Non-interventional cardiac diagnostics: computed tomography, magnetic resonance and real-time three-dimensional echocardiography. Techniques and clinical applications.

New cardiovascular imaging modalities, including computed tomography (CT), magnetic resonance (MR) imaging and real-time three-dimensional echocardiography, have great potential for providing important and additional information concerning cardiac function and pathology. With significant and extremely fast technical improvements, non-invasive cardiac imaging has become a focal point in the diagnosis of cardiac disease. Thereby CT has been shown to allow the visualization of coronary arteries concerning calcifications, significant stenoses and coronary plaques, whereas MR imaging demonstrated its ability to evaluate cardiac morphology and function as well as perfusion imaging and viability assessment. As CT and MR, real-time three-dimensional echocardiography has increasingly progressed in the last years offering the potential for routine clinical application, e.g. in the evaluation of valve disease, the assessment of left ventricular thrombi or the guidance of intracardiac catheter placement. This article will provide a brief overview of each technique, possible clinical applications and their perspectives. Because both, CT and MR, have been successfully applied to visualize the coronary arteries, this article focuses on the abilities and limitations of CT and MR coronary artery imaging.

Coronary calcifications in young patients with first, unheralded myocardial infarction: a risk factor matched analysis by electron beam tomography.

OBJECTIVE: To compare the presence and extent of coronary calcifications in young patients with first, unheralded acute myocardial infarction with matched controls without a history of coronary artery disease. METHODS: In 102 patients under 60 years of age (19-59 years, mean 41 years; 88% male), electron beam tomography was done 1-14 days after acute myocardial infarction, before any coronary intervention. Coronary calcifications were quantified using the Agatston score. Age related calcium centiles were determined based on the Mayo Clinic "epidemiology of coronary calcification" study, and results were compared with a group of 102 controls without coronary artery disease, matched for sex, age, and risk factors. RESULTS: Calcifications were present in 95.1% of patients with acute myocardial infarction and in 59.1% of controls (p = 0.008). The mean (SD) Agatston score was 529 (901) in the infarct patients versus 119 (213) in the controls (p < 0.001). An Agatston score above the 50th centile was present in 87.2% of infarct patients and 47.0% of controls (p = 0.006), and above the 90th centile in 60.7% of infarct patients and only 5.8% of controls (p = 0.001). CONCLUSIONS: In young patients with their first, unheralded acute myocardial infarction, the presence and extent of coronary calcium are significantly greater than in matched controls.

Interleukin-6 is a major effector molecule of short-term G-CSF treatment inducing bone metabolism and an acute-phase response.

OBJECTIVE: The biological steps leading to hematopoietic progenitor cell (HPC) mobilization from the bone marrow to the peripheral blood compartment during G-CSF treatment are still poorly defined. In this study, we investigated G-CSF-mediated secretion of cytokines as potential mediators. MATERIALS AND METHODS: Plasma and urine samples from G-CSF-mobilized donors for HPC transplantation were collected before and during mobilization therapy. Interleukin-6 (IL-6), alkaline phosphatase (ALP), bone-specific ALP (bone ALP), C-reactive protein (CRP), lipopolysaccharide binding protein (LPB), CD34+ cells and urinary deoxypyridinoline (DPD) concentrations were measured and statistically correlated. RESULTS: IL-6 was highly elevated at days 4 and 5 of G-CSF treatment. G-CSF administration led to elevation of IL-6 parallel to the appearance of CD34+ cells in the peripheral blood. Major metabolic changes such as high bone ALP plasma concentration and urinary excretion of deoxypyridinoline (DPD), indicating stimulation of bone metabolism, were observed. Elevated concentrations of CRP and LPB indicated an acute-phase response. Furthermore, CRP concentrations correlated significantly with the percentage of mobilized CD34+ cells. CONCLUSION: Based on these findings, we propose IL-6 as a major physiological effector molecule of G-CSF treatment that induces bone metabolism and an acute-phase reaction along with mobilization of CD34+ cells in the peripheral blood. IL-6 may be responsible for osteopenia observed during short- and long-term G-CSF treatment. These observations may also have implications for G-CSF treatment of patients with plasmocytoma.

Noninvasive coronary angiography by magnetic resonance imaging, electron-beam computed tomography, and multislice computed tomography.

In recent years, several techniques for noninvasive imaging of the coronary artery lumen (noninvasive coronary angiography) have been developed. These techniques include magnetic resonance imaging, electron-beam computed tomography, and, most recently, multislice computed tomography. Each of these techniques has specific advantages and disadvantages. Currently, EBCT seems to permit the most robust coronary artery imaging. In the future, imaging modalities will have to be further improved and validated in order to define specific areas for potential clinical applications.

Variability of repeated coronary artery calcium measurements by electron beam tomography.

