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Cardiac Pacemakers

By L. Brent Mitchell, MD

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Patient Education

The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic drugs, cardioversion-defibrillation, implantable cardioverter-defibrillators (ICDs), pacemakers (and a special form of pacing, cardiac resynchronization therapy), or a combination, is used.

Pacemakers sense electrical events and respond when necessary by delivering electrical stimuli to the heart. Permanent pacemaker leads are placed via thoracotomy or transvenously, but some temporary emergency pacemaker leads can be placed on the chest wall.

Indications for pacemaker placement

Indications are numerous (see Table: Indications for Permanent Pacemakers) but generally involve symptomatic bradycardia or high-grade atrioventricular (AV) block. Some tachyarrhythmias may be terminated by overdrive pacing with a brief period of pacing at a faster rate; the pacemaker is then slowed to the desired rate. Nevertheless, ventricular tachyarrhythmias are better treated with devices that can cardiovert and defibrillate as well as pace ( implantable cardioverter defibrillators).

Indications for Permanent Pacemakers

Arrhythmia

Indicated (Established by Evidence)

Possibly Indicated and Supported by Bulk of Evidence

Possibly Indicated But Less Well Supported by Evidence

Not Indicated

Sinus node dysfunction

Symptomatic bradycardia, including symptomatic frequent sinus pauses and bradycardia due to essential drugs (alternatives contraindicated)

Symptomatic chronotropic incompetence (heart rate cannot meet physiologic demands)

Heart rate of < 40 beats/min when symptoms have not been clearly associated with the bradycardia

Syncope of unexplained origin with significant sinus node dysfunction seen on ECG or triggered in an electrophysiologic study

Heart rate of < 40 beats/min in minimally symptomatic patients while awake

Asymptomatic bradycardia

Symptoms consistent with bradycardia but clearly shown not to be associated with it

Symptomatic bradycardia due to nonessential drugs

AV block

Any 3rd-degree or 2nd-degree AV block associated symptomatic bradycardia or ventricular arrhythmia

Third-degree or advanced 2nd-degree AV block at any anatomic level if associated with one of the following:

  • Arrhythmias and other disorders requiring drugs that cause symptomatic bradycardia

  • Documented asystole 3.0 sec (≥ 5.0 sec in atrial fibrillation), any escape rate of < 40 beats/min, or escape rhythm below the AV node in awake, asymptomatic patients

  • Escape ventricular rates of > 40 beats/min in patients with cardiomegaly or LV dysfunction

  • Catheter ablation of the AV junction

  • Postoperative block not expected to resolve after surgery

  • Neuromuscular disorders with AV block (eg, myotonic muscular dystrophy, Kearns-Sayre syndrome, limb-girdle dystrophy, Charcot-Marie-Tooth disease [peroneal atrophy])

  • Exercise (ie, occurring during) in patients without myocardial ischemia

Asymptomatic 3rd-degree AV block at any anatomic level when average ventricular rates during waking are 40 beats/min in patients without cardiomegaly

Asymptomatic type II 2nd-degree AV block with narrow QRS complex (pacemaker is indicated if QRS complex is wide)

Asymptomatic 2nd-degree AV block within or below His bundle level, detected during an electrophysiologic study

First- or 2nd-degree AV block with symptoms suggesting pacemaker syndrome

AV block in patients who are taking a causative drug or have drug toxicity if block is expected to recur even after drug is withdrawn

AV block of any degree (including 1st) associated with neuromuscular disorders in which conduction abnormalities may progress unpredictably (eg, myotonic muscular dystrophy, limb-girdle dystrophy, Charcot-Marie-Tooth disease [peroneal atrophy] with or without symptoms)

Asymptomatic 1st-degree AV block

Asymptomatic type I 2nd-degree AV block at the AV node level or not known to be within or below His bundle level

AV block expected to resolve or unlikely to recur (eg, due to drug toxicity or Lyme disease or occurring asymptomatically during transient increases in vagal tone or during hypoxia in sleep apnea syndrome)

Tachyarrhythmias

Sustained, pause-dependent VT, with or without prolonged QT interval

High-risk patients with congenital long QT syndrome

Symptomatic recurrent SVT reproducibly terminated by pacing when ablation and/or drugs fail (except when there is an accessory AV connection capable of high-frequency antegrade conduction)

Prevention of symptomatic, recurrent atrial fibrillation refractory to drugs when sinus node dysfunction coexists

Frequent or complex ventricular ectopy without sustained VT when long QT syndrome is absent

Torsades de pointes VT with reversible causes

Prevention of AF in patients without another indication for pacing

After acute MI

Persistent 2nd-degree AV block in the His-Purkinje system with bilateral BBB or 3rd-degree AV block within or below the His-Purkinje system

Transient advanced 2nd- or 3rd-degree AV block below the AV node level and associated with BBB

Persistent symptomatic 2nd- or 3rd-degree AV block

None

Persistent 2nd- or 3rd-degree AV block at the AV node level

Transient AV block without intraventricular conduction defects

Transient AV block with isolated left anterior fascicular block

Acquired BBB or fascicular block without AV block

Persistent 1st-degree AV block with BBB or fascicular block

Multifascicular block

Advanced 2nd-degree or intermittent 3rd-degree AV block

Type II 2nd-degree AV block

Alternating BBB

Syncope not shown to be due to AV block after other likely causes (especially VT) are excluded

