When sinus node fails to produce an impulse, another focus in the heart takesover the duty

      and the ensueing rhyhtm is now called
escape rhythm.

  Many different foci in the heart can produce regular impulses to depolarize the ventricles in order to

      sustain a stable cardiac rhythm.

  The focus with the highest frequency will be the dominant focus.

  In a normal heart, sinus node is the dominant pacemaker and sinus rhythm is the dominant rhythm since

      sinus node produces impulses with the highest frequency.

  The disease process resulting in escape rhythm is more important than the escape rhythm itself.



Escape rhythms

  Atrial escape rhythm: Every P wave is followed by a QRS complex but the shape of the P wave is different

      than that of the sinus beat. QRS complex is narrow and the heart rate is generally
> 60/minute.

 
Atrioventricular (AV) nodal rhythm: No P wave is expected to preceed the QRS complex.

      QRS complexes are narrow. Heart rate is between
40-60/minute.

 
Ventricular escape rhythm (idioventricular rhythm): Since QRS complexes originate from the ventricles,

      they are wide and there are no preceding P waves. Heart rate is
25-40/minute.





ECG 1. Above is the Holter tracing from a patient with Sick Sinus Syndrome (SSS). There is
nodal escape rhythm . When
P waves originating from the sinus node
does not come at the expected time, nodal rhythm ensues with QRS complexes
lacking
P waves before the QRS complexes .
984 miliseconds (time interval between two sinus beats) < 1375 miliseconds (time interval between two nodal beats):
Nodal escape rhythm is (should be) slower than the sinus rhythm.

Click here for a more detailed ECG





ECG 2. The ECG above belongs to a 9 years-old girl who had previously undergone closure of the atrial septal defect (ASD).
The first four beats from the left are sinus beats .
When the sinus node fails to give impulse in the expected time period
the ectopic atrial focus takes over: atrial escape rhythm .

Pediatric Cardiologist Dr. Mahmut Gokdemir has donated the above ECG to our website.

Click here for a more detailed ECG