Sectional and segmental variability of left ventricular function: experimental and clinical studies using ultrafast computed tomography

Quantitative evaluation of regional left ventricular function by multidetector computed tomography

OBJECTIVE

: Because most contemporary workstations offer quantitative analysis of regional function by multidetector computed tomography, we aimed to establish typical values for normal, hypokinetic, and akinetic regions, and to establish optimal thresholds to differentiate between normal and abnormal values.

METHODS

: For 33 patients, quantitative regional functional parameters were compared with visual analysis by both multidetector computed tomography and echocardiography. Normal values were established to normalize for segmental variability. Optimal thresholds were established to differentiate between normal and abnormal segments by receiver operating characteristic analysis.

RESULTS

: Akinetic, hypokinetic, and normokinetic segments demonstrated significant differences (P < 0.0001) for end-systolic thickness (mean [95% confidence interval], 9.4 [4.5-14.3], 11.7 [7.2-16.2], and 14.3 mm [8.2-20.3 mm]), respectively; thickening, 24% [-22% to 71%], 45% [-16% to 106%], and 82% [10%-154%]), respectively; and motion, 3.5 [-2.0 to 8.9], 6.1 [-0.2 to 12.4], and 8.5 mm [1.8-15.3 mm], respectively). Thickening performed best with area under the curve of 0.87 and sensitivity equal to specificity of 82%. Intraobserver variability was good, but interobserver variability was only moderate.

CONCLUSIONS

: Quantification of regional myocardial function can be performed to assist the physician in mapping left ventricular function.

Cellular mechanisms of arrhythmogenic cardiac alternans

Despite the strong association between mechanical dysfunction of the heart and sudden death due to arrhythmias, the causal relationship is not well understood. Cardiac alternans has been linked to arrhythmogenesis and can be mediated by intracellular calcium handling. Given the integral role intracellular calcium plays in contractile function, calcium-mediated alternans may represent an important mechanistic link between mechanical dysfunction and electrical instability. This relationship, however, is not well understood due to complex feedback between membrane currents, intracellular calcium, and contraction. This manuscript describes the cellular mechanisms of cardiac alternans. Through several pathways, calcium transient alternans is coupled to repolarization alternans that can form a substrate for reentrant excitation. Abnormal intracellular calcium cycling, either impaired release or impaired reuptake of sarcoplasmic reticulum calcium, is a cellular mechanism of calcium transient alternans. Thus, cardiac alternans is an important mechanistic link between mechanical dysfunction and sudden cardiac death.

Left ventricular mass in 169 healthy children and young adults assessed by three-dimensional echocardiography

The aims of this study were to establish normal values of left ventricular (LV) mass in children and young adults using three-dimensional echocardiography (3-DE) and to compare 3-DE LV mass estimates with those obtained by conventional echocardiographic methods. We studied 169 healthy subjects aged 2-27 years by digitized 3-D, two-dimensional (2-D), and M-mode echocardiography. 3-D echocardiography was performed by using rotational acquisition of planes at 18 degrees intervals from apical view with ECG gating and without respiratory gating. 3-DE gave smaller LV mass estimates than 2-DE and M-mode echocardiography (p < 0.001). Agreement analysis resulted in a bias of -9.3 +/- 36.5 g between 3-DE and 2-DE, and -18.5 +/- 47.9 g between 3-DE and M-mode. For the analysis, the subjects were divided into five groups according to body surface area (BSA): 0.5-0.75, 0.75-1.0, 1.0-1.25, 1.25-1.5, and greater than 1.5 m(2). LV mass/BSA by 3-DE was 45.6 (5.1), 54.3 (7.7), 55.2 (7.9), 58.8 (8.1), and 65.0 (9.9) g/m(2). LV mass/end diastolic volume (EDV) by 3-DE was 0.9 (0.1) g/ml in the BSA group of 0.5-0.75 m(2) and 1.0 (0.2) g/ml in the other BSA groups. LV mass increased linearly in relation to BSA, height, and body mass (r = 0.93, 0.90, and 0.92, respectively; p < 0.001 for all). The results showed a linear increase in LV mass, whereas LV mass/EDV ratio remained unchanged. However, LV mass estimates by 3-DE were lower than those obtained by 2-DE and M-mode echocardiography. The data obtained by 3-DE from 169 healthy subjects will serve as a reference for further studies in patients with various cardiac abnormalities.

Technology Insight: cardiac CT angiography

Noninvasive coronary angiography has been the holy grail of cardiovascular medicine for decades. Cardiac CT angiography obtained with multislice CT technology is finally reaching the high standard in spatial resolution that is achieved by invasive X-ray coronary angiography. The latest 64-slice CT technology is a fast and safe modality for imaging the heart and coronary arteries, with scans taking seconds to complete. The temporal resolution of cardiac CT is still inferior, however, to that of invasive angiography, echocardiography or cardiac MRI. As such, this technique is still highly susceptible to motion artifacts created by the beating heart, and blooming artifacts due to the presence of calcium in the atherosclerotic plaque and to metallic implants. The routine use of agents to lower the heart rate before scanning is still required in most patients, and the timing of the contrast injection is critical for obtaining high-quality diagnostic cardiac images. Furthermore, cardiac CT angiography exposes the patient to substantial amounts of ionizing radiation and nephrotoxic contrast agents and, therefore, patients must be carefully selected based on a thorough understanding of the current clinical indications. In this review, I discuss the current multidetector row CT technology, safety issues, imaging protocols, clinical applications, and some of the challenges that still lie ahead with this modality.

Characterizing the normal heart using quantitative three-dimensional echocardiography

We present normative data on cardiac volume, geometry and shape derived using three-dimensional echocardiography (3-DE). Three-dimensional reconstructions were created using the piecewise smooth surface subdivision (PSSS) reconstruction technique of the left and right ventricular (LV and RV) endocardium and the mitral and tricuspid annuli (MA and TA) of 67 normal subjects. We derived LV end-diastolic (ED) and end-systolic (ES) volume indices (VI) of 76.5 +/- 16.8 ml m(-2) and 35.3 +/- 14.1 ml m(-2), LV ejection fraction (EF) of 56.1 +/- 9.93%, RV EDVI and ESVI of 93.2 +/- 20.0 ml m(-2) and 49.9 +/- 13.5 ml m(-2) and RVEF of 47.3 +/- 7.69%, along with data on the geometry and shape of the MA, TA, LV and RV. There was no pattern of consistent understatement or overstatement of volumes or dimensions compared with other imaging modalities, and observed variance in data can largely be accounted for through examination of the physics or protocol of each modality.

Comparison of multidetector computed tomography versus echocardiography for assessing regional left ventricular function

Multidetector computed tomography (MDCT) of the heart is a rapidly developing technique mainly used to evaluate the coronary arteries. However, it is also capable of evaluating ventricular function. It compares well with magnetic resonance imaging in calculating volumes and ejection fractions, but little has been reported on its ability to assess left ventricular (LV) segmental wall motion (LVSWM). This study compared semiquantitative LVSWM scoring by MDCT with echocardiography as the gold standard. Thirty-nine patients underwent MDCT angiography on a 16-slice scanner. Short- and long-axis LV slices were created at different phases of the cardiac cycle and visually evaluated using cine mode. Echocardiography was performed <48 hours after MDCT for 21 patients after acute myocardial infarctions and <1 month after MDCT for 18 patients without acute myocardial infarctions. Two blinded observers scored the MDCT and echocardiographic examinations according to the 16-segment model, scoring each segment from 1 (normal) to 3 (akinetic). Segmental dysfunction was found in 27 patients by echocardiography and in 24 by MDCT. An identical score was given by the 2 methods in 502 of 616 assessable segments (82%). Using a binary analysis (normal or abnormal), there was 89% agreement (546 of 616 segments). MDCT had a sensitivity of 66% (103 of 155 segments) and a specificity of 96% (443 of 461 segments) compared with echocardiography as the gold standard. Most disagreements occurred in the right coronary artery segments. In conclusion, MDCT can be used to evaluate LVSWM, showing good agreement with echocardiography, except for the right coronary artery segments.

