Architecture of the left ventricle: insights for optimal surgical ventricular restoration
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The normal left ventricular shape has been defined as prolate ellipsoid. This shape is an adaptation to evolution. A knowledge of its unique macro and micro architecture forms the cornerstone in the understanding of its complex function. The left ventricle has a unique architecture with three different myofiber orientations, the longitudinal, circumferential and oblique fibers. The oblique orientation of fibers is essential for effective clockwise and anticlockwise torsional movements during systole and diastole, for optimal ventricular ejection and filling. The orientation and fiber angle decide the shape of the ventricle. An ellipsoid shape is vital for optimal function. Pathological disease states such as ischemic heart disease, valvular heart disease and cardiomyopathies cause a loss of obliquity of the myofibers. The myofibers become more horizontal resulting in ventricular dilatation and increased sphericity. The change from ellipsoid to globular shape with disease heralds the onset of left ventricular dysfunction and initiates the cascade of heart failure. Several strategies have been successful in reverting ventricular dilatation and sphericity to a more ellipsoid geometry. Pharmacological therapies like beta blockade and angiotensin converting enzyme inhibition have proven beneficial in early stages of heart failure with pathological remodeling. However, these agents in isolation are limited in reversing pathological remodeling in advanced heart failure. In some cases of advanced heart failure due to postinfarction left ventricular aneurysms, ventricular volume reduction with restoration surgeries have a role in restoring ventricular geometry with beneficial clinical outcomes. Surgical ventricular restoration has progressively evolved from the 1950s. Initially, aneurysmal resection and linear repair was done. This was gradually replaced by endoventricular patch plasty, which had better results. The resulting left ventricle was smaller in size but still continued to have a spherical configuration. Exclusion of the infarct area with a smaller longitudinal patch results in realignment of the non-diseased ventricular fibers with a resulting ellipsoid shape. This ellipsoid shape ensures clinical benefits. The geometry of the endoventricular patch thus holds the key to optimal ventricular shape in these patients. The technique to optimally restore a diseased ventricle to normal continues to evolve. This requires insights into the normal architecture and function, and the pathophysiologic effects of disease.