Download Implantable Cardioverter-Defibrillator

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Pacemakers and Implantable Cardioverter-Defibrillators
Permanent Pacemakers
• A variety of factors contribute to optimal cardiac functioning, including
atrioventricular (AV) synchronization and the chronotropic and inotropic
responses to neuro-hormonal stimuli.
• Alterations in the normal sequence of atrial and ventricular filling and
contraction can result in deterioration of hemodynamics and
subsequent symptoms at rest, during exercise, or both.
• In persons who have light-headedness, syncopal spells, shortness of
breath, and more rarely chest pain or other cardiovascular symptoms
owing to these problems, a permanent pacemaker:
• improves symptoms,
• enhances exercise performance, and
• improves quality of life.
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Pacemakers and Implantable Cardioverter-Defibrillators
Permanent Pacemakers
Indications for a permanent pacemaker include the following:
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Sinus node dysfunction
Third-degree block and advanced second-degree AV block
Hypersensitive carotid sinus syndrome
Symptomatic bradycardia
Sustained pause-dependent ventricular tachycardia (see ½ down page)
Left ventricular systolic dysfunction
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A typical pacemaker system consists of two basic components: a pulse
generator and either one or two pacing wires.
In a traditional pacemaker the pacing wires are insulated and are
implanted transvenously into the right atrium, right ventricle, or both.
With a biventricular pacemaker, a lead is also placed in the left ventricle.
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Pacemakers and Implantable Cardioverter-Defibrillators
Permanent Pacemakers
The two main functions of the leads are sensing and pacing.
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• Sensing involves detecting electrical signals (i.e., P-waves and R-waves)
from the heart. When these signals are not sensed at the proper timing,
the pacemaker generator fires an impulse (Pacing) that causes the atria
or ventricles (or both) to contract.
• Optimally, the pacing system uses an atrial and ventricular lead to
maintain AV synchrony, which serves to optimize cardiac output at rest
and during exercise
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Pacemakers are described by a standardized code. The first letter represents
the chamber paced; the second is the chamber sensed; and the third
denotes the response to a sensed event. The fourth position is used to
indicate that the pacemaker has rate-response capabilities.
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Pacemakers and Implantable Cardioverter-Defibrillators
Permanent Pacemakers
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Standardized coding example: VVIR
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• The ventricle (V) is the chamber being paced and sensed.
• When the pacemaker senses a normal ventricular contraction, the
pacemaker is inhibited (I)
• The (R) indicates that the pulse generator is rate-responsive during
exercise.
• The response by the pacemaker is to either trigger or inhibit a pacing
stimulus, depending on the absence or presence, respectively, of atrial
or ventricular conduction, separately or in combination, relative to the
range of heart rates that are programmed into the pacer.
A commonly used mode of pacing is the DDDR, which has dual-chamber (i.e.,
atrium and ventricle) pacing and inhibiting and has rate-response capability.
The DDDR pacemaker is widely regarded as the optimal pacing mode in
individuals who have normal sinoatrial (SA) node function, because it provides
AV synchrony and uses the client’s own sinus rhythm to guide ventricular
stimulation.
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Pacemakers and Implantable Cardioverter-Defibrillators
Implantable Cardioverter-Defibrillator
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An implantable cardioverter-defibrillator (ICD) is another electronic device
that can be permanently implanted in individuals who either have a history
of, or are at increased risk for, a life-threatening ventricular dysrhythmia.
Implantable cardioverter-defibrillators electrically terminate life-threatening
ventricular tachyarrhythmia (heartbeat is fast and irregular).
Implantable cardioverter-defibrillators can detect atrial and ventricular
arrhythmias, can provide corrective pacing and defibrillation, and can be
programmed with multiple protocols and the ability to record an
electrocardiogram.
