NOTE: for acute management of unstable bradycardia see section ACLS.

Background and Key Definitions

The decision to treat a conduction disorder with permanent pacemaker implantation is driven by three central tenants:

1. Absolute indication for pacing (e.g. complete heart block, advanced infranodal block).
2. Clear correlation of symptoms with the arrhythmia.
3. Persistence despite addressing reversible causes.

Definition of terms

• Sinus node dysfunction (SND): sinus rate <50 bpm and/or pause >3 seconds (in consideration with patient-specific factors).
• Tachycardia-bradycardia syndrome: bradycardic rhythm (sinus brady, atrial or sinus pause) alternating with abnormal atrial tachycardic rhythm (atrial tachycardia, flutter, or fibrillation).
• Chronotropic incompetence: failure to increase heart rate to expected level during increased period of demand.
• First degree AV block: P waves conducting 1:1 with QRS, however PR >200ms.
• Second degree AV block: P waves with constant rate, and QRS present but not conducting 1:1
  • Mobitz type 1: periodic nonconducted P waves with prolonging PR intervals until a dropped beat.
  • Mobitz type 2: periodic nonconducted P wave with constant PR interval until a dropped beat
• Advanced AV block: two or more consecutive P waves without AV conduction.
• Third degree AV block: no evidence of AV conduction (separate P waves and QRS).
• Ventricular conduction disease includes LBBB, RBBB, non-specific intraventricular conduction delay, and fascicular blocks (left anterior or posterior).

Evaluation

Reversible causes:

• Medications: beta-blockers, calcium-channel blockers, anti-arrhythmics, and many others
• Toxic-metabolic derangements: hyper/hypokalemia, digoxin toxicity
• Myocardial ischemia/infarction
• Cardiac trauma
• Infection, including bacterial endocarditis
• Obstructive sleep apnea
• Increased vagal tone from any number of causes

Cardiac Rhythm Monitors

	Duration	Characteristics	Comments
Holter	24 – 72 h	Continuous recording Patient-triggering capacity	Use for frequent events Must wear + carry
Event Monitor	2 – 6 wks	Patient-activated or device-activated recordings	Limited use with incapacitating symptoms
External Patch Recorder	2 – 14 days	Continuous recording Patient-triggering capacity	Leadless, water resistance, only 1-lead, not real time reporting
External Loop Recorder	Weeks - months	Continuous recording Patient-triggering capacity Device-triggering capacity	Useful for rarer events
Mobile Outpatient Telemetry	30 days	Continuous recording with a central monitoring station that is attended Patient-activated or device-activated	High-risk patients
Implantable Cardiac Monitor	2 – 3 years	Subcutaneously implanted Continuous monitoring, triggered by patient or family member	Recurrent infrequent symptoms

Temporary Cardiac Pacing

Transcutaneous: adhesive pads externally. Most rapidly available. Limited by capture and patient discomfort.

• Identify needed voltage for capture before absolute need.
• Ensure electric capture results in appropriate perfusion (i.e. feel patient’s pulse).

Transvenous: endocardial lead placement via central venous access (requires ICU). Can remain in place days-weeks, but may limit patient mobility. Transition to permanent pacemaker as soon as indicated.

Epicardial leads: surgically placed.

Common indications: must weigh risks of placing a wire against potential benefits.

• Temporary treatment of symptomatic bradyarrhythmia (until permanent pacemaker can be implanted or underlying condition reversed).
• Restoration of AV synchrony in acute MI (inferior MI, right ventricular MI), heart failure, hypertrophic obstructive cardiomyopathy.
• Prophylaxis for potential bradycardia which may produce symptoms or hemodynamic instability in acute MI or post-cardiac surgery.
• Prophylaxis to prevent pause-dependent ventricular tachycardia.

Transvenous pacing complications: suspect rupture of the intraventricular septum by the temporary pacer wire if any one of the following occur: chest pain, pericarditis (friction rub), transition from LBBB to RBBB pattern on ECG (except in temporary biventricular pacing).

Class I Indications for Permanent Pacemaker Implantation

Sinus dysfunction

• SND or chronotropic incompetence with directly attributable symptoms (lightheadedness, syncope, fatigue, etc.).
• Symptomatic sinus bradycardia due to guideline-directed therapy that is required and does not have an alternative.

AV block

• Acquired second-degree Mobitz type II, high-grade, or third-degree AV block without reversible causes.
• Permanent AF and symptomatic bradycardia.
• Symptomatic AV block due to guideline-directed therapy that is required and does not have an alternative.

Conduction disorders

• Syncope and bundle branch block with EP study demonstrating HV interval >70ms or infranodal block.
• Alternating bundle branch block.