Very prolonged HV interval (100 msec) in asymptomatic patients, detected incidentally during an electrophysiologic study

Nonphysiologic, infra-His block induced by pacing, detected incidentally during an electrophysiologic study

Neuromuscular disorders in which conduction abnormalities may progress unpredictably (eg, myotonic muscular dystrophy, limb-girdle dystrophy, Charcot-Marie-Tooth disease [peroneal atrophy] with or without symptoms)

Fascicular block without AV block or symptoms

Fascicular block with 1st-degree AV block and without symptoms

Congenital heart disorders

Advanced 2nd- or 3rd-degree AV block causing symptomatic bradycardia, ventricular dysfunction, or low cardiac output

Sinus node dysfunction correlated with symptoms during age-inappropriate bradycardia

Postoperative high-grade 2nd- or 3rd-degree AV block that is not expected to resolve or that persists 7 days after surgery

Congenital 3rd-degree AV block with a wide QRS escape rhythm, complex ventricular ectopy, or ventricular dysfunction

Congenital 3rd-degree AV block in infants with a ventricular rate of < 55 beats/min or with a congenital heart disorder and a ventricular rate of < 70 beats/min

Sustained pause-dependent VT, with or without prolonged QT, when pacing has been documented as effective

Congenital heart disorder and sinus bradycardia to prevent recurrent episodes of intra-atrial reentrant tachycardia

Congenital 3rd-degree AV block persisting after age 1 yr if average heart rate is < 50 beats/min, ventricular rate pauses abruptly for 2 or 3 times the basic cycle length, or associated symptoms due to chronotropic incompetence occur

Asymptomatic sinus bradycardia in children with a complex congenital heart disorder and resting heart rate of < 40 beats/min or pauses in ventricular rate of > 3 sec

Patients with a congenital heart disorder and impaired hemodynamics due to sinus bradycardia or loss of AV synchrony

Unexplained syncope in patients who have had congenital heart disorder surgery that was complicated by transient 3rd-degree AV block with residual fascicular block

Transient postoperative 3rd-degree AV block that converts to sinus rhythm with residual bifascicular block

Congenital 3rd-degree AV block in asymptomatic infants, children, adolescents, or young adults with an acceptable ventricular rate, a narrow QRS complex, and normal ventricular function

Asymptomatic sinus bradycardia after biventricular repair of a congenital heart disorder in patients with resting heart rate of < 40 beats/min or pauses in ventricular rate of > 3 sec

Transient postoperative AV block when AV conduction returns to normal

Asymptomatic postoperative bifascicular block with or without 1st-degree AV block and without prior transient 3rd-degree AV block

Asymptomatic type I 2nd-degree AV block

Asymptomatic sinus bradycardia when the longest RR interval is < 3 sec and minimum heart rate is > 40 beats/min

Hypersensitive carotid sinus syndrome and neurocardiogenic syncope

Recurrent syncope due to spontaneously occurring carotid sinus stimulation or to carotid sinus pressure that induces asystole of > 3 sec

Recurrent syncope without obvious triggering events and with a hypersensitive cardioinhibitory response (ie, carotid sinus pressure induces asystole of > 3 sec)

Significantly symptomatic neurocardiogenic syncope associated with bradycardia documented clinically or during tilt-table testing

Hyperactive cardioinhibitory response to carotid sinus stimulation without symptoms or with vague symptoms (eg, dizziness, light-headedness)

Situational vasovagal syncope that can be averted by avoidance

Postcardiac transplantation

Persistent inappropriate or symptomatic bradycardia expected to persist

Other established indications for permanent pacing

None

Prolonged or recurrent relative bradycardia limiting rehabilitation or discharge after postoperative recovery

Syncope after transplantation even when bradyarrhythmia has not been demonstrated

None

Hypertrophic cardiomyopathy

Same as established indications for sinus node dysfunction or AV block

None

Medically refractory, symptomatic hypertrophic cardiomyopathy when resting or induced LV outflow is significantly obstructed

Asymptomatic or medically controlled hypertrophic cardiomyopathy

Symptomatic hypertrophic cardiomyopathy with no evidence of LV outflow obstruction

Cardiac resynchronization therapy (CRT) for patients with severe systolic heart failure

CRT (with or without an ICD) for patients with LVEF ≤ 35%, LBBB,

QRS duration ≥ 0.15 sec, sinus rhythm, and NYHA class II, class III, or ambulatory class IV heart failure symptoms during optimal medical therapy

CRT (with or without an ICD) for patients with LVEF ≤ 35%, sinus rhythm, LBBB, QRS duration 0.12–0.149 sec, and NYHA class II, class III, or ambulatory class IV heart failure symptoms during optimal medical therapy

CRT for patients with LVEF ≤ 35%, sinus rhythm, non-LBBB, QRS duration ≥ 0.15 sec, and NYHA class III or ambulatory class IV heart failure symptoms during optimal medical therapy