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Pacemakers and Implantable Cardioverter-Defibrillators
Implantable Cardioverter-Defibrillator
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Indications for an ICD include the following:
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• Survivor of cardiac arrest due to ventricular fibrillation (VF) or
sustained ventricular tachycardia (VT)
• Structural heart disease with VT
• History of syncope of undetermined origin with clinically relevant VF or
sustained VT induced during an electrophysiology study
• Left ventricular dysfunction due to myocardial infarction (post ≥40
days) with an ejection fraction (EF) ≤35
• Nonischemic dilated cardiomyopathy with an EF ≤35%
• Nonsustained VT due to myocardial infarction with an EF ≤40% and VF
or sustained VT induced during electrophysiology study
Combination Pacemaker–Defibrillator Devices
Some implantable devices are capable of providing both pacing and defibrillation.
Recent evolution in terminology of pacemakers and defibrillators is toward calling
them cardiac resynchronization therapy (CRT), with subclasses that provide pacing
alone (CRT-P) and those that provide both pacing and defibrillation (CRT-D)
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Pacemakers and Implantable Cardioverter-Defibrillators
Management and Medications
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Medical management of individuals with a permanent pacemaker or ICD is
aimed at the control of accelerated ventricular rates and irregular rhythms with
the management of comorbidities, such as coronary artery disease and
cardiomyopathy. Common medications include the following:
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Angiotensin-converting enzyme (ACE) inhibitors
β-adrenergic blockers
Calcium channel blockers
Vasodilators
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Pacemakers and Implantable Cardioverter-Defibrillators
Effects on the Exercise Response
Permanent Pacemakers
• Improves exercise tolerance
• Rate-Adaptive pacemakers increase pacing with exercise (physiological sensoring)
• Patients should be cautious when starting new activities and should be
educated about symptoms that may represent an inappropriate heart rate
response, such as shortness of breath and light-headedness
Implantable Cardioverter-Defibrillators
• Patients should be advised not to exercise at a heart rate above the defibrillation
threshold. (ie. persons with an ICD would get shocked only when they had a lifethreatening dysrhythmia – not during an elevation in hear rate with increasing
exercise intensity)
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Pacemakers and Implantable Cardioverter-Defibrillators
Effects of Exercise Training
Benefits of exercise in patients with ICD’s include (similar to general
population):
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Increased exercise capacity
Reduced risk of mortality
Improved cardio-metabolic risk factors
Reduced depression
Improved quality of life
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Recommendations for Exercise Testing
Exercise testing can be useful in the evaluation of a rate-responsive
pacemaker and to guide the programming of the upper heart rate limit.
Pacemakers, but not ICDs, limit the utility of an exercise test in the
assessment of myocardial ischemia because they reduce the sensitivity to
detect repolarization changes in the ECG.
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Recommendations for Exercise Testing
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Special considerations for exercise testing in an individual with a pacemaker or ICD:
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• Medications should be taken as prescribed and at least 3 h before testing.
• The device’s programmed upper limits should be identified before testing.
• To avoid an inappropriate shock, the test should be stopped before the heart
rate is within 10 beats of the anti-tachycardia pacing or defibrillation threshold
of the ICD.
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Recommendations for Exercise Programming
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Recipients of a pacemaker or ICD should be encouraged to be physically
active. Any underlying heart disease or comorbidities have more influence on
the ability to exercise than the presence of a pacemaker or an ICD does.
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Recommendations for Exercise Programming
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Special considerations for exercise training among individuals with a
pacemaker or ICD:
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• Rigorous activities involving the upper extremities should be limited during
the first 3 to 4 weeks after implantation to allow the incision to heal.
• Medications should be taken as prescribed and at least 3 h before exercise.
• Individuals should be aware of their pacemaker or ICD heart rate
thresholds.
• Target heart rate can be determined from a maximal exercise test but may
not be necessary for all individuals.
• Exercise heart rate should be kept 10 beats or more below the antitachycardia pacing or defibrillation threshold of the ICD.
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