraoperative ECG monitors even provide a “pacemaker”
mode for evaluating the ECG complex, which enhances the pacemaker signal and prevents "double"
counting of the heart rate. During monitoring, 60-cycle interference must be eliminated or
minimized in order to see a clear ECG complex including the pacemaker spike. Although not
normally required for pacemaker evaluation, an arterial line used to monitor cardiovascular function
also can provide additional evaluation of pacemaker function.

Electrical equipment, electro-surgical units, and the grounding pad
Electrosurgical unit (ESU) devices used to coagulate bleeding vessels and cut tissue are the most
common cause of intraoperative interference with the ECG signal, also with pacemakers programmed
into the demand mode or when a rate-adaptive sensors.17 Other electrical devices, such as a
neuromuscular stimulator, also may interfere with pacemaker function. It is important to understand
that interference can occur altering both the ECG signal and pacemaker function even when
manufacturer recommendations or other guidelines are followed for placement of the grounding pad
and current settings. Bipolar units, and harmonic18 or electrically isolated scalpels are best to minimize
such interference, but may not be used due to surgical preference or equipment availability. Filters to
suppress interference from ESUs are rarely incorporated into the operating room.19

Placement of the grounding pad
   The grounding pad should be placed according to the manufacturer’s recommendations.
Whenever possible, the pad should be placed as far from the pacemaker as possible and in such a
way that a straight line between it and the surgical site does not intersect the pacemaker generator.
New Generation Pacemakers in the Operating Room                                                    5

Despite these precautions, experience has shown that it is unrealistic to assume that unipolar
electrosurgical interference will not affect pacemaker circuitry.

Use of the magnet
   The operating room is an electrically rich environment. The use of a magnet is intended to
overcome (override) electrical interference that may otherwise affect pacemaker function. Part of the
preoperative evaluation should include the application of a magnet over the pacemaker generator to
document the pacemaker’s response.

What does a magnet do?
   When a magnet is placed over the generator of a permanent pacemaker, it converts the
pacemaker mode from synchronous to asynchronous, i.e., from a demand mode to a fixed rate mode.
Depending on prior pacemaker programming by the cardiologist, the magnet will cause the device
to pace either the atria alone, both the atria and the ventricle, or only the ventricle. The paced rate
that results when the magnet is applied will be a previously programmed synchronous rate or the
manufacturer's pre-programmed rate. Sometimes, the manufacturer can be identified by the rate
produced when a magnet is applied to the generator. For example, if application of the magnet
produces fixed rate pacing at 100 beats per minute for 3 beats followed by 85 beats per minute, the
pacemaker is a Medtronic® product. Guidant, now Boston Scientific®, pacemakers are
programmed to pace at 100 beats per minute when a magnet is applied. St. Jude® pacemakers are
programmed to pace at 98.5 beats per minute when a magnet is applied.

Recommendations for intraoperative use of a magnet
   Several recent articles recommend against the use of a magnet during surgery to avoid
pacemaker reprogramming due to electrosurgical interference.20,21 However, ESU activation can
inadvertently reprogram a permanent pacemaker whether or not a magnet has been placed over the
generator.22,23 Consequently, I see no reason to avoid the use of a magnet. In fact, I recommend
testing the magnet mode in advance of surgery (see Pacesetter® “Vario” magnet mode, page 2),
then having the magnet available throughout surgery, to use if necessary. Unless there is clinical
reason to convert the pacemaker to the asynchronous mode, it may be best to allow the pacemaker to
function as programmed during surgery.
    ICDs should be deactivated preoperatively if electrocautery use is planned during surgery. This is
accomplished by placing a magnet over the ICD generator for the duration of surgery. There is one
exception–the Ventak™ ICD manufactured by CPI. Placement of a magnet over this model will elicit
an R-wave synchronous beep for 30 seconds followed by a continuous tone, indicating deactivation of
the device. At this point, the magnet should be removed. Reactivation of the Ventak™ requires
replacing the magnet over the ICD generator to elicit a continuous tone for 30 seconds, followed by R-
wave synchronous beeping, indicating reactivation of the device. At this point, the magnet should be
removed. Failure to deactivate an ICD during surgery may cause the ICD to interpret ESU output as
abnormal cardiac activity and to deliver a shock to treat a perceived arrhythmia.
New Generation Pacemakers in the Operating Room                                                        6

                        Intraoperative Pacemaker Emergencies
    Pacemaker wires in contact with the heart are potential sources for conduction of electrical
current directly to the heart, which can result in ventricular fibrillation if a wire loses its insulation
and electrical current entering the wire is conducted to the myocardium.