Advances in cardiovascular CT imaging: CT clinical imaging

Recent advances in cardiovascular CT imaging have dramatically changed the way we evaluate cardiac and great vessel disease. The superb spatial and faster temporal resolutions of the newer scanners, have allowed CT to gain acceptance not only in defining cardiac and great vessel anatomy but also has allowed its entry into the field of functional and perfusion imaging. This paper reviews the current status of CT in clinical imaging of the heart and great vessels.

Intracellular calcium handling heterogeneities in intact guinea pig hearts

Regional heterogeneities of ventricular repolarizing currents and their role in arrhythmogenesis have received much attention; however, relatively little is known regarding heterogeneities of intracellular calcium handling. Because repolarization properties and contractile function are heterogeneous from base to apex of the intact heart, we hypothesize that calcium handling is also heterogeneous from base to apex. To test this hypothesis, we developed a novel ratiometric optical mapping system capable of measuring calcium fluorescence of indo-1 at two separate wavelengths from 256 sites simultaneously. With the use of intact Langendorff-perfused guinea pig hearts, ratiometric calcium transients were recorded under normal conditions and during administration of known inotropic agents. Ratiometric calcium transients were insensitive to changes in excitation light intensity and fluorescence over time. Under control conditions, calcium transient amplitude near the apex was significantly larger (60%, P < 0.01) compared with the base. In contrast, calcium transient duration was significantly longer (7.5%, P < 0.03) near the base compared with the apex. During isoproterenol (0.05 microM) and verapamil (2.5 microM) administration, ratiometric calcium transients accurately reflected changes in contractile function, and, the direction of base-to-apex heterogeneities remained unchanged compared with control. Ratiometric optical mapping techniques can be used to accurately quantify heterogeneities of calcium handling in the intact heart. Significant heterogeneities of calcium release and sequestration exist from base to apex of the intact heart. These heterogeneities are consistent with base-to-apex heterogeneities of contraction observed in the intact heart and may play a role in arrhythmogenesis under abnormal conditions.

Parametric visualization methods for the quantitative assessment of myocardial motion

RATIONALE AND OBJECTIVES

The authors performed this study to evaluate three-dimensional (3D) and four-dimensional (4D) techniques for quantifying and visualizing myocardial motion.

MATERIALS AND METHODS

The 4D method was performed by using 3D reconstructions of the complete, in vivo, canine heart before and after acute myocardial infarction. Images were obtained with the Dynamic Spatial Reconstructor (1-3) at 15 time points throughout one cardiac cycle. The authors used 0.75-mm-thick sections to allow creation of deformable models at each time point. For the 3D method, electron-beam computed tomographic reconstructions were obtained in anesthetized pigs from eight adjacent short-axis sections of the left ventricle. Data were acquired before and after selective microembolization of the left anterior descending coronary artery at 11 time points throughout one complete cardiaccycle. The authors used 8-mm-thick sections, which did not enable the use of the volumetric 4D approach with deformable models. For the 3D method, images were processed by radially dividing the tomographic images into small circumferential sectors. Color encoding was used for the derived local magnitudes of wall dynamics.

RESULTS

The 4D method provided endocardial peak velocities, excursions, and strains throughout systole and diastole. The 3D method provided regional thickness or regional rates of left ventricular wall thickening throughout the cardiac cycle.

CONCLUSION

Functional parametric maps of disturbances in regional contractility and relaxation facilitate appreciation of the effect of altered structure-to-function relationships in the myocardium.

Comparison between ECTb and QGS for assessment of left ventricular function from gated myocardial perfusion SPECT

BACKGROUND

The most widely distributed software packages to compute left ventricular (LV) volume and ejection fraction (EF) from gated perfusion tomograms are QGS and the Emory Cardiac Toolbox (ECTb). Because LV modeling and time sampling differ between the algorithms, it is necessary to document relationships between values produced by them and to establish normal limits individually for each software package in order to interpret results obtained for individual patients.

METHODS AND RESULTS

Gated single photon emission computed tomography technetium 99m sestamibi myocardial perfusion studies were collected and analyzed for 246 patients evaluated for coronary artery disease. QGS and ECTb values of ejection fraction (EF), end-diastolic volume (EDV), and end-systolic volume were found to correlate linearly (r = 0.90, 0.91, and 0.94, respectively), but EF and EDV were significantly lower for QGS than with ECTb (53% +/- 13% vs 61% +/- 13 and 102 +/- 45 mL vs 114 +/- 50 mL, respectively). To compare calculations for healthy subjects between the two software packages, data were also selected for 50 other patients at low likelihood for coronary artery disease, for whom EF and EDV were significantly lower for QGS compared with ECTb (62% +/- 9% vs 67% +/- 8% and 84 +/- 26 mL vs 105 +/- 33 mL, respectively). The ECTb lower limit was 51% for EF and the upper limits were 171 mL for EDV and 59 mL/m(2) for mass-indexed EDV, compared with limits of 44%, 137 mL, and 47 mL/m(2) for QGS.

CONCLUSIONS

Although correlations were strong between the two methods of computing LV functional values, statistical scatter was substantial and significant biases and trends observed. Therefore, when both software packages are used at the same site, it will be important to take these differences into consideration and to apply normal limits specific to each set of algorithms.

Parametric display of myocardial function

Quantitative assessment of regional heart motion has significant potential to provide more specific diagnosis of cardiac disease and cardiac malfunction than currently possible. Local heart motion may be captured from various medical imaging scanners. In this study, 3-D reconstructions of pre-infarct and post-infarct hearts were obtained from the Dynamic Spatial Reconstructor (DSR)[Ritman EL, Robb RA, Harris LD. Imaging physiological functions: experience with DSR. Philadelphia: Praeger, 1985; Robb RA, Lent AH, Gilbert BK, Chu A. The dynamic spatial reconstructor: a computed tomography system for high-speed simultaneous scanning of multiple cross sections of the heart. J Med Syst 1980;4(2):253-88; Jorgensen SM, Whitlock SV, Thomas PJ, Roessler RW, Ritman EL. The dynamic spatial reconstructor: a high speed, stop action, 3-D, digital radiographic imager of moving internal organs and blood. Proceedings of SPIE, Ultrahigh- and High-speed Photography, Videography, Photonics, and Velocimetry 1990;1346:180-91.] (DSR). Using functional parametric mapping of disturbances in regional contractility and relaxation, regional myocardial motion during a cardiac cycle is color mapped onto a deformable heart model to facilitate appreciation of the structure-to-function relationships in the myocardium, such as occurs in regional patterns of akinesis or dyskinesis associated with myocardial ischemia or infarction resulting from coronary artery occlusion.

Measurements of left ventricular dimensions using real-time acquisition in cardiac magnetic resonance imaging: comparison with conventional gradient echo imaging

This study investigates the use of real-time acquisition in cardiac magnetic resonance imaging (MRI) for measurements of left ventricular dimensions in comparison with conventional gradient echo acquisition. Thirty-one subjects with a variety of left ventricular morphologies to represent a typical clinical population were studied. Short-axis data sets of the left ventricle (LV) were acquired using a conventional turbo-gradient echo and an ultrafast hybrid gradient echo/echo planar sequence with acquisition in real-time. End-diastolic volume (EDV), end-systolic volume (ESV), ejection fraction (EF) and left ventricular mass (LV mass) were measured. The agreement between the two acquisitions and interobserver, intraobserver and interstudy variabilities were determined. The bias between the two methods was 5.86 ml for EDV, 0.23 ml for ESV and 0.94% for EF. LV mass measurements were significantly lower with the real-time method (mean bias 14.38 g). This is likely to be the result of lower spatial resolution and chemical shift artefacts with the real-time method. Interobserver, intraobserver and interstudy variabilities were low for all parameters. In conclusion, real time acquisition in MRI can provide accurate and reproducible measurements of LV dimensions in subjects with normal as well as abnormal LV morphologies, but LV mass measurements were lower than with conventional gradient echo imaging.

