Bengt Wranne

Particle trace visualization of intracardiac flow using time-resolved 3D phase contrast MRI

The flow patterns in the human heart are complex and difficult to visualize using conventional two‐dimensional (2D) modalities, whether they depict a single velocity component (Doppler echocardiography) or all three components in a few slices (2D phase contrast MRI). To avoid these shortcomings, a temporally resolved 3D phase contrast technique was used to derive data describing the intracardiac velocity fields in normal volunteers. The MRI data were corrected for phase shifts caused by eddy currents and concomitant gradient fields, with improvement in the accuracy of subsequent flow visualizations. Pathlines describing the blood pathways through the heart were generated from the temporally resolved velocity data, starting from user‐specified locations and time frames. Flow trajectories were displayed as 3D particle traces, with simultaneous demonstration of morphologic 2D slices. This type of visualization is intuitive and interactive and may extend our understanding of dynamic and previously unrecognized patterns of intracardiac flow. Magn Reson Med 41:793–799, 1999.

Transit of Blood Flow Through the Human Left Ventricle Mapped by Cardiovascular Magnetic Resonance

BACKGROUND The transit of blood through the beating heart is a basic aspect of cardiovascular physiology which remains incompletely studied. Quantification of the components of multidirectional flow in the normal left ventricle (LV) is lacking, making it difficult to put the changes observed with LV dysfunction and cardiac surgery into context. METHODS Three dimensional, three directional, time resolved magnetic resonance phase-contrast velocity mapping was performed at 1.5 Tesla in 17 normal subjects, 6 female, aged 44+/-14 years (mean+/-SD). We visualized and measured the relative volumes of LV flow components and the diastolic changes in inflowing kinetic energy (KE). Of total diastolic inflow volume, 44+/-11% followed a direct, albeit curved route to systolic ejection (videos 1 and 2), in contrast to 11% in a subject with mildly dilated cardiomyopathy (DCM), who was included for preliminary comparison (video 3). In normals, 16+/-8% of the KE of inflow was conserved to the end of diastole, compared with 5% in the DCM patient. Blood following the direct route lost or transferred less of its KE during diastole than blood that was retained until the next beat (1.6+/-1.0 millijoules vs 8.2+/-1.9 millijoules, p<0.05); whereas, in the DCM patient, the reduction in KE of retained inflow was 18-fold greater than that of the blood tracing the direct route. CONCLUSION Multidimensional flow mapping can measure the paths, compartmentalization and kinetic energy changes of blood flowing into the LV, demonstrating differences of KE loss between compartments, and potentially between the flows in normal and dilated left ventricles.

Noninvasive Measurement of Time-Varying Three-Dimensional Relative Pressure Fields Within the Human Heart

Understanding cardiac blood flow patterns is important in the assessment of cardiovascular function. Three-dimensional flow and relative pressure fields within the human left ventricle are demonstrated by combining velocity measurements with computational fluid mechanics methods. The velocity field throughout the left atrium and ventricle of a normal human heart is measured using time-resolved three-dimensional phase-contrast MRI. Subsequently, the time-resolved three-dimensional relative pressure is calculated from this velocity field using the pressure Poisson equation. Noninvasive simultaneous assessment of cardiac pressure and flow phenomena is an important new tool for studying cardiac fluid dynamics.

Echocardiographic assessment of ejection fraction in left ventricular hypertrophy.

