Search PubMed⌕ Search

Biomedical subjects

K Bachmann

Publications and source records attributed to K Bachmann.

At least 55 records · Page 3Linked to original sources
PubMed1998

Curved multiplanar reconstructions for the evaluation of contrast-enhanced electron beam CT of the coronary arteries.

OBJECTIVE: We investigated the applicability of curved multiplanar reconstructions for the evaluation of contrast-enhanced electron beam CT scans of the coronary arteries. SUBJECTS AND METHODS: Thirty-two patients (43-72 years old; mean age, 58 years old) underwent electron beam CT. After injection of i.v. contrast medium, 40 axial cross sections of the heart were acquired, triggered to the ECG during breath-hold (3-mm slice thickness, 1-mm overlap). Curved multiplanar reconstructions were obtained separately for each coronary artery. The reconstructions were independently evaluated by two investigators for the presence of high-grade stenoses and occlusions. The results were then compared with coronary angiography results, of which the two investigators had been unaware. RESULTS: Because of degraded image quality, 15 (12%) of the 128 vessels (left main, left anterior descending, left circumflex, and right coronary arteries in 32 patients) were excluded from evaluation. In the remaining 113 vessels, 16 (89%) of 18 high-grade stenoses and occlusions were correctly detected (89% sensitivity). Absence of significant stenosis was correctly detected in 87 (92%) of 95 vessels (92% specificity). The negative and positive predictive values were 98% and 67%, respectively. CONCLUSION: Curved multiplanar reconstructions are useful in the evaluation of contrast-enhanced electron beam CT scans of coronary arteries.

Adult↗
PubMed1997

Detection of high-grade restenosis after PTCA using contrast-enhanced electron beam CT.

BACKGROUND: Contrast-enhanced electron beam computed tomography (EBCT) has been shown to permit noninvasive visualization of the coronary arteries. We determined the value of EBCT to noninvasively detect high-grade restenosis after percutaneous transluminal coronary angioplasty (PTCA). METHODS AND RESULTS: Fifty patients (37 to 68 years of age), were investigated by EBCT at a mean interval of 9 months after PTCA of coronary artery stenoses. Forty axial cross-sections of the heart (3-mm slice thickness, 1-mm overlap) were acquired triggered to the ECG after intravenous injection of contrast agent. Three-dimensional reconstructions of the coronary arteries were rendered with a lower threshold of 80 HU to selectively visualize the contrast-enhanced vessel lumen. EBCT results were compared with conventional quantitative coronary angiography (QCA) performed within 1 week. In 6 patients, the PTCA segment could not be evaluated because of impaired image quality. Sixteen of the remaining 44 patients had high-grade restenoses in QCA (>70% diameter reduction), which was correctly detected by EBCT in 15 cases (94% sensitivity). There were 5 false-positive EBCT results of high-grade restenosis (82% specificity). CONCLUSIONS: EBCT with intravenous injection of contrast agent permits the noninvasive diagnosis of restenosis after PTCA, with high sensitivity and sufficient specificity.

Adult↗
PubMed1997

Usefulness of respiratory gated magnetic resonance coronary angiography in assessing narrowings > or = 50% in diameter in native coronary arteries and in aortocoronary bypass conduits.

Magnetic resonance coronary angiography (MRCA) is a promising method for the assessment of proximal coronary artery stenosis. Conventional 2-dimensional techniques require repetitive breath holds to image multiple sections. This may lead to misregistrations if the respiratory level is not exactly reproduced. In the present study, MRCA was performed using a 3-dimensional approach with navigator echo-based respiratory gating. In 73 patients (55 men and 18 women) who were referred for cardiac catheterization, the assessment of significant stenoses (> or = 50%) was performed in the proximal and midsegments of the coronary arteries after multiplanar reconstruction of the visualized coronary arteries. In addition, in 8 patients with coronary artery bypass grafts the patency of the transplants was evaluated. After withdrawing 8 patients from analysis because of poor image quality, stenosis evaluation was possible in 236 of 455 reviewed coronary segments (52%). In the other 219 cases, either the visualization of the vessel segment was indistinct (30%) or the segment was located outside the imaging volume (18%). In total, 28 of 43 significant coronary stenoses could be correctly identified (65%). Evaluation of bypass graft patency was possible in 7 patients. All 4 occluded and 13 of 15 patent grafts were correctly classified. Thus, respiratory gated MRCA is a feasable method for the assessment of hemodynamically significant coronary stenoses and bypass graft patency. However, technical improvements are mandatory to improve accuracy of the method.

