Multi-site-frequency electromechanocardiography for the prediction of ejection fraction and stroke volume in heart failure.

Background: Methods for stroke volume (SV) and ejection fraction (EF) measurements require the presence of qualified physicians and are not suited for continuous monitoring.

Aim: To develop an automated non-invasive method for the measurement and continuous monitoring of SV and EF.

Methods: We have designed a method for the measurement of EF and SV using multiple-site-impedance (z0) measurements, applying multiple frequencies of 5, 40 and 200 kHz whereby various segments of the human body, including volume changes within these segments, could be defined electrically. The obtained variables were used to train neuronal nets and related by multiple regression analyses to cardiac output (CO) as measured by a partial rebreathing Fick method (CO(r-fick)) or EF as measured by echocardiography (EF(echo)), respectively. A total of 129 subjects (48 with normal heart function and 81 with CHF, NYHA I-IV) were investigated.

Results: The multiply derived values of z0 and of change of impedance (dz/dt) were shown, by multiple regression analysis, to be significantly related to CO(r-fick) and to EF(echo), (total r=0.77, n=35, p<0.001, and r=0.81, n=47, p<0.001, respectively.). By training a neuronal net with the electrical data of 67 (out of 94) subjects, EF(echo) could be predicted in the remaining 27 subjects which were unknown to the neuronal net with a combined r=0.71 (p<0.001,n=27). In contrast, conventional impedance cardiography (ICG) was unable to predict either CO(r-fick) or EF(echo).

Conclusion: The new method, which we call multi-site-frequency electromechanocardiography (msf-ELMC) appears promising for the automated electrical measurement of the mechanical heart action in patients with normal and reduced cardiac function.