Per Steinar Halvorsen

Agreement between PiCCO pulse-contour analysis, pulmonal artery thermodilution and transthoracic thermodilution during off-pump coronary artery by-pass surgery

Background:  Haemodynamic instability during off‐pump coronary artery bypass surgery (OPCAB) may appear rapidly, and continuous monitoring of the cardiac index (CI) during the procedure is advisable. With the PiCCO monitor, CI can be measured continuously and almost real time with pulse‐contour analysis and intermittently with transthoracic thermodilution. The agreement between pulmonal artery thermodilution CI (Tpa), transthoracic thermodilution CI (Tpc) and pulse‐contour CI (PCCI) during OPCAB surgery has not been evaluated sufficiently.

Detection of myocardial ischaemia by epicardial accelerometers in the pig

BACKGROUND We describe a novel technique for continuous real-time assessment of myocardial ischaemia using a three-axis accelerometer. METHODS 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. RESULTS LAD occlusion induced ischaemia, shown by lengthening in systolic strain in the LV apical anterior region (P<0.01) and concurrent changes in LAD accelerometer circumferential velocities during systole (P<0.01) and during the isovolumic relaxation phase (P<0.01). The changes in accelerometer circumferential velocities during LAD occlusion were greater compared with the changes during the interventions on global function (P<0.01). For the LAD accelerometer circumferential velocities, sensitivity was 94-100% and specificity was 92-94% in detecting ischaemia. CONCLUSIONS 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.

Intracoronary Shunt Prevents Ischemia in Off-Pump Coronary Artery Bypass Surgery

BACKGROUND The purpose of this study was to evaluate the role of intracoronary shunt during off-pump coronary artery bypass surgery. METHODS Fifty-six patients undergoing off-pump coronary artery bypass using the left internal mammary artery to bypass the left anterior descending coronary artery were randomly assigned to have the bypass performed with intracoronary shunt or by occlusive snaring. Ischemia during grafting was monitored by tissue Doppler. Hemodynamic status and indicators of ischemia were monitored, and on-table and postoperative angiography were performed. RESULTS In patients with retrograde filling of the left anterior descending coronary artery, ischemia did not develop, but occlusion of antegradely perfused vessels caused ischemia in 26 of 33 patients. Ischemia was reversed in 14 of 16 shunted patients, and in 3 of 17 nonshunted cases (p = 0.004). Angiography showed a trend toward improved on-table angiographic results in shunted patients. After 3 months, graft patency was 100%, but 1 patient treated without shunt required reintervention and 15 patients had new angiographic lesions, equally distributed between shunted and nonshunted patients. CONCLUSIONS Intracoronary shunt prevents ischemia during grafting of the left anterior descending coronary artery and provides satisfactory immediate- and short-term graft patency.

Randomized prospective trial of saphenous vein harvest site infection after wound closure with and without topical application of autologous platelet-rich plasma.

OBJECTIVE Wound infection is still a common problem after open long saphenous vein harvesting. Platelets are important for the healing process. The hypothesis was that spraying of the wounds with platelet-rich plasma might reduce the frequency of harvest site infections. METHODS From January to October 2008, 140 patients undergoing first-time coronary artery bypass grafting were randomized into two groups of 70 patients. Both groups had standard surgical leg wound closure and care except topical application of platelet-rich plasma as adjunctive treatment in the active treatment group. End points were wound infection and cosmetic result at 6 weeks. RESULTS The follow-up was 100% complete. Nine patients (13%) in the treatment group and eight (11%) in the control group experienced harvest site infection (p=0.80). The overall cosmetic result was also similar between the groups (p=0.34), but the top score was borderline and more frequent in the treatment group (p=0.050). CONCLUSION Topical application of autologous platelet-rich plasma on vein harvest wounds did not reduce the rate of surgical site infection.

Feasibility of a three-axis epicardial accelerometer in detecting myocardial ischemia in cardiac surgical patients

OBJECTIVE We investigated the feasibility of continuous detection of myocardial ischemia during cardiac surgery with a 3-axis accelerometer. METHODS Ten patients with significant left anterior descending coronary artery stenosis underwent off-pump coronary artery bypass grafting. A 3-axis accelerometer (11 x 14 x 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%. RESULTS Ischemia 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). CONCLUSIONS The epicardial accelerometer detects myocardial ischemia with great accuracy. This novel technique has potential to improve monitoring of myocardial ischemia during cardiac surgery.

Advantages of strain echocardiography in assessment of myocardial function in severe sepsis: an experimental study.

Objectives:Cardiovascular failure is an important feature of severe sepsis and mortality in sepsis. The aim of our study was to explore myocardial dysfunction in severe sepsis. Design:Prospective experimental study. Setting:Operating room at Intervention Centre, Oslo University Hospital. Subjects:Eight Norwegian Landrace pigs. Interventions:The pigs were anesthetized, a medial sternotomy performed and miniature sensors for wall-thickness measurements attached to the epicardium and invasive pressure monitoring established, and an infusion of Escherichia coli started. Hemodynamic response was monitored and myocardial strain assessed by echocardiography. Measurements and Main Results:Left ventricular myocardial function was significantly reduced assessed by longitudinal myocardial strain (–17.2% ± 2.8% to –12.3% ± 3.2%, p = 0.04), despite a reduced afterload as expressed by the left ventricular end-systolic meridional wall stress (35 ± 13 to 18 ± 8 kdyn/cm2, p = 0.04). Left ventricular ejection fraction remained unaltered (48% ± 7% to 49% ± 5%, p = 0.4) as did cardiac output (6.3 ± 1.3 to 5.9 ± 3 L/min, p = 0.7). The decline in left ventricular function was further supported by significant reductions in the index of regional work by pressure-wall thickness loop area (121 ± 45 to 73 ± 37 mm × mm Hg, p = 0.005). Left ventricular myocardial wall thickness increased in both end diastole (11.5 ± 2.7 to 13.7 ± 2.4 mm, p = 0.03) and end systole (16.1 ± 2.9 to 18.5 ± 1.8 mm, p = 0.03), implying edema of the left ventricular myocardial wall. Right ventricular myocardial function by strain was reduced (–24.2% ± 4.1% to –16.9% ± 5.7%, p = 0.02). High right ventricular pressures caused septal shift as demonstrated by the end-diastolic transseptal pressure gradient (4.1 ± 3.3 to –2.2 ± 5.8 mm Hg, p = 0.01). Conclusions:The present study demonstrates myocardial dysfunction in severe sepsis. Strain echocardiography reveals myocardial dysfunction before significant changes in ejection fraction and cardiac output and could prove to be a useful tool in clinical evaluation of septic patients.

