Abstract:
The present invention provides a heart valve measurement tool in the form of an obturator. The obturator is specifically configured to measure the size of the annulus of the heart to be fitted with a prosthetic heart valve. A plurality of obturators of varying sizes are utilized to determine the appropriate valve size.

Description:
FIELD OF THE INVENTION 
     This invention relates to heart valve measurement tools and, in particular, to improved obturators which are specifically configured to measure the size of the annulus of the heart to be fitted with a prosthetic heart valve and the method of using the obturators. 
     BACKGROUND OF THE INVENTION 
     Replacement of diseased or malfunctioning heart valves requires that the replacement valve be appropriately sized to fit the annulus of the valve that is being replaced. In order to determine the required valve size, the patient&#39;s valve annulus needs to be measured. One method of measuring the valve annulus includes taking X-rays of the patient&#39;s heart and measuring the diameter of the annulus from the X-rays. However, due to the inaccuracies of X-rays, this method is not very reliable and only an approximate estimate of the valve annulus sizes can be made. 
     Another method of measuring the valve annulus involves the use of calipers and the like to measure the valve diameter. This method requires that the measurement be made by the surgeon during the valve-replacement procedure. Once the annulus diameter is measured, the valve annulus circumference is calculated and, subsequently, the appropriately-sized replacement valve is determined. This method, however, has several disadvantages. Due to the limited amount of space in the heart, it is difficult to properly located the measurement tools within the heart at the site of the annulus. In addition, a human valve annulus is not perfectly round or circular and, therefore, calculations of valve annulus circumference are imprecise. 
     U.S. Pat. No. 5,163,955 assigned to Autogenics, assignee of the present invention, describes improved tools for sizing the annulus by use of a series of sized obturators. 
     Therefore, there is a need for a heart valve annulus measurement device and method whereby a patient&#39;s valve annulus may be accurately measured to determine the appropriate replacement valve size. In addition, the device or method should facilitate valve annulus measurement so that the measurement may be performed in a time-efficient manner. 
     SUMMARY OF THE INVENTION 
     The present invention provides a device that is used during heart-valve replacement to measure the size of the annulus of the heart. During valve-replacement surgery, the diseased or malfunctioning heart valve is removed from the patient. The prosthetic replacement valve, having a base with predetermined circumference, is implanted at the valve annulus. The obturators of the present invention are improvements over those disclosed in the &#39;955 patent and provide the necessary valve annulus measurements in order to implant the appropriately sized replacement valve. 
     The preferred embodiment of the present invention comprises a plug or obturator which is configured in a plurality of different sizes. The shape of the obturator closely resembles the shape of the replacement valve and the annulus of the heart. Each obturator has several predetermined dimensions which are used to accurately measure the annulus of the heart so that the appropriate size for the replacement valve may be determined. 
     The obturator is comprised of four sections. The first section has a threaded center-hole where a handle can be screwed into the obturator. The handle is used to push the obturator into the valve annulus. The second section is comprised of outwardly-tapered walls and includes the bottom portion of the threaded center-hole. The third section of the obturator corresponds to the base-piece of the replacement valve. Thus, the first, second and third sections of the obturator are configured to closely resemble the replacement prosthetic heart valve. 
     The fourth section of the obturator corresponds to the patient&#39;s heart valve in-flow diameter. Additionally, the four section is used to probe the annulus to determine whether there are any obstructions. 
     In use, a surgeon or technician successively plugs the annulus of the heart with the various-sized obturators until the appropriately sized obturator is determined. In addition to determining that the obturator fits securely into the patient&#39;s annulus, the surgeon or technician must also visually inspect the fit of the third section of the obturator. If the third section rests above or on top of the annulus, then the obturator is the correct size for the annulus. Thus, by utilizing the obturator, the appropriately sized prosthetic replacement heart valve is determined. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the obturator of the present invention. 
     FIG. 2 is a cross-sectional top view of the device of FIG. 1. 
     FIG. 3 is a cross-sectional side view of the device of FIG. 1. 
     FIG. 4 illustrates both cross-sectional top and side views of a replacement valve and the obturator of FIGS. 2 and 3. 
     FIG. 5 is a cross-sectional view of the obturator of FIG. 1 seated within the annulus of a heart. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The obturator 10 shown in the FIGURES is used to size the annulus of the heart valve to be fitted with a prosthetic heart valve 50. Once the valve annulus size is determined, the corresponding appropriately sized prosthetic heart valve 50 is implanted in the patient&#39;s heart. A significant feature of the preferred embodiment of this invention is that the obturator is configured to resemble both the replacement prosthetic heart valve and the annulus of the human heart. 
     As shown in FIG. 4, each section of obturator 10 has predetermined heights and diameters that correspond to the various diameters and heights of a prosthetic heart valve 50. Referring to FIGS. 1-3, the first section 12 of the obturator 10 has the shape of a solid cylinder and is comprised of vertical walls 14 and an internally threaded hole 16 located along the axis at the center of the cylinder. The diameter &#34;Z&#34; of the threaded hole 16 is appropriately sized so as to mate with a handle 20. The diameter of the first section 12 is defined as &#34;B&#34; and its height is defined as &#34;D&#34;. 
     The second section 22 of the obturator 10 has the shape of an upright solid cone frustum, having a height defined as &#34;E&#34;. The second section 22 is comprised of outwardly tapered walls 24, wherein the uppermost cross-sectional diameter formed by the walls 24 of the second section 22 is equal to that formed by the walls 14 of the first section 12. Thus, the small diameter of the second section is also designated by the letter &#34;B&#34;. The large diameter formed by the walls 24 is defined as &#34;C&#34;. The threaded hole 16 of the first section 12 continues into a portion of the second section 22, along the axis of the second section 22. 
