The principle of the Conductance Catheter Technique is based on the measurement of electrical conductance between ring electrodes on a cardiac catheter positioned in the left ventricle with its tip in the apex. The system makes up to seven separate cross-sectional measurements of volume and the software calculates the total volume of the chamber. Pressure changes within the left ventricle are measured and combined with the volume data to form real-time pressure-volume loops (PV-loops) over successive cardiac cycles.

Measurement of the volumes of the cardiac chambers plays an essential role in the diagnosis of cardiac diseases. Continuous, on line, measurement of left ventricular volume in combination with simultaneous left ventricular pressure gives detailed insight into the pump function and performance of the heart. By plotting these two signals against each other in the pressure-volume plane, the resultant loops dynamically display the filling, contracting, ejecting and relaxation phase of the working ventricle.

From the pressure-volume loop, parameters can be directly determined which objectively quantify many aspects of cardiac function and performance. Cardiac performance is determined not only by intrinsic myocardial factors (contractility) but also by external factors such as pre-load (filling volume), after-load (resistance against which the heart ejects) and heart rate. In cardiac disease, generally, compensation mechanisms are invoked to maintain cardiac output despite decreased intrinsic cardiac function.

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