Sinus rhythm
The SA node normally acts as a pacemaker
and sets the heart rate are 60-100/min.
Sinus bradycardia
This occurs when the Sa node paces the heart at a rate of 60/min or slower
Although the cycles are widely separated
the P, QRS, and T waves are still grouped together in a normal pattern.
Sinus tachycardia
Here is the SA node sets the rate at 100 beats or more per minute.
Again because it arises from the SA node
the P, QRS and T waves are relatively normal but the rate faster.
Sinus arrhythmia
Again arises from the SA node but as an arrhythmia will be irregular.
The complexes will have the P, QRS, T waves
but it is important to note the p waves will all be identical.
The PR intervals are constant.
Generally slowing of the rate occurs during inspiration.
Wandering pacemaker
This is an irregular rhythm caused by pacing discharges
from a variety of differing atrial foci.
It is characterized by P waves of varying shape.
The PR intervals may vary.
There is a P wave for each QRS complex.
Sinus arrest
Occurs when the SA node fails to initiate atrial depolarization.
This can be caused by a number of factors
including carotid sinus massage, digoxin, and organic cardiac disease.
Atrial fibrillation
Is caused by multiple ectopic foci firing in the atria.
None of the impulses totally depolarizes the atria
and only the occasional impulse gets through the AV node to stimulate the ventricles.
Therefore, it is difficult to identify any real P Waves.
This rhythm is always irregularly irregular
and may have slow or fast ventricular response rates.
Atrial flutter
Originates in an atrial ectopic focus
but because there is only one ectopic focus discharging the P waves are all identical.
Escape and premature beats
Escape beats are the response of a focus to a pause in pacemaking activity
Premature beats are produced by an ectopic focus discharging prematurely
Atrial escape beats
When the SA node fails to produce a normal stimulus (sinus block)
the heart remains temporarily silent.
The foci in other areas will recognize the lack of pacing and become impatient.