     Still referring to FIGS. 1-3, the third section 26 of the obturator 10 has inwardly-tapered walls 28, having the shape of an inverted solid cone frustum. The large diameter formed by the walls 28 of the third section 26 is adjacent to the large diameter of the second section 22. The third section 26 has small and large diameters designated by the letters &#34;G&#34; and &#34;A&#34;, respectively. The height of the third section 26 is defined as &#34;F&#34;. 
     The fourth section 30 of the obturator 10 of the present invention has the shape of a solid cylinder. The fourth section 30 is formed by vertical walls 32, similar to those of the first section 12. The diameter of the cylinder of the fourth section 30 is defined as &#34;H&#34; and is smaller than the diameter of the first section 12. 
     The obturator 10 is advantageously formed of a plastic, biocompatible material, such as Polysulfone. Other materials, which provide a rigid structure that is non-deformable upon insertion of the obturator 10 into the heart valve annulus, may also be used. 
     The obturator 10 is configured to resemble the prosthetic heart valve 50 and the annulus of the heart. Several dimensions of the obturator 10 correspond to those of a predetermined size prosthetic heart valve 50. For example, referring to FIG. 4, the large diameter &#34;C&#34; of the second section 22 of the obturator 10 corresponds to the inner-diameter &#34;X&#34; of the base-piece 52 of the replacement valve 50. In addition, the large diameter &#34;A&#34; of the third section 26 of the obturator 10 corresponds to the outer-diameter &#34;Y&#34; of the base-piece 52 of the replacement valve 50. These dimensional similarities aid the surgeon or technician in determining the appropriate size for the replacement valve for the annulus of the heart. 
     Referring to FIGS. 2 and 3, certain other dimensions of the obturator 10 are advantageously held constant, regardless of the size of the obturator 10. The first such dimension is the height &#34;I&#34; of the fourth section 30. As described below, the fourth section 30 is inserted into the annulus formed by excising the patient&#39;s natural valve. The depth of section 30 probes the annulus to determine whether there are any obstructions; therefore, a substantially constant depth of this section is desirable for all sizes of obturators regardless of their annulus opening size. The second dimension, which is advantageously held constant, is the diameter &#34;Z&#34; of the threaded hole 16. As a result, a single handle 20 can be used for any and all of the sized obturators. The third and final constant dimension is the height or depth &#34;J&#34; of the hole 16. This dimension ensures that a sufficient length of the threaded handle 20 can be screwed into each obturator 10. These dimensions are thus arbitrary and remain constant regardless of valve size, since valve sizing is not dependent upon these obturator dimensions. 
     The method of using the obturator 10 of the present invention is as follows. During the heart valve replacement procedure, it will be understood that the surgeon or technician is provided with a plurality of obturator 10 sizes. As described in the &#39;955 patent, these obturators are advantageously arranged in a first kit including the common handle 20. The surgeon or technician screws the handle 20, having an externally threaded section 21, into the threaded hole 16 of one of the obturators 10 and plugs the obturator 10 into the annulus of the patient&#39;s heart. If the obturator 10 securely fits into the annulus, as shown in FIG. 5, the obturator dimension or size is noted and the appropriately sized replacement valve 50 is determined. If, however, the obturator 10 does not fit within the annulus of the heart, the surgeon or technician successively plugs the annulus of the heart with the obturators 10 until the appropriate size of the annulus is determined. 
     The determination of a secure fit is, to some extent, based upon the individual surgeon&#39;s or technician&#39;s judgement and experience. However, certain requirements must be satisfied in order to ensure an appropriate fit. One requirement is that the valve annulus is free from obstruction. This requirement is satisfied by sliding the fourth section 30 of the obturator 10 completely into the annulus of the heart so that the third section 26 of the obturator 10 rests on the walls of the annulus, as shown in FIG. 5. Thus, one may assume that the annulus is sufficiently free from obstructions. 
     An additional requirement is that the fourth section of the obturator can be easily placed inside the collapsed annulus. If the fourth section of the obturator is too large, the surgeon or technician will experience great difficulty in fitting the obturator into the annulus of the heart. If, however, the fourth section easily fits within the annulus, the surgeon or technician must next determine if the fourth section is too small. 
     Proper sizing of the replacement prosthetic heart valve is very important. A particular feature of this invention is that it notifies the surgeon during the sizing procedure that a particular valve may be too small, notwithstanding that the fourth section 30 of the obturator 10 seems to properly fit within the open annulus of the heart. This is accomplished by visually inspecting the fit of the inverted cone frustum third section 26 of the obturator 10 to the annulus of the heart. If any portion of the inverted cone frustum section 26 of the obturator 10 fits within the open annulus of the heart, then the obturator 10, and subsequently the replacement valve, is too small and the surgeon is advised to test a larger obturator 10. However, if the inverted cone frustum section 26 of the obturator 10 rests above or on top of the annulus, as shown in FIG. 5, then the obturator 10 is the correct size for the annulus. From this measurement, the surgeon or technician can then obtain the appropriately sized replacement valve. 
     It should be appreciated that a range of obturator sizes corresponds to the various annulus sizes of the heart. For example, replacement of the mitral or atrioventricular valve utilizes a set of obturators ranging in size from 23 mm to 31 mm. For the aortic or pulmonary valves, obturator sizes may vary within the range of 19 mm through 29 mm. Replacement of valves in young children may require valves as small as 14 mm. 
     Obviously, numerous variations and modifications can be made without departing from the spirit of the present invention. Therefore, it should be clearly understood that the forms of the present invention described above and shown in the figures of the accompanying drawings are illustrative only and are not intended to limit the scope of the present invention.