Biomedical subjects

L L Creswell

Publications and source records attributed to L L Creswell.

At least 19 recordsLinked to original sources

PubMed1996

Obesity is not a risk factor for significant adverse outcomes after cardiac surgery.

BACKGROUND: Obese patients undergoing cardiac surgery are often thought to have prohibitive perioperative risk despite the lack of sufficient data to support this assumption. METHODS AND RESULTS: To assess the significance of obesity as a risk factor in patients undergoing cardiac surgery, we analyzed data from 2299 patients undergoing procedures requiring cardiopulmonary bypass from January 1, 1991, to December 31, 1993. Obesity was defined by use of the body mass index, defined as weight in kilograms divided by height in meters squared. Potential adverse outcomes analyzed included operative mortality, deep sternal wound infection, superficial sternal wound infection, infection at the saphenous vein harvest site, stroke, renal failure, adult respiratory distress syndrome, prolonged mechanical ventilation, pneumonia, sepsis, atrial arrhythmias, pulmonary embolism, need for early reexploration for bleeding, and ventricular arrhythmias. To control for the confounding effects of other risk factors, we performed a multivariate logistic regression analysis. Potential covariates considered in the logistic model included age, sex, race, history of reoperation, congestive heart failure, prior myocardial infarction, renal failure, diabetes, hypertension, chronic obstructive pulmonary disease or stroke, and cardiopulmonary bypass and aortic cross-clamp time. Twenty-five percent of patients (567/2299) were classified as obese. The results of the multivariate regression demonstrated that obesity was a risk factor only for superficial sternal wound infection (P < .001; odds ratio, 2.3), leg infections (P = .005; odds ratio, 1.8), and atrial dysrhythmias (P = .04; odds ratio, 1.2). Notably, obesity did not predispose toward increased pulmonary complications or deep sternal wound infection (P = .65). CONCLUSIONS: With the exception of superficial wound complications and atrial dysrhythmias, obesity is not a significant multivariate risk factor for adverse outcomes. The results indicate that obese patients may safely undergo cardiac surgery with due attention to technical considerations designed to minimize wound complications.

Adult↗

PubMed1996

Magnetic resonance imaging provides evidence for remodeling of the right ventricle after single-lung transplantation for pulmonary hypertension.

BACKGROUND: In end-stage pulmonary hypertension (PH), the degree of right ventricular (RV) dysfunction has been considered so severe as to require combined heart-lung transplantation. Nevertheless, left ventricular (LV) and RV hemodynamics return to relatively normal levels after single-lung transplantation (SLT) alone. Accordingly, to test the hypothesis that LV and RV systolic function improves after SLT and that the dilated, thick-walled RV reverts to more normal geometry, we used cine MRI and finite-element (FE) analysis to study patients with end-stage PH. METHODS AND RESULTS: Seven patients with end-stage PH underwent cine MRI before and after SLT, and eight normal volunteers were also imaged with cine MRI. Short-axis images at the midventricular level were analyzed with customized image-processing software. The LV and RV ejection fractions, velocity of fiber shortening, RV end-diastolic (ED) and end-systolic (ES) chamber areas, and RV ES and ED wall thicknesses were calculated directly from the MRI images. Two-dimensional FE models of the heart were constructed from the MRI images at early diastole. LV and RV pressures were measured in the patients with a cardiac catheterization before and after SLT. Models were solved to yield diastolic LV, RV, and septal wall stresses. By use of a nonlinear optimization algorithm, LV and RV diastolic maternal properties were determined by minimization of the leastsquares difference between FE model-predicted and MRI-measured LV, RV, and epicardial chamber areas and circumferences. The results demonstrated a substantial reduction in RV wall stress after SLT (1.8 x 10(5) dynes/cm2 pre-SLT to 2 x 10(4) dynes/cm2 post-SLT; P < .001). The average RV diastolic elastic modulus was reduced significantly after SLT (1.5 x 10(6) dynes/cm2 pre-SLT to 1 x 10(5) dynes/cm2 post-SLT; P = .01), but there was no change in the LV elastic modulus. RV velocity of fractional shortening increased significantly after SLT (0.23 pre-SLT to 0.58 post-SLT, P = .02), and RV ED and ES wall thicknesses were reduced significantly (ED, 0.86 cm pre-SLT to 0.65 cm post-SLT, P = .03 and ES, 1.06 cm pre-SLT to 0.72 cm post-SLT, P = .005). CONCLUSIONS: These results provide evidence supporting the contention that LV and RV systolic function improved after SLT for end-stage PH and that the RV underwent significant remodeling within 3 to 6 months after lung transplantation.

