Echocardiography

Synonyms

Cardiac ultrasound; cardiac echo; echocardiogram; swallow echo; ultrasound cardiography (UKG); ultrasound examination of the heart; echo;

First author

The importance of echoreflection, the concept of echocardiography, was first demonstrated by Lazzaro Spallanzani (1729 - 1799), who used reflective echoes from bats as navigation.

Ultrasound was first used in medicine by the Austrian neurologist Karl- Theo Dussik for imaging the brain ventricles.

The Swedish cardiologist Inge Edler (1911- 2001) is referred to as the "father of echocardiography", who in 1953, together with the physicist Hellmuth Hertz, marked the beginning of a non-invasive diagnostic technique for examining the heart (Singh 2007). He developed the so-called M- mode, which remained the only echocardiographic method for 20 years (Bartel 2013).

The Doppler effect was first described by the Austrian physicist Christian Doppler (1803 - 1853) (Striebel 2014).

Epicardial echocardiography was first performed in the 1970s (Edrich 2003).

Echocardiography is a special form of sonography that can be used to examine the heart and the vessels near the heart (Striebel 2014).

Echocardiography uses high-frequency sound waves that are able to penetrate the body. They are reflected by relevant structures to produce an image (Kasper 2015).

An echocardiography device consists of three different assemblies:

• 1. beamformer to generate the transmitting pulses and control the signal processing during reception.
• 2.Transducer to convert electrical vibrations into mechanical ones and vice versa.
• 3.Scan converter for correct image geometry on the monitor (Bartel 2013).

There are several ways of performing echocardiography:

• 1. transthoracic echocardiography (TTE):

For TTE, the sector transducer is used, alternatively a convex transducer. First subcostal, then apical and finally parasternal ultrasound is performed (Wilhelm 2018).

• 2. transesophageal echocardiography (TEE):

Here, the transducer is at the tip of an endoscope that is inserted into the esophagus. This allows a more accurate view of the heart structures. A probe with a higher frequency is usually used, which leads to better image quality and higher spatial resolution (Kasper 2015).

• 3. intraoperative epicardial echocardiography:

The transducer packed in a sterile sheath is placed on the epicardial surface of the heart intraoperatively after opening the pericardium. In the meantime, the intraoperative form of echocardiography has been largely replaced by transesophageal echocardiography (TEE) and only in cases of contraindications for TEE or when it is impossible to insert the TEE probe atraumatically, this examination procedure is used (Edrich 2003).

• 4. interventional echocardiography:

This new field of application of echocardiography has developed only recently (Erbel 2017).

Execution

The patient lies on the left side for echocardiography, with the left hand placed behind the head to spread the intercostal spaces (Wilhelm 2018).

The examination sequence is:

- 2- D- echocardiography

- M- mode in the long and short axis parasternal.

- Doppler echocardiography

If necessary:

- 3- D- echocardiography

- Stress echocardiography

- Transesophageal echocardiography (Wilkenshoff 2008)

Indications

The clinical indications for echocardiography are defined in the "European Association for Cardiovascular and the American College of Cardiology" and include:

- thoracic pain

- shortness of breath

- syncope

- palpitations

- heart murmurs

- Screening of asymptomatic patients with hereditary heart diseases such as Marfan syndrome (Chan 2020)

No indication represents e.g.:

Routine for asymptomatic patients with a grade 1 or 2 mean systolic murmur, but a cardiologist should always be consulted if there is any doubt about the significance of the murmur (Kasper 2015).

One differentiates in echocardiography between different technical methods:

• A- mode (amplitude mode):

This represents the simplest representation of the echo signals. It is primarily used for neurological and ophthalmological diagnostics (Haller 2010).

• B- Mode (Brightness- Mode):

This is a 2-D real-time mode. It is used for structural imaging and is most commonly used in ultrasound imaging.

B- Mode is used for structural imaging and forms the basis of ultrasound procedures (Haller 2010).

• M- Mode (Motion- Mode), also referred to as TM- Mode (Time Motion):

In this echocardiography procedure, the dynamic change of one-dimensional information regarding the structure of the heart and its dimension over time are mapped (Bartel 2013). In M- mode, it is a 1-D representation (Menche 2005).

Although two-dimensional echocardiography has largely supplanted M- Mode echocardiography, because of its high temporal resolution and accuracy, M- Mode echocardiography continues to be used(Kasper 2015) for quantitative measurement of cardiac dimensions and qualitative assessment of motion patterns (Bartel 2013).

