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Biomedical subjects

Michael Handke

Publications and source records attributed to Michael Handke.

11 recordsLinked to original sources
PubMed2006

Transesophageal real-time three-dimensional echocardiography methods and initial in vitro and human in vivo studies.

OBJECTIVES: The purpose of this study was to develop a transesophageal probe that: 1) enables on-line representation of the spatial structures of the heart, and 2) enables navigation of medical instruments. BACKGROUND: Whereas transthoracic real-time 3-dimensional (3D) echocardiography could recently be implemented, there is still no corresponding transesophageal system. Transesophageal real-time 3D echocardiography would have great potential for numerous clinical applications, such as navigation of catheters. METHODS: The newly developed real-time 3D system is based on a transesophageal probe in which multiple transducers are arranged in an interlaced pattern on a rotating cylinder. This enables continuous recording of a large echo volume of 70 mm in length and a sector angle of 120 degrees . The presentation of the volume-reconstructed data is made with a time lag of <100 ms. The frame rate is up to 20 Hz. In addition to conventional imaging, the observer can obtain a stereoscopic image of the structures examined with red/blue goggles. RESULTS: It was shown in vitro on ventricle- and aorta-form agar models and in vivo that the system enables excellent visualization of the 3D structures. Shape, spatial orientation, and the navigation of various catheters (e.g., EPS-catheter, Swan-Ganz-catheter), stents, or atrial septal defect occluders could be recorded on-line and stereoscopically depicted. The size of the echo sector enables a wide field of view without changing the position of the probe. CONCLUSIONS: Transesophageal real-time 3D echocardiography can be technically realized with the system presented here. The in vitro and in vivo studies show particularly the potential for navigation in the heart and large vessels on the basis of stereoscopic images.

Aorta↗
PubMed2006

Combined measurement of carotid stiffness and intima-media thickness improves prediction of complex aortic plaques in patients with ischemic stroke.

BACKGROUND AND PURPOSE: We hypothesized that for the prediction or exclusion of aortic thrombi or plaques >or=4 mm, the combination of intima-media thickness (IMT) and distensibility (DC) of the common carotid arteries would be superior to the measurement of IMT alone. METHODS: We prospectively included 208 stroke patients (mean age, 60 years) undergoing transesophageal echocardiography for screening of aortic plaques. IMT and DC were determined by ultrasound, and DC was quantified by measuring blood pressure and the common carotid arteries diameter change on M-mode ultrasound during the cardiac cycle. RESULTS: Negative predictive values of IMT <0.9 mm and DC >or=24x10(-3)/kPa for the exclusion of aortic atheroma >or=4 mm were similar (92.0% and 91.7%, respectively). However, negative predictive values increased to 98.2% and to 100.0% for the exclusion of aortic thrombi when both parameters were combined. Positive predictive values of IMT >or=0.9 mm and DC <24 were lower (46.3%, 41.1%; respectively), but they also increased in combination (54.3%). CONCLUSIONS: Our findings suggest that IMT and DC represent different vessel wall properties and that measuring both parameters provides optimized characterization of carotid atherosclerosis. Combining IMT and DC increases the predictive power of carotid ultrasound, making transesophageal echocardiography dispensable for assessment of the aorta for those with normal carotid arteries and indispensable for those patients with carotid atherosclerosis.

Adult↗
PubMed2006

Therapeutic strategies after examination by transesophageal echocardiography in 503 patients with ischemic stroke.

BACKGROUND AND PURPOSE: Transesophageal echocardiography (TEE) is the gold standard in detecting high-risk (ie, aortic thrombi) and potential sources (ie, patent foramen ovale [PFO]) of cerebral embolism. We sought to evaluate the additional information and therapeutic impact provided by TEE in stroke patients and to characterize patients in whom TEE is indispensable. METHODS: We included 503 consecutive patients (mean age 62.2 years) with acute brain ischemia. Each patient received TEE and the following routine diagnostics: ultrasound of brain supplying arteries, ECG or Holter-ECG, transthoracic echocardiography, and brain imaging (computed tomography or MRI). Stroke etiology was classified according to the Trial of Org 10172 in Acute Stroke Treatment (TOAST) criteria. High-risk sources in TEE were: aortic thrombi or plaques > or =4 mm, thrombi in left atrial cavity/left atrial appendage, spontaneous echo contrast, and left atrial flow velocity <30 cm/s. Potential sources in TEE were PFO, atrial septal aneurysm, and aortic plaques <4 mm. RESULTS: Stroke etiology was determined by routine diagnostics in 276 of 503 patients (54.9%). Of the remaining 227 patients (undetermined etiology), 212 (93.4%) were candidates for oral anticoagulation (OA). TEE revealed a high-risk source, with indication for OA in 17 of them (8.0%). A potential source leading to OA was found in an additional 48 patients (22.6%). The remaining 147 patients (69.3%) were treated by platelet inhibitors or statins. CONCLUSIONS: TEE strongly influenced secondary prevention and led to OA in one third of our patients with stroke of undetermined etiology. TEE is indispensable in all patients being candidates for OA when routine diagnostics cannot clarify stroke etiology.