Adolescent↗

PubMed1996

Myocardial material property determination in the in vivo heart using magnetic resonance imaging.

OBJECTIVES: To determine nonlinear material properties of passive, diastolic myocardium using magnetic resonance imaging (MRI) tissue-tagging, finite element analysis (FEA) and nonlinear optimization. BACKGROUND: Alterations in the diastolic material properties of myocardium may pre-date the onset of or exist exclusive of systolic ventricular dysfunction in disease states such as hypertrophy and heart failure. Accordingly, significant effort has been expended recently to characterize the material properties of myocardium in diastole. The present study defines a new technique for determining material properties of passive myocardium using finite element (FE) models of the heart, MRI tissue-tagging and nonlinear optimization. This material parameter estimation algorithm is employed to estimate nonlinear material parameter sin the in vivo canine heart and provides the necessary framework to study the full complexities of myocardial material behavior in health and disease. METHODS AND RESULTS: Material parameters for a proposed exponential strain energy function were determined by minimizing the least squares difference between FE model-predicted and MRI-measured diastolic strains. Six mongrel dogs underwent MRI imaging with radiofrequency (RF) tissue-tagging. Two-dimensional diastolic strains were measured from the deformations of the MRI tag lines. Finite element models were constructed from early diastolic images and were loaded with the mean early to late left ventricular and right ventricular diastolic change in pressure measured at the time of imaging. A nonlinear optimization algorithm was employed to solve the least squares objective function for hte material parameters. Average material parameters for the six dogs were E = 28,722 +/- 15984 dynes/cm2 and c = 0.00182 +/- 0.00232 cm2/dyne. CONCLUSION: This parameter estimation algorithm provides the necessary framework for estimating the nonlinear, anisotropic and non-homogeneous material properties of passive myocardium in health and disease in the in vivo beating heart.

Algorithms↗

PubMed1996

Reexploration for bleeding is a risk factor for adverse outcomes after cardiac operations.

OBJECTIVE: Although previous studies have included early reexploration for bleeding as a risk factor in analyzing adverse outcomes after cardiac operations, reexploration for bleeding has not been systematically examined as a multivariate risk factor for increased morbidity and mortality after cardiac surgery. Furthermore, multivariate predictors of the need for reexploration have not been identified. Accordingly, we performed a retrospective analysis of 6100 patients requiring cardiopulmonary bypass from January 1, 1986, to December 31, 1993. METHODS: Eighty-five patients who had ventricular assist devices were excluded from further analysis because of the prevalence of bleeding and the significant morbidity and mortality associated with placement of a ventricular assist device, unrelated to reexploration. In the remaining 6015 patients, potential adverse outcomes analyzed included operative mortality, mediastinitis, stroke, renal failure, adult respiratory distress syndrome, prolonged mechanical ventilation, sepsis, atrial arrhythmias, and ventricular arrhythmias. To control for the confounding effects of other risk factors, we performed a multivariate logistic regression analysis. Potential covariates considered in the logistic model included age, sex, race, history of reoperation, urgency of the operation, congestive heart failure, prior myocardial infarction, renal failure, diabetes, hypertension, chronic obstructive pulmonary disease or stroke, and the bypass and crossclamp time. RESULTS: The overall incidence of reexploration was 4.2% (253/6015). Four independent risk factors--increased patient age (p < 0.001), preoperative renal insufficiency (p = 0.02), operation other than coronary bypass (p < 0.001), and prolonged bypass time (p = 0.0.3)--were identified as predictors of the need for reexploration. The preoperative use of aspirin, heparin, or thrombolytic agents and the bleeding time were not identified as predictors. Reexploration for bleeding was identified as a strong independent risk factor for operative mortality (p = 0.005), renal failure (p < 0.0001), prolonged mechanical ventilation (p < 0.0001), adult respiratory distress syndrome (p = 0.03), sepsis (p < 0.0001), and atrial arrhythmias (p = 0.006). CONCLUSION: These data indicate that meticulous attention to surgical hemostasis and possibly application of recently developed modalities designed to facilitate perioperative correction of coagulopathy could improve outcomes after cardiac operations.

