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 measu ring stroke volume and cardiac output at rest and/or during exercise. However, the results are still controversial, especially when measurem ents are obtained during exercise and data on reproducibility during e xercise are lacking. Twenty-five consecutive patients (20 men and 5 wo men, mean age 48 +/- 9 years) in sinus rhythm with documented coronary artery disease and a previous myocardial infarct were studied. Patien ts were divided into 2 groups. Group A had ischemic cardiomyopathy, ch aracterized by left ventricular (LV) enlargement and LV ejection fract ion depression (35 +/- 8%). Group B had normal LV dimensions and eject ion 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 obt ained at rest and at the end of each work rate stage with 3 methods: i mpedance, thermodilution, and direct Fick. Group A reached a lower pea k oxygen uptake (56%), peak work load (60%), and peak systolic blood p ressure (69%) than group B. Cardiac output and stroke volume were sign ificantly greater at submaximal and peak exercise in group B than in g roup A (p<0.0001). There were no significant differences in stroke vol ume and cardiac output in the 3 techniques at any matched work rate. T here was no significant difference between measurements obtained by 2 experienced observers or between those obtained on 2 exercise tests pe rformed on 2 different days. These results demonstrate that impedance cardiography is a noninvasive, simple, accurate, and reproducible meth od of measurement of cardiac output and stroke volume over a wide rang e of workloads.