Noninvasive Measurement of CO Using Impedance Cardiography in Patients With CHD

This study will test the capability of a non-invasive instrument (the PhysioFlow impedance cardiography instrument) to measure cardiac output in patients with congenital heart disease (CHD). This instrument works by placing electrodes on the skin of a patient and measuring electrical impedance through the chest, which is proportional to blood volume and blood flow at any given time. The instrument has been validated in patients with structurally normal hearts, but in the only two studies using it for patients with CHD, it was deemed too inaccurate for clinical use. The manufacturer of the device would require access to data on the patients in order to improve its accuracy, and that has not been feasible thus far. This study would begin by comparing cardiac output based on the PhysioFlow monitor to standard techniques, then after possible changes to the instrument to enhance accuracy, would test the instrument again in the same way.