Heart pump that structures end-diastolic ventricular geometry for optimal filling and ventricular pump function

Abstract

A cardiac assist device (10) for acting on a heart (11) having an actual end-diastolic conformation in vivo and an ideal end-diastolic conformation that would cause the heart (11) to pump more efficiently. The cardiac assist device (10) has a shell configuration (13) with a top opening (24), a base (21), and a maximum interior diameter (MD) between the top opening (24) and the base (21). The shell configuration (13) has a total long axis length (TL). The shell configuration (13) has a major axis that follows a curvature rotated about a major axis. At last one inflatable membrane (26) extends from said shell configuration (13), wherein said shell configuration (13) and said at least one inflatable membrane (26) act upon said heart (11) to alter said actual end-diastolic conformation toward said ideal end-diastolic conformation.

Description

[0001]HEART PUMP THAT STRUCTURES END-DIASTOLIC VENTRICULAR GEOMETRY FOR OPTIMAL FILLING AND VENTRICULAR PUMP FUNCTION TECHNICAL FIELD OF THE INVENTION In general, the present invention relates to systems and methods of restructuring the heart’s end-diastolic ventricular geometry with a cardiac assist device to produce optimal diastolic filling and improve ventricular pump function. More particularly, the present invention is directed toward achieving optimal ventricular pump function by idealizing end-diastolic ventricular structure and / or geometry which also improves the likelihood of heart recovery when using a cardiac assist device to assist the pump function. BACKGROUND ART Due to a variety of reasons, not all hearts pump blood in an efficient manner. In some instances, the heart may even stop pumping altogether. Such hearts can often benefit from the use of a cardiac assist device. The cardiac assist device is advanced to the heart, wherein the cardiac assist device applies physical forces to the heart’s ventricular surface for mechanically assisting pumping blood though the heart’s ventricular chambers. The cardiac assist device can provide the necessary forces for such pumping in an arrested heart or assisting such pumping in a weak heart. These forces preferably result in proper structural changes of the heart muscle to aid in the recovery of such pump function in an injured, dysfunctional heart. Such forces that lead to ideal geometric and / or structural shape can facilitate underlying myocardial function and have the therapeutic effect promoting return of the heart’s native pumping and / or contractile function. In the prior art, there are many cardiac assist devices that act on the ventricles of the heart and apply compressive forces to the ventricles. The applied forces can assist in the systolic contractions of the heart. As such, such cardiac assist devices are designed to help the ventricles of the heart propel blood out of the ventricular chambers. The heart is a complex organ that pumps blood through the lungs and systemic circulation. Like all pumps, the heart needs to empty and fill effectively with respect to its ideal functionality. In order for a heart to pump blood effectively and efficiently, a heart needs to both efficiently fill and efficiently empty. In the prior art, most cardiac assist devices that physically apply forces to the heart are designed to control the compressive forces that act on the heart to assist its emptying. When the compressive forces are released, these cardiac assist devices return to a nominal shape in order to engage another compression cycle. The forces applied to the heart during such a return can have secondary effects on the heart’s pumping function. This return to a nominal shape fails to augment filling and / or diastolic function and may have negative effects on optimal filling. Such negative effects have been shown to impair the heart’s filling in studies that measure related functional parameters of heart pump function. Many prior art cardiac assist devices have not been specifically designed to assist the heart in filling and overcoming this problem. Consequently, the forces applied during the return of such cardiac assist devices into a nominal shape for compression may impair the heart in filling and / or limit the heart’s expansion during its diastolic or filling phase. Positioning and / or enabling the heart’s ventricular walls toward a more ideal end-diastolic conformation without over-distension of the heart muscle can help optimize its filling and pumping capacity. Bringing the heart to an ideal end- diastolic volume further optimizes the likelihood for recovering function of the injured, dysfunctional heart. The forces that a cardiac assist device applies to the heart during systolic compression can then further achieve greater stroke volume through the enhancement of pump priming during diastole. The use of cardiac assist devices that only compress the heart have important implications on the ability of the heart to fill and on the diastolic heart function. Such cardiac assist devices have a tendency to be derogatory in this manner and impair ventricular filling. This effect can be simply due to its physical presence which inhibits ideal expansion. Like conditions occur during cardiac tamponade or constrictive pericarditis in which fluid outside the heart or reaction to inflammation around the heart can lead to impaired