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.

Objectives: This study sought to investigate how regional left ventricular (LV) function modifies septal motion in left bundle branch block (LBBB). Background: In LBBB the interventricular septum often has marked pre-ejection shortening, followed by immediate re-lengthening (rebound stretch). This motion, often referred to as septal flash, is associated with positive response to cardiac resynchronization therapy (CRT). Methods: In 10 anesthetized dogs we induced LBBB by radiofrequency ablation and occluded the circumflex (CX) (n=10) and left anterior descending (LAD) (n=6) coronary arteries, respectively. Myocardial dimensions were measured by sonomicrometry and myocardial work by pressure-segment length analysis. In 40 heart failure patients with LBBB, including 20 with post-infarct scar and 20 with non-ischemic cardiomyopathy, myocardial strain was measured by speckle-tracking echocardiography and myocardial work by pressurestrain analysis. Scar was assessed by cardiac magnetic resonance imaging with late gadolinium enhancement. Results: During LBBB each animal showed typical septal flash with pre-ejection shortening and rebound stretch, and reduced septal systolic shortening (p<0.01). CX occlusion caused LV lateral wall dysfunction and abolished septal flash due to loss of rebound stretch (p<0.0001). Furthermore, CX occlusion restored septal systolic shortening to similar level as before induction of LBBB and substantially improved septal work (p<0.001). LAD occlusion, however, accentuated septal flash by increasing rebound stretch (p<0.05). Consistent with the experimental findings, septal flash was absent in patients with LV lateral wall scar due to lack of rebound stretch (p<0.001), and septal systolic shortening and septal work far exceeded values in non-ischemic cardiomyopathy (p<0.0001). Septal flash was present in most patients with anteroseptal scar. Conclusions: LV lateral wall dysfunction and scar abolished septal flash and markedly improved septal function in LBBB. Therefore, function and scar in the LV lateral wall should be taken into account when using septal motion to evaluate dyssynchrony.

Aims: There are conflicting data and no consensus on how to measure acute response to cardiac resynchronization therapy (CRT). This study investigates which contractility indices are best markers of acute CRT response. Methods:In 8 anesthetized dogs with left bundle branch block we measured left ventricular (LV) pressure by micromanometer and end-diastolic (EDV) and end-systolic volumes (ESV) by sonomicrometry. Systolic function was measured as LV ejection fraction (EF), peak rate of LV pressure rise (LV dP/dt max ) and as a gold standard of contractility, LV end-systolic elastance (E es ) and volume axis intercept (V 0 ) calculated from end-systolic pressure-volume relations (ESPVR). Responses to CRT were compared to inotropic stimulation by dobutamine. Results: Both CRT and dobutamine caused reduction in ESV (P<0.01) and increase in LV dP/dt max (P<0.05). Both interventions shifted the ESPVR upwards indicating increased contractility, but CRT which reduced V 0 (P<0.01), caused no change in E es . Dobutamine markedly increased E es , which is the typical response to inotropic stimulation. Preload (EDV) was decreased (P<0.01) by CRT, and there was no change in EF. When adjusting for the reduction in preload, CRT increased EF (P=0.02) and caused a more marked increase in LV dP/dt max (P<0.01).Conclusions: Increased contractility by CRT could not be identified by E es which is a widely used reference method for contractility. Furthermore, reduction in preload by CRT attenuated improvement in contractility indices such as EF and LV dP/dt max . These results suggest that changes in LV volume may be more sensitive markers of acute CRT response than conventional contractility indices.

A miniaturized accelerometer fixed to the heart can be used for monitoring of cardiac function. However, an accelerometer cannot differentiate between acceleration caused by motion and acceleration due to gravity. The accuracy of motion measurements is therefore dependent on how well the gravity component can be estimated and filtered from the measured signal. In this study we propose a new method for estimating the gravity, based on strapdown inertial navigation, using a combined accelerometer and gyro. The gyro was used to estimate the orientation of the gravity field and thereby remove it. We compared this method with two previously proposed gravity filtering methods in three experimental models using: (1) in silico computer simulated heart motion; (2) robot mimicked heart motion; and (3) in vivo measured motion on the heart in an animal model. The new method correlated excellently with the reference (r > 0.93) and had a deviation from reference peak systolic displacement (6.3 ± 3.9 mm) below 0.2 ± 0.5 mm for the robot experiment model. The new method performed significantly better than the two previously proposed methods (p < 0.001). The results show that the proposed method using gyro can measure cardiac motion with high accuracy and performs better than existing methods for filtering the gravity component from the accelerometer signal.