CRT for patients with LVEF ≤ 35% in AF who otherwise meet criteria for CRT and AV node ablation or pharmacologic therapy will allow near 100% ventricular pacing

CRT for patients with LVEF ≤ 35% who are undergoing new or replacement device with anticipated > 40% ventricular pacing

LVEF ≤ 30% caused by ischemic heart disease) in sinus rhythm, QRS duration ≥ 0.15 sec, and NYHA class I heart failure symptoms during optimal medical therapy

LVEF ≤ 35%, sinus rhythm, non-LBBB, QRS duration 0.12–0.149 sec, and NYHA class III or ambulatory class IV heart failure symptoms during optimal medical therapy

LVEF ≤ 35%, sinus rhythm, non-LBBB, QRS duration ≥ 0.15 sec, and II heart failure symptoms during optimal medical therapy

NYHA class I or II symptoms and non-LBBB QRS pattern with QRS duration < 0.15 sec

Comorbidity and/or frailty that will limit survival with good functional status to < 1 yr

AF = atrial fibrillation; AV = atrioventricular; BBB = bundle branch block; EF = ejection fraction; HV interval = interval from the start of the HIS signal to the beginning of the 1st ventricular signal; ICD = implantable cardioverter-defibrillator; LBBB = left bundle branch block; LV = left ventricular; NYHA = New York Heart Association; SVT = supraventricular tachycardia; VT = ventricular tachycardia.

Data from Epstein AE, DiMarco JP, Ellenbogen KA, et al: 2012 ACCF/AHA/HRS focused update incorporated into the ACCF/AHA/HRS 2008 Guidelines for device-based therapy of cardiac rhythm abnormalities. Circulation 117(21):e350–e408, 2008 and Circulation127(3):e283–e352, 2013.

Types of pacemakers

Types of pacemakers are designated by 3 to 5 letters (see Table: Pacemaker Codes), representing which cardiac chambers are paced, which chambers are sensed, how the pacemaker responds to a sensed event (inhibits or triggers pacing), whether it can increase heart rate during exercise (rate-modulating), and whether pacing is multisite (in both atria, both ventricles, or more than one pacing lead in a single chamber). For example, a VVIR pacemaker paces (V) and senses (V) events in the ventricle, inhibits pacing in response to sensed event (I), and can increase its rate during exercise (R).

VVI and DDD pacemakers are the devices most commonly used. They offer equivalent survival benefits. Compared with VVI pacemakers, physiologic pacemakers (AAI, DDD, VDD) appear to reduce risk of atrial fibrillation (AF) and heart failure and slightly improve quality of life.

Advances in pacemaker design include lower-energy circuitry, new battery designs, and corticosteroid-eluting leads (which reduce pacing threshold), all of which increase pacemaker longevity. Mode switching refers to an automatic change in the mode of pacing in response to sensed events (eg, from DDDR to VVIR during AF).

Pacemaker Codes

I

II

III

IV

V

Chamber Paced

Chamber Sensed

Response to Sensed Event

Rate Modulation

Multisite Pacing

A = Atrium

A = Atrium

O = None

O = Not programmable

O = None

V = Ventricle

V = Ventricle

I = Inhibits pacemaker

A = Atrium

D = Dual (both)

D = Dual (both)

T = Triggers pacemaker to stimulate ventricles

R =Rate-modulated

V = Ventricle

D = Dual (both): For events sensed in ventricles, inhibits; for events sensed in atria, triggers

D = Dual (both)

Complications of pacemaker use

Pacemakers may malfunction by oversensing or undersensing events, failing to pace or capture, or pacing at an abnormal rate. Tachycardias are an especially common complication. Rate-modulating pacemakers may increase stimuli in response to vibration, muscle activity, or voltage induced by magnetic fields during MRI. In pacemaker-mediated tachycardia, a normally functioning dual-chamber pacemaker senses a ventricular premature or paced beat transmitted to the atrium through the AV node or a retrograde-conducting accessory pathway, which triggers ventricular stimulation in a rapid, repeating cycle.

Additional complications associated with normally functioning devices include cross-talk inhibition, in which sensing of the atrial pacing impulse by the ventricular channel of a dual-chamber pacemaker leads to inhibition of ventricular pacing, and pacemaker syndrome, in which AV asynchrony induced by ventricular pacing causes fluctuating, vague cerebral (eg, light-headedness), cervical (eg, neck pulsations), or respiratory (eg, dyspnea) symptoms. Pacemaker syndrome is managed by restoring AV synchrony by atrial pacing (AAI), single-lead atrial sensing ventricular pacing (VDD), or dual-chamber pacing (DDD), most commonly the latter.

Environmental interference comes from electromagnetic sources such as surgical electrocautery and MRI, although MRI may be safe when the pacemaker generator and leads are not inside the magnet. Cellular telephones and electronic security devices are a potential source of interference; telephones should not be placed close to the device but are not a problem when used normally for talking. Walking through metal detectors does not cause pacemaker malfunction as long as patients do not linger.

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* This is the Professional Version. *