Absence of electrical activity for a period of time. Caused by one of the following mechanisms:
- Sinus Arrest - SA node failing to fire so no impulse is conducted.
- Sinus Exit Block - SA node fires but the tissue surrounding the SA node "smothers" the impulse and is not conducted.
Sinus Pause, Arrest
Rhythm: The underlying rhythm is regular. The pause will cause the overall rhythm to be irregular. After pause rhythm will return to regular.
Rate: Underlying may be normal, but the pause will cause it to decrease. The more pauses or the longer they are will slow the overall rate.
P waves: P wave is absent during the pause. Underlying: 1 per QRS, all the same size, shape and direction. Positive in Lead II.
PR Interval: Absent during the pause. Underlying: 0.12 - 0.20 seconds and constant.
QRS Complex: Absent during the pause. Underlying <0.12 seconds.
Common Causes: myocarditis, MI, hyperkalemia, ischemia, heart failure, medications (beta-blockers, calcium channel blockers), increased vagal tone, sick sinus syndrome.
Hemodynamic Effect: Dependent on length, frequency and cardiac output. Some may be asymptomatic. May have signs/symptoms of drop in cardiac output (weakness, dizziness, lightheadedness, syncope).