The present disclosure is directed to systems and methods for creating an interatrial shunt to redistribute blood from one cardiac chamber to another to address pathologies such as heart failure (“HF”), myocardial infarction (“MI”) and pulmonary arterial hypertension (“PAH”).
Pulmonary arterial hypertension (PAH) occurs when the pressure within the blood vessels and lungs becomes too high. PAH may be caused by obstruction in the arteries in the lung such as the development of scar tissue in the blood vessels of the lungs, but in many cases, the cause is unknown. Under normal conditions, the pressure within the right side of the heart and the blood vessels of the lungs is lower than the rest of the body which maximizes oxygenation of the blood in the lungs. With PAH, the heart must work harder under greater pressure to pump blood through the arteries in the lungs, weakening the heart muscles over time. As a result, the heart may be unable to sufficiently pump blood to the lungs to be oxygenated to keep the body functioning normally.
Heart failure is the physiological state in which cardiac output is insufficient to meet the needs of the body or to do so only at a higher filling pressure. There are many underlying causes of HF, including myocardial infarction, coronary artery disease, valvular disease, hypertension, and myocarditis. Chronic heart failure is associated with neurohormonal activation and alterations in autonomic control. Although these compensatory neurohormonal mechanisms provide valuable support for the heart under normal physiological circumstances, they also play a fundamental role in the development and subsequent progression of HF.
For example, one of the body's main compensatory mechanisms for reduced blood flow in HF is to increase the amount of salt and water retained by the kidneys. Retaining salt and water, instead of excreting it via urine, increases the volume of blood in the bloodstream and helps to maintain blood pressure. However, the larger volumes of blood also cause the heart muscle, particularly the ventricles, to become enlarged. As the heart chambers become enlarged, the wall thickness decreases and the heart's contractions weaken, causing a downward spiral in cardiac function. Another compensatory mechanism is vasoconstriction of the arterial system, which raises the blood pressure to help maintain adequate perfusion, thus increasing the load that the heart must pump against.
In low ejection fraction (EF) heart failure, high pressures in the heart result from the body's attempt to maintain the high pressures needed for adequate peripheral perfusion. However, as the heart weakens as a result of such high pressures, the disorder becomes exacerbated. Pressure in the left atrium may exceed 25 mmHg, at which stage fluids from the blood flowing through the pulmonary circulatory system transudate or flow out of the pulmonary capillaries into the pulmonary interstitial spaces and into the alveoli, causing lung congestion and, if untreated, the syndrome of acute pulmonary edema and death.
Table 1 lists typical ranges of right atrial pressure (RAP), right ventricular pressure (RVP), left atrial pressure (LAP), left ventricular pressure (LVP), cardiac output (CO), and stroke volume (SV) for a normal heart and for a heart suffering from HF. In a normal heart beating at around 70 beats/minute, the stroke volume needed to maintain normal cardiac output is about 60 to 100 milliliters. When the preload, after-load, and contractility of the heart are normal, the pressures required to achieve normal cardiac output are listed in Table 1. In a heart suffering from HF, the hemodynamic parameters change (as shown in Table 1) to maintain peripheral perfusion.
HF is generally classified as either systolic heart failure (SHF) or diastolic heart failure (DHF). In SHF, the pumping action of the heart is reduced or weakened. A common clinical measurement is the ejection fraction, which is a function of the blood ejected out of the left ventricle (stroke volume) divided by the maximum volume in the left ventricle at the end of diastole or relaxation phase. A normal ejection fraction is greater than 50%. Systolic heart failure generally causes a decreased ejection fraction of less than 40%. Such patients have heart failure with reduced ejection fraction (HFrEF). A patient with HFrEF may usually have a larger left ventricle because of a phenomenon called “cardiac remodeling” that occurs secondary to the higher ventricular pressures.
In DHF, the heart generally contracts normally, with a normal ejection fraction, but is stiffer, or less compliant, than a healthy heart would be when relaxing and filling with blood. Such patients are said to have heart failure with preserved ejection fraction (HFpEF). This stiffness may impede blood from filling the heart and produce backup into the lungs, which may result in pulmonary venous hypertension and lung edema. HFpEF is more common in patients older than 75 years, especially in women with high blood pressure.
