Patent Application
20080009733
The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate presently preferred embodiments of the invention, and, together with the general description given above and the detailed description given below, serve to explain features of the invention.
The various embodiments will be described in detail with reference to the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
As used herein, the terms “about” or “approximately” for any numerical values or ranges indicates a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein. Also, as used herein, the terms “patient”, “host” and “subject” refer to any human or animal subject and are not intended to limit the systems or methods to human use, although use of the subject invention in a human patient represents a preferred embodiment.
The methods of the various embodiments enable physicians to obtain more complete and comprehensive visualizations of the function and status of the ventricles of the heart. In the various embodiments, ultrasonic imaging of the chambers of the heart via intracardiac echocardiography provide measurements to establish a quantitative evaluation of the pumping function of the heart as a whole and of the individual performance of the various heart chambers. The embodiment methods monitor the regional ejection fraction during the systolic period in a phased analysis of the regional wall motion to give a temporal sequence of regional ventricular ejection. This phase analysis determines the timing of wall motion of these segments. An axial assessment can be performed along the long axis of the ventricle to determine apical to basal sequencing of ventricular ejection. A user-friendly display of the analysis results is provided to aid the clinician in understanding the results. Presenting the analysis results superimposed upon an image or stylized model of the heart enables the clinician to recognize ventricle regions requiring intervention, such as pacing, and to position pacing leads, for example, for best therapeutic results. The various methods may also be performed before and after interventions to measure the impact of the therapies upon heart function. In an embodiment, the assessment methods are performed after cardiac pacemaker settings are adjusted to enable the clinician to identify settings, such as the timing of pacing of each lead, which optimize heart function.
The various embodiments involve placement of a phased array ultrasound imaging catheter within the various chambers of the heart. By imaging the various anatomies of the heart during the heart's normal operation, assessments of the hearts ability to eject the appropriate volume of blood can be made. Examples of phased array ultrasound imaging catheters suitable for placement in the left pulmonary artery for ventricular mapping and methods of using such devices in cardiac diagnosis are disclosed in U.S. Patent Application Publication Nos. 2004/0127798 to Dala-Krishna, et al., 2005/0228290 to Borovsky, et al., and 2005/0245822 to Dala-Krishna, et al., each of which is incorporated herein by reference in their entirety. A suitable phased array ultrasound imaging catheter is the ViewMate™ which is commercially available from EP MedSystems, Inc. of West Berlin, N.J.
An embodiment of the present invention provides a method to outline the inner lining of the ventricle during different phases of the cardiac cycle. The inner lying of the ventricle, the endocardium, can be imaged using ultrasound imaging techniques employing ultrasound delivered by a phased array ultrasound transducer mounted on a catheter, such as described in U.S. Patent Application Publication Nos. 2004/0127798 and 2005/0245822. Ultrasound energy is reflected from the endocardial surface and from tissue layers within the endocardium of the lower chamber of the heart. Reflected ultrasound is detected by the phased array ultrasound transducer, where the sound energy is converted into electrical pulses which can be processed to render a two-dimensional image of the inner lining of the heart. Ultrasound energy is also reflected from the heart valves and other anatomic structures allowing the ultrasound equipment to resolve the anatomic positions of these structures as well.
The methods of the various embodiments permit automated tracking as well as manual identification of the endocardial surface of the right and left ventricle.
To acquire images of the endocardial surface of the right and left ventricle, a phased array ultrasound imaging catheter is positioned within the heart via percutaneous cannulation using standard cardiac catheterization techniques of the femoral vein or the subclavian or jugular veins.
