A. Components

1. Pacemaker types are designated by 3 or four letters
   1. First letter - pacing (which or both ventricles), for example: A, V, or D (dual)
   2. Second letter - where electrical impulses are sensed (which one or both ventricles)
   3. Third letter - response to sensing event: pacer is inhibited, activated or both after sensing
   4. Fourth letter - rate responsive mode present (R)
   5. Fifth letter - new addition; indicates chamber(s) in which multisite pacing is delivered
2. Pacing
   1. Lithium-Iodide battery generates electrical impulse (2-4 milliamps)
   2. Pacer wires run from battery pack (with computer control) to various parts of heart
   3. One or two leads positioned in R Ventricle (V), Atrium (A), or both (D for dual)
   4. Pulse generator (battery pack) implanted subcutaneously in shoulder area
3. Sensing - V, A or D
4. Mode - Triggered (T) or Inhibited (I) when sensing occurs
5. Rate Responsive (R) - usually to motion, oxygen levels, others (see below)
6. Histerricis - waiting period: pacer begins at heart rate < Z, but paces at rate > Z
7. Note: by holding magnet over a pacemaker, pacer becomes X__ (pacing mode only)
8. In 2002, 225,000 pacemakers implanted in USA, 600,000 worldwide
9. 29,000 ICDs implanted in USA in 1997 (see below)
10. Pacemakers and ICDs generally safe in airport security systems but prefer manual exam [17]

B. Indications for Pacemakers

1. Sick Sinus Syndrome (Sinus Node Dysfunction) [2]
   1. Overall, sinus node dysfunction is most common indication for pacemakers [4]
   2. Conduction delays - sinus bradycardia with symptoms
   3. Tachy-Brady Syndrome
   4. Sinus pauses >3.5-4 seconds or recurrent syncope with sinus pauses
   5. Not typically indicated for asymptomatic patients
   6. Biventricular pacing associated with reduced risk of atrial fibrillation (AFib) and slight improvement in symptoms compared with ventricular only pacing [3]
2. AV Conduction Abnormalities [2]
   1. Complete heart block / Stokes' Adams attacks (3°)
   2. Heart Block 2° with Mobitz Type II pattern ± Symptoms
   3. Symptomatic Mobitz Type I 2° Block
   4. Primary (1°) heart block with severe symptoms (usually ventricular underfill)
   5. Alternating Bundle Branch Blocks (may progress to 3° AVB)
   6. Induced complete AV-Block following catheter ablation in AFib
   7. Bifascicular or Trifascicular Block with symptoms (? transient complete heart block)
   8. AV conduction anomalies in class III or IV congestive heart failure [20]
3. Symptomatic Atrial Tachyarrhythmias
   1. Uncontrolled with medications
   2. AV nodal ablation with pacemaker insertion
4. Post-MI
   1. Mostly as above
   2. Persistent 1° AV Bock with associated BBB (not present before MI)
5. Recurrent Vasovagal (Neurocardiogenic) Syncope [4]
   1. Especially with cardiovascular collapse
   2. Includes carotid sinus hypersensitivity
   3. Autonomic nervous system disease
   4. Mainly used in patients with little or no warning signs of impending syncope
   5. Pacing is not indicated for all patients with neurocardiogenic syncope
6. Congestive Heart Failure (CHF) [7,8,9,20]
   1. CHF with Intraventricular Conduction Delay (IVCD) is an indication for a pacemaker ± ICD
   2. Pacemeker therapy for CHF called cardiac resynchronization therapy [27]
   3. IVCD occurs in ~30% of patients with CHF
   4. Delay in AV timing likely contributes to symptoms (QRS >130 msec)
   5. In severe CHF, biventricular pacing improves symptoms, cardiac function, and reduces hospitalizations and mortality [4,7,8,27]
   6. Resynchronization in CHF patients with normal (<120ms) QRS complex of no benefit [30]
   7. Dilated cardiomyopathy and left sided conduction delay may also benefit
7. Newer Indications
   1. Varying degrees of evidence to support indications here
   2. Hypertrophic obstructive cardiomyopathy - dual chamber pacing, short AV interval
   3. Long QT Syndrome - relatively high heart rates prevent Torsade des Pointes (TDP)
   4. Antitachycardia pacing - ventricular response rates >200 beats per minute can respond
   5. Dilated Cardiomyopathy - dual chamber pacing with normalizatin of AV interval
   6. Paroxysmal AFib - atrial pacing may reduce incidence of AF in patients with sinus node dysfunction
   7. Dual lead RA pacing in paroxysmal AFib
   8. Broader range of patients with heart failure
   9. Atrial overdrive pacing reduces episodes of central or obstructive sleep apnea [10]
   10. Atrial overdrive pacing had no benefit in OSA patients with implanted dual chamber pacemakers [23]

