Exercise ultrafast computed tomography for the detection of coronary artery disease

Coronary artery motion during the cardiac cycle and optimal ECG triggering for coronary artery imaging

RATIONALE AND OBJECTIVES

Our purpose was to investigate the motion characteristics of the coronary arteries and determine optimal electrocardiographic (ECG) trigger time during the cardiac cycle to minimize motion artifacts.

METHODS

Contrast-enhanced multislice movie studies of electron beam tomography (EBT) images were performed on 70 subjects. The EBT datasets, which covered an entire cardiac cycle at 58-ms intervals, were acquired for a short-axis view of the heart with ECG triggering. The pixel values along x and y axes were measured at multiple intervals during the cardiac cycle to establish the motion distance and velocity of three major coronary arteries.

RESULTS

Coronary artery motion varied greatly throughout the cardiac cycle in three major coronary arteries and increased with the patient's baseline heart rate. The greatest and lowest velocities of coronary arterial movement during the cardiac cycle were determined. Based on the lowest velocity of right coronary artery movement during the cardiac cycle, the optimal ECG trigger times were located at approximately 35% (31.4%-37.6%) or 70% (68.7%-71.4%) of the R-R interval in patients whose resting heart rate was < or =70 beats per minute (bpm); at 50% (47.2%-61.1%) of the R-R interval in the 71- to 100-bpm group; and at 55% (52.8%-59.1%) of the R-R interval in the >100-bpm group. Our data demonstrated that the motion characteristics of the left circumflex artery were quite similar to those of the right coronary artery and that the left anterior descending coronary artery had no significant differences in motion throughout the cardiac cycle. A minimum scan speed of 35.4 to 75.5 ms per slice is needed to completely diminish cardiac motion artifacts (in-plane coronary artery motion with <1-mm displacement).

CONCLUSIONS

For coronary artery screening, the optimal ECG trigger time should be determined according to the patient's heart rate, thus greatly reducing motion and motion artifacts during 100-ms acquisitions.

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.

Coronary artery motion in electron beam tomography

PURPOSE

The purpose of this work was to evaluate coronary artery motion characteristics and determine optimal electron beam tomography (EBT) scan time during the cardiac cycle to image the coronary arteries.

METHOD

This study evaluated the movement of coronary arteries in 20 EBT cine studies, at rest and during stress, obtained for evaluating coronary artery disease. The proximal, middle, and distal segments of each coronary artery were measured at multiple times during the cardiac cycle. The motion distance (mm) and velocity (mm/s) of each segment of the coronary arteries were then measured to establish the motion that occurs in the x and y axes during different times in the cardiac cycle.

RESULTS

Coronary artery velocity ranged from 22.4 to 108.6 mm/s. The least motion (and slowest speed) occurred between 30-50 and 40-60% of the R-R interval at rest and stress, respectively. The right coronary artery moved the greatest in the x and y planes (highest speed and spatial change), followed in decreasing order by the circumflex, left main, and left anterior descending arteries. The phase of the cardiac cycle with the greatest coronary artery motion was between 0 and 20% of the R-R interval.

CONCLUSION

Coronary artery motion varies greatly throughout the cardiac cycle. To minimize cardiac motion during tomographic imaging of the coronary arteries, we recommend 40-50% R-R interval as an electrocardiographic trigger time and avoiding the use of image acquisition times of >100 ms.

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.

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.

Understanding right and left ventricular systolic function and interactions at rest and with exercise in primary pulmonary hypertension

The effort limitation in primary pulmonary hypertension (PPH) is thought to result from an inability to increase cardiac output with exercise. The precise mechanism, however, is unknown. We studied right ventricular (RV) and left ventricular (LV) function and interactions in 16 patients with PPH with electron beam computed tomography (EBCT) at rest and during supine bicycle exercise. RV and LV volumes and masses were measured at systole and diastole, and ejection fraction and cardiac index computed. Resting RV end-diastolic volume (215 +/- 72 ml) and mass (110 +/- 45 g) were increased, whereas stroke volume (65 +/- 26 ml) and ejection fraction (31 +/- 8%) were decreased. LV end-diastolic volume (80 +/- 31 ml) was decreased, whereas ejection fraction remained normal (66 +/- 9%). Cardiac index was at the lower limit of normal (2.26 +/- 0.72 L/min/m2). During exercise, RV end-diastolic volume was unchanged (196 +/- 63 ml, p = NS) but stroke volume (52 +/- 29 ml, p < 0.05) and ejection fraction (26 +/- 10%, p = 0.08) decreased. LV end-diastolic (52 +/- 22 ml, p < 0.001), end-systolic (17 +/- 8 ml, p < 0.001), and stroke volumes (35 +/- 20 ml, p < 0.001) decreased, whereas ejection fraction (65 +/- 15%, p = NS) and cardiac index remained unchanged (2.17 +/- 0.93 L/min/m2, p = NS). the ratio of RV/LV stroke volume at rest (1.21 +/- 1.06) increased with exercise (1.74 +/- 1.13, p = 0.09).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Left ventricular wall motion analysis in patients with acute myocardial infarction using magnetic resonance imaging