filling. Furthermore, the pressure and flow profiles used to power such cardiac assist devices are dependent upon the design of the cardiac assist devices with respect to both the diastolic and systolic components of the pumping cycle. An ideal strain dynamic of the cardiac assist device acting on the heart’s surface can best facilitate the transfer of forces to the heart in order to optimize its pumping function. These idealized strain patterns are unique for both compression or systolic function and expansion or diastolic function. Furthermore, an idealized end-diastolic geometry of the heart provides for the most ideal degree of filling or end-diastolic expansion. This structural or geometric condition can be controlled by the device’s shape. As such, the heart is drawn into an ideal shape. This aids in overcoming the restrictive nature of cardiac assist devices while avoiding over-expansion of the heart, which can be harmful. Over-stretching the heart could lead to injury of the heart’s native function. This is therefore important to consider when a cardiac assist device is designed to achieve a greater end- diastolic shape that is slightly greater than the end-diastolic geometry or shape of the normal functioning, uninjured heart. Additionally, facilitating diastolic filling and promoting diastolic pump function has important therapeutic implications on heart recovery. This is particularly important to diastolic pump dysfunction which is present in most forms of heart failure and has no effective treatments. It is known that the heart assumes certain natural shapes both when functioning normally and when functioning in various pathologic conditions. Pathologic conditions that change the heart’s geometry are called “remodeling” and are generally derogatory to the heart’s function. These structural changes can be reversed by treating the underlying cause such as valve dysfunction by replacing or repairing the valve or improving blood flow to an ischemic area of the heart. As such, reverse- remodeling can be achieved when pertinent treatment strategies are successful. Accordingly, the right and left ventricles of the heart also assume certain natural shapes when functioning normally. When the heart fails and / or struggles to pump blood, the shape of the heart and its ventricles can become progressively abnormal as the abnormal shape further impairs pump function and causes more injury. Furthermore, the ability of the heart to fill often becomes impaired with such conditions of dysfunction or remodeling. The impairment in the heart’s ability to fill, or diastolic dysfunction, frequently is more pronounced than the impairment in the heart’s ability to empty, or systolic dysfunction. Such conditions typically result in dilation of the ventricular chambers. As such, the ventricles become more rounded or spherical in shape. This has led to variables that describe the curvature of the heart’s surface, wherein the curvature of the heart’s surface relates directly to aspects of the heart’s health or condition. One of the primary variables that describes the curvature of the heart’s surface is the sphericity index. The sphericity index is a measurement that is derived from measuring the short axis of the ventricular chamber(s) divided by the long axis of the respective ventricle(s). The sphericity index of the left ventricular (LV) chamber is the LV short axis divided by the LV long axis. The sphericity index of the right ventricle (RV) is the RV short axis divided by the RV long axis. The simplest surrogate or representation of the sphericity index is made by calculating this index at the point where maximal dilation of the short axis occurs. A variation of the sphericity index can also be applied to the outer surface of the ventricles where the greatest short axis of the outer surface of the heart is related to the longest axis of the heart between the atrioventricular groove and the apex of the heart. This variable is referred to as the global sphericity index. The global sphericity index can also be calculated for multiple regions of the heart along its long axis. This measurement is termed the regional sphericity index. As such, if a heart is segmented into multiple selected regions along its long axis, then the selected regional sphericity indices can be calculated. The regional sphericity indices can then be used to properly size a cardiac assist device to achieve an ideal end- diastolic conformation for the heart. The global sphericity index and / or the regional sphericity indices provide indications as to whether or not the heart is conformed in an “ideal” end- diastolic shape with respect to its outer epicardial surface. This outer epicardial surface can be expressed mathematically by relating the greatest short axis dimension and its long axis. These mathematical relationships apply to the left and right ventricles as a unit. Therefore, the measure of either the long or short axis of the heart can be used to arrive at an ideal shape of the heart using either global sphericity index and / or the regional sphericity indices. The regional indices can further be applied when the cardiac assist device to be used will only act on certain regions of the heart. More complex formulations have enabled more precise and meaningful characterization of the heart’s geometry and shape. One such example is use of the regional sphericity indices to characterize segments of the