What is the treatment for a stable pediatric patient with a bradycardic (abnormally slow heart rate) second-degree type 2 block?

Treatment of Stable Pediatric Patient with Bradycardic Second-Degree Type 2 (Mobitz II) Block

Permanent pacemaker implantation is indicated for pediatric patients with Mobitz type II second-degree AV block, even when hemodynamically stable and asymptomatic, because this rhythm carries high risk of sudden progression to complete heart block. 1, 2

Immediate Assessment and Stabilization

While the patient is currently stable, you must:

• Establish continuous cardiac monitoring to detect progression to higher-degree block 3
• Assess for any subtle symptoms including fatigue, exercise intolerance, syncope, presyncope, or dyspnea that may indicate hemodynamic compromise 1, 2
• Evaluate for reversible causes including:
  • Lyme carditis or other infectious etiologies
  • Drug toxicity (beta-blockers, calcium channel blockers, antiarrhythmics, digoxin)
  • Electrolyte abnormalities
  • Cardiac sarcoidosis or infiltrative disease 1, 2

Acute Medical Management (If Needed During Evaluation)

If the patient develops symptoms or hemodynamic compromise while awaiting definitive therapy:

• Atropine is reasonable (0.5 mg IV, may repeat every 3-5 minutes) if the block is believed to be at the AV nodal level, though Mobitz type II is typically infranodal and may not respond 1, 4, 5
• Beta-adrenergic agonists (isoproterenol, dopamine, dobutamine, or epinephrine) may be considered if coronary ischemia is unlikely 1, 2
• Temporary transvenous pacing is reasonable for symptomatic patients refractory to medical therapy 1, 2
• Temporary transcutaneous pacing may be considered as a bridge until transvenous or permanent pacing is established 1, 6

Definitive Management: Permanent Pacing

The cornerstone of treatment is permanent pacemaker implantation, which should proceed even in asymptomatic patients. 1, 2 This recommendation is based on:

• Mobitz type II block is typically infranodal (intra- or infra-Hisian), indicating diffuse conduction system disease 1
• Progression to complete heart block is common and sudden, making observation unsafe 1
• Symptoms are frequent and prognosis is compromised without pacing 1
• Paced patients have significantly better survival compared to unpaced patients (78% vs 41% five-year survival in one study) 7

Important Caveats for Pediatric Patients

• Age-related differences exist in normal heart rate ranges and conduction system anatomy, requiring pediatric-specific evaluation 3
• Genetic evaluation may be warranted, as inherited conduction disorders can present in childhood 3
• Congenital heart disease should be excluded, as it may coexist with conduction abnormalities 3

When to Delay Permanent Pacing

Permanent pacing should be delayed only if:

• Transient or reversible causes are identified (e.g., acute Lyme carditis, drug toxicity), in which case medical therapy and supportive care including temporary pacing should be provided first 1, 2
• However, if the patient is on chronic stable doses of medically necessary beta-blockers or antiarrhythmics, it is reasonable to proceed directly to permanent pacing without drug washout 1, 2

Critical Pitfall to Avoid

Do not confuse Mobitz type II with Mobitz type I (Wenckebach). Mobitz type I typically has a benign course when the QRS is narrow and the block is at the AV nodal level, whereas Mobitz type II indicates infranodal disease requiring pacing regardless of symptoms. 1, 2 The key distinguishing feature is that Mobitz type II has constant PR intervals before the dropped beat, while Mobitz type I shows progressive PR prolongation before the dropped beat. 1

Prognosis

• Without pacing, chronic second-degree type II block has poor prognosis with five-year survival of approximately 41-61% 7
• With permanent pacing, five-year survival improves to approximately 78%, similar to age-matched normal population 7
• Early diagnosis and appropriate management are critical to prevent sudden death in pediatric patients 3