Measurement Of Wall Thickening Research Articles

Relationship between infarct transmurality and regional myocardial function at different levels of the left ventricle in patients with first-time ST-elevation myocardial infarction

Introduction The relationship between regional myocardial function and the transmural extent of infarction (TEI) is complex, and there is considerable overlap in wall thickening measurements between normal and infarcted segments. Some of this overlap is caused by tethering from neighbor segments, but could possibly also be caused by errors in wall thickening measurements due to: 1)through-plane motion in basal segments, and 2)oblique orientation of the image plane relative to the left ventricular (LV) wall in apical segments.

Adenosine triphosphate stress myocardial contrast echocardiography detects coronary artery stenosis with greater sensitivity than wall-motion abnormality measurements

Although stress myocardial contrast echocardiography (MCE) can be used to detect coronary stenosis, its efficacy relative to other methods, such as detection of wall-motion abnormalities, remains unknown. Thus, the goal of this study was to compare the sensitivity of MCE versus wall-motion abnormality detection in the assessment of coronary artery stenosis. Nine dogs with severe but nonflow limiting stenosis in the circumflex coronary artery underwent evaluation with real-time MCE along the short-axis view during infusion of Optison. The equation of y = a (1 - e -betat ) + c, which fits the replenishment curve of MCE, was calculated in the midseptum (normal region) and in the lateral wall (ischemic region) before and during adenosine triphosphate infusion. Wall-motion abnormalities were also evaluated by visual assessment and by measurement of wall thickening. Area under the receiver operating characteristic curve in beta- and A x beta-value, and percent wall thickening, was 0.963, 0.963, and 0.889, respectively, indicating that the diagnostic accuracy for detecting the coronary artery stenosis by real-time MCE was higher than that by the wall-motion assessment. Real-time MCE has higher sensitivity in detecting coronary stenosis during adenosine triphosphate stress test when compared with wall-motion assessment.

Serial motion assessment by reference tracking (SMART): application to detection of local functional impact of chronic myocardial ischemia.

To compare measurements of wall motion and thickening with and without correcting for cardiac twisting and shortening. Inversion recovery Gd-DPTA perfusion and cine motion MRI were performed on 12 pigs with chronic ischemia induced by ameroid occluder. Analyses were based on conventional fixed plane imaging and serial motion assessment by reference tracking (SMART). Normal motion was 31.3 +/- 1.9%, and normal wall thickening was 41.4 +/- 2.2%. At the maximum perfusion defect, SMART wall motion was 10.5 +/- 2.4% and fixed wall motion was 20.6 +/- 1.7% (p < 0.004), SMART wall thickening was 20.1 +/- 4.4%, and fixed wall thickening was 32 +/- 1.9% (p < 0.03). SMART measurements of wall thickening and motion detect much smaller thickening and motion in ischemic myocardium than fixed radial metrics. SMART data, covering the entire heart, should prove twice as sensitive to abnormalities in motion and thickening, such as any produced by ischemic heart disease or improved by treatment.

The effect of normalization in reducing variability in regional wall thickening

This study was performed to evaluate a new method for measuring regional left ventricular wall thickening in terms of its variability, normal range, and diagnostic sensitivity. Two-dimensional echocardiographic images in the parasternal short-axis view of 44 normal patients and 17 patients with recent myocardial infarction were analyzed. Regional wall thickness was measured according to the centerline method at 100 chords. Wall thickening at each chord i was calculated as the change in wall thickness between end diastole and end systole at chord i, normalized by the average end-diastolic thickness of the wall segment extending from chord (i − n) to chord (i + n). Five widths of the normalization segment, defined as (2n + 1), were tested: 1 (baseline method), 5, 11, 15, and 21 chords. Widening the normalization segment significantly reduced point-to-point variability by up to 20% ( p = 0.0001) evenly over the entire left ventricular contour. The magnitude of reduction approached a plateau at a normalization segment width of 11 chords. The normal mean and standard deviation for regional wall thickening were also reduced slightly but significantly in a progressive and uniform manner. The apparent severity of hypokinesis worsened by up to 0.1 ± 0.1 SD ( p = 0.006) as the normalization segment was widened. The circumferential extent of hypokinesis was not lengthened significantly until the normalization segment was 21 chords wide. The magnitude of hyperkinesis was unchanged. Normalizing over a wider segment of the myocardium reduces variability in the measurement of wall thickening, widens the separation between normal patients and those with disease, and enhances the diagnostic accuracy of quantitative two-dimensional echocardiography. The optimal normalization segment width is 11 chords. (J Am Soc Echocardiogr 1997;10:197-204.)