Both variants of HF have been treated using pharmacological approaches, which typically involve the use of vasodilators for reducing the workload of the heart by reducing systemic vascular resistance, as well as diuretics, which inhibit fluid accumulation and edema formation, and reduce cardiac filling pressure. No pharmacological therapies have been shown to improve morbidity or mortality in HFpEF whereas several classes of drugs have made an important impact on the management of patients with HFrEF, including renin-angiotensin antagonists, beta blockers, and mineralocorticoid antagonists. Nonetheless, in general, HF remains a progressive disease and most patients have deteriorating cardiac function and symptoms over time. In the U.S., there are over 1 million hospitalizations annually for acutely worsening HF and mortality is higher than for most forms of cancer.
In more severe cases of HFrEF, assist devices such as 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. Chronic left ventricular assist devices (LVAD), and cardiac transplantation, often are used as measures of last resort. However, such assist devices typically are intended to improve the pumping capacity of the heart, to increase cardiac output to levels compatible with normal life, and to sustain the patient until a donor heart for transplantation becomes available. Such mechanical devices enable propulsion of significant volumes of blood (liters/min), but are limited by a need for a power supply, relatively large pumps, and pose a risk of hemolysis, thrombus formation, and infection. Temporary assist devices, intra-aortic balloons, and pacing devices have also been used.
Various devices have been developed using stents to modify blood pressure and flow within a given vessel, or between chambers of the heart. Implantable interatrial shunt devices have been successfully used in patients with severe symptomatic heart failure. By diverting or shunting blood from the left atrium (LA) to the right atrium (RA), the pressure in the LA is lowered or prevented from elevating as high as it would otherwise (left atrial decompression). Such an accomplishment would be expected to prevent, relieve, or limit the symptoms, signs, and syndromes associated of pulmonary congestion. These include severe shortness of breath, pulmonary edema, hypoxia, the need for acute hospitalization, mechanical ventilation, and death.
U.S. Pat. No. 9,067,050 to Gallagher describes an arteriovenous stent assembly including a stent and a pull wire operated flow control mechanism. The stent has a tubular body that defines a fluid passageway between a first end and a second end thereof. The pull wire mechanism includes a portion disposed around the tubular stent in at least one loop. The at least one loop may be selectively tightened or loosened remotely from the stent to regulate the rate of blood flow through the tubular stent.
U.S. Pat. Pub. No. 2013/0178784 to McNamara describes devices and methods for treating heart disease by normalizing elevated blood pressure in the left and right atria of a heart of a mammal. Devices may include an adjustable hydraulic diameter stent portion which can be manually adjusted in vivo. Methods are provided for adjusting the flow rate of the devices in vivo.
Temporary interatrial shunt devices such as those described in U.S. Pat. Pub. No. 2018/0280667 to Keren, the entire contents of which is incorporated herein by reference, include components for retrieving the shunt upon completion of the treatment.
U.S. Pat. Pub. No. 2017/0128705 to Forcucci describes a retrieval device for treating heart failure. Specifically, the retrieval device requires both a first retrieval portion joining the proximal end of a proximal portion of the retrieval device and a second retrieval portion joining the distal end of a distal portion of the retrieval device.
U.S. Pat. No. 5,035,706 to Giantureo describes a self-expanding stent formed of stainless steel wire arranged in a closed zig-zag configuration. The stent is compressible into a reduced diameter size for insertion into and removal from a body passageway. The stent can include a monofilament thread passing through successive eyes at one end of the stent, the thread passing through each eye at least once and through some of the eyes a second time. The trailing ends of the thread extend from the stent and outside the body passageway. The stent can be retrieved from the body passageway by threading a tube over the free ends of the thread until the tube is adjacent the stent. The diameter at one end of the stent is reduced by pulling the free ends of the thread through the tube. A sheath concentrically disposed over the tube is introduced into the body passageway and over the remaining length of the stent to further compress the stent for removal from the passageway.
In view of the foregoing drawbacks of previously known systems and methods, there exists a need for improved in vivo adjustment and retrieval of an interatrial shunt device, particularly a stent having flared ends.
