J. D. Thomas

Doin’ the twist: new tools for an old concept of myocardial function

It has been known for some time that the heart rotates during the cardiac cycle in concert with radial and longitudinal motion. With advances in imaging technology, it has been appreciated that the apex and base of the heart rotate in different directions, resulting in a twisting or torsional motion. A new echocardiographic technique, “speckle tracking imaging”, permits accurate quantification of this motion. Torsion as well as the timing and magnitude of the rate of torsion (torsional velocity) may provide important new insights into cardiac physiology and disease.

Is Doppler tissue velocity during early left ventricular filling preload independent

Background: Transmitral Doppler flow indices are used to evaluate diastolic function. Recently, velocities measured by Doppler tissue imaging have been used as an index of left ventricular relaxation. Objective: To determine whether Doppler tissue velocities are influenced by alterations in preload. Methods: Left ventricular preload was altered in 17 patients (all men, mean (SD) age, 49 (8) years) during echocardiographic measurements of left ventricular end diastolic volume, maximum left atrial area, peak early Doppler filling velocity, and left ventricular myocardial velocities during early filling. Preload altering manoeuvres included Trendelenberg (stage 1), reverse Trendelenberg (stage 2), and amyl nitrate (stage 3). Systolic blood pressure was measured at each stage. Results: In comparison with baseline, left ventricular end diastolic volume (p = 0.001), left atrial area (p = 0.003), peak early mitral Doppler filling velocity (p = 0.01), and systolic blood pressures (p = 0.001) were all changed by preload altering manoeuvres. Only left ventricular myocardial velocity during early filling remained unchanged by these manoeuvres. Conclusions: In contrast to standard transmitral Doppler filling indices, Doppler tissue early diastolic velocities are not significantly affected by physiological manoeuvres that alter preload. Thus Doppler tissue velocities during early left ventricular diastole may provide a better index of diastolic function in cardiac patients by providing a preload independent assessment of left ventricular filling.

Assessment of internal mammary artery and saphenous vein graft patency and flow reserve using transthoracic Doppler echocardiography

OBJECTIVE To investigate transthoracic Doppler echocardiography in the identification of coronary artery bypass graft (CABG) flow for assessing graft patency. DESIGN The initial study group comprised 45 consecutive patients with previous CABG undergoing elective cardiac catheterisation for recurrent ischaemia. The Doppler variables best correlated with angiographic graft patency were then tested prospectively in a further 84 patients (test group). SETTING Three tertiary referral centres. INTERVENTIONS Flow velocities in grafts were recorded at rest and during hyperaemia induced by dipyridamole (0.56 mg/kg/4 min), under the guidance of transthoracic colour Doppler flow mapping. Findings on transthoracic Doppler were compared with angiography. MAIN OUTCOME MEASURES Feasibility of identifying open grafts by Doppler and diagnostic accuracy for Doppler detection of significant (⩾ 70%) graft stenosis. RESULTS In the test group the identification rate for mammary artery grafts was 100%, for saphenous vein grafts to left anterior descending coronary artery 91%, for vein grafts to right coronary artery 96%, and for vein grafts to circumflex artery 90%. Coronary flow reserve (the ratio between peak diastolic velocity under hyperaemia and at baseline) of < 1.9 (95% confidence interval 1.83 to 2.08) had 100% sensitivity, 98% specificity, 87.5% positive predictive value, and 100% negative predictive value for mammary artery graft stenosis. Coronary flow reserve of < 1.6 (95% CI 1.51 to 1.73) had 91% sensitivity, 87% specificity, 85.4% positive predictive value, and 92.3% negative predictive value for significant vein graft stenosis. CONCLUSIONS Transthoracic Doppler can provide non-invasive assessment of CABG patency.

Estimation of cardiac reserve by peak power: validation and initial application of a simplified index

OBJECTIVES To validate a simplified estimate of peak power (SPP) against true (invasively measured) peak instantaneous power (TPP), to assess the feasibility of measuring SPP during exercise and to correlate this with functional capacity. DESIGN Development of a simplified method of measurement and observational study. SETTING Tertiary referral centre for cardiothoracic disease. SUBJECTS For validation of SPP with TPP, seven normal dogs and four dogs with dilated cardiomyopathy were studied. To assess feasibility and clinical significance in humans, 40 subjects were studied (26 patients; 14 normal controls). METHODS In the animal validation study, TPP was derived from ascending aortic pressure and flow probe, and from Doppler measurements of flow. SPP, calculated using the different flow measures, was compared with peak instantaneous power under different loading conditions. For the assessment in humans, SPP was measured at rest and during maximum exercise. Peak aortic flow was measured with transthoracic continuous wave Doppler, and systolic and diastolic blood pressures were derived from brachial sphygmomanometry. The difference between exercise and rest simplified peak power (Δ SPP) was compared with maximum oxygen uptake (V˙O2max), measured from expired gas analysis. RESULTS SPP estimates using peak flow measures correlated well with true peak instantaneous power (r = 0.89 to 0.97), despite marked changes in systemic pressure and flow induced by manipulation of loading conditions. In the human study, V˙O2max correlated with Δ SPP (r = 0.78) better than Δ ejection fraction (r = 0.18) and Δ rate–pressure product (r = 0.59). CONCLUSIONS The simple product of mean arterial pressure and peak aortic flow (simplified peak power, SPP) correlates with peak instantaneous power over a range of loading conditions in dogs. In humans, it can be estimated during exercise echocardiography, and correlates with maximum oxygen uptake better than ejection fraction or rate–pressure product.