Reproducibility of Echocardiographically Determined Myocardial Wall Thickening

In Response: The purpose of our article was to examine the accuracy and precision of wall thickening measurements using transesophageal echocardiography (TEE) in a manner that would be feasible for clinicians working with patients in the operating room [1]. We found small inter- and intraobserver bias, which demonstrated that, when many measurements are averaged, the accuracy of wall thickening measurements was quite good. However, the reproducibility (precision) of individual measurements was poor, as demonstrated by the high standard deviations of the inter- and intraobserver differences. On the basis of these data, we concluded that single TEE-derived wall thickening measurements are not precise at the present time in the operating room setting. Drs. Bashein and Sheehan have presented four criticisms of our article. We offer the following responses: 1. Though it is possible that the angle of the ultrasound beam to the tissue plays a role in border resolution, there are many other factors that contribute to the reproducibility of wall thickening measurements. If beam angle were the dominant factor in determining reproducibility, one would expect that the longitudinal measurements in our study (where the myocardium was always perpendicular to the direction of the ultrasound) would have had the lowest variability. However, the bias and the limits of agreement in the longitudinal measurements showed less accuracy and precision than in the short axis. Also, when the short-axis data are divided into the two groups suggested by Bashein and Sheehan (0 and 180 degrees, and 90 and 270 degrees), accuracy is only marginally better in the perpendicular measurements (0 and 180 degrees) versus the parallel measurements (90 and 270 degrees)--0.04 mm vs 0.34 mm, respectively. However, the standard deviation (precision) of the data are nearly equal and poor in both the perpendicular and the parallel measurements--1.50 mm and 1.84 mm, respectively. Thus, it appears that the presentation of the pooled data did not "unfairly condemn" the technique. 2. As stated in the article, the measurement technique used in this study was chosen because all currently used echo equipment is capable of these individual measurements. The method suggested by Bashein and Sheehan is impractical for several reasons: not all echo equipment has the software for contour-based analysis; clinicians do not have the time to perform on-line tracings of the entire epicardium and endocardium; and the entire epicardium and endocardium borders are not always visible. 3. We do not know of any measurement technique that works on moving (nonstatic) video frames. Of course, the observers reviewed the dynamic video sequence before performing the measurements. 4. Bashein and Sheehan claim "excessive variability" in our data as compared with those of Force et al. [2], who reported an average intraobserver variability of 3.8%. This was actually only a measurement of accuracy and not precision. In fact, for our two observers, the overall intraobserver variability (accuracy) in wall thickening was 2.8%, which is better than that reported by Force et al. Force et al. did not report the precision of their data (standard deviation or the limits of agreement), and thus it is not possible to compare the studies, because a small bias does not imply reproducibility of the measurements. In the absence of more data from Force et al., it is inaccurate to characterize the variability of our data as "excessive." In conclusion, our study used state-of-the-art TEE equipment in a clinically relevant fashion with the appropriate statistical analysis technique to examine the accuracy and precision of wall thickening measurements. The suggestions made by Drs. Bashein and Sheehan are neither clinically feasible nor statistically appropriate. Although in a laboratory setting it may be possible to reduce the variability of wall thickening measurements, we showed that there is a lack of precision in single measurements of wall thickening. Steven Konstadt, MD, FACC David Reich, MD Department of Anesthesiology, Mount Sinai Medical Center, New York, NY 10029-6574

Are wall thickening measurements reproducible?

An early transesophageal echocardiography (TEE) study reported that there was high inter- and intraobserver variability in measurements of wall thickening (WT). This study reevaluated TEE for the measurement of WT in the transverse plane and, for the first time, evaluated it in the longitudinal plane. Ten patients were studied with a biplane TEE probe inserted and positioned to obtain a transverse short-axis (SA) view of the left ventricle at the midpapillary muscle level. A longitudinal transgastric long-axis (LA) view of the left ventricle was then obtained. This measurement sequence was performed four times in each patient. Off-line analysis was performed independently by two observers. In each tomographic cut of the ventricle, four locations for measurement were defined. WT was measured in three consecutive beats, and the results averaged (WT1). The observers repeated the measurements (WT2) 2 wk later, and the intra- and interobserver differences (mm) were calculated. Average differences for the intraobserver comparisons of wall thickening were small (0.08-0.24 mm), but the high standard deviations (1.17-2.44 mm) suggest significant variability between individual measurements. Thus it appears that measurements of wall thickening with small mean intraobserver bias may be possible, but to offset the potential for variability, multiple measurements are necessary. Also, careful standardization of location and edge definition is important to limit interobserver variability.

Quantitative analysis of regional wall thickening by transesophageal echocardiography

To develop a method for quantitative analysis of regional left ventricular function from transesophageal two-dimensional echocardiograms, we conducted studies 10 and 20 minutes after induction of anesthesia in 16 patients with normal hearts who were undergoing minor orthopedic operations. Wall thickening was measured with the centerwall method along 100 chords drawn perpendicular to a line constructed around the center of the ventricular wall, midway between the endocardial and epicardial contours. Thickening, either normalized by the length of the end-diastolic perimeter or expressed as a percentage of the end-diastolic wall thickness at each chord, was compared with measurements of endocardial motion. Wall motion was relatively diminished in the anteroseptal region and enhanced on the contralateral wall, but wall thickening was homogeneous throughout the contour. Normalized wall thickening was significantly less variable (standard deviation/mean, 0.47 +/- 0.13) in the normal population than were either percent wall thickening (0.53 +/- 0.012) or wall motion (0.51 +/- 0.09) (p less than 0.005 for both comparisons). There was no significant change in regional or global function between 10 minutes and 20 minutes after the induction of anesthesia. In summary, normalized wall thickening as a parameter of regional left ventricular function is more homogeneous and less variable in subjects with normal hearts than is endocardial motion because wall thickening measurements are not subject to cardiac translocation artifacts. This low variability suggests that normalized wall thickening measured by the centerwall method may prove particularly useful for intraoperative and postoperative monitoring of regional left ventricular function by transesophageal echocardiography in patients undergoing both cardiac and noncardiac surgical procedures.

Effect of exercise intensity and duration on regional function during and after exercise-induced ischemia.

Transient reversible myocardial dysfunction has been documented after episodes of exercise-induced ischemia. This study was undertaken to determine whether the duration or intensity of exercise affects the severity of postischemic dysfunction in this setting. Ten dogs were instrumented with ultrasonic microcrystals for measurement of wall thickening, with circumflex coronary artery flow probes, and with hydraulic occluders. Dogs performed low-intensity exercise, which was sufficient to increase coronary perfusion 50% above control, and high-intensity exercise, which was sufficient to double coronary blood flow. To investigate the effects of exercise intensity on postischemic dysfunction, we had dogs perform high-intensity exercise for 5 minutes in the presence of a stenosis. On the alternate day, dogs performed low-intensity exercise for 10 minutes in the presence of a stenosis. These two protocols provide equivalent coronary flow debts. Mean transmural blood flow during high-intensity exercise without stenosis (2.61 +/- 0.54 ml/min/g) was significantly higher than that during low-intensity exercise (1.74 +/- 0.61 ml/min/g, p less than 0.002). During high-intensity exercise with coronary artery stenosis, subendocardial blood flow was significantly lower than that during low-intensity exercise with stenosis (0.64 +/- 0.40 versus 1.08 +/- 0.28 ml/min/g, p less than 0.02). This difference in subendocardial perfusion was associated with greater degrees of regional dysfunction during exercise (circumflex wall thickening was 44 +/- 23% of control for high-intensity exercise versus 60 +/- 18% of control for low-intensity exercise, p less than 0.01). In addition, from 10 to 30 minutes after exercise, wall thickening in myocardium perfused by the circumflex coronary artery remained significantly lower after high-intensity exercise than that after low-intensity exercise. To assess the effects of exercise duration on the severity of postischemic dysfunction, we had dogs perform low-intensity exercise in the presence of a coronary stenosis for 10 minutes and low-intensity exercise for only 5 minutes on alternate days. Systolic wall thickening was significantly lower after low-intensity exercise for 10 minutes than after low-intensity exercise for 5 minutes. High-intensity exercise results in greater degrees of subendocardial hypoperfusion and greater degrees of regional dysfunction both during and after exercise-induced ischemia than does low-intensity exercise. Second, exercise duration also exerts an effect on the severity of postischemic dysfunction, although the magnitude of this effect is less important than the effect of exercise intensity.

Quantitative regional curvature analysis: Validation in animals of a method for assessing regional ventricular remodelling in ischemic heart disease

Recent studies show the impact of left ventricular shape and remodelling on patient prognosis. This mandates the development of quantitative methods for measuring shape. Quantitative regional curvature analysis (QRCA) was developed to quantitate shape on a regional basis so that measurements would not be constrained to assessment of only global shape and would, therefore be applicable to ischemic heart disease. To validate QRCA, eleven dogs were instrumented with coronary occluders and radiopaque markers on the epicardium and endocardium to provide fiducial points for calculation of shape, motion and thickening. These parameters were measured in the anterior and inferior walls, at rest, during left anterior descending occlusion and finally during circumflex occlusion. QRCA showed increased curvature (increased globularity) in each wall when thickening and motion deteriorated during occlusion. The most marked shape changes occurred in the inferior wall whereas the most marked deterioration of function was detected by wall thickening measurements of the anterior wall. Thus, QRCA detects regional ventricular shape disorders coincident with regional dysfunction induced by ischemia. These changes show regional heterogeneity and demonstrate the potential importance of this measurement as opposed to simple, global measures of shape. QRCA is, therefore, suitable for monitoring acute changes of shape that occur during acute ischemia.

