PR Interval

Can be scanned on screening schedule.

• Indications for P-R interval:
  • +SSA and/or +SSB.
  • Fetal bradycardia, suspected heart block.
• Performed between 16 and 34 weeks.
  • 16-24 weeks = weekly.
  • 24-34 weeks = every 2 weeks.
• Normal range is 90-150ms.
• Prolonged P-R Interval (over 150ms) indicates current or developing heart block.
• Procedure:
  • Obtain tri-phasic waveform by placing Doppler gate inside LV, adjacent to Mitral valve and Aortic valve simultaneously. This location will demonstrate LV filling and emptying.
  • Use Time-Slope calipers to measure the horizontal distance from the onset of atrial systole (mitral inflow) to the onset of ventricular systole (LVOT outflow).