C. Selected Examples

1. VVI
   1. Ventricular pacing and sensing; inhibited when ventricle fires on its own
   2. Useful for patients with ablated AV nodes
   3. Fairly inexpensive
   4. Provides reasonably good quality of life except in patients with SA node dysfunction
   5. Efficacy similar to DDD pacemakers for elderly (>70 years) with high grade AV block [22]
   6. Preferred modality in patients with heart failure and ventricular arrhythmias [12]
   7. Pacemaker syndrome can develop, usually in patients with normal LV function [4]
2. VVT
   1. Ventricular pacing and sensing
   2. Triggers on ventricular firing - fires into the R wave
3. AAI
   1. Usually single chamber right atrial pacing
   2. For sinus node dysfunction and good AV conduction
   3. However, AV block develops in up to 5% of patients annually with sick-sinus syndrome
   4. Atrial pacing associated with less AFib development than DDD pacing in patients with sick sinus syndrome [4]
   5. Can also be associated with pacemaker syndrome
4. DDD
   1. Dual sensing and firing (pacer wires placed in RA appendage and RV apex)
   2. Excellent for providing atrial kick; can adjust PR interval to allow filling
   3. Normally the mode is inhibited, but triggering can occur
   4. Relatively expensive
   5. Generally should be used in patients with sinoatrial nodal dysfunction
   6. Not superior to single chamber pacemakers in elderly with high grade AV block [22]
   7. Can be programmed with rate-responsive PR changes (similar to physiologic situation)
   8. Should not be used in patients with ICD and CHF (see below) [12]
5. DVI
   1. Dual pacing mode with ventricular sensing
   2. Has been abandoned due to reentrant arrhythmia production
6. Types of Rate Sensors
   1. Physical activity
   2. Minute-ventilation
   3. QT interval
   4. Stroke-volume
   5. None of these are ideal
   6. Combination sensors are now available
   7. Physiologic pacing provides little benefit over ventricular pacing for preventing stroke or cardiovascular death [13]

D. Complications of Pacemakers

1. Acute placement related complications ~5%
   1. Pneumothorax
   2. Hemothorax
   3. Air embolism
   4. Lead perforation, malposition, diaphragmatic stimulation
   5. Pocket related complications: hematoma, wound pain, pocket erosion, infection
   6. Evacuation of pocket in 1-2% of implants
2. Infection [6]
   1. Anywhere along wire or box path
   2. May also cause lead-associated endocarditis
   3. Coagulase negative staphyloccci and Staph aureus most common
   4. Endocarditis treated with 6 weeks of antibiotics
   5. Non-endocarditis pacemaker (or ICD) treated with 14 days of antibiotics
   6. Surgical removal of entire system at initiation of antibiotics
   7. Replacement of entire system once antibiotic treatment course is completed
3. Equipment breakage
4. Malfunction
   1. Failure to sense
   2. Failure to fire
   3. Abnormal firing
5. Pacemaker Syndrome
   1. Usually due to inadequate pacer rate
   2. This leads to low cardiac output, particularly during exertion
   3. Most common in patients with VVI machines and sinus (SA) node dysfunction
   4. Less common in patients with AV nodal dysfunction
6. Symptoms of Pacemaker Syndrome
   1. Headache
   2. Disturbed mentation
   3. Neck pulsations
   4. Fatigue / letheragy
   5. Exercise intolerance
   6. Postural hypotension (lightheadedness, near-syncope, syncope)
7. Increased Risk of AFib
   1. Dual chamber pacing maintains AV synchrony in patients with sinus-node disease
   2. High percentage of ventricular-only pacing causes ventricular desynchronization
   3. Ventricular desynchronization has been linked to increased risk of AFib
   4. Minimizing ventricular-only pacing with newer pacemakers lead to 40% less AFib [29]

