Assessment of 3D motion increases the applicability of accelerometers for monitoring left ventricular function.

OBJECTIVES: Miniaturized accelerometers attached to the epicardium have been shown to provide useful clinical information. However, attachment of such a sensor has been cumbersome due to requirement of aligning the three sensor axes with the cardiac coordinate axes, limiting clinical utility. We propose a new method to process the three-dimensional (3D) accelerometer signal that does not require such alignment. METHODS: In 20 open-chest pigs, miniaturized 3D accelerometers were fixated on the epicardium in apical and basal regions of left ventricle. Accelerations in circumferential, longitudinal and radial directions were measured and a 3D velocity vector was calculated. Systolic velocity along the 3D vector and velocities in circumferential, longitudinal and radial directions were compared with the positive time derivate of left ventricular pressure during changes in global left ventricular function (epinephrine, esmolol and fluid loading) and to strain echocardiography during left anterior descending artery occlusion. RESULTS: Distinct changes in all accelerometer velocities were observed during alterations on global and regional left ventricular function. Accelerometer 3D and circumferential systolic velocities in apical region best reflected left ventricular function during interventions on global function by correlating significantly with the positive time derivate of left ventricular pressure, r = 0.83 and r = 0.86, respectively. The accelerometer 3D velocity also demonstrated equally good capacity as circumferential velocity in discriminating coronary occlusion from interventions on global left ventricular function with sensitivity/specificity of 0.90/0.83 and 0.90/0.86, respectively. CONCLUSIONS: Accelerometer 3D systolic velocity showed very good correspondence to changes in global and regional left ventricular function. Our results demonstrate that by the use of the accelerometer 3D motion vector, no alignment of the sensor with the cardiac coordinate axes was required. This increases potential clinical applicability of the accelerometer in cardiac surgery.

Early assessment of strain echocardiography can accurately exclude significant coronary artery stenosis in suspected non-ST-segment elevation acute coronary syndrome.

BACKGROUND: Many patients with suspected non-ST-segment elevation acute coronary syndrome (NSTE-ACS) do not have significant coronary artery disease. The current diagnostic approach of repeated electrocardiography and cardiac biomarker assessment requires observation for >6 to 12 hours. This strategy places a heavy burden on hospital facilities. The objective of this study was to investigate whether myocardial strain assessment by echocardiography could exclude significant coronary artery stenosis in patients presenting with suspected NSTE-ACS. METHODS: Sixty-four patients presenting to the emergency department with suspected NSTE-ACS without known coronary artery disease, inconclusive electrocardiographic findings, and normal cardiac biomarkers at arrival were enrolled. Twelve-lead electrocardiography, troponin T assay, and echocardiography were performed at arrival, and all patients underwent coronary angiography. Significant coronary stenosis was defined as >50% luminal narrowing. Global myocardial peak systolic longitudinal strain was measured using speckle-tracking echocardiography. Left ventricular ejection fraction and wall motion score index were calculated. RESULTS: No significant stenosis in any coronary artery was found in 35 patients (55%). Global peak systolic longitudinal strain was superior to conventional echocardiographic parameters in distinguishing patients with and without significant coronary artery stenosis (area under the curve, 0.87). Sensitivity and specificity were calculated as 0.93 and 0.78, respectively, and positive predictive value and negative predictive value as 0.74 and 0.92, respectively. Feasibility of the strain measurements was excellent, with 97% of segments analyzed. CONCLUSIONS: Myocardial strain by echocardiography may facilitate the exclusion of significant coronary artery stenosis among patients presenting with suspected NSTE-ACS with inconclusive electrocardiographic findings and normal cardiac biomarkers.

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/cm, 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.

Assessment of wasted myocardial work: a novel method to quantify energy loss due to uncoordinated left ventricular contractions.

