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Sensitive methods for the early detection of myocardial dysfunction are still needed, as ischemia is a leading cause of decreased ventricular function during and after heart surgery. The aim of this study was to test the hypothesis that low-grade ischemia could be detected quantitatively by a miniaturized epicardial ultrasound transducer (Ø = 3 mm), allowing continuous monitoring.In 10 pigs, transducers were positioned in the left anterior descending and circumflex coronary artery areas. Left ventricular pressure was obtained by a micromanometer. The left internal mammary artery was grafted to the left anterior descending coronary artery, which was occluded proximal to the anastomosis. Left internal mammary artery flow was stepwise reduced by 25%, 50%, and 75% for 18 min each. From the transducers, M-mode traces were obtained, allowing continuous tissue velocity traces and displacement measurements. Regional work was assessed as left ventricular pressure-displacement loop area. Tissue lactate measured from intramyocardial microdialysis was used as reference method to detect ischemia.All steps of coronary flow reduction demonstrated reduced peak systolic velocity (P.05) and regional work (P.01).The decreases in peak systolic velocity and regional work were closely related to the degree of ischemia, demonstrated by their correlations with lactate (R = -0.74, P.01, and R = -0.64, P.01, respectively). The circumflex coronary artery area was not affected by any of the interventions.The epicardially attached miniaturized ultrasound transducer allowed the precise detection of different levels of coronary flow reduction. The results also showed a quantitative and linear relationship among coronary flow, ischemia, and myocardial function. Thus, the ultrasound transducer has the potential to improve the monitoring of myocardial ischemia and to detect graft failure during and after heart surgery.

The aim of this study was to investigate experimental conditions for efficient and controlled in vivo liver tissue ablation by magnetic resonance (MR)-guided high-intensity focused ultrasound (HIFU) in a swine model, with the ultimate goal of improving clinical treatment outcome. Histological changes were examined both acutely (four animals) and 1 wk after treatment (five animals). Effects of acoustic power and multiple sonication cycles were investigated. There was good correlation between target size and observed ablation size by thermal dose calculation, post-procedural MR imaging and histopathology, when temperature at the focal point was kept below 90°C. Structural histopathology investigations revealed tissue thermal fixation in ablated regions. In the presence of cavitation, mechanical tissue destruction occurred, resulting in an ablation larger than the target. Complete extra-corporeal MR-guided HIFU ablation in the liver is feasible using high acoustic power. Nearby large vessels were preserved, which makes MR-guided HIFU promising for the ablation of liver tumors adjacent to large veins.

A miniaturized accelerometer sensor attached to the heart may be applied for monitoring cardiac motion. Proper understanding of the sensor measurements is required for successful development of algorithms to process the signal and extract clinical information. In vivo testing of such sensors is limited by the invasive nature of the procedure. In this study we have developed a mathematical simulation model of an accelerometer attached to the heart so that testing initially may be performed on realistic, simulated measurements. Previously recorded cardiac motion by sonomicrometric crystals was used as input to the model. The three dimensional motion of a crystal attached to the heart served as the simulated motion of the accelerometer, providing the translational acceleration components. A component of gravity is also measured by the accelerometer and fused with the translational acceleration. The component of gravity along an accelerometer axis varies when the axis direction slightly rotates as the accelerometer moves during the cardiac cycle. This time-varying gravity component has substantial effects on the accelerometer measurements and was included in the simulation model by converting the motion to prolate spheroidal coordinates where the axis rotation could be found. The simulated accelerometer signal was filtered and integrated to velocity and displacement. The resulting simulated motion was consistent with previous accelerometer recordings during normal and ischemic conditions as well as for alterations of accelerometer orientation and patient positions. This suggests that the model could potentially be useful in future testing of algorithms to filter and process accelerometer measurements.

