23. Passive heterotopy. Causes, forms and consequences

Passive heterotopy?

refers to the situation when an ectopic focus takes over as the pacemaker and works at a lower frequency than the SA node.

these aren’t pathological rhythms but rather compensatory mechanisms and “safety nets” that take over when the SA node cannot conduct signals properly

what are the types of passive heterotopic abnormalities?

escape beats

escape rhythms

what are the kinds of escape rhythms we can have?

junctional escape rhythms

ventricular escape rhythms

what are the most common disorders/diseases preventing the SA node from conducting its signals to the ventricles?

• 3rd degree SA-block

• 2nd degree SA-block

  • mobitz type I

  • mobitz type II

• 3 degree AV-block

• sinus arrest

complications of passive heterotropy?

The low heart rate of escape rhythms means that the cardiac output is low. The patient can experience symptoms of forward heart failure. Symptoms of cerebral hypoperfusion like fatigue, dizziness and syncope can occur.

If escape rhythm never kicks in asystole continues and the patient dies.

Stokes-Adams attack?

If the SA block or AV block occurs suddenly it might take some time for the escape rhythm to kick in. During this time there is asystole and no cardiac output, and the patient can lose consciousness. This is called a Stokes-Adams attack.

Stokes-Adams attacks can occur in other cardiac abnormalities as well.

what is an escape beat?

An escape beat originates from a heterotopic pacemaker, but unlike an extrasystole it occurs later than expected according to the current heart rate.

Escape beats may originate in the junction or the ventricles. Their morphology is similar to that of the escape rhythms.

Junctional escape rhythms?

these rhythms originate in the junction between the atria and ventricles, often in parts of the his-bundle

Junctional escape rhythm morphology on ECG?

• bradycardia (40-60/min)

• P-wave

  • can be absent, if present it is negative

  • can be before the QRS complex, if the pacemaker is in the higher part of the junction

  • can be “inside” the QRS complex, if the pacemaker is in the middle of the junction

  • can be after the QRS complex, if the pacemaker is in the lower part of the junction

• QRS complex is normal

Accelerated junctional escape rhythm?

HR can be 60-100/min

ventricular escape rhythms?

these rhythms originate in the ventricular myocardium

ventricular escape rhythms on ECG?

• Bradycardia (20 – 40/min)

• P wave does not precede QRS QRS complex is wide

• It might have similar morphology as in LBBB or RBBB

• Secondary ST-segment abnormalities