Age Factors↗

PubMed1996

Spline surface interpolation for calculating 3-D ventricular strains from MRI tissue tagging.

A method is developed and validated for approximating continuous smooth distributions of finite strains in the ventricles from the deformations of magnetic resonance imaging (MRI) tissue tagging "tag lines" or "tag surfaces." Tag lines and intersections of orthogonal tag lines are determined using a semiautomated algorithm. Three-dimensional (3-D) reconstruction of the displacement field on tag surfaces is performed using two orthogonal sets of MRI images and employing spline surface interpolation. The 3-D regional ventricular wall strains are computed from an initial reference image to a deformed image in diastole or systole by defining a mapping or transformation of space between the two states. The resultant mapping is termed the measurement analysis solution and is defined by determining a set of coefficients for the approximating functions that best fit the measured tag surface displacements. Validation of the method is performed by simulating tag line or surface deformations with a finite element (FE) elasticity solution of the heart and incorporating the measured root-mean-square (rms) errors of tag line detection into the simulations. The FE-computed strains are compared with strains calculated by the proposed procedure. The average difference between two-dimensional (2-D) FE-computed strains and strains calculated by the measurement analysis was 0.022 +/- 0.009 or 14.2 +/- 3.6% of the average FE elasticity strain solution. The 3-D displacement reconstruction errors averaged 0.087 +/- 0.002 mm or 2.4 +/- 0.1% of the average FE solution, and 3-D strain fitting errors averaged 0.024 +/- 0.011 or 15.9 +/- 2.8% of the average 3-D FE elasticity solution. When the rms errors in tag line detection were included in the 2-D simulations, the agreement between FE solution and fitted solution was 24.7% for the 2-D simulations and 19.2% for the 3-D simulations. We conclude that the 3-D displacements of MRI tag lines may be reconstructed accurately; however, the strain solution magnifies the small errors in locating tag lines and reconstructing 3-D displacements.

Animals↗

PubMed1995

Coronary artery disease in patients with type A aortic dissection.

The usefulness of preoperative coronary arteriography in patients with type A dissection of the aorta is controversial. To determine the prevalence of arteriosclerotic coronary artery disease in patients with type A dissection of the aorta, we reviewed our experience in 62 patients (42 with acute dissection and 20 with chronic dissection) who underwent operation between January 1, 1986, and December 31, 1993. Among 23 patients with acute dissection who underwent coronary arteriography, 8 (34.8%) had one or more coronary artery lesions causing a greater than 50% narrowing. Among 14 patients with chronic dissection who underwent coronary arteriography, 6 (42.9%) had one or more coronary artery lesions causing a greater than 50% narrowing. There were no fatal complications associated with coronary arteriography. Four patients with acute dissection and 6 patients with chronic dissection underwent coronary artery bypass grafting at the time of operative repair of the aortic dissection, with no operative deaths. On the basis of these findings and the success of combined coronary artery bypass grafting and aortic repair, we recommend that patients with an acute type A dissection who are in stable condition and all patients with a chronic type A dissection of the aorta should undergo preoperative coronary arteriography.