Quantitative regional curvature analysis: Validation in animals of a method for assessing regional ventricular remodelling in ischemic heart disease

Recent studies show the impact of left ventricular shape and remodelling on patient prognosis. This mandates the development of quantitative methods for measuring shape. Quantitative regional curvature analysis (QRCA) was developed to quantitate shape on a regional basis so that measurements would not be constrained to assessment of only global shape and would, therefore be applicable to ischemic heart disease. To validate QRCA, eleven dogs were instrumented with coronary occluders and radiopaque markers on the epicardium and endocardium to provide fiducial points for calculation of shape, motion and thickening. These parameters were measured in the anterior and inferior walls, at rest, during left anterior descending occlusion and finally during circumflex occlusion. QRCA showed increased curvature (increased globularity) in each wall when thickening and motion deteriorated during occlusion. The most marked shape changes occurred in the inferior wall whereas the most marked deterioration of function was detected by wall thickening measurements of the anterior wall. Thus, QRCA detects regional ventricular shape disorders coincident with regional dysfunction induced by ischemia. These changes show regional heterogeneity and demonstrate the potential importance of this measurement as opposed to simple, global measures of shape. QRCA is, therefore, suitable for monitoring acute changes of shape that occur during acute ischemia.

Effect of aortic constriction on the functional border zone.

To evaluate how aortic constriction affects nonischemic myocardium adjacent to the perfusion boundary (the "functional border zone"), we measured systolic wall thickening (dWT) with sonomicrometers in eight anesthetized, open-chest dogs. The locations of the wall thickening measurements relative to the perfusion boundary (PB) were determined with myocardial blood flow (microspheres) maps constructed from multiple, small tissue samples. In nonischemic myocardium more than 10 mm from the PB produced by circumflex coronary occlusion, dWT increased significantly from 2.57 +/- 0.62 (mean +/- SD) to 3.24 +/- 0.73 mm (P less than 0.01). Within 10 mm of the PB, however, dWT did not change significantly (2.48 +/- 0.79 to 2.38 +/- 0.66 mm, NS). When the aorta was mechanically constricted, peak systolic pressure increased approximately 50%. Wall thickening decreased to the same relative degree in nonischemic muscle less than 10 mm and more than 10 mm from the perfusion boundary. By fitting sigmoid curves to the data, we estimated the extent of nonischemic dysfunction. It averaged 26 +/- 6 degrees (6-8 mm of endocardial circumference) during coronary occlusion alone and it was not significantly different (29 +/- 11 degrees) after aortic constriction. Thus elevated afterload affects nonischemic myocardium uniformly and does not increase the size or relative severity of the functional border zone.

Regional differences in left ventricular response to atrial pacing in the dog: Mapping of segmental function by two-dimensional echocardiography

Two-dimensional echocardiography was applied in 10 closed-chest dogs to evaluate, in several left ventricular (LV) short-axis cross sections and subsegments, the regional contractile response to right atrial pacing. Compared with sinus rhythm (81 ± 10 beats/min), which exhibited a moderate 7.2 ± 12.0% (mean ± standard deviation) base-to-apex increment in function, this gradient was significantly augmented to 34 ± 12% by pacing at a heart rate of 180 beats/min. Measurements of wall thickening and perimeter shortening exhibited similar trends. Differences also were observed in subsegments of individual cross sections: in sinus rhythm the base-to-apex difference in function was relatively minor in the anterior and lateral aspects of the left ventricle (−9.1 ± 18% and −1.9 ± 19%), whereas a significant increase was noted in posterior and midseptal zones (18 ± 17% and 22 ± 30%). In response to pacing, the anterior and lateral wall base-to-apex gradients were significantly augmented (25 ± 8% and 35 ± 34%), but there was no further change in the posterior or septal regions. In conclusion, apical regions of the canine left ventricle responded to right atrial pacing with significant augmentation of contractile function, whereas more basal levels showed little response. Circumferentially, response to atrial pacing was most pronounced in the anterior and lateral segments.