In-Body to On-Body Ultrawideband Propagation Model Derived From Measurements in Living Animals

Ultrawideband (UWB) radio technology for wireless implants has gained significant attention. UWB enables the fabrication of faster and smaller transceivers with ultralow power consumption, which may be integrated into more sophisticated implantable biomedical sensors and actuators. Nevertheless, the large path loss suffered by UWB signals propagating through inhomogeneous layers of biological tissues is a major hindering factor. For the optimal design of implantable transceivers, the accurate characterization of the UWB radio propagation in living biological tissues is indispensable. Channel measurements in phantoms and numerical simulations with digital anatomical models provide good initial insight into the expected path loss in complex propagation media like the human body, but they often fail to capture the effects of blood circulation, respiration, and temperature gradients of a living subject. Therefore, we performed UWB channel measurements within 1-6 GHz on two living porcine subjects because of the anatomical resemblance with an average human torso. We present for the first time, a path loss model derived from these in vivo measurements, which includes the frequency-dependent attenuation. The use of multiple on-body receiving antennas to combat the high propagation losses in implant radio channels was also investigated.

Detecting myocardial ischaemia using miniature ultrasonic transducers — a feasibility study in a porcine model

BACKGROUND Detection of myocardial ischaemia during and after cardiac surgery remains a challenge. Echocardiography is more sensitive in ischaemia detection than echocardiography (ECG) and haemodynamic monitoring, but demands repeated examinations for monitoring over time. We have developed and validated an ultrasonic system that permits continuous real-time assessment of myocardial ischaemia using miniature epicardial ultrasound transducers. METHODS In an open-chest porcine model (n=8), prototype ultrasound transducers were fixed on the epicardium in the left anterior descending and circumflex coronary artery supply regions, providing continuous measurement of transmural myocardial velocities. Peak systolic velocity and post-systolic velocity were recorded simultaneously with ECG, left ventricular pressure and arterial pressure. Two-dimensional (2D) echocardiographic strain was used as a reference. Global changes were induced by infusing fluid, epinephrine, nitroprusside and esmolol. Regional changes were induced by occluding the left anterior descending coronary artery (LAD). Subsequent LAD stenosis was performed in a subgroup, with flow reduction to 50% of baseline level and further to occlusion. RESULTS Systolic velocity in the LAD region decreased during LAD occlusion (0.9+/-0.1 to 0.1+/-0.1 cm s(-1), P<0.01), whereas post-systolic velocity increased (0.3+/-0.1 to 2.3+/-0.1 cm s(-1), P<0.01). No changes occurred in the circumflex coronary artery (CX) region. Severe ischaemia was confirmed by reduction in 2D echocardiography strain calculations. Changes in myocardial velocities assessed by miniature transducer during ischaemia differed from changes during all global interventions. Significant reduction in systolic velocity occurred at 50% LAD flow (0.9+/-0.1 to 0.5+/-0.1 cm s(-1), P=0.02) with further decrease on following occlusion (0.0+/-0.0 cm s(-1), P<0.01). Post-systolic velocity increased both from baseline to 50% LAD flow, and further to occlusion. CONCLUSION The epicardial transducers provided continuous assessment of regional myocardial function and detected ischaemia with high sensitivity and specificity. Further development of this system may provide a useful tool for myocardial monitoring during and after cardiac surgery.

Automatic real-time detection of myocardial ischemia by epicardial accelerometer

OBJECTIVE Myocardial 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. METHODS In 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. RESULTS Systolic 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). CONCLUSIONS Automatic 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.

Validation of cardiac accelerometer sensor measurements

In this study we have investigated the accuracy of an accelerometer sensor designed for the measurement of cardiac motion and automatic detection of motion abnormalities caused by myocardial ischaemia. The accelerometer, attached to the left ventricular wall, changed its orientation relative to the direction of gravity during the cardiac cycle. This caused a varying gravity component in the measured acceleration signal that introduced an error in the calculation of myocardial motion. Circumferential displacement, velocity and rotation of the left ventricular apical region were calculated from the measured acceleration signal. We developed a mathematical method to separate translational and gravitational acceleration components based on a priori assumptions of myocardial motion. The accuracy of the measured motion was investigated by comparison with known motion of a robot arm programmed to move like the heart wall. The accuracy was also investigated in an animal study. The sensor measurements were compared with simultaneously recorded motion from a robot arm attached next to the sensor on the heart and with measured motion by echocardiography and a video camera. The developed compensation method for the varying gravity component improved the accuracy of the calculated velocity and displacement traces, giving very good agreement with the reference methods.