Eileen M. McMahon

Impact of acute moderate elevation in left ventricular afterload on diastolic transmitral flow efficiency: analysis by vortex formation time.

BACKGROUND The formation of a vortex alongside a diastolic jet signifies an efficient blood transport mechanism. Vortex formation time (VFT) is an index of the optimal conditions for vortex formation. It was hypothesized that left ventricular (LV) afterload impairs diastolic transmitral flow efficiency and therefore shifts the VFT out of its optimal range. METHODS In 9 open-chest pigs, LV afterload was elevated by externally constricting the ascending aorta and increasing systolic blood pressure to 130% of baseline value for 3 minutes. RESULTS Systolic LV function decreased, diastolic filling velocity increased only during the late (atrial) phase from 0.46 +/- 0.06 to 0.63 +/- 0.19 m/s (P = .0231), and end-diastolic LV volume and heart rate remained unchanged. VFT decreased from 4.09 +/- 0.27 to 2.78 +/- 1.03 (P = .0046). CONCLUSION An acute, moderate elevation in LV afterload worsens conditions for diastolic vortex formation, suggesting impaired blood transport efficiency.

Delayed Onset of Subendocardial Diastolic Thinning at Rest Identifies Hypoperfused Myocardium

Background—Onset of myocardial relaxation is highly energy dependent. Perfusion and therefore energy substrate delivery are predominantly reduced in the subendocardial myocardium in the early stages of progressive ischemia. We hypothesized that delayed onset of subendocardial diastolic thinning will functionally identify regionally hypoperfused resting myocardium. Methods and Results—Progressive left anterior descending coronary artery stenosis was induced by an ameroid occluder and maintained for 1 or 2 weeks (end point) in 12 dogs. M-mode tissue Doppler images of the anterior apical and middle segments (testing region) and middle inferior segment (control region) were acquired selectively in the subendocardium and subepicardium. The time to the onset of thinning was measured with the use of tissue Doppler velocity (TOTv) and a thickness function (TOTt). At the end point in the testing region, myocardial flow was significantly lower in the subendocardial layer (P<0.05) in all animals, whereas viability staining showed preserved transmural viability in 10 dogs and thin subendocardial necrosis in 2 dogs. Both TOTv and TOTt were significantly (P<0.01) prolonged in the testing region. The mean difference between subendocardial and subepicardial TOTv values versus that in the control region identified the ischemic region, even when only dogs with hypoperfused but transmurally viable myocardium were considered (P<0.05). Systolic and diastolic myocardial velocities did not identify subendocardial hypoperfusion. Conclusions—In resting myocardium subtended to progressive coronary stenosis, a delayed onset of subendocardial thinning suggests an early stage of hypoperfusion, before the development of local wall motion abnormalities.

Patients With Alzheimer Disease Have Altered Transmitral Flow Echocardiographic Analysis of the Vortex Formation Time

Objective. There is considerable epidemiologic evidence that Alzheimer disease (AD) is linked to cardiovascular risk factors and associated with an increased risk of symptomatic left ventricular (LV) dysfunction. Formation of a vortex alongside a diastolic jet signifies an efficient blood transport mechanism. The vortex formation time (VFT) is an index of optimal conditions for vortex formation. We hypothesized that AD and its associated cardiovascular risk factors impair diastolic transmitral flow efficiency and, therefore, shift the VFT value out of its optimal range. Methods. Echocardiographic studies were performed on 45 participants in total: 22 patients with AD diagnosed according to the American Psychiatric Associations criteria and 23 age‐matched individuals as a control group with cognitive function within normal limits. Results. The echocardiographic ratio of the early to atrial phases of the LV filling velocities was significantly lower in the AD group (mean ± SD, 0.67 ± 14) when compared with the control individuals (0.79 ± 0.14; P = .003). The interventricular septum diastolic thickness, left ventricular posterior wall diastolic thickness, and right ventricular end‐diastolic diameter were significantly higher in the AD group (P ≤ 0.04). The mitral annular diameters in the control and AD groups were nearly identical (P = .725). The time‐velocity integral of the E wave had a lower value in the AD group than in the control group (P = .05), whereas the VFT was significantly lower in the AD group (P = .018). Conclusions. Our study suggests that patients with AD have impaired transmitral flow efficiency of diastolic filling, as measured by the VFT, compared with age‐matched control individuals.