OBJECTIVE To investigate the value of Simpson’s rule, Teichholz’s formula, and recording of mitral ring motion in assessing left ventricular ejection fraction (EF) in patients with left ventricular hypertrophy. DESIGN Left ventricular ejection fraction calculated by Simpson’s rule and by Techholz’s formula and estimated by mitral ring motion was compared with values obtained by radionuclide angiography. SETTING Secondary referral centre. PATIENTS 16 patients with left ventricular hypertrophy and a clinical diagnosis of hypertrophic cardiomyopathy or hypertension. RESULTS Calculation by Teichholz’s formula overestimated left ventricular ejection fraction by 10% (p = 0.002) and estimation based on mitral ring motion—that is, long axis measurements—underestimated ejection fraction by 19% (p = 0.002), without significant correlation between ring motion and ejection fraction. There was no significant difference between mean values of ejection fraction calculated by Simpson’s rule and measured by the reference method, but a considerable scatter about the regression line with a standard error of the estimate of 9.3 EF%. CONCLUSIONS In patients with left ventricular hypertrophy the ejection fraction, calculated by Teichholz’s formula or Simpson’s rule, is a poor measure of left ventricular function. When mitral ring motion is used for the assessment in these patients the function should be expressed in ways other than by the ejection fraction.

A Comparison of Regional Myocardial Velocity Information Derived by Pulsed and Color Doppler Techniques: An In Vitro and In Vivo Study

The objective was to compare velocity information derived from either a tissue mimicking phantom or normal contracting myocardium by both pulsed wave and color Doppler myocardial imaging (PWDMI and CDMI). Both CDMI and PWDMI allow quantitative assessment of regional myocardial contraction and relaxation velocities, but their potential clinical applications have not yet been investigated. Moreover, no information is available as to whether they can be used interchangeably for regional velocity assessment. For the in vitro study, a rotating, circular‐shaped, tissue‐mimicking sponge driven by a motor at speeds of 15, 30, 60, 90 rpm was used to derive velocity data from the same eight points of interest by using PWDMI or CDMI techniques. For the in vivo study, 25 normal subjects were examined at rest using parasternal and apical approaches. Velocity profiles were derived from the same 26 areas of interest (18 left ventricular segments, 3 right ventricular segments, and 5 measurement points for the tricuspid and mitral annuli) for each technique. Peak maximal velocities were detected by PWDMI and peak mean velocities were measured using CDMI. The results of the in vitro study phantom showed excellent correlation (r = 0.99, P < 0.001) and satisfactory agreement (0.04 cm/sec; 3.3 cm/sec) between both Doppler techniques. PWDMI velocities were higher than CDMI velocities by up to 20% and overestimated the real velocity value (0.37 ± 0.29 cm/sec) while CDMI underestimated predicted velocity by 1.35 ± 0.36 cm/sec. Good correlation (r = 0.87, P < 0.001), but poor agreement (−2.1 cm/sec; 5.4 cm/sec) was shown in vivo for all segments with regard to peak systolic and diastolic velocities. Both Doppler techniques cannot be used interchangeably for comparing peak velocities in the clinical situation. However, with adequate temporal resolution, they can be used interchangeably for velocity profile recording and for timing of events.

Echocardiographic assessment of arrhythmogenic right ventricular cardiomyopathy

OBJECTIVE To evaluate new echocardiographic modes in the diagnosis of arrhythmogenic right ventricular cardiomyopathy (ARVC). DESIGN Prospective observational study. SETTING University Hospital. SUBJECTS 15 patients with ARVC and a control group of 25 healthy subjects. METHODS Transthoracic echocardiography included cross sectional measurements of the right ventricular outflow tract, right ventricular inflow tract, and right ventricular body. Wall motion was analysed subjectively. M mode and pulsed tissue Doppler techniques were used for quantitative measurement of tricuspid annular motion at the lateral, septal, posterior, and anterior positions. Doppler assessment of tricuspid flow and systemic venous flow was also performed. RESULTS Assessed by M mode, the total amplitude of the tricuspid annular motion was significantly decreased in the lateral, septal, and posterior positions in the patients compared with the controls. The tissue Doppler velocity pattern showed decreased early diastolic peak annular (EA) velocity and an accompanying decrease in early (EA) to late diastolic (AA) velocity ratio in all positions; the systolic annular velocity was significantly decreased only in the lateral position. Four patients had normal right ventricular dimensions and three were judged to have normal right ventricular wall motion. The patient group had also a significantly decreased tricuspid flow E:A ratio. CONCLUSIONS Tricuspid annular measurements are valuable, easy to obtain, and allow quantitative assessment of right ventricular function. ARVC patients showed an abnormal velocity pattern that may be an early but non-specific sign of the disease. Normal right ventricular dimensions do not exclude ARVC, and subjective detection of early changes in wall motion may be difficult.