In order to properly position the phased array ultrasound imaging catheter, a long preformed intravascular sheath 10 is advanced under fluoroscopic control into the right atrium 4 of the heart 1, as shown in
For imaging the left ventricle 3, the ultrasound transducer 14 needs to be positioned within the right ventricle. This can be accomplished by passing a guide wire 11 through the sheath 10, and under fluoroscopy control, passing the guide wire 11 through the tricuspid valve 9. The sheath 10 is then directed over the guide wire 11 into the orifice of the tricuspid valve 9 and advanced into the right ventricular cavity 2, as illustrated in
Instead of a using a sheath 10 to position the ultrasound phased array catheter 13 in the heart 1, a steerable ultrasound catheter, such as disclosed in U.S. Patent Publication 2005/0228290, can be used and guided directly under fluoroscopy control into position within orifice of the tricuspid valve or within the right atrium, as illustrated in
With the catheter phased array transducer 14 properly positioned within the heart, an ultrasound system, such as the ViewMate® Intracardiac Ultrasound Catheter System manufactured by EP MedSystems, Inc. of West Berlin, N.J., is connected to the catheter, an example of which is illustrated in
When the catheter is positioned within a patient's heart, the ultrasound system generates electrical pulses which cause the ultrasound transducers in the phased array transducer 14 to emit ultrasound pulses. By a controlling the phase lag of the pulses emitted by each transducer element within the phased array, a combined sound wave is generated with a preferential direction of propagation. Echoes from structures within the heart are received by the transducer elements and transformed into electrical pulses by the transducer. The electrical pulses are carried via the cables 50, 52 to the processor 53. The processor 53 analyzes the electrical pulses to calculate the distance and direction from which echoes were received based upon the time of arrival of the echoes received on each transducer element. In this manner, ultrasound energy can be directed in particular directions, such as scanned through a field of regard 15, and the resulting echoes interpreted to determine the direction and distance from the phased array that each echo represents.
Scanning the ultrasound energy through a field of regard 15 generates a two-dimensional (2D) image of the heart, examples of which are shown in
Since the scan rate of a phased array ultrasound transducer is much faster than the cardiac cycle, each scan presents a 2-D image at a particular time or phase in the cycle. Thus, individual scans, or a plurality of scans obtained at a particular phase or relative time within the cardiac cycle over a number of beats combined into an average image, can be used to provide a “freeze frame” image of the heart at particular instants within the cardiac cycle. Methods for combining and averaging multiple scans at a particular phase or relative time within the cardiac cycle (time gating) are described in U.S. application Ser. No. 11/002,661 published as U.S. Patent Publication No. 2005/0080336 to Byrd, et al., the entire contents of which are incorporated herein by reference in their entirety.
The freeze frame capability of B-mode images is used to obtain recordings particularly at the onset of QRS complex, which is near the end of diastole, and at the beginning of the T wave which is near the end of systole.
Automated edge-seeking algorithms or manual delineation of the endocardial signals is performed on the obtained images throughout the entire ventricle. Edge-seeking algorithms locate the edges of structure (e.g., ventricle walls) by noting a steep change in brightness (indicating echo intensity) from pixel to pixel. Alternatively, the cardiologist may define the edge of the endocardial surface 5′, 7′ in the image by manually tracing the edge using an interactive cursor (such as a trackball, light pen, mouse, or the like) as may be provided by the ultrasound imaging system. By identifying the edges of structure within an ultrasound image, an accurate outline of ventricle walls can be obtained and other image data ignored. The result of this analysis is a set of images and dimensional measurements defining the position of the ventricle walls at the particular instants within the cardiac cycle at which the “freeze frame” images were obtained. The dimensional measurements defining the interior surface 5′ or 7′ of the endocardium can be stored in memory of the ultrasound system and analyzed using geometric algorithms to determine the volume of the ventricle.
For the left ventricle 3, an image of most of if not the entire endocardium is obtained, preferably from the base of the aortic valve to the left ventricular apex and across back to the base of the aortic valve. An illustration of such an ultrasound image at diastole is provided in
Having obtained dimensional measurements of the left ventricle 3 from the ultrasound images at or near diastole and systole, the ultrasound system processor can calculate the volume in the ventricle at both instances and, from the ratio of these two volumes, calculate the ejection ratio of the left ventricle 3.
While
Another embodiment of the invention provides a method for the detecting and analyzing the segmental, regional, and global pumping efficiencies of the ventricles. In this embodiment, the long axis 80 of the left ventricle 3 is defined from the mid point 81 of the aortic valve plane 82 to the left ventricular apex 83, as illustrated in
The area in each segment as defined by the radial axes is then planimetered and automatically computed. The area in each sector of the ventricle or the fractional shortening along the radian in the sector can be used as a measure of regional ventricular function and ejection fraction. The difference in area between the measured area in the end-diastolic image and the measured area in the end-systolic image characterizes the regional ejection fraction for the region of the heart subtended by each such pair of corresponding sectors and may be used to estimate the regional ejection fraction for the measured segment. This estimate is based upon the assumption that the length of the long axis 80, 90 does not change significantly during contraction, so that the change in volume is proportional to the change in area of a transverse cross section. In this manner, the regional ejection fraction for each of the segments can be easily calculated by the ultrasound system processor to provide ejection fractions for multiple regions of the ventricle.