"R on T" ventricular arrhythmia caused by a temporary or permanent pacemaker
     If the pacemaker spike falls on the T-wave in a vulnerable heart, ventricular tachycardia or
fibrillation may occur. This complication, although rare, may be avoided by programming the
pacemaker into an inhibited or synchronous mode. When a pacemaker is placed in the asynchronous
or fixed rate mode, it may compete with QRS complexes caused by the patient’s intrinsic heart rate.
Intermittent use of the magnet will limit risk to the shortest possible intervals.

Temporary pacemaker failure
    The most common cause of temporary pacemaker failure is the loss of contact between an
electrode wire and the heart. In this case, pacemaker spikes appear on the monitor without QRS
complexes. To restore cardiac pacing, the pacing electrode must be advanced until it comes into
contact with the myocardium to “capture” or pace the heart.
    The absence of a pacemaker spike means one of two things — there is no energy left in the
battery or one of the electrode wires is disconnected from the generator. Temporary pacemakers
usually are powered by 9-volt batteries that can be replaced when depleted of energy. Most often,
the problem is the loss of a connection between the generator and the wires.
    The pacemaker "threshold" for capture usually is below 5 milliamps for ventricular pacing but as
high as 20 milliamps for atrial pacing. Adjustments in pacemaker "output" may be required after the
leads are placed. Like permanent pacemakers, ESU activation may inhibit a temporary pacemaker in
the demand mode. When necessary, the pacing mode can be manually adjusted to the fixed rate
(asynchronous) mode.

Permanent pacemakers
    When the battery is depleted, pacing will stop. Before this happens, the pacemaker is
programmed to reduce its rate to save energy. At these low rates, 30 to 40 beats per minutes, pacing
can continue for up to several months before the pacemaker finally fails to pace. As far as I can tell,
abrupt failure to pace has not been reported to occur during surgery.24 Occasionally, the ESU will
inadvertently reprogram the permanent pacemaker (see above). The effect of this reprogramming is
to change the rate of pacing significantly, but it will not cause pacing failure. When this occurs, a
cardiologist should be consulted to reprogram the pacemaker. Surgical manipulation of the
pacemaker generator also may render the pacemaker temporarily ineffective. However,
manipulation resulting in disconnection of a lead wire will produce pacemaker failure; transthoracic
pacing is then indicated. Myocardial infarction of the right ventricle, the standard location of
ventricular pacing wires, may result in pacing that fails to capture the heart, necessitating
transcutaneous pacing until lead wires can be placed in a more favorable location of the heart.
New Generation Pacemakers in the Operating Room                                                     7

Transthoracic cardiac pacing
   Transthoracic or transcutaneous pacing (the terms are used interchangeably) is the modality
recommended for emergencies requiring cardiac pacing, and is now an intrinsic feature of standard
defibrillators. When a patient with a pacemaker is undergoing surgery, a standard defibrillator with
this pacing capability should be available to provide emergency pacing.

