Objective: A miniaturized accelerometer can be incorporated in temporary pacemaker leads which are routinely attached to the epicardium during cardiac surgery and provide continuous monitoring of cardiac motion during and following surgery. We tested if such a sensor could be used to assess volume status, which is essential in hemodynamically unstable patients. Methods: An accelerometer was attached to the epicardium of 9 pigs and recordings performed during baseline, fluid loading, and phlebotomy in a closed chest condition. Alterations in left ventricular (LV) preload alter myocardial tension which affects the frequency of myocardial acceleration associated with the first heart sound (f _S1 ). The accuracy of f _S1 as an estimate of preload was evaluated using sonomicrometry measured end-diastolic volume (EDV _SONO ). Standard clinical estimates of global end-diastolic volume using pulse index continuous cardiac output (PiCCO) measurements (GEDV _PiCCO ) and pulmonary artery occlusion pressure (PAOP) were obtained for comparison. The diagnostic accuracy of identifying fluid responsiveness was analyzed for f _S1 , stroke volume variation (SVV _PiCCO ), pulse pressure variation (PPV _PiCCO ), GEDV _PiCCO , and PAOP. Results: Changes in f _S1 correlated well to changes in EDV _SONO (r ² =0.81, 95%CI: [0.68, 0.89]), as did GEDV _PiCCO (r ² =0.59, 95%CI: [0.36, 0.76]) and PAOP (r ² =0.36, 95%CI: [0.01, 0.73]). The diagnostic accuracy [95%CI] in identifying fluid responsiveness was 0.79 [0.66, 0.94] for f _S1 , 0.72 [0.57, 0.86] for SVV _PiCCO , and 0.63 (0.44, 0.82) for PAOP. Conclusion: An epicardially placed accelerometer can assess changes in preload in real-time. Significance: This novel method can facilitate continuous monitoring of the volemic status in open-heart surgery patients and help guiding fluid resuscitation.

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