Adult↗
PubMed1997

Noninvasive, three-dimensional visualization of coronary artery bypass grafts by electron beam tomography.

Electron beam tomography (EBT, ultrafast computed tomography [CT], cine CT) combines unique temporal and high spatial resolution and is especially well suited for cardiac imaging. We established and evaluated a protocol for the noninvasive visualization and assessment of aortocoronary artery bypass grafts. Twenty-five patients with 56 bypass grafts were studied by EBT. Forty contiguous cross-sectional images were acquired triggered to the electrocardiogram during breathhold and intravenous injection of contrast agent. Three-dimensional reconstructions of the heart and bypass grafts were performed and compared with selective angiography of the bypass grafts. In 1 patient with 2 bypass grafts, a technically inadequate EBT examination was obtained. In the remaining patients (54 grafts), all 13 bypass occlusions were diagnosed with a sensitivity and specificity of 100%. Evaluation for hemodynamically relevant stenosis was possible in 84% of cases (36 of 43 patent grafts) and yielded a sensitivity of 100% (5 of 5 high-grade stenoses correctly detected) and specificity of 97% (1 false-positive diagnosis of high-grade graft stenosis). The main reasons for impaired ability to evaluate the scans were breathing artifacts and misplacement of the imaging volume, causing parts of the bypass grafts to be cut off. EBT permits noninvasive determination of bypass graft occlusion and relevant stenosis with high accuracy.

Coronary Artery Bypass↗
PubMed1997

[Non-invasive coronary diagnosis with EBT (electron beam tomography). Population screening for coronary heart disease--reliability imaging of coronary stenoses].

Electron beam tomography (EBT) is currently the fastest high resolution imaging procedure available. A modern non-invasive method, it provides an accurate spatial representation of the heart including the coronary arteries. Enabling the quantitative detection of microcalcifications in the coronary arteries--a reliable parameter of early-stage CAD-EBT now makes it possible to screen large population strata. In addition, the direct, non-invasive representation of coronary arteries and coronary arterial stenoses has now become possible. Although at present, EBT will probably not completely replace invasive coronary angiography, in specific areas such as evaluating the long-term results of coronary angioplasty (PTCA) or coronary bypass, the method could make invasive diagnostic procedures superfluous.

Adult↗
PubMed1997

Myocardial damage assessed by indium-111-antimyosin: correlation with persistent enteroviral ribonucleic acid in dilated cardiomyopathy.

The persistence of enteroviral ribonucleic acid (RNA) in the myocardium has been implicated as a pathogenetic factor in idiopathic dilated cardiomyopathy. Enteroviral persistence may lead to myocardial cell membrane damage, resulting in increased uptake of antimyosin antibodies. To further evaluate this hypothesis, a direct comparison of myocardial antimyosin uptake with the presence of enteroviral RNA was performed in ten patients (one female, nine male; 53+/-8 years) with chronic dilated cardiomyopathy. Planar antimyosin images were obtained 48 h after the injection of indium-111-labelled antimyosin Fab. Using a region of interest technique, the heart to lung uptake ratio (HLR) was calculated as a semiquantitative parameter of myocardial tracer uptake. Cardiac catheterization was performed to assess left ventricular function and to obtain myocardial biopsy samples. In the biopsy samples, gene amplification by polymerase chain reaction (PCR) was used to specifically detect enteroviral RNA. In the ten patients, the left ventricular ejection fraction was 39%+/-11% and the end-diastolic volume 131+/-46 ml/m2. The HLR was 1.72+/-0.21 and showed no correlation with functional parameters. In two patients with a positive PCR consistent with persisting enteroviral RNA, the HLR was not higher than that in eight patients with a negative PCR (1.46+/-0. 18 vs 1.78+/-0.18, respectively). These results suggest that increased uptake of 111In-antimyosin in chronic idiopathic dilated cardiomyopathy cannot be explained by pure persistence of enteroviral RNA. Other pathogenetic factors such as myocardial autoantibodies or microvascular spasm may be responsible for myocyte membrane damage detected by antimyosin.

