Diagnostic Methods - Hemodynamics and Ventricular Function

The feasibility of using continuous on-line recording of intraventricular electrical impedance to measure ventricular stroke volume was assessed in 12 patients at cardiac catheterization with a multielectrode impedance catheter and a 1.3 kHz measuring current of 4 ,A. Stroke volumes determined by electrical impedance were compared with stroke volumes determined by the thermodilution technique in 10 patients and correlated with an r value of .95. Directional changes in impedance recordings throughout the cardiac cycle were also compared with volume curves obtained from six patients by radionuclide ventriculography, and in all instances the agreement between the two volume recordings was excellent. For all patients, on-line measurements of impedance showed a beat-by-beat decrease in stroke volume with the Valsalva maneuver and the administration of amyl nitrite, as well as an immediate increase in stroke volume in the contraction following an extra-systolic beat. Similar directional changes in stroke volume were recorded in both left and right ventricles. Left ventricular pressure-volume relationships were assessed with simultaneous left ventricular pressure recordings and volume signals recorded from the impedance catheter to determine if impedance measurements of volume can be used clinically. Pressure-volume diagrams were subsequently plotted, and for all patients these diagrams showed characteristic isovolumetric contraction and relaxation phases as well as typical ejection and filling periods. Moreover, beat-by-beat sequential pressure-volume diagrams constructed for patients during the administration of amyl nitrite revealed a linear end-systolic pressure-volume relationship. We conclude that measurement of intracavitary electrical impedance can be used to monitor instantaneous changes in stroke volume in patients and may be helpful in the construction of pressure-volume diagrams and the assessment of left ventricular end-systolic pressure-volume relationships. Circulation 69, No. 4, 703-710, 1984. THE CONTINUOUS on-line recording of intraventricular electrical impedance has been proposed as a means of instantaneously determining stroke volume and cardiac output.'l Previous studies of animals4 have found a high correlation between intracardiac impedance measurements and stroke volume determined by standard techniques, but there have been only preliminary reports on the use of impedance meaFrom the Charles A. Dana Research Institute and the Harvard-Thorndike Laboratory of the Beth Israel Hospital, Departments of Medicine (Cardiovascular Division) and Radiology, Beth Israel Hospital and Harvard Medical School, Boston. Address for correspondence: Raymond G. McKay, M.D., Cardiovascular Division, Beth Israel Hospital, 330 Brookline Ave., Boston, MA 02215. Received Aug. 3, 1983; revision accepted Dec. 22, 1983. Dr. McKay is 1983-1984 Merck Fellow of the American College of Cardiology. Presented in part at the Annual Scientific Sessions of the American Federation of Clinical Research in Washington. D.C., in April, 1983. Vol. 69, No. 4, April 1984 surements in humans.56 The purpose of our study was to assess the feasibility of monitoring instantaneous stroke volume with an impedance catheter technique in patients studied at cardiac catheterization. The validity of changes of stroke volume measured by the impedance catheter was assessed by comparing impedance recordings with simultaneously measured stroke volumes determined by thermodilution. The ability of the impedance catheter to measure relative changes in volume throughout the cardiac cycle was also assessed by comparing volume signals recorded from the impedance catheter with volume curves obtained simultaneously by radionuclide ventriculography. Beat-tobeat changes in stroke volume induced by the Valsalva maneuver, administration of amyl nitrite, and stimulation of premature ventricular impulses were assessed by impedance measurements in all patients. Moreover, 703 by gest on N ovem er 2, 2017 http://ciajournals.org/ D ow nladed from