Administration, Oral↗
PubMed2005

Predictors of left atrial spontaneous echocardiographic contrast or thrombus formation in stroke patients with sinus rhythm and reduced left ventricular function.

The objective of the present study was to identify predictors of left atrial spontaneous echocardiographic contrast (SEC) or thrombus in patients with stroke with sinus rhythm and left ventricular dysfunction. Of 500 consecutive patients with stroke, 48 with sinus rhythm and reduced left ventricular ejection fractions (EFs) < or =45% were examined. Ten patients presented with SEC or thrombus. The patients with SEC or thrombus had larger left atrial diameters (47 +/- 4 vs 42 +/- 6 mm, p <0.05), smaller EFs (30 +/- 9% vs 38 +/- 8%, p <0.01), and slower left atrial appendage (LAA) flow velocities (42 +/- 13 vs 61 +/- 17 cm/s, p <0.01). Multivariate analysis identified EF < or =35% and LAA flow velocity < or =55 cm/s as predictors of SEC or thrombus (p <0.05). Patients with stroke with sinus rhythm and moderate- to high-grade reduction of the left ventricular EF represent a risk group for a left atrial source of embolism and should undergo transesophageal echocardiography.

Adolescent↗
PubMed2005

Left atrial appendage flow velocity as a quantitative surrogate parameter for thromboembolic risk: determinants and relationship to spontaneous echocontrast and thrombus formation--a transesophageal echocardiographic study in 500 patients with cerebral ischemia.

BACKGROUND: Hemostasis in the left atrial (LA) appendage (LAA) is an important cause in the formation of thrombi. Determination of the LAA flow velocity (LAAV) could be a quantitative parameter for estimating thromboembolic risk. The objective of this study was to: (1) determine the relationship between LAAV and qualitative parameters with elevated thromboembolic risk (thrombus/spontaneous echocontrast [SEC]); and (2) define factors that influence LAAV. METHODS: In all, 500 patients with stroke were examined consecutively by transesophageal echocardiography. In addition to measurement of the LAAV, the atrial appendage was examined for the presence of thrombi or SEC. RESULTS: LAAV differed significantly among patients with sinus rhythm (71 +/- 16 cm/s), paroxysmal atrial fibrillation (AF) and in sinus rhythm during transesophageal echocardiography (46 +/- 13 cm/s), paroxysmal AF and AF during transesophageal echocardiography (32 +/- 12 cm/s), and chronic AF (27 +/- 9 cm/s, P < .001). Independent of the rhythm, the risk of thrombus/SEC increased significantly at an LAAV less than 55 cm/s. At an LAAV 55 cm/s or more there is only a minimal risk of thrombus/SEC (negative predictive value 100% and 99%, respectively). Multivariate analysis showed that LAAV is the strongest predictor for the occurrence of thrombus/SEC (P < .0001). Further multivariate analysis showed that left ventricular ejection fraction, LA size, (paroxysmal) AF, age, and sex are independent parameters influencing LAAV. CONCLUSION: Independent of the basic rhythm, there is a close relationship between LAAV and qualitative parameters of elevated thromboembolic risk. LAAV could, therefore, be a quantitative surrogate parameter for risk stratification. It is influenced by both cardiac and extracardiac factors.

Adult↗
PubMed2003

New three-dimensional echocardiographic system using digital radiofrequency data--visualization and quantitative analysis of aortic valve dynamics with high resolution: methods, feasibility, and initial clinical experience.

BACKGROUND: Common 3D systems have only limited spatial and temporal resolution (frame rate of 25 Hz). Thin structures such as cardiac valves are not imaged exactly; rapid movement patterns cannot be precisely recorded. The objective of the present project was to achieve radiofrequency (RF) data transmission to the 3D workstation to improve image resolution. METHODS AND RESULTS: A commercially available echocardiographic system (5-MHz transesophageal echocardiography probe) with an integrated raw data interface enables transmission of RF data (up to 40 megabytes per second). A 3D data set may contain up to 3 gigabytes, so that all of the high-resolution ultrasound information of the 2D image is available. Frame rates of up to 168 Hz result in temporal resolution 6 times that of standard 3D systems. The applicability of the system and the image quality were tested in 10 patients. The structure of the aortic valve and the dynamic changes were depicted by volume rendering. The changes in the orifice areas were measured in frame-by-frame planimetry. The mean number of frames recorded per cardiac cycle was 122+/-16. The improved structural resolution enabled a detailed imaging of the morphology of the aortic cusps. The rapid systolic movement patterns were recorded with up to 51 frames. The high number of frames enabled creation of precise area-time diagrams. Thus, the individual phases of aortic valve movement (rapid opening, slow valve closing, and rapid valve closing) could be analyzed quantitatively. CONCLUSIONS: A 3D system based on RF data enables high-resolution imaging of cardiac movement patterns. This offers new perspectives for qualitative and quantitative analyses, especially of cardiac valves.