Use of a new myocardial centroid for measurement of regional myocardial dysfunction by electron beam computed tomography: comparison with technetium-99m sestamibi infarct size quantification

RATIONALE AND OBJECTIVES

The study compared the performance of conventional endocardial and epicardial centroid algorithms with the new "myocardial" centroid algorithm in patients with anterior myocardial infarction. "Floating" endocardial or epicardial centroid algorithms, commonly used in tomographic imaging methods to assess regional motion, may misrepresent left ventricular regional myocardial function in the presence of markedly asymmetric left ventricular contraction.

METHODS

A new centroid algorithm based on regional myocardial mass distribution was tested in 29 patients with a first anterior myocardial infarction and was compared with conventional centroid algorithms. Direct comparisons in 60 equal sectors at one midventricular level per patient were performed between electron beam computed tomography and technetium-99m sestamibi single-photon emission computed tomography. The thresholds of regional myocardial function used to define infarction were varied for regional ejection fraction from 20% to 40% and for regional wall thickening from 0 to 4 mm. Regression and Bland-Altman analysis were used to compare infarct size by regional myocardial function with infarct size by sestamibi single-photon emission computed tomography.

RESULTS

The new myocardial centroid showed the least shift toward infarcted myocardium from diastole to systole and had the highest amplitudes of the measurement curves for regional ejection fraction and regional wall thickening. The optimal regional myocardial function thresholds for each centroid algorithm for regional ejection fraction were endocardial, 30% (R = 0.62; mean difference to sestamibi, -0.5% +/- 22.1% tomographic infarct size points); epicardial, 30% (R = 0.79; mean difference, 2.2% +/- 13.1% tomographic infarct size points); and new myocardial, 25% (R = 0.88; mean difference, -0.6% +/- 9.5% tomographic infarct size points). The optimal thresholds for regional wall thickening were endocardial, 1 mm (R = 0.70; mean difference, -2.2% +/- 14.3% tomographic infarct size points); epicardial, 1 mm (R = 0.78; mean difference, -4.6% +/- 12.7% tomographic infarct size points); and new myocardial, 2 mm (R = 0.71; mean difference, 2.1% +/- 14.1% tomographic infarct size points). The best agreement (R = 0.88) between electron beam computed tomography infarct size and sestamibi single-photon emission computed tomography infarct size was achieved with regional ejection fraction and the new myocardial centroid algorithm.

CONCLUSIONS

In asymmetrically contracting left ventricles, the new myocardial centroid algorithm is superior to conventional methods for tomographic analysis of regional myocardial function.

Normal limits for left ventricular ejection fraction and volumes estimated with gated myocardial perfusion imaging in patients with normal exercise test results: influence of tracer, gender, and acquisition camera

BACKGROUND

Myocardial imaging with tracers such as technetium-99m sestamibi or thallium-201 is extensively used as a means of measuring myocardial perfusion. With gated acquisition, these tracers can also be used as a means of measuring left ventricular ejection fraction (EF) and end diastolic and end systolic volumes (EDV and ESV, respectively). The objective of this study was to determine the normal range of EF, EDV, and ESV and to evaluate differences caused by either the tracer used, the gender of the patient, or the acquisition camera used.

METHODS AND RESULTS

A total of 1513 consecutive patients (mean age, 60+/-12 years [SD]) who had normal results on Bruce exercise tests had either Tc-99m sestamibi (n = 884) or Tl-201 (n = 629) injected at peak stress. Although all patients were referred for the evaluation of chest pain or dyspnea and many had cardiac risk factors, all had normal exercise capacity corrected for age, no electrocardiographic signs of ischemia, normal results on perfusion scans, and normal wall motion determined by means of quantitated gated single photon emission computed tomography (QGS). Scans were acquired on 1 of 3 different cameras. The mean EF for all patients who had gated Tc-99m sestamibi scans was 63% +/- 9%, not different from patients who had gated Tl-201 scans (63% +/- 9%). However, when the gender of the patient was considered, the mean EF for women was 66% +/- 8% with Tc-99m sestamibi (n = 519), higher than the mean EF for men (58% +/- 8%, n = 365, P<.0001). Similarly, the mean EF for women studied with Tl-201 (67% +/- 8%, n = 326) was higher than that of men (59% +/- 7%, n = 303,P<.0001). Patients with diabetes mellitus (n = 153) had a slightly reduced EF (62% +/- 10%, P<.001). In a subset of 240 patients, 140 patients studied with Tc-99m sestamibi and 100 studied with Tl-201, the EDV and ESV for women (n = 124) was estimated by means of QGS to be lower (57 +/- 17 mL and 19 +/- 11 mL, respectively) than those for men (74 +/- 22 mL-and 29 +/- 13 mL, respectively; n = 116; P<.001 for each comparison). No clinically significant differences in EF or volumes were noted based on tracers used or acquisition camera. For patients with normal results on exercise treadmill tests and perfusion imaging, the lower limit of normal for EF with gated perfusion imaging with QGS was 50% for women and 43% for men. For EDV and ESV, the upper limit of normal was 91 mL and 40 mL, respectively, for women and 119 mL and 55 mL, respectively, for men.

CONCLUSIONS

No significant differences related to either tracer or acquisition camera used were noted for EF, suggesting equivalency for clinical trials for patients with normal results on exercise tests. However, EF, EDV, and ESV determined by means of gated perfusion imaging need to be corrected for gender.

Accurate measures of left ventricular ejection fraction using electron beam tomography: a comparison with radionuclide angiography, and cine angiography

BACKGROUND

Quantitative determination of ejection fraction is predicated on precise measurement of end-diastolic and end-systolic volumes of the left ventricle. Contrast enhanced electron beam tomography (EBT), with excellent temporal and spatial resolution, has the potential for highly accurate measures of ejection fraction.

METHODS

EBT protocol used a short axis scan of the left ventricle (8-12 levels, apex to base) during infusion of iodinated contrast. To assess the accuracy of the measured left ventricular ejection fraction (LVEF), we compared EBT with first-pass radionuclide angiography (RNA) and cine angiography (CINE).

RESULTS

A total of 41 patients (26 men and 15 women) underwent all three tests within 1 week. Resting ejection fraction using each modality was assessed in a linear regression model to assess inter-test correlation with the other two modalities. Correlation between CINE and EBT was high (r = 0.90, intercept 4.67, p < 0.001). Similarly, correlation of CINE and RNA (r = 0.87, intercept -5.48, p < 0.001) and between EBT and RNA (r = 0.87, intercept -4.6, p < 0.001) were high. In a subset of those patients with LVEF < or = 40%, correlation was consistently high between EBT and CINE. However, correlations were poor for the comparisons between RNA and CINE (r = 0.40), and between the RNA and EBT (r = 0.47). The mean differences of measured ejection fractions between each of the imaging modality were small. However, there was only modest agreement between each of the comparisons as measured using 95% confidence interval (CI) on Bland-Altman plots.

CONCLUSION

These data indicate that the LVEF results are comparable among EBT, RNA, and CINE and can be used interchangeably to assess ventricular function for LVEF > 40%. For LVEF < or = 40%, we demonstrated some disparate results between cine angiography and RNA and between EBT and RNA, indicating that CINE or EBT may provide more accurate assessment.

Use of electron beam tomography to quantify cardiac diastolic function

The examples provided in this article indicate that EBT, in addition to allowing for detailed descriptions of cardiac anatomy and contraction characteristics in man, can also be used to evaluate global and regional LV diastolic function using an approach previously validated for applications in radionuclide angiography. EBT is an established imaging modality that has been shown to be highly applicable to quantitative determination of ventricular mass, RV and LV volumes, and global and regional ventricular systolic and diastolic function in a variety of cardiac pathologic states. The attractiveness of EBT lies not so much in a single determination of systolic function or diastolic filling in a given individual, but in the strength of an easily acquired, highly reproducible, and accurate serial imaging method in patients following pharmacologic or interventional therapy for a specific cardiac disease.