- Indications for M- Mode include:

- Functional diagnostics of the heart and valves (Haller 2010) especially in:

- constructive pericarditis

- pericardial effusion

- cardiac tamponade

- hypertrophic obstructive cardiomyopathy

- pulmonary hypertension

- obstruction of the left ventricular outflow tract

- to assess right ventricular function (most common)

(Chan 2020)

• 1- D- Echocardiography:

One-dimensional imaging, the "time-motion procedure," is the M- mode (Menche 2005). It is used to visualize the anatomy and function of the heart (Herold 2022). It was historically the only way to sonographically assess the heart and is still used today in combination with 2- D- echocardiography to quantify the dimensions of the cardiac cavity (Bach 2013).

• 2- D- Echocardiography:

Formerly also referred to as B- mode (Chan 2020). This is used to visualize the anatomy and function of the heart (Herold 2022). 2- D- echocardiography provides real-time imaging of sectorial cross-sectional images of the heart (Bartel 2013).

This form of echocardiography is used to assess the:

- Cardiac cavities

- heart walls

- pericardium

- myocardium

- Endocardium (Wilkenshoff 2008)

2-D echocardiography is often the first method of imaging in cases of suspected cardiac dysfunction. It is used primarily for the classification of heart failure (Chan 2020).

• 3- D- Echocardiography:

This is used to create three-dimensional images (Wilkenshoff 2008). The image quality of 3-D echocardiography currently lags behind two-dimensional echocardiography (Kasper 2015).

- Quantitatively, it can be used to determine, for example:

- severity of mitral regurgitation

- morphology and function of existing prosthetic valves

- spatial assessment of the valves

- septal defects (Wilkenshoff 2007)

- Qualitative can be determined e.g.:

- assessment of left and right ventricular function

- quantification of regional left ventricular volumes

- Valve opening area of aortic stenosis or mitral stenosis, respectively

- Calculation of volumes of the atria (Wilkenshoff 2008)

• Doppler echocardiography:

Doppler echocardiography is differentiated into 3 systems:

- 1. line Doppler (continuous wave Doppler = CW Doppler):

This is used to record the flow velocities along a sound beam.

- 2. point Doppler (pulsed Doppler = PW):

This measures blood flow velocities at a single point.

- 3. area Doppler (color Doppler) = color-coded Doppler echocardiography (FDE) (see below).

The mean flow velocities are determined by many measurement volumes (Moltzahn 2000). The blood flow velocities are color coded, according to convention blood flows towards the transducer as red and away from the transducer as blue (BART = blue away, red towards). (Siegenthaler 2006). Both colors become brighter with increasing blood flow velocity (Moltzahn 2000).

This form of examination allows hemodynamic assessment of, for example:

- the stroke volume

- the pressure gradients

- the heart valve regurgitation

- the intracardiac shunts (Chan 2020)

• Color-coded duplex sonography (FKDS), occasionally referred to as triplex sonography (Marshall 2013):

Here, the color coding does not have to be selected for a narrowly circumscribed examination area - as is the case with Doppler sonography - but can be displayed two-dimensionally over a large area of a moving image (Marshall 2013).

With the FKDS, individual measurements can be performed over the color Doppler sonic window, in which movements are visualized in the color window. Here, too, movements toward the transducer are represented as "red" and movements away from the transducer are represented as "blue" (Blank 2019).

The following examinations are possible with FKDS:

- An additional assessment of the vessel walls (plaques [Scriba 2013]).

- morphological assessment of heart and valves

- in the case of septal defects for the assessment of shunt flows

- in case of stenosis for estimation of pressure gradients (so called CW- Doppler)

- in case of valve insufficiency assessment of reflux flows (Herold 2022)

• Stress echocardiography (stress echo):

Here, echocardiography is performed after physical exertion or pharmacological stress (e.g., administration of dobutamine). It can be used primarily to detect circulatory disturbances of the heart (Menche 2005).

Indications for exercise echocardiography include:

- Patients with coronary artery disease (CAD) with clinical suspicion of CAD without pathological ECG. The sensitivity is 85-90% (Thelen 2010).

- for the clarification of coronary artery disease (Thelen 2010)

- after acute myocardial infarction

- preoperative cardiac risk assessment

- cardiomyopathies

- valvular vitiation, etc. (Wilkenshoff 2008)

• Contrast echocardiography:

Here, a special echo contrast agent (Menche 2005) is administered i. v. to enhance the color Doppler effect and Doppler effect (Erbel 1999).

- Indications for right heart contrast echocardiography include:

- V. a. pulmonary artery embolism

- V. a. cor pulmonale

- V. a. shunt flow in e. g. ASD, VSD, patