Electrical Cardiometry (EC)
Electrical Cardiometry is a method for the non-invasive determination of stroke volume (SV), cardiac output (CO), and other hemodynamic parameters in adults, children, and neonates. Electrical Cardiometry has been validated against “gold standard” methods such as thermodilution and is a proprietary method trademarked by Cardiotronic, Inc.
How it works
The placement of four skin sensors on the neck and left side of the thorax allow for the continuous measurement of the changes of electrical conductivity within the thorax. By sending a low amplitude, high frequency electrical current through the thorax, the resistance that the current faces (due to several factors) is measured. Through advanced filtering techniques, Electrical Cardiometry (EC) is able to isolate the changes in conductivity created by the circulatory system. One significant phenomenon, which is picked up is associated with the blood in the aorta and its change in conductivity when subjected to pulsatile blood flow. This occurrence is mainly due to the change in orientation of the erythrocytes (RBCs).
During diastole, the RBCs in the aorta assume a random orientation, which causes the electrical current to meet more resistance, resulting in a lower measure of conductivity. During systole, pulsatile flow causes the RBCs to align parallel to both the blood flow and electrical current, resulting in a higher conductivity state. By analyzing the rate of change in conductivity before and after aortic valve opening, or in other words, how fast the RBCs are aligning, EC technology derives the peak aortic acceleration of blood and the left ventricular ejection time (flow time). The velocity of the blood flow is derived from the peak aortic acceleration and used within our patented algorithm to derive stroke volume.
Electrical Cardiometry vs. Traditional Bioimpedance (Impedance Cardiography)
Because of similar setup, Electrical Cardiometry (EC) is often confused with the traditional bioimpedance technology most commonly known as Impedance Cardiography (ICG).
Though both methods use sensors placed on the thorax, traditional bioimpedance or ICG methods rely on the assumption of periodical volumetric changes in the aorta to determine stroke volume (SV) and cardiac output (CO). In short, ICG attributes the steep increase in the conductivity waveform (dZ) to a volumetric expansion of the aorta during systole, while EC contributes the increase in conductivity to the orientation change of the RBCs to determine the velocity of the blood flow. Thus, the algorithm and evident accuracy of EC compared to ICG is what separates the two methods. EC has proven as an accurate method for measuring cardiac output in a wide spectrum of patient conditions and patient populations including neonates and children, while ICG is limited to relatively healthy adults.
From Theory to our Patented Algorithm
Once the skin sensors are placed on the patient, the user must input the weight and height of the patient (neontate, child or adult) and the EC monitor does the rest.
The EC monitors measure the changes in conductivity due to the alignment of RBCs before and after aortic valve opening, and uses this to derive the peak aortic accleration (ACC) and the left ventricle ejection time (LVET).