Breathhold cine MRI of left ventricular function in patients with obstructive sleep apnea: work-in-progress

Obstructive sleep apnea (OSA) is a sleep-related breathing disorder that can cause left ventricular (LV) dysfunction. In patients with OSA, the LV dysfunction is usually evaluated by echocardiography. The purpose of this study was to evaluate whether the use of breathhold cine MRI for the study of LV dysfunction would be feasible and well tolerated by patients with OSA. Six volunteers and five patients underwent a breathhold cine MRI study of the LV using a 1.5 Tesla MR imager. Cine MRI was performed using a breathhold k-space segmented TurboFLASH technique during end-expiration. Systolic thickening of the LV septal wall was 49% +/- 16% in normals vs. 25% +/- 10.5% in patients (p < 0.05). Systolic thickening of the LV free wall was 42% +/- 12% in normals vs. 22% +/- 9% in patients (p < 0.05). There was a significant difference in end-diastolic wall thickness between the two groups. All patients tolerated the procedure well. The total duration of each study was relatively short (less than 11 min). Breathhold MRI techniques can be used to study LV dysfunction in patients with respiratory disability such as OSA.

Effect of exercise on left and right ventricular ejection fraction and wall motion

OBJECTIVE

We evaluated the diagnostic value of response of left and right ventricular ejection fraction and wall motion to exercise using electron beam computed tomography.

METHODS AND RESULTS

We attempted to determine the value of exercise electron beam computed tomography for detecting coronary artery disease, including evaluation of the right ventricular ejection fraction and wall motion abnormalities. A study of 35 patients undergoing electron beam tomography exercise cine studies and coronary artery angiography for the evaluation of chest pain was performed. Of the 18 patients with significant coronary disease (> or = 50% luminal diameter stenosis in at least one coronary artery), 17 (94%) had failure to increase global left ventricular ejection fraction with exercise. Fourteen of 18 (78%) developed a wall motion abnormality during peak exercise, and eight (44%) developed a regional right ventricular wall motion abnormality during peak exercise. Of the 17 patients without obstructive disease, 14 (82%) had a increase in ejection fraction > or = 5% and none had an abnormal response in left ventricular wall motion during peak exercise (specificity = 100%). The change in right ventricular ejection fraction with exercise was not a significant predictor of obstructive coronary disease in this study (P=NS). Using different criteria during stress to predict coronary disease, the accuracy was 89% (31/35) using an increase of <5% in ejection fraction, 89% (31/35) using the development of a new or worsened wall motion abnormality, and 91% (32/35) using both left ventricular criteria.

CONCLUSION

Our study suggests that exercise electron beam computed tomography appears to be a useful tool for the detection of coronary disease. A increase of <5% in ejection fraction and abnormal left ventricular response to exercise were important predictors, while the exercise induced changes of right ventricular ejection fraction was not a significant predictor of obstructive disease. Both left and right ventricular wall motion abnormalities are useful and important parameters in identifying patients with obstructive disease from those with normal coronary arteries.

Determination of normal regional left ventricular function from cine-MR images using a semi-automated edge detection method

A semi-automated edge detection method for the delineation of the endo- and epicardial borders of the left ventricle from cine MR images has been developed. The feasibility of this was demonstrated by processing end diastolic and end systolic ECG-gated images of four short axis images in 10 healthy subjects. The first derivative method combined with a 2D weighted polynomial fitting procedure was used to determine the endo- and epicardial borders, which then allowed determination of the wall motion, wall thickening, and ejection fraction, of the left ventricle. The results show that the end-systolic radial wall motion varies from (32+/-8)% to (76+/-12)%, and wall thickening from (0.60+/-0.46) cm to (1.26+/-0.50) cm. An average ejection fraction of (69+/-6)% was found which agrees well with literature values. The method described, for the delineation of the borders, reduces considerably the long and tedious operator time inherent in manual measurement and greatly increases the reproducibility of the measurements.

Coronary atherosclerosis and its effect on cardiac structure and function: evaluation by electron beam computed tomography

Coronary artery disease affects millions of Americans annually. In evaluating coronary artery disease, it is important to develop diagnostic methodology that can screen patients before the onset of symptoms or cardiac events and, in addition, evaluate the functional aspects of coronary artery disease, including any residual effects on the heart after events have occurred. Electron beam computed tomography allows the identification of coronary calcium, which is a marker for coronary atherosclerotic disease, and also allows the quantification of cardiac function, which may be altered from coronary atherosclerosis or the occurrence of a cardiac event. Thus, electron beam computed tomographic imaging is having a major impact on the diagnosis and follow-up on coronary artery disease.

Reproducibility of right and left ventricular volume measurements by electron-beam CT in patients with congestive heart failure

The applicability and reproducibility of electron-beam computed tomography (EBCT) was tested to define left and right ventricular volumes in patients with congestive heart failure in a clinical setting.

METHODS

Ten patients (mean age 64 +/- 11 years) with dilated hearts and stable congestive heart failure (functional class III-IV) were studied. After determination of the individual circulation time, two serial short axis polytomographic EBCT studies were performed within a mean interval of 14.8 +/- 10 days. Following intravenous contrast administration, biventricular end-diastolic volumes (LVEDV, RVEDV), end-systolic volumes (LVESV, RVESV), and left ventricular muscle mass (LVMM) were determined using previously developed techniques.

RESULTS

Adequate contrast opacification in both ventricular cavities was obtained in all patients at baseline and at follow-up. Values were 323.4 +/- 99.3 (mean +/- SD) and 332.6 +/- 105.4 ml for LVEDV, 249.3 +/- 75.6 and 250.5 +/- 79.3 ml for LVESV, 236.8 +/- 56.2 and 251.2 +/- 72.7 ml for RVEDV, 179.8 +/- 76.4 and 188.3 +/- 64.0 ml for RVESV, and 207.7 +/- 70.6 and 204.9 +/- 81.9 g for LVMM (p = NS, respectively, paired t-test). Linear regression analysis correlating biventricular volumes and left ventricular muscle mass measurements in the serial scans yielded r-values in the range of 0.89 to 0.95 and a small SEE. The SE of the mean differences between left and right ventricular ejection fraction measurements was 1 point, respectively.

CONCLUSION

EBCT studies of ventricular volumes in patients with dilated hearts and congestive heart failure are highly reproducible and offer the potential for serial assessment of these patients in whom quantitation of ventricular volumes has been shown to be of prognostic value.

Measurement of myocardial infarct size by electron beam computed tomography: a comparison with 99mTc sestamibi

RATIONALE AND OBJECTIVES

The authors sought to determine, using a variety of regional left ventricular ejection fraction (EF) and wall thickening (WTh) criteria, the applicability to measure left ventricular (LV) infarct size using electron-beam CT (EBCT) in patients as compared with technetium 99m (99mTc) sestamibi scanning as reference standard.

METHODS

Twelve patients (age 57 +/- 11 years) underwent 99mTc sestamibi scanning and EBCT at hospital discharge after an acute index anterior myocardial infarction. Left ventricular infarct size was defined using standard 99mTc sestamibi scanning. Regional EF and WTh were analyzed on each EBCT scan with use of a floating epicardial centroid method. In five contiguous LV tomograms, the amount of infarcted myocardium was estimated using the following EF and WTh criteria: EF < or = 35%, 30%, 25%, 20%, and WTh < or = 2 mm, 1 mm, and 0 mm.

RESULTS

Infarct size measured with 99mTc sestamibi was 33.3% (+/- 18.3%) (mean +/- SD, range 6%-54%) of the LV. Using an EF < or = 35% or absolute WTh < or = 2 mm as criteria for infarcted myocardium, EBCT yielded 28% (+/- 17%) and 27% (+/- 16%), respectively (P = NS, paired Student's t test, versus 99mTc sestamibi). Although, with use of the other criteria, EBCT tended to underestimate infarct size compared with 99mTc sestamibi, a close correlation across the entire range of infarct size determinations (range, 0.72-0.82) regardless of the underlying criteria suggested an internal consistency of the data.

CONCLUSIONS

Quantitative analysis of regional myocardial function by EBCT allows an estimate of anterior infarct size when compared with 99mTc sestamibi. This suggests that in addition to previously established applications after acute myocardial infarction such as examination of cardiac volumes and mass, EBCT also may provide for infarct size determination.