The microvascular oxygen saturation (SmvO(2)) in the skin and tongue (sublingual mucosa) in pigs (n=6) was characterised using diffuse reflectance spectroscopy (DRS). The correlation between arterial oxygen saturation (SaO(2)) and SmvO(2) as well as the spatial heterogeneity of SmvO(2) was examined during hypoxia. DRS uses shallow-penetrating visible light to assess microvascular oxygen saturation (SmvO(2)) in superficial tissue. Hypoxia was induced by gradual reduction in ventilation or reduction of the inspiratory oxygen fraction. The spatial heterogeneity of SmvO(2) was expressed as the coefficient of variation (CV) of repeated SmvO(2) measurements. Baseline SmvO(2) before interventions was 20.2% (10.3%-38.1%, median with range) in groin skin, 32.9% (13.0%-49.3%) in the ear and 42.2% (32.1%-51.5%) in the tongue. SmvO(2) in the groin was significantly lower than venous oxygen saturation (SvO(2)) (p

ObjectiveMyocardial ischemia may be detected with epicardial accelerometers. We developed and tested automated algorithms for real-time detection of myocardial ischemia by accelerometer measurements in both experimental and clinical settings.MethodsIn 10 pigs, an accelerometer was fixed to the epicardium in the area perfused by left anterior descending coronary artery. Acceleration and electrocardiogram were simultaneously recorded, and the QRS complex was automatically detected for exact timing of systole. Peak circumferential velocity and displacement were automatically calculated from epicardial acceleration signal within 150 milliseconds after peak R on electrocardiography. Global myocardial function was reduced by esmolol infusion, and regional function was altered by temporary left anterior descending occlusion. Automated ischemia detection analyses were tested in 7 patients during off-pump coronary artery bypass grafting. Left anterior descending coronary artery was occluded for 3 minutes before grafting. In both models, echocardiographic myocardial circumferential strain was used to confirm ischemia.ResultsSystolic displacement changed most during left anterior descending occlusion. Negative displacement during ischemia was found in pigs (11.5 ± 2.3 to −1.2 ± 2.8 mm, P < .01); regional hypokinesia was found in clinical study (12.8 ± 8.1 to 3.5 ± 4.4 mm, P < .01). Ischemia was confirmed by echocardiography in both settings. Esmolol infusion induced smaller changes in automated accelerometer measurements than did left anterior descending occlusion (P < .01).ConclusionsAutomatic real-time detection of myocardial ischemia with epicardial accelerometer was feasible. Automated ischemia detection analysis may be used for continuous monitoring of myocardial ischemia during cardiac surgery.

We describe a novel technique for continuous real-time assessment of myocardial ischaemia using a three-axis accelerometer.In 14 anaesthetized open-chest pigs, two accelerometers were sutured on the left ventricle (LV) surface in the perfusion areas of the left anterior descending (LAD) and circumflex (CX) arteries. Acceleration was measured in the longitudinal, circumferential, and radial directions, and the corresponding epicardial velocities were calculated. Regional LV dysfunction was induced by LAD occlusion for 60 s. Global LV function was altered by nitroprusside, epinephrine, esmolol, and fluid loading. Epicardial velocities were compared with strain by echocardiography during LAD occlusion and with aortic flow and LV dP/dt(max) during interventions on global LV function.LAD occlusion induced ischaemia, shown by lengthening in systolic strain in the LV apical anterior region (P0.01) and concurrent changes in LAD accelerometer circumferential velocities during systole (P0.01) and during the isovolumic relaxation phase (P0.01). The changes in accelerometer circumferential velocities during LAD occlusion were greater compared with the changes during the interventions on global function (P0.01). For the LAD accelerometer circumferential velocities, sensitivity was 94-100% and specificity was 92-94% in detecting ischaemia.Myocardial ischaemia can be detected with epicardial three-axis accelerometers. The accelerometer had the ability to distinguish ischaemia from interventions altering global myocardial function. This novel technique may be used for continuous real-time monitoring of myocardial ischaemia during and after cardiac surgery.

