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

Limitations in the current screening practice of assessing left ventricular ejection fraction for a primary prophylactic implantable defibrillator in southern Ontario

BACKGROUND

Screening echocardiography (ECHO) is commonly performed to determine whether the patient's left ventricular ejection fraction (LVEF) is appropriate for primary prophylactic implantable cardiac defibrillator (ICD) referral. However, radionuclide ventriculography (RNA) is used by many implantation centres for decision making.

OBJECTIVE

To determine whether current screening ECHO techniques are effective in identifying patients suitable for primary prophylactic ICD referral.

METHODS

Correlation, sensitivity, specificity and likelihood ratios (LRs) of semiquantitative and numerical quantitative ECHO LVEFs were calculated for predicting RNA LVEFs that met implantation criteria (LVEF less than 30% and less than 35%).

RESULTS AND DISCUSSION

Among 193 patients, the LRs for a semiquantitative ECHO predicting an RNA LVEF of less than 30% (negative LR was 0.21 to 0.69 and positive LR was 1.22 to 2.83) or RNA LVEF of less than 35% (negative LR was 0.24 to 0.73 and positive LR was 1.33 to 3.46) demonstrated that current screening ECHO techniques are ineffective. However, the positive predictive value of grade 4 ECHO was 93.0%, suggesting that these patients may not require further LVEF investigation before implantation. Among 102 patients, current quantitative ECHO techniques did not improve the screening characteristics.

CONCLUSIONS

Current screening ECHO techniques may not be adequate for screening patients for consideration of a primary prophylactic ICD, but a grade 4 ECHO finding has a high positive predictive value in meeting implantation LVEF criteria. Improved screening standards should increase the number of patients referred with appropriate LVEF for primary prophylactic ICD implantation.

Assessment of Cardiac Function Using Multidetector Row Computed Tomography

In patients with suspected or documented heart disease, a precise quantitative and qualitative assessment of cardiac function is critical for clinical diagnosis, risk stratification, management and prognosis. Cardiac CT is increasingly being used in diagnosis of coronary artery disease. Initially multi-detector row computed tomography (MDCT) was used chiefly for detecting coronary artery stenosis and assessment of cardiac morphology. Electron beam computed tomography has been shown to provide a highly accurate ejection fraction (+/-1%), with 50 ms image acquisition per image. Retrospective electrocardiographic gating allows for image reconstruction in any phase of the cardiac cycle. Thus, end systolic and end diastolic images can be produced to assess ventricular volumes and function. Despite lower temporal resolution than electron beam computed tomography, the ability of MDCT to assess ejection fraction is preserved. In the assessment of cardiac function, MDCT has been shown to be in good agreement with echocardiography, cineventriculography, single photon emission computed tomography and magnetic resonance imaging. The fast technical development of scanner hardware along with multisegmental image reconstruction has led to rapid improvement of spatial and temporal resolution and significantly faster cardiac scans. The same data that is acquired for MDCT angiography can also be used for evaluation of cardiac function. Considering contrast media application, radiation exposure, and limited temporal resolution, MDCT solely for analysis of cardiac function parameters seems not reasonable at the present time. However, because the data is already obtained during coronary evaluation, the combination of noninvasive coronary artery imaging and assessment of cardiac function with MDCT is a suitable approach to a conclusive cardiac workup in patients with suspected coronary artery disease. MDCT seems suitable for assessment of cardiac function by MDCT when results are held in comparison to magnetic resonance imaging as the reference standard. Given the radiation dose and contrast requirement, referring a patient to MDCT only for evaluation of function is not warranted, but rather adds important clinical information to the already acquired data during retrospective triggering for MDCT angiography.

Potential Indications for Coronary Angiography by Computed Tomography

Recent advances in computed tomography technology have made possible angiographic images of relatively small, moving vascular structures such as the coronary arteries. Computed tomographic coronary angiography is an exciting modality which has several obvious advantages over invasive catheterization, such as its relatively noninvasive nature and rapid speed of acquisition. However, significant drawbacks still exist, including limitations of spatial and temporal resolution and radiation exposure. Computed tomographic coronary angiography appears best suited as a diagnostic modality for the patient population with a low-to-moderate pretest probability of coronary artery disease, and for specific indications such as the imaging of coronary anomalies and bypass grafts and before biventricular pacemaker placement and atrial fibrillation ablation.

Quantification of Functional Mitral Valve Regurgitation in Patients With Congestive Heart Failure

OBJECTIVES

We sought to determine the agreement between electron-beam computed tomography (CT) and cardiac catheterization for the quantification of mitral regurgitation and to evaluate their association with echocardiographic assessment.