Antibodies, Monoclonal↗
PubMed1997

[Online measurement of retinal artery branches in type II diabetic patients. Initial clinical trials before and after laser coagulation].

UNLABELLED: By the use of a new online measuring system the effect of argon-laser coagulation in diabetics on the diameters of retinal arteries was measured. METHOD: The vessel diameter of retinal branch arteries were measured in patients with type-II diabetes before and after (0.5 h) argon-laser coagulation. Ten patients without previous laser treatment were included in this study. Measurements were taken in all four quadrants by the use of a new automatic online measuring system. RESULTS: The new technique allowed measurements to be made within an acceptable period of time and with little strain on patients. After argon-laser coagulation 56.7% of retinal arteries showed a significant vasodilation. No significant changes in vessel diameter were found in 18.9% of these arteries, whereas 24.3% showed significant vasoconstriction. CONCLUSION: The new online measuring system is able to measure the effects of photocoagulation on an individual basis with a noninvasive technique. The first findings presented here confirm previous studies of larger groups, with a considerable reduction in efforts required.

Aged↗
PubMed1997

[Noninvasive coronary angiography with electron beam tomography: methods and clinical evaluation in post-PTCA follow-up].

Electron beam tomography (EBT) is a computed tomography technique with unique spatial and temporal resolution. The aim of the study was to establish and evaluate a protocol for the non-invasive visualization and detection of stenoses of the coronary arteries. Following phantom studies, 103 patients were investigated. Among these, 25 patients after coronary angioplasty (PTCA) were included in a prospective, blinded comparison to coronary angiography. After injection of contrast agent in a peripheral vein, 40 axial cross sections of the heart were acquired, triggered to the ECG (slice thickness 3 mm, 1 mm overlap, pixel size 0.29 x 0.29 mm). Three-dimensional reconstructions of the heart and coronary arteries were performed in the form of "shaded surface display," the results were compared to coronary angiography. In the reconstructions, the proximal and mid section of the LAD was visualized in 94% and 85%, image quality was reduced for the right coronary artery (89%/64%) and left circumflex (74%/54%), mainly due to movement artifacts. EBT displayed a sensitivity of 100% (9/9) for the detection of occlusions and high-grade restenoses in patients after PTCA, due to one false-positive result, specificity was 92% (12/13). Three PTCA patients could not be evaluated due to respiration artifacts. Contrast-enhanced electron beam tomography (EBT) permits the visualization of coronary arteries and the detection of stenoses and occlusions with high sensitivity and specificity.

Adult↗
PubMed1997

Effects of magnetic resonance imaging on cardiac pacemakers and electrodes.

In phantom studies we investigated the effects of magnetic resonance imaging (MRI) on pacemakers and electrodes. Twenty-five electrodes were exposed to MRI in a 1.5T scanner with continuous registration of the temperature at the electrode tip. Eleven pacemakers (five single chamber and six dual chamber) were exposed to MRI. Pacemaker output was monitored to detect malfunction in VOO/DOO and VVI/DDD modes. A temperature increase at the electrode tip of up to 63.1 degrees C was observed during 90 seconds of scanning. In seven electrodes the temperature increase exceeded 15 degrees C. Although no pacemaker malfunctions were observed in asynchronous pacing mode (VOO/DOO), inhibition and rapid pacing were observed during spin-echo imaging if the pacemakers were set to VVI or DDD mode. Pacemaker function was not impaired during scanning with gradient-echo sequences. Next to pacemaker dysfunction, electrode heating has to be considered a possible adverse effect when exposing patients with pacemakers to MRI.

Animals↗
PubMed1997

Molecular evidence for an extinct parent of the tetraploid species Microseris acuminata and M. campestris (Asteraceae, Lactuceae).