Aortic Valve↗
PubMed2003

In vivo analysis of aortic valve dynamics by transesophageal 3-dimensional echocardiography with high temporal resolution.

OBJECTIVES: Knowledge of aortic valve function has been obtained from experimental studies. The aim of the present study was to investigate characteristics of aortic valve motion in humans. METHODS: Fifty-six patients were studied: 19 with normal valve and good systolic left ventricular function (Group NL), 12 with normal valve and reduced left ventricular function (Group CMP), and 25 with aortic stenosis and good left ventricular function (Group AS). The frame rate was doubled (50 Hz) compared with previous 3-dimensional systems. A mean of 38 +/- 9 images were acquired per cardiac cycle, with 14 +/- 4 images during the systole. The changes in shape and orifice area were analyzed over time. RESULTS: With normal valves, valve movement proceeded in 3 phases: rapid opening, slow closing, rapid closing. Stenotic valves showed a slower opening and closing movement. The times to maximum opening in Groups NL, CMP, AS were 76 +/- 30, 88 +/- 18 (P =.06), and 130 +/- 29 (P <.01) ms, respectively. It was inversely correlated to the maximum orifice area (r = -0.59, P <.001). The opening velocities in Groups NL, CMP, AS were 42 +/- 23, 28 +/- 9 (P <.05), and 5 +/- 2 (P <.001) cm(2)/s, respectively. There was a close correlation between the opening velocity and the maximum orifice area (r = 0.87, P <.001). Slow valve closings occurred at a velocity of 8.0 +/- 5.2, 5.3 +/- 2.0 (P =.21), 2.8 +/- 1.1 (P <.01) cm(2)/s, respectively, and rapid closings in Groups NL and CMP at 50 +/- 23, 29 +/- 8 (P <.01) cm(2)/s. The results show good agreement with experimental data. CONCLUSION: Rapid aortic valve movement can be recorded by 3-dimensional echocardiography and analyzed quantitatively. Time and velocity indices of valve dynamics are influenced by valvular and myocardial factors. A comparable in vivo analysis is not possible with any other imaging procedure.

Aortic Valve↗
PubMed2003

Three-dimensional echocardiographic determination of cardiac output at rest and under dobutamine stress: comparison with thermodilution measurements in the ischemic pig model.

Determination of cardiac output is a potentially important clinical application of three-dimensional (3-D) echocardiography since it could replace invasive measurements with the Swan-Ganz-catheter. To date, there are no studies available to determine whether cardiac output measured by thermodilution can be predicted reliably under changing hemodynamic conditions. Fifteen pigs with ischemic myocardium were examined under four hemodynamic conditions at rest and under pharmacological stress with 5, 10, and 20 microg/kg/min dobutamine. The 3-D datasets were recorded by means of transesophageal echocardiography. The endocardial definition was enhanced by administering the contrast agent FS069 (Optison). Cardiac output was calculated as the product of stroke volume (end-diastolic - end-systolic volume) and heart rate. The invasive measurements were performed with a continuous thermodilution system. In general, there was moderate correlation between 3-D echocardiography and thermodilution(r = 0.72, P < 0.001). At rest, the 3-D echocardiographic measurements were slightly but significantly lower than the invasive measurements (mean difference 0.6 +/- 0.5L/min,P < 0.001). Under stress with 5, 10, and 20 microg/kg/min dobutamine, there was a marked increase in the deviation (1.3 +/- 0.5L/min,P < 0.001; 1.6 +/- 0.7 L/min,P < 0.001; and 2.1 +/- 1.1L/min,P < 0.001, respectively). The deviation was based on two factors: (1). Under stress, the decreasing number of frames per cardiac cycle acquired with 3-D echocardiography led to imprecise recording of end-diastolic and end-systolic volumes, and thus to an underestimation of cardiac output. At least 30 frames per cardiac cycle are needed to eliminate this effect. (2). There is a systematic difference between 3-D echocardiographic and invasive measurements, which is independent of the imaging rate. This is based on an overestimation of the true values by thermodilution. In conclusion, cardiac output can be determined correctly by 3-D echocardiography for normal heart rates at rest. At elevated heart rates, the temporal resolution of 3-D systems currently available is not adequate for reliable determination. In performing and evaluating future clinical comparative studies, the systematic difference between 3-D echocardiography and thermodilution, based on overestimation by thermodilution, must be taken into account.

