Methods and devices for self-adjustable intra-atrial shunt

Abstract

The present teaching provides devices and methods for treating heart disease by normalizing elevated blood pressure in the left and right atria of a heart. Various embodiments of the devices allow left-to-right blood flow through their flow elements. The flow element of the device is designed to self-adjust the amount of blood flow in response to the left atrial pressure fluctuation.

Description

METHODS AND DEVICES FOR SELF-ADJUSTABLE INTRA-ATRIAL SHUNTCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of U.S. Provisional Application No. 63 / 673,783, filed July 21, 2024, the entirety of which is incorporated herein by reference.FIELD

[0002] The present teaching relate to a device and methods to treat or ameliorate diastolic heart failure by balancing the flow and pressure of the pulmonary valve. An example of the present teaching relates to a device that can be used to intervene or change (e.g., reduce) the blood pressure in a heart chamber by creating a shunt and optionally regulating the blood flow through the shunt to enhance the therapeutic effect of the shunt. The present teaching further relate to a method of utilizing such a device, for example, in treatment of congestive heart failure-related conditions, for example, acute cardiogenic pulmonary edema typically caused by an elevated pressure in a left side chamber in a heart.BACKGROUND

[0003] The human circulatory system is a two-part system and its purpose is to bring oxygen-bearing blood to all the tissues of the body. When the heart contracts, it pushes the blood out into two major loops or cycles. In the systemic loop, the blood circulates into the body’s cardiovascular system, bringing oxygen to all the organs, structures, and tissues, and collecting carbon dioxide waste. In the pulmonary loop, the blood circulates to and from the lungs, to exchange carbon dioxide for oxygen. The systemic cycle is controlled by the left side of the heart and the pulmonary cycle by the right side of the heart.

[0004] The systemic loop begins when the oxygen-rich blood coming from the lungs enters the left atrium of the heart. As the left atrium fills, it presses open the mitral valve and the blood flows down into the left ventricle. When the ventricles contract during a heartbeat, the blood in the left ventricle is forced into the aorta. The blood leaving the aorta brings oxygen to all the body’s cells through the network of smaller arteries and capillaries.

[0005] The oxygen-depleted blood from the body returns to the heart through the network of veins. All of the blood from the body is eventually collected into the two largest veins: the superior vena cava, which collects blood from the upper body, and the inferior vena cava, which collects blood from the lower body. Both vena cava empty the blood into the right atrium of the heart. From here the blood begins its journey through the pulmonary cycle.

[0006] From the right atrium, the blood descends into the right ventricle through the tricuspid valve. When the right ventricle contracts, the blood is pushed through the pulmonary valve into the pulmonary artery that branches into two main parts: one going to the left lung, one to the right lung. The fresh, oxygen-rich blood returns to the left atrium of the heart through the pulmonary veins.

[0007] Although the circulatory system is made up of two cycles, both cycles take place at the same time. The contraction of the heart muscle starts in the two atria, which push the blood into the two ventricles. Then the walls of the ventricles compress and force the blood out into the two arteries: the aorta to the body and the pulmonary artery to the lungs. Afterwards, the heart muscle relaxes, allowing blood to flow in from the veins and fill the atria again.

[0008] Congestive heart failure (CHF) is a condition affecting millions of people worldwide. CHF results from a weakening or stiffening of the heart muscle that commonly is caused by myocardial ischemia (due to, e.g., myocardial infarction) or cardiomyopathy (e.g., myocarditis, amyloidosis). CHF causes reduced cardiac output and inadequate blood to meet the needs of body tissue. CHF is generally classified into systolic heart failures (SHF) or diastolic heart failures (DHF).

[0009] In a SHF, the pumping action of a heart is reduced or weakened. A normal ejection fraction (EF), which is a function of the volume of blood ejected out of the left ventricle (stroke volume) divided by the maximum volume remaining in the left ventricle at the end of the diastole or relaxation phase, is greater than 50%. In a systolic heart failure, EF is decreased to less than 50%. A patient with SHF may have an enlarged left ventricle because of cardiac remodeling developed to maintain adequate stroke-volume. This pathophysiological phenomenon is often associated with increased atrial pressure and left ventricular filling pressure.

