Original article: cardiovascular
Mechanism underlying mechanical dysfunction in the border zone of left ventricular aneurysm: a finite element model study

https://doi.org/10.1016/S0003-4975(00)02338-9Get rights and content

Abstract

Background. The global left ventricular dysfunction characteristic of left ventricular aneurysm is associated with muscle fiber stretching in the adjacent noninfarcted (border zone) region during isovolumic systole. The mechanism of this regional dysfunction is poorly understood.

Methods. An anteroapical transmural myocardial infarct was created by coronary arterial ligation in an adult Dorset sheep and was allowed to mature into left ventricular aneurysm for 10 weeks. The animal was imaged subsequently using magnetic resonance imaging with simultaneous recording of intraventricular pressures. A realistic mathematical model of the three-dimensional ovine left ventricle with an anteroapical aneurysm was constructed from multiple short-axis and long-axis magnetic resonance imaging slices at the beginning of diastolic filling.

Results. Three model simulations are presented: (1) normal border zone contractility and normal aneurysmal material properties; (2) greatly reduced border zone contractility (by 50%) and normal aneurysmal material properties; and (3) greatly reduced border zone contractility (by 50%) and stiffened aneurysmal material properties (by 1000%). Only the latter two simulations were able to reproduce experimentally observed stretching of border zone fibers during isovolumic systole.

Conclusions. The mechanism underlying mechanical dysfunction in the border zone region of left ventricular aneurysm is primarily the result of myocardial contractile dysfunction rather than increased wall stress in this region.

Section snippets

Creation of left ventricular aneurysm

The study was performed in compliance with the animal welfare regulations and the “Guide for the Care and Use of Laboratory Animals” as revised in 1996 [10]. The extremely reproducible ovine model of LV aneurysm described by Markovitz and colleagues [11] was used. An adult Dorset sheep was sedated with ketamine (15 mg/kg intramuscularly), masked, and then intubated and ventilated with a mixture of isoflurane and oxygen. The surface electrocardiogram and the arterial pressure (left femoral

Normal border zone contractility

Figure 5A shows the model configuration obtained for an LV chamber pressure of 1 kPa (7.5 mm Hg) and normal diastolic material properties throughout the wall (including the aneurysm). Figure 5B shows the model configuration obtained for an LV chamber pressure of 8 kPa (60 mm Hg), normal contractility in the remote and BZ regions, and no contractility in the apical aneurysm. Although the chamber volumes are the same in both figures, the corresponding myocardial strain distributions are quite

Comment

In summary, we developed the most realistic mathematical model of the infarcted LV to date and used it to study the mechanism underlying mechanical dysfunction in the BZ region of LV aneurysm. When the aneurysm in the model had normal diastolic material properties, BZ contractility had to be reduced to only half of that in regions remote from the aneurysm to predict the previously observed stretching of BZ fibers during isovolumic systole. Similarly, a 50% reduction in BZ contractility was

Acknowledgements

The authors gratefully acknowledge Glen W. Foster, RT, for his patience and expertise in performing the imaging experiments, Ruth Okamoto, DSc, for assistance with the analysis of the images, and Diane Toeniskoetter and Dennis Gordon for assistance with the animal experiments. This study was supported by National Institutes of Health grant R01-HL-58759 (J.M.G.).

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