Evaluation and Management of Mobitz I and Mobitz II AV Block
Mobitz type II second-degree AV block requires permanent pacemaker implantation regardless of symptoms, while Mobitz type I (Wenckebach) typically requires pacing only when symptomatic or associated with structural heart disease. 1
Diagnostic Criteria and Recognition
- Mobitz type I (Wenckebach) is characterized by progressive PR interval prolongation before a blocked P wave, with the PR interval shortening after the blocked beat 2
- Mobitz type II is characterized by constant PR intervals before and after blocked P waves without progressive prolongation 2, 3
- It's essential to distinguish 2:1 Wenckebach physiology from true Mobitz type II AV block, which can be achieved with stress testing or electrophysiology studies (EPS) in unclear cases 1
Initial Evaluation
- For both types, perform comprehensive cardiac evaluation including history, physical examination, ECG, echocardiogram to assess for underlying structural heart disease 1
- For Mobitz I with symptoms of unclear etiology, ambulatory electrocardiographic monitoring is reasonable to establish correlation between symptoms and rhythm abnormalities 1
- For patients with exertional symptoms who have Mobitz I at rest, exercise treadmill testing is recommended to determine potential benefit from permanent pacing 1
- For patients with Mobitz II, place transcutaneous pacing pads immediately due to high risk of progression to complete heart block 2
Management of Mobitz Type I (Wenckebach)
- Mobitz I can be present in otherwise normal, well-trained endurance athletes and is more commonly observed during sleep 1
- If QRS complex is abnormal or shortest PR interval is excessively prolonged (≥0.3 second), 24-hour ECG monitoring is warranted 1
- Permanent pacing is indicated for:
- Symptomatic patients with Mobitz I where symptoms are clearly attributable to the AV block 1
- Patients with Mobitz I and coexisting bundle-branch block or risk for progression to higher-degree AV block 1
- Patients who develop symptomatic Mobitz I as a consequence of necessary medical therapy that cannot be discontinued 1
- Atropine may temporarily improve AV conduction in acute settings by abolishing vagal cardiac slowing, but is not a long-term solution 4
Management of Mobitz Type II
- Mobitz II is always considered abnormal and requires evaluation regardless of symptoms 1
- Permanent pacemaker implantation is recommended for all patients with acquired Mobitz II second-degree AV block not attributable to reversible causes, regardless of symptoms 1, 2
- Mobitz II is typically located below the AV node (infranodal) and has higher risk of progression to complete heart block 3, 5
- Continuous cardiac monitoring is essential until permanent pacemaker is placed 2
Special Considerations
- In patients with neuromuscular diseases (muscular dystrophy, Kearns-Sayre syndrome) with evidence of second-degree AV block, permanent pacing is recommended regardless of symptoms 1
- For patients with infiltrative cardiomyopathy (sarcoidosis, amyloidosis) and Mobitz II, permanent pacing with additional defibrillator capability if needed is reasonable 1
- Permanent pacing should not be performed in patients with asymptomatic vagally mediated AV block 1
- In patients who had acute AV block due to a reversible and non-recurrent cause with complete resolution after treatment, permanent pacing should not be performed 1
Long-term Monitoring
- After pacemaker implantation, regular device checks are needed to ensure proper function 2
- In patients with dual-chamber pacemakers, programming should aim to maintain native AV conduction when possible to prevent pacing-induced ventricular dysfunction 2
- A retrospective study of older patients with Mobitz I showed that cardiac implantable electronic device placement was associated with a 46% reduction in mortality 6