heart surface. Another accurate means of arriving at an ideal end-diastolic conformation of the heart is achieved by using a two-dimensional formulation of the heart’s outer surface along one or more regions from the base to the apex. A cardiac assist device that fits over a specified region of the heart can affect one or more regions from the base to the apex. This region or regions can be used as a surrogate for the dimensions of the cardiac assist device over the entire heart. An even more accurate method of arriving at an ideal end-diastolic conformation of the heart uses a three-dimensional formulation that describes the entire conformation of the outer heart surface at its ideal end-diastolic geometry. Importantly, the long or short axis of the heart can be used to define this end-diastolic geometry. The outer ventricular surface can also be assessed by direct measurements when the heart is exposed at the time of surgical procedures. Additionally, a device that pumps the heart can serve as a means of measuring the heart during the end-diastolic phase of pumping and assess the optimization of this relationship. It has been discovered that these measurements of geometric shapes can be used to achieve an optimal end-diastolic conformation of the heart as related to the sizing of the cardiac assist devices. These geometric measurements can further optimize and control the operation and functionality of pumps that power the cardiac assist devices as it relates to the diastolic or filling of the heart. Modern computer imaging software has enabled are intricate three-dimensional understanding of the heart’s dynamic conformational changes during its diastolic and systolic phases. Such three- dimensional imaging can be used to calculate accurate strain analyses of the heart. These strain analyses allow interpretation of cellular or myocardial contraction and relaxation that occurs within the heart’s muscular structure. The myocardial cells are aligned in a complex array of directions. Therefore, the appropriate strain pattern of contraction within the myocardium is important for achieving the normal pump function of the heart. As such, the myocardial forces within the ventricular muscle that the heart generates during its diastolic and systolic phases can be determined. Knowing the normal and abnormal strain profiles of the heart during conditions of normal cardiac pump function and abnormal cardiac pump function, can be used to guide the optimal forces needed to assist the heart during the diastolic and systolic phases. What is difficult is creating and installing a cardiac assist device that is capable of generating those forces in vivo. In analyzing the forces required by a heart and determining the shape and sizes of a cardiac assist device that best produce those forces, it is relatively simple for a cardiac assist device to compress the heart and assist the systolic phase. Assisting diastolic function or filling begins with conforming the heart to an ideal end-diastolic shape. The ideal end-diastolic shape for the cardiac assist device can best be described by a discovered curved shape that is rotated around a long axis. This shape can then take into account the ideal end-diastolic conformation of the entire outer surface of the right and left ventricles that should be achieved for idealizing pump function. This shape can be arrived at by knowing either the heart’s short or long axis measurement before the device is installed. The long axis is the preferred measure and having both is the most informative for initial device sizing. A need therefore exists for an improved cardiac assist system that has a size and shape that better meets the needs of a heart during both its diastolic and systolic phases. In this manner, the forces applied to the heart can result in better pump function of the arrested heart as well as better assistance to the native pump function. In this manner, the forces of a device can be used to primarily aid in the filling of the heart and only provide systolic compression forces as needed. The therapeutic effects of promoting diastolic pump function can thereby lead to improved recovery of the heart’s native function. This need is met by the present invention as described and claimed below. DISCLOSURE OF THE INVENTION The present invention is a system and method of increasing the pumping efficiency of an individual’s heart. The heart is either scanned or measured directly in vivo to determine the dimensions of the long axis and / or the short axis. These dimensions can be used to determine the ideal end-diastolic shape for selecting a cardiac assist device. Alternatively, a sphericity index for the heart or a variation thereof can be measured to arrive at the size of a needed cardiac assist device if measures of the long axis and / or short-axis cannot be obtained. A cardiac assist device is selected that acts to adjust the sphericity index of the heart to be closer to the value of one at its end-diastolic conformation. The sphericity index can be used to verify ideal end-diastolic positioning of the heart during assist device support. Further changes in device selection can then be guided by how the heart’s shape adjusts to the assist device. In this manner, a very dilated, dysfunctional heart may become smaller after a short period of time and a smaller device exchanged for improved end-diastolic fit. On the other hand, an under-sized