A geometric deformable model for echocardiographic image segmentation

Gradient vector flow (GVF), an elegant external force for parametric deformable models, can capture object boundaries from both sides. A new geometric deformable model is proposed that combines GVF and the geodesic active contour model. The level set method is used as the numerical method of this model. The model is applied for echocardiographic image segmentation.

Three dimensional reconstruction (shape and motion) of tricuspid annulus in normals and in patients after tricuspid annuloplasty with a flexible ring

Knowledge of tricuspid annular shape, size and motion is critical for surgical repair of the tricuspid valve. However these characteristics for the valve are poorly understood. The authors reconstructed the three dimensional shape and motion of the tricuspid annulus in 2 normals and 2 patients who underwent tricuspid valve repair using a flexible annuloplasty ring. The data were acquired with EKG and respiratory gating. The algorithm allows for quantitative analysis of annular area and excursion over a cardiac cycle. The preliminary results show that the shape and motion of tricuspid annulus is preserved by the flexible tricuspid valve annuloplasty ring.

Estimation of diastolic intraventricular pressure gradients from color Doppler M-mode spatiotemporal velocities: analytical Euler equation solution

The importance of left ventricular diastolic function continues to drive experimental efforts to understand underlying processes involved in filling dynamics and challenge researchers to develop improved methods to evaluate cardiac function. Diastolic intraventricular pressure gradients can be estimated from spatiotemporal velocity distributions obtained from color Doppler M-mode echocardiography. The Euler equation describes incremental pressure changes as a function of time-varying velocities along a streamline. Integration of these local pressure gradients allows comparison of pressure at different levels within the ventricle. The authors have demonstrated that the pressure drop at the apex was more and occurred earlier when compared to mid-ventricular and basal pressures. The quantification of these intraventricular gradients may assist in the evaluation of diastolic function.<<ETX>>

Impact of temporal resolution on flow quantification by real-time 3D color Doppler echocardiography: numerical modeling and animal validation study

Real-time, 3D color Doppler echocardiography (RT3D) is capable of quantifying flow at the LV outflow tract (LVOT). However, previous works have found significant underestimation for flow rate estimation due to finite scanning time (ST) of the color Doppler. The authors have, therefore, developed a mathematical model to correct the impact of ST on flow quantification and validated it by an animal study. Scanning time to cover the entire cross-sectional image of the LVOT was calculated as 60 ms, and the underestimation due to temporal averaging effect was predicted as 18/spl plusmn/7%. In the animal experiment, peak flow rates were obtained by spatially integrating the velocity data front the cross-sectional color images of the LVOT. By applying a correction factor, there was an excellent agreement between reference flow rate by an electromagnetic flow meter and RT3D (A/spl uml/=-5.6 ml/s, r=0.93), which was significantly better than without correction (p<0.001). Real-time, color 3D echocardiography was capable of quantifying flow accurately by applying the mathematical correction.

Non-invasive characterization of total arterial compliance by simultaneous acquisition of pressure and flow: advantages of the pulse pressure method

The authors compare three proposed indices of total arterial compliance (Ctot) in normal volunteers (n=9) and patients with coronary artery disease (n=14) using a non-invasive approach (echo-Doppler and carotid tonometry): (1) the pulse pressure method (PPM), (2) the area method (AM) and (3) the stroke volume-to-pulse pressure ratio (SV/PP). The best agreement was found between the PPM and SV/PP. Compliance estimates were lower in the patient group (PPM: 1.2/spl plusmn/0.4 vs. 1.6/spl plusmn/0.2; AM: 1.6/spl plusmn/0.6 vs. 2.8/spl plusmn/1.3; SV/PP: 1.8/spl plusmn/0.6 vs. 2.4/spl plusmn/0.4), being older (64/spl plusmn/14 vs. 35/spl plusmn/4 y) and with known atherosclerosis. The best correlation between compliance and age was found with PPM (r/sup 2/=0.52). AM varied with the chosen computation interval in diastole. These preliminary data describing the very first use of the PPM on non-invasive human recordings suggest that PPM could be a more robust estimator of Ctot than the widely used AM, and that SV/PP could be a reasonable simpler surrogate.

Real-time 3D echocardiographic data analysis for left ventricular volume estimation

A new computerized semi-automatic method for left ventricular chamber segmentation is presented. The left ventricle is imaged by real-time three-dimensional echocardiography. This real-time data acquisition method allows accurate evaluation of chamber size and shape, even in case there are cavities with irregular geometry. The surface detection model is based on a partial differential equation that propagates interfaces with curvature dependent speeds. The equation is solved by applying numerical methods for conservation laws. The method consists of one step only. Initial conditions are manually established on a small subset of slices of the entire volume. The solution obtained is a surface corresponding to the surface between LV cavity and LV endocardium. This mathematical model is applied to sequences of frames of human hearts (volume range: 34-109 ml) imaged by real-time 3D echocardiography. Volume estimates show an excellent correlation with those obtained by manual tracing (r=0.99).