Cardiac pacemakers play an important role in the treatment of heart disease due to cardiac rhythm disturbances. They have the ability to pace the heart (ie, discharge an electrical stimulus to initiate a wave of depolarization throughout the heart). Pacemakers have a characteristic pattern that is easy to recognize on an ECG. The pacemaker produces its own wave of depolarization that marks the ECG with a pacer spike as shown in Fig. 11-33. Improved technologies have increased the application of pacemakers and pacemaker principles to the treatment of other types of heart disease including coronary artery disease and heart failure. Because the use of pacemakers has increased (and will likely further increase as technological advancements continue), as well as the potential role of physical therapy for persons with cardiac pacemakers, this section will be devoted to the cardiac pacemaker. This potential role includes assisting with the (1) establishment of pacing parameters (with electrophysiologic physicians) to obtain optimal functional and exercise outcomes and (2) establishment of safe functional and exercise activities for patients with pacemakers and automatic implanted cardioverter-defibrillators (AICDs). The indications for a pacemaker, types of pacemakers, as well as pacemaker codes and pacing modes will be presented so that the physical therapist can provide optimal physical therapy to patients with cardiac pacemakers.
Indications for a Cardiac Pacemaker
The indications for a cardiac pacemaker are listed in Box 11-3 and include a sick sinus syndrome, complete heart block, or cardiac denervation as in cardiac transplantation. Several other indications exist and for each of these reasons the primary goal is to improve the synchrony of myocardial mechanics (chamber filling and emptying) to enhance cardiac function such as the stroke volume, cardiac output, and ejection fraction.
Box 11-3 Indications for a Cardiac Pacemaker ||Download (.pdf)
Box 11-3 Indications for a Cardiac Pacemaker
Sick sinus syndrome
Complete heart block
Cardiac denervation as in cardiac transplantation
Severe cardiac rhythm disturbances
Easily provoked angina
Congestive heart failure
The types of pacemakers that are currently available are listed in Table 11-7. Four basic types of pacemakers exist and include fixed-rate pacemakers, demand pacemakers, atrial-triggered pacemakers, and ventricular-triggered pacemakers. The most common pacemakers are demand pacemakers, which pace the heart on demand and most frequently will pace the ventricle. To fully understand the pacemakers listed in Table 11-7, it is necessary to review the three-letter pacemaker codes, which have been expanded over the years to five-letter codes.
Table 11-7 Different Types of Pacemakers ||Download (.pdf)
Table 11-7 Different Types of Pacemakers
Type of Pacemaker
Pacemaker ICHD Codea
Response to Sensed Activity
Demand AV sequential
Fixed-rate AV sequentialb
Fixed-rate AV simultaneousb
Universal, fully automatic
Inhibited on channel
Sensed (either the atria or the ventricle) and triggered on alternate channel (either the atria or the ventricle)
The coding of pacemakers began in 1974 and outlined a three-letter coding sequence, which made it easy for one to understand the cardiac chamber being paced (the first letter of the code and can be an A for atrium, V for ventricle, or D for dual atrium and ventricle), the cardiac chamber being sensed (the second letter of the code and can be an A for atrium, V for ventricle, D for dual atrium and ventricle, or O for none), and the mode of response (the third letter of the code and can be I for inhibited, T for triggered, D for atrial triggered and ventricular inhibited, R for reverse, or O for none). Because the initial 3-letter code was introduced, two additional codes have been added to keep pace with the technological advancements applied to pacemakers. The two additional codes represent programmability (the fourth letter of the code and can be a P for programmable rate and/or output, M for multiprogrammable, or O for none) and tachyarrhythmia functions (the fifth letter of the code and can be a B for burst, N for normal rate competition, S for scanning, E for externally activated, or O for none). It is now apparent that adding these two additional codes to the original 3-letter code system produces a 5-position pacemaker code.