Animals↗
PubMed2002

Quantitative assessment of aortic stenosis by three-dimensional anyplane and three-dimensional volume-rendered echocardiography.

Aortic stenosis is a challenge for three-dimensional (3-D) echocardiographic image resolution. This is the first study evaluating both 3-D anyplane and 3-D volume-rendered echocardiography in the quantification of aortic stenosis. In 31 patients, 3-D echocardiography was performed using a multiplane transesophageal probe. Within the acquired volume dataset, five parallel cross sections were generated through the aortic valve. Subsequently, volume-rendered images of the five cross sections were reconstructed. The smallest orifice areas of both series were compared with the results obtained by two-dimensional (2-D) transesophageal planimetry and those calculated by Doppler continuity equation. No significant differences were found between Doppler (0.76 +/- 0.18 cm(2)), 2-D echocardiography (0.78 +/- 0.24 cm(2)), and 3-D anyplane echocardiography (0.72 +/- 0.29 cm(2)). The orifice area measured smaller (0.54 =/- 0.31 cm(2), P < 0.001) by 3-D volume-rendered echocardiography. Bland-Altmann analysis indicated that for 3-D anyplane echocardiography, the mean difference from Doppler and 2-D echocardiography was - 0.04 +/- 0.24 cm(2) and - 0.06 +/- 0.23 cm(2), respectively. For 3-D volume-rendered echocardiography, the mean difference was -0.23 +/- 0.24 cm(2) and - 0.25 +/- 0.26 cm(2), respectively. In the subgroup with good resolution in the 3-D dataset, close limits of agreement were obtained between 3-D echocardiography and each of the reference methods, while the subgroup with poor resolution showed wide limits of agreement. In conclusion, planimetry of the stenotic aortic orifice by 3-D volume-rendered echocardiography is feasible but tends to underestimate the orifice area. Three-dimensional anyplane echocardiography shows better agreement with the reference methods. Accuracy is influenced strongly by the structural resolution of the stenotic orifice in the 3-D dataset.

Adult↗
PubMed2002

Percutaneous aortic valve replacement: an experimental study. I. Studies on implantation.

OBJECTIVE: The purpose of this preliminary study was to devise a new surgical procedure for minimally invasive aortic valve implantation with a transluminal technique. METHODS: The new collapsible heart valve was prepared by mounting a porcine aortic valve, taken from a freshly slaughtered pig, into a self-expandable nitinol stent by means of a suture technique. The outer diameter of the valved stent ranged from 15 to 23 mm, and the length ranged from 21 to 28 mm. Before implantation in vivo, these valved stents were tested in an in vitro circulatory system. Only in vitro-tested valved stents with a pressure gradient of less than 7 mm Hg and regurgitation of I degrees or less were used for transluminal aortic valve implantation in vivo. Six of these valved stents were implanted in the descending aorta and 8 in the ascending aorta of anesthetized pigs. The catheter delivery system (22F) was extraperitoneally inserted through the left iliac artery or the infrarenal aorta. Measurements for transvalvular gradient, valvular opening and closure, blood-flow characteristics, regurgitation, and macroscopic analysis were performed at baseline and after the observation period (164 +/- 48 minutes). RESULTS: This preliminary study contained 14 animals. One animal died of ventricular fibrillation. Technical failure occurred in 2 pigs as a result of stent twisting. At the end of the observation period, the 11 successfully implanted valved stents demonstrated low transvalvular gradients (mean end-systolic Deltarho(max) of 5.4 +/- 3.3 mm Hg for the descending aorta group, 5.4 +/- 1.2 mm Hg for the supracoronary group, and 5.4 +/- 1.1 mm Hg for the subcoronary group), which did not differ from their in vitro gradients. Two-dimensional echocardiography demonstrated complete valvular closure and opening in 5 of 5 cases. Angiography indicated only a physiologic jet of regurgitation (0 degrees ) in 8 animals and mild (I degrees ) regurgitation in 3 animals. Color Doppler ultrasonography indicated no regurgitation in 5 of 5 cases and minor paravalvular leakage in 1 case. CONCLUSION: Aortic valved stents can be successfully implanted without thoracotomy by using a transluminal catheter technique. Long-term function of the valves remains to be established.

Animals↗