The present disclosure overcomes the drawbacks of previously-known systems and methods by providing a retrievable apparatus for temporary, continuously adjustable, shunting of blood across an atrial septum of a patient. For example, the apparatus may include a catheter having a proximal end and a distal end, and a plurality of wires extending distally from the distal end of the catheter and forming a stent having a flared proximal region, a flared distal region, and a neck region therebetween. The stent may transition between a contracted delivery state within a transseptal delivery sheath and an expanded deployed state upon retraction of the delivery sheath, such that the neck region may be positioned within a puncture of the atrial septum of the patient in the expanded deployed state. The apparatus further may include a cinching tube extending distally from the distal end of the catheter toward the neck region of the stent, the cinching tube having a lumen extending therethrough, and a cinching cord having first and second ends, the cinching cord extending around the neck region of the stent such that the first and second ends pass through an outlet of the cinching tube and extend proximally through the lumen of the cinching tube, forming a loop around the neck region. Moreover, movement of the first and second ends of the cinching cord relative to the cinching tube changes the tension in the cinching cord that is looped around the neck region of the stent. For example, moving the first and second ends of the cinching cord proximally relative to the cinching tube causes the loop around the neck region of the stent to tighten, thereby causing the neck region of the stent to transition from the expanded deployed state to a more contracted state. Conversely, relaxing the tension by moving the first and second ends of the cinching cord distally relative to the cinching tube causes the loop around the neck region of the stent to loosen, thereby allowing the superelastic neck region of the stent to expand from a contracted state to a more expanded state. In this way, the orifice through the neck region of the stent may be adjusted to allow greater or lesser flow while the stent is in its deployed configuration within the body of a patient.
The apparatus further may include a sheath having a proximal end, a distal end, and a lumen extending therethrough, the lumen sized and shaped to receive the catheter and the stent in its contracted delivery state. For example, when the stent is disposed within the lumen of the sheath in the contracted delivery state, proximal movement of the sheath relative to the catheter causes the stent to be exposed from the distal end of the sheath and transition from the contracted delivery state to the expanded deployed state. Moreover, the catheter may be slidably disposed within the lumen of the sheath such that as the sheath moves distally relative to the catheter and over a suitably-shaped plurality of wires extending from the distal end of the catheter, the flared proximal region of the stent transitions from the expanded deployed state to the contracted delivery state as the distal end of the sheath slides over it. Further, as the sheath moves distally relative to the catheter from the neck region of the stent toward the flared distal region, the flared distal region of the stent transitions from the expanded deployed state to the contracted delivery state such that the entire stent may be drawn into the sheath.
A diameter of the flared proximal region of the stent may increase from the neck region towards the catheter until reaching an apex of the flared proximal region in the expanded deployed state, and then decrease from the apex of the flared proximal region toward the distal end of the catheter in the expanded deployed state. In addition, the apparatus may include a biocompatible material encapsulating the distal region, the neck region, and at least a portion of the flared proximal region of the stent. For example, the biocompatible material may extend a preselected distance beyond the flared distal region of the stent to thereby reduce injury to surrounding tissue during deployment and retrieval of the stent. Moreover, the biocompatible material may encapsulate the portion of the flared proximal region of the stent between the neck region and the apex of the flared proximal region.
In one embodiment, the cinching tube may extend distally from the distal end of the catheter toward the neck region of stent along an inner surface of the flared proximal region and the neck region of the stent. Alternatively, the cinching tube may extend distally from the distal end of the catheter toward the neck region of stent along an outer surface of the flared proximal region and the neck region of the stent. The neck region of the stent may include a plurality of eyelets disposed circumferentially around the neck region of the stent. Accordingly, the cinching cord may extend through one or more eyelets of the plurality of eyelets around the neck region. Moreover, the biocompatible material may include one or more openings adjacent to the neck region of the stent, the one or more openings aligned with the plurality of eyelets. In some embodiments, one or more eyelets of the plurality of eyelets may include a radiopaque material. Additionally, the cinching tube may include a fairlead adjacent to the outlet of the cinching tube. The fairlead may guide the first and second ends of the cinching cord through the outlet of the cinching tube.
In addition, the catheter further may include a guidewire lumen extending therethrough, the guidewire lumen sized and shaped to receive a guidewire. In another embodiment, the catheter may include a guidewire tube slidably disposed within a guidewire lumen extending therethrough, sized and shaped to receive a guidewire. The guidewire tube may be longer than the catheter, such that it may be extended distally through the neck and beyond the distal flange of the stent. In a preferred embodiment, the guidewire tube may be retracted such that its distal end is even with the distal end of the catheter.