Comparison of exercise electron beam computed tomography and sestamibi in the evaluation of coronary artery disease

This blinded, single center study prospectively compares exercise electron beam computed tomography (EBCT) with stress technetium-99m (Tc-99m) sestamibi single-photon emission computed tomography (SPECT) in 33 patients undergoing coronary angiography for evaluation of chest pain. Patients undergoing routine cardiac catheterization for the diagnosis of chest pain were imaged at rest using EBCT. Patients exercised on a semi-supine ergometer, and exercise EBCT was immediately followed by injection of Tc-99m sestamibi for assessment of myocardial ischemia. At peak exercise, Tc-99m SPECT, followed immediately by nonionic contrast material, was injected intravenously to directly compare these 2 imaging techniques. Patients were reimaged with Tc-99m SPECT at rest 24 to 48 hours after stress. Exercise EBCT, which was analyzed using a global ejection fraction measure, had a sensitivity of 81% and a specificity of 76%, compared with angiography. Using the development of a new regional wall motion abnormality as evidence of obstructive coronary artery disease (CAD), EBCT yielded a specificity of 100% and a sensitivity of 88%. Reversible perfusion defects identified by SPECT, as evidence of obstructive CAD, revealed a sensitivity of 75% and a specificity of 71%. The specificity of regional wall motion analysis by EBCT was significantly better than SPECT (p <0.01) in this population. This study demonstrates regional wall motion assessed by EBCT to be as sensitive and more specific than SPECT myocardial perfusion imaging in identifying obstructive CAD as defined by angiography.

Breath-hold dobutamine magnetic resonance myocardial tagging: normal left ventricular response

Analysis of the changes in myocardial deformation produced by adrenergic stress has been limited by the imaging techniques used. We used rapid magnetic resonance imaging (MRI) myocardial tagging to map the dose-dependent response to incremental dobutamine in the normal human left ventricle. Thirteen volunteers underwent breath-hold tagged cine MRI during dobutamine infusion. Images were acquired throughout systole to a peak dose of 20 microg/kg/min. End-systolic percent circumferential shortening (%S) was measured at 3 transmural locations and 4 circumferential locations at 3 long-axis positions. Mean circumferential shortening velocity (CSV) was also calculated at each location and dose. Mean %S reached a maximum of 26 +/- 3% at 10 microg/kg/min compared with 21 +/- 4% at baseline (p <0.003). Peak %S was reached by 10 microg/kg/min before a significant increase in heart rate or blood pressure and was unchanged at higher doses. In contrast, CSV increased linearly with dobutamine dose from 4.4 +/- 0.9 mm/s at baseline to 9.8 +/- 1.4 mm/s at 20 microg/kg/min (p <0.0001). Breath-hold tagged dobutamine MRI is safe and effective in detecting regional and transmural changes in function during incremental dobutamine. CSV increased continuously across the dobutamine dose range. At low dose (< or =10 microg/kg/min) %S increased without any change in blood pressure or heart rate. Maintenance of peak %S beyond 10 microg/kg/min in the presence of decreasing systolic intervals resulted from a continued increase in CSV. Thus, CSV may be the preferred measure of contractile function during dobutamine stimulation in human myocardium.

Quantitative evaluation of regional myocardial perfusion using fast X-ray computed tomography

Clinical quantitation of regional myocardial perfusion using a minimally invasive and easily applied technique could allow for ready quantitation of the functional significance of coronary disease, allow for further understanding of flow reserve in various cardiomyopathic and hemodynamic overload (pressure versus volume) conditions, and possibly provide basic information needed regarding the development and clinical significance of coronary collateral vessels and diseases of the myocardial microcirculation. Electron beam CT (EBCT) is a unique cardiac imaging modality that allows for rapid acquisition tomographic slices of the heart with excellent spatial resolution. It has been demonstrated to provide accurate measurements of cardiac anatomy, biventricular function, myocardial mass, and estimates of mural atherosclerotic plaque burden via quantification of coronary calcium. The application of classical indicator techniques for use by fast x-ray computed tomography techniques such as electron beam CT has been shown to allow quantitative analysis of regional myocardial perfusion throughout the myocardium. Initial studies using central intravenous contrast injection in experimental animals showed a close correlation of regional myocardial perfusion as quantitated by electron beam CT with measurements using radiolabeled microspheres at resting and moderately increased flow states. At high flow states, however, electron beam CT significantly underestimated absolute myocardial perfusion and thus myocardial flow reserve. Using another fast CT device, the Dynamic Spatial Reconstructor (DSR), concepts of intramyocardial vascular blood volume and its relation to myocardial flow have been established. By adapting these concepts to electron beam CT scanning and accounting for the increase in intramyocardial vascular blood volume at vasodilatation, the ability to correctly quantitate perfusion states up to approximately 400 mL.min-1. 100 g-1 using central intravenous contrast administration was demonstrated. This implies that studies can be done with intravenous injection methods for characterization of regional myocardial perfusion up to the normal flow reserve of approximately 4:1. Important physiologic and clinical abnormalities in flow reserve generally result in a ratio < 3:1. Electron beam CT offers the capability to quantitate regional myocardial perfusion in both the clinical and research setting. Of particular interest is the ability to provide quantitative regional myocardial perfusion which can be coupled to the evaluation of cardiac anatomy and function as well as mural coronary atherosclerotic calcium burden during the same scanning session. Thus, electron beam CT has the potential to become a valuable, minimally invasive clinical tool for comprehensive analysis of cardiac function and coronary status.

Regional three-dimensional geometry of the normal human left ventricle using cine computed tomography

The aim of this study is to provide accurate three-dimensional measurements of left ventricular geometrical indices in relation to regional myocardial function. The analysis of the three-dimensional regional geometry and function of left ventricles of ten normal human volunteers is based on three-dimensional reconstructions of the left ventricle from cine computed tomography images, at end diastole and end systole, demonstrating normal left ventricular spatial, geometrical, and functional variability. Regional wall thickness, curvature and surface normals, as well as wall thickening and endocardial wall motion, are calculated and mapped for the entire left ventricle. The circumferential asymmetry of the left ventricle is reflected by the smaller circumferential and meridional curvatures at the septum. Thickening is highest at the anterior and lateral walls. Longitudinally, circumferential curvature increases toward the apex, whereas both wall thickness and wall thickening at end systole are largest at the midventricular level, decreasing toward the apex and base. This study describes the circumferential and apex-to-base variations in regional left ventricular geometric parameters of the normal human left ventricle, using three-dimensional imaging and analysis.

Normal nonuniformity of left ventricular contraction. Assessment by cine MR imaging with presaturation myocardial tagging

PURPOSE

To identify the normal performance of left ventricular (LV) regional contraction using cine MR imaging with presaturation myocardial tagging.

MATERIAL AND METHODS

Sixteen normal volunteers were examined on a 1.5 T MR system with tagging cine sequences. Tags were applied at end-diastole as 2 parallel black lines on short-axis and 4-chamber sections, and the fractional shortenings were calculated at 7 LV locations.

RESULTS

The following results were obtained with significance: a transmural gradient of contractility in the short-axis section; prolonged late-systolic endocardial shortening and epicardial early termination in the free wall; initial delay of shortening in the anterior wall; apical predominance of contractility; predominance of circumferential shortening in the free wall and of meridional shortening in the septum. These findings could be associated with myocardial fiber architecture, presumed wall stress and temporal asynergy of excitation.

CONCLUSION

Cine MR imaging with myocardial tagging proved to be useful in assessing the nonuniformity of LV contraction.

