Systolic function of the univentricular heart: comparison of the Simpson's rule with acoustic quantification

Acoustic quantification (AQ) is a new method of obtaining real-time information about systolic ventricular function. This method establishes a ;blood-tissue interface' and computes an intraventricular blood volume in real time to derive a beat to beat instantaneous ejection fraction. AQ assessment of systolic function has been reported previously in patients with normal cardiotypes and varying degrees of myocardial dysfunction.

To determine the potential utility of AQ in patients with abnormal ventricular morphology, in whom systolic function may be difficult to measure by traditional methods.

Seventeen children (nine females) ranging in age from five days to 18 years (mean 6.9 years) with univentricular left ventricle heart morphology underwent a prospective and comparative echocardiographic study of ventricular function with the use of AQ and manual planimetry (single plane Simpson's rule). Imaging was done during steady state without sedation. Routine scan planes were performed, followed by repeat scanning of the univentricle from the apical four-chamber view in the AQ mode. Subsequently, manual planimetry using Simpson's rule was performed from an online graphical analysis package to measure systolic and diastolic frames from the conventional replay images. These data were used to calculate ejection fraction using standards previously established. The results were then compared with real-time AQ results.

Tertiary care referral center.

Scan time for the combined standard and AQ imaging averaged 45 mins (range 35 to 65 mins). Measured ejection fraction by AQ and manual planimetry were 44 +/- 11% and 46 +/- 10%, respectively. Statistical analysis by repeated measures ANOVA with Bonferroni/Dunn correction (F = 0.6, df = 1,32, P = 0.44) demonstrated significant agreement between AQ and manual planimetry with an intraclass correlation coefficient of 0.93. Bland-Altman analysis was used to provide a graphic display of the clinical significance of differences in the comparison of the two methods of measurement.

These findings support the use of AQ for continuous online determination of indexes of systolic function for patients with univentricular left ventricle morphology. The variability in the morphology inherently present within this group of patients results in a wider variability of determined ejection fraction. Particular attention must be directed to the technical aspects of image acquisition and AQ application to ensure accuracy.