0071643192.pdf

THIRD-DEGREEAV BLOCK

Generally unstable rhythm resulting in syncope and often hypotension.

Third-degree AV block (third-degree heart block) can be due to damage at the

AV node or at the infranodal conducting system.

CAUSES

Causes are similar to second-degree AV block. Be sure to consider medications

such as β-blockers and Ca channel blockers as a cause.

In the setting of ACS, third-degree AV block may be either nodal or infranodal.

■ Nodalthird-degree AV block is seen primarily with inferior MI and is

typically transient.

■ Infranodalthird-degree AV block is seen in large anteroseptal MI from

damage to the infranodal conducting system and is often permanent.

ECG FINDINGS(SEEFIGURE1.6)

■ No P waves conducted

■ Nodal block →junctional escape rhythm, narrow complexes.

■ Infranodal block →ventricular escape rhythm, wide complexes.

TREATMENT

■ Nodal

■ Atropine and transcutaneous pacing if symptomatic

■ Temporary transvenous pacemaker often required

■ Infranodal

■ Avoid: Atropine(may worsen the conduction rate).

■ Isoproterenol (to increase ventricular rate) and transcutaneous pacing

if symptomatic, until

■ Transvenous pacemaker placement

■ If congenital and asymptomatic, may not require immediate therapy

EXTRASYSTOLES

Extrasystoles are ectopic impulses occurring in addition to regular sinus beats.

■ Premature atrial contraction

■ Premature ventricular contraction

RESUSCITATION FIGURE 1.5. Second-degree AV block type II.

FIGURE 1.6. Third-degree AV block.

Inferior MI →third-degree AV

block with junctional escape

(40–60 bpm) and narrow

complexes.

Anterior MI →third-degree

AV block with ventricular

escape (<40 bpm) and wide

complexes.

Atropine may actually worsen

the conduction ratio with

infranodal AV block (Mobitz II

or infranodal third degree).