To determine the origin of the tetraploid annuals Microseris campestris and M. acuminata, chloroplast RFLP, RAPD and ITS sequence variability among nine populations of the two polyploids and 14 populations of the diploid annuals M. elegans and M. douglasii have been surveyed. Previously described variable chloroplast restriction sites infer M. douglasii as the possible maternal parent of both tetraploid species. However, the chloroplast genome typical for M. douglasii has now also been found in some plants of M. elegans. RAPD analysis revealed 172 polymorphic DNA markers that defined all four species as genetically distinct groups, but demonstrated closer associations between M. douglasii and M. acuminata, and between M. elegans and M. campestris. Sequencing of the ITS-1 and ITS-2 region yielded 73 phylogenetically informative sites. Thirty basepair mutations separated the annual Microseris species from the outgroup, Uropappus lindleyi. The putative interspecific allotetraploid M. campestris contained only one type ITS sequence that, on the basis of eight synapomorphic substitutions was derived from M. elegans. The single ITS of M. acuminata shares six common sites with M. douglasii. Surprisingly, six sites were synapomorphic for the two tetraploids, M. campestris and M. acuminata, suggesting recombination within the ITS of both species with that of a common, now extinct, parental taxon, possibly the donor of the M. douglasii type chloroplasts found in both tetraploids. These results confirm the interpretation of M. campestris as derived from M. douglasii (extinct population) and M. elegans, and resolve the unknown origin of M. acuminata as an intraspecific hybrid between two very distinct populations of M. douglasii, one of them the same extinct M. douglasii form that contributes to M. campestris.

Base Sequence↗
PubMed1997

Visualization of the coronary arteries in three-dimensional reconstructions using respiratory gated magnetic resonance imaging.

OBJECTIVE: To assess the applicability of respiratory-gated magnetic resonance coronary angiography, combined with three-dimensional image reconstruction, for visualizing the coronary arteries. METHODS: Twenty subjects (three healthy volunteers and 17 patients without stenoses detected by coronary angiography) were investigated. Magnetic resonance imaging was performed in a 1.5 T scanner using ECG-triggered gradient-echo sequences to acquire a volume data set consisting of 24-48 contiguous axial cross-sections of the heart (2 mm slice thickness, 1.17 mm x 1.17 mm in-plane resolution). Navigator-echo-based retrospective respiratory gating was used to minimize respiratory motion artifacts. Three-dimensional reconstructions of the heart were rendered using surface-display techniques. The length of the visualized coronary arteries was measured in curved multiplanar reconstructions. RESULTS: In the three-dimensional reconstructions, the left main artery (LMA) and left anterior descending artery (LADA) were visualized in 17 cases, the left circumflex artery (LCXA) in 15, and the right coronary artery (RCA) in 16 cases. Vessel continuity was uninterrupted in all 17 cases for the LMA, in 14 for the LADA, eight for the LCXA, and 13 for the RCA. The mean lengths of the visualized vessels were 14 +/- 7 mm for the LMA, 65 +/- 13 mm for the LADA, 45 +/- 16 mm for the LCXA, and 37 +/- 26 mm for the RCA. Reasons for impaired visibility of the LCXA and RCA were poor image quality due to there being a low contrast:noise ratio, motion artifacts, and incomplete coverage by the imaging volume. CONCLUSIONS: Navigator-echo-based magnetic resonance imaging is a promising technique for investigating the coronary arteries. Acquisition of a volume data set permits three-dimensional displays of the coronary vessels.

Case-Control Studies↗
PubMed1997

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.

Angioplasty, Balloon, Coronary↗
PubMed1997

Quantitative angiographic analysis of PTCA-induced coronary vasoconstriction in single-vessel coronary artery disease.

