Chapter 5

Remember…  If sinus node loses its pacemaking role for whatever reason, the next fastest site will take over.  Rhythms that start in the atria are called atrial arrhythmias.  For some reason, the atria become faster, either by irritability or escape.

What would change on the EKG?  Unusual P wave, since atrial depolarization is seen on the EKG as a P wave.  It can be flattened, notched, peaked, sawtoothed, or even diphasic (it goes first above the isoelectric line and then dips below it).  There are 5 atrial arrhythmias to discuss.

Different morphology of P waves:

(1) Wandering Pacemaker  The pacemaker will be the SA node, the atria, and the AV junction.  When this occurs, the P waves are interspersed sinus and atrial beats.  Sometimes, the pacemaker site will drop even lower than the AV junction, causing inverted or absent P waves.

 Because the pacemaker site may originate in different areas, the PRI will vary, and an irregular R-R pattern.  PRI will still be less than.20 seconds.

Rules for Wandering Pacemaker  Regularity: slightly irregular  Rate: usually normal, bpm  P wave: morphology changes from one complex to the next  PRI: less than.20 seconds; may vary  QRS: less than.12 seconds

Ectopics  It is really a single beat.  Originates from an ectopic focus (a site outside of the SA node).  Usually the cause is that a site became irritable and overrode the SA node.

How can we tell if it is an irritability or an escape beat?  Irritable beat will be earlier  Escape beat will be later, because it will only occur after the normal beat should have been present.

(2)Premature Atrial Contraction  An atrial ectopic that is caused by irritability  PAC  The P wave which initiated the PAC might be “lost” in the previous T wave  Any PAC with QRS >.12 seconds is a “PAC with a Wide QRS”

Rules of PAC’s  Regularity: will usually be regular except for the PAC, but depends on underlying rhythm  Rate: usualy normal; depends on underlying rhythm  P wave: flattened, notched, lost in the T wave  PRI: seconds; can exceed.20 seconds  QRS: less than.12 seconds

Atrial Tachycardia  When a single focus in the atria becomes so irritable that it begins to fire very regularly and overrides the SA node for the entire rhythm.  This is called …AT.  Same as PAC except that it is an entire rhythm rather than one beat.

Cont. Atrial Tachy.  Usually very rapid, with a rate range between bpm.  Because it is so fast, P waves are usually hidden in the previous T wave.  If you see a very regular supraventricular rhythm that has atrial P waves and a rate of bpm, you should consider it to be AT.

Rule for Atrial Tachycardia  R-R constant; rhythm is regular.  Atrial and ventricular rates are regular; rate bpm.  One P wave for every QRS complex; can be hidden in T waves, flattened, or notched.  PRI between seconds and constant.  QRS complex less than.12 seconds.

Atrial Flutter  Atria are firing more than 250 bpm.  Sawtooth appearance (fluttering or F waves).  Range between bpm.  So what is the problem with this fast rate?

The problem with atrial flutter…  The ventricles don’t have enough time to fill with blood between each beat.  The ventricles continue to pump, but don’t have adequate volume to pump out into the body.  The AV node tries to block some of the impulses to the ventricles, and this causes the sawtooth pattern of P waves. There is not a QRS for each P wave.

See the sawtooth pattern?

Rules for atrial flutter  Atrial rhythm is regular. Ventricular may be irregular (irregular R-R intervals).  Atrial rate bpm.  Sawtooth appearance of P wave.  PRI is not measured.  QRS <.12 seconds, can be difficult.

Atrial Fibrillation  Atria are no longer beating, they are quivering ineffectively (fibrillating).  No discernible P waves.  Atrial rate is > 350 bpm.  Grossly irregular R-R interval, very chaotic.  Normal QRS, because ventricles still fire, so <.12 seconds.

A. Fib with a controlled vent. Response:  Ventricular rate is less than 100 bpm.  Usually patient not symptomatic.

A. Fib with a rapid vent. Response:  Ventricular rate > 100 bpm.  Patient usually symptomatic.

Rules for Atrial Fibrillation  Grossly irregular  Atrial rate > 350 bpm; ventricular varies.  No discernible P waves (f waves).  PRI not measurable.  QRS <.12 seconds.

PRACTICE, PRACTICE, PRACTICE!!!  Practice strips pages