Comparison of impedance cardiography with thermodilution and direct fick methods for noninvasive measurement of stroke volume and cardiac output during incremental exercise in patients with ischemic cardiomyopathy

In the last decade, an inexpensive and simple noninvasive method (i.e., transthoracic electrical bioimpedance cardiography, has been tested in healthy subjects and patients with various heart diseases for measuring stroke volume and cardiac output at rest and/or during exercise. However, the results are still controversial, especially when measurements are obtained during exercise and data on reproducibility during exercise are lacking. Twenty-five consecutive patients (20 men and 5 women, mean age 48 +/- 9 years) in sinus rhythm with documented coronary artery disease and a previous myocardial infarct were studied. Patients were divided into 2 groups. Group A had ischemic cardiomyopathy, characterized by left ventricular (LV) enlargement and LV ejection fraction depression (35 +/- 8%). Group B had normal LV dimensions and ejection fraction (62 +/- 9%). After a familiarization study, all patients underwent an exercise test with gas exchange analysis and hemodynamic measurements. Stroke volume and cardiac output were simultaneously obtained at rest and at the end of each work rate stage with 3 methods: impedance, thermodilution, and direct Fick. Group A reached a lower peak oxygen uptake (56%), peak work load (60%), and peak systolic blood pressure (69%) than group B. Cardiac output and stroke volume were significantly greater at submaximal and peak exercise in group B than in group A (p<0.0001). There were no significant differences in stroke volume and cardiac output in the 3 techniques at any matched work rate. There was no significant difference between measurements obtained by 2 experienced observers or between those obtained on 2 exercise tests performed on 2 different days. These results demonstrate that impedance cardiography is a noninvasive, simple, accurate, and reproducible method of measurement of cardiac output and stroke volume over a wide range of workloads.