Each of the specific letters within each of the code positions after the second letter is related to specific actions of the pacemaker, which gives it greater or lesser clinical utility. Table 11-7 alludes to this, but further discussion of the actual pacing modes is needed to fully appreciate pacemaker capabilities and the role of the physical therapist when working with patients who have received a permanent pacemaker.
The available pacing modes can be interpreted from Table 11-7. A quick review of the actual available modes of pacing should facilitate a better appreciation for the pacemaker. Table 11-7 identifies three of the listed pacemakers as obsolete. The reason for this is due to the rather primitive mode of pacing, a fixed rate of pacing of either the atria or the ventricle.
The second type of pacemaker listed in Table 11-7 is the P-triggered ventricular pacemaker that has a VAT coding. The V indicates that the cardiac chamber being paced is the ventricle, A indicates that the cardiac chamber sensing the electrical activity in the heart is the atria, and T indicates that the mode of response is to trigger a paced beat in the ventricle when the atrium senses the SA node's wave of depolarization that cannot proceed past the AV node. This type of pacemaker is used in patients with normal SA node function and without bradycardia or atrial tachyarrhythmias (because with this type of pacemaker it is the role of the atria to signal the pacemaker to discharge an action potential to the ventricle). When the pacemaker sensor in the atria senses electrical activity, it triggers the pacemaker to pace the ventricle at a rate commensurate with the normal and needed atrial rate of discharge from the SA node. This is truly a physiologically favorable pacing mode. It is also easy to understand why a patient with bradycardia or atrial tachyarrhythmias would not be a good candidate for such a pacemaker, because the pacemaker would be pacing the ventricle either too slow or too fast. The atrial-synchronized, ventricular-inhibited pacemaker (with an ICHD code of VDD) and the QRS-triggered and -inhibited ventricular pacemakers (with ICHD codes of VVT and VVI, respectively) function in much the same way as the P-triggered ventricular pacemaker (with VAT code), only they sense from the atrium and ventricle (for the VDD pacemaker) or the QRS wave from the ventricle (for the VVT and VVI pacemakers), but all similarly pace the ventricle.
The demand AV sequential pacemaker with an ICHD coding of DVI is another type of pacemaker that attempts to provide more physiologically sound pacing (like the P-triggered ventricular pacemaker). It attempts to synchronize the atrial and ventricular electrical activity of the heart, which may result in better mechanical activity of these cardiac chambers and improved cardiac function. This pacemaker is used in patients with atrial bradyarrhythmias with or without impaired AV node function. It is not used in patients with prolonged bouts of atrial fibrillation or flutter. When a patient with this DVI coded pacemaker experiences sinus bradycardia, the ventricle senses a need to pace the atrium and ventricle (the “D” code) and inhibits pacing when the ventricle no longer senses sinus bradycardia. Despite the fact that this pacemaker attempts to pace the heart in a truly physiologic manner, it is unable to (1) alter the paced rate (the heart rate) to increased physiologic demands and (2) maintain AV synchronous pacing during periods of normal sinus rhythm and AV block.
The last pacemaker listed in Table 11-7 is the universal, fully automatic pacemaker with DDD coding. The DDD pacemaker is used in patients with (1) atrial bradyarrhythmias with or without impaired AV node conduction and (2) normal sinus node function, but with impaired AV node conduction. When a patient with this DDD-coded pacemaker experiences sinus bradycardia or impaired AV node conduction, either the atrium or ventricle senses (the second “D” code) the abnormality and inhibits pacing where pacing was sensed and then triggers either the atria or ventricle to pace in the chamber where no electrical activity was sensed (the first “D” code). Although there are really no significant disadvantages to the universal, fully automatic pacemaker, the other pacemakers presented previously have several important advantages and disadvantages that are worthy of further discussion. This discussion will hopefully further clarify the modes and mechanism of action of pacemakers.
Advantages and Disadvantages of Available Pacing Modes
The advantages and disadvantages of the currently available pacing modes are listed in Table 11-8. It is apparent from this table that the patient with a pacemaker other than the universal, fully automatic pacemaker will likely have limited cardiac function due to suboptimal AV contraction (and other characteristics inherent in the different types of pacemakers), which is likely to affect functional activities. Because of this and other pacemaker issues, the next section will present a more complete listing of pacemaker modes and functions (rate modulation, cardiac resynchronization therapy [CRT], and implantable cardioverter defibrillator [ICD] therapy).