MATERIAL AND METHODS

Fifty patients with congestive heart failure were examined both by electron-beam CT and catheterization to calculate mitral regurgitation volume and fraction based on the difference between the left ventricular stroke and aortic flow volume. The severity of regurgitation was also compared with visual assessment by echocardiography (grade, 0-4+).

RESULTS

The mean values for the mitral regurgitation volume and fraction did not differ significantly between electron-beam CT and catheterization (mean differences: 0.2 mL/m2 and -0.9%, P > 0.05 each, limits of agreement: -14.0 to 14.4 mL/m2 and -26.3 to 24.5%, respectively) and showed a good correlation (r = 0.79 and r = 0.76, respectively; P < 0.05 each). Good levels of correlation were observed between echocardiographic severity grading and quantitative measurements of regurgitation volume and fraction, which were somewhat better between echocardiography and electron-beam CT (rS = 0.78 and rS = 0.84, respectively; P < 0.05 each) than between echocardiography and catheterization (rS = 0.72 and rS = 0.81, respectively; P < 0.05 each).

CONCLUSION

Our results suggest that electron-beam CT allows for quantification of mitral valve regurgitation with similar accuracy as cardiac catheterization. Measurements with both modalities correlated well with the results of echocardiographic assessment.

Comparison of Electron Beam Computed Tomography With Magnetic Resonance Imaging in Assessment of Right Ventricular Volumes and Function

OBJECTIVE

Intraindividual comparison of right ventricular volumes and function using electron beam computed tomography (EBT) and magnetic resonance imaging (MRI).

METHODS

Twenty-seven patients with a known cardiac history were referred for evaluation of ventricular function parameters. The following standardized protocols were used: contrast-enhanced multislice mode EBT and gradient echo sequence MRI. Right ventricular end-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), and ejection fraction (EF) were calculated using a slice summation method. Interobserver variability was calculated.

RESULTS

The correlation between the 2 methods was: r = 0.901 for EDV, r = 0.938 for ESV, r = 0.823 for SV, and r = 0.953 for EF. Electron beam computed tomography overestimated EDV and ESV slightly when compared with MRI (P < 0.05). No significant differences (P > 0.05) were found between SV and EF. Mean values determined by EBT and MRI were as follows: 168.6 +/- 62.3 mL and 153.7 +/- 59.1 mL for EDV, 104.7 +/- 60.4 mL and 95.1 +/- 54.8 mL for ESV, 63.2 +/- 19.3 mL and 58.7 +/- 19.8 mL for SV, and 40.2% +/- 14.1% and 40.2% +/- 13.6% for EF, respectively. Interobserver variability ranged between 1.0% and 3.2%.

CONCLUSION

Electron beam computed tomography shows good agreement with a close correlation and an acceptable interobserver variability for right ventricular volumes and global function, with a small but significant overestimation of EDV and ESV when compared with MRI.

Comparison of LV mass and volume measurements derived from electron beam tomography using cine imaging and angiographic imaging

PURPOSE

To estimate the variation of left ventricular (LV) mass and volume measurement with cine and angiography by electron beam tomography (EBT).

METHOD AND MATERIALS

Sixty-three consecutive patients (41 men, 22 women; age range 46-91) referred for cardiac imaging for clinical indications underwent cine and coronary artery electron beam angiography (EBA) studies on the same day. The cine images consisted of 144 images (12 slices/level x 12 levels), taken 12 frames/s for a full cardiac cycle. The EBA images consisted of 50-70 slices triggered at end-systole, with an acquisition time of 100 ms/slice. Slice thickness was 8 mm for the cine images and 1.5 mm for the EBA images. A total volume of 120-180 ml of nonionic contrast was used for each subject. The LV mass (myocardial tissue volume), LV cavity volume and total LV volume (tissue + cavity) measurements were completed using the software from the EBT computer console (G.E., S. San Francisco, CA).

