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The Use of a Stand-of Device in High Pulse Repetition Frequeny Doppler Echocardiography
Abstract
An interesting case of severe mitral stenosis in which Doppler echocardiographic evaluation was greatly enhanced by use of a stand-off pad is discussed. When employing high pulse repetition frequency (HPRF) Doppler, it may be difficult to place the sample volume at the area of interest while remaining in HPRF mode, because it is not always clear that there is a certain minimum sample volume depth below which a system will not operate in HPRF. This and other related technical constraints vary from machine to machine. This case illustrates that sample volumes can be manipulated by using a stand-off pad, thereby making use of HPRF possible. The specifications of the HPRF mode on the Acuson 128XP (Acuson, Mountain View, CA) are examined in detail, and possible applications of this technique in similar difficult situations that may arise in clinical practice are discussed.
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To study the effect of heart rate changes on Doppler measurements of mitral valve area atrial pacing was performed in 14 patients with mitral stenosis andsinus rhythm. Continuous wave Doppler and haemodynamic measurements were performed simultaneously at rest and during pacing-induced tachycardia. (1) Mitral valve area was determined using the conventional pressure half time method. (2) Additionally, mitral valve area was calculated with a combined Doppler and thermodilution technique according to the continuity equation. (3) Simultaneous invasive measurements were used for calculation of the mitral valve area according to the Gorlin formula. With increasing heart rate (69 ± 13−97 ± 15−114 ± 13 beats min⁻¹) mitral valve area either determined by the continuity equation (1.0 ± 0.2−1.0 ± 0.3−1.1± 0.4 cm²) or the Gorlin formula (1.2±0.3−1.2±0.4−1.3±0.4cm²) remained constant. Both methods correlated closely not only at rest (r=0.88, SEE=0.11 cm², P<0.001), but also during atrial pacing (first level: r=0.95, SEE=0.10 cm², P<0.001 second level: r=0.95, SEE=0.13 cm², P<0.001). In contrast, mitral valve area calculated according to the pressure half time method increased significantly during atrial pacing (1.0 ± 0.3−1.8 ±0.5 − 2.O ± 0.5 cm²). Mitral valve area determined either by the pressure half time method or the Gorlin formula correlated in patients with heart rates ≤80 beats min⁻¹ (r=0.75, SEE = 0.15 cm², p <0.01), while no significant correlation was found in patients with heart rates above 80 beats min⁻¹.
Our conclusion is that while the pressure half time method progressively overestimates mitral valve area with increasing heart rate, the accuracy of the continuity equation method based on a combined Doppler/thermodilution technique is independent of heart rate changes in patients with mitral stenosis and sinus rhythm. This method is superior to the pressure half time method in patients with mitral stenosis and heart rates exceeding 80 beats min⁻¹.
In 25 patients with acute myocardial infarction and in 25 normal subjects, pulsed-wave Doppler echocardiography was performed in the apical four-chamber view with the sample volume first between the mitral leaflet tips and then at the mitral anulus. The early filing wave (E) and late filling wave (A) peak velocities measured from Doppler strip charts were significantly (p less than 0.001) higher at the tips in both groups. E velocity increase was greater than A velocity increase, producing a significantly (p less than 0.001) higher E/A velocity ratio at the tips than at the anulus. The deceleration time was longer at the tips than at the anulus (p less than 0.001) in both groups. Therefore it is important to know sample volume location in the interpretation of mitral inflow velocity. It is critical to maintain the same sample volume location in serial assessments of left ventricular diastolic filling characteristics.
Evaluation of diastolic filling of the heart has been difficult because of its complexity and the numerous interrelated contributing factors. Previous determinations have depended on high-fidelity, invasive measurements of instantaneous pressure, volume, mass, and wall stress, which could not be done on a routine clinical basis. With the advent of Doppler echocardiography, intracardiac blood flow velocities can now be noninvasively assessed. For application of this technique to evaluation of diastolic function in patients with heart disease, it is necessary to understand what the Doppler-derived variables represent. It is also necessary to know how they are affected by changes in loading conditions and changes in myocardial relaxation. In this review, we provide an interpretation of the mitral valve, tricuspid valve, and systemic and pulmonary venous inflow velocities in the normal patient and in various disease states.
Left ventricular inflow was studied with pulsed Doppler echocardiography in 12 normals and 12 patients with a dilated left ventricle as a result of ischemic heart disease. To study the influence of left ventricular relaxation on both the transmitral and apical diastolic flow patterns, we applied range ambiguity. This provides simultaneous display of Doppler shifts obtained at different depths. The diastolic Doppler shift curves at the mitral valve and apical level in normals had the same time of onset, whereas there was an apparent time delay in the patients with heart disease (range 160-360 ms). This might be caused by absence of a normal apical wall motion in these patients.
The role of ultrasonography in the imaging of superficially located structures is enhanced by the appropriate application of basic physical principles. Emphasis is placed on the understanding of axial and lateral resolution, variable and dynamic focusing systems, and fluid-path scanners. Knowledge of these principles is useful in daily practice and in the evaluation of new equipment.