Abstract
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. 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 ( fS1). The accuracy of fS1 as an estimate of preload was evaluated using sonomicrometry measured end-diastolic volume (EDV[Formula: see text]). Standard clinical estimates of global end-diastolic volume using pulse index continuous cardiac output (PiCCO) measurements (GEDV[Formula: see text]) and pulmonary artery occlusion pressure (PAOP) were obtained for comparison. The diagnostic accuracy of identifying fluid responsiveness was analyzed for fS1, stroke volume variation (SVV[Formula: see text]), pulse pressure variation (PPV[Formula: see text]), GEDV[Formula: see text], and PAOP. Changes in fS1 correlated well to changes in EDV[Formula: see text] ( r2=0.81, 95%CI: [0.68, 0.89]), as did GEDV[Formula: see text] ( r2=0.59, 95%CI: [0.36, 0.76]) and PAOP ( r2=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 fS1, 0.72 [0.57, 0.86] for SVV[Formula: see text], and 0.63 (0.44, 0.82) for PAOP. An epicardially placed accelerometer can assess changes in preload in real-time. This novel method can facilitate continuous monitoring of the volemic status in open-heart surgery patients and help guiding fluid resuscitation.
Highlights
T EMPORARY pace leads are routinely placed on the heart during open heart surgery
We have previously demonstrated this concept of monitoring cardiac function in real time, including automatic detection of myocardial ischemia and evaluation of inotropic state [1]–[4]
The results from the receiver operating characteristics (ROC) analysis to identify the states of fluid responsiveness using fS1, SVVPiCCO, PPVPiCCO, GEDVPiCCO, pulmonary artery occlusion pressure (PAOP), and heart rate are shown in Fig. 8 including the area under the ROC curve (AUC)
Summary
Miniaturized accelerometers can be combined with temporary pace leads providing a possibility to extract more valuable clinical information of hemodynamic status of the patient without any added surgical procedure. Such information can include heart wall motion and ventricular function. It is accepted that central venous pressure poorly predicts left ventricular preload status and response to a fluid challenge [5] Despite this fact, the central venous pressure remains the routine method for continuous assessment of the volemic state in cardiac surgery. Thermodilution based methods and echocardiography are tools to guide hemodynamic optimization but can only be used intermittently
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