Inductance cardiography (thoracocardiography): a novel, noninvasive technique for monitoring left ventricular filling.

PURPOSE

Thoracocardiography noninvasively records left ventricular volume curves by an inductive plethysmographic transducer transversely encircling the chest near the xiphoid process. Amplitudes of thoracocardiographic curves track stroke volume as previously validated by thermodilution. We investigated whether thoracocardiographic curves reflect left ventricular filling.

MATERIALS AND METHODS

We studied nine men in horizontal and 30 degrees head-up position during tidal breathing and Valsalva maneuvers. The ratio of peak slope of left ventricular volume curves during early rapid filling relative to that during atrial contraction (E/A ratio) and isovolumic relaxation time (interval from aortic component of second heart sound to early rapid filling onset) were measured with thoracocardiography and compared with Doppler-echocardiographic-derived indices of transmitral flow velocity.

RESULTS

Isovolumic relaxation times estimated by the two methods agreed closely (bias = -2 ms, limits of agreement = -28 to +24 ms, 75 comparisons). E/A ratios by thoracocardiography and Doppler echocardiography were significantly correlated (R = 0.53, n = 75, P<.001), but individual values differed. Both methods provided identical trends of changes in E/A ratios with interventions in 50 of 66 (76%) comparisons.

CONCLUSIONS

Thoracocardiography reflects characteristics of left ventricular filling similar to Doppler echocardiography. Because it does not require hand-holding a transducer, thoracocardiography has the potential for continuous monitoring of mechanical cardiac performance.