Table 11-8 Advantages and Disadvantages of Different Pacemakers ||Download (.pdf)
Table 11-8 Advantages and Disadvantages of Different Pacemakers
Type of Pacemaker
Fixed rate of pacing
Maintains normal sinus rhythm
Does not maintain control of the ventricular synchronous AV rate contraction, because the atria are not paced
Long history of use
Does not maintain synchronous AV contraction because the atria are not paced
Fixed rate of pacing
Demand AV sequential
Maintains synchronous AV contraction during sinus bradycardia
Does not maintain synchronous AV contraction when normal sinus rhythm with AV block
Fixed-rate AV sequentiala
Fixed rate of pacing
Fixed-rate AV simultaneousa
Fixed rate of pacing
Maintains normal sinus control of the ventricular rate
Does not maintain synchronous AV contraction, because the atria are not paced
Universal, fully automatic
Maintains synchronous AV contraction and normal sinus control of the ventricular rate during NSR and during sinus bradycardia
Additional Pacemaker Modes and Functions
Table 11-9 provides an overview of the pacemaker codes previously reviewed as well as two additional symbols that have become increasingly important in the management of patients requiring a pacemaker. The two additional symbols sit in the fourth and fifth positions of the pacemaker code. The fourth symbol identifies the programmable rate modulation function of the pacemaker while the fifth symbol identifies the antitachyarrhythmia function of the pacemaker. Pacemakers with letters in these positions have one of more of the functions listed in Table 11-9.
Table 11-9 Pacemaker Code Classificationa ||Download (.pdf)
Table 11-9 Pacemaker Code Classificationa
First Symbol Pacing Location
Second Symbol Sensing Location
Third Symbol Response to Pacing
Fourth Symbol Programmability/Modulation
Fifth Symbol Antitachyarrhythmia Function
O = none
N = none
N = none
O = none
O = none
A = atrium
A = atrium
I = inhibited
S = simple programmable
P = pacing
V = ventricle
V = ventricle
T = triggered
M = multiprogrammable
S = shock
D = dual
D = dual
d = dual
C = communicating
R = rate modulation
D = dual
Rate modulation refers to the pacemaker's ability to modulate heart rate based on activity or physiologic demands.19–23 Pacemakers usually are fit with one or two (dual) sensors including various derivatives of two methods consisting of (1) activity or motion based and (2) physiological based with the most common sensor being one that measures minute ventilation. The sensors and pacemaker attempt to promote a normal sinus node response to increasing HR with exertional demands.24
The type of sensor(s) utilized may impact the ability of the pacer to respond to various exercise modalities.25 Motion/activity sensors result in sluggish HR response to activities that are smooth such as on the bicycle ergometer or with supine, seated, or standing exercise, and rapid response to ambulation. However, these pacers have poor proportionality (ie, faster rates when descending stairs than when ascending) and poor specificity (ie, inappropriate high rates when riding over a bumpy road).26 In patients with motion sensors, activities that promote movement of the thorax (hallway ambulation) or treadmill protocols that include increases in both speed and grade, should be utilized to trigger an increase in HR. QT sensors and ventilatory driven sensors may require longer warm-up periods because of delayed responses to activity; however, these sensors have good proportionality and specificity. QT sensors are the only sensors that respond to emotional stress; however, medication and electrolyte level changes may impact responsiveness of HR with QT interval sensors.26
Combinations of sensors, or dual sensor rate modulation pacers, seem to offer the best HR response to immediate activity demands by exploiting strengths and counteracting weaknesses of individual sensors. Ventilation sensors provide the predominant contribution during intense effort with activity sensors failing to reach required HRs for optimal hemodynamic response.27–30
The upper limit of the pacemaker rate modulation should be known since blood pressure may not be adequately maintained if the upper limit is exceeded. Thus, blood pressure should be properly monitored in patients with pacemakers that have been programmed to provide rate modulation. Increases in heart rate above the upper limit of the pacemaker modulation rate will stimulate the pacemaker to introduce a Wenckebach (Mobitz I) atrioventricular heart block rhythm that can result in reductions in blood pressure and shortness of breath. The best mechanism to identify such a phenomenon may be to simply monitor the ECG during exercise.31
While the majority of pacemakers implanted in the United States generate a rate response, not all pacers are equipped with rate modulation, and therefore some patients have heart rates that may not change with activity. In patients with pacemakers not equipped with rate modulation, low-level activity with small incremental increases in metabolic demand are preferred. Assessment of RPE, blood pressure, and symptoms should be utilized to monitor tolerance to exercise.
