Fetal Heart Rate Testing: Tachycardia

Introduction

• Description: Tachycardia is an increase in the baseline heart rate, generally above 160 beats/min. Mild tachycardia is generally defined as 161–180 beats/min, and severe tachycardia as greater than 180 beats/min for more than 3 minutes.

• Prevalence: Mild fetal tachycardia is observed during approximately 2% of labors.

• Predominant Age: Reproductive age.

• Genetics: No genetic pattern.

Etiology and Pathogenesis

• Causes: Maternal fever (most common), intra-amniotic infection (fetal tachycardia may occur even before maternal fever is present), fetal congenital heart disease, depressed fetal oxygenation, fetal acidosis, fetal anemia or blood loss, medication effects (atropine, terbutaline), maternal hypotension.

• Risk Factors: Maternal, fetal, or uterine infection.

Signs and Symptoms

• Increased fetal heart rate (baseline) above 160 beats/min (frequently associated with an apparent loss of beat-to-beat variability)

Diagnostic Approach