Internal Medicine

0521779407-19 CUNY1086/Karliner 0 521 77940 7 June 4, 2007 21:21

1350 Sinoatrial Block

Signs & Symptoms

■Generally asymptomatic. Fatigue, worsening of congestive heart fail-

ure, syncope or near-syncope may occur.

tests

■Basic Tests

➣12-lead ECG:

➣Pauses due to periodic absence of P waves.

➣First Degree SA exit block: cannot be recognized on ECG (con-

duction defect occurs within the SA node)

➣Second Degree SA exit block:

➣Type I SA exit block (SA Wenckebach): P-P interval duration pro-

gressively shortens before pause. The longest P-P interval (pause)

is shorter than 2 times the shortest P-P interval.

➣Type II SA exit block (Mobitz II SA exit block): Duration of pause

is a multiple of the regular P-P intervals.

➣Third degree SA block: cannot be distinguished on ECG. Sug-

gested by complete absence of P waves.

■Specific Diagnostic Test

➣Holter monitoring. In electrophysiology study, intracardiac

recording records atrial depolarization but not sinus node activ-

ity.

differential diagnosis

■Sinus pauses or arrest from absence of sinus node activity (in SA

block, sinus node impulse is present but fails to depolarize the

atrium).

■AV nodal block: P-P interval is always regular.

management

What to Do First

■Usually requires no treatment. Adjustment of existing beta and cal-

cium blockers, clonidine, and antiarrhythmic drug regimen.

General Measures

■As above

specific therapy

Permanent Pacemaker Implantation

■If chronotropic incompetence from SA exit block causes fatigue,

worsening of congestive heart failure, syncope or near-syncope

(Type I indication).