device with the sphericity index is less than one and greater expansion of the heart is thereby determined necessary to improve assist. The cardiac assist device has a shell configuration that facilitates the heart’s outer surface to achieve an ideal end-diastolic shape. The shell passes around either the entire heart’s surface or part of the heart’s surface. In this manner, the shell configuration encircles the ventricles of the heart or can have segments that act upon selected areas of the ventricles. In either situation, the shell acts to bring the heart into a more ideal end-diastolic shape. The shell configuration has a top opening, a base, and a maximum interior diameter. The maximum interior diameter is at a first elevation between the top opening and the base. The shell configuration has a total length that extends along a major axis from the center of the top opening to the base. The shell configuration follows an elliptical or similar curvature that is rotated about said major axis, wherein the curvature follows a curve equation that is a function of both the maximum interior diameter and the total length. The shell configuration defines a top opening that has a maximum opening diameter that is no greater than the maximum interior diameter within the shell configuration. The maximum opening diameter is a function of the maximum interior diameter minus a constant. A beltline offset is defined on the shell configuration between the top opening and the elevation of where the maximum interior diameter is measured. The beltline offset has a height that is a function of the maximum interior diameter plus a constant. Likewise, the total length of the shell configuration is equal to the maximum interior diameter plus a constant. BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the present invention, reference is made to the following description of exemplary embodiments thereof, considered in conjunction with the accompanying drawings, in which: FIG. 1 shows an exemplary embodiment of an overall system that contains a cardiac assist device in accordance with the present invention; FIG. 2 shows a heart sectioned into areas for which sphericity, or measurements, of either the long or short axis can be used to calculate size for the cardiac assist device pertaining to the ideal end-diastolic shape; FIG. 3 shows an exemplary cardiac assist device shown in conjunction with a heart for dimensional reference; FIG. 4 is a chart that contains calculated values for total long axis length (TL), maximum short-axis diameter (MD), beltline offset (BL), volume, sphericity, adjusted sphericity, opening diameter and percentage coverage size for a selection of different sized cardiac assist devices; FIG. 5 is a graph that plots maximum short axis diameter as a function of volume for the different sized cardiac assist devices listed in Fig. 4; FIG. 6 is a graph that plots maximum short axis diameter as a function of its location with respect to the beltline offset (BL) for the different sized cardiac assist devices listed in Fig. 4; FIG. 7 is a graph that plots maximum short axis diameter as a function of the top opening size for the different sized cardiac assist devices listed in Fig. 4; FIG. 8 shows an alternate embodiment of a cardiac assist device containing separate and distinct contact heads; and FIG. 9 is a top view of the alternate embodiment of FIG. 8. DETAILED DESCRIPTION OF BEST MODE FOR CARRYING OUT THE INVENTION Although the present invention system and methodology can be embodied in many ways, only two exemplary embodiments are illustrated and described. The exemplary embodiments are being shown for the purposes of explanation and description. The exemplary embodiments are selected in order to set forth some of the best modes contemplated for the invention. The illustrated embodiments, however, are merely exemplary and should not be considered as limitations when interpreting the scope of the appended claims. Referring to Fig. 1 in conjunction with Fig. 2, a heart 11 is shown in conjunction with a cardiac assist device 10. The cardiac assist device 10 acts upon the heart 11 to assist the heart 11 in pumping. The cardiac assist device 10 is powered by a programmable pump 12. The pump 12 produces a pressure or flow profile that operates the cardiac assist device 10. Anatomical dimensions for the heart 11 can be obtained by measuring the heart 11 in vivo. Alternatively, a medical imaging system 14 can be used to image the heart 11 and to obtain anatomical dimensions needed to size the cardiac assist device 10. The medical imaging system 14 can be an x-ray imaging system, a CT imaging system, an MRI imaging system, an ultrasound imaging system, a nuclear medicine, or a fluorescence imaging system. As will be explained, the cardiac assist device 10 is designed to bias the heart 11 into an ideal end- diastolic conformation. The data obtained from imaging is used to determine dimensional variables for the heart 11 including long axis length (L1), short axis length (L2), and the transverse cardiac diameter D1 at the atrio-ventricular groove 15. Knowing the long axis length (L1) of the heart 11, the needed total length (TL) of a cardiac assist device can be determined. Knowing the short axis length (L2), the needed maximum width (MD) of a cardiac assist device can be determined. As such, the dimensions of the heart are used to determine the ideal device fit based