Effect of Increased Blood Oxygen Affinity on Work Performance of Rats

Influence of altered blood oxygen affinity on maximal performance ability was evaluated in trained rats exercising to exhaustion in a graded treadmill test. Modification of blood oxygen affinity was achieved both by 2,3-diphosphoglycerate depletion, accomplished by exposure of animals to CO(2) and by exchange transfusion with blood exposed to bisulfite or stored in acid citrate dextrose, and by carbamylation of hemoglobin, produced by exchange transfusion of blood incubated with potassium cyanate. A decrease in oxygen tension at half-saturation of hemoglobin (P(50)) from 36 to 23 mm Hg produced a decrease in resting central venous oxygen pressure of about 12 mm Hg. During exercise it caused an average decrease in work performance of about 10%, which was equivalent to that performance decrement caused by a decrease in hemoglobin concentration of approximately 10%. When superimposed on anemia, this change in blood oxygen affinity again caused a similar decrease in performance over and above that due to anemia alone. A marked rightward shift of the in vivo oxygen dissociation curve during severe exercise may have compensated for the reduced in vitro P(50).

Left ventricular contraction pattern changes with age in normal adults

Left ventricular ejection fraction is known to be unchanged or slightly increased with advancing age. This echocardiographic study, including 40 healthy subjects 18 to 70 years old, shows that this is a net effect of decreased contractions in the long axis and increased in the short axis. From age 18 to 70 years, the longitudinal shortening decreases by 20% (P < .001) and the short-axis diameter shortening increases by 18% (P=.012). Multiple regression analysis showed strong correlation to age for both short- and long-axis contractions and no significant additional explicatory power when the variables systolic blood pressure, left ventricular wall thickness, heart rate, or sex were included. There was no significant correlation between diameter changes during the isovolumic phases and age. The findings have practical implications when calculating ejection fraction from M-mode measurements. Teichholzs formula will overestimate ejection fraction in elderly subjects, and calculation of ejection fraction from mitral ring motion will overestimate it in young subjects.

Left ventricular involvement in arrhythmogenic right ventricular cardiomyopathy – a scintigraphic and echocardiographic study

Background:  Left ventricular involvement in arrhythmogenic right ventricular cardiomyopathy (ARVC) is a common finding in autopsy studies. In clinical studies using myocardial scintigraphy, MRI and echocardiography, contradictory results have been reported. In this study, we therefore investigated a group of 15 patients with ARVC using thallium‐201 (Tl) single‐photon emission tomography (SPECT) and echocardiography including assessment of mitral annular motion with M‐mode and pulsed tissue Doppler.

Noninvasive assessment of valve area in patients with aortic stenosis

A noninvasive method for quantification of aortic orifice area in patients with aortic stenosis is presented and compared with cardiac catheterization data in 24 patients (mean age 67 years). A continuous wave 2 MHz Doppler ultrasound instrument was used to measure the maximal velocity of the aortic jet, and time-averaged pressure drop was obtained by planimetry from the maximal velocity spectral recording using a simplified Bernoulli equation. Left ventricular ejection time was also measured from the spectral recording. Stroke volume was determined with a carbon dioxide-rebreathing method. Noninvasively determined aortic valve areas showed a close correlation with those determined at cardiac catheterization, but mean pressure gradients measured noninvasively were slightly but significantly higher than those measured at catheterization, leading to an underestimation of valve areas with the noninvasive technique, especially when valve areas were large. Neglect of blood flow velocity in the left ventricular outflow tract and recovery of static pressure downstream from the aortic orifice contribute to the difference in the pressure measurements. All patients with a valve area less than 1 cm2 at catheterization, however, also had an area less than 1 cm2 at the noninvasive investigation. This noninvasive approach to the evaluation of the severity of aortic stenosis seems promising for routine clinical use.