QUANTIFICATION OF MYOCARDIAL FUNCTION IN 3 DIMENSIONS

心肌应力应变的临床与实验应用

The clinical and experimental application of myocardial stress-strain descriptors of systolic and diastolic ventricular function awaits accurate three-dimensional (3-D) description of IN VIVO biventricular cardiac geometry. Anatomic three-dimensional reconstruction by ECG-gated magnetic resonance imaging (MRI) of the heart, unlike other 3-D scanning modalities, is capable of clearly delineating the blood/chamber wall interface in intact animals. A true 3-D geometrical description, including wall thickness, has therefore become available by NON-INVASIVE scanning without infusion of contrast agents. The goal of this proposal is to interface this modality with chamber pressure determinations to allow the application of stress-strain descriptors of biventricular cardiac function. Phase I (validation and development) involves the comparison of myocardial dimensional descriptions obtained by ECG-gated 3-D MRI in intact, anesthetized dogs with (1) subsequent scans of the excised hearts, (2) standard quantitative contrast ventriculography, and (3) necropsy determinations in the same animals. A specially designed calibration phantom will allow validation of 3-D MRI measurements. The description of biventricular cardiac geometry supplied by 3-D cardiac MRI scanning will then be interfaced with chamber pressure data obtained simultaneously in the same animals for application of indices of systolic and diastolic function. Phase II (laboratory application will involve the use of 3-D cardiac MRI assessment of cardiac geometry to perform biventricular 3-D stress analysis. This will include use of the finite-element method, as well as currently used standard models employing systolic (end-systolic) and diastolic stress-strain analyses. The biventricular conservation of ventricular wall stress will be assessed by graphic display of global 3-D stress determinations over the entire biventricular geometrical model supplied by 3-D MRI reconstruction. Studies in the intact, normal canine circulation will be compared with those in animals with both acute and chronic ipsilateral alteration of ventricular wall stress. Subsequent stress displacement to the contralateral ventricular chamber walls will be assessed in addition to clarification of the role of septal mediation in this energy transference. Further definition of these biventricular stress-strain relationships may challenge, or at least further define, our basic understanding of ventricular interaction.