Patent Application
20070299479
The accompanying drawings, which are incorporated herein and constitute part of this specification, illustrate 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.
Phased array ultrasound imaging catheters are used for performing intracardiac echocardiography. Examples of phased array ultrasound imaging catheters 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.
Referring to
Positioning of the intracardiac echo catheter 13 within the right ventricle may be accomplished before or after an implantable cardiac resynchronization stimulator device has been positioned in the patient with stimulator electrodes attached to the left and right ventricle walls. Typically, the intracardiac echo catheter 13 is used during the stimulator electrode attachment procedure since the imaging data can aid the practitioner in properly positioning the electrodes.
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.
Edge detection algorithms applied in the ultrasound system to the ultrasound echo image data to identify the endocardial surface of the left ventricular wall 5 can generate an image of the ventricle structures such as illustrated in
For the left ventricle 3, an image of most of if not the entire endocardium can be 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
Ventricle ejection fraction can be estimated based on linear dimensional measurements of the ventricle without calculating the volume of the ventricle. 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. This change in area of a region 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.
Calculation of 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.
Overall global ejection fraction can be estimated by summing all of the regional ejection fractions obtained according to the above methods. 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 and evaluation of ventricular dysynchronous contraction is possible.
The foregoing measurements and estimations of regional and global ventricle ejection fraction can be performed in sinus rhythm or atrial fibrillation prior to applying resynchronization stimulation in order to document the baseline state of an individual patient.
Once a baseline state of the patient's heart function has been obtained according to the methods described above, the practitioner can use spectral Doppler ultrasound to measure the aortic flow velocity, the time duration of the aortic ejection, and its maximum velocity (step 125). Methods for measuring aortic flow velocity, the time duration of the aortic ejection and maximum velocity are obtained by measuring the Doppler shift of the ultrasound echoes as is well known in the cardiac ultrasound imaging practice. Other measurements, such as an estimate of the volume of blood ejected, can be used instead of or in addition to these measurements. Spectral Doppler ultrasound measurements are also obtained in sinus rhythm or atrial fibrillation prior to applying resynchronization stimulation in order to document the baseline state in an individual patient.
B-mode and M-mode measurements of left ventricular ejection fraction, maximum aortic flow velocity, overall aortic flow with an area computation and an aortic ejection time provide the practitioner with information useful for setting the current timing configuration of the patient's cardiac resynchronization stimulator device. The resynchronization stimulator device configuration parameters include at least the atrioventricular interval and the interventricular delay timing.
Using the atrioventricular interval and the interventricular delay timing settings obtained from the patient's baseline measurements, the practitioner initially programs the implantable resynchronization stimulator device and initiates stimulator operation.
With stimulator operation initiated, the above measurement steps, beginning with the application of the endocardial surface edge detection, are repeated. The measurement steps provide measurements of ventricle dimensions which are used to estimate ventricle ejection fraction which is indicative of the heart's function with the initial resynchronization stimulator device settings. In particular, measurements and estimations indicative of the heart's function include one or more of the left ventricular ejection fraction, maximum aortic flow velocity, overall aortic flow with an area computation and an aortic ejection time.
The practitioner then adjusts the programmed atrioventricular interval parameter values to a new setting or settings (step 135) and the measurements are repeated. The measurement steps provide measurements of the heart's left ventricular ejection fraction, maximum aortic flow velocity, overall aortic flow with an area computation and an aortic ejection time with the new resynchronization stimulator device settings. When each set of measurements is obtained, the practitioner again adjusts the programmed atrioventricular interval parameter values to new settings (repeating step 135) and repeats the measurement steps to obtain ventricular ejection fraction, maximum aortic flow velocity, overall aortic flow with an area computation and aortic ejection time values. By incrementally adjusting settings and repeating this process, the measures of ventricle function can be acquired at across a range of atrioventricular interval parameter settings. In performing this sequence, the practitioner adjust the atrioventricular intervals in increments of between about 5 and about 10 milliseconds to cover the range of settings. The range of atrioventricular interval settings may be between about 100 milliseconds and about 250 milliseconds.
As the above steps are repeated, but before a new atrioventricular interval parameter is set, the system or practitioner notes which device configuration produces the maximum aortic flow and the best left ventricular ejection fraction so far (step 130), as well as noting the measurements produced thereby.
When the optimal heart efficiency measurements over the full range of atrioventricular intervals have been obtained, or when it is clear that no better measurements will been obtained, the adjust-measure-repeat cycle is ended (step 140), and the atrioventricular interval which produced the optimal measurements (the optimal atrioventricular interval) is stored in memory along with the final optimal left ventricular ejection fraction, maximum aortic flow velocity, overall aortic flow with an area computation and an aortic ejection time measurements (memorized by step 130).
After determining the optimal atrioventricular interval, interventricular conduction delay is then optimized as follows. With the atrioventricular interval setting of the implantable cardiac resynchronization stimulator device fixed at the optimal atrioventricular interval, the flow and ejection fraction measurements described above are repeated with the stimulator device settings adjusted for each set of measurements to an interventricular delay in a sequence of interventricular delays ranging preferably from about 0 to about 120 milliseconds in increments of about 5 to about 10 milliseconds (step 175). Additionally, measurements are taken with the interventricular delay set so the left ventricle precedes the right ventricle and/or so the right ventricle precedes the left ventricle. At each delay value in the range, the specific delay is associated with the flow and ejection measurement values, such as noted by the practitioner or stored in memory as a linked data set.
As the flow and ejection measurements are taken at each interval setting of the interventricular delay (note that steps 150 through 165 repeat the measurements taken in steps 110 through 125), the optimal flow and ejection measurements so far and the associated delay parameter are retained (step 170). When the measurements over the full range of intervals have been obtained, or when it is clear that no better measurements will be obtained, the adjust-measure-repeat cycle is ended (step 180) and the interventricular delay which produced the optimal measurements (the optimal interventricular delay) is retained along with the final optimal measurements (as memorized in step 170).
The final retained atrioventricular and interventricular delay parameters are set in the resynchronization stimulator device, and a set of measurements are conducted to determine the percent increase in aortic flow and the percent improvement in the left ventricular ejection fraction achieved compared to the baseline measurements (step 190).
Finally, B-mode ultrasound images are analyzed for evidence of actual resynchronization of the left and right ventricles under stimulation by the device (step 195). This resynchronization is measured by comparing the timing delay of movements within the septum on the posterior wall.
In pilot studies, improvement in left ventricle ejection fraction of greater than 10% was observed following use of this method, with virtually each patient showing improvement. Such outcomes represent substantial improvement in therapeutic results over current experience where 30-40% of patients fail to show improvement with cardiac resynchronization devices.
It should be noted that there are other embodiments or improvements that would be obvious to those familiar with the field of this invention. For example, the order of the two parametric optimizations (atrioventricular and interventricular parameters) may be reversed. Also, the optimizations can be iterated and interleaved, which will allow detecting interdependencies (such as false maximums) between atrioventricular and interventricular delay values and refining both atrioventricular and interventricular delay values together. Also, steps of the method may be performed in a different order than illustrated in
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.