Quantitative coronary angiography was applied to investigate the degree and extent of coronary vasoconstriction following percutaneous transluminal coronary angioplasty (PTCA) in single-vessel disease of segments distal to the PTCA site (n = 46) and of control segments in nonmanipulated vessels (n = 33) before PTCA, 15 minutes after PTCA, and again 10 minutes after 10 mg sublingual isosonbide dinitrate (ISDN) in 46 patients receiving neither nitrates nor calcium channel blockers prior to PTCA. Furthermore, the degree of coronary vasoconstriction was compared with ergonovine-induced vasoconstriction (n = 8) as well as in patients with and without restenosis during follow-up angiography 4 months later. PTCA induced a moderate, but significant, vasoconstriction in both distal and control segments, with a reduction in coronary diameter from 2.34 +/- 0.58 to 2.26 +/- 0.55 mm (P = 0.011) and from 2.70 +/- 0.62 to 2.60 +/- 0.65 mm (P = 0.004), respectively. No correlation between the degree of vasoconstriction on the one side and lesion severity and PTCA-induced mechanical stretch, judged by the sum of the products of inflation pressure and time, on the other side was found. Vasoconstriction was within the limits achievable with the potent vasoconstrictor ergonovine and did not differ in patients with or without restenosis. ISDN led to a significant vasodilatation in all segments. In conclusion, coronary vasoconstriction following PTCA is present in the coronary tree in a rather diffuse way. It is not associated with stenosis severity or PTCA-induced mechanical stretch, suggesting a complex underlying mechanism. ISDN-reversible vasoconstriction was within the limits achievable with ergonovine and did not differ with regard to restenosis.

Administration, Sublingual↗
PubMed1997

Estimating xenobiotic half-lives in humans from rat data: influence of log P.

The nature of empirical allometric expressions relating dispositional and kinetic parameters for a given xenobiotic across multiple mammalian species is well known. It has also been demonstrated that a simple allometric relationship may be used to predict kinetic parameters for humans based merely on data for multiple xenobiotics from rats. We decided to explore reasons for the variance in the data arising from the latter method. We were particularly interested in learning whether any physicochemical characteristics of xenobiotics might account for outlying data points (i.e., poor prediction of human half-life from rat half-life). We have explored the influence of lipid solubility as reflected by a xenobiotic's log P value because adipose tissue comprises a significantly larger percentage of total body weight in humans than in rats. We used half-life data from the literature for 127 xenobiotics. A data subset of 102 xenobiotics for which we were able to find estimates of log P values, including several with extremely large log P values, was also analyzed. First and second order models, including and excluding log P, were compared. The simplest of these models can be recast as the familiar allometric relationship having the form Y = a(Xb). The remaining models can be seen as extensions of this relationship. Our results suggest that incorporation of log P into the prediction of xenobiotic half-life in humans from rat half-life data is important only for xenobiotics with extremely large log P values such as dioxins and polychlorinated biphenyls. Moreover, a second order model in logarithm of rat half-life accommodates all data points very well, without specifically accounting for log P values.

Animals↗
PubMed1997

Platelet activation in embolic and preembolic status of patients with nonrheumatic atrial fibrillation.

STUDY OBJECTIVE: Information on platelet activation possibly associated with a preembolic or embolic status in nonrheumatic atrial fibrillation (AF) with special regard to the role of platelet membrane activation markers (P-selectin and CD63). STUDY POPULATION: The study included 60 patients with nonrheumatic AF; 28 of them had a history of an embolic event. The age-matched control group consisted of 28 healthy subjects (13 men and 15 women). INTERVENTIONS: Patients underwent transesophageal echocardiography to detect eventual intracardiac thrombus or spontaneous echo contrast that would represent a preembolic status. Blood samples were taken from all persons to evaluate markers for platelet activation under these conditions. RESULTS: Measurements of hematologic variables did not differ significantly between normal subjects and patients presenting with AF but no preembolic or embolic status. Elevated concentrations of fibrinogen were significantly related to the presence of left atrial spontaneous echo contrast. The amount of circulating platelets expressing P-selectin and CD63 was significantly higher in the patients positive for both spontaneous echo contrast and left atrial thrombus or embolic events. Furthermore, in these groups, significantly more leukocyte-platelet conjugates were present. CONCLUSION: Platelet activation indicated by platelet membrane activation markers occurs in embolic and preembolic status of patients with nonrheumatic AF.

Aged↗