Assessment of left ventricular volume and mass by cine magnetic resonance imaging in patients with anterior myocardial infarction intra-observer and inter-observer variability on contour detection

Remodeling of the left ventricle after myocardial infarction can be documented by calculation of left ventricular volume and mass, using endocardial and epicardial tracings of multilevel multiphase short-axis cine magnetic resonance (MR) imaging series. We assessed left ventricular volume and mass from 8 slices and during 12 phases of the cardiac cycle in seven patients with an anterior wall myocardial infarction; one patient was studied twice, leaving eight MR examinations to be evaluated. Purpose of this study was to assess the intra-observer and inter-observer variability of epicardial volume, endocardial volume, and left ventricular mass from contours manually traced by two independent observers. For the eight MR examinations, epicardial volume was found to be 292 +/- 51 ml (mean +/- SD) at end-diastole, which decreased to 237 +/- 55 ml at end-systole. Endocardial volume was 141 +/- 31 ml at end-diastole, which decreased to 79 +/- 27 ml at end-systole. Left ventricular ejection fraction was 45 +/- 8%. Mean left ventricular mass, when averaged over all patient studies and all phases, was 159 +/- 30 g. Intra-observer and inter-observer variability were found to be 3.5% and 5.2% for endocardial volume, 2.0% and 2.5% for epicardial volume, and 3.6% and 3.6% for left ventricular mass, respectively. The contour analysis showed a statistically significant phase effect in the endocardial contour in the midventricular slices, which was resolved after establishing a more precise definition for the tracing of the endocardial border. In conclusion, left ventricular volume and mass in patients with an anterior wall myocardial infarction can be assessed with high reproducibility and reliability from manual contour tracings. A precise protocol for the definition of endocardial and epicardial contours is required to obtain reproducible and reliable results.

Regional left ventricular wall thickness and systolic function during the first year after index anterior wall myocardial infarction: serial effects of ventricular remodeling

There is controversy regarding changes in regional left ventricular systolic function and thickness during remodeling after infarction. To address this, electron beam computed tomography was done in 22 patients with an index anterior wall infarction at discharge, 6 weeks, 6 months and 1 year, and global ventricular chamber volumes and mass quantified. A mid-ventricular short-axis scan from each study was divided into 4, 90 degrees sectors (anterior, septal, lateral and posterior walls). Regional wall thickness, ejection fraction, and absolute and percent wall thickening were determined and compared with 10 normal adults. Global infarct size was estimated at 24.2%+/- 3.4% of the ventricle. In these subjects, the ventricular chamber enlarged steadily during the year, while global ventricular mass initially decreased during the first 6 weeks, but then increased by 1 year. Regional ejection fraction changed little during the year, apart from the lateral wall, which was less than normal. Absolute wall thickening was reduced in the anterior (infarct) and septal walls throughout the year, but was normal and unchanged in the posterior and lateral walls. Regional percent wall thickening was not different from normal individuals. The anterior wall was thinned at discharge and tended to thin further during the year. The lateral wall was thinner than normal 6 weeks after infarction, but remained unchanged thereafter. The posterior wall tended to thin for the first 6 months, but the values at any time were not above normal. There was little change in septal wall thickness throughout the year. It is concluded that, after a moderate size, uncomplicated index anterior infarction, regional systolic function remains generally unaffected by remodeling. However, regional walls tend to thin and/or remain at normal thickness. These data confirm differential regional patterns after anterior infarction for systolic function, muscle atrophy and/or minimal hypertrophy which accompany serial changes in global ventricular chamber volumes and mass.

Serial changes in regional right ventricular free wall and left ventricular septal wall lengths during the first 4 to 5 years after index anterior wall myocardial infarction

OBJECTIVES

This study investigated serial changes in regional right ventricular free wall and interventricular septal wall lengths during the first 4 to 5 years after an index anterior wall myocardial infarction.

BACKGROUND

We previously demonstrated that remodeling after anterior wall myocardial infarction was a biventricular process; however, regional changes in biventricular topology were not investigated.

METHODS

Serial electron beam computed tomographic scanning was performed in 19 patients at five times (hospital discharge and at 6 weeks, 6 months, 1 year and 4 to 5 years) after an index anterior wall myocardial infarction, and global and regional right ventricular free wall and interventricular septal wall lengths were quantified.

RESULTS

At a mean (+/- SD) of 1,642 +/- 171 days (4 to 5 years) after infarction, global end-diastolic and end-systolic right ventricular free wall and interventricular septal wall lengths increased in parallel by 13% to 23% as global left and right ventricular volumes increased 22% to 29% from hospital discharge to 4 to 5 years after infarction. When global right ventricular free wall was compared with interventricular septal wall lengths, percent increases at end-diastole and end-systole were not statistically different at any time during the study period. Distinct regional changes in both right ventricular free wall and interventricular septal wall lengths after infarction were most dramatic during the first 6 weeks and primarily confined to the most apical levels. However, further and significant increases in both were observed by 4 to 5 years after infarction.

CONCLUSIONS

Changes in both right ventricular free wall and interventricular septal wall lengths were apparent during the 4 to 5 years after the index anterior wall infarction, and the combination of both contributed to global increases in right and left ventricular chamber volumes. Regional changes in both right ventricular free wall and interventricular septal wall lengths were almost exclusively confined to their respective apices and progressed generally in parallel; however, the cause-and-effect relation remains speculative at the present time.

Use of sonomicrometry and multidimensional scaling to determine the three-dimensional coordinates of multiple cardiac locations: feasibility and initial implementation

We describe a new method which uses sonomicrometry and the statistical technique of multidimensional scaling (MDS) to measure the three-dimensional (3-D) coordinates of multiple cardiac locations. We refer to this new method as sonomicrometry array localization (SAL). The new method differs from standard sonomicrometry in that each piezoelectric transducer element is used as both transmitter and receiver and the set of intertransducer element distances is measured. MDS calculates the 3-D coordinates of each sonomicrometry transducer element from the set of intertransducer element distances. The feasibility of this new method was tested with mathematical simulations which demonstrated the ability of MDS to compensate for signal error and missing intertransducer element distances. We describe the design elements of a modified digitally controlled sonomicrometer in which a single transducer element can sequentially broadcast to as many as eight receiver elements. That design is used to validate SAL in a water bath and in ex vivo and living hearts. Correlation with caliper measurement in the water bath (y int. = 3.91 +/- 3.36 mm, slope = 1.04 +/- 0.05, r2 = 0.969 +/- 0.027) and with radiography in ex vivo (y int. = -0.87 +/- 0.92 mm, slope = 0.97 +/- 0.02, r2 = 0.960 +/- 0.023) and in vivo hearts (y int. = 2.98 +/- 2.59 mm, slope = 1.01 +/- 0.06, r2 = 0.953 +/- 0.031) was excellent. Sonomicrometry array localization is able to accurately measure the 3-D coordinates of multiple cardiac locations. It can potentially measure myocardial deformation and remodeling after ischemic or valvular injury.

Serial changes in left and right ventricular systolic and diastolic dynamics during the first year after an index left ventricular Q wave myocardial infarction

OBJECTIVES

This study quantified serially biventricular emptying and filling after infarction and related these to changes in volume, muscle mass, wall stress and contractility.

BACKGROUND

There are limited data on serial changes in ventricular dynamics after infarction.

METHODS

Forty patients had serial electron beam computed tomographic examinations during the first year after index Q wave infarction (21 anterior, 19 inferior), and global biventricular volumes, peak rates of emptying and filling and left ventricular muscle masses were quantified. Mean mid-left ventricular end-systolic wall stresses, rate-corrected velocities of circumferential shortening and two indexes of left ventricular contractility--the end-systolic wall stress/volume ratio and the end-systolic wall stress/rate-corrected velocity of circumferential shortening relation--were estimated in each instance.

RESULTS

Patients with anterior infarction had an increase in biventricular chamber volume of 15% to 35% by 1 year. Global biventricular peak rates of emptying and filling were decreased by 20% to 30% from hospital discharge to 6 weeks but thereafter remained unchanged. Despite a significant increase in mean wall stresses, the end-systolic wall stress/volume ratio remained unchanged during the year. The rate-corrected velocities of circumferential shortening declined serially after anterior infarction but did so in proportion to the increase in mean wall stresses, consistent with no net change in left ventricular contractility. Patients with inferior infarction showed a trend toward similar changes, but the magnitudes did not reach significance.

CONCLUSIONS

Left (and right) ventricular global peak rates of emptying and filling during the first year after infarction can be altered in the absence of additional ischemic injury but are more consistent with responses to changes in left ventricular afterload than changes in intrinsic ventricular performance or contractility. Serial changes in left ventricular afterload after infarction are largely due to progressive chamber enlargement and limited development of compensatory hypertrophy during the first year. Intrinsic global left ventricular contractile performance was not altered by postinfarction cardiac remodeling in the patients examined.

