FETAL EXTRASYSTOLES  

  • Fetal extrasystoles are the most common fetal arrhythmia that results in an irregular fetal heart rate (early or premature beat).
  • Benign and usually self-limiting and do not generally compromise cardiac function.
  • Extrasystoles usually last < 750 msec.
  • Premature atrial contractions are more common than those of ventricular or junctional origin (however differentiation between the three types may be difficult and often impossible).
  • Patients should be counseled to avoid stimulating drugs like caffeine, cocaine, adrenergic drugs (pseudoephedrine) and beta-mimetic tocolytics.
  • Two main types: Atrial PAC (more frequent and has a P wave). Ventricular PAC (no P wave).

 

ULTRASOUND OF PREMATURE ATRIAL CONTRACTION (PAC)



  • Either conducted or non conducted and occurs in about 1-2% of pregnancies.
  • They are usually benign and resolve spontaneously.
  • 1-2% are associated with structural cardiac defects (most commonly Ebstein’s, tricuspid valve dysplasia and cardiac tumors).
  • 1% risk for the development of supraventricular tachycardia.
  • Non-conducted:
    No aortic flow following the premature atrial systole when sampling the normal aortic outflow tract. Following the PAC there is a pause. The next beat is a sinus beat with normal atrial and ventricular contraction
  • Conducted:
    Aortic flow can be demonstrated following premature atrial systole. Following the PAC there is ventricular contraction then a pause prior to the resumption of sinus rhythm.

 

 

 

Video clip of Premature Atrial Contraction – umbilical artery waveform

 

M-mode echocardiography

Premature movement of the posterior atrial wall.

 

 

 

 

 

 

Non-conducted Premature Atrial Contraction

 

  • Compensatory pause following PAC.
  • No ventricular contraction.

 

Doppler studies

Passive E wave filling of the ventricle during ventricular systole.
Premature A wave appearing close to or superimposed on the E wave.
If the premature A wave is not obscured by in the passive filling phase, the time to the next A wave may be the same as between normal beats (compensatory pause).

 

 

 

 

ULTRASOUND OF PREMATURE VENTRICULAR CONTRACTION
  • Usually resolve spontaneously prior to delivery.
  • Those that persist into neonatal period usually resolve within 6 weeks.
  • Rarely results in more complex arrhythmias (supraventricular tachycardia in 0.4-1% of cases). Fetuses should therefore be scanned once or twice weekly.
  • Can be associated with:
    • Myocarditis (cardiomyopathy).
    • Cardiac tumors (rhabdomyomas)
    • Long QT syndrome.
    • Complete AV block with slow ventricular escape rhythm.

M-mode echocardiography

Place cursor through atrial and ventricular wall to observe the mechanical results of the electrical event.

 

Doppler studies

LV just below the AV valve annulus to assess the atrio-ventricular contraction sequence.

 

 

 

 

COMPLICATIONS

There is a 0.5% risk of supraventricular tachycardia (SVT) developing in fetuses with premature atrial extrasystole. One-week follow up is recommended to reduce the risk of the fetus developing non-immune hydrops from sustained SVT.
 

 

 

REFERENCES
  1. Copel JA, Friedman AH, Kleinman CS. Management of fetal cardiac arrhythmias. Obstet Gynecol Clin North Am 1997;24:201-211.