Transcardiac conductance for continuous measurement of left ventricular volume: validation vs. angiography in patients

Objective. To test the feasibility of the transcardiac conductance (TCC) method for continuous, on-line measurement of absolute left ventricular (LV) volume and to validate the method by comparison with biplane angiography. Design and setting. Prospective clinical feasibility and validation study in a cardiac catheterization laboratory in a university hospital. Patients and interventions. Ten patients scheduled for electrophysiological studies (n=5), percutaneous transluminal coronary angioplasty (n=3), and left- and right-sided cardiac catheterization (n=2) were enrolled in the feasibility study. Twenty patients scheduled for diagnostic left- and right-sided cardiac catheterization were included in the validation study. The latter were studied at baseline and during right atrial pacing 30 beats/min above baseline. Measurements and results. In the feasibility study satisfactory ventricular volume signals were obtained by TCC in eight of ten patients. In the validation study calibration factors (alpha and V-p) for TCC were obtained by thermodilution and hypertonic saline dilution, to yield absolute LV volume. Results indicate a good linear correlation with angiographic volume (R-2=0.78) with an intercept of 10+/-15 ml, not significantly different from 0 and slope of 1.17+/-0.16. Mean calibration factors alpha and V-p were 0.017+/-0.002 (interpatient variability 0.018) and 75.1+/-0.4 ml (interpatient variability 35.4 ml), respectively. Conclusions. The TCC method provides on-line and continuous LV volume signals in patients in a relatively noninvasive way. Calibration yields absolute LV volumes with a good linear correlation in comparison to biplane LV angiography. TCC appears to be a promising methodology for monitoring absolute LV volume in the ICU.