[0010] DHF is a heart failure refers to a decline in performing one or both ventricles of the heart during the diastole. Generally, DHF is a failure of the ventricle to adequately relax and expand, resulting in a decrease in the stroke volume of the heart. Thus, DHF is characterized by elevated diastolic pressure in the left ventricle, despite essentially normal / physiologic end diastolic volume (EDV). In a DHF patient, the stiffness of the left ventricular makes it more difficult for blood to enter it from the left atrium. As a result, pressure rises in the atrium and is transmitted back to the pulmonary venous system, thereby increasing its hydrostatic pressure and promoting pulmonary edema. DHF afflicts between 30% and 70% of those patients with CHF.

[0011] Presently, there are very few treatment options for patients suffering from DHF. Treatments for CHF include: (1) pharmacological treatments, (2) assisting systems, and (3) surgical treatments. Pharmacological treatments, e.g., with diuretics, are used to reduce the workload of a heart by reducing blood volume and preload. While drug treatment improves quality of life, it has little effect on survival. Assisting devices, e.g., mechanical pumps, are used to reduce the load on the heart by performing all or part of the pumping function normally done by the heart. However, in a chronic ischemic heart, high-rate pacing may lead to increased diastolic pressure, calcium overload, and damage to the muscle fibers. There are at least three surgical procedures for treatment of a heart failure: (1) heart transplant, (2) dynamic cardiomyoplasty, and (3) the Batista partial left ventriculectomy. These surgical treatments are invasive and have many limitations.

[0012] There are several known techniques that can be used to treat the symptoms of DHF. Without attempting to characterize the following references, for example, United States Patent No. 8,091,556 by Keren et al. discloses the use of an interatrial pressure relief shunt with a valve and a tissue affixation element at each end of the shunt; United States Patent No. 8,043,360 by McNamara et al. discloses the use of an interatrial pressure vents allowing sufficient flow from the left atrium to the right atrium to relieve elevated left atrial pressure and resulting patient symptoms; and United States Patent Application Publication No.20050165344 by Dobak discloses a pressure relief system with an interatrial septal conduit and an emboli barrier or trap mechanism to prevent thrombi or emboli crossing the conduit into the left sided circulation causing cryptogenic stroke. Dobak also discloses a conduit with a one-way valve which directs blood flow from the left atrium to the right atrium.

[0013] The constantly evolving nature of heart failure represents a significant challenge for the treatment. Therefore, there is a need for novel and adaptable methods and devices for treating DHF, for example, by reducing the flow and / or the pressure in the pulmonary circulation system, and the pressure in the left atrium.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] FIG. 1 is a perspective view of an exemplary atrial shunt device placed cross an atrial opening in accordance with the present teaching;

[0015] FIGs. 2a-2b are perspective views of an exemplary atrial shunt with flow element recovery mechanism in accordance with the present teaching;

[0016] FIG. 3 is a perspective view of an exemplary flow element recovery mechanism in accordance with the present teaching;

[0017] FIG. 4 is a perspective view of an exemplary atrial shunt with flow element recovery mechanism in accordance with the present teaching.DETAILED DESCRIPTION

[0018] The present teaching provides devices deployed across a patient's atrial septum, the atrial shunt device, a frame, and a flow element. The frame has distal and proximal anchors engaging the left and right sides of the atrial septum respectively. The frame also has an axial body which provides a sliding guide and a position recovery mechanism to the flow element. The flow element of the device is configured to slide distally and proximally along the sliding guide of the frame. The flow element creates a shunt or passageway, allowing blood flow across the aperture. The present teaching is described more fully hereinafter with reference to the accompanying drawings, which show certain embodiments of the present teaching. The present teaching may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to illustrate various aspects of the present teaching. Like numbers refer to like elements throughout.

[0019] Generally, the left atrium has a higher pressure than the right atrium, and the blood tends to flow from the left atrium across the shunt to the right atrium. The amount of blood allowed to flow from the left to right atria is determined by the shunting size of the device.The greater the shunting size, the greater the amount of blood flows to the right atrium, and the greater the left heart decompresses.

[0020] The present embodiment discloses an atrial shunt device that is, upon implantation, capable of adapting to the left-to-right atrial pressure difference and spontaneously adjusting shunting size after implantation. According to one embodiment of the present teaching, the device securely situates in an opening created in the atrial septum. As the left-to-right atrial pressure difference increases, the device automatically adjusts itself to a configuration of greater left-to-right blood shunt. As the left-to-right atrial pressure difference decreases, the device then spontaneously recovers itself to a configuration of less left-to-right blood shunt.