Implantable cardioverter defibrillators
    External defibrillator pads should be placed on all patients with and ICD undergoing anesthesia
and surgery in case the need to treat an arrhythmia arises. Most, if not all, patients with these
devices have severe myocardial dysfunction, a history of coronary artery disease, or end-stage
cardiomyopathy from any cause– the ICD was inserted to treat a life threatening arrhythmia.25 Since
ICDs are normally deactivated during surgery, a true arrhythmia will require treatment. If the ICD is
a Ventak™ (see above), treatment requires external defibrillation. For any other ICD model,
removing the magnet from the ICD generator will allow it to function normally and deliver a shock.
However, external defibrillation is never contraindicated in a patient with an ICD. In fact,
defibrillation shocks of higher energy than the ICD can deliver may be indicated during surgery.
    Recently developed ICDs also can function as anti-bradycardia pacemakers. For these newer
models, a magnet placed over the ICD will deactivate only the antitachycardia function, NOT the
anti-bradycardia function(s). Accordingly, pacemaker spikes and cardiac pacing may occur despite
the presence of a magnet. This should not be interpreted as pacemaker failure: in fact, the
pacemaker is functioning precisely as programmed. When a patient with an ICD is taken to the
operating room, it may be prudent to have a cardiologist familiar with these devices immediately

Defibrillation-pacemaker insulation
    If a patient with a pacemaker requires defibrillation during surgery, the pacemaker may be
reprogrammed. Current permanent pacemakers are designed to prevent strong electrical current or
electromagnetic interference from altering their programmed function. Potentially, defibrillation or
any strong electrical current can damage the pacemaker circuitry or alter the settings. Manufacturers
have incorporated a type of circuit breaker into the pacemaker generator to prevent high voltage
from any source, e.g., defibrillator or ESU, from entering and potentially damaging or
reprogramming the pacemaker. Despite this safeguard, it is prudent to check a pacemaker after
defibrillation, or after surgery requiring use of an ESU, to ensure that the device is still functioning
as programmed.

                                          Pacemaker Basics
Historical background
   As far back as the 1790’s, physicians attempted to revive drowning victims with artificial
ventilation and electricity to stimulate the heart. Interestingly, at least one author emphasized the
importance of re-establishing respiration and even suggested at that time that a tube be inserted into
New Generation Pacemakers in the Operating Room                                                     8

the trachea and attached to a bellows to ventilate the lungs and prevent gastric distention. By the
1880’s, animal experiments were successful in pacing the heart at 60-70 beats per minute. This
inspired physicians to seek similar results in humans. During the 1920’s in Australia and the 1930’s
in the U.S., needle electrode devices were inserted directly into the hearts of patients after the
accepted methods of resuscitation for this period failed to revive the heart. These reports are
believed to be the first in which humans benefited from cardiac pacing devices, introducing the term
“artificial pacemaker.” “Modern” pacemaker history began in 1952 when Zoll developed the first
external pacemaker. In 1958, Furman inserted a transvenous-pacing device into the right ventricle,
first in animals, then in humans, and produced successful cardiac pacing. Soon thereafter, the first
permanent, battery-powered pacemaker was implanted.26
    Implantable devices to treat ventricular tachycardia and ventricular fibrillation were first
reported in humans in 1980. Numerous studies attest to their efficacy for symptomatic ventricular
arrhythmias. Now, internal devices are used for treatment of atrial fibrillation.

Pacemaker hardware and programming features
    No matter how complex a pacemaker, the goal of the device is simple. For patients with
symptomatic bradycardia or symptoms possibly due to bradycardia, the pacemaker provides a
cardiac impulse. In adults, the paced heart rate generally is programmed between 60-90 beats per
minute. Some of the basic components of the technology include:

1. Pulse generator. The electrical impulse is formed in the pulse generator. Permanent pacing
devices now use lithium-powered batteries with an operating life of 5 to 20 years, dependent on how
often pacing is required. Standard 9-volt batteries usually power temporary pacemaker pulse
generators. The terms "pulse generator" and "pacemaker" are often used interchangeably.

2. Pacing electrode wires. The electrical impulse formed in the pulse generator is transmitted to the
endocardial or epicardial surface through insulated stainless steel or platinum alloy wires. These wires
also function as part of the pulse generator’s sensing system for detection of the patient’s intrinsic
cardiac electrical activity.