Right ventricular free wall circumferential strain reflects graded elevation in acute right ventricular afterload

This study was designed to evaluate the concurrent changes in the right ventricular free wall (RVFW) movement in experimentally induced, acute mild, moderate, and severe right ventricle (RV) afterload conditions. In 14 open-chest pigs (weight 43 +/- 4 kg) with preserved pericardia, acute mild (>35 and <50 mmHg), moderate (> or =50 and < or =60 mmHg), and severe (>60 mmHg) increases in RV systolic pressure (RVSP) were induced by constriction of the pulmonary artery. At each step, longitudinal, radial, and circumferential strains and strain rates were measured in both the RVFW and the interventricular septum. The mean RVSPs were 31.0 +/- 4.3 mmHg at baseline and 41.1 +/- 2.7 mmHg during mild, 52.7 +/- 3.4 mmHg during moderate, and 61.7 +/- 1.6 mmHg during severe afterload conditions. The RVFW circumferential strains showed significant differences among baseline, mild, moderate, and severe afterload conditions (-10.5 +/- 3.9, -8.3 +/- 3.3, -5.4 +/- 2.7, and -7.5 +/- 5.3%, respectively, P = 0.008) and had significant linear correlation with RVSP (r = 0.636, P < 0.001) if the severe condition was excluded. Decrease of the RVFW circumferential strain magnitude is the most distinct response in acute mild and moderate RV afterload that could aid in detection of clinical conditions associated with acutely increasing RV afterload.

Flow Velocity Vector Fields by Ultrasound Particle Imaging Velocimetry In Vitro Comparison With Optical Flow Velocimetry

We performed an in vitro study to assess the precision and accuracy of particle imaging velocimetry (PIV) data acquired using a clinically available portable ultrasound system via comparison with stereo optical PIV.

Selective echocardiographic analysis of epicardial and endocardial left ventricular rotational mechanics in an animal model of pericardial adhesions

AIMS Diagnosis of pericardial adhesions is challenging. Twisting of the left ventricle (LV) is essential for normal LV functioning. We experimentally characterized the impact of pericardial adhesions on epicardial and endocardial LV rotational mechanics with velocity vector imaging (VVI). METHODS AND RESULTS In nine open-chest pigs, the heart was exposed while preserving the pericardium. Early-stage pericardial adhesions were simulated by instilling tissue glue to pericardial space. Using VVI, LV rotational mechanics was quantitatively assessed endocardially and epicardially along with haemodynamic data at baseline and following the experimental intervention. End-diastolic volume, ejection fraction, stroke volume, late diastolic filling velocity, and LV endocardial torsion decreased significantly. LV epicardial torsion showed only a trend towards decrease (P = 0.141). Endocardial twist and torsion decreased significantly (P = 0.007) from 8.6 +/- 2.2 degree and 1.497 +/- 0.397 degree/cm to 5.3 +/- 1.8 degree and 0.97 +/- 0.38 degree/cm, respectively; epicardial twist showed a trend towards a decrease in its magnitude. Gradients of endocardial/epicardial twist and torsion did not significantly change. CONCLUSION The model suggests that early-stage pericardial adhesions reduce both epicardial and endocardial LV twist and torsion without a significant alteration in their transmural gradient. Selective endocardial/epicardial analysis of LV twisting mechanics may have a diagnostic role in detection of early formation of pericardial adhesions.

Left Ventricular Flow Analysis: Recent Advances in Numerical Methods and Applications in Cardiac Ultrasound

The left ventricle (LV) pumps oxygenated blood from the lungs to the rest of the body through systemic circulation. The efficiency of such a pumping function is dependent on blood flow within the LV chamber. It is therefore crucial to accurately characterize LV hemodynamics. Improved understanding of LV hemodynamics is expected to provide important clinical diagnostic and prognostic information. We review the recent advances in numerical and experimental methods for characterizing LV flows and focus on analysis of intraventricular flow fields by echocardiographic particle image velocimetry (echo-PIV), due to its potential for broad and practical utility. Future research directions to advance patient-specific LV simulations include development of methods capable of resolving heart valves, higher temporal resolution, automated generation of three-dimensional (3D) geometry, and incorporating actual flow measurements into the numerical solution of the 3D cardiovascular fluid dynamics.

