1. Pacemakers and Implantable Cardioverter-Defibrillators
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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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Permanent Pacemakers
Indications for a permanent pacemaker include the following:
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
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.

3. Pacemakers and Implantable Cardioverter-Defibrillators
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Permanent Pacemakers
The two main functions of the leads are sensing and pacing.
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
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.

4. Pacemakers and Implantable Cardioverter-Defibrillators
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Permanent Pacemakers
Standardized coding example: VVIR
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.

5. Pacemakers and Implantable Cardioverter-Defibrillators
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Implantable Cardioverter-Defibrillator
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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Implantable Cardioverter-Defibrillator
Indications for an ICD include the following:
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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Management and Medications
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:
Angiotensin-converting enzyme (ACE) inhibitors
β-adrenergic blockers
Calcium channel blockers
Vasodilators

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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 life-threatening dysrhythmia – not during an elevation in hear rate with increasing exercise intensity)

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Effects of Exercise Training
Benefits of exercise in patients with ICD’s include (similar to general population):
Increased exercise capacity
Reduced risk of mortality
Improved cardio-metabolic risk factors
Reduced depression
Improved quality of life
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
Special considerations for exercise testing in an individual with a pacemaker or ICD:
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.
Recommendations for Exercise Programming
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
Special considerations for exercise training among individuals with a pacemaker or ICD:
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 anti-tachycardia pacing or defibrillation threshold of the ICD.
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