In 120 patients, the mean interscan variability of coronary calcium quantification by electron beam tomography was 19.9% (median 7.8%) for the traditional calcium score, and 16.2% (median 5.7%) for volumetric scoring. Although this difference was not significant, there was a significant influence of the total amount of calcium, number of acquired images, and image noise on interscan reproducibility.

Contrast enhanced electron beam computed tomography to analyse the coronary arteries in patients after acute myocardial infarction.

OBJECTIVE: To evaluate the accuracy of contrast enhanced electron beam computed tomography (EBCT) after acute myocardial infarction in determining patency of the infarct related artery and detecting high grade stenoses and occlusions in the coronary vessels. DESIGN: Case study using blinded comparison with invasive coronary angiography. PATIENTS: 36 patients (mean age 53 years) 4-70 days after acute myocardial infarction. INTERVENTIONS: The patients were studied by EBCT and invasive coronary angiography. For EBCT, 50 axial images of the heart (3 mm slice thickness) were acquired. They were triggered by the ECG during breath holding, after intravenous injection of contrast agent. The original images, surface reconstructions, and maximum intensity projections were evaluated for the presence of high grade stenoses and occlusions of the coronary arteries. MAIN OUTCOME MEASURES: EBCT results were compared with invasive coronary angiography. RESULTS: Of a total of 144 coronary arteries (left main, left anterior descending, left circumflex, and right coronary artery in 36 patients), 29 (20%) were unevaluable by EBCT. In the remaining arteries, 33 of 36 high grade lesions were correctly detected (92% sensitivity). Specificity was also 92% (73/79). Patency of the infarct related artery was correctly detected in 15 of 16 cases (94%). Five of the 14 occluded infarct related arteries (35%) were mistaken as stenotic but patent, and six could not be assessed. CONCLUSIONS: EBCT is very accurate in detecting significant coronary artery lesions in patients after acute myocardial infarction, but differentiation between occluded and patent infarct related arteries is currently unreliable.

Imaging of the coronary arteries using magnetic resonance angiography.

Magnetic resonance imaging of the coronary arteries is difficult due to the tortuous course of these vessels, their small diameter, and their rapid movement caused by respiration and cardiac contraction. Initial investigations could demonstrate the feasibility of non-invasive magnetic resonance coronary angiography using 2-dimensional turbo-FLASH gradient-echo sequences in repeated breathholds of approximately 16 heart beats duration. Further developments, especially the design of navigator-echo-based respiratory gated 3-dimensional imaging sequences, permitted the acquisition of contiguous volume data sets of the heart which eliminated many limitations of 2-dimensional repeated breathhold sequences. With a spatial resolution of approximately 1.2 x 1.2 x 2 mm and a temporal resolution of approximately 126 ms, several authors reported sensitivities of 70-80% and specificities of approximately 90% for the detection of coronary artery stenoses. Further improvements can be expected from new, intravascular contrast agents and from ultrafast sequences which permit acquisition of a sufficiently large imaging volume within one single breathold.

Noninvasive detection of coronary artery stenosis using contrast-enhanced three-dimensional breath-hold magnetic resonance coronary angiography.

OBJECTIVES: The purpose of this study was to evaluate a contrast-enhanced three-dimensional (3D) breath-hold magnetic resonance (MR) technique for detection of coronary artery stenoses. BACKGROUND: The accuracy of previously published MR coronary angiography protocols varies widely. Recently, coronary artery imaging using T1-shortening contrast agent has become possible, but so far there are no data concerning its clinical application. METHODS: Magnetic resonance coronary angiography was performed in 50 patients with suspected coronary artery disease. Magnetic resonance data acquisition using an ultrafast 3D gradient-echo sequence lasted over 32 heartbeats within one single breath-hold. Twenty milliliters of gadopentetate dimeglumine was injected at a flow rate of 1 ml/s for two successive studies covering the main coronary arteries in single-oblique planes. Stenosis assessment by MR was compared with significant (diameter stenosis > 50%) stenoses on X-ray angiography. Evaluation was limited to the proximal and mid-coronary artery segments. RESULTS: Two hundred sixty-eight of 350 artery segments (76.6%) could be evaluated. Left circumflex coronary artery was only evaluable in 50% of cases by MR. In the evaluable segments, 48 of 56 stenoses and 193 of 212 nonstenotic segments were correctly classified by MR. On a patient basis, MR correctly identified 34 of 36 patients with and 8 of 14 patients without significant coronary stenoses as demonstrated by X-ray angiography (sensitivity 94.4%, specificity 57.1%). CONCLUSIONS: Oblique projection contrast-enhanced MR coronary angiograms obtained within one single breath-hold permit identification of patients with coronary stenoses in the proximal and mid segments of the major coronary arteries with satisfactory accuracy.