Acute Disease↗

PubMed1995

Mechanical dysfunction in the border zone of an ovine model of left ventricular aneurysm.

BACKGROUND: The pathophysiology of regional mechanical dysfunction in the border zone (BZ) region of left ventricular aneurysm was studied in an ovine model using magnetic resonance imaging tissue-tagging and regional deformation analysis. METHODS: Transmural infarcts were created in adult Dorsett sheep (n = 8) by ligation of the distal homonymous coronary artery and were allowed to mature into left ventricular aneurysms for 8 to 12 weeks. Animals were imaged subsequently using double oblique magnetic resonance imaging with radiofrequency tissue tagging. Short axis slices were selected for analysis that included predominantly the septal component of the aneurysm as well as adjacent BZ regions in the anterior and posterior ventricular walls. Dark grid patterns of magnetic presaturations were placed on the myocardium and tracked as they deformed during the diastolic, isovolumic systolic, and systolic ejection phases of the cardiac cycle. Regional ventricular wall strains were calculated in BZ regions and regions remote from the aneurysm and compared with strains measured in corresponding regions from normal control sheep (n = 6). RESULTS: Diastolic midwall circumferential strains (fiber extensions) were relatively preserved, but abnormal circumferential lengthening strains were observed in the BZ regions during isovolumic systole. Peak circumferential strains ranged from 0.04 to 0.07 in the BZ regions but averaged -0.05 in the normal hearts (p = 0.002 for the anterior BZ and p = 0.001 for the posterior BZ). Midwall end-systolic fiber strains were depressed in the anterior BZ (-0.03 to -0.09 for the BZ versus -0.11 for the normal heart, p < 0.0001) but not in the posterior BZ (p = 0.19). CONCLUSIONS: Our data support the theory that the stretching of BZ fibers during isovolumic systole contributed to a reduction in fiber shortening during systolic ejection and thus reduced the overall contribution of these fibers to forward ventricular output.

Animals↗

PubMed1995

An inverse approach to determining myocardial material properties.

Passive myocardial material properties have been measured previously by subjecting test samples of myocardium to in vitro load-deformation analysis or, in the intact heart, by pressure-volume relationships. A new method for determining passive material properties, described in this paper, couples a p-version finite element model of the heart, a nonlinear optimization algorithm and a dense set of transmural measured strains that could be obtained in the intact heart by magnetic resonance imaging (MRI) radiofrequency tissue tagging. Unknown material parameters for a nonlinear, nonhomogeneous material law are determined by solving an inverse boundary value problem. An objective function relating the least-squares difference of model-predicted and measured strains is minimized with respect to the unknown material parameters using a novel optimization algorithm that utilizes forward finite element solutions to calculate derivatives of model-predicted strains with respect to the material parameters. Test cases incorporating several salient features of the inverse material identification problem for the heart are formulated to test the performance of the inverse algorithm in typical experimental conditions. Known true material parameters can be determined to within a small tolerance and random noise is shown not to affect the stability of the inverse solution appreciably. On the basis of these validation experiments, we conclude that the inverse material identification problem for the heart can be extended to solve for unknown material parameters that describe in vivo myocardial material behavior.

Algorithms↗

PubMed1995

Swallowing dysfunction after cardiac operations. Associated adverse outcomes and risk factors including intraoperative transesophageal echocardiography.