Impact of pericardial adhesions on diastolic function as assessed by vortex formation time, a parameter of transmitral flow efficiency

BackgroundPericardial adhesions are a pathophysiological marker of constrictive pericarditis (CP), which impairs cardiac filling by limiting the total cardiac volume compliance and diastolic filling function. We studied diastolic transmitral flow efficiency as a new parameter of filling function in a pericardial adhesion animal model. We hypothesized that vortex formation time (VFT), an index of optimal efficient diastolic transmitral flow, is altered by patchy pericardial-epicardial adhesions.MethodsIn 8 open-chest pigs, the heart was exposed while preserving the pericardium. We experimentally simulated early pericardial constriction and patchy adhesions by instilling instant glue into the pericardial space and using pericardial-epicardial stitches. We studied left ventricular (LV) function and characterized intraventricular blood flow with conventional and Doppler echocardiography at baseline and following the experimental intervention.ResultsSignificant decreases in end-diastolic volume, ejection fraction, stroke volume, and late diastolic filling velocity reflected the effects of the pericardial adhesions. The mean VFT value decreased from 3.61 ± 0.47 to 2.26 ± 0.45 (P = 0.0002). Hemodynamic variables indicated the inhibiting effect of pericardial adhesion on both contraction (decrease in systolic blood pressure and +dP/dt decreased) and relaxation (decrease in the magnitude of -dP/dt and prolongation of Tau) function.ConclusionPatchy pericardial adhesions not only negatively impact LV mechanical functioning but the decrease of VFT from normal to suboptimal value suggests impairment of transmitral flow efficiency.

Correlation of automated function imaging (AFI) to conventional strain analyses of regional and global right ventricular function.

BACKGROUND Automated function imaging is a software tool available to facilitate the efficiency of workflow when analyzing left ventricular strain. In this study, automated function imaging was compared with a conventional approach for the analysis of right ventricular strain in normal and pressure-overloaded right ventricles. METHODS Twelve pigs were subjected to graded acute right ventricular systolic pressure overload. Intraclass and interclass correlation coefficients (ICCs) with 95% confidence intervals were used for statistical evaluation, with grading based on the kappa statistic as follows: ICC >0.75 = excellent, 0.4 to 0.75 = good, and <0.40 = poor. RESULTS Intraobserver and interobserver variability for both regional and global strains consistently ranged from good to excellent (ICC, 0.50-0.99), with good agreement between the conventional and automated methods. CONCLUSION Automated function imaging correlates well with conventional strain analysis of the right ventricle. Automated function imaging is a practical tool for measuring regional and global longitudinal strain in both normal and pressure-overloaded right ventricles.

Quantification of Left Ventricular Twisting Mechanics by Velocity Vector Imaging in an Animal Model of Pericardial Adhesions

Diagnosis of constrictive pericarditis remains clinically challenging. Untwisting of the left ventricle (LV) is essential for normal LV diastolic function. Echocardiography is able to measure LV twisting mechanics. We designed an animal model of constrictive pericarditis to determine how pericardial-epicardial adhesions impair LV twisting mechanics. In eight open-chest pigs, the heart was exposed while preserving the pericardium. We simulated early constrictive pericarditis by pericardial constriction and patchy adhesions induced with instant glue and pericardial-epicardial stitches. Using Velocity Vector Imaging (VVI), LV magnitudes of twisting and untwisting were measured along with hemodynamic data at baseline and after the experimental intervention. Significant decreases in end-diastolic volume, ejection fraction, stroke volume, and late diastolic filling velocity reflected the effects of the pericardial adhesions. Magnitude of LV untwisting rate decreased from -80+/-23 degrees /s to -26+/-10 degrees /s (p=0.0009). LV twisting rate dropped from 78+/-20 degrees /s to 40+/-8 degrees /s (p=0.0039) and LV twist magnitude decreased from 9+/-2 degrees to 5+/-2 degrees (p=0.0081). Patchy pericardial adhesions are associated with reductions in LV untwisting rate and twisting magnitude, consistent with a negative impact of constrictive pericarditis on systolic and diastolic function. Impairments in LV twisting mechanics may have a diagnostic role in the detection of early stages of constrictive pericarditis.