OBJECTIVES:To test the hypothesis that two populations of myocardial fibres-fibres aligned parallel to the surfaces of the wall and an additional population of fibres that extend obliquely through the wall-when working in concert produce a dualistic, self stabilising arrangement.METHODS:Assessment of tensile forces in the walls of seven porcine hearts by using needle probes. Ventricular diameter was measured with microsonometry and the intracavitary pressure through a fluid filled catheter. Positive inotropism was induced by dopamine, and negative inotropism by thiopental. The preload was raised by volume load and lowered by withdrawal of blood. Afterload was increased by inflation of a balloon in the aortic root. The anatomical orientation of the fibres was established subsequently in histological sections.RESULTS:The forces in the fibres parallel to the surface decreased 20-35% during systolic shrinkage of the ventricle, during negative inotropism, and during ventricular unloading. They increased 10-30% on positive inotropic stimulation and with augmentation in preload and afterload. The forces in the oblique transmural fibres increased 8-65% during systole, on positive inotropic medication, with an increase in afterload and during ventricular shrinkage, and decreased 36% on negative inotropic medication. There was a delay of up to 147 ms in the drop in activity during relaxation in the oblique transmural fibres.CONCLUSION:Although the two populations of myocardial fibres are densely interwoven, it is possible to distinguish their functions with force probes. The delayed drop in force during relaxation in obliquely oriented fibres indicates that they are hindered in their shortening to an extent that parallels any increase in mural thickness. The transmural fibres, therefore, contribute to stiffening of the ventricular wall and hence to confining ventricular compliance.

Surgical strategies recently introduced to improve ventricular function have been based on the concepts of reduction of ventricular diameter, synchronization of myocardial activity, passive support of diastolic ventricular shape, and active support of systolic ventricular constriction. They have depended on several established theoretical assumptions, not all of which are totally valid. Clinical results have proved markedly variable. This is especially true for procedures designed to reduce the radius of the left ventricle. Some have reported up to 80% mortality, whereas others achieve results comparable with those for heart transplantation. Because of this, the method runs the risk to be rejected, or else, its more widespread application will be postponed until essential details concerning the basic concepts have been elucidated. It is these details which we discuss in this review.

Objectives: To test the hypothesis that two populations of myocardial fibres—fibres aligned parallel to the surfaces of the wall and an additional population of fibres that extend obliquely through the wall—when working in concert produce a dualistic, self stabilising arrangement. Methods: Assessment of tensile forces in the walls of seven porcine hearts by using needle probes. Ventricular diameter was measured with microsonometry and the intracavitary pressure through a fluid filled catheter. Positive inotropism was induced by dopamine, and negative inotropism by thiopental. The preload was raised by volume load and lowered by withdrawal of blood. Afterload was increased by inflation of a balloon in the aortic root. The anatomical orientation of the fibres was established subsequently in histological sections. Results: The forces in the fibres parallel to the surface decreased 20235% during systolic shrinkage of the ventricle, during negative inotropism, and during ventricular unloading. They increased 10230% on positive inotropic stimulation and with augmentation in preload and afterload. The forces in the oblique transmural fibres increased 8265% during systole, on positive inotropic medication, with an increase in afterload and during ventricular shrinkage, and decreased 36% on negative inotropic medication. There was a delay of up to 147 ms in the drop in activity during relaxation in the oblique transmural fibres. Conclusion: Although the two populations of myocardial fibres are densely interwoven, it is possible to distinguish their functions with force probes. The delayed drop in force during relaxation in obliquely oriented fibres indicates that they are hindered in their shortening to an extent that parallels any increase in mural thickness. The transmural fibres, therefore, contribute to stiffening of the ventricular wall and hence to confining ventricular compliance.

Background. Because of the variation in the surgical procedures designed to reduce ventricular radius, along with differences in hospital care, it is difficult to disentangle the factors that may contribute to the success or failure of the partial left ventriculectomy. Methods and Results: We undertook partial left ventriculectomy in 18 patients, 10 suffering from idiopathic dilated cardiomyopathy and 8 from ischemic heart disease. We assessed the amount of reduction in wall stress, the systolic thickening of the ventricular wall, and the extent of connective tissue in the excised segment of the wall. Of the overall group, six patients died, three from infarction, one of stroke, one with asystole, and one with ventricular fibrillation. The mean decrease in measured mesh tension was 40% (p < 0.001). Most patients exhibited improvements postoperatively in terms of the systolic thickening of the posterior and superior free walls of the left ventricle. In those in whom the events could be monitored, life-threatening arrhythmias posed complications in three of four patients with ischemic heart disease, and in two of six patients suffering from idiopathic dilated cardiomyopathy. In one patient, death was associated with a transmural alignment of fibrous tissue. Conclusions: Our measured reductions in myocardial mesh tension were in keeping with the anticipated theoretical reduction in wall stress expected from partial ventriculectomy. The basic concept underscoring surgical maneuvers to reduce ventricular radius, therefore, is sound. A potential trap is the resection of the marginal artery. Critical myofibrosis was a rare complication. Arrhythmias, which are common, can successfully be treated by implantation of antitachycardic and defibrillatory devices.