What are the indications for pacemaker implantation in patients with symptomatic bradycardia, including those with atrioventricular (AV) block, sick sinus syndrome, or other forms of bradycardia?

Pacemaker Indications for Symptomatic Bradycardia

Permanent pacemaker implantation is indicated for any patient with documented symptomatic bradycardia, including those with sick sinus syndrome, atrioventricular block, or bradycardia resulting from necessary medical therapy. 1

Sick Sinus Syndrome (SND)

Class I Indications (Definite Need for Pacing)

• Documented symptomatic bradycardia including frequent sinus pauses that produce symptoms requires permanent pacemaker implantation 1
• Symptomatic chronotropic incompetence (inability to increase heart rate appropriately with activity) is an absolute indication for pacing 1
• Symptomatic sinus bradycardia resulting from required drug therapy for medical conditions mandates pacemaker implantation 1

Class IIa Indications (Reasonable to Implant)

• Heart rate less than 40 bpm when symptoms consistent with bradycardia exist but clear temporal correlation has not been documented 1
• Syncope of unexplained origin when clinically significant sinus node dysfunction is discovered or provoked during electrophysiological studies 1

Class IIb Indications (May Consider)

• Minimally symptomatic patients with chronic heart rate less than 40 bpm while awake may be considered for pacing 1

Class III (Do NOT Implant)

• Asymptomatic patients with SND should not receive pacemakers 1
• Patients whose symptoms have been clearly documented to occur in the absence of bradycardia should not be paced 1
• Symptomatic bradycardia due to nonessential drug therapy that can be discontinued is not an indication 1

Acquired Atrioventricular Block in Adults

Critical Distinction: Type II vs Type I Second-Degree AV Block

Mobitz Type II second-degree AV block requires permanent pacemaker implantation even if asymptomatic due to high risk of sudden progression to complete heart block and sudden cardiac death 2. This block shows constant PR intervals before and after blocked P waves, representing infranodal disease with unpredictable progression 2.

In contrast, Mobitz Type I (Wenckebach) at the AV node level typically does not require pacing unless symptomatic 2.

Class I Indications for AV Block

• Advanced second-degree or third-degree AV block associated with symptomatic bradycardia, ventricular dysfunction, or low cardiac output 1
• Mobitz Type II second-degree AV block, even if asymptomatic, because the block is infranodal with unreliable escape mechanisms 2
• Asystole ≥3.0 seconds or escape rate <40 bpm in awake patients 2
• Postoperative advanced second-degree or third-degree AV block that persists at least 7 days after cardiac surgery and is not expected to resolve 1, 3

Third-Degree (Complete) Heart Block

All patients with third-degree AV block require permanent pacemaker implantation when symptomatic or associated with hemodynamic compromise 1, 3. Dual-chamber (DDD/R) pacemakers are the preferred device to maintain atrioventricular synchrony and optimize hemodynamics 3.

Pediatric and Congenital Heart Disease Populations

Class I Indications

• Congenital third-degree AV block with wide QRS escape rhythm, complex ventricular ectopy, or ventricular dysfunction 1, 3
• Congenital third-degree AV block in infants with ventricular rate less than 55 bpm, or with congenital heart disease and ventricular rate less than 70 bpm 1, 3
• Symptomatic sinus bradycardia with correlation of symptoms during age-inappropriate bradycardia 1

Class IIa Indications

• Congenital third-degree AV block beyond the first year of life with average heart rate less than 50 bpm, abrupt pauses 2-3 times the basic cycle length, or symptoms due to chronotropic incompetence 1
• Sinus bradycardia with complex congenital heart disease with resting heart rate less than 40 bpm or pauses longer than 3 seconds 1

Device Selection Considerations

Dual-chamber (DDD/R) pacemakers are the preferred mode for most patients with AV block to maintain atrioventricular synchrony and prevent pacemaker syndrome 3, 4. Rate-responsive capability (DDD/R) should be added when chronotropic incompetence is present 3.

For sick sinus syndrome without AV block, dual-chamber pacemakers are cost-effective compared to single-chamber atrial pacemakers, with an incremental cost-effectiveness ratio of £6,506 4. The risk of developing complete AV block (approximately 8-9% over 5-10 years) argues for dual-chamber implantation programmed to minimize unnecessary ventricular pacing 4, 5.

Critical Pitfalls to Avoid

• Never delay pacemaker implantation in Mobitz Type II block waiting for symptoms, as progression can be sudden and life-threatening 2
• Distinguish physiological bradycardia (autonomic conditions, athletic training) from pathological bradycardia requiring pacing 1
• Ensure temporal correlation between symptoms and documented bradycardia before implanting for sick sinus syndrome 1
• Avoid pacing for bradycardia due to nonessential medications that can be discontinued 1