[0021] Fig. 1 illustrates one embodiment of the present teaching. The device has a frame and a flow element. Referring to Fig. 1, the frame of the device has a distal anchor, a proximal anchor, and an axial body. As shown in Fig. 1, the frame is configured to be positioned across an opening between the left and right atrium of the heart, with the distal anchor and the proximal anchor of the frame engaging the perspective side of the atrial septum. As shown in Fig. 1, in the deployed configuration of the device, the distal and proximal anchors have radially outward free ends, and radially inward ends joining the axial body of the frame. According to one embodiment, the distal and proximal anchors are in the shape of annual flanges with a plurality of flange segments. When the device is delivered through a delivery catheter, both distal and proximal anchors of the frame extend in the direction parallel to the axial body of the frame. Upon deployment in vivo, both distal and proximal anchors turn radially outward. In one embodiment, the radially outward free ends of the distal and proximal anchors engage the atrial septum. In another embodiment, at least one of the deployed distal and proximal anchors forms a substantially plane surface engaging the atrial septum.

[0022] In one embodiment, both distal and proximal anchors oppose the adjacent septal tissue with minimum pressure, and the atrial septum fits inside a gap in between the distal and proximal anchors. In another embodiment, the distal and proximal anchors contact and apply pressure to the atrial septal tissue.

[0023] In one embodiment, each flange segment is formed of two individual strut elements, such as those disclosed in the US patent No. 8,043,360. In an alternative embodiment, each flange segment is formed of a single strut. In another embodiment, manydesign configurations could be incorporated for the distal and proximal anchors as long as they serve the function for securing the device at the atrial opening. Additionally, one skill in the art should also understand that the distal and proximal anchors could have the same configuration or different configuration from each other.

[0024] Continue referring to Fig. 1, the axial body of the frame joins the distal and proximal anchors of the frame and is configured to be positioned across the atrial opening. As shown in Figs. 1-2, the axial body has a generally tubular profile with an axial luminal, which opens at its distal and proximal ends. In one embodiment, the axial body is configured to maintain the size of the opening on the atrial septum. In one embodiment, the axial body of the frame fits inside the opening on the atrial septum. In another embodiment, the axial body of the frame applies a radially outward pressure against the surrounding septal tissue. According to one embodiment of the present teaching, the axial body of the frame is configured to have significant material coverage over the septal tissue in order to prevent endothelialization. In one embodiment, the material coverage of the axial body of the frame is more than 25%. In one embodiment, the axial body of the frame has a maximum diameter of 10mm. According to one embodiment, the distal end of the axial body of the frame aligns with the left atrial side of the septal tissue. In another embodiment, the proximal end of the axial body of the frame extends into the right atrium with the proximal end of the axial body extending proximally beyond the right atrial side of the septal tissue.

[0025] According to one embodiment of the present teaching, the axial body is designed to allow a flow element slidaly engage the frame of the device. Continue referring to Fig. 1, the flow element of the device has a generally tubular shape, with a proximal end, and an open distal end. The flow element is configured to fit inside the axial lumen of the axial body of the frame. In one embodiment, the axial body provides guidance to the flow element, thereby allowing the flow element moves proximally and distally along, and inside the axial body of the frame. According to one embodiment, a gap, between the exterior luminal surface of the flow element and the interior luminal surface of the frame body, allows peripheral blood flow between left and right atrium. In one embodiment of the present teaching, the gap between the flow element and the frame body is about 1mm.

[0026] Continue referring to Fig. 1, the flow element has a closed proximal end, an open distal end and a plurality of flow orifices along its tubular wall. In one embodiment the flow orifices on the tubular wall of the flow element allows the blood to enter and exit the tubular lumen of the flow element. Upon deployment in vivo, a distal portion of the flow element is inside the left atrium, a proximal portion is inside the right atrium. Thus, upon deployment in vivo, the left atrial blood enters the open distal end and the flow orifices of the flow element inside the left atrium, and exits the flow orifices of the flow element exposed inside the right atrium.

