Continuous Estimation of Acute Changes in Preload Using Epicardially Attached Accelerometers

Abstract

<italic>Objective:</italic> 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. <italic>Methods:</italic> 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 (<inline-formula><tex-math notation= LaTeX >$f_{S1}$</tex-math></inline-formula>). The accuracy of <inline-formula><tex-math notation= LaTeX >$f_{S1}$</tex-math></inline-formula> as an estimate of preload was evaluated using sonomicrometry measured end-diastolic volume (EDV<inline-formula><tex-math notation= LaTeX >$_{\\text{SONO}}$</tex-math></inline-formula>). Standard clinical estimates of global end-diastolic volume using pulse index continuous cardiac output (PiCCO) measurements (GEDV<inline-formula><tex-math notation= LaTeX >$_{\\text{PiCCO}}$</tex-math></inline-formula>) and pulmonary artery occlusion pressure (PAOP) were obtained for comparison. The diagnostic accuracy of identifying fluid responsiveness was analyzed for <inline-formula><tex-math notation= LaTeX >$f_{S1}$</tex-math></inline-formula>, stroke volume variation (SVV<inline-formula><tex-math notation= LaTeX >$_{\\text{PiCCO}}$</tex-math></inline-formula>), pulse pressure variation (PPV<inline-formula><tex-math notation= LaTeX >$_{\\text{PiCCO}}$</tex-math></inline-formula>), GEDV<inline-formula><tex-math notation= LaTeX >$_{\\text{PiCCO}}$</tex-math></inline-formula>, and PAOP. <italic>Results:</italic> Changes in <inline-formula><tex-math notation= LaTeX >$f_{S1}$</tex-math></inline-formula> correlated well to changes in EDV<inline-formula><tex-math notation= LaTeX >$_{\\text{SONO}}$</tex-math></inline-formula> (<inline-formula><tex-math notation= LaTeX >$r^2=0.81$</tex-math></inline-formula>, 95%CI: [0.68, 0.89]), as did GEDV<inline-formula><tex-math notation= LaTeX >$_{\\text{PiCCO}}$</tex-math></inline-formula> (<inline-formula><tex-math notation= LaTeX >$r^2=0.59$</tex-math></inline-formula>, 95%CI: [0.36, 0.76]) and PAOP (<inline-formula><tex-math notation= LaTeX >$r^2=0.36$</tex-math></inline-formula>, 95%CI: [0.01, 0.73]). The diagnostic accuracy [95%CI] in identifying fluid responsiveness was 0.79 [0.66, 0.94] for <inline-formula><tex-math notation= LaTeX >$f_{S1}$</tex-math></inline-formula>, 0.72 [0.57, 0.86] for SVV<inline-formula><tex-math notation= LaTeX >$_{\\text{PiCCO}}$</tex-math></inline-formula>, and 0.63 (0.44, 0.82) for PAOP. <italic>Conclusion:</italic> An epicardially placed accelerometer can assess changes in preload in real-time. <italic>Significance:</italic> This novel method can facilitate continuous monitoring of the volemic status in open-heart surgery patients and help guiding fluid resuscitation.