E. Implantable Cardioverter-Defibrillators (ICD) [14,26]

1. Multifunctional devices with highly technical programmable capabilities
   1. Pulse generator
   2. One or more leads for pacing and defibrillation electrodes
   3. Sealed titanium can encloses a lithium-silver vanadium oxide battery and circuits
   4. Subcutaneous implantation of ICD on chest wall now usually possible
   5. Single chamber pacing with ICD appears to be device of choice [4]
2. Prevention of Sudden Cardiac Death (SCD) [11]
   1. Improves survival in patients with history of life-threatening ventricular arrhythmia
   2. Improves survival as primary prophylaxis in patients at high risk for ventricular arrhythmia
   3. These groups include Class II - IV CHF patients with left ventricular (LV) dysfunction [28]
   4. ICD in CHF Class II-III with LV dysfunction reduces death ~20% overall [28}
   5. Cardiac resynchronization (see below) in patients with advanced CHF improves symptoms, quality of life, and survival
3. Secondary Prevention for Arrythymia
   1. Cardiac arrest due to ventricular tachycardia (VT) or ventricular fibrillation (VF)
   2. Sustained VT, especially with structural heart disease
   3. Unexplained syncope with inducible, sustained VT or VF
   4. Unexplained syncope with advanced structural heart disease and no other cause of syncope
4. Primary Prevention
   1. Coronary artery disease (CAD) with LV dysfunction and inducibile VT
   2. Chronic CAD with LV ejection fraction (LVEF) <30% with reasonable cost [21]
   3. Reduce mortality in post-MI patients with LVEF <35-40% [15]
   4. Particularly beneficial in post-MI with resultant LVEF <35% [26]
   5. Adds ~1.8 quality-adjusted life years in post-MI with LVEF <30% [21]
   6. Prophylactic use of ICD after MI of no overall benefit for all-comers [18]
   7. High risk inherited or acquired arrhythmia conditions such as Long QT syndrome, Brugada Syndrome, hyertrophic cardiomyopathy
5. ICD for CHF with Biventricular Pacing [7]
   1. For QRS >130msec, LV dilitation, LVEF <35%, advanced CHF
   2. Biventricular pacing with ICD reduced mortality and hospitalizations in severe CHF [7]
   3. Note: 50% of patients with severe CHF die from arrhythmias
   4. Prophylactic ICD in dilated cardiomyopathy patients with LVEF <35% reduced risk of sudden death from arrhythmia [5]
   5. Single-lead, shock-only ICD therapy reduced overall CHF (Class II or III) mortality 23% [19]
6. Patients should carry an emergency identification number
7. Overpenetrated radiograph should show device identifier
8. Modes of Current ICD Models
   1. Recognition of heart rate is mainstay of identification system
   2. High energy and low energy shocks can be delivered
   3. Antitachycardia pacing can also be delivered to terminate ventricular tachycardias
   4. Backup pacing in VVI mode highly preferable over DDD mode in paiients with LVEF <40% [12]
9. Complications (Table 4, Ref [14])
   1. Infection (see below)
   2. Erosion
   3. Hematoma
   4. Pneumothorax
   5. Lead dislodgment
   6. Inadequate defibrillation threshold
   7. Connection problems
   8. Lead malfunctions or fractures
   9. Electromagnetic interference
   10. Frequent shocks, appropriate or inappropriate - reduces quality of life (see below)
   11. Acceleration of VT
   12. Psychological reactions
   13. Longer or additional hospitalization
   14. Death in ~1.2% overall [28]
10. Infections of ICD [16]
    1. Complete device removal required
    2. Treatment with systemic antimicrobial agents (see below) [6]
    3. Reimplantation at a remote anatomic site is effective and safe
11. Causes of Appropriate Shocks [25]
    1. VF
    2. Monomorphic VT
    3. Polymorphic VT
    4. Torsades de pointes
12. Causes of Inappropriate Shocks [25]
    1. AFib
    2. Atrial Flutter
    3. Atrial tachycardia
    4. Supraventricular tachycardia
    5. Junctional tachycardia
    6. Sinus tachycardia
    7. Multiple premature ventricular contractions
    8. Oversensing of T waves
    9. Double counting of QRS complex
    10. Oversensing due to lead failure or insulation break
    11. Oversensing of diaphragmatic myopotentials
    12. Electromagnetic interference
13. Evaluation of ICD Shocks
    1. Multiple shocks requires emergent evaluation with electrophysiology evaluation
    2. If electrical storm present, institute antiarrhythmic (usually amiodarone)
    3. Consider anxiolytics, evaluate ischemia, optimize anti-tachycardia pacing
    4. For refractory VT, consider ablation, left ventricular assist device, transplantation
    5. For single shocks, if clinical situation deteriorating, then emergent evaluation
    6. For single shocks with stable clinical picture, evaluate whether shock was appropriate
    7. Always assess for reversible causes of ischemia, which can induce arrhythmias
    8. Prophylactic electrophysiologically guided catheter ablation in patients with MI eligible for ICD reduced post-iCD appropriate shocks significantly without side effects [31]
14. ICD and Anti-Arrhythmic Agents
    1. ICDs have been compared mainly to amiodarone in patients with advanced CAD
    2. For patients with LVEF <35%, ICD generally better
    3. Main problem with ICD is reduced quality of life associated with sporadic shocks
    4. ß-adrenergic blockers should be used even in patients with ICD (or on amiodarone)
    5. Sporadic shocks can be reduced with sotalol (57% reduction) or amiodarone (73% reduction) when added to ß-blockers compared with ß-blockers alone [24]
    6. Amiodarone is associated with increased risk of pulmonary and hypothyroid disease compared with sotalol but is more effective at reducing sporadic shocks [24]
    7. Amiodarone is the preferred agent for patients with multiple shock ICD, electrical storm [25]