In accordance with another aspect of the present disclosure, a method for temporarily shunting blood across an atrial septum of a patient is provided. For example, the method may include: delivering the distal end of the sheath over a guidewire across the puncture of the atrial septum of the patient into the left atrium; inserting the catheter-stent system over the proximal end of the guidewire and into the proximal hub of the sheath; advancing the catheter until the flared distal region of the stent exits from the distal tip of the sheath, allowing the flared distal region to transition from the contracted delivery state to the expanded deployed state within the left atrium; retracting the sheath and the catheter-stent system as a unit until the flared distal region of the stent encounters the septal wall between the left and right atria; further retracting the sheath proximally while holding the catheter stationary to expose the flared proximal region of the stent, allowing it to transition from the contracted delivery state to the expanded deployed state within the right atrium such that the neck region of the stent is positioned within the puncture of the atrial septum, the flared proximal region of the stent coupled to the distal end of the catheter via a plurality of wires; and shunting blood across the atrial septum via the stent between the atria responsive to a pressure differential across the atrial septum. Further, the method may include adjusting the shunting of blood by moving the first and second ends of the cinching cord that extends around the neck region of the stent relative to the cinching tube to allow the neck to expand to a larger diameter or to cinch the neck to a smaller diameter.
Accordingly, distal movement of the first and second ends of the cinching cord that extends around the neck region of the stent relative to the cinching tube allows the neck region of the stent to transition between a contracted state and an expanded state. Conversely, proximal movement of the first and second ends of the cinching cord relative to the cinching tube tightens the cinching cord around the neck region of the stent, causing it to compress to a smaller diameter.
The method further may include advancing the sheath distally relative to the catheter and over the plurality of wires to transition the flared proximal region of the stent from the expanded deployed state to the contracted delivery state; moving the first and second ends of the cinching cord proximally relative to the cinching tube to transition the neck region of the stent from the expanded deployed state to the contracted delivery state; advancing the sheath distally relative to the catheter over the neck region; further advancing the sheath distally over the flared distal region of the stent to transition the flared distal region of the stent from the expanded deployed state to the contracted delivery state; and removing the sheath, the catheter, and the stent as a unit from the patient.
Embodiments of the present invention are directed to devices for temporarily shunting blood between heart chambers, e.g., across the atrial septum of the heart, and thus may be useful in treating subjects suffering from heart failure, pulmonary hypertension, or other disorders associated with elevated left or right atrial pressure. For example, the inventive device may include a delivery catheter that remains coupled to an expandable stent portion via a plurality of wires, the expandable stent having an hourglass or “diabolo” shape, preferably formed of a shape memory metal as described in U.S. Pat. No. 9,629,715 to Nitzan, assigned to the assignee of the present invention, the entire contents of which are incorporated herein by reference. The temporary shunt devices described herein are configured to lodge the stent portion securely in the atrial septum, preferably the fossa ovalis, to function as an interatrial shunt, allowing blood flow between the atria in response to a blood pressure gradient. In one application, the inventive device may be placed to provide short-term acute relief of excess pressure in one of the atria. Upon completion of the treatment, a cinching cord coupled to the stent portion may be used in conjunction with a delivery sheath to retrieve and remove the temporary shunt device from the patient. For example, the cinching cord may be retracted to reduce the orifice of the stent portion, and as the delivery sheath is advanced over the plurality of wires toward an apex of the wires proximal to the proximal flange of the stent portion, the proximal flange gradually compresses to facilitate retrieval of the stent portion into the delivery sheath. In another application, the inventive device may be placed temporarily in the heart of a patient and the shunt diameter adjusted, as described further herein, to determine the optimum degree of shunting to be provided by a subsequent permanent shunt device. Upon completion of this determination, the present temporary adjustable shunt device would be removed from the patient using the delivery sheath and cinching cord as described further herein. In another application, the inventive device may be used in a patient in conjunction with an extracorporeal membrane oxygenation (ECMO) system.
Referring now to
Stent portion 200 along with distal region 104 of delivery catheter 106 and the distal end of sheath 108 are configured to be transvascularly delivered to the patient's atrial septum. The proximal end of delivery catheter 106 may be operatively coupled to handle 150 at proximal region 102, such that each component may be individually actuated via one or more actuators, e.g., buttons, knobs, etc. of handle 150, as described in further detail below. As described in further detail below, system 100 further may include delivery, adjustment, and retrieval elements, e.g., a cinching cord, to facilitate in adjusting stent portion 200 to control blood flow therethrough and for retrieval thereof, such that the proximal ends of the cinching cord also may be operatively coupled to and actuated by handle 150.