3. Pacemaker codes. All pulse generators are assigned a five-letter NBG code that describes the
pacemaker's potential pacing possibilities (See Table 1). The most common code for permanent
pacemakers is the DDD code (see below). The acronym "NBG" represents the combined efforts of the
North American Society of Pacing and Electrophysiology (NASPE) and the British Pacing and
Electrophysiology Group (BPEG); 27,28 the "G" actually stands for generic! Although this coding
system is helpful (particularly the first 3 letters of the code), it is not complete — it does not identify
electrode type, power source, whether the pacing system is temporary or permanent, or how the
pacemaker will respond when a magnet is placed over the generator (the latter being essential
information for anesthesiologists encountering pacemakers programmed in the demand mode). Newer
pacemakers sometimes defy even the five-letter NBG code, requiring further explanation to clarify
    New Generation Pacemakers in the Operating Room                                                     9

    some of their unique features.29 The increasing complexity of these devices often requires
    communication with a cardiologist.

                                                       Table 1

      I                     II                   III                    IV                           V
   Chamber               Chamber             Response to          Programmable                Anti-tachycardia
    Paced                 Sensed              Sensing*            Functions; Rate               Function(s)

V--ventricle           V—ventricle         T--triggers pacing    P-- programmable rate          P--pacing
A--atrium              A—atrium            I--inhibits pacing        and/or output              S--shock
D--dual (A + V)        D--dual (A + V)     D--dual (T + I)       M--multiprogrammable           D--dual (P + S)
O--none                O--none             O--none                    for rate, output,         O--none
                                                                      sensitivity, etc.
*Synonyms for terms:                                             C--communicating
O = asynchronous or fixed rate                                        functions (telemetry)
I = synchronous or demand                                        R--rate modulation

    Temporary cardiac pacing
       Temporary transvenous or epicardial pacing is commonly used in acute settings such as a
    myocardial infarction, sudden onset of high degree second- or third-degree atrioventricular (A-V)
    block, or postoperative management of cardiac surgical patients. Temporary devices also can be
    used for diagnosis as well as treatment of certain cardiac arrhythmias.
        Atrial pacemaker wires may be helpful in the diagnosis of wide complex rhythms. This
    necessitates the use of two atrial electrode wires: one is attached to the right arm lead, the other to
    the left arm lead of the ECG machine. The remaining ECG leads are then placed in the standard
    locations. In this configuration, lead I will record an atrial electrogram, revealing the relationship
    between atrial activity and the QRS complex. This can be useful to identify the origin of the
        Temporary atrial and ventricular lead wires also can be useful to treat some tachycardias. New
    onset atrial flutter and/or non-hemodynamically significant supraventricular or ventricular
    tachycardia may be terminated by "overdrive" pacing of the appropriate cardiac chamber. Using
    temporary pacemaker wires to terminate these arrhythmias may avoid the need for pharmacological
    management with undesirable side effects. Atrial pacing cannot terminate Atrial fibrillation.

    Permanent cardiac pacing: the DDD Pacing System
        The DDD pacing system is the most commonly used programming mode for pacemakers
    implanted today. In this mode of function, both atria and ventricle are sensed and paced (as
    programmed) and the A-V interval varies with changes in heart rate. This versatility improves
    hemodynamic performance both at rest and during exercise, decreases the incidence of atrial
New Generation Pacemakers in the Operating Room                                                    10

fibrillation and thromboembolic events, and reduces the incidence of pacemaker syndrome. The
more recently developed pacemakers are rate-adaptive, i.e., they can modulate heart rate in response
to changes in the level of patient activity. This rate-adaptive feature is most often linked to sensors
that detect changes in motion or minute ventilation and adjust the paced heart rate accordingly.
Since the pacemaker can change the paced rate, the chambers paced, and/or vary the A-V interval,
determining whether the pacemaker is functioning appropriately by analyzing only a single ECG can
be difficult.

Implantable cardioverter defibrillators
    ICDs defibrillate life-threatening ventricular tachycardia (VT) or ventricular fibrillation. In
1993, a four-letter coding system was established to describe the features that can be programmed
into an ICD. Originally, all devices were VVEO (see Table 2); the common code now is VVEV. In
this mode, the ICD will analyze the ventricular electrogram, then initiate anti-tachycardia ventricular
pacing if the VT rate is “slow”. If it detects rapid VT or ventricular fibrillation, the ICD will deliver
a shock. If asystole is present after termination of the arrhythmia, the device will function as a
ventricular pacemaker. Other bradycardia modes are now available and ICDs often can be
programmed similarly to pacemakers for bradycardia.

