Biomedical subjects

Thomas Buck

Publications and source records attributed to Thomas Buck.

21 records · Page 2Linked to original sources

PubMed2002

[Echocardiography diagnosis of diastolic heart failure].

BACKGROUND: Left ventricular diastolic dysfunction can be diagnosed if clinical signs of heart failure and normal ejection fraction are found. Beside clinical signs of heart failure and criteria from catheterization studies like abnormal left ventricular relaxation, filling and/or compliance echocardiography provides valuable parameters for the assessment of diastolic dysfunction. ECHOCARDIOGRAPHIC DEGREES OF SEVERITY: By the use of various parameters diastolic dysfunction can be differentiated into four degrees of severity, which are of great prognostic importance. If more than one echocardiographic parameter is used, sensitivity for the assessment of diastolic dysfunction becomes nearly 100%. Conventional parameters include isovolumetric relaxation time (IVRT) measured by pulsed Doppler, the ratio of rapid filling and atrial filling velocity (E/A), deceleration time of rapid mitral inflow as well as the ratio of systolic and diastolic pulmonary venous flow velocities. In patients with signs of diastolic heart failure and a normal E/A ratio pulmonary venous flow pattern can help to unmask "pseudonormalization" as the transition from abnormal relaxation to restriction. These parameters, however, are preload-dependent and do not provide intrinsic left ventricular properties. Even in atrial fibrillation, left ventricular filling pressure can be assessed. NEW METHODS: Two novel approaches, color Doppler M-mode of left ventricular inflow and tissue Doppler of the mitral annulus, are relatively preload-independent and allow direct estimation of relaxation and filling pressure. By the means of real-time 3-D echocardiography we developed a new method for the non-invasive assessment of rapid filling rate (PFR), thereby completing the echocardiographic approaches to determine diastolic dysfunction. CONCLUSION: The broad spectrum of approaches available today makes echocardiography the first choice for the assessment of diastolic dysfunction.

Echocardiography↗

PubMed2002

[Echocardiography flow quantification for determining the severity of heart valve insufficiency].

BACKGROUND: Beyond conventional echocardiographic Doppler methods allowing only semiquantitative estimation of the severity of valvular regurgitation, new approaches are attempting to quantify regurgitant flow as a measure of left ventricular volume overload. Different concepts are leading to significant differences in accuracy and feasibility in clinical routine between the methods. We are reviewing the existing methods with their advantages and limitations as well as the underlying hemodynamic concepts. ECHOCARDIOGRAPHIC METHODS FOR ESTIMATION OF SEVERITY: Semiquantitative methods are jet area/jet length method, proximal jet width as well as the pressure half-time method. Determination of regurgitant flow is permitted by means of the continuity method, PISA ("Proximal Isovelocity Surface Area") method, ACOM ("Automated Cardiac Output Measurement") technique, and the PVI ("Power-Velocity Integral") method. Grading of severity is usually based on a scale from 1 to 3 or 1 to 4 where semiquantitative methods are limited by a significant overlap of the individual degrees and therefore only provide rough estimates of severity. Compared to this, quantitative methods allow quantitative determination of regurgitant flow, regurgitant volume, regurgitant fraction, and effective regurgitant orifice area based on different Doppler flow measurements, that are again affected by specific limitations: (1) the continuity method is considerably limited because it is measuring the flow through two different valves; (2) the PISA method is dependent on the geometry of the proximal flow convergence zone and requires highly skilled observers; (3) the ACOM method is also dependent on the geometry of the proximal flow convergence zone und ideally requires three-dimensional color Doppler datasets; (4) the PVI method provides direct measurement of regurgitant flow from a pulsed Doppler signal of sufficient high quality, however, this method is not widely available, yet. For the decision which method to apply the following should be taken into account: (1) interpretation of semiquantitative findings depends on the extent by which the methods' estimation of flow deviates from a measurement of flow; (2) accuracy of the quantitative methods depends on the underlying hemodynamic concept and the simplifying assumptions. CONCLUSION: Current echocardiography provides a broad spectrum of semiquantitative und quantitative Doppler methods for the estimation of regurgitant flow. Since semiquantitative methods only allow rough estimates of severity, quantitative measurement of regurgitant volume/fraction or effective regurgitant orifice area should be attempted in any case with uncertainty whether regurgitation is mild, moderate, or severe.

Aortic Valve Insufficiency↗

PubMed2002

Real-time three-dimensional echocardiography for improved evaluation of diastolic function using volume-time curves.

BACKGROUND: Accurate assessment of left ventricular function is of the greatest importance in clinical cardiology for decision making. Diastolic dysfunction is getting more concern as a cause of heart failure while, currently used non-invasive modalities for diagnosing diastolic abnormalities have significant limitations. Dynamic left ventricular volume change was applied for the evaluation of diastolic function by various techniques that have been demonstrated to be of diagnostic value. However, it has not been accepted into clinical practice because existing techniques are either invasive, inaccurate, expensive or time consuming. REAL-TIME THREE-DIMENSIONAL ECHOCARDIOGRAPHY: Real-time three-dimensional (3-D) echocardiography is a new ultrasound technique that provides transthoracic volumetric images of the heart in real time. Thereby, the acquired images are ideally suited for the assessment of dynamic left ventricular volume change. Generation and analysis of left ventricular volume-time curves by real-time 3-D echocardiography has been demonstrated to be feasible in normal subjects and patients and accuracy of volume-time curves was good compared to magnetic resonance imaging. We compare the new real-time 3-D echo approach with the advantages and limitations of existing noninvasive and invasive techniques.

Cardiac Volume↗