Referring now to
As shown in
Stent portion 200 may be encapsulated with biocompatible material 210 along the outer surface of frame 201 in the direction from the distal end of flared distal region 202 towards the proximal end of flared proximal region 206, and along the inner surface of frame 201 in the direction from the proximal end of flared proximal region 206 towards the distal end of flared distal region 202. In one embodiment, biocompatible material 210 may extend a preselected distance, e.g., 1-2 mm, beyond flared distal region 202 to thereby reduce injury to surrounding tissue during deployment and retrieval of stent portion 200. In addition, system 100 further may include cinching tube 116 extending distally from the distal end of catheter 106 toward neck region 204 of stent portion 200 for housing cinching cord 120, as described in further detail below.
As shown in
As shown in
Alternatively, a first end of cinching cord 120 may be pulled proximally while the second end of cinching cord 120 remains stationary, such that the diameter of the portion of cinching cord 120 surrounding neck region 204 will decrease, thereby causing neck region 204 to transition from the expanded deployed state toward the contracted delivery state. Additionally, if the first end of cinching cord 120 is eased distally while the second end of cinching cord 120 remains stationary, the diameter of the portion of cinching cord 120 surrounding neck region 204 will increase, thereby permitting superelastic neck region 204 to transition from the contracted delivery state toward the expanded deployed state.
The first and second ends of cinching cord 120 may be operatively coupled to an actuator of handle 150, such that the actuator may be actuated to provide the relative movements of the first and second ends of cinching cord 120 described above. Alternatively, the first and second ends of cinching cord 120 may be affixed to the distal end of cinching control rod 126 that is operatively coupled at its proximal end to an actuator of handle 150.
As shown in
Moreover, frame 201 of stent portion 200 may include eyelets 203 disposed circumferentially about neck region 204, such that cinching cord 120 may pass through at least some of eyelets 203. For example, as shown in
Accordingly, biocompatible material 210 encapsulating frame 201 may include one or more openings corresponding to eyelets 203, such that cinching cord 120 may pass through eyelets 203 and biocompatible material 210. In one embodiment, cinching tube 116 may extend from the distal end of catheter 106 and along the outer surface of biocompatible material 210 to neck region 204, and cinching cord 120 may pass around neck region 204 through eyelets 203 such that the first and second ends of cinching cord 120 enters outlet 118 adjacent to the outer surface of biocompatible material 210. In another embodiment, cinching tube 116 may extend from the distal end of catheter 106 and along the inner surface of biocompatible material 210 to neck region 204, and cinching cord 120 may pass through biocompatible material 210 around neck region 204 and through eyelets 203 such that the first and second ends of cinching cord 120 enters outlet 118 adjacent to the inner surface of biocompatible material 210. In some embodiments, one or more eyelets of eyelets 203 may include a radiopaque material such as tantalum to allow easier visualization of diameter of neck region 204, e.g., by fluoroscopy, as shown in
As shown in
Flared proximal region 206 of stent portion 200 may be formed by wires 206a having a, e.g., zig-zag shape, extending circumferentially around the longitudinal axis of stent portion 200, such that each of the proximal apices of wire 206a is coupled to the distal end of either wire 208d or wire 208e. For example, each of wires 208d may diverge into two additional wires of wire 206a, which are adjacent to the two additional wires diverging from each of wires 208e, and each of wires 208f may diverge into two additional wires of wire 206a, which are adjacent to the two additional wires diverging from each of wires 208g. Moreover, the cross-sectional area of stent portion 200 may decrease from the distal ends of wires 208d and 208e toward neck region 204, thereby forming apex 207, e.g., a maximum cross-sectional, at the junction between proximal connection region 208 and flared proximal region 206 of stent portion 200.