[0027] According to one embodiment, the overall longitudinal length of the flow element is greater than the overall longitudinal length of the axial body of the frame. According to one embodiment, the flow element slides along the longitudinal axis of the axial body of the frame. When the flow element is at its most proximal position, the distal end of the flow element aligns with the distal end of the axial body of the frame, and the proximal end of the flow element extends proximally beyond the proximal end of the axial body of the frame and into the right atrium. In this most proximal position, a maximum amount of the flow orifices on the tubular surface of the flow element exposes inside the right atrium, thereby allowing a maximum amount of left-to-right blood shunt.

[0028] In another embodiment of the present teaching, when the flow element is at its most distal position in relation to the frame body, the proximal end of the flow element aligns the proximal end of the axial body of the frame, and the distal end of the flow element extends distally beyond the distal end of the axial body of the frame and into the left atrium. In this most distal position, a minimum amount of the flow orifices on the tubular surface of the flow element exposes inside the right atrium, and thereby allowing a minimum amount of left-to-right blood shunt.

[0029] According to one embodiment, an effective shunt length is the length of the flow element extending beyond the proximal end of the axial body of the frame. In one embodiment, the maximum effective shunt length is the length of the flow element extending beyond the proximal end of the axial body of the frame when the distal end of the flow element aligns with the distal end of the frame body. In another embodiment, the device is designed to have no effective shunt length when the proximal end of the flow element aligns with the proximal end of the axial body of the frame.

[0030] In one embodiment of the present teaching, the flow element has an overall length of 25mm. In another embodiment, the length of the flow element is at least twice the length of the axial body of the frame. In another embodiment, the maximum effective shunt length is at least 10mm.

[0031] In one embodiment of the present teaching, the flow element has a general tubular shape throughout its entire length. In another embodiment, the flow element has a cone shaped proximal portion in addition to the tubular shaped rest of portions, for example as shown in Figs. 1 & 2a- 2b. One skilled in the art should understand that the specific shape of the flow element shown and described in the exemplar embodiments should not be used to limit the scope of the present teaching.

[0032] In one embodiment of the present teaching, the distal end of the flow element has a stopper, configured to prevent the distal end of the flow element from sliding proximally beyond the distal end of the frame body. In another embodiment, the proximal end of the flow element also has a stopper, configured to prevent the proximal end of the flow element from sliding distally beyond the proximal end of the frame body.

[0033] In one embodiment, the flow element has an open distal end, and a closed proximal end. In another embodiment, the proximal end of the flow element has a small orifice. Such a small orifice allows a small amount of blood flow through. In one embodiment, the small proximal orifice is configured to allow a delivery system, including delivery wire, delivery catheter, to extend through. In one embodiment such a proximal end orifice has a maximum diameter of 3mm.

[0034] According to one embodiment of the present teaching, for example as shown in Fig. 1, the flow orifices distribute along the entire tubular surface of the flow element. In another embodiment, not shown in the figures, the flow orifices distribute only along the effective shunt length of the flow element. In one embodiment, the flow orifices evenly distribute along the effective shunt length or entire length of the flow element. In another embodiment, the effective shunt length of the flow element has a greater density of the flow orifices along the longitudinal length of the flow element gradually increasing from the proximal end of the flow element toward distal end of the flow element. In one embodiment, the flow orifice is randomly distributed along the tubular surface of the flow element. In another embodiment, the flow orifice distributes in an organized pattern alongthe tubular surface of the flow element. In one embodiment, all flow orifices have the same size. In another embodiment, the flow orifices vary in size and shape, for example, the bigger flow orifices are placed near the proximal end portion of the flow element; and smaller size flow orifices are placed along the middle and distal end portions of the flow element. In another exemplary embodiment, the smaller flow orifices are placed near the proximal end of the flow element. In one embodiment, the flow orifices have a general diameter of 1-4 mm. In another embodiment, the total surface area of the flow orifices is about 10-50% of the tubular surface of the effective shunt portion.

[0035] Now referring to Fig. 2, in addition to the slidable attachment between the flow element and the axial body of the frame, the flow element also joins to the frame by a recovery mechanism. The recovery mechanism is designed to return the flow element to its minimum effective shunt position. According to one embodiment of the present teaching, the flow element is designed to move spontaneously under the influences of left atrial pressure. That is, when the left atrial pressure increases, the left-to-right atrial pressure difference becomes greater than the pre-designed resistance provided by the recovery mechanism, the flow element moves proximally toward the right atrium, increasing the effective shunt length and thereby allowing a greater left-to-right atrial blood shunt. When the left atrial pressure decreases, and the left-to-right atrial pressure difference reduces to a level less than the pre-designed resistance force provided by the recovery mechanism of the device, the recovery mechanism retracts the flow element distally, reducing the effective shunt length and the left-to-right atrial blood shunt.