Dynamic magnetic resonance (MR) imaging of the left ventricle was performed in 13 patients with acute myocardial infarction and in 11 healthy volunteers. Visual assessment of cine MR video loops correctly located the infarction of 12 of 13 patients. Quantitative analysis of absolute and relative wall thickening, area ejection fraction, and radial shortening fraction accurately distinguished hearts with and without infarction (p < .001). This distinction could also be made using the number of segments with decreased and the number of segments with decreased + increased wall motion (p < .001). Localization of the infarction by quantitative MR methods was limited, probably due to relative low temporal resolution. Combined evaluation of qualitative and quantitative MR imaging data provides useful information on wall motion dynamics after acute 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.

Noninvasive definition of anatomic coronary artery disease by ultrafast computed tomographic scanning: a quantitative pathologic comparison study

OBJECTIVES

The aim of this study was to determine the relation between coronary artery calcification detected by ultrafast computed tomographic scanning and histopathologic coronary artery disease.

BACKGROUND

Recent studies suggest that discrete coronary artery calcification as visualized by ultrafast computed tomographic scanning may facilitate the noninvasive detection or estimation, or both, of the in situ extent of coronary disease. Such quantitative relations have not been established.

METHODS

Thirteen consecutive perfusion-fixed autopsy hearts (from eight male and five female patients aged 17 to 83 years) were scanned by ultrafast computed tomographic scanning in contiguous 3-mm tomographic sections. The major epicardial arteries were dissected free, positioned longitudinally and scanned again in cross section. Coronary artery calcification in a coronary segment was defined as the presence of one or more voxels with a computed tomographic density > 130 Hounsfield units. Each epicardial artery was sectioned longitudinally, stained and measured with a planimeter for quantification of cross-sectional and atherosclerotic plaque areas at 3-mm intervals, corresponding to the computed tomographic scans. A total of 522 paired coronary computed tomographic and histologic sections were studied.

RESULTS

Direct relations were found between ultrafast computed tomographic scanning coronary artery calcium burden and atherosclerotic plaque area and percent lumen area stenosis. However, the range for plaque area or percent lumen stenosis, or both, associated with a given calcium burden was broad. Three hundred thirty-one coronary segments showed no calcification by computed tomography. Although atherosclerotic disease was found in several corresponding pathologic specimens, > 97% of these noncalcified segments were associated with nonobstructive disease (< 75% area stenosis); if no calcification was determined in an entire coronary vessel, all corresponding coronary disease was found to be nonobstructive. To determine the relation between arterial calcification and any atheromatous disease, computed tomographic calcium burden for each segment was paired with the histologic absence or presence of disease. Ultrafast computed tomographic scanning had a sensitivity and specificity of 59% and 90% and a negative and positive predictive value of 65% and 87%, respectively. A direct correlation was found (r = 0.99) between total calcium burden calculated from tomographic scans of the heart as a whole and scans of the arteries obtained in cross section.

CONCLUSIONS

The detection of coronary calcification by ultrafast computed tomographic scanning is highly predictive of the presence of histopathologic coronary disease, but the use of this technique to define the extent of coronary disease may be limited. However, the absence of coronary calcification at any site is highly specific for the absence of obstructive disease.

Magnetic resonance imaging vs. ultrafast computed tomography for cardiac diagnosis

Ultrafast computed tomography (CT) and magnetic resonance imaging (MRI) generate high resolution tomographic cardiac images. Ultrafast CT requires intravenous injection of x-ray contrast combined with an image acquisition time of 50 msec. MRI requires no contrast injection, but has relatively long acquisition times due to gating. Both technologies can be used to evaluate cardiac chamber and great vessel dimensions, intracardiac and extracardiac masses, ventricular hypertrophy, left ventricular mass, congenital heart disease, regional and global left ventricular function, right ventricular function and pericardium. MRI is highly useful for detection and semi-quantitation of valvular regurgitation while ultrafast CT is not. Aortic and mitral valve stenosis can be detected by both, but MRI is the preferred study. Though both techniques can be used to assess coronary artery bypass graft status, ultrafast CT is the preferred method. It is concluded that ultrafast CT and MRI have broad applications for cardiac diagnosis.

Patterns of global and regional systolic and diastolic function in the normal right ventricle assessed by ultrafast computed tomography

A detailed evaluation of global and regional systolic function and diastolic filling of the human right ventricle has not been previously reported. Ultrafast computed tomography enables simultaneous imaging of the right and left ventricles at an 8 mm slice thickness with a scanning rate of 17 frames/s (50 ms acquisition intervals). In 10 normal men (mean age 26 +/- 4 years) early diastolic filling data were fit to a third order polynomial curve and the peak rate of diastolic filling and time to peak filling were determined globally and regionally at three distinct ventricular levels (apex to base) within each ventricle. The right and left ventricular stroke volumes were not statistically different (89 +/- 8 ml and 90 +/- 8 ml, p = NS), neither were the peak filling rates as referenced to the stroke volume (4.9 +/- 0.9 and 5.3 +/- 0.8 stroke volumes/s, p = NS). Time to peak filling rate was not different between the two ventricles (154 +/- 33 and 161 +/- 18 ms, p = NS). However, reference of stroke volumes and absolute peak filling rates to end-diastolic volumes demonstrated lower dynamic values for the right ventricle (ejection fraction: right ventricle 57 +/- 4%; left ventricle 68 +/- 5%, p less than 0.05, and peak filling rate: right ventricle 2.7 +/- 0.4 end-diastolic volumes/s; left ventricle 3.6 +/- 0.5, p less than 0.05, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Doppler echocardiography and ultrafast cine computed tomography during dynamic exercise in chronic parenchymal pulmonary disease

In an effort to better understand the cardiac contribution to exercise limitation in chronic lung disease, 21 patients with advanced chronic pulmonary parenchymal disease and 10 normal control subjects were evaluated for changes in right ventricular (RV) pressure, volume and function during incremental, symptom-limited supine bicycle exercise. Patients underwent sequential exercise tests with Doppler echocardiography and ultrafast cine computed tomography (CT). RV systolic pressure during exercise was determined by saline-enhanced Doppler of tricuspid regurgitation. RV ejection fraction, end-diastolic volume, stroke volume and cardiac index were obtained by CT at rest and peak exercise. Sixteen of the 21 study patients also exercised on high-flow oxygen. In the control subjects RV systolic pressure increased from 21 +/- 6 mm Hg (mean +/- standard deviation) at rest to 32 +/- 8 mm Hg at peak exercise, whereas in patients with lung disease, RV systolic pressure increased from 42 +/- 17 to 81 +/- 26 mm Hg (both p less than 0.01). Compared with the control subjects, the patients with lung disease had significantly lower mean values for RV ejection fraction at rest (47 +/- 7 vs 55 +/- 7%) and at peak exercise (47 +/- 9 vs 57 +/- 3%, respectively, both p less than 0.05). The patients who demonstrated oxyhemoglobin desaturation during exercise showed the most abnormal cardiac responses, with marked increases in mean RV systolic pressure, decreases in mean RV ejection fraction and blunted increases in cardiac index and RV stroke volume. Although acute oxygen supplementation was associated with a slight decrease in RV systolic pressure at peak exercise and a longer duration of exercise, there was no significant improvement in RV function. Doppler echocardiography and CT provide complementary and potentially useful information about right-sided heart pressures and RV ejection fraction during exercise in patients with advanced chronic lung disease. Oxyhemoglobin desaturation during exercise is a marker for the most abnormal pulmonary vascular reserve, as indicated by RV contractile dysfunction and limited ability to increase cardiac index.

Patterns of regional diastolic function in the normal human left ventricle: an ultrafast computed tomographic study

The detailed evaluation of regional diastolic filling at multiple ventricular levels in the normal human left ventricle has not previously been reported. Ultrafast computed tomography was used to characterize global and regional early diastolic filling in the left ventricle of 11 normal male volunteers. Regional early diastolic filling data from six distinct ventricular levels (apex to base) were fit to a third-order polynomial curve, and the peak rate of diastolic filling and time of peak filling were determined. Peak filling rate was 259 +/- 17 ml/s (+/- SEM) as a global average, where peak filling rate referenced to end-diastolic volume and stroke volume across the levels examined was 3.78 +/- 0.17 s-1 and 4.83 +/- 0.20 s-1, respectively. Average filling fraction was 39 +/- 1%, and time to peak filling from end-systole was 145 +/- 5 ms. Regional (tomographic) peak filling rates, except for the most apical level examined, were not statistically different across the ventricle. Filling fraction and time to peak filling were remarkably constant from one level to another. However, reference of regional peak filling rate to regional end-diastolic volume demonstrated significant nonuniformity from apex (120% of average for all levels) to base (87% of average for all levels). Peak filling rate referenced to tomographic stroke volume was less variable and not statistically different across the ventricle as a whole.(ABSTRACT TRUNCATED AT 250 WORDS)