Relation of initial infarct size to extent of left ventricular remodeling in the year after acute myocardial infarction

OBJECTIVES

This study attempted to determine the relation between infarct size after acute myocardial infarction and subsequent left ventricular remodeling using precise clinical measurements.

BACKGROUND

Animal studies have demonstrated that the degree of left ventricular remodeling after myocardial infarction is linearly related to infarct size. Clinical studies have not clearly replicated these results because of imprecise measurements and failure to adjust for patency of the infarct-related artery.

METHODS

Infarct size was measured from technetium-99m (Tc-99m) sestamibi perfusion images in 14 patients (12 with an anterior, 2 with an inferior infarction) by a threshold method previously described and expressed as percent of the left ventricle (32 +/- 17% left ventricle [mean +/- SD], range 6% to 58%). Absolute end-systolic volume, end-diastolic volume and ejection fraction were determined by electron beam computed tomographic images performed at discharge and at 6 weeks, 6 months and 1 year after myocardial infarction. All patients had documented infarct-related artery patency after reperfusion therapy.

RESULTS

At hospital discharge, there was no correlation between infarct size and end-systolic and end-diastolic volumes or ejection fraction. There was significant left ventricular dilation in the study group over the next year. As remodeling progressed, there was closer correlation between infarct size and ejection fraction and end-systolic volume measures (infarct size vs. end-systolic volume, from r = 0.43 at discharge to r = 0.80 at 1 year; infarct size vs. ejection fraction, from r = -0.39 at discharge to r = -0.84 at 1 year). There was a strong inverse correlation between infarct size at discharge and subsequent changes over the next year in end-systolic volume (r = 0.63, p = 0.02) and ejection fraction (r = -0.66, p = 0.01).

CONCLUSION

Infarct size as measured by Tc-99m sestamibi at hospital discharge after an index infarction is predictive of subsequent change in left ventricular volume and function in the year after myocardial infarction. Patients with a large infarct demonstrated the greatest degree of dilation in the setting of patency of the infarct-related artery.

Assessment of cardiac volumes and left ventricular mass by cine computed tomography before and after mitral balloon commissurotomy

We used cine computed tomography (CT) to determine whether decreased mitral valve gradients and pulmonary artery pressures resulted in decreased right ventricular and atrial volumes after percutaneous mitral balloon commissurotomy (MBC). In patients treated for severe mitral stenosis, previous studies have shown that after the mitral valve gradient decreases, the left atrial volume is reduced and left ventricular stroke volume is increased. The effects of commissurotomy on right heart chamber sizes have been difficult to assess with angiography and echocardiography. Moreover, in follow-up studies performed after surgery, changes in cardiac chamber volumes occurring after the mitral valve gradient and pulmonary pressure are reduced are confounded by the effects of thoracotomy. Our group has previously demonstrated that cine CT can accurately measure both left and right cardiac chamber volumes. We studied 11 female patients before, immediately after, and at 1 year after MBC, and 9 female control subjects of comparable age. To assess cardiac chamber volumes, we used cine CT. To assess the effects of MBC, we used cardiac catheterization and Doppler echocardiography.(ABSTRACT TRUNCATED AT 250 WORDS)

Some aspects of cardiac heterogeneity

It is remarkable that the heart, which obviously functions as a homogenous pump, shows such a high degree of heterogeneity. There are often contradictory or controversial results as far as transmural gradients are concerned (78). These discrepancies or inconsistencies, however, can at least in part be explained by species differences. Of particular interest is the heterogeneity that is due to the separation into two hearts. In view of the differences in the morphology and function of the left and right heart, it is surprising that the whole organ works in a rather homogenous fashion. In the past, the right heart has received not as much attention as the left heart. This is in particular true for small laboratory animals. It becomes more and more evident that compared to the left ventricle, the right ventricle reacts to various stimuli in a quantitatively different manner. More research on the right heart is therefore needed. Collectively, the data summarized in this article may be interpreted in that the heart not only works as a homogeneous unit, but may even benefit from the heterogeneity of its different parts or subunits under normal as well as under various pathophysiological conditions. Analysis of the processes involved in creating cardiac heterogeneity can provide new insights into the mechanism of adaptation of the heart.

Left ventricular volume and mass: Comparative study of two-dimensional echocardiography and ultrafast computed tomography

This study was undertaken to define the accuracy of two-dimensional echocardiography in the determination of left ventricular end-diastolic and end-systolic volumes, stroke volume, ejection fraction, and mass when compared to ultrafast cine computed tomography in the same 56 patients. Single-plane and biplane modified Simpson's rule, single-plane and biplane ellipsoidal formula, bullet formula (biplane only), and biapical Simpson's rule methods were utilized. Linear regression analysis showed the strongest correlation with the modified biplane Simpson's rule (mean r = 0.897). In valvular heart disease (n = 12) and dilated cardiomyopathy (n = 6), the mean correlation coefficients for all methods were high (r = 0.894 and 0.911, respectively). The mean correlation coefficient for all methods in patients with prior myocardial infarction (n = 25) was relatively poor (r = 0.643). Intraobserver and interobserver variabilities for all methods were low (r = 0.980 and 0.965, respectively). It is concluded that calculations of left ventricular volumes and mass by two-dimensional echocardiography are accurate and reproducible in patients with a global effect on the left ventricle and were less acceptable in patients with segmental (ischemic) left ventricular involvement. The best measurement technique is a modified biplane Simpson's rule.

Automated myocardial edge detection from breath-hold cine-MR images: evaluation of left ventricular volumes and mass

This paper describes an automated edge detection method for the delineation of the endo- and epicardial borders of the left ventricle from magnetic resonance (MR) images. The feasibility of this technique was demonstrated by processing temporal series of cardiac MR images obtained in 12 healthy subjects and acquired from the apex to the base of the heart in multiple anatomic short axis planes with a breath-hold cine-MR acquisition sequence. This procedure allows the entire heart to be imaged in less than 5 min. The automatic program correctly identified the edges in most cases. In poor contrasted images, a fast and user-friendly interactive procedure was used to correct the border delineation. The proposed method for the contour tracing requires a limited degree of control by the user and thus considerably reduces the tedious and long operator time inherent in the usual manual contour tracing tool. The left ventricular volumes were directly measured from these sets of contours by using the Simpson rule, allowing the end-diastolic volumes (EDV), the end-systolic volumes (ESV), the ejection fraction (EF) and the myocardial mass to be determined. The values measured in this study with the dedicated software were similar to the literature values (EDV = 78.3 ml/m2; ESV = 21.1 ml/m2; EF = 73%). Associated with the ultrafast breath-hold cine-MR imaging, the described edge detection method provides an efficient clinical tool for the direct assessment of cardiac function.

Evaluation of left ventricular mass: comparison of ultrafast computed tomography, magnetic resonance imaging, and contrast left ventriculography

We measured and compared left ventricular mass in 20 patients by ultrafast computed tomography (UFCT), magnetic resonance imaging (MRI), and contrast left ventriculography (LVG). Left ventricular mass was calculated by UFCT and MRI in two ways: (1) excluding papillary muscles and trabeculae (LV mass), and (2) including papillary muscles and trabeculae (LV mass + PM&T) by Simpson's method. Left ventricular mass excluding papillary muscles and trabeculae (LV mass) in LVG was calculated by Rackley's method by biplane angiocardiography. LV mass was significantly larger in LVG than in MRI and UFCT (p < 0.01). Although LV mass was significantly larger in MRI than in UFCT (p < 0.01), there was no significant difference in LV mass + PM&T between UFCT and MRI. Interobserver and intraobserver variability showed good correlation of coefficient in both UFCT and MRI. We therefore conclude that left ventricular mass is best measured by including papillary muscles and trabeculae by Simpson's method in UFCT or MRI.

