The presence of a narrow QRS complex makes the site of delay even more likely to be at the AV node. Wenckebach block with a wide complex QRS may be due to AV nodal or infranodal conduction delay. Electrophysiological studies have proved that Mobitz II block is due to an infranodal His-Purkinje system conduction delay. Type I block localized to the His-Purkinje system has the same risks as type II block. Mobitz II block carries a high risk of progression to complete heart block, often with associated cardiovascular collapse.
Most patients are asymptomatic.
Patients may experience dizziness, lightheadedness, or syncope, but these are uncommon. Patients may have symptoms of myocardial ischemia or myocarditis. Patients may have a history of organic heart disease. Mobitz II block Patients may be asymptomatic but are more likely to present with dizziness, lightheadedness, or syncope. Patients may have symptoms of myocardial ischemia or a history of organic heart disease.