Influence of Doppler sample volume location on the assessment of changes in mitral inflow velocity profiles

Correlation of left ventricular diastolic filling characteristics with right ventricular overload and pulmonary artery pressure in chronic thromboembolic pulmonary hypertension

OBJECTIVES

This study was designed to determine a quantitative relationship between right ventricular (RV) pressure overload and left ventricular (LV) diastolic filling characteristics in patients with chronic thromboembolic pulmonary hypertension (CTEPH).

BACKGROUND

Right ventricular pressure overload in patients with CTEPH causes abnormal LV diastolic filling. However, a quantitative relationship between RV pressure overload and LV diastolic function has not been established.

METHODS

We analyzed pre- and postoperative diastolic mitral inflow velocities and right heart hemodynamic data in 39 consecutive patients with CTEPH over the age of 30 (55 +/- 11 years) with mean pulmonary artery pressure >30 mm Hg who underwent pulmonary thromboendarterectomy (PTE).

RESULTS

After PTE, mean pulmonary artery pressure (mPAP) decreased from 50 +/- 11 to 28 +/- 9 mm Hg (p < 0.001) while cardiac output (CO) increased from 4.4 +/- 1.1 to 5.7 +/- 0.9 l/m (p < 0.001). Mitral E/A ratio (E/A) increased from 0.74 +/- 0.22 to 1.48 +/- 0.69 (p < 0.001). E/A was < 1.25 in all patients pre-PTE. After PTE, all patients with E/A >1.50 had mPAP <35 mm Hg and CO >5.0 l/min. E/A correlated inversely with mPAP (r = 0.55, p < 0.001) and directly with CO (r = 0.53, p < 0.001).

CONCLUSIONS

E/A is consistently abnormal in patients with CTEPH and increases post-PTE. Moreover, E/A varies inversely with mPAP and directly with CO. Following PTE, E/A >1.5 correlates with the absence of severe pulmonary hypertension (mPAP >35 mm Hg) and the presence of normal cardiac output (> 5.0 l/m).

Effects of age, body weight, and heart rate on transmitral and pulmonary venous flow in clinically normal dogs

OBJECTIVE

To determine the influence of age, body weight (BW), heart rate (HR), sex, and left ventricular shortening fraction (LVSF) on transmitral and pulmonary venous flow in clinically normal dogs.

ANIMALS

92 client-owned dogs 3 months to 19 years old.

PROCEDURE

Transthoracic Doppler echocardiography recordings of transmitral flow and pulmonary venous flow were obtained in conscious unsedated dogs. Influence of age, BW, HR, sex, and LVSF on diastolic variables was assessed, using statistical methods such as ANOVA on ranks and univariate and multivariate forward stepwise linear regression analyses.

RESULTS

Age significantly influenced isovolumic relaxation time (IVRT, r = 0.56), ratio between peak velocity of the early diastolic mitral flow wave-to-peak velocity of late diastolic mitral flow wave (E:A; r = -0.44), deceleration time of early diastolic mitral flow (DTE; r = 0.26), and peak velocity of atrial reversal pulmonary venous flow wave (AR-wave; r = 0.37). Significant changes of mitral inflow and pulmonary venous flow variables were evident only in dogs > 6 and > 10 years old, respectively. Body weight significantly influenced DTE (r = 0.63), late diastolic flow duration (r = 0.60), and AR duration (r = 0.47), whereas HR significantly affected DTE (r = -0.34), IVRT (r = -0.33), and peak velocity of AR (r = 0.24). Sex or LVSF (range 22 to 48%) did not influence any echocardiographic variables.

CONCLUSIONS AND CLINICAL RELEVANCE

Age, BW, and HR are important factors that affect filling of the left atrium and left ventricle in clinically normal dogs.

Age-dependent changes in spatial and temporal blood velocity distribution of early left ventricular filling

This study describes early diastolic inflow dynamics based on three-directional magnetic resonance velocity data and investigates age-dependent changes in early diastolic inflow characteristics. We examined 26 young healthy volunteers age 25 (3) years (mean, SD), and 23 healthy older volunteers age 63 (8) years. Three-directional magnetic resonance velocity mapping was performed in a long axis plane through the heart. Transverse velocity profiles were read in five different positions in the early diastolic inflow stream of the left ventricle. The size and timing of the maximum velocities at each level were recorded and the repeatability of the method was tested. Compared with the younger group, the older group was characterized by: 1) lower maximum velocity in all positions, 2) increased deceleration of blood downstream from the mitral leaflet tips, and 3) delayed velocity propagation. The described method was repeatable and enabled detection of the age-dependent differences between groups of normal subjects. In conclusion, the early diastolic inflow pattern changes with age, probably reflecting changes in the diastolic function of the myocardium.