Poststenotic coronary blood flow following percutaneous transluminal coronary angioplasty.

Poststenotic intracoronary flow velocity measurements both prior to and following percutaneous transluminal coronary angioplasty (PTCA) by use of a Doppler-tipped guidewire allow estimation of haemodynamic improvement due to interventional procedures. Since poststenotic coronary artery vasoconstriction routinely occurs after PTCA, haemodynamic improvement may be overestimated when measured by flow velocity alone. In 38 patients scheduled for elective PTCA in single vessel disease (left anterior descending = 19; left circumflex = 9; right coronary artery = 10) change of poststenotic coronary blood flow (CBF) was calculated by the combined use of intracoronary flow velocity measurement (average peak velocity: APV) and quantitative coronary angiography (cross sectional area: CSA) both prior to and following PTCA. Poststenotic coronary diameters revealed a small but significant decrease following PTCA (2.9 +/- 0.5 versus 2.7 +/- 0.5 mm, p < 0.001, 33 of 38 analysed vessels, i.e. 86.8%), whereas APV demonstrated a significant increase due to PTCA (17.0 +/- 8 versus 41.5 +/- 16, p < 0.001). Along with the increment in poststenotic flow velocity, poststenotic CBF increased highly significantly following PTCA (33 +/- 25 versus 73 +/- 41 ml min(-1), p < 0.001). In spite of a significant decrease in poststenotic coronary diameter, a highly significant increment of poststenotic flow due to PTCA can be demonstrated paralleling increment of poststenotic coronary Doppler-flow velocity.

Evaluation of successful PTCA by transstenotic flow velocity ratios.

Doppler probes mounted on the tip of a guidewire allow the measurement of coronary blood flow velocities, not only proximal but also distal to stenoses eligible for percutaneous transluminal coronary angioplasty (PTCA). The objective of this study was to determine the improvement of transstenotic Doppler flow velocity ratios following PTCA and to investigate the possible impact on restenosis during follow-up control angiography three months later. Doppler flow velocity measurements were performed in 29 patients with 29 stenoses eligible for PTCA. Results of PTCA were morphologically evaluated by computer-assisted quantitative coronary angiography (QCA) and measured hemodynamically by determining transstenotic Doppler flow velocity ratios. Successful PTCA according to QCA was present in all cases with a reduction of mean diameter stenosis from 66 +/- 8% to 35 +/- 7%. Resting spectral peak velocities and velocity integrals were markedly reduced distal to lesions (all P < 0.001), resulting in mean transstenotic flow velocity and velocity integral ratios of less than 0.60 prior to PTCA. Owing to endoluminal enlargement, significant improvement of transstenotic Doppler ratios was observed in mean ratios greater than 0.90 (all P < 0.0001). In patients with restenosis, transstenotic ratios following PTCA demonstrated a tendency to be smaller than in patients without restenosis. Transstenotic Doppler flow velocity ratios are diminished in severe coronary stenoses. Improvement of these ratios provides information on hemodynamic success of interventional procedures. Thus, the determination of intracoronary Doppler flow velocity ratios contributes, in addition to angiographic estimation, to the evaluation of stenoses severity and success of interventional procedures.

Doppler flow velocity measurements during coronary angioplasty.

In addition to further studies using Doppler catheters to assess blood flow velocity during coronary angioplasty this study intends to evaluate the functional significance of coronary stenoses and to estimate their hemodynamic relevance prior to and after percutaneous transluminal coronary angioplasty (PTCA). Diameters of coronary artery stenoses were quantified by means of the cardiovascular angiographic analysis system (CAAS) both prior to and following successful PTCA in 37 patients. During coronary artery angioplasty a 12 M:Hz 0.018-in. Doppler-tipped guidewire was used to measure prestenotic and poststenotic parameters of coronary artery flow velocity both prior to and following PTCA. The minimal stenosis diameter was raised from 1.01 +/- 0.58 to 1.76 +/- 0.73 mm (P < 0.0001), the percent diameter stenosis decreased from 63 +/- 11 to 35 +/- 6% (P < 0.0001). Prestenotic average (APV) and maximum peak velocity (MPV), peak velocity integral (PVI), average systolic (ASPV) and diastolic (ADPV) peak velocity, systolic (SPVI) and diastolic (DPVI) peak velocity integral, and diastolic/systolic velocity ratio showed--in contrast to further studies--a considerably significant difference (P < 0.05), whereas poststenotic Doppler data (APV, MPV, PVI, ASPV, DSPV, SPVI, DPVI, DSVR) differed highly significantly (P < 0.0001) prior to and following PTCA. Prestenotic and poststenotic measurements of coronary artery flow velocity differed significantly before and after PTCA and offer the potential for estimating both the hemodynamic relevance of coronary artery stenoses and success of PTCA.