The frequency, importance to patient outcomes, and independent predictors of postoperative swallowing dysfunction documented by barium cineradiography were examined in 869 patients undergoing cardiac operations over a 12-month period. Swallowing dysfunction was diagnosed in 34 patients (4% incidence) and was associated with documented pulmonary aspiration in 90% of these patients, increased frequency of pneumonia (p < 0.0001), need for tracheostomy (p = 0.0002), length of stay in the intensive care unit (p = 0.0001), and duration of hospitalization after the operation (p = 0.0001). Independent predictors of postoperative swallowing dysfunction determined by multivariate logistic regression included age (p < 0.001), length of tracheal intubation after the operation (p = 0.001), and intraoperative use of transesophageal echocardiography (p = 0.003). Dysfunctional swallowing after cardiac operations, a serious complication significantly related to postoperative respiratory morbidity and extended length of hospitalization, is more common in older patients. An association between intraoperative use of transesophageal echocardiography and swallowing dysfunction was also observed in our patients.

Aged↗

PubMed1995

Revascularization after acute myocardial infarction.

BACKGROUND: The optimal timing for coronary artery bypass grafting (CABG) after acute myocardial infarction (MI) remains controversial. METHODS: We examined our experience retrospectively in 3,942 patients who underwent CABG between 1986 and 1993, including 2,296 patients after acute MI. RESULTS: The operative mortality associated with increasing time intervals between MI and CABG were 9.1%, 8.3%, 5.2%, 6.5%, and 2.9%, for less than 6 hours, 6 hours to 2 days, 2 to 14 days, 2 to 6 weeks, and more than 6 weeks, respectively. In comparison, the operative mortality was 2.5% for patients with no history of acute MI. The incidence of permanent stroke and perioperative MI were greater and the length of postoperative hospitalization was longer for patients undergoing CABG early after MI. For patients undergoing operation electively, however, the operative mortality associated with increasing time intervals between MI and CABG were less, at 0.0%, 3.6%, 2.1%, 6.4%, and 2.1% for less than 6 hours, 6 hours to 2 days, 2 to 14 days, 2 to 6 weeks, and more than 6 weeks, respectively. For patients undergoing CABG within 14 days of MI, the operative mortality was 5.3% for those receiving an intraaortic balloon pump preoperatively for postinfarction angina, but 11.8% for those who underwent urgent/emergent operation without intraaortic balloon pump support. CONCLUSIONS: Elective CABG can be accomplished with acceptable morbidity and mortality early after acute MI if an elective operation is possible. In addition, the intraaortic balloon pump should be used aggressively in patients with postinfarction angina to allow for elective rather than urgent/emergent operation.

Adult↗

PubMed1994

Potential ablation of accessory atrioventricular pathways: injection of alcohol into the atrioventricular groove.

Accessory atrioventricular (AV) pathways responsible for the Wolff-Parkinson-White syndrome have been treated successfully by surgical and radiofrequency catheter ablation techniques. In this study, we explored the feasibility of permanent chemical ablation of accessory pathways by direct injection of 100% ethanol into the canine AV groove. Right coronary artery blood flow and AV compartment pressure were measured in 5 adult mongrel dogs (part I) during injection of saline solution (10 to 15 mL) into the right AV groove. Atrioventricular groove compartment pressure increased from 1 +/- 1 to 31 +/- 12 mm Hg (p < 0.0001) and right coronary artery blood flow increased slightly from 117 +/- 17 to 138 +/- 44 mL/min (p = not significant). In 8 additional dogs (part II), 100% ethanol (10 mL) was injected into the left AV groove. After 6 weeks (n = 6) or 12 weeks (n = 2), histologic examination of the left AV groove demonstrated localized fibrous replacement of injured epicardial muscle, with only scant inflammatory infiltrate. Mild intimal fibrosis and intimal proliferation were present in the circumflex artery and its larger branches, but no significant luminal narrowing was evident. Angiograms at 12 weeks (n = 2) demonstrated no significant narrowing of the circumflex artery. In summary, injection of 100% ethanol into the AV groove is capable of locally ablating myocardial tissue, presumably including conductive tissues, while sparing the coronary arteries.

Animals↗

PubMed1994

An experimental method for evaluating constitutive models of myocardium in in vivo hearts.