The definition of axes and radians is further illustrated in
The embodiment method may approximate the area of each sector or region in an image of the ventricular cavity 2 or 3 being examined as the sum of the areas of multiple, small, disjoint, abutting triangles which effectively subdivide and cover the sector or region. For example, each triangle may have the long axis bisection point 85, 95 as one vertex, and two sides defined by radials 87 from the bisecting midpoint 85, 95 terminating at the edge of the endocardial wall 5′ or 7′.
As an alternative or addition to the area method of estimating ejection fraction, the change in length of each of the radials 84, 86, 87 can provide information characterizing the instantaneous ejection fraction by monitoring the endocardial wall motion in the direction along each radial. These radials 84, 86, 87 relate to specific anatomic regions of the imaged heart ventricle. The values and relative timing of the regional ejection fractions, which correspond to the various radials 84, 86, 87, can be used to assess the effect of alternative interventions as described herein.
This embodiment for calculating regional ejection fractions can also be accomplished at various predefined points in the systolic cycle, such as, for example, at or near early (˜33%), mid (˜50%), late (˜67%) and end (˜100%) points of the systolic period of ventricular contraction. This can be accomplished by subtracting the area of each segment at the predefined point in the cycle from the area of the segment measured at diastole. This evaluation provides a novel and useful method for detecting and diagnosing ventricular dysynchronous contraction.
In another embodiment of the invention calculates an overall global ejection fraction by summing all of the regional ejection fractions obtained according to the above method. The global ejection fraction can be measured at different predefined points in the systolic cycle, such as at or near early (˜33%), mid (˜50%), late (˜67%) and end (˜100%) points of the systolic period of ventricular contraction. This calculation permits evaluation of ventricular ejection fraction at different points in the cardiac cycle. By calculating the ventricular ejection fraction at different points in the cardiac cycle, detection of ventricular dysynchronous contraction is possible.
In another embodiment, instead of defining a long axis 80, 90 of the ventricle, the ultrasound processor can compute the centroid of the edge trace of the endocardium wall and bisect the edge trace about the centroid to define a point from which to extend radians for calculating ejection fraction according to the methods described herein.
Under normal circumstances, the overall ejection fraction increases during systole until the end of systole. The various embodiment methods allow for estimation of ejection fraction when segments of the ventricle are not contracting in coordination with one another. In ventricular dysynchronous contraction, some portions of the ventricle wall contract out of phase (early, late or not at all) with the rest of the ventricle. Such ventricular dysynchronous contraction results in ineffective or incomplete ejection of blood from the heart, which is indicative of heart disease and can lead to formation of blood clots which may cause embolisms or stroke. This embodiments enable estimation and detailed analysis of the ejection fraction as it changes over the course of a cardiac cycle, especially when regions of the ventricle are not contracting in normal coordination.
In an embodiment, regional ejection fraction during the systolic period can be monitored in a phased analysis of the regional wall motion to give the temporal sequence of regional ventricular ejection. The phase analysis determines the timing of wall motion each of the ventricular segments with respect to each other.
In another embodiment, an axial assessment of ventricular function can be performed along the long axis of the ventricle using methods similar to those for measuring along radians to determine apical-to-basal sequencing of ventricular ejection.
In another embodiment, fractional shortening along each of the radial axes is measured to allow for assessment of instantaneous fractional shortening. This embodiment is as an alternative to the area method for computation of regional wall motion embodiment method described above. In this embodiment, the regions defined by the radial axes can be related to specific anatomic regions of the heart ventricle to assess the effect of interventions as described herein. By measuring the shortening of each radial axis defined within the ventricle, a simple measure of the phase and relative contraction of regions of the ventricle is obtained. In a situation where the clinician seeks to identify regions of a ventricle that are lagging during contraction, such as in a condition of incoordinate ventricle contraction, a simple measure of radian length versus time is sufficient to identify the timing and relative magnitude of regional contraction motions.