Right ventricular dilatation and remodeling the first year after an initial transmural wall left ventricular myocardial infarction

Left ventricular (LV) remodeling after LV myocardial infarction was described previously. Little is known regarding concomitant adaptation, if any, in right ventricular (RV) volumes after LV infarction. To examine this issue, cine-computed tomography was used to determine serial changes in absolute global LV and RV volumes in 27 patients without clinical heart failure during the first year after an initial Q-wave myocardial infarction (14 anterior and 13 inferior). The patient group with anterior wall LV infarction showed progressive increases in LV and RV volumes from hospital discharge to 1 year (end-diastolic volumes +25 and +13%, respectively; and end-systolic volumes +35 and +15%, respectively). In patients with inferior wall LV infarction, both LV end-diastolic and end-systolic volumes increased significantly during the study period (+13 and +15%, respectively). Despite a trend for RV end-diastolic volume to be increased at 1 year, neither end-diastolic nor end-systolic volume increased significantly after hospital discharge following inferior wall LV infarction. Absolute RV end-diastolic volume was not significantly different between the infarct groups at any time after infarction. In conclusion, global changes occur in both LV and RV volumes during the first year after an initial infarction regardless of infarct location. The magnitude of these changes was greater after anterior than inferior wall LV infarction.

Ultrasonic backscatter system for automated on-line endocardial boundary detection: evaluation by ultrafast computed tomography

OBJECTIVES

The purpose of this study was to evaluate the accuracy of the recently developed echocardiographic on-line endocardial border detection system using ultrafast computed tomography, an independent and proved tomographic imaging modality.

BACKGROUND

The automated system for on-line endocardial border detection identifies the blood-tissue interface by acoustic quantification of the ultrasonic backscatter signal.

METHODS

Eighteen subjects were screened by conventional echocardiography and acoustic quantification. Ten of these, with high quality echocardiographic images, were also examined by ultrafast computed tomography. Comparable image planes at the midpapillary level were analyzed. Measurements of left ventricular cavity area were compared at end-diastole and end-systole and time course analyses of cavity area during the cardiac cycle were performed.

RESULTS

There was good correlation between values for left ventricular end-diastolic area (r = 0.99), end-systolic area (r = 0.93) and fractional area change (r = 0.91) using the two methods. The on-line backscatter system underestimated end-diastolic area (p < 0.001), but the negative bias was small (-1.6 cm2) and the 95% confidence intervals were narrow (-3.6 cm2 to +0.4 cm2). In contrast, the backscatter system overestimated end-systolic area (p < 0.02); the positive bias for this variable was also small (+2.6 cm2) but the confidence intervals were relatively wide (+7.9 to -2.8 cm2). The negative bias of backscatter values for cavity area was fairly constant during diastole and early systole (range -5% to -10%), but during the second half of systole, backscatter values increased progressively relative to computed tomographic values. Real time values for fractional area change measured by the backscatter system were 13% smaller than those determined by ultrafast computed tomography (p < 0.001), with wide confidence intervals (+3% to -30%). Absolute peak rates of area change during systole and diastole were lower by 39% (p < 0.001) and 41% (p < 0.01), respectively, using the on-line ultrasonic backscatter system. Time course analyses revealed the errors to be consistent with cardiac cycle-dependent alterations in gain sensitivity of the ultrasonic backscatter system.

CONCLUSIONS

The ultrasonic backscatter system is associated with cyclic cavity area measurement errors that need to be addressed if its early promise for on-line assessment of ventricular function is to be fulfilled. Incorporation of an electrocardiographically triggered time-varying gain control may improve accuracy for on-line analysis of ventricular performance.

Variation in left ventricular regional wall stress with cine magnetic resonance imaging: normal subjects versus dilated cardiomyopathy

We measured the variation of end-systolic wall stress and its relation to regional ejection fraction in short-axis planes through the left ventricle in normal subjects and in patients with dilated cardiomyopathy (DCM) by cine magnetic resonance imaging. There was a gradual increase in end-systolic wall stress but a gradual decrease in ejection fraction from apex to base in normal subjects (14 +/- 6 to 52 +/- 15 kdyne/cm2, 78% +/- 12% to 62% +/- 8%) and in patients with DCM (49 +/- 28 to 130 +/- 30 kdyne/cm2, 40 +/- 18 to 23% +/- 9%). The end-systolic wall stress in patients with DCM was higher than in normal subjects at every level (p < 0.01). We conclude that there is a variation in end-systolic wall stress in both normal subjects and patients with DCM with regional ejection fraction inversely related to regional end-systolic wall stress.

Nonparallel changes in global left ventricular chamber volume and muscle mass during the first year after transmural myocardial infarction in humans

OBJECTIVES

This study was designed to serially assess time-dependent changes in both chamber volume and myocardial muscle mass after infarction in humans.

BACKGROUND

Dilation of the left ventricular chamber has been previously described after transmural myocardial infarction.

METHODS

Global left ventricular chamber volumes and muscle mass were quantified by using cine computed tomographic scanning in 18 patients at hospital discharge and 6 weeks, 6 months and 1 year after an initial transmural myocardial infarction (12 anterior and 6 inferior). No patient had heart failure during the initial hospital stay or on any subsequent follow-up visit.

RESULTS

The patients with anterior myocardial infarction (estimated infarct extent 27 +/- 2% of left ventricle) demonstrated a progressive increase in left ventricular end-diastolic volume from 148 +/- 9 ml (mean +/- SEM) at hospital discharge to 180 +/- 9 ml at 1 year after infarction (p < 0.001). However, global left ventricular muscle mass decreased significantly during the 1st 6 weeks after infarction but returned by 1 year to nearly the value determined at hospital discharge (177 +/- 13 vs. 165 +/- 10 g, p = NS). The changes in global muscle mass did not parallel the steady and progressive increases in chamber end-diastolic volume. The end-diastolic chamber volume to muscle mass ratio, an index of global left ventricular wall tension, increased steadily after hospital discharge but remained level by 1 year after infarction. The time course of changes in global end-systolic chamber volume was roughly proportional to the concomitant changes in end-diastolic volume. During this same time period, left ventricular stroke volume remained constant or improved from that determined at baseline. Global left ventricular end-diastolic and end-systolic volumes remained relatively static during the 1st year in the patient subgroup with inferior wall myocardial infarction (estimated infarct extent 10 +/- 1% of left ventricle), but global muscle (myocardial) mass initially decreased and then increased in a pattern similar, although of smaller magnitude, to that observed in patients with anterior wall myocardial infarction.

CONCLUSIONS

Overall, left ventricular end-diastolic and end-systolic chamber volumes increase progressively from hospital discharge to 1 year after an initial transmural myocardial infarction in patients with a moderately large anterior wall infarction but remain stable in patients with a small inferior wall infarction. Concurrently, total left ventricular muscle mass decreases significantly during the initial 6 weeks after infarction (presumed largely secondary to changes in the necrotic segments) but then returns to the hospital discharge baseline values by 1 year. These data are consistent with the late development of, at most, limited ventricular hypertrophy in the noninfarcted myocardium that occurs well after the early and progressive left ventricular chamber dilation observed in patients with a moderate to large myocardial infarction. These data, in particular as applied to patients with anterior infarction, suggest that ventricular wall tension is significantly elevated at least during the 1st year after an initial transmural myocardial infarction. These observations may explain the potential utility of agents aimed at reducing afterload or ventricular wall tension during the early convalescent phase after myocardial infarction.

Ultrafast CT and the cardiovascular system

Ultrafast computed tomography (CT) is a new imaging technique that relies on electron beam technology. Its rapid image acquisition speeds make it ideal for evaluating the cardiovascular system. The high-resolution, flow, and cine-modes are unique and provide complimentary information about cardiovascular anatomy, function, and flow dynamics. Ultrafast CT can provide quantitative measurements of cardiac output, ejection fraction, ventricular volumes, and ventricular mass as well as evaluation of segmental cardiac function. This technique can be used to assess coronary artery bypass graft patency as well as to screen for coronary artery calcium. Intracardiac thrombus or tumor, valvular disease, and disorders of the pericardium can be evaluated and characterized using ultrafast CT. The diagnosis of congenital lesions of the heart and great vessels is facilitated by this imaging modality, which can help determine complex anatomic abnormalities and quantitate shunt lesions. Acquired lesions of the great vessels, such as aortic dissection and aneurysm, can be diagnosed by ultrafast CT, which can also be used for serial examination and conservative management.