Lothar Koch | Johannes Gutenberg-Universität Mainz (original) (raw)

Papers by Lothar Koch

European Heart Journal, 1996

Biomedizinische Technik/Biomedical Engineering, 1996

Mit der direktorialen Atherektomie ist eine erfolgreiche Revaskularisation von koronaren Gefäßen ... more Mit der direktorialen Atherektomie ist eine erfolgreiche Revaskularisation von koronaren Gefäßen möglich, besonders in größeren Gefäßen mit exzentrischen Plaqueablagerungen. Aufgrund der hohen Perforationsgefahr der Gefäßwand ist die Anwendung von Lasertechnologie in koronaren Gefäßen kritisch. Eine gezielte Positionierung und ein kontrollierter Schneidvorgang könnten diese Gefahr reduzieren und es ermöglichen, die Vorteile der Laseratherektomie zu nutzen.

Coronary Artery Disease, 1993

Pathologic studies have revealed that coronary arteries undergo compensatory enlargement in the p... more Pathologic studies have revealed that coronary arteries undergo compensatory enlargement in the presence of atherosclerosis. In order to assess coronary artery remodeling in vivo, we used intravascular ultrasound to examine 46 patients (36 men and 10 women; aged 58.2 +/- 6.8 years) with non-calcified plaques. The vessel, lumen, and plaque areas of the atherosclerotic and of normal proximal and distal segments were determined. A total of 92 atherosclerotic segments were analyzed. The degree of stenosis ranged from 9.2 to 92.8% (mean 34.1 +/- 16.9%) and the plaque area from 2 to 19.6 mm2 (mean 6.3 +/- 3.6 mm2). The vessel area of the atherosclerotic segment (mean 20.4 +/- 7.3 mm2) was larger than that of the proximal segment (mean 18.7 +/- 7.3 mm2, P = 0.018). The vessel area increased in proportion to plaque area. This relationship can be described using the equation y = 23.5(1-e-0.35x). The difference between the vessel area in the atherosclerotic segment and that in the proximal normal segment correlated with the percentage of stenosis (r = 0.53, P < 0.005) until the degree of stenosis exceeded 45%. This study indicates that coronary artery remodeling, previously observed in pathologic studies, can be evaluated using intravascular ultrasound in vivo. As a result of the compensatory enlargement of the vessel, coronary angiography cannot be used to detect or exclude the early signs of coronary atherosclerosis.

Basic Research in Cardiology, 2000

The evaluation of regional myocardial blood flow (RMBF) during cardiac catheterization is of part... more The evaluation of regional myocardial blood flow (RMBF) during cardiac catheterization is of particular diagnostic interest. The purpose of this investigation was to validate x-ray densitometric parameters for the evaluation of RMBF. In five anesthetized dogs, arterial flow in the circumflex coronary artery was measured continuously with an electromagnetic flowmeter, and RMBF was determined by colored microspheres. Five different perfusion levels were created by mechanical obstruction of the coronary artery or by intravenous infusion of adenosine. At each steady-state perfusion level, digital subtraction coronary angiograms were obtained for densitometric analysis. Results documented a close correlation between the related time parameters 1/Mean Transit Time (1/MTT, r 2 = 0.969), and 1/Rise Time (1/RT, r 2 = 0.965) and RMBF over a wide range between 0.36 ml/(min • g) and 11.16 ml/(min • g). Maximum myocardial contrast density (Imax) also showed a good, but inverse correlation (r 2 = 0.889) with RMBF and, therefore, did not reflect vascular volume. Contrast medium Appearance Time (AT) showed no correlation to RMBF (r 2 = 0.017). Repeat densitometric measurements for different perfusion levels revealed a good reproducibility for MTT (

The International Journal of Cardiac Imaging, 1996

BaclCg~ound: Intravascular ultrasound (IVUS) permits quantitative assessment of the lumen diamete... more BaclCg~ound: Intravascular ultrasound (IVUS) permits quantitative assessment of the lumen diameter and area of coronary arteries. The experimental study was performed to evaluate the accuracy of diameter and area measurements. Methods and results: Lumen quantitation (lumen diameter D and cross-sectional area A) in lucite tubes (lumen diameter 2.5 to 5.7 mm, Plexiglas TM) was performed using a mechanical IVUS system (HP console, 3.5F catheter, Boston Scientific, 30 MHz). The influence of fluid type (blood, water and saline solution), fluid temperature (20°C/37°C), catlieter to catheter variation, gain setting and ultrasound frequency (12, 20 and 30 MHz) was determined. In blood at 20°C there was a constant deviation of the measured diameter from the true luminal diameter of-0.29 i-0.04 mm (p <0.06). In water and saline solution at 20°C the mean deviation from true diameter was-0.21 ±-0.06 mm (p<0.06). At 37°C, the deviation in blood was greater than at 20 ° (-0.34 4-0.02 ram) which is > 10% in a 3mm tube (p<0.06). Three of the ten catheters tested in water at 20°C underestimated true diameter by more than-0.3 ram. The deviation from true diameter (5ram tube) with varying gain settings was-0.14 mm to-0.23 mm compared to-0.19 mm at standard settings (p>0.288). At 12 MHz diameter measured was overestimated. The error in absolute area estimation increased with increasing diameter tested in blood at 37°C @1.21 to-2,72mm2), whereas the relative error ([Measured Area-True Area]/True Area x 100 [%]) was more striking at smaller diameters (up to-25% in the 2.5 mm tube). Conclusion: Luminal diameters and areas are underestimated by this particular IVUS system. When IVUS imaging and measurements are made during coronary interventions this error should be taken into account with regard to appropriate sizing of the device and the assessment of the postprocedure result. Because systematic errors might also occur in other IVUS systems (not tested in this study), it is advisable to ensure that each system is validated prior to clinical use, especially when exact measurements are required.