RESULTS

The LV mass, cavity volume and total LV volumes at end-systole were 124.11 g, 45.66 and 163.86 ml when derived from the cine images and 130.74 g, 41.31 and 165.82 ml when derived from the EBA images. There were no significant differences between the cine and EBA-derived measurements, however the EBA-derived measurements showed slightly larger LV mass (mean 6.63 g), smaller cavity volume (mean -4.35 ml) and larger total LV volume (mean 1.96 ml, all p > 0.05) than did the cine-derived measurements. Based on case-by-case observations, these differences appear to be related to the higher spatial resolution of the thinner EBA images which allows better discrimination between papillary and trabecular muscle and LV. This leads to slightly smaller cavity size estimations and greater LV mass measurements. There was significant correlation between cine and EBA-derived measurements. Formulas were developed for relating the measurements made from the two modalities as follows: For LV mass: EBA value = 0.91 x cine value + 17.09, R = 0.95, p < 0.001; For LV cavity volume: EBA value = 1.06 x cine value - 6.91, R = 0.96, p < 0.001; For total LV volume: EBA value = 0.98 x cine value + 5.09 in ml, p < 0.001. The mean differences in measurements using the two modalities were 8.1, 18.2 and 6.5% for LV mass, LV cavity volume and total LV volume, respectively.

CONCLUSION

Both cine and EBA images were useful for measuring LV mass and volume with good intertest agreement. Cardiac volume and mass measurements derived from cine EBT studies probably slightly underestimate LV mass and overestimate LV volume.

Transitions: noninvasive coronary angiography using electron beam computed tomography: technique, clinical application, future prospective

Electron beam computed tomography has been available clinically for 20 years. It is the only computed tomography scanner specifically developed for cardiac imaging. Over the past decade, with improvements in methodology and computer software, electron beam computed tomography has been shown to provide an excellent method to perform noninvasive coronary angiography. This article looks at the historical aspects of electron beam computed tomography and comments on how to perform and interpret electron beam angiography studies. The expanding development of noninvasive coronary and peripheral angiography methods using computed tomography will have a significant influence on cardiovascular specialists and their practices.

Clinical utility of computed tomography and magnetic resonance techniques for noninvasive coronary angiography

OBJECTIVE

The purpose of this study was to provide a comprehensive review of the literature relating to electron beam angiography (EBA), magnetic resonance angiography, and spiral computed tomography, currently the three most promising noninvasive methods to visualize obstructions in the coronary tree.

BACKGROUND

Given the high costs and invasiveness of coronary angiography, there is increased interest in noninvasive coronary angiography, which has made great strides to become a clinically useful tool to augment conventional coronary angiography (CCA).

METHODS

MEDLINE searches were performed to include all articles related to noninvasive angiography utilizing either magnetic resonance imaging (MRI), multi-row detector spiral computed tomography (MDCT), and electron beam tomography (EBT). Weighted analysis was performed to define the published sensitivity and specificity for each technique.

RESULTS

Electron beam angiography (EBA) provides an overall sensitivity of 87% and specificity of 91% for the detection of obstructive coronary artery disease (CAD). Four-level MDCT data demonstrated an overall sensitivity of 59% and specificity of 89%, with higher accuracy in two recent studies of 16-level detector devices. Magnetic resonance angiography demonstrated sensitivity for detection of obstructive CAD of 77% and specificity of 71%.

CONCLUSIONS

Noninvasive coronary angiography is a rapidly developing technique and currently not an alternative to CCA in all cases. All three methods are currently used clinically in certain centers with appropriate expertise. Selective use should prove both cost-effective and provide a safer, less-invasive method for patients to determine the need for medical versus revascularization therapy.

Measurement of cardiac output from a test-bolus injection in multislice computed tomography

The aim of this study was to assess the feasibility of non-invasive determination of cardiac function from test-bolus data in multislice spiral computed tomography (MSCT). In 25 patients enhancement data gathered from a standardized test-bolus injection were analyzed. The test-bolus examination was performed prior to a retrospectively ECG-gated MSCT of the heart. A time-attenuation curve was obtained in the ascending aorta at the level of the pulmonary arteries. A gamma variate fit was applied to the curve in order to exclude recirculation and get pure first-pass data. Using the known amount of iodine injected, cardiac output (CO), and stroke volume (SV) were determined from integration of the fitted contrast enhancement curve using a reformation of the Stewart-Hamilton equation. Results were compared with CO and SV calculated from the geometric analysis of the retrospectively gated MSCT data using the ARGUS Software (Siemens, Forchheim, Germany). The CO and SV determined from test-bolus analysis and from geometric analysis correlated well with Pearson's correlation coefficients of 0.87 and 0.88, respectively. The standard deviation of the difference between both methods was 0.51 l/min for CO (8.6%) and 11.0 ml for SV (12.3%). Non-invasive quantification of CO seems to be feasible from a standard test-bolus injection. It provides valuable information on cardiac function without additional radiation or application of contrast material.