Beta-adrenergic stimulation enhances left ventricular diastolic performance in normal subjects

To determine the effects of beta-adrenergic stimulation on transmitral Doppler echocardiography flow characteristics of left ventricular diastolic filling, we studied 10 healthy volunteers aged 23-31 years (mean age, 26.6 years) during intravenous infusion of isoprenaline in consecutive steps of 0.1, 0.2, 0.4, 0.75, and 1.5 micrograms/min (each for 15 min). Saline control infusion was given in the same manner in a crossover and blinded protocol. Compared with the infusion of placebo, stepwise increasing doses of isoprenaline caused a dose-related increase in early and late diastolic filling velocities and velocity-time integrals, a lengthening of the acceleration time, and a shortening of the deceleration and filling time. The chosen method proved highly sensitive, as statistically significant changes were detectable at the lowest dose of 0.1 microgram/min for all variables except velocity-time integral of late filling and deceleration time (> or = 0.2 microgram/min). The effects related to dose in a log-linear fashion except for the lengthening of the acceleration time (early ceiling), the increase of peak early filling velocity (increased steepness at higher doses), and the shortening of the filling time. Inclusion of the associated increases in heart rate and systolic blood pressure and the decrease in diastolic blood pressure blunted all treatment contrasts except for the increase of peak early filling velocity. In addition, the hemodynamics with respect to heart rate and loading conditions were not altered at low dosages of drug (< 0.4 microgram/min). Effects of at least the peak early filling velocity must be interpreted as an active adrenergically mediated myocardial relaxation process. These findings have potentially important clinical implications for this noninvasive, readily available, and convenient technique in clinical pharmacology, stress testing, and possibly therapeutic interventions in diastolic dysfunction in humans.

Doppler evaluation of left and right ventricular diastolic function: a technical guide for obtaining optimal flow velocity recordings

Doppler mitral flow velocities and related variables are used to assess left (LV) and right ventricular filling and, indirectly, ventricular diastolic function. Three abnormal ventricular filling patterns (impaired relaxation and pseudonormal and restrictive physiology) are recognized in patients with various heart diseases and have been related to alterations in LV diastolic properties and filling pressures. More recently, these variables have been used to assess the hemodynamic effects of drug therapy or heart surgery and prognosis in patients with restrictive and dilated cardiomyopathies. Despite these encouraging results, widespread clinical use of these Doppler techniques has been hampered by difficulties in obtaining accurate and reproducible measurements from Doppler flow velocity recordings. This is due, in part, to an underappreciation of factors such as cardiac filling mechanics, Doppler examination principles, and ultrasound machine settings, which can markedly affect the quality of the flow velocity recordings. The purpose of this article is to provide the technical information for performing a systematic and comprehensive Doppler evaluation of LV diastolic function that can be used on a routine basis. This information includes discussing the different flow velocity recordings required for a Doppler assessment of LV diastolic function, their proper recording technique, and the common technical pitfalls.

Dobutamine stress Doppler echocardiography: reproducibility and physiologic left ventricular filling patterns

Qualitatively, dobutamine stress echocardiography has become an established procedure. Quantitative results are in great demand but this is still difficult due to limited endo- and epicardial border definition. Transmitral Doppler variables are strictly quantitative and less subjective. Furthermore, ischemic alterations precede systolic ones (ischemic cascade). There are preliminary reports of the utility of dobutamine stress Doppler echocardiography, but proof of reproducibility and left ventricular filling patterns are still lacking. Fourteen healthy volunteers (10 men, 4 women, median age 25.9 years, range 21-32 years) were investigated according to the usual dobutamine stress echocardiographic protocol (5, 10, 15, 20, 30, 40 and 40 micrograms/kg/min + 0.5 mg atropine). At each titration step a standardized transmitral PW-Doppler recording with the sample volume positioned at the opened mitral leaflet tips was analyzed three times by two independent, experienced investigators. Of the early, late, and mean velocities (VmaxE, VmaxA, Vmean), time integrals (VTI-E, VTI-A, VTI), their ratios (E/A, E/A VTI), and various time intervals (Tacc, Tdec, E- and A-duration, FillT), VmaxE (0.82 to 1.09 m/s; P < 0.0001), VTI-E (16.17 to 17.19 cm; P < 0.0001) and Vmean (0.29 to 0.82 m/s; P < 0.0001) were found to have the greatest discriminatory power, commencing already at a dose of 10-15 micrograms/kg/min dobutamine. VmaxE and VTI-E demonstrated the smallest intra- and interobserver variation without any increase in variability during incremental dose titration. Assessment of the early diastolic filling pattern by Doppler echocardiography is a valuable quantitative and reproducible adjunct to conventional dobutamine stress echocardiography. Further controlled studies in coronary artery disease patients have to confirm, whether lower dobutamine doses could be used in the test and sensitivity increased due to better data acquisition in cases of limited echogenicity, less subjectivity, and earlier onset of ischemic alterations.