                                                  Table 2

       I                           II                      III                       IV
    Chamber                 Anti-tachycardia           Tachycardia            Anti-bradycardia
    shocked                 pacing chamber              detection             pacing chamber

    O--none                     O--none             E--electrogram               O--none
    A--atrium                   A--atrium           H--hemodynamic               A--atrium
    V--ventricle                V--ventricle                                     V--ventricle
    D--dual (A + V)             D--dual (A + V)                                  D--dual (A + V)

                                        Future Directions
    Early pacing devices were large and simple by today's standards. Advances in technology have
resulted in smaller devices with abundant programming options. Battery life will extend to ensure
that the life of the pacemaker surpasses the life expectancy of the patient, eliminating the need for
replacement surgery. New rate-adaptive sensors will improve the pacemaker's response to patient
activity. However, still lacking is industry-wide standardization of pacemaker components, which
would clearly benefit clinicians. The development of a "universal" machine would allow us to
interrogate and/or re-program any pacemaker, independent of the manufacturer.
    Future ICD devices will deliver shocks of increasing output and "remember" and record the
required energy level. They will also include programmable functions permitting them to act as
DDD pacemakers to manage bradycardia when necessary.30
New Generation Pacemakers in the Operating Room                                                    11

   Electrical therapy for atrial fibrillation is now a very active area of investigation for
researchers and industry, promising significant health benefits to patients and economic
rewards to companies. From the already overwhelmed clinician’s perspective, the
emergence of internal atrial defibrillating devices will add another challenge in our
perioperative management.
    Pacemakers are inherently simple devices: they provide a cardiac impulse when one is lacking or
defibrillate a heart whose rhythm is rapid. Pacemaker complexity derives from the increasing
number of possible programmable modalities and the increase in memory capability to allow ECG
or arrhythmia storage. Before the patient enters the operating room, clinicians should obtain as
much information as possible about the specific pacemaker. For permanent pacemakers, a magnet
should be placed over the pacemaker generator before surgery to verify that it can be converted to a
fixed rate-pacing mode. ICD devices should be deactivated preoperatively, then reactivated after an
ESU is no longer used. ESUs can inhibit a pacemaker programmed in the demand or synchronous
mode no matter where the grounding pad is placed. If the ESU results in pacemaker inhibition, a
magnet placed over the generator will convert the pacemaker from synchronous or demand mode to
a fixed rate or asynchronous mode. ESU interference with the demand mode is much less likely to
occur when a bipolar unit is used. ESU activation also can inadvertently reprogram a permanent
pacemaker whether or not a magnet has been applied. After surgery, all pacemakers should be
checked with the appropriate interrogating device to confirm proper settings before a patient is
discharged. A temporary pacemaker also should be changed to the fixed rate-pacing mode if an ESU
is used. A cardiologist, or pacemaker specialist, should be consulted to assist with pacemaker
evaluation and programming whenever necessary.

The author wishes to thank Winifred Von Ehrenburg for her editorial assistance and Charles Witherell RN,
CS, MSN Clinical Nurse Specialist, cardiac electrophysiology, for his technical assistance.


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New Generation Pacemakers in the Operating Room                                                    12

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Internet sites that may be helpful:
New Generation Pacemakers in the Operating Room                                                                    13 US Food and Drug Administration- Center for Devices and Radiological Health.
An interesting site about medical devices, pacemakers, and implantable cardioverter defibrillators. Check for recalls
here. American Heart Association information for pacemaker
patients. American Heart Association information for patients
with implantable cardioverter defibrillators. American Heart Association updates regarding
guidelines for implantation of pacemakers and cardioverter defibrillators.

                                                                                              William A. Shapiro, M.D.
                                                                                University of California, San Francisco
                                                                       Department of Anesthesia and Perioperative Care
                                                                                                       August 10, 2011

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