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ECHONOMY
Tools for Echocardiographic Calculations
Muhamed Saric, MD, PhD
New York University
 

Qp-Qs

Purpose
To calculate the ratio of pulmonic (Qp) to systemic (Qs) blood flow in atrial septal defect (ASD), ventricular septal defect (VSD) or patent ductus arteriosus (PDA) by quantitative Doppler.

Technical Hints
In ASD and VSD, flow across the right ventricular outflow tract (RVOT) represents Qp, and the flow across the left ventricular outflow tract (LVOT) represents Qs. The opposite is true for PDA.

Calculator
  LVOT RVOT

Diameter (d; in cm)

Velocity time integral (VTI; in cm)

Heart rate (beats per minute)


 		  

Answers
  LVOT RVOT

Cross-sectional area (cm2)

Stroke volume (mL)

Flow (L/min)

Qp : Qs (if ASD or VSD)

Qp : Qs (if PDA)

Formulas

LVOT or RVOT Area = (1/2 * d)2 * pi

Stroke Volume  = Outflow Tract Area *  VTI

Reference
Vargas-Barrón J, Sahn DJ, Valdes Cruz LM, Lima CO, Goldberg SJ, Grenadier E, et al. Clinical utility of two-dimensional Doppler echocardiographic techniques for estimating pulmonary to systemic blood flow ratios in children with left to right shunting atrial septal defect, ventricular septal defect or patent ductus arteriosus. J Am Coll Cardiol 1984;3:169-78.