Warren R. Janowitz

Ultrafast Computed Tomography as a Diagnostic Modality in the Detection of Coronary Artery Disease: A Multicenter Study

BACKGROUND Ultrafast computed tomography (CT), by acquiring images of the proximal coronary arteries, detects coronary calcifications and has been demonstrated to be highly sensitive for the detection of coronary artery disease in many small studies. The aim of this study was to determine the relationship between ultrafast CT scanning and coronary angiography in a large number of symptomatic patients. METHODS AND RESULTS The study population consisted of 710 patients from six participating centers. A multivariate logistic regression model was used to evaluate the individual contributions of age, number of calcified vessels, and the calcium score for the probability of angiographically significant disease. Of the 710 patients enrolled, 427 patients had significant angiographic disease, and coronary calcification was detected in 404, yielding a sensitivity of 95%. Of the 23 patients without calcifications, 19 (83%) had single-vessel disease at angiography. Of the 283 patients without angiographically significant disease, 124 had negative ultrafast CT coronary studies, for a specificity of 44%. An increasing number of vessels with calcification present on ultrafast CT was found to increase specificity for the presence of obstructive coronary artery disease in at least one vessel (P < .0001). As the log of the calcium score increases, the probability of multivessel obstructive disease increases (P < .0001). CONCLUSIONS Ultrafast CT scanning is an noninvasive, non-exercise-dependent test with an excellent sensitivity for the detection of coronary artery disease. The presence of calcifications in multiple vessels and in younger populations correlates with higher specificities for obstructive disease, making ultrafast CT coronary scanning a very useful diagnostic test.

Differences in prevalence and extent of coronary artery calcium detected by ultrafast computed tomography in asymptomatic men and women

Coronary artery calcium is a marker of atherosclerosis in asymptomatic subjects. Ultrafast computed tomography (CT) can detect and quantify coronary calcium, simply and noninvasively, with greater sensitivity than can other techniques. The prevalence and extent of coronary calcium in a large population of asymptomatic men and women were measured and compared. Coronary calcium studies were performed in an asymptomatic population of 1,396 male and 502 female subjects (age range 14 to 88 years). The prevalence of calcium, and the distribution of total calcium scores (which reflect the amount of calcium present) were determined and compared for men and women at 5- and 10-year intervals. The prevalence of calcium in women was half that of men, until the age of 60 years when the difference diminished. The mean total calcium score distributions of men between the ages of 40 and 69 years were virtually identical to those of women between the ages of 50 and 79. The quantitative data obtained by Ultrafast CT showed very close agreement with autopsy studies of coronary calcium. Ultrafast CT is a sensitive technique to measure coronary calcium in both men and women. The differences in prevalence and extent of coronary calcium appear to be parallel to those observed in the clinical incidence of coronary artery disease in men and women. Ultrafast CT may have a greater impact on the treatment of women than of men, because it can be used to provide objective evidence of coronary atherosclerosis.

Triage of patients presenting with chest pain to the emergency department: implementation of coronary CT angiography in a large urban health care system.

OBJECTIVE There is growing evidence supporting the use of coronary CT angiography (CTA) to triage patients in the emergency department (ED) with acute chest pain and low risk of acute coronary syndrome (ACS). We hypothesized that coronary CTA can guide early management and safely discharge patients by introducing a dedicated patient management protocol. SUBJECTS AND METHODS We conducted a prospective cohort study in three EDs of a large health care system (> 1300 beds). Five hundred twenty-nine patients (mean age, 52.1 years; 56% women) with chest pain, negative cardiac enzyme results, normal or nondiagnostic ECG findings, and a thrombolysis in myocardial infarction (TIMI) risk score of 2 or less were admitted and underwent CTA. A new dedicated chest pain triage protocol (levels 1-5) was implemented. On the basis of CTA findings, patients were stratified into one of the following four groups: 0, low (negative CTA findings); 1, mild (1-49% stenosis); 2, moderate (50-69% stenosis); or 3, severe (≥ 70% stenosis) risk of ACS. Outcome measures included major adverse cardiac events (MACEs) during the first 30 days after CTA, downstream testing results, and length of stay (LOS). LOS was compared before and after implementation of our chest pain triage protocol. RESULTS Three hundred seventeen patients (59.9%) with negative CTA findings and 151 (28.5%) with mild stenosis were discharged from the ED with a very low downstream testing rate and a very low MACE rate (negative predictive value = 99.8%). Twenty-five patients (4.7%) had moderate stenosis (n = 17 undergoing further testing). Thirty-six patients (6.8%) had stenosis of 70% or greater by CTA (n = 34 positive by invasive angiography or SPECT-myocardial perfusion imaging). The sensitivity of CTA was 94%. The rate of MACEs in patients with stenosis of 70% or greater (8.3%) was significantly higher (p < 0.001) than in patients with negative CTA findings (0%) or those with mild stenosis (0.2%). A 51% decrease in LOS-from 28.8 to 14.0 hours--was noted after implementation of the dedicated chest pain protocol (p < 0.001). CONCLUSION Chest pain patients with negative or mild nonobstructive CTA findings can be safely discharged from the ED without further testing. Implementation of a dedicated chest pain triage protocol is critical for the success of a coronary CTA program.