The use of pacemakers and implantable cardioverter defibrillator (ICD) therapy has increased considerably over the past decade because of the lifesaving defibrillation provided to patients with fatal arrhythmias as well as one or more of the indications listed in Table 11-10.19,32–44 Despite the mostly favorable effects of ICD therapy (defibrillating a patient who experiences a life-threatening cardiac arrhythmia), patients with ICD have significant psychological ramifications from the possibility of sudden defibrillation and frequently limit their functional and exercise activities in fear of defibrillation.32–34 Support groups for patients with ICD appear to help decrease the anxiety and fear associated with ICD therapy.
Table 11-10 Indications for an Implantable Cardioverter-Defibrillator ||Download (.pdf)
Table 11-10 Indications for an Implantable Cardioverter-Defibrillator
Cardiac arrest due to VT or VF
Spontaneous sustained VT with structural heart disease
Spontaneous sustained VT without structural heart disease that is not amenable to other treatments
Nonsustained VT in patients with coronary disease, prior MI, left ventricular dysfunction, and inducible VF or sustained VT at EPS that is not suppressible by a class I antiarrhythmic drug
Left ventricular dysfunction with an ejection fraction ≤ 30% at least 1 month post-MI and 3 months post–coronary artery revascularization surgery
Severe symptoms (eg, syncope) attributable to ventricular tachyarrhythmias in patients awaiting cardiac transplantation
Ventricular tachyarrhythmias due to a transient or reversible disorder that is likely to substantially reduce the risk of recurrent arrhythmia
a. unexplained etiology with typical or atypical right bundle branch block and ST-segment elevations
b. advanced structural heart disease without clear etiology
c. unexplained etiology without inducible VT and without structural heart disease
Only through the actual performance of functional and exercise tasks can a patient realize their functional and exercise abilities, which highlights the important role for physical therapists in the care of persons receiving ICD therapy.24–34,45–47 The physical therapist's role in the examination and management of patients with ICD can be substantial and could include one or more of the tasks outlined in Table 11-11. Of these tasks the most important are likely to understand the reasons for ICD implantation and each patient's ICD discharge heart rate for defibrillation. Maintaining the patient's heart rate below the ICD discharge heart rate will prevent defibrillation that may occur accidentally due to the increase in heart rate from exercise. However, newer and more sophisticated pacemakers with ICD capacity are able to interrogate the morphology of the heart rhythm and differentiate an expected sinus tachycardia during exercise from a fatal ventricular tachycardia.
Table 11-11 Potential Role of Physical Therapists for Patients with Implantable Cardioverter-Defibrillators ||Download (.pdf)
Table 11-11 Potential Role of Physical Therapists for Patients with Implantable Cardioverter-Defibrillators
Identify the reasons for ICD implantation.
Identify the ICD discharge heart rate for defibrillation.
Identify the level of anxiety and fear associated with the ICD.
Identify the patient's functional and exercise abilities while monitoring symptoms, heart rate, blood pressure, and the electrocardiogram and not allowing the heart rate to exceed the ICD discharge heart rate for defibrillation.
Communicate functional and exercise results with the patient's primary physician and the EPS team.
