Doppler sonography (synonyms: Doppler effect sonography, Doppler echography) of the heart is a diagnostic procedure in cardiology that is part of echocardiography (synonyms: ultrasound of the heart; cardiac ultrasound). Doppler sonography is a medical imaging procedure that can dynamically visualize fluid flows (primarily blood flow). It is used to assess blood flow velocity and, in cardiology, to diagnose cardiac and valvular defects. Particularly in the case of pathological vascular phenomena, Doppler sonographic examination represents the basis of the diagnostic procedure, since both the velocity distribution in the respective vessel section is assessed and an exact representation of the direction of flow can be made. Furthermore, Doppler sonography makes it possible to reproduce the temporal change in the velocity of the blood flow. The factors obtained in this way can then be used to calculate the volume flow rate and the pathophysiologically important flow resistances.
Indications (areas of application)
The indications for performing Doppler sonography of the heart depend on the particular Doppler procedure.
- Valvular heart disease (valvular heart disease) such as aortic valve stenosis or insufficiency, mitral valve stenosis or insufficiency – Doppler sonography is used to assess the flow conditions in the area of the heart valves, so that in addition to the simple determination of stenoses (narrowing) and insufficiencies (inadequacy or inability, in this case, of the valve to close), the dynamic relevance of the valvular heart disease can also be determined. Insufficiencies are identified by the flow “in the wrong direction”, while stenoses can be identified by an increase in flow velocity by the lighter color.
- Stress examination of the heart – During stress echocardiography (ultrasound examination under stress), tissue Doppler can be used to detect even minor ischemic damage (e.g., myocardial ischemia/reduced blood flow to the myocardium in suspected cases of hemodynamically significant coronary artery disease (CAD)). It can also be used for vital signs diagnosis in known CHD.
- Detection of accessory (additional) conduction pathways – In the presence of an additional conduction pathway as in Wolff-Parkinson-White syndrome (WPW syndrome; cardiac arrhythmia triggered by an electrically circular excitation (circus movement) between the atria (atrium cordia) and the ventricles/heart chambers). an accessory conduction pathway can be identified using tissue Doppler.
The procedure
Doppler sonography is based on the principle that ultrasound waves are emitted at a defined frequency into the tissue, where they scatter on circulating erythrocytes (red blood cells). Due to this scattering, a portion of the ultrasound waves returns to the transducer, which thus serves on the one hand as a transmitter and on the other hand also as a receiver of the sound waves. The erythrocytes thus act as a boundary surface at which the sound waves are reflected, so that a frequency increase occurs when the distance between the transducer and the boundary surface decreases and the frequency decreases when the distance increases. However, the so-called Doppler effects occur not only in flowing blood, but also in other moving organic structures, such as vessel walls. Various Doppler techniques are used on the heart: continuous wave Doppler (CW Doppler), color/pulsed wave Doppler (PW Doppler), and tissue Doppler.
- Continuous Wave Doppler (CW Doppler sonography) – The continuous wave Doppler technique is based on the simultaneous (simultaneous) operation of a sound transmitter and receiver in the transducer of the Doppler device. By using high frequency signals and applying electronic filters, it is possible to determine both velocity and direction of flow using the Doppler method. In contrast to other methods, high velocities can be determined. However, the determination of the respective tissue depth from which the signal originates is only possible to a limited extent.
- Pulsed Wave Doppler (PW Doppler sonography) – The Pulsed Wave Doppler technique, in contrast to Continuous Wave Doppler, has the ability to define an anatomic region in which the flow velocity of blood can be determined. To determine the respective velocity, the change in the distance of the scattering particles present in the measurement volume is measured per unit of time. Based on this, the method is an indirect method for determining the Doppler frequency in the time domain.
- Tissue Doppler sonography (synonym: tissue Doppler sonography): – Tissue Doppler is of particular importance in the diagnosis of heart disease, as the procedure can be used to visualize and assess the myocardium (heart muscle). Strain (elasticity) and strain rate (rate of elasticity) are determined to use tissue Doppler. The use of these parameters allows assessment of the contractility (ability of cardiac muscle cells to contract) of specific tissue sections of the myocardium, so that regional wall motion abnormalities (WBS) caused by, for example, ischemia (undersupply of blood) can be better detected.