ObjectiveWe investigated the feasibility of continuous detection of myocardial ischemia during cardiac surgery with a 3-axis accelerometer.MethodsTen patients with significant left anterior descending coronary artery stenosis underwent off-pump coronary artery bypass grafting. A 3-axis accelerometer (11 × 14 × 5 mm) was sutured onto the left anterior descending coronary artery–perfused region of left ventricle. Twenty episodes of ischemia were studied, with 3-minute occlusion of left anterior descending coronary artery at start of surgery and 3-minute occlusion of left internal thoracic artery at end of surgery. Longitudinal, circumferential, and radial accelerations were continuously measured, with epicardial velocities calculated from the signals. During occlusion, accelerometer velocities were compared with anterior left ventricular longitudinal, circumferential, and radial strains obtained by echocardiography. Ischemia was defined by change in strain greater than 30%.ResultsIschemia was observed echocardiographically during 7 of 10 left anterior descending coronary artery occlusions but not during left internal thoracic artery occlusion. During ischemia, there were no significant electrocardiographic or hemodynamic changes, whereas large and significant changes in accelerometer circumferential peak systolic (P < .01) and isovolumic (P < .01) velocities were observed. During 13 occlusions, no ischemia was demonstrated by strain, nor was any change demonstrated by the accelerometer. A strong correlation was found between circumferential strain and accelerometer circumferential peak systolic velocity during occlusion (r = −0.76, P < .001).ConclusionsThe epicardial accelerometer detects myocardial ischemia with great accuracy. This novel technique has potential to improve monitoring of myocardial ischemia during cardiac surgery.

Purpose Microbubbles in hepatic veins during hepatic radiofrequency (RF) ablation is a well-known observation. In this experimental study, we examined the association between microbubbles in the pulmonary artery and alterations in mean pulmonary arterial pressure (MPAP) during hepatic RF ablation with a perfusion electrode system. Materials and Methods Sixteen domestic pigs were included in the study. Twelve animals were randomly assigned to RF ablation with maintained ( n = 6) or interrupted ( n = 6) hepatic inflow. Four animals were assigned to a control group where interruption of hepatic inflow but no RF ablation was performed. Microbubbles in the pulmonary artery were recorded by transesophageal echocardiography and scored according to the number of bubbles per heart cycle. Mean pulmonary arterial pressure was continuously registered by a pulmonary artery catheter. The association between the microbubble score and increase in MPAP during ablation was examined using Spearman's rank correlation coefficient. Results Echocardiographic recordings were acquired in 9 of 12 animals in the two treatment groups. Microbubbles in the pulmonary artery were present in four animals in each treatment group. Mean pulmonary arterial pressure increased from a baseline value of 17.7 mm Hg ± 2.3 to a maximum value of 29.7 mm Hg ± 7.7 during ablation ( P = .018). A significant association was found between the microbubble score and increase in MPAP ( P = .001). Conclusions Microbubbles were detected in the pulmonary artery during hepatic RF ablation both during maintained and interrupted hepatic inflow. A strong association was found between microbubbles in the pulmonary artery and increased MPAP. The clinical implications of our findings are to be determined.

Purpose Right ventricular (RV) failure during treatment of end stage heart failure with left ventricular assist device (LVAD) is a severe complication. No method for continuous monitoring on RV function exists. We successfully used an epicardial 3-axis accelerometer for real time monitoring of RV contractility during LVAD implantation. Methods and Materials A 61 years old male patient with end stage heart failure (LV EF 20%, MPAP 31 mmHg), IABP and inotropic support received LVAD treatment (bridge to transplantation). LVAD implantation was performed with extra corporal circulation (ECC). A 3-axes accelerometer (2x2x5 mm) was sutured on the RV anterior wall after chest opening. RV accelerations in longitudinal, cirumferential and radial directions were simultaneously sampled and the calculated velocities signals were displayed in real time on a monitor together with ECG. Results RV function was possible to monitor in real time with the accelerometer and velocities looked similar to tissue velocities obtained by echocardiography. Systolic contraction and diastolic filling were easily identified Figure 1 . A severely depressed RV function was detected with the accelerometer after aortic cross clamp removal (reperfusion), with loss of longitudinal and circumferential contractions. It was possible to precisely monitor recovery of RV function during reperfusion, weaning from ECC and initiation of LVAD, and to identify differences in RV contraction directions during loading and unloading. Conclusions RV function can be precisely monitored in real time by use of a 3-axes accelerometer. The method has a great potential in detecting clinical adverse outcomes during LVAD treatment.