A new experimental method for the evaluation of myocardial constitutive models combines magnetic resonance (MR) radiofrequency (RF) tissue-tagging techniques with iterative two-dimensional (2-D) nonlinear finite element (FE) analysis. For demonstration, a nonlinear isotropic constitutive model for passive diastolic expansion in the in vivo canine heart is evaluated. A 2-D early diastolic FE mesh was constructed with loading parameters for the ventricular chambers taken from mean early diastolic-to-late diastolic pressure changes measured during MR imaging. FE solution was performed for regional, intramyocardial ventricular wall strains using small-strain, small-displacement theory. Corresponding regional ventricular wall strains were computed independently using MR images that incorporated RF tissue tagging. Two unknown parameters were determined for an exponential strain energy function that maximized agreement between observed (from MR) and predicted (from FE analysis) regional wall strains. Extension of this methodology will provide a framework in which to evaluate the quality of myocardial constitutive models of arbitrary complexity on a regional basis.

Animals↗

PubMed1993

Hazards of postoperative atrial arrhythmias.

Between January 1, 1986, and December 31, 1991, 4,507 adult patients underwent cardiac surgical procedures requiring cardiopulmonary bypass. Of these patients, 3,983 patients who did not undergo operation for supraventricular tachycardia and who were in normal sinus rhythm preoperatively form the study group for the present study. Postoperatively, all patients were monitored continuously for the development of arrhythmias until the time of hospital discharge. The incidence of atrial arrhythmias requiring treatment for the most commonly performed operative procedures were as follows: coronary artery bypass grafting, 31.9%; coronary artery bypass grafting and mitral valve replacement, 63.6%; coronary artery bypass grafting and aortic valve replacement, 48.8%; and heart transplantation, 11.1%. For all patients considered collectively, the risk factors associated with an increased incidence of postoperative atrial arrhythmias (p < 0.05 by multivariate logistic regression) included increasing patient age, preoperative use of digoxin, history of rheumatic heart disease, chronic obstructive pulmonary disease, and increasing aortic cross-clamp time. Postoperative atrial fibrillation was associated with an increased incidence of postoperative stroke (3.3% versus 1.4%; p < 0.0005), increased length of hospitalization in the intensive care unit (5.7 versus 3.4 days; p = 0.001) and postoperative nursing ward (10.9 versus 7.5 days; p = 0.0001), increased incidence of postoperative ventricular tachycardia or fibrillation (9.2% versus 4.0%; p < 0.0005), and an increased need for placement of a permanent pacemaker (3.7% versus 1.6%; p < 0.0005). These data provide a basis for targeting specific patient subgroups for prospective, randomized trials of therapeutic modalities designed to decrease the incidence of postoperative atrial arrhythmias.

Atrial Fibrillation↗

PubMed1993

Myocardial contractile state in dogs with chronic mitral regurgitation: echocardiographic approach to the peak systolic pressure/end-systolic area relationship.

Analysis of the pressure-dimension relationship provides a sensitive index of myocardial contractility, but widespread application of this method is limited because it requires invasive measurement techniques. The recent development of two-dimensional echocardiographic automatic boundary detection permits accurate and reproducible on-line measurement of ventricular cavity areas that can be combined with ventricular pressure measurements to derive instantaneous pressure-area relationships. In anesthetized closed-chest dogs with chronic mitral regurgitation, the slope of the ventricular pressure-area relationship was determined by obtaining baseline measurements (at baseline and after infusion of methoxamine or nitroglycerin) and measurements after infusion of a positive inotropic drug (dobutamine) alone and concurrently with methoxamine or nitroglycerin. The slope of the ventricular pressure-area relationship was altered significantly (p = 0.0002) and in the expected direction (steeper slope) from baseline to the enhanced myocardial inotropic state after dobutamine infusion. Thus on-line echocardiographic measurements of ventricular cavity area facilitate the implementation of elastance determinations to serially evaluate the myocardial contractile state under conditions of alterations in preload, afterload, and the inotropic state. This method is promising for the noninvasive evaluation of left ventricular function modified by diverse pathologic conditions.