In the various embodiments, the ultrasound system processor will complete the analysis by generating a display of the computed regional and global ejection fractions, or regional fractional shortening (contraction) measurement, in some useful format for inspection by the cardiologist. The format of the display may simply be the regional ejection fractions presented as numbers related to their respective sectors. Each number can be superimposed and centered on its corresponding sector on the image taken at the time of the cycle for which the set of ejection fractions were computed. Alternatively, the numbers can be superimposed on a stylized model, cartoon or image (e.g., an X-ray image) of the heart. Similarly, where the measured factor is relative timing of contraction movements of different regions of the ventricle, as may be measured to detect, diagnose and/or treat ventricle dyssynchrony or incoordinate ventricular contraction, the relative contraction time or delay can be displayed superimposed on the corresponding sector
Superimposing measured performance values on an image or stylize model of the heart can reveal the performance of each ventricle sector or region at the time in the cardiac cycle corresponding to the particular ultrasound image. Such a display can aid the clinician in identifying ventricle regions that have poor function or exhibit lagging or inadequate movement during the contraction cycle. Use of a stylized model of the heart may aid the clinician in recognizing the particular regions of the ventricle involved, particularly since ultrasound images sometimes include speckle and other noise which may render the image difficult to understand. Thus, by presenting the ventricle performance measures superimposed upon a heart image or model, the various embodiments assist the clinician in identify locations of dysfunction and, in particular, sites for administering intervention or therapy, such as sites for attaching pacemaker pacing leads to the ventricle wall.
In another embodiment of the display function, the system processor may perform a computational step to plot or generate a line graph representing the value of the regional ejection fraction, contraction movement or radian length for a given sector or radian of the ventricle as it changes over the cardiac cycle. In such a graph, one axis can represent the sequential phases of the cardiac cycle, and another axis represents the ejection fraction (or contraction movement or radian length) for the sector over the time of a cardiac cycle. Plots of the various ventricle sectors may be superimposed (or plotted one over the other) in a display to show the timing relationship of contraction of the sectors. The plotted line of each sector may be represented by a different graph line in the display, where each line is distinguished by color or style (solid, dashed, dotted, and so forth). In this manner, the plots can further reveal the relative temporal motion of the regions of the heart to which the sectors correspond. Such a display will graphically reveal ventricle regions that lag or contract in an uncoordinated fashion relative to the rest of the ventricle and provide an easy to interpret summary of the relative synchronization of various regions of the ventricle. This display can also be used to identify a region or regions that will benefit from pacing, and thus aid in identifying optimum locations for positioning pacing leads within the ventricle.
Data for a formatted display may be computed from a single cardiac cycle or systolic portion of a single cycle. Alternatively, data in the formatted display (whether numeric or graphical) for a given sector and a given time in the cardiac cycle can be the average of many measurements for the given sector at the same given time in each cycle of a plurality of cardiac cycles (for example, ten consecutive cycles).
In another embodiment of the display function, the ultrasound images may be ultrasound system processor can monochromatically shade each ventricle sector or region using a color representing the value of the local quantitative assessment measurement (e.g., ejection fraction, contraction wall movement and regional radian length) computed for the time the image was acquired. For example, red may correspond to the greatest ejection fraction, blue corresponds to the least ejection fraction, and other colors of the spectrum between red and violet (orange, yellow, green, and cyan) correspond to intermediate values. Such color coding can efficiently communicate the measured heart function parameter without masking the image or stylized model of the heart, and thus aid the cardiologist in identifying locations for intervention or treatment.
In a variation of the preceding embodiment, the display can use color to indicate relative timing (i.e., phase within the cardiac cycle) at which the quantitative assessment measurements (e.g., ejection fraction, contraction wall movement and regional radian length) of each ventricle sector or region peaks in the cardiac cycle (i.e., when in the cardiac cycle the contraction ceases for each region). For example, red may be used to shade those regions in which the ejection fraction value peaks first in the cardiac cycle, with other colors of the spectrum (orange, yellow, green, blue, violet) shading the regions for which the local ejection fraction value peaks at relatively later points in the cardiac cycle.
In yet another embodiment, the ultrasound system processor can be programmed to display a replay of the acquired ultrasound images and associated quantitative assessment measurements (e.g., ejection fraction, contraction wall movement and regional radian length) in slow motion or stepwise under cardiologist control.
The various embodiments are intended to aid the cardiologist in recognizing, diagnosing and treating various ventricular function maladies. By measuring and displaying ejection fraction, both globally and regionally, the cardiologist can identify the need for treatment. By displaying the quantitative assessment measurements (e.g., ejection fraction, contraction wall movement and regional radian length) against an image or stylized model of the ventricle, the various embodiments enable the cardiologist to identify particular locations in the ventricle for intervention and treatment.
