Joseph C. Walker

Theoretical Impact of the Injection of Material Into the Myocardium A Finite Element Model Simulation

Background— To treat cardiac injuries created by myocardial infarcts, current approaches seek to add cells and/or synthetic extracellular matrices to the damaged ventricle to restore function. Because definitive myocardial regeneration remains undemonstrated, we propose that cardiac changes observed from implanted materials may result from altered mechanisms of the ventricle. Methods and Results— We exploited a validated finite element model of an ovine left ventricle with an anteroapical infarct to examine the short-term effect of injecting material to the left ventricular wall. The models mesh and regional material properties were modified to simulate expected changes. Three sets of simulations were run: (1) single injection to the anterior border zone; (2) therapeutic multiple border zone injections; and (3) injection of material to the infarct region. Results indicate that additions to the border zone decrease end-systolic fiber stress proportionally to the fractional volume added, with stiffer materials improving this attenuation. As a potential therapy, small changes in wall volume (≈4.5%) reduce elevated border zone fiber stresses from mean end-systole levels of 28.2 kPa (control) to 23.3 kPa (treatment), similar to levels of 22.5 kPA computed in remote regions. In the infarct, injection improves ejection fraction and the stroke volume/end-diastolic volume relationship but has no effect on the stroke volume/end-diastolic pressure relationship. Conclusions— Simulations indicate that the addition of noncontractile material to a damaged left ventricular wall has important effects on cardiac mechanics, with potentially beneficial reduction of elevated myofiber stresses, as well as confounding changes to clinical left ventricular metrics.

Magnetic resonance imaging-based finite element stress analysis after linear repair of left ventricular aneurysm

OBJECTIVE Linear repair of left ventricular aneurysm has been performed with mixed clinical results. By using finite element analysis, this study evaluated the effect of this procedure on end-systolic stress. METHODS Nine sheep underwent myocardial infarction and aneurysm repair with a linear repair (13.4 +/- 2.3 weeks postmyocardial infarction). Satisfactory magnetic resonance imaging examinations were obtained in 6 sheep (6.6 +/- 0.5 weeks postrepair). Finite element models were constructed from in vivo magnetic resonance imaging-based cardiac geometry and postmortem measurement of myofiber helix angles using diffusion tensor magnetic resonance imaging. Material properties were iteratively determined by comparing the finite element model output with systolic tagged magnetic resonance imaging strain measurements. RESULTS At the mid-wall, fiber stress in the border zone decreased by 39% (sham = 32.5 +/- 2.5 kPa, repair = 19.7 +/- 3.6 kPa, P = .001) to the level of remote regions after repair. In the septum, however, border zone fiber stress remained high (sham = 31.3 +/- 5.4 kPa, repair = 23.8 +/- 5.8 kPa, P = .29). Cross-fiber stress at the mid-wall decreased by 41% (sham = 13.0 +/- 1.5 kPa, repair = 7.7 +/- 2.1 kPa, P = .01), but cross-fiber stress in the un-excluded septal infarct was 75% higher in the border zone than remote regions (remote = 5.9 +/- 1.9 kPa, border zone = 10.3 +/- 3.6 kPa, P < .01). However, end-diastolic fiber and cross-fiber stress were not reduced in the remote myocardium after plication. CONCLUSION With the exception of the retained septal infarct, end-systolic stress is reduced in all areas of the left ventricle after infarct plication. Consequently, we expect the primary positive effect of infarct plication to be in the infarct border zone. However, the amount of stress reduction necessary to halt or reverse nonischemic infarct extension in the infarct border zone and eccentric hypertrophy in the remote myocardium is unknown.

Unusual Posterior Fossa Dural Arteriovenous Malformation in a Neonate: Case Report

We report the case of an infant born with an unusual posterior fossa dural arteriovenous malformation that was supplied by the entire intracranial circulation. The lesion caused hydrocephalus and congestive heart failure that led to the infants death.

TCT-725 Point-of-Care Genetic Testing of Eleven CYP2C19 Single Nucleotide Polymorphisms Identifies Extensive and Reduced Metabolizers of Clopidogrel With High Accuracy in Patients With Coronary Artery Disease

Point-of-Care Genetic Testing of Eleven CYP2C19 Single Nucleotide Polymorphisms Identifies Extensive and Reduced Metabolizers of Clopidogrel With High Accuracy in Patients With Coronary Artery Disease

In Vivo Myocardial Material Properties and Stress Distributions in Normal and Failing Human Hearts

A noninvasive method for estimating myocardial material properties in vivo would be of great value in the design and evaluation of new surgical and medical strategies to treat and/or prevent heart failure. Once the material properties for the myocardium are established, the effect of therapeutic changes on regional geometry (i.e., surgical remodeling) and/or material properties (i.e., medicine, gene therapy, and cell therapy) can be evaluated and the success or failure of a proposed therapy predicted. With clinical experience, such a method could be used as a diagnostic modality to risk stratify patients early after a myocardial infarction (MI) who are at risk for adverse remodeling and the development of heart failure.