Animals↗

PubMed1992

Intraaortic balloon counterpulsation: patterns of usage and outcome in cardiac surgery patients.

Between January 1, 1986, and May 6, 1991, 7,884 cardiac surgical procedures requiring cardiopulmonary bypass were performed at our institution, including 672 (9.8% of adult procedures) performed in 669 patients that were associated with preoperative (n = 240), intraoperative (n = 353), or postoperative (n = 79) use of an intraaortic balloon pump. The mean age of recipients was 65.3 years (range, 16 to 89 years). Intraaortic balloon pump usage increased during the study period from 6.4% of patients (83/1,298) in 1986 to 12.7% of patients (169/1,333) in 1990. The relative distribution between preoperative (mean, 35.7%), intraoperative (52.5%), and postoperative (11.8%) insertion remained nearly constant during the study period. The overall operative (30-day) mortality for patients with preoperative, intraoperative, or postoperative insertion of the intraaortic balloon pump was 19.6%, 32.3%, and 40.5%, respectively (X2 = 16.4; p less than 0.001). Although use of the intraaortic balloon pump in the intraoperative and postoperative settings is accompanied by a favorable outcome in most patients, the high associated mortality suggests the need for earlier use of the intraaortic balloon pump or other supportive measures such as the ventricular assist device.

Angina, Unstable↗

PubMed1992

Pressure-gated acquisition of cardiac MR images.

Electrocardiographically gated magnetic resonance (MR) image acquisition is not optimal for the quantification of in vivo cardiac deformation, because of the cycle-length dependence of cardiac mechanical events. The authors developed a method for acquisition of cardiac MR images gated to the first derivative of left-ventricular-developed pressure and used the method in a canine model. Application of this method may improve myocardial stress-strain analyses.

Animals↗

PubMed1991

Regional myocardial stress distribution from magnetic resonance image-based mathematical models.

The instantaneous regional stress distribution within the myocardium, which cannot be directly measured, has been estimated using improved numerical methods and nonaxisymmetric biventricular geometry. To do this, we have employed computer-aided solid mathematical modeling to generate a three-dimensional representation for an ex vivo canine biventricular unit using magnetic resonance imaging. A two-dimensional transverse section was isolated from the solid mathematical model for regional stress analysis using p-version finite element analysis. Loading conditions and material property descriptions were taken from published reports. Analyses showed the maximum principal stresses to range from -1.76 X 10(5) to 8.52 X 10(5) dynes/cm2 during systolic loading, and from -3.85 X 10(4) to 1.13 X 10(5) dynes/cm2 during diastolic loading. This study demonstrates that magnetic resonance image-based solid mathematical biventricular models are suitable for regional stress analysis using p-version finite element analysis. p-Version finite element analysis using magnetic resonance image-based cardiac representations facilitates in vivo stress-strain analyses and may allow the clinical estimation of regional myocardial stress.

Animals↗

PubMedDate not supplied

Hybrid DANTE and phase-contrast imaging technique for measurement of three-dimensional myocardial wall motion.

Characterization of myocardial stress and strain is necessary for a complete understanding of myocardial function. The precise quantification of regional myocardial strain is complicated by its time-varying pattern and regional variation resulting from the anisotropy of the myocardium and by complex torsional and shortening motions of the heart during the cardiac cycle. The authors have developed a technique for point-specific tracking of myocardial motion along all three axes in a constant selected section of myocardium by combining prospective section selection with in-plane DANTE (delays alternating with nutations for tailored excitation) tissue tagging and phase-contrast detection of motion perpendicular to the image plane. With this technique, it is possible to determine point-specific myocardial strain values in vivo.

Animals↗