What type of pacemaker is recommended for a patient with 2nd degree heart block?

Pacemaker Selection for Second-Degree Heart Block

For second-degree heart block, a dual-chamber (DDD/DDDR) pacemaker is the recommended device, as it maintains atrioventricular synchrony and prevents pacemaker syndrome, with the specific urgency and indication depending on whether the block is Mobitz Type I or Type II. 1, 2

Critical Distinction: Type I vs Type II Block

The type of second-degree block fundamentally determines management urgency:

Mobitz Type II (Infranodal Block)

• Permanent pacemaker implantation is indicated even in asymptomatic patients due to unpredictable progression to complete heart block and sudden cardiac death. 1, 2
• Type II block shows constant PR intervals before and after blocked P waves, representing all-or-none conduction without visible changes in AV conduction time. 2, 3
• The site of block is almost always infranodal (within or below the His bundle), particularly when associated with wide QRS complexes. 2, 4
• Do not delay pacemaker implantation waiting for symptoms to develop—progression can be sudden and life-threatening. 2

Mobitz Type I (Wenckebach/AV Nodal Block)

• Permanent pacemaker implantation is not indicated for asymptomatic Type I second-degree AV block at the supra-His (AV node) level. 1
• Pacing is only required if symptomatic bradycardia is present or if electrophysiological study demonstrates the block occurs at intra-His or infra-His levels. 1, 2

Optimal Pacemaker Mode Selection

Primary Recommendation: Dual-Chamber (DDD/DDDR)

Dual-chamber pacing is the Class I indication for AV node disease, including second-degree AV block, regardless of symptom status. 2

Rationale:

• Maintains atrioventricular synchrony, which is physiologically superior to single-chamber ventricular pacing. 2
• Prevents pacemaker syndrome (fatigue, dyspnea, exercise intolerance from loss of AV synchrony). 1, 5
• Significantly reduces atrial fibrillation risk (odds ratio 0.79,95% CI 0.68-0.93). 5
• Improves exercise capacity compared to ventricular-only pacing. 5

Alternative Options (Limited Circumstances)

Single-Chamber Ventricular Pacing (VVI/VVIR):

• Acceptable only for sedentary patients with limited activity levels, significant medical comorbidities, technical limitations, or patients in permanent atrial fibrillation. 2
• Never use single-chamber atrial pacing (AAI) in AV block—the conduction disease is below the atrium and will not be addressed. 2

Single-Lead VDD Pacing:

• Can be useful in younger patients with normal sinus node function and isolated AV block, providing AV synchrony with a single ventricular lead that senses atrial activity. 2

Special Considerations for Adult Congenital Heart Disease

For patients with congenital heart disease requiring pacing:

• AAIR or DDDR pacemaker implantation is recommended for symptomatic sinus node dysfunction and those with pause-dependent ventricular tachycardia. 1
• Programming should aim to maintain native AV conduction when possible to minimize risk of pacing-induced ventricular dysfunction. 1
• Transvenous systems can be used in most patients, though certain cases (single ventricle, Fontan circulation, significant intracardiac shunts) require epicardial leads due to lack of access or thromboembolism risk. 1

Mandatory Pre-Implantation Exclusions

Before proceeding with permanent pacing, exclude reversible causes:

• Electrolyte abnormalities (particularly hyperkalemia). 1, 2
• Drug toxicity (digitalis, beta-blockers, calcium channel blockers). 1, 2
• Lyme disease—may require only temporary pacing with antibiotic treatment. 1, 2
• Transient vagal tone increases or hypoxia in sleep apnea syndrome. 1, 2
• Perioperative factors (hypothermia, inflammation near AV conduction system). 2

Post-Myocardial Infarction Context

Permanent pacemaker implantation is indicated for postoperative Mobitz II second- or third-degree AV block that is not expected to resolve or persists beyond 7-10 days. 1

For acute MI with persistent Type II block or advanced AV block with bilateral bundle branch block, permanent pacing is required. 2

High-Risk Features Requiring Urgent Pacing

Regardless of block type, permanent pacemaker is indicated for:

• Symptomatic bradycardia (syncope, presyncope, dizziness, fatigue, exercise intolerance). 1
• Documented asystole ≥3.0 seconds or escape rate <40 bpm in awake patients. 1, 2
• Heart failure or congestive symptoms associated with the block. 1
• Exercise-induced second-degree AV block in the absence of myocardial ischemia. 1

Critical Diagnostic Pitfall

2:1 AV block cannot be definitively classified as Type I or Type II and may require electrophysiological study or stress testing to determine the level of block before deciding on pacing urgency. 2, 3