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Functional Architecture of the Heart: Torsional Contraction and Spiral Flow


J. Yasha Kresh, PhD, FACC, FAHA
Jkresh@drexelmed.edu

Pablo Huang, MS
Psh25@drexel.edu

Howard J. Eisen, MD
Heisen@drexelmed.edu
Drexel University College of Medicine
Philadelphia, PA, USA



Most, if not all, treatment modalities to correct and/or replace cardiac structural abnormalities are rooted in representing the heart as a pressure generating source for propelling blood circulation. Not until very recently has the helical structural arrangement of the cardiac muscle and the torsional dynamics (twisting and untwisting) of the ventricles during ejection and relaxation gained wider recognition and clinical impact. Much of this occurred in the past decade with the advent of sophisticated non-invasive dynamic 3-D imaging (i.e., Echo, MRI) of the blood-flow velocity patterns, exhibiting spiraling / vortical streamlines emanating from the ventricles. The specific molecular signaling pathways and significance (adaptation, pathogenesis) related to the more complex, momentum imparted, spiral flow in normal physiology and its alteration in heart failure leading to the onset of vascular pathophysiological states (atherosclerosis, thrombosis) needs to be fully elucidated.

Spiral blood flow, capable of organizing multi-directional streams, has been associated with flow stability (decreased turbulence), cardiovascular disease process deterrence, improved lumen-wall oxygen transport, and washout effects by reducing blood element adhesion to vessel walls [1, 2, 3, 4]. The phases of the cardiac cycle produce variable helical content in the flow, which may modulate plaque formation by regulating the wall shear stress (WSS) mediated mechanotransduction signaling pathways of endothelial cells [4, 5]. Shear stress operates on a number of spatio-temporal scales known to regulate focal endothelial gene expression; it can signal WSS-induced atheromatous and/or thrombotic susceptibility due to flow disturbances resulting from physiological branching/curvature, stenosis (remodeling) and presence of intravascular devices [6, 7].

Remarkably, despite the increasing recognition that spiral flow may play a pivotal role in preserving endothelial homeostasis via the regulation of laterally directed forces and the normalization of WSS gradients, very few existing implantable cardiovascular devices (total artificial heart, ventricular assist device, grafts, stents) incorporate helical features into their design considerations for fluid dynamic optimization. Mechanical circulatory support (MCS), for example, is increasingly being used for long-term hemodynamic augmentation in heart failure patients. Re-establishing native spiral fluid flow structures may improve device functional patient compatibility. In its current form, mechanical heart valve replacements continue to generate flow disturbances - such as induced jetting, flow separation, and shear stress gradient increase - leading to platelet activation and blood trauma [8].

Intriguingly, the incorporation of helical design forms integrated into bypass grafts was shown to enhance flow uniformity at anastomoses, absence of noted recirculation regions, decrease in platelet aggregation, and mixing of low-high momentum fluid within vessels [9]. Stent designs containing helical features were associated with reduced neointimal hyperplasia in stented arteries, compared to conventional straight stents [10]. In our ongoing studies, we have been able to demonstrate that induced spiral flow was associated with diminished fluid jet dynamic pressure. The reduction in fluid jet force impact is particularly important in ventricular assist device outflow cannula designs, and an important consideration in general anastomoses.

Translational Perspective:

The precarious (unintended) scrambling of spiral flow that may be caused by bileaflet mechanical valves, due to their inherent design criteria, has not been examined as a source for disrupting physiologically protective conditions attributable to spiral flow. In our preliminary studies, the preservation/propagation of generated spiral flow has been demonstrated to be valve-specific; the valve orifice geometry and leaflets play a crucial role in flow-pattern (de-)modulation.

The incorporation of spiral flow into the outflow track of mechanical circulatory systems and devices may contribute materially to the reduction of aneurysm-promoting wall forces (vascular lumen mechanical integrity) and increase transport efficiency across the cannula - aorta interface, optimize device energy demand, and attenuate the degree of aortic insufficiency. The impetus remains for designing continuous-flow mechanical circulatory assist devices and other interventional therapies (e.g., macro/micro patterned helical stents) that incorporate the proven beneficial attributes of spiral flow dynamics. The more biologically-inspired designs may provide opportunities for minimizing blood element damage (e.g. vWF uncoiling, RBC lysing, platelet activation), facilitating more precise/safer anticoagulation therapies. ■

Disclosure Statement: The authors have no commercial relationships to disclose. Dr. Eisen discloses that he is not an expert on the topic of this article and defers all questions to Dr. Kresh and Mr. Huang.


References:

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