[0036] According to one embodiment of the present teaching, the device is designed to have a pre-engineered “initial” configuration with the recovery mechanism of the device at its relaxed state and the flow element positioned at its most distal position with the proximal end of the flow element aligns the proximal end of the axial body of the frame. When the left atrial pressure increases to a level that the left-to-right atrial pressure difference is greater than the designed resistance of the recovery mechanism, the flow element slides proximally and stops at a position that the distal retraction force of the recovery mechanism equals to the proximal pushing force applied by the left atrial pressure. As the flow element slides proximally, the effective shunt length increases and more flow orifices are exposed inside the right atrium, allowing more left-to-right blood shunt. The increased left-to-rightblood shunt results in a decrease in left atrial pressure. When the left atrial pressure decreases to a level that the left-to-right atrial pressure difference is less than the designed resistance of the recovery mechanism, the flow element is then retracted distally by the recovery mechanism and stops at another position where an equilibrium is reached. According to one embodiment of the present teaching, when the left-to-right atrial difference is equal or greater than maximum retraction force pre-engineered for the recovery mechanism, the flow element moves to its most proximal position, allowing a maximum left-to-right blood shunt.

[0037] Thus, according to one embodiment of the present teaching, the flow element is designed to spontaneously move distally or proximally along the axial body of the frame in response to the left atrial pressure fluctuation. In another embodiment, the effective shunt length of the flow element is spontaneously adjusted in response to the left atrial pressure fluctuation. In another embodiment of the present teaching, the device creates a spontaneously adjustable shunt and thereby allows the amount of blood flow from left atrium to right atrium to be regulated by the left atrial pressure.

[0038] Continue referring to Figs. 2a-2b, an exemplary embodiment of the atrial shunt device is illustrated. As shown in Fig. 2a. The atrial shunt device has a frame and a flow element. The frame has a plurality of distal anchors, a plurality of proximal anchors, an axial body, and a flow element recovery mechanism. The distal anchors join the distal end of the axial body, the proximal anchors join the proximal end of the axial body, and the flow element recovery mechanism joins the axial body. As shownin the Fig. 2a, once deployed in vivo, the distal anchors of the frame are positioned against the atrial septum inside the left atrium; the proximal anchors of the frame is positioned against the atrial septum inside the right atrium; the axial body is positioned across an atrial opening, and the flow element recovery mechanism extends beyond the proximal end of the axial body of the frame proximally into the right atrium.

[0039] Continue referring to Figs. 2a-2b, the flow element slidably connects to the axial body of the frame with an annular gap formed between the flow element and the axial body. As shown in the figures, the flow element has a general tubular profile with a cone shaped proximal end portion. A plurality of flow orifice distributes along the tubular surface of the flow element. The flow orifices allow inflow and / or outflow of the blood. The distal end ofthe flow element is open and allows inflow of the blood. The proximal end of the flow element has a small orifice which allows a small amount of the blood to flow through. The flow element is configured to slide along the longitudinal axis of the axial body of the frame. In one embodiment, not shown in the figures, a guiding mechanism is incorporated inside the axial body of the frame making sure the flow element sliding steady along the longitudinal axis of the axial body of the frame. Upon deployment in vivo, since left atrial pressure is higher than the right atrial pressure, blood from left atrium enters the distal open end of the flow element as well flow orifices exposed inside the left atrium, and exited flow orifices exposed inside the right atrium. Also shown in Fig. 2a, the proximal end of the flow element connects to the proximal free ends of the flow element recovery mechanism. Since the exemplary flow element recovery mechanism, at its fully relaxed state, extends proximal beyond the proximal end of the axial body of the frame, the exemplary atrial shunt shown in Figs. 2a-2b is designed to provide a baseline i.e. minimum, left-to-right blood shunt.