Current status of mechanical computed tomography in cardiac imaging

Mechanical computed tomography (CT) scanners have undergone significant improvements in their ability to perform cardiac imaging. Previously limited by cardiac motion artifacts and slow acquisition speeds, newer-generation scanners are able to obtain multiple slices with a temporal resolution of <100 msec, minimizing motion artifacts to levels comparable to electron-beam computed tomography (EBCT). This is done using various approaches, including (1) prospective and retrospective electrocardiographic gating, (2) multislice detectors, and (3) partial and segmented reconstruction algorithms. The major CT manufacturers are putting significant resources into protocol optimization and cardiac applications development, including coronary calcium quantification, functional analysis, and coronary CT angiography. Given the rapid pace of development, higher in-plane and z-axis spatial resolution, and superior signal-to-noise ratio of mechanical scanners, it is evident that they will be capable of performing cardiac imaging with a quality approaching or possibly surpassing that of existing EBCT scanners. This article summarizes the current status of mechanical CT scanners in cardiac imaging.

Cardiovascular Risk Factors and Coronary Atherosclerosis in Retired National Football League Players

A high prevalence of obesity exists in National Football League (NFL) players as determined by body mass index (BMI). It is not established whether increased BMI is associated with a greater prevalence of cardiovascular (CV) risk factors or coronary atherosclerosis in former NFL players than in nonathletes. This study compared CV risk factors and coronary atherosclerosis in retired NFL players to 2 groups of community controls, the population-based Dallas Heart Study and the preventive medicine cohort, the Aerobics Center Longitudinal Study. Retired NFL players (n = 201) were matched for ethnicity, age, and BMI (Aerobics Center Longitudinal Study, age only). CV risk factors were assessed by survey and screening visit. Coronary atherosclerosis was measured by computed tomography as coronary artery calcium (CAC). Compared to population-based controls, retired NFL players had a significantly lower prevalence of diabetes, hypertension, sedentary lifestyle, and metabolic syndrome, yet a higher prevalence of impaired fasting glucose and hyperlipidemia. However, there was no significant difference in the prevalence of detectable CAC (46% vs 48.3%, p = 0.69) or distribution of CAC (0 to 10, 10 to 100, 100 to 400, > or =400, p = 0.11). Comparing retired NFL players to the physically active preventive medicine controls, there was no difference in the amount of CAC. In retired NFL players, age and hyperlipidemia, not body size, were the most significant predictors of CAC. In conclusion, despite their large body size, retired NFL players do not have a greater prevalence of CV risk factors or amount of CAC than community controls.

A Noninvasive Technique for the Study of Cardiac Hemodynamics Utilizing C15O2 Inhalation1

A new technique for the study of cardiac hemodynamics is described which utilizes single-breath inhalation of C15O2 (T 1/2 = 124 sec.) and the recording of activity vs. time curves with scintillation counters placed externally over the left ventricle and right lung. The results from 10 normal volunteers and 28 patients with acquired or congenital heart disease have been compared to the findings at cardiac catheterization. The technique is safe, rapid, and nontraumatic, and yielded no false positives or negatives in this series.

Volumetric Single-Beat Coronary Computed Tomography Angiography: Relationship of Image Quality, Heart Rate, and Body Mass Index. Initial Patient Experience With a New Computed Tomography Scanner.