Finally, it has been reported that inappropriate discharge of an ICD may occur from transcutaneous electrical nerve stimulation (TENS) and other electromagnetic therapy that may be provided by a physical therapist.36–39 Thus, it is important to obtain a comprehensive history of a patient known to have a pacemaker to determine if it has ICD capacity. Physical therapists should consult with referring physicians before providing patients with an ICD pacemaker with any form of electromagnetic therapy.
For example, several case reports exist whereby neuromuscular electrical stimulation (NMES) has resulted in electromagnetic interference causing false sensing and leading to inappropriate defibrillation in patients with AICDs, which results in cardiac arrhythmias or painful shocks.36–39 Interference has been observed during both NMES of the trapezius and the quadriceps of patients, indicating that individual testing for interference is warranted before NMES should be utilized in patients with ICDs. Electromagnetic energy (EME) from household devices, airport security, and cell phones can also cause inappropriate shocks and interfere with pacemaker function by either creating a sensed beat or delaying the sequence of a paced beat. Patients should be advised to discuss the possibility of EME with their cardiologist since the major determinant of response is based on the manufacturer of their device. Some general guidelines include the following: the potential for EME is proportional to the strength of the environmental source; the closer the source to the implantable device, the greater the risk (with <10 cm distance even cell phones can create EME—therefore, patients are advised to use cell phones on the side opposite of the implantable device); security systems are usually safe as long as the patient does not linger at the source; and security staff should be advised of the location of an implantable device to avoid bringing a electromagnetic wand within close proximity.36–39
Cardiac Resynchronization Therapy
Cardiac resynchronization therapy (CRT) is a medical treatment that is used to synchronize the electrical, physiologic, and mechanical events of the heart via a pacemaker.48–52 It has become useful in the management of patients with heart failure.
A simplified explanation of CRT is the process that is used to synchronize AV as well as right and left ventricular depolarization and contraction in hopes of eliciting a more efficient and effective cardiac contraction. Although CRT has been a potential therapeutic modality for the past 6 to 8 years, it is only now receiving greater clinical use. This is surprising in view of the benefits that have been observed in much of the CRT literature, which has been summarized in Table 11-12.48–52 Furthermore, several important predictors of mortality have also been improved with CRT including left ventricular size, norepinephrine levels, heart rate and heart rate variability, peak oxygen consumption, New York Heart Association classification, and 6-minute walk test distance ambulated.48–52 Although the improvements in these important indices of survival in CHF are noteworthy, investigation of the specific effects of CRT on mortality are needed. Nonetheless, the improvements in many of the manifestations of CHF shown in Table 11-12 are likely to improve the functional abilities and quality of life of individuals with CHF.48–52
Table 11-12 Potential Beneficial Effects of Cardiac Resynchronization Therapy on the Manifestations of Chronic Heart Failure ||Download (.pdf)
Table 11-12 Potential Beneficial Effects of Cardiac Resynchronization Therapy on the Manifestations of Chronic Heart Failure
Adverse Manifestation of CHF
Potential Beneficial Effect
1. Prolonged AV conduction delay
Improved AV conduction delay
2. Delayed ventricular activation
Improved ventricular activation
3. Disorganized ventricular contraction
Improved ventricular contraction
4. Impaired ventricular filling (eg, MR,
Improved ventricular filling limited filling period, suboptimal atrial systole)
5. Abnormal ventricular wall motion
Improved ventricular wall motion
6. Abnormal ventricular size
Improved ventricular size
7. Abnormal myocardial O2 consumption
Improved myocardial O2 consumption
8. Abnormal catecholamine levels
Improved catecholamine levels
9. Abnormal heart rate and HRV
Improved heart rate and HRV
10. Poor functional status (eg, 6MWT)
Improved functional status
11. Low levels of peak O2 consumption
Improved peak O2 consumption
12. Poor NYHA classification (eg, classes 3–4)
Improved NYHA classification
13. Frequent hospitalization
Less frequent hospitalization
The beneficial effects of CRT in persons with CHF are likely due to the combined effects of numbers 1 to 5 in Table 11-12. The improvements in atrioventricular conduction; ventricular filling, activation and contraction; and improved ventricular wall motion likely produce the remaining beneficial effects (numbers 6–12) in Table 11-12.17–22 Despite the potential beneficial effects of CRT on the manifestations of CHF, there are several potential adverse effects of CRT in persons with CHF including infection, bleeding disorders, pacemaker dysfunction, and possibly increased arrhythmias.
