Measuring Stroke Volume: Impedance Cardiography vs Phase-Contrast Magnetic Resonance Imaging

BACKGROUND: Determination of cardiac output requires measurement of both heart rate and stroke volume. Techniques for measuring heart rate are widespread, and 1 technique for bedside monitoring of stroke volume is electrical impedance cardiography. OBJECTIVES: To determine the accuracy and precision of stroke volume measured via impedance cardiography and whether the technique can be used to detect trends. METHODS: Eleven healthy research participants (22-52 years old) were examined with simultaneous impedance cardiography and phase-contrast magnetic resonance imaging at rest and during exercise. Bland-Altman analysis with repeated-measures correction was used to compare stroke volumes determined with the 2 methods. The suitability of impedance cardiography for detecting trends in stroke volume was analyzed by using the Critchley radial limits of agreement method. RESULTS: < .001). Corresponding 95% limits of agreement were 64 mL, a 73% overestimate or underestimate of stroke volume at rest. Critchley radial limits of agreement indicated poor concordance of stroke-volume trends. CONCLUSIONS: Impedance cardiography had low accuracy and precision in measuring absolute stroke volume and was a poor detector of stroke-volume trends.