EKG - Escapes and Extrasystoles

Question 1

The average automatic rate of the firing from the SA Node is _____

Answer 1

70-80 bpm

Question 2

The automatic rate of the surrounding Atrial tissue is about _____

Answer 2

60-80 bpm

Question 3

The automatic rate of the AV bundle (junction) is about _____

Answer 3

40-60 bpm

Question 4

The automatic rate of the Ventricular tissue is about ____

Answer 4

20-40 (15-40) bpm

Question 5

Escape Rhythms

Answer 5

If the pacemaker cells stop pacing the heart completely, an escape focus will start to pace the heart at its inherent rate
We call these the Escape Rhythms:
○ Atrial Escape Rhythm
○ Junctional Escape Rhythm
○ Ventricular Escape Rhythm

Question 6

Atrial Escape Rhythm

Answer 6

With SA node arrest, an Atrial focus quickly escapes overdrive suppression and
becomes the dominant pacemaker.
○ Inherent rate of 60-80 bpm

Question 7

Atrial escape rhythm EKG findings

Answer 7

P Waves are present but are
generally not identical to the P
Waves seen with sinus rhythm

Question 8

Junctional Escape Rhythm

Answer 8

● In the absence of regular pacing stimuli from above (SA node or Atria), an
automaticity focus in the AV bundle may escape overdrive suppression to become
the active pacemaker.
○ Inherent rate of 40-60 bpm

Question 9

EKG findings of junctional escape rhythms

Answer 9

● This conducts mainly to the ventricles
producing a (generally) narrow QRS.
● The pacer sends a retrograde impulse
into the atria as well, which may cause
a retrograde, inverted P wave.
○ This inverted P wave may be before,
in, or after the QRS

Question 10

Ventricular Escape Rhythm

Answer 10

● When ventricular purkinje fibers are not regularly stimulated by pacers
above (SA, Atrial, or junctional), ventricular pacers escape overdrive
suppression and become the active pacemaker.
○ Inherent rate of 15-40 bpm

Question 11

Ventricular Escape Rhythm EKG findings

Answer 11

● Can occur during complete AV
blocks, even if the SA node is firing
(as in the example to the right).
● Notice how the QRS complexes are
wide, which is characteristic of
ventricular rhythms

Question 12

Extrasystoles

Answer 12

Rather than occur secondary to a paused pacemaker like you see with
Escape Beats and Rhythms, Premature Contractions (Extrasystoles) occur
secondary to an irritable focus and happen before another beat is expected
(hence the name, compared to Escapes).

Question 13

Premature Contractions (extrasystoles) Include:

Answer 13

○ Premature Atrial Contractions
○ Premature Junctional Contractions
○ Premature Ventricular Contractions

Question 14

Premature Atrial Contractions

Answer 14

PACs occur when an irritable atrial focus gets excited and fires before the SA
node is scheduled to fire.
○ A P Wave is generally visible, but may look different than a normal P
Wave from the SA node origin.

Question 15

_____ generally resets the normal SA node pacing (not always) because the
depolarization of the atria also depolarizes the SA node

Answer 15

PACs

Question 16

Premature Junctional Contractions

Answer 16

● Premature Junctional Contractions occur when an irritable focus in the AV
bundle fires before the SA node is scheduled to fire.
● A P wave may be visible, and if so, is usually inverted and may be before, during,
or after the QRS. There may be no visible P wave

Question 17

_____ can sometimes reset the normal SA node pacing because the depolarization wave moving up the atria might also depolarizes the SA node.

Answer 17

PJCs

Question 18

Premature Ventricular Contractions

Answer 18

● Premature Ventricular Contractions occur when an irritable ventricular focus
fires before the SA node is scheduled to fire.
○ The QRS is wide and usually there is no P wave (the normal SA node P
wave is lost in the wide QRS)

Question 19

Bigeminy and Trigeminy

Answer 19

● If the ratio is one normal sinus beat to one PVC, the rhythm is a Bigeminy.
● If the ratio is two normal sinus beats to one PVC, it is a Trigeminy.