on the device shaping the heart into an optimal end- diastolic geometry. Estimates of the calculated device fit can be made by calculating either the global sphericity index 17 and / or the regional sphericity index 19 of the heart 11 as an alternative means for arriving at device fit. These measurements can be repeated while the cardiac assist device 10 is on the heart 11 to determine if the device fit is ideal or the device should be changed. In this manner, the cardiac assist device 10 itself provides a means for making such measurements. Importantly, the heart’s shape could change differently than anticipated with the cardiac assist device 10 being activated. In these circumstances, the long-axis L1 of the heart 11 and internal length of the cardiac assist device 10 would be similar under ideal pumping circumstances. Maintaining this relationship + / -5% during pumping would be the principal guide for changing the cardiac assist device 10. The data measured from the heart 11 is used to calculate a defined end-diastolic geometric shape for the heart 11 that provides the most benefit. In situations where the heart 11 has a relatively normal morphology and a relatively sudden onset of heart function, the pumping of the heart 11 is ideal when the cardiac assist device 10 expands the normal heart 11 into a defined geometric shape. In other conditions in which the heart 11 is over-dilated either from acute injury or from chronic heart failure where the ventricle has undergone remodeling or dilatation of its walls, the cardiac assist device 10 is best when it conforms the end-diastolic shape of the heart 11 to a somewhat smaller, less dilated shape. This will allow for an ideal end- diastolic conformation for heart pump function but serve to reduce the end-diastolic conformation of the heart 11 to one that is not damaging to the heart and better for heart recovery. Importantly, the heart’s shape can change or undergo reverse- remodeling during assist which could indicate changing the cardiac assist device 10 should be considered. In this case, the long axis L1 of the heart 11 in relation to the long axis of the device would be the most important consideration. Surrogates such as the sphericity index and / or regional sphericity indices can be used in place of the more complex geometric formulation over the heart 11 with an intended end-diastolic sphericity index of one (1)+ / - 5%. In other words, the cardiac assist device 10 assists the heart 11 such that the end of the diastolic geometric configuration or the sphericity index (as a surrogate) promotes filling within a specified region during pump assist. The regional sphericity index 19 provides greater detail as a surrogate of the more complex formulation of the end-diastolic device conformation along the long axis (L1)of the heart 11. However, more accurate two-dimensional or three-dimensional formulations can be used for both the measurement of the heart 11 and for predicting the ideal end-diastolic conformation of the heart 11 when the cardiac assist device 10 fits over and acts on the heart 11. In this manner, when the cardiac assist device 10 is acting on either the entire heart 11 or on a specific region of the heart 11, the calculated surrogate, such as the regional sphericity index 19, provides a means for determining device fit and / or functionality for a region or for the entire heart 11. Referring to Fig. 2 and Fig. 3 in conjunction with Fig. 1, it can be seen that the heart 11 has a long axis (L1) that extends from the atrio- ventricular groove 15 to the ventricular apex 20. The heart 11 also has a short axis (L2). The global sphericity index 17 can be measured for multiple areas A1-An between the ventricular apex 20 and the atrio-ventricular groove 15. By measuring the global sphericity index 17 for the multiple areas A1-An, a very detailed data set can be collected that can be used to precisely size a cardiac assist device 10. The measurement for the long axis (L1) and the short axis (L2) of the heart 11 can be used to size the cardiac assist device 10. The long axis (L1) of the heart 11 can be used to determine the maximum diameter (MD) of the cardiac assist device 10. Likewise, the short axis (L2) of the heart 11 can be used to determine maximum short axis dimeter (MA) of the cardiac assist device 10. It is best if both dimensions are measured. However, in a scenario where only one of the dimensions can be measured, the other can be determined using the following equation: Equation 1 MA = .901979MD + 6.1758 Or reconfigured as: MD = (MA – 6.1758) / .901979 In general, the global long axis (L1) of the heart 11 is less subject to lengthening than is the short axis (L2). During conditions of heart failure and secondary remodeling, the short axis (L2) of the heart 11 is the predominant axis of dilation. Therefore, the global sphericity index 17 generally increases in most acute and chronic heart failure conditions. When applying the pump 12 to support the cardiac assist device 10, the sphericity index 17 can be used for both sizing the cardiac assist device 10 and programming the pump 12. In situations of heart failure, the cardiac assist device 10 will be sized to reduce the global sphericity index 17 toward a more ideal ratio of one (1). In situations where remodeling has not occurred, the cardiac assist device 10 will be sized as to slightly increase the global sphericity index 17 to one (1) for more optimal diastolic assist and promotion of filling. The measurement can be used to predict and select the optimal size of a cardiac assist device 10 for the heart 11. See Block 22 in Fig. 1. The sizing of the heart 11 can be determined using standard imaging techniques. The global sphericity index 17 can be used before and during application of the cardiac assist device 10. More specifically, the global sphericity index 17 can be used before application for sizing and during application to assess the heart’s changing dimension(s). When preparing for an operation, a surgeon has access to medical measurements / scans of the heart 11 that provide various dimensions. The surgeon then selects a cardiac assist device 10 from an inventory 23 of different sized options. Alternatively, if a rapid production machines is available, a custom cardiac assist device 10 can be manufactured to the needs of the surgeon during the operation. Determining the best size of the cardiac assist device 10 for a particular heart 11 is the challenge. Referring to Fig. 3, it will be understood that each cardiac assist device 10 has a shell configuration 13. The shell configuration 13 can encircle the ventricles of the heart 11 or can contact only sections of the heart 11. Each shell configuration 13 has a top opening 24 with an opening diameter (OD). Each cardiac assist device 10 also has a maximum diameter (MD) that is the widest interior diameter of the shell configuration 13. The maximum diameter (MD) is for the shell configuration 13 and ignores the inward extension of the inflatable membranes 26 within the cardiac assist device 10. The maximum diameter (MD) can be offset below the opening diameter (OD). This produces a belt line offset (BL) on the shell configuration 13. Accordingly, the belt line offset (BL) refers to the distance from the top opening 24 to the elevation of the maximum diameter (MD). Each cardiac assist device 10 also has a total length (TL), which is the distance from the top opening 24 to the low point of an opposite base 21 on the shell configuration 13. Referring to Fig. 4, metrics are shown for a variety of cardiac assist devices that may be provided to a surgeon in a selection inventory. The data table of Fig. 4 shows all the collected and calculated data per cardiac assist device from a small size to a large size. Using the physical dimensions of the cardiac assist devices shown Fig. 2 and Fig. 3, the sphericity and adjusted sphericity of Fig. 4 can be calculated. The equation of sphericity is as follows: Equation 2 Sphericity = MD / TL The adjusted sphericity is determined using Equation 3. Equation 3 MD Adjusted Sphericity = ------ ((TL-BL)X2) Adjusted sphericity considers the offset of the beltline (BL)in the calculation. Percent size coverage is a calculation of the area of the heart 11 covered by the cardiac assist device 10. It is obtained by first finding the spread of the data. Half the difference between a selected maximum diameter(MD)and the next smallest maximum diameter (MD) is added to half the difference of the selected maximum diameter and the next largest maximum diameter (MD) with all being divided by the spread. This formula is not relevant for the largest and smallest sizes. There is also expected to be a very large spread between a neonatal size and the smallest adult size. Referencing the physical dimensions of the cardiac assist device 10 shown in Fig. 2 and Fig. 3, and also referring to Fig. 5 in conjunction with Fig. 4, it will be understood that the data was calculated using the maximum diameter (MD) as a basis. As shown in Fig. 5, the volume increases as the maximum diameter (MD) increases. A polynomial trendline 27 is fitted to the data and shows a relationship provided by Equation 4 below: Equation 4 Volume = 138.2(MD)2 – 10094(MD) + 209707 ± 5% where R value for the trendline is 0.9982. Referring to Fig. 6, while using the physical dimensions of the cardiac assist device 10 shown in Fig. 2 and Fig. 3, a plot for the beltline offset (BL) is shown. In the plot, a linear trendline is fitted to the data using Equation 5 below: Equation 5 Beltline offset (BL) = .2056(MD) + 6.1758 ±5% The R value of the trendline is .6515. Referring to Fig. 7, while using the physical dimensions of the cardiac assist device 10 shown in Fig. 2 and Fig. 3, the opening size is plotted. A linear trendline is fitted to the data with Equation 6 below: Equation 6 Opening Size = 1.004(MD)-6.5085 ±5% The R Value is .9914. With reference to the tables and charts of Fig. 4 through Fig. 7 and using the physical dimensions of the cardiac assist device 10 shown in Fig. 2 and Fig. 3, there is evidence that there is a preferred sphericity for the cardiac assist device 10 when measured both as adjusted sphericity and without adjustment. The coefficient of variability for sphericity is extremely low. The R value for the trendlines are also relatively low. As a consequence, the target across all sizes for sphericity should be the mean of the measured cardiac assist devices. Having a mean sphericity within one standard deviation is crucial to proper functioning of the cardiac assist device 10. There is also a strong linear correlation for the top opening 24. Accordingly, the trendline equation given for the top opening 24 is useful for further engineering and development of cardiac assist devices of different sizes. The beltline offset (BL) is more variable and