Pacemakers and Physical Therapy
As mentioned previously, the potential role of physical therapy in the care of persons with pacemakers includes assisting with the (1) establishment of pacing parameters (with electrophysiological physicians [EP]) to obtain the best functional and exercise outcomes and (2) establishment of safe functional and exercise activities for patients with pacemakers and AICDs. An additional role for the physical therapist may be consultation with an EP to determine the type of pacemaker to be implanted in a patient based on functional and exercise tasks examined by the physical therapist. The methods by which a physical therapist may provide optimal physical therapy to patients with cardiac pacemakers and AICDs are presented in Table 11-13. The typical pacemaker ECG tracing is shown in Fig. 11-33. It is important to note that the pacemaker is easy to identify by the presence of one or more pacer spikes such as those shown in Fig. 11-33. The absence of a pacer spike in a patient who previously demonstrated such a spike may indicate pacemaker malfunctioning or pacing alterations. Likewise, pacer spikes in locations of the cardiac cycle where they should not be may be suggestive of pacemaker malfunctioning. If such ECG findings are observed and are accompanied by increased symptoms and decreased functional abilities, pacemaker malfunctioning is highly likely. In either case, consultation with EP physicians may be needed to better understand the goals of the EP physicians and to contribute to a patient's overall care.
Table 11-13 Methods to Provide Optimal Physical Therapy to Patients with Pacemakers ||Download (.pdf)
Table 11-13 Methods to Provide Optimal Physical Therapy to Patients with Pacemakers
Observe patient and ECGa
Recognition of optimal pacemaker function evidenced by a comfortable, healthy looking patient with appropriate pacing spikes at appropriate intervals and locations of the cardiac cycle or pacemaker malfunction evidenced by an uncomfortable, apprehensive patient without appropriate pacing spikes at appropriate intervals and locations of the cardiac cycle
Question and measure
Use a dyspnea or angina scale or Borg RPEa
Recognition of optimal pacemaker function evidenced by less dyspnea or angina and lower Borg RPE or pacemaker malfunction evidenced by increased dyspnea or angina and higher Borg RPE
Measure ECG, SBP, DBP, PP, exercise tolerance, and achieved workloada
Recognition of optimal pacemaker function evidenced by increased exercise tolerance and greater workloads, greater SBP, lower DBP, and a wider PP or pacemaker malfunction evidenced by decreased exercise tolerance and attainment of lower workloads, lower SBP, greater DBP, and a narrow PP
Perhaps the best methods of contributing to the care of patients with pacemakers are to monitor (1) the ECG for signs of pacemaker failure, (2) the ECG at rest and during exercise or functional tasks, (3) symptoms (eg, shortness of breath, Borg rating of perceived exertion) at rest and during exercise or functional tasks, and (4) the systolic and diastolic blood pressure at rest and during exercise or functional tasks.
Much of the methodology presented in the cardiac examination chapter (Chapter 10) applies to the patient with a cardiac pacemaker, but evaluation of symptoms and the cardiovascular response to exercise or functional tasks is critically important in the pacemaker patient. In fact, examination of symptoms and the cardiovascular response of a patient with a pacemaker can provide important information to EP to help to establish optimal pacemaker-sensing and pacing modes. Observing a patient's symptoms, cardiovascular response, and achieved workloads or duration of exercise, we can identify the best pacemaker settings for a particular patient. This type of direct physical therapist–physician consultation and teamwork are likely to maximize a patient's full potential in the realms of cardiovascular and functional outcomes.