Examples of interventions and treatments that may be assessed using the various embodiment method include, for example, restoration of blood flow (angioplasty), insertion of a stent, resynchronization of ventricular contraction by use of implantable heart devices (e.g., biventricular and multi-ventricular pacing techniques), the use of drugs to study the performance of these heart segments, and combinations of these treatments. In particular, the embodiments which provide regional quantitative assessment measurements (e.g., ejection fraction, contraction wall movement and regional radian length) graphically localized on a heart image or model at different phases of the cardiac cycle can reveal to the cardiologist regions of the ventricle which require pacing in order to resynchronize or re-coordinate ventricle contraction. For example, a region that contracts late—and thus out of phase—with surrounding portions of the ventricle, may be a suitable site for attaching a pacemaker pacing lead. In this manner, the pacing lead can be positioned at the region which will most benefit from the pacing stimulus. Displaying the results on an image or model of the heart may also help the cardiologist plan and implement the procedure for attaching the pacer lead in the selected region.
The various embodiments can also be employed to quantitatively assess the impact of the intervention(s) by being repeated after the intervention. In this embodiment, the measurements and calculations according to the embodiment methods described herein are obtained before and after the intervention and the results compared. In this manner, measurements taken before the intervention provide a baseline quantitative assessment measurement (e.g., ejection fraction, contraction wall movement and regional radian length) which can be taken to measurements obtained after the intervention. Comparisons may be on a global or regional basis to assess effects of the intervention on both total ejection fraction and on regional ejection fraction and ventricular dysynchronous contraction.
This embodiment provides the cardiologist with quantitative assessments of the impact of the treatment which can be used to modify or adjust subsequent interventions. In particular, this embodiment can assist the cardiologist in selecting pacemaker settings, such as timing and pulse wave forms (e.g., magnitude, pulse width, and pulse phase), which yield optimized ventricular function. In this manner, the measurements and calculations according to the embodiment methods described herein are obtained after a particular set of pacemaker settings are implemented. The pacemaker settings are then adjusted and the measurements repeated. If the quantitative assessment measurement improves, the cardiologist may continue adjusting the parameter (such as pace timing) until subsequent measurements indicate degraded ventricular function. If the quantitative assessment measurement degrades after a setting change, the cardiologist may reverse the direction of parameter adjustment (e.g., increasing or decreasing the pacing lag time) and repeat the quantitative assessment measurement. In this manner, the cardiologist can use the quantitative assessment measurements according to the various embodiments in order to optimize pacemaker based on measured ventricular function.
In another embodiment, after the edges of the ventricle walls have been recognized, step 102, the method constructs a number of axis and radians for measuring ventricle ejection fraction, step 110. Step 110 can be performed for either ventricle 2 or 3. For the right ventricular cavity 2, the algorithm of step 110 defines a long axis 90 to extend from the mid plane of the tricuspid 9 of the pulmonic valve plane to the right ventricular apex 93. For the left ventricular cavity 3, the algorithm of step 110 defines the long axis 80 to extend from the mid point 91 of the aortic valve plane 91 to the left ventricular apex 83. The algorithm of step 110 defines a midpoint 85, 95, which bisects the long axis 80, 90 at the midpoint between the valvular plane 82, 92 and the apex 83, 93. The algorithm of step 110 then constructs a transverse line or plane 84, 94. The algorithm of step 110 then constructs radials 86, 96 in the plane of the cross-sectional image at an acute angle to the transverse axis 84, 94 crossing the midpoint 81, 91. The algorithm of step 110 may construct further radials 87 extending from the midpoint 85, 95 of the long axis 80, 90 at a plurality of angles (e.g., multiples of 30 or 45 degrees) with respect to the long axis 80, 90. Each radial 87 terminates where it intersects the endocardial wall 5′ or 7′ in the ultrasound image. Each half of the long axis 80, 90 also forms a radial. The area of each region defined by the axes and radians is the calculated, step 111. The area calculation in step 111 is repeated for each region, loop 112, and for each point in the cardiac cycle at which images were obtained, loop 113. The ejection fraction of each region is then calculated as the difference in area in the region between two points in the cardiac cycle, step 114. Step 114 may be repeated for each region to obtain all regional ejection fractions. Finally, the method can be performed before and after an intervention to compare the ejection fractions to determine if there was any impact from the intervention, step 106.
While the foregoing description and
While the present invention has been disclosed with reference to certain preferred embodiments, numerous modifications, alterations, and changes to the described embodiments are possible without departing from the sphere and scope of the present invention, as defined in the appended claims. Accordingly, it is intended that the present invention not be limited to the described embodiments, but that it have the full scope defined by the language of the following claims, and equivalents thereof.