Special circumstances

• After acute MI with SND or AV block meeting criteria above, permanent pacemaker is indicated AFTER a waiting period (generally at least >72 hours).
• Post-surgical (CABG, afib, TAVR/SAVR, tricuspid valve surgery, mitral valve surgery, surgical myectomy, alcohol septal ablation) SND or AV block with persistent symptoms or hemodynamic instability.
• Adult congenital heart disease with symptomatic SND, chronotropic incompetence, symptomatic bradycardia, or in specific cases with congenital complete AV block.
• Certain patients with neuromuscular diseases and high degree block.

Of note, pacing is NOT indicated in reflex mediated syncope (carotid sinus hypersensitivity, vasovagal, or situational) except in the case of recurrent syncope with loop recorder asystole.

Cardiac Resynchronization Therapy

(CRT; biventricular pacing) can improve survival and quality of life in patients with ischemic or non-ischemic left ventricular systolic dysfunction.

Class I Indication: sinus rhythm, LVEF ≤ 35%, QRS ≥ 150 ms, and NYHA functional class II, III or ambulatory IV despite maximal medical therapy.

• BLOCK-HF trial published after guidelines suggests CRT benefit specifically in patients with an indication for pacing (AV block), LVEF ≤ 50%, NYHA I, II, or II with sinus rhythm or atrial fibrillation.

His bundle pacing is an alternative option to biventricular pacing in patients with reduced EF or those at high risk for RV pacing induced cardiomyopathy.

Permanent Pacemakers

Transvenous: traditional technology, able to accommodate RV lead, atrial leads, biventricular leads, and ICD function.

•  Generator (battery powered) subcutaneously implanted.

•  Leads placed transvenously and connected to generator.

Leadless: new technology, as of 2020 only able to accommodate RV lead pacing.

•  Battery-powered devices “fixed” into RV.

Generic Pacemaker Codes
Chamber Paced	Chamber Sensed	Response to Sensed Beat	Rate–Response
O – none	O – none	O – none	R – rate-response activated
A – atrium	A – atrium	T – triggered
V – ventricle	V – ventricle	I – inhibited
D – both	D – both	D – triggered and initiated

Pacing modes: chosen based on pacemaker indication and device used.

• VVI: ventricular pacing on demand; output inhibited by sensed QRS. Indicated in patients with a-fib with complete AV block or symptomatic bradycardia. VVIR pacers can increase and decrease in response to sensor input, up to a programmed level, and are used for those with a-fib who do not mount a heart rate during exercise. Don't use in patients with sinus rhythm because of the loss of AV synchrony during pacing; in addition, retrograde atrial activation can induce atrial fibrillation in these patients.
• AAI: atrial pacing is inhibited by sensed P-wave events. Indicated for sick sinus syndrome with intact AV node conduction. Use AAIR in patients with chronotropic incompetence. Do not use in patients with extensive conduction system disease and those with atrial flutter/fibrillation. Yearly, up to 5% of patients with sick sinus syndrome will develop AV block, which could make this pacer inadequate in the future.
• DDD: the generator can sense and pace both atria and ventricles. During sinus bradycardia, atrial and, if necessary, ventricular pacing occurs. During AV block, ventricular pacing occurs following either a spontaneous or paced atrial impulse. Indicated for AV block with intact sinus node function. Use DDDR in patients with chronotropic incompetence. Rapid ventricular response can occur during atrial tachycardias—this is prevented by setting an upper rate limit or using a mode-switching device.
• DDI: similar to DDD but during atrial tachycardias, the device effectively operates in VVI mode as the atrial impulse is inhibited. Indicated in sick sinus syndrome, hypersensitive carotid sinus syndrome, and malignant vasovagal syndrome. The disadvantage is that this DDI cannot maintain AV synchrony during AV block. 
• VDD: devices with a single ventricular lead can also have sensing electrodes in the right atrium that allow tracking of atrial rhythm. This allows for atrioventricular synchrony with only one lead. Implantation is simpler than for dual-chamber devices, with less risk of lead displacement and implantation-associated trauma. Indicated for high-grade AV block with intact sinus node function.

Brignole M, Auricchio A, Baron-esquivias G, et al. 2013 ESC Guidelines on cardiac pacing and cardiac resynchronization therapy: the Task Force on cardiac pacing and resynchronization therapy of the European Society of Cardiology (ESC). Developed in collaboration with the European Heart Rhythm Association (EHRA). Eur Heart J. 2013;34(29):2281-329.

Curtis AB, Worley SJ, Adamson PB, et al. Biventricular pacing for atrioventricular block and systolic dysfunction. N Engl J Med. 2013;368(17):1585-93.

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: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2013;61(3):e6-75.

Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. Circulation. 2019;140(8):e382-e482.

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Varosy PD, Chen LY, Miller AL, Noseworthy PA, Slotwiner DJ, Thiruganasambandamoorthy V. Pacing as a Treatment for Reflex-Mediated (Vasovagal, Situational, or Carotid Sinus Hypersensitivity) Syncope: A Systematic Review for the 2017 ACC/AHA/HRS Guideline for the Evaluation and Management of Patients With Syncope: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2017;70(5):664-679.