Left ventricular (LV) dyssynchrony reduces myocardial efficiency because work performed by one segment is wasted by stretching other segments. In the present study, we introduce a novel noninvasive clinical method that quantifies wasted energy as the ratio between work consumed during segmental lengthening (wasted work) divided by work during segmental shortening. The wasted work ratio (WWR) principle was studied in 6 anesthetized dogs with left bundle branch block (LBBB) and in 28 patients with cardiomyopathy, including 12 patients with LBBB and 10 patients with cardiac resynchronization therapy. Twenty healthy individuals served as controls. Myocardial strain was measured by speckle tracking echocardiography, and LV pressure (LVP) was measured by micromanometer and a previously validated noninvasive method. Segmental work was calculated by multiplying strain rate and LVP to get instantaneous power, which was integrated to give work as a function of time. A global WWR was also calculated. In dogs, WWR by estimated LVP and strain showed a strong correlation (r = 0.94) and good agreement with WWR by the LV micromanometer and myocardial segment length by sonomicrometry. In patients, noninvasive WWR showed a strong correlation (r = 0.96) and good agreement with WWR using the LV micromanometer. Global WWR was 0.09 ± 0.03 in healthy control subjects, 0.36 ± 0.16 in patients with LBBB, and 0.21 ± 0.09 in cardiomyopathy patients without LBBB. Cardiac resynchronization therapy reduced global WWR from 0.36 ± 0.16 to 0.17 ± 0.07 (P < 0.001). In conclusion, energy loss due to incoordinated contractions can be quantified noninvasively as the LV WWR. This method may be applied to evaluate the mechanical impact of dyssynchrony.

Epicardial ultrasonography: a potential method for intraoperative quality assessment of coronary bypass anastomoses?

BACKGROUND: Intraoperative quality assessment in coronary artery bypass surgery confirms graft patency and enables revision of failing grafts. The aim of this study was to evaluate graft quality intraoperatively by epicardial ultrasonography and to compare this technique with transit time flow measurements and intraoperative angiography, and to evaluate the ability of these methods to predict long-term patency as described by follow-up angiography. METHODS: Thirty-nine patients with mean age of 66 years (SD 9.5) who underwent off-pump coronary artery bypass surgery with internal mammary artery graft to the left anterior descending coronary artery were included. Epicardial ultrasonography and transit time flow measurement were performed after completion of the anastomoses, and coronary angiography after closure of the chest. Follow-up angiography was carried out after 156 days (SD 50). RESULTS: Diameter measurements obtained by epicardial ultrasonography correlated poorly with the same diameter measurements obtained by angiography. Epicardial ultrasonography revealed 5 abnormal grafts (13%), transit time flow measurements none, and intraoperative angiography 9 (23%). At follow-up angiography, 4 grafts (11%) were pathologic. Epicardial ultrasonography and transit time flow measurements indicated no need for graft revision; intraoperative angiography suggested need for revision in 3 cases. CONCLUSIONS: Epicardial ultrasonography could be a useful method for intraoperative assessment of graft anastomosis quality, but needs to demonstrate its ability to predict grafts in need of revision. Angiography must be considered the gold standard in intraoperative imaging.

Detection of ischemia and new insight into left ventricular physiology by strain Doppler and tissue velocity imaging: assessment during coronary bypass operation of the beating heart.

BACKGROUND AND OBJECTIVES: Detection of myocardial ischemia in humans by strain Doppler and tissue velocity imaging was validated in a novel, experimentally designed study model during coronary bypass operation of the beating heart. METHODS: Assessment of ischemia was made with an opened chest and pericardium inherent in the operative procedure. Longitudinal strain and tissue velocity of interventricular septal regions were measured by transesophageal echocardiography during occlusion of the left anterior descending coronary artery (LAD). RESULTS: Unexpectedly, baseline velocities demonstrated that the apical and basal septum moved toward each other during systole. This occurred when the apex was dislodged from the pericardial sac to obtain access to the LAD, without any change in strain. The preceding motion of all septal regions toward the apex was reestablished after the heart was repositioned within the pericardium. In 16 patients with antegrade LAD flow, strain Doppler detected ischemia during LAD occlusion by disclosing systolic lengthening of the apical septum ( P <.01) and reduced shortening of the mid septum ( P <.05). The location and degree of ischemic changes coincided with the concomitant deterioration of wall motion. Tissue velocity changed in the basal and mid septum ( P <.05) but not in the apical region, explained by tethering effects and the distinctive motion pattern at baseline. There was no evidence of ischemia by invasive hemodynamic measures. In 7 patients with retrograde LAD flow, there were no significant changes in strain or tissue velocity measurements during LAD occlusion. CONCLUSIONS: Strain by Doppler is a sensitive means for detecting myocardial ischemia, also capable of correctly localizing the ischemia, as opposed to tissue velocity assessment. However, velocity measurements provided new physiological information by disclosing the normal longitudinal motion of the heart to be dependent on the pericardial sac enveloping the apex, irrespective of the structural integrity of the pericardium.