[0040] Fig. 2a illustrates an exemplary embodiment of the atrial shunt device at its minimum shunting configuration. As shown in Fig. 2a, the flow element recovery mechanism is fully relaxed, the flow element is at its most distal position inside the axial body of the frame, and the distal end of the flow element extends distally beyond the distal end of the axial body of the frame and into the left atrium. In this configuration, the device allows minimum left-to-right blood flow. Fig. 2b illustrates an exemplary embodiment of the atrial shunt device at its maximum shunting configuration. As shown in Fig. 2b, the flow element recovery mechanism is under maximum tension, i.e. fully extended proximally; the flow element is at its most proximal position inside the axial body of the frame, (compared to the configuration shown in Fig. 2a); and the distal end of the flow element aligns the distal end of the axial body of the frame. In this configuration, the device allows a maximum left-to-right blood flow.

[0041] Fig. 3 is an illustration of a partial view of the proximal anchors and flow element recovery mechanism in an elongated delivery profile. As shown in Fig. 3, the exemplary flow element recovery mechanism is a plurality of tension springs extending proximally from the proximal end of the frame body. As shown in the exemplary embodiment in Fig.3, each tension spring has a zigzag spring portion with a proximal end portion. The zigzagspring portion of the tension spring, also known as no-sag spring portion, is made from two dimensional S-shaped wire. The proximal end portion has a proximal end configured to join the proximal end of flow element, and an enlarged surface portion, such as the loop portion, constructed to prevent tension spring from twisting. According to one embodiment of the present teaching, the enlarged surface section is generally oriented to conform to the tubular surface of the flow element. In one embodiment of the present teaching, the proximal end of the tension spring and the proximal end of the flow element are joined by suture or similar material. In another embodiment of the present teaching, the proximal end of the tension spring and the proximal end of the flow element are attached to each other via other mechanisms known to those skilled in the art. In addition, one skilled in the art should understand that the shape and configuration of the proximal end portion of the tension spring shown in Fig. 3, is merely an example of the present teaching and therefore should not be viewed as limiting.

[0042] According to one embodiment of the present teaching, under a highly elevated left atrial pressure, the flow element moves to its most proximal position and the tension springs of the flow element recovery mechanism are subject to a maximum tension and extend into their most elongated state, and as a consequence, the atrial shunt device delivers the greatest left-to-right shunt. As the left atrial pressure decreases, the tension springs recover and shorten, the flow element is then forced (by the recovery mechanism) to move distally. As a result, the left-to-right blood shunt reduces spontaneously.

[0043] According to one embodiment of the present teaching, the tension strength of the S- shaped wire spring is configured to respond to the difference between the left and right atrial pressure (AP). Based on Hooke’s law, the force (F) required to extend the spring is determined by the stiffness (k) of the spring and the extended distance (x) of the spring, i.e. F=kx. According to one embodiment of the present teaching, the tension spring of the device is pre-engineered to allow optimum response to a patient’s left atrial pressure fluctuation.

[0044] In one exemplary embodiment of the present teaching, one tension spring is placed in between every two proximal anchors, as shown in Fig. 3. In one embodiment, there are the same number of tension springs as the proximal anchors. For example, the atrial shunt device could have 2-9 proximal anchors and 2-9 tension springs. In another embodiment,there are fewer tension springs compared to the proximal anchors and all tension springs are distributed evenly among the proximal anchors. Although two dimensional S- shaped wire formed tension springs are shown in the exemplary embodiment, one skilled in the art should understand that other spring design, or other mechanical design that allows automatic stress / strain recovery, could be incorporated as a flow element recovery mechanism.

[0045] Fig. 4 illustrates another exemplary embodiment of the atrial shunt device. Similar to the embodiment shown in Figs. 2a-2b & 3, this exemplary atrial shunt device also has a frame with a plurality of distal anchors, a plurality of proximal anchors and an axial body. The exemplary atrial shunt device also has a flow element slidably joining to the axial body of the frame with an annular gap. Similarly, upon deployment, the distal anchors of the frame are positioned against the atrial septum inside the left atrium; the proximal anchors of the frame are positioned against the atrial septum inside the right atrium; the axial body is positioned across an atrial opening. Unlike the embodiment shown in Figs. 2a-2b &3, this exemplary flow element recovery mechanism extends from the radial free ends of the distal anchor of the frame distally and radially inward. One end of the flow element recovery mechanism joins the radial free ends of the distal anchor, the other end of the flow element recovery mechanism joins the distal end of the flow element.

