Continuous Estimation of Acute Changes in Preload Using Epicardially Attached Accelerometers

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.