From the Guidelines
Mobitz Type 2 atrioventricular block requires permanent pacing, regardless of symptoms, due to its high risk of progression to complete heart block and associated morbidity and mortality. This condition is characterized by intermittently dropped heartbeats without warning, with consistent PR intervals before the blocked beat, making it more dangerous and unpredictable than Mobitz Type 1 1. The 2019 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay recommends permanent pacing for patients with acquired second-degree Mobitz Type II atrioventricular block, high-grade atrioventricular block, or third-degree atrioventricular block not attributable to reversible or physiologic causes 1.
Key Considerations
- Mobitz Type 2 atrioventricular block typically occurs due to disease in the His-Purkinje system below the AV node, often from coronary artery disease, myocardial infarction, or fibrosis.
- On an ECG, normal P waves with some P waves not followed by QRS complexes are seen, while the PR interval remains constant before blocked beats.
- Treatment typically involves permanent pacemaker implantation, as medications are generally ineffective.
- Temporary pacing may be needed in emergency situations, and atropine can be used as a bridging therapy.
Recommendations
- Permanent pacing is recommended for patients with Mobitz Type 2 atrioventricular block, regardless of symptoms 1.
- Patients with Mobitz Type 2 should be monitored closely in a hospital setting until definitive treatment is provided, as this condition carries significant risk for sudden cardiac events.
- The decision to implant a pacemaker should be made with respect to whether the AV block will be permanent, and reversible causes of AV block should be corrected first 1.
From the Research
Definition and Characteristics of Mobitz Type 2
- Mobitz type II second-degree atrioventricular block is characterized by periodic atrioventricular block with constant PR intervals in the conducted beats 2.
- It is an old term that refers to an electrocardiographic pattern describing an all-or-none conduction without visible changes in the AV conduction time or PR intervals before and after a single non-conducted P wave 3.
- An unchanged PR interval after the block is a key feature of Mobitz type II block 3.
Diagnosis and Differentiation
- The diagnosis of Mobitz type II block requires a stable sinus rate, as a vagal surge can cause simultaneous sinus slowing and AV nodal block, resembling Mobitz type II AVB 3.
- Mobitz type II block must be distinguished from other causes of pauses, such as nonconducted premature atrial contractions and atrial tachycardia with block 2.
- Atypical forms of Wenckebach AVB may be misinterpreted as Mobitz type II AVB when a series of PR intervals are constant before the block 3.
- Concealed His bundle or ventricular extrasystoles may mimic both Wenckebach and/or type II AVB (pseudo-AVB) 3.
Clinical Significance and Prognosis
- Mobitz type II block is more likely to progress to complete heart block and Stokes-Adams arrest compared to Mobitz type I block 2.
- Correctly identified Mobitz type II AVB is invariably at the level of the His-Purkinje system and is an indication for a pacemaker 3.
- The site of the block in Mobitz type II is almost always below the AV node, whereas in Mobitz type I block, the site is usually within the AV node 2.