shows a less prominent relationship. The curve at the maximum diameter is very subtle and small inconsistencies in the manufacturing process between cardiac assist devices leads to large deviations in this measurement. Based on this information, it has been determined that the interior shape the cardiac assist device 10 should match is that of a truncated ellipse revolved about its major axis with the sphericity based on the mean sphericity of the current models, such as is shown in Fig. 6. The cardiac assist device 10 is shaped as a three-dimensional ellipse, or a slight variation thereof. A preferred 2-Dimensional curve of the ellipse would be given by Equation 7 and Equation 8 shown below: Equation 7 (x2 / (MD / 2)2) + (y2 / (TL-(0.2056MD + 6.1758))2) = 1 Equation 8 MD / (2(TL - (0.2056MD + 6.1758))) = 0.7180 The variable (MD) is the maximum diameter and (TL) is the total long axis length. The ellipse is truncated such that the opening size is equal to 1.004MD -6.5085. The data on opening size is strongly correlated to maximum diameter (MD), as indicated by Equation 7. This system of equations can also be expressed as a function of total long axis length (TL) as expressed by Equation 9 and Equation 10 below: Equation 9 TL = (x2 (6.1758 + 0.205MD) - 1.54395 MD2 - 0.0514 MD3 - 0.25 √(y2MD2 (-4 x2 + MD2))) / (x2 - 0.25 MD2) Equation 10 TL = .902MD + 6+ / - 7% The 7% used in the above equation is approximately equal to one standard deviation based on collected data. This 2-dimensional curve is then revolved about its major axis to create a 3-dimensional volume. All the prior equations set forth above are used to calculate a configuration for a cardiac assist device 10 that will optimize the shape of the heart at diastole. All of the equations depend to some degree upon the maximum diameter (MD) of the cardiac assist device 10. The fact that the maximum diameter (MD) is termed a diameter implies that the cardiac assist device 10 completely encircles the heart 11. However, that need not be the case. There are many instances where a full cardiac assist device cannot be placed around the circumference of a heart. This can be due to the presence of scar tissue, bypass alterations and / or abnormalities on the heart. In such instances, cardiac assist devices that only act upon specific areas of the heart are used. Referring to Fig. 8 in conjunction with Fig. 9, it can be seen that a cardiac assist device 40 can be comprised of one or more independent contact heads 42. The contact heads 42 are generally spoon- shaped and contact the exterior of the heart 11 in one or more regions surrounding the heart 11. The contact heads 42, when combined form the overall cardiac assist device40. The contact heads 42 are sized and positioned to follow elliptical curvatures 45 determined by Equation 7 and Equation 8 that has a maximum diameter (MD). The maximum diameter (MD) will depend upon the size of the heart 11 and the contact points on the heart 11. With the maximum diameter (MD) known, the total length (TL) can be calculated using Equation 9 and / or Equation 10. The volumes can be calculated using Equation 4. The opening size can be calculated using Equation 6. The belt line offset can be calculated using Equation 5. The curvatures can be calculated using Equation 7 and Equation 8. These values are used in the selection of the sizes and shapes of the contact heads 42. Since the contact heads 42 are each independent and contact the heart 11 in a different region of the heart 11, some mechanism is required to maintain the maximum diameter (MD), since all other variables are a function of the maximum diameter (MD). Each of the contact heads 42 has a curved shell body 44 and an inflatable membrane 46. The curvatures of the shell bodies 44 are determined, in part, by the calculations of Equation 9 and Equation 10. At least one guide 48 engages each of the contact heads 42. The guides 48 are flexible enough to move with the heart 11 as the heart 11 changes shape. However, the guides 48 have enough rigidity to maintain the contact heads 42 at a selected average maximum diameter (MD) when the heart 11 is at diastole. It will be understood that during the diastolic, or filling phase, of the heart pump cycle, the heart 11 expands. The expansion of the heart 11 is to be assisted, not resisted. To assist the heart 11, the inflation pressure within the inflatable membranes 46 is reduced. This creates a reduced pressure between the exterior of the heart 11 and the interior of the contact heads 42. The reduced pressure helps the heart 11 expand. The elastomeric material of the inflatable membranes 46 adhere to the tissue of the heart 11 due to surface adhesion forces that are inherent between smooth surfaces in a wet environment. The result is that the inflatable membranes 46, reinforced by the guides 48, physically pull upon the heart 11 as they deflate. This assists the heart’s ability to expand. The shape of the heart 11 at full diastole is influenced by the contact heads 42, wherein the diastolic shape is that of the 3D ellipse defined by Equation 8 and Equation 9. It will be understood that the embodiments of the present invention that are illustrated and described are merely exemplary and that a person skilled in the art can make many variations to those embodiments. All such embodiments are intended to be included within the scope of the present invention as defined by the claims.

