Introduction .– Stroke volume (SV-ETT) is hitherto evaluated by transthoracical Doppler (TTE) as: (circular) cross sectional area(CSAO) × velocity time integral (VTI). Cardiac output (CO) can thereof be derived as: SV-ETT × heart frequency (HF). Based on previous transesophageal Doppler studies showing that the aortic valve-opening surface is in fact triangular, we developed a modified triangular valve model of the aortic valve-opening surface (CSAΔ), for transthoracic SV calculation referring it to bioimpedance measurement of SV (SV-Bio) as another non-invasive method in our paediatric ICU.

Method .– In 24 newborns after arterial switch for transposition of the great arteries, CSAO was measured in the long axis view. CSAΔ was measured in the short axis view by measuring two orthogonal aortic valve diameters at the leaflet level, then calculating their average. CSAO/CSAΔ were then multiplied by VTI in the five-chamber view with the sample at the same level to obtain SV-ETT and then compared to SV-Bio measured at the same time.

Results .– Mean SV in the CSAO model was 6.9 ± 2.1 mL compared to 3.4 ± 1.1 mL in the CSAΔ model ( P < 0.0001). Mean SV-Bio was 3.8 ± 1.3 mL. Correlation between SV-ETT/SV-Bio was good ( r = 0.88) in both models with regression linear fits of 1.604 + 1.472x for CSAO and 0.7794 + 0.7261x for CSAΔ. Bias of CSAO was + 3.4 mL whereas bias of CSAΔ was −0.3 mL. Corresponding findings for CO.

Conclusion .– Compared to Bioimpedance as another non-invasive technique for the evaluation of stroke volume and cardiac output in the paediatric cardiac ICU, the new transthoracic triangular aortic Doppler model reflects “the real” stroke volume and thus cardiac output better than the hitherto used cross sectional area model. This may be of importance in paediatric and neonatological ICU’s where echocardiography is the only technique available for the evaluation of cardiac output.