[0046] The exemplary embodiment shown in Fig. 4, as the flow element recovery mechanism is fully relaxed, the flow element is at its most distal position inside the axial body of the frame with the proximal end of the flow element aligns the proximal end of the axial body (not shown in Fig. 4), and the distal end of the flow element extends distally beyond the distal end of the axial body of the frame and into the left atrium. In this configuration, no significant left-to-right blood shunts through the flow element. When the flow element recovery mechanism is under maximum tension, the flow element is at its most proximal position inside the axial body of the frame, with the proximal end of the flow element extends proximally beyond the proximal end of the axial body of the frame, the distal end of the flow element is adjacent or could even align the distal end of the axial body of the frame. In this configuration, the device allows a maximum left-to-right blood flow through the flow element of the device.

[0047] According to one embodiment of the present teaching, the flow element recovery mechanism could be the same or similar to the exemplar embodiment shown in Fig. 3, i.e. aplurality of tension springs that is capable to stretch under stress and recover once relaxed. Accordingly, once the left atrial pressure increases so the left-to-right pressure difference is greater than the resistance of the tension spring, the flow element is pushed distally, causing the tension spring to stretch. When the left atrial pressure decreases so that the left-to-right pressure difference is less than the resistance of the tension spring, the tension springs recover and pull the flow element distally.

[0048] In another embodiment, the tension springs and the distal anchors of the frame are of a unity. The curved portion, where the distal anchors and tension springs join each other as shown in Fig. 4, are pre-engineered with a certain degree of bending resistance. As the left-to-right pressure difference increases beyond the pre-engineered bending resistance of the tension springs, the flow element moves proximally, allowing more left-to-right blood flow through the flow element. When the left-to-right pressure difference reduces below to the tension spring resistance strength, the tension spring recovers and pulls the flow element distally, thereby reducing the left-to-right blood flow through the flow element.

[0049] According to one embodiment, the atrial shunt device has an elongated delivery configuration and a radially expanded deployed configuration. At the elongated delivery configuration, the flow element and the axial body of the device collapse radially into a smaller radial profile. The distal anchors, the proximal anchors, and the tension mechanism all extend longitudinally parallel to the longitudinal axis of the axial body of the frame, and the longitudinal axis of the flow element. As a result, the atrial shunt device in its elongated delivery profile has a generally elongated profile with reduced radial size. At the radially deployed configuration, the flow element and the axial body of the device expand radially into a greater radial profile. Both the distal and proximal anchors extend radially away from the axial body from the respective ends of the axial body. The tension mechanism assumes its pre-engineered relaxed state. For example the tension springs of Figs 2a- 2b extend proximally and longitudinally from the axial body of the frame. In another example, the tension springs of Fig. 4 extend radially inward from the radial free ends of the distal anchors of the frame, and join the distal end of the flow element.

[0050] According to another embodiment of the present teaching, upon deployment across an opening on the atrial septum, the atrial shunt device is exposed to both left and right atrial pressure. Most time, the left atrial pressure is higher than the right atrial pressure,when the left-to-right pressure difference is less than the pre-engineered resistance of the recovery mechanism, the atrial shunt device allows a pre-designed minimum blood flow from left atrium to right atrium. Such minimum blood flow is a combination of flow through the gap between the flow element and axial body, through the proximal orifice (when applicable), and through the flow orifices exposed inside the right atrium when the flow element is at its most distal position, i.e. when the recovery mechanism is at its relaxed state, such as shown in Fig. 2a.

[0051] When the left atrial pressure increases, and the left-to-right atrial pressure difference becomes greater than the designed resistance threshold of the flow element recovery mechanism, the flow element is pushed proximally by the left atrial pressure, allowing the proximal end of the flow element extends beyond the proximal end of the frame body, and a greater amount of flow orifices along the tubular surface of the flow element exposes inside the right atrium. At this point, in addition to the pre-designed minimum blood flow, a greater amount of blood flows through the flow element and exits the flow orifice exposed proximally beyond the proximal end of the axial body of the frame. Such left-to-right blood shunt, in turn, relieves the left atrial pressure and thereby reduces the left-to-right atrial pressure difference.

[0052] When the left-to-right atrial pressure difference is less than the designed resistance threshold of the flow element recovery mechanism, the flow element recovery mechanism relaxes, recovers, and pulls the flow element distally. As the flow element moves distally, the amount of the flow orifices along the tubular surface of the flow element exposed inside the right atrium also decreases, such that the left-to-right blood shunt through the flow element reduces.