Claims

CLAIMS 1. A cardiac assist device (10) for acting on a heart (11) having an actual end-diastolic conformation in vivo and an ideal end-diastolic conformation that would cause the heart to pump more efficiently, said device comprising: a shell configuration (13) having at least one segment, said shell configuration (13) having a top opening (24), a base (21), and a maximum interior diameter at a first elevation between said top opening (24) and said base (21), wherein said shell configuration (13) has a total long axis length (TL) from said top opening (24) to said base (21), wherein said shell configuration (13) has a major axis, and wherein said shell configuration (13) follows a curvature that is rotated about said major axis, at last one inflatable membrane (26) that extends from said shell configuration (13), wherein said at least one inflatable membrane (26) pushes and pulls against the heart (11), wherein said shell configuration (13) and said at least one inflatable membranes (26) act upon said heart (11) to alter said actual end-diastolicconformation toward said ideal end-diastolic conformation.

2. The cardiac assist device (10) according to claim 1, wherein the heart (11) is measured to determine regional sphericity indices (19) for the heart (11) and wherein said shell configuration (13) and said at least one inflatable membranes (26) act upon said heart (11) to alter said regional sphericity indices (19).

3. The cardiac assist device (10) according to claim 1, wherein the heart (11) is measured to determine a global sphericity index (17) and wherein said shell configuration (13) and said at least one inflatable membranes (26) act upon said heart (11) to alter said global sphericity index (17) to a value closer to one.

4. The cardiac assist device (10) according to claim 1, wherein said curvature is an elliptical curvature that follows an equation of: (x2 / (MD / 2)2) + (y2 / (Tl-(0.2056MD + 6.1758))2) = 1 with MD being said maximum interior diameter and TL being said total long axis length.

5. The cardiac assist device (10) according to claim 1, wherein said top opening (24) has a maximum opening diameter that is less than said maximum interior diameter (MD) of said shell configuration (13).

6. The cardiac assist device (10) according to claim 5, wherein said maximum open diameter is equal to 1.004 times said maximum interior diameter minus 6.5085 plus and minus a margin of error of five percent.

7. The cardiac assist device (10) according to claim 4, wherein a beltline offset (BL) is defined on said shell configuration (13) between said top opening (24) and said first elevation of said maximum interior diameter (MD).

8. The cardiac assist device according to claim 7, wherein said beltline offset (BL) has a height equal to said maximum interior diameter times .2056 plus 6.1758 plus and minus a margin of error of five percent.

9. The cardiac assist device (10) according to claim 1, wherein said total long axis length(TL)is equal to said maximum interior diameter (MD) plus 6.1756 plus and minus a margin of error of five percent.

10. The cardiac assist device (10) according to claim 7, wherein said sphericity index is a measure of a diameter of the heart (11) divided by a length of the heart.

11. The cardiac assist device according to claim 9, wherein said shell configuration (13) has a volume determined by the following equation: Volume = 138.2(MD)2 – 10094(MD) + 209707 plus and minus a margin of error of five percent where MD is said maximum interior diameter.

12. The cardiac assist device (10) according to claim 1, wherein said maximum interior diameter and said total long axis length follow the following mathematical relationship: MD / (2(TL - (0.2056MD + 6.1758))) = 0.7180 where MD is said maximum interior diameter and TL is said total long axis length.

13. The cardiac assist device (10) according to claim 1, wherein said shell configuration (13) includes a plurality of shell segments, wherein each of said shell segments is supported by at least one guide (48).

14. A cardiac assist device (10) for acting on a heart (11) having an actual end-diastolic conformation in vivo and an ideal end-diastolic conformation that would cause the heart (11) to pump more efficiently, said device comprising: a shell configuration (13) having at least one segment, said shell configuration (13) having a top opening (24), a base (21), and a maximum interior diameter (MD) at a first elevation between said top opening (24) and said base (21), wherein said shell configuration (13) has a total long axis length (TL) from said top opening (24) to said base (21), wherein said shell configuration (13) has a major axis, and wherein said shell configuration (13) follows a curvature that is rotated about said major axis, wherein said shell configuration (13) is shaped and sized to alter said actual end-diastolic conformation in vivo toward said ideal end-diastolic conformation.

15. The cardiac assist device (10) according to claim 14, wherein the heart (11) has a sphericity index at said end-diastolic conformation and said shell configuration (13) alters said sphericity index at said end-diastolic conformation to a value closer to one.

16. The cardiac assist device (10) according to claim 14, wherein said curvature is an elliptical curvature that follows an equation of: (x2 / (MD / 2)2) + (y2 / (TL-(0.2056MD + 6.1758))2) = 1 with MD being said maximum interior diameter and TL being said total long axis length.

17. The cardiac assist device (10) according to claim 14, wherein said top opening (24) has a maximum opening diameter that is no greater than said maximum interior diameter (MD) of said shell configuration (13).

18. The cardiac assist device (10) according to claim 14, wherein a beltline offset (BL) is defined on said shell configuration (13) betweensaid top opening (24) and said first elevation of said maximum interior diameter (MD), wherein said beltline offset (BL) has a height equal to said maximum interior diameter times .2056 plus a constant of 6.1758 plus or minus five percent.

19. The cardiac assist device (10) according to claim 14, wherein said sphericity index is a measure of a diameter of the heart (11) divided by a length of the heart (11).

20. The cardiac assist device (10) according to claim 14, wherein said shell configuration (13) has a volume determined by the following equation, Volume = 138.2(MD)2 – 10094(MD) + 209707 where MD is said maximum interior diameter.

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