SECOND-DEGREEAV BLOCKTYPEI (WENCKEBACH, MOBITZI)
Characterized by gradually increasing block at the AV nodedue to prolonga-
tion of the AV-nodal refractory period; can occur in normal hearts
CAUSES
Similar to first-degree AV block. In ACS, it is commonly associated with
inferior MI.
ECG FINDINGS(SEEFIGURE1.4)
■ PR progressively elongates until one QRS complex is dropped.
■ P waves regular
■ Not all P waves conducted past AV node
■ PR interval generally > 0.2 seconds.
■ QRS complexes appear “grouped.”
TREATMENT
■ Unlikely to cause serious signs or symptoms
■ Treat underlying condition.
SECOND-DEGREEAV BLOCKTYPEII (MOBITZII)
A significant rhythm since it is associated with damage to the conducting system
below the AV node (infranodal)and can progress without warning to complete
heart block.
CAUSES
Mobitz II does notoccur in healthy hearts. Causes include:
■ ACS (commonly anteroseptal MI)
■ Infectious disease (eg, Lyme disease, rheumatic fever)
■ Infiltrative myocardial disease (eg, sarcoidosis)
■ Structural heart disease (congenital or surgical)
■ Medications
ECG FINDINGS(SEEFIGURE1.5)
■ PR interval constant
■ P waves regular
■ QRS complex regularly or randomly dropped
TREATMENT
■ Symptomatic bradycardia →transcutanous pacing.
■ Transvenous pacemaker placement (required, unless chronic)
■ Atropine is nothelpful (may actually worsen conduction ratio).
■ Admission (unless chronic)
RESUSCITATIONFIGURE 1.4. Second-degree AV block type I.
First-degree heart block,
Wenckebach, and RBBB can
all occur in a healthy heart.Second-degree AV block type
II (Mobitz II) = damage to the
infranodal conducting system.Inferior MI →reversible AV
block.
Anteroseptal MI →
permanent infranodal
conduction system damage.