[0053] Various embodiments have been illustrated and described herein by way of examples, and one of ordinary skill in the art will appreciate that variations can be made without departing from the spirit and scope of the present teaching. The present teaching is capable of other embodiments or of being practiced or carried out in various other ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.

[0054] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which thispresent teaching belongs. Methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present teaching. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.

Claims

WE CLAIM:

1. An implantable medical device for regulating a left atrial pressure, comprising: a flow element comprising a distal portion configured for blood to enter and a proximal portion configured for blood to exit; wherein the distal portion is configured to be positioned inside of a left atrium, and the proximal portion is configured to be positioned inside of a right atrium; wherein an effective device length is configured to increase when the left atrial pressure elevates; and wherein the effective device length is configured to reduce when the left atrial pressure recovers.

2. The implantable medical device of claim 1, further comprising a flow element recovery mechanism joining the flow element, wherein the flow element recovery mechanism comprises a first configuration when the left atrial pressure elevates and the effective device length increases, and a second configuration when the left atrial pressure recovers and the effective device length decreases, and wherein the flow element recovery mechanism transitions from the first configuration to the second configuration spontaneously when the left atrial pressure recovers.

3. The implantable medical device of claim 1, wherein the flow element is configured to slide proximally as the effective device length increases.

4. The implantable medical device of claim 1, wherein the flow element is configured to slide distally as the effective device length reduces.

5. An implantable medical device for regulating a left atrial pressure, comprising, a flow element comprising a distal portion configured for blood to enter and a proximal portion configured for blood to exit; wherein the distal portion is configured to be positioned inside of a left atrium, and the proximal portion is configured to be positioned inside of a right atrium; andwherein the implantable medical device is configured to spontaneously reduce its effective device length when a pressure difference between the left atrium and right atrium decreases.

6. The implantable medical device of claim 5, wherein the implantable medical device is configured to spontaneously increase the effective device length when a pressure difference between the left atrium and the right atrium increases.

7. The implantable medical device of claim 5, further comprising a flow element recovery element configured to join the flow element, wherein the flow element recovery element comprises a spring mechanism configured to extend when the pressure difference between the left atrium and right atrium increases and recover when the pressure difference between the left atrium and right atrium decreases.

8. An implantable medical device for regulating a left atrial pressure, comprising: a frame, a flow element, and a flow element recovery mechanism; wherein the frame includes a plurality of distal anchors, a plurality of proximal anchors, and an axial body joining the plurality of the distal anchors and the plurality of the proximal anchors at its distal end and proximal end, respectively; wherein the flow element has a general tubular profile and is configured to slidably engage to the axial body of the frame, and comprises: an open distal end forming a flow inlet for blood entering the flow element, a closed proximal end, and a plurality of flow orifices along its tubular surface forming a flow outlet for blood exiting the flow element; and wherein the flow element recovery mechanism is configured to join the flow element and comprises a tensioned configuration when the closed proximal end of the flow element extends proximally beyond the plurality of the proximal anchors of the frame to a first distance and a relaxed configuration when the closed proximal end of the flow element extends proximally beyond the plurality of the proximal anchors of the frame at a second distance.

9. The implantable medical device of claim 8, wherein the flow element is configured to be positioned across an atrial septum with the open distal end of the flow element inside a left atrium, the closed proximal end of the flow element inside a right atrium.

10. The implantable medical device of claim 9, wherein the flow element recovery mechanism is configured to automatically recover from the tensioned configuration to the relaxed configuration when a pressure difference between the left atrium and the right atrium decreases.

11. The implantable medical device of claim 10, wherein the flow element recovery mechanism comprises a plurality of tension springs configured to join the proximal end of the axial body of the frame to the closed proximal end of the flow element.

12. The implantable medical device of claim 10, wherein the flow element recovery mechanism comprises a plurality of tension springs configured to join the distal end of the axial body of the frame to the open distal end of the flow element.

13. The implantable medical device of claim 10, wherein the flow element is configured to slide against the axial body of the frame in response to a change in the pressure difference between the left atrium and right atrium.

14. The implantable medical device of claim 13, wherein the flow element moves proximally in response to an increase of the pressure difference between the left atrium and right atrium.

15. The implantable medical device of claim 13, wherein the element moves proximally in response to a decrease of the pressure difference between the left atrium and right atrium.

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