Right Ventricular Volumetry by Catheter Measurement of Conductance

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Abstract
The electrical conductivity of blood is sufficiently higher than that of myocardium to make feasible the detection of cardiac volume changes hy measurement of intraventricuiar fluid conductance. An eight-electrode catheter was used to inject an aiternating current (100 μA or less, at 1500 Hz) via the two electrodes nearest the ventricular base and apex, then the resulting five voltage differences between adjacent pairs of the six intervening electrodes were measured. When current amplitude was held constant, the cross-sectional area of the ventricuiar cavity slice defined hy planes perpendicular to the catheter through the relevant pair of electrodes was inversely proportional (to the first order) to the voltage difference. Measurement of multiple segments compensated for isovolumic cavity shape changes. The technique had previously been shown to measure left ventricular volume successfully, but the geometry of the right ventricle made this measurement more problematical. Using open-chested, anesthetized greyhounds, we compared the catheter-measured right ventricuiar volume change with stroke volume as measured by a pulmonary arterial electromagnetic blood flowmeter. With optimal catheter placement, good correlation between stroke volume and catheter-measured volume changes was achieved when stroke volume was perturbed on a heat-to-heat hasis. In six data records from three dogs, involving two different means of varying stroke volume (rapid injection of blood and sinus node irritation), the correlations yielded r2 values between 0.82 and 0.98. The method detected ineffective (nonejecting) beats associated with normal-appearing QRS complexes and was thus a more reliable indicator of cardiac mechanical function than an eiectrocardiogram.