As shown in
Moreover, flared distal region 202 may be formed of first distal region 202a, and second distal region 202b distal to first distal region 202a. Each of first distal region 202a and second distal region 202b may be formed of a wire having a zig-zag shape and each extending circumferentially around the longitudinal axis of stent portion 200. The proximal apices of the wire forming first distal region 202a may be coupled to the distal apices of wire 204b of neck region 204. In addition, the distal apices of the wire forming first distal region 202a may be coupled to the proximal apices of the wire forming second distal region 202b. As shown in
As will be understood by a person having ordinary skill in the art, although
Frame 201 may transition between a contracted delivery state and an expanded deployed state, such that frame 201 is biased toward the expanded deployed state. Accordingly, frame 201 may be advanced in its contracted state through sheath 108 in its contracted delivery state, for delivery to the atrial septum of the patient, e.g., over guidewire 101. Upon exposure from sheath 108, e.g., via retraction of sheath 108 relative to catheter 106, frame 201 may self-expand to transition from the contracted delivery state to the expanded deployed state at the atrial septum as described in further detail below with reference to
As shown in
Referring now to
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Referring now to
Cartridge 170, stent portion 200 and distal end 104 of delivery catheter 106 may be placed over the proximal end of guidewire 101 by extending the distal end of guidewire tube 103 from its parked location within guidewire lumen 114 to its extended location beyond the distal flange of the crimped stent within cartridge 170, as shown in
As shown in
Referring now to
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Moreover, as shown in
As described above with regard to stent portion 200, although
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The initiation of the retrieval of stent portion 300 is illustrated in
As shown in
Next, sheath 108′ may be further advanced distally relative to catheter 106′ such that the distal end of sheath 108′ receives flared proximal region 206′ as shown in
The inventors tested a prototype of the described device in a living sheep. After gaining femoral venous access a standard transseptal puncture was performed and an Anchorwire™ transseptal guidewire was placed through the puncture into the LA. Following well-established practice, a 15F Ventura™ introducer sheath was placed over this guidewire through the atrial septum and into the LA.
The stent was loaded into the cartridge using a tapered loader and sliding the cartridge over the proximal connection wires, the distal connection wires, and the proximal, neck and distal portions of the stent, positioning the entire stent within the narrow loading tube portion of the cartridge, all at the distal end of the delivery catheter. The loading tube portion of the cartridge was then inserted into the delivery sheath hub, and the delivery catheter was advanced through the sheath until just the distal flange of the stent emerged from the distal end of the sheath.
The stent and delivery system were further prepared on the bench to set a length stopper on the delivery catheter between the handle and the cartridge to prevent advancing the neck of the stent beyond the end of the sheath. Accurately setting this stopper allows the stent to be confidently half-deployed within the left atrium (i.e. only the distal flange released from the sheath) by advancing the delivery catheter until this stopper encounters the cartridge. Once the stopper has been set in the correct location, the half-deployed stent is retracted back into the sheath as shown in
TABLE 2 shows results of an exemplary study of the inventive system in an ovine animal model. After deploying the stent across the atrial septum as described above, the control handle was actuated to select shunt orifice diameter by adjusting the length of cinching cord 120 as described above. Pre-calibrated control handle settings from 5 mm to 8 mm were selected in 1 mm steps, then varied from 8 mm back down to 4 mm. At each setting the shunt orifice diameter was determined by intracardiac ultrasound (ICE) and the stent frame diameter was measured by X-ray using the delivery system head diameter as a reference. Despite some apparent backlash in the X-ray measurements, the data shows that shunt orifice diameter may be increased and decreased over the design range with reasonably accurate control over flow orifice diameter.
Following the above deployment, adjustment and measurements, the delivery sheath was advanced over the apex region of the connecting wires, compressing the proximal flared region of the stent. The cinching cord was maximally tightened to compress the neck region of the stent, allowing the sheath to be advanced over the wires extending from the delivery system to the apex at the proximal end of the stent, thereby compressing the proximal flared end of the stent to allow it to be pulled into the delivery sheath, following which the remainder of the stent may be easily pulled entirely into the delivery sheath, and the entire system safely removed from the body. It would be obvious to one skilled in the art that the ability to vary the size of an interatrial shunt would advantageously allow a physician to determine the optimum shunt diameter for the treatment of conditions involving excessive pressure in one of the atria, such as heart failure or pulmonary artery hypertension.
While various illustrative embodiments of the invention are described above, it will be apparent to one skilled in the art that various changes and modifications may be made therein without departing from the invention. The appended claims are intended to cover all such changes and modifications that fall within the true scope of the invention.
This application claims the benefit of U.S. Provisional Patent Application No. 63/197,279, filed Jun. 4, 2021, the entire contents of which are incorporated by reference herein.
Number | Date | Country | |
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63197279 | Jun 2021 | US |