Mobitz II occurs when the infranodal conduction system intermittently fails, resulting in intermittently “dropped” P waves but consistent PR intervals when conducted. Mobitz II usually occurs with preexisting conduction disease (e.g., combination of bundle branch and fascicular blocks), is always pathologic, and more likely to progress to complete heart block.
Second Degree Atrioventricular Block – Mobitz II
Examples
Second Degree Atrioventricular Block – Mobitz II
When consecutive P waves are non-conducted, it is referred to as "high grade" atrioventricular block, and should be treated the same as complete heart block (i.e., pacemaker placement).
Second Degree Atrioventricular Block – Mobitz II
Second degree atrioventricular block, Mobitz II with 3:1 conduction. When consecutive atrial beats are non-conducted, it is referred to as high-grade atrioventricular block. This patient progressed to complete heart block.
Second Degree Atrioventricular Block – Mobitz II
Second degree atrioventricular block, Mobitz II, with variable conduction.
Second Degree Atrioventricular Block – Mobitz I
This rhythm is challenging but there three conducted P waves and the rest are dropped. Intermittent failure of conduction is defined as second degree atrioventricular block. Mobitz II conduction is due to infranodal conduction disease and is characterized by constant PR intervals.1 The PR intervals for the conducted P waves are constant, therefore, this rhythm is most likely second degree atrioventricular block with Mobitz II conduction.References
- Costa D Da, Brady WJ, Edhouse J. Bradycardias and Atrioventricular conduction block. Br Med J. 2002;324(March):535-538.
- de Pádua F, Pereirinha A, Marques N, Lopes MG, Macfarlane PW. Conduction Defects. In: Macfarlane PW, van Oosterom A, Pahlm O, Kligfield P, Janse M, Camm J, eds. Comprehensive Electrocardiology. London: Springer London; 2010:547-604.
- Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS Guideline on the Evaluation and Management of Patients With Bradycardia and Cardiac Conduction Delay: A Report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines and the Heart Rhyth. Circulation. 2019;140(8):e382-e482.