References

1. Kusumoto FM and Goldschlager N. 2002. JAMA. 287(14):1848
2. Mangrum JM and DiMarco JP. 2000. NEJM. 342(10):703
3. Lamas GA, Lee KL, Sweeney MO, et al. 2002. NEJM. 346(24):1854
4. Trohman RG, Kim MH, Pinski SL. 2004. Lancet. 364(9446):1701
5. Kadish A, Dyer A, Daubert JP, et al. 2004. NEJM. 350(21):2151
6. Darouiche RO. 2004. NEJM. 350(14):1422
7. Bristow MR, Saxon LA, Boehmer J, et al. 2004. NEJM. 350(21):2140
8. McAlister FA, Ezekowitz JA, Wiebe N, et al. 2004. Ann Intern Med. 141(5):381
9. Bradley DJ, Bradley EA, Baughman KL, et al. 2003. JAMA. 289(6):730
10. Garrigue S, Bordier P, Jais P, et al. 2002. NEJM. 346(6):404
11. Goldberger Z and Lampert R. 2006. JAMA. 295(7):809
12. DAVID Trial Investigators. 2002. JAMA. 288(24):3115
13. Connolly SJ, Kerr CR, Gent M, et al. 2000. NEJM. 342(19):1385
14. DiMarco JP. 2003. NEJM. 349(19):1836
15. Moss AJ, Zareba W, Hall WJ, et al. 2002. NEJM. 346(12):877
16. Chua JD, Wilkoff BL, Lee I, et al. 2000. Ann Intern Med. 133(8):604
17. Possick SE and Barry M. 2004. Ann Intern Med. 141(2):146
18. Hohnloser SH, Kuck KH, Dorian P, et al. 2004. NEJM. 351(24):2481
19. Bardy GH, Lee KL, Mark DB, et al. 2005. NEJM. 352(3):225
20. Cleland JGF, Daubert JC, Erdmann E, et al. 2005. NEJM. 352(15):1539
21. Al-Khatib SM, Anstrom KJ, Eisenstein EL, et al. 2005. Ann Intern Med. 142(8):593
22. Toff WD, Camm AJ, Skehan JD. 2005. NEJM. 353(2):145
23. Simantirakis EN, Schiza SE, Chrysostomakis SI, et al. 2005. NEJM. 353(24):2568
24. Connolly SJ, Dorian P, Roberts RS, et al. 2006. JAMA. 295(2):165
25. Gehi AK, Mehta D, Gomes JA. 2006. JAMA. 296(23):2839
26. Zimetbaum PJ. 2007. JAMA. 297(17):1909 (Case Discussion)
27. McAlister FA, Ezekowitz J, Hooton N, et al. 2007. JAMA. 297(22):2502
28. Ezekowitz JA, Rowe BH, Dryden DM, et al. 2007. Ann Intern Med. 147(4):251
29. Sweeney MO, Bank AJ, Nsah E, et al. 2007. NEJM. 357(10):1000
30. Beshai JF, Grimm RA, Nagueh SF, et al. 2007. NEJM. 357(24):2461
31. Reddy VY, Reynolds MR, Neuzil P, et al. 2007. NEJM. 357(26):2657