Background Cardiac computed tomography (CT) image quality (IQ) is very important for accurate diagnosis. We propose to evaluate IQ expressed as Likert scale, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR) from coronary CT angiography images acquired with a new volumetric single-beat CT scanner on consecutive patients and assess the IQ dependence on heart rate (HR) and body mass index (BMI). Methods We retrospectively analyzed the data of the first 439 consecutive patients (mean age, 55.13 [SD, 12.1] years; 51.47% male), who underwent noninvasive coronary CT angiography in a new single-beat volumetric CT scanner (Revolution CT) to evaluate chest pain at West Kendall Baptist Hospital. Based on patient BMI (mean, 29.43 [SD, 5.81] kg/m2), the kVp (kilovolt potential) value and tube current were adjusted within a range of 80 to 140 kVp and 122 to 720 mA, respectively. Each scan was performed in a single-beat acquisition within 1 cardiac cycle, regardless of the HR. Motion correction software (SnapShot Freeze) was used for correcting motion artifacts in patients with higher HRs. Autogating was used to automatically acquire systolic and diastolic phases for higher HRs with electrocardiographic milliampere dose modulation. Image quality was assessed qualitatively by Likert scale and quantitatively by SNR and CNR for the 4 major vessels right coronary, left main, left anterior descending, and left circumflex arteries on axial and multiplanar reformatted images. Values for Likert scale were as follows: 1, nondiagnostic; 2, poor; 3, good; 4, very good; and 5, excellent. Signal-to-noise ratio and CNR were calculated from the average 2 CT attenuation values within regions of interest placed in the proximal left main and proximal right coronary artery. For contrast comparison, a region of interest was selected from left ventricular wall at midcavity level using a dedicated workstation. We divided patients in 2 groups related to the HR: less than or equal to 70 beats/min (bpm) and greater than 70 bpm and also analyzed them in 2 BMI groupings: BMI less than or equal to 30 kg/m2 and BMI greater than 30 kg/m2. Results Mean SNR was 8.7 (SD, 3.1) (n = 349) for group with HR 70 bpm or less and 7.7 (SD, 2.4) (n = 78) for group with HR greater than 70 bpm (P = 0.008). Mean CNR was 6.9 (SD, 2.7) (n = 349) for group with HR 70 bpm or less and 5.9 (SD, 2.2) (n = 78) for group with HR 70 bpm or greater (P = 0.002). Mean SNR was 8.8 (SD, 3.2) (n = 249) for group with BMI 30 kg/m2 or less and 8.1 (SD, 2.6) (n = 176) for group with BMI greater than 30 kg/m2 (P = 0.008). Mean CNR was 7.0 (SD, 2.8) (n = 249) for group with BMI 30 kg/m2 or less and 6.4 (SD, 2.4) (n = 176) for group with BMI greater than 30 kg/m2 (P = 0.002). The results for mean Likert scale values were statistically different, reflecting difference in IQ between people with HR 70 bpm or less and greater than 70 bpm, BMI 30 kg/m2 or less, and BMI greater than 30 kg/m2.

Detection of Left-to-Right Shunts by Inhalation of Oxygen-15-Labeled Carbon Dioxide

The general properties of 15O-labeled carbon dioxide have been reviewed1,2 and published.3 The most striking property of this gas is that, when inhaled, it causes the sudden labeling of pulmonary venous blood water and, subsequently, a mathematically predictable clearance from the lungs into the left heart. This property, as we will see, can be most useful in the detection and quantitation of left-to-right intracardiac shunts. We will outline the general methods of shunt detection and quantitation here, and with this as background, a method utilizing the special properties of C15O2 inhalation will be developed and demonstrated.

The Use of C15O2 in the Evaluation of Cardiac Abnormalities

Carbon dioxide labeled with oxygen- 15 (t 1/2 = 124 sec) is a uniquely useful tracer for cardiopulmonary studies because it can be introduced selectively into the left heart by the simple noninvasive process of inhalation and breath-holding. Externally placed scintillation counters coupled with a high-speed multichannel recorder can be used to measure the rate of clearance of the tracer from the lungs and the rate of filling and emptying of the left heart. The presence of left-to-right intracardiac shunts or mitral or aortic valvular lesions can be inferred from the count rate vs. time curves. Scintigraphic images of the left ventricle in systole and diastole may be made using standard commercially available scintillation camera systems.

Myocardial Imaging with Thallium-201

Since myocardial imaging was first described in 1962,1 many isotopes of rubidium, cesium, nitrogen, potassium, iodine-labeled fatty acids, and others have been utilized as myocardial imaging agents. Their physical and biological characteristics, however, are not well suited to allow myocardial imaging to be done clinically on a routine basis. The ideal agent would be an isotope with a high photon flux with energies that are easily imaged on a gamma camera and with a physical half-life that will permit distribution and a reasonable shelf life of the product, low radiation exposure, and a high myocardial-to-background uptake ratio. Obviously, this agent should also reflect myocardial blood flow accurately.