Left ventricular blood flow patterns in normal subjects: a quantitative analysis by three-dimensional magnetic resonance velocity mapping

OBJECTIVES

Magnetic resonance velocity mapping was used to investigate the hypothesis of a vortex motion within the left ventricle interacting with mitral valve motion and inflow velocity.

BACKGROUND

In vitro flow visualization studies have suggested the presence of a large anterior vortex inside the left ventricle during mitral inflow. However, to our knowledge the occurrence of this phenomenon has not been demonstrated in the human left ventricle.

METHODS

Magnetic resonance velocity mapping was performed in 26 healthy volunteers using a flow-adjusted gradient sequence for three-dimensional flow velocity acquisition in the long-axis plane of the left ventricle. By computer processing, the flow vectors in the left ventricle were visualized and animated dynamically.

RESULTS

The early diastolic mitral inflow was apically directed, and a large counterclockwise anterior vortex was created within the left ventricle shortly after the onset of the mid-diastolic semiclosure of the anterior mitral leaflet. During mid-diastolic diastasis, mitral inflow ceased until the flow accelerated again at atrial systole. The final closure of the mitral valve was preceded by a smaller vortex seen at the tips of the mitral leaflets. At systolic ejection, all flow vectors were directed toward the left ventricular outflow tract. The anterior vortex had a radius of 1.62 +/- 0.24 cm (mean +/- SD), and the average angular velocity (i.e., the rotation of an element about the center of the vortex within the central core) was 30.08 +/- 9.98 radians/s. The maximal kinetic energy of the anterior vortex was 4.3 x 10(-4) +/- 7.1 x 10(-5) J.

CONCLUSIONS

The hypothesis of a diastolic vortex formation in the human left ventricle was confirmed, and its close temporal relation to the motion of the anterior mitral leaflet was demonstrated.

Comparison between transesophageal Doppler echocardiography and nuclear cardioangiography for the evaluation of left ventricular filling during coronary artery bypass grafting

This study examines the relative contribution of early (E) and atrial (A) filling of the left ventricle. Ten patients were studied under anesthesia before and after coronary artery bypass grafting (CABG) using measurements of the mitral velocity-time integral (VTI) with transesophageal pulsed Doppler echocardiography and nuclear angiocardiography simultaneously. Thermodilution cardiac output measurements were made simultaneously in order to express the E and A filling in quantitative terms. The mean difference between methods in estimating E filling was -1.0 mL and the figures for the mean +/- 2 SD were 5.7 and -7.8 mL, r = 0.98 using regression analysis. The mean difference during A filling was 0.9 mL and the corresponding figures for the mean +/- 2 SD were 7.9 and -6.1 mL, r = 0.88. There was a reduction in the volume entering the left ventricle during the E filling (42-26 mL) and in the A phase (27-22 mL) from before surgery in comparison to after CABG. There was good agreement between transesophageal Doppler echocardiographic and nuclear angiocardiographic methods concerning the volume contribution during E and A phases of left ventricular filling.

Two-dimensional mitral flow velocity profiles in pig models using epicardial Doppler echocardiography

OBJECTIVES

This study investigated the velocity distribution across the natural mitral valve.

BACKGROUND

Information about the blood velocity distribution across the mitral valve is of interest in basic fluid dynamic studies of the natural mitral valve and is needed for precise cardiac output estimates by Doppler echocardiography.

METHODS

The velocity distribution across the mitral valve was measured by epicardial Doppler echocardiography in ten 90-kg anesthetized pigs. By rotating the ultrasound transducer in 30 degrees intervals from the apical position, we constructed two-dimensional velocity profiles across the left ventricular inflow tract from diameters from each rotation arranged around a reference point. The time-averaged mitral velocity profile was calculated to estimate the error in cardiac output calculations that may occur with pulsed Doppler ultrasound when a single sample volume is used to record the mean velocity across the mitral orifice.

RESULTS

The time-averaged diastolic cross-sectional mitral velocity profiles at the level of the mitral annulus and leaflet tips were variably skewed because of the development of a large anterior vortex in the left ventricle during the deceleration of early diastolic inflow and atrial systole. The ratio of the time-velocity integral of the center sample volume to the spatially averaged time-velocity integral was 1.13 +/- 0.15 (mean +/- SD) (range 0.80 to 1.32). Using regression analysis, we found a correlation between the degree of nonuniformity of the cross-sectional velocity distribution and the peak velocity of the anterior vortex (r = 0.65, p < 0.01).

CONCLUSIONS

The assumption of a flat mean velocity profile across the mitral valve can introduce errors of +13 +/- 15% (mean +/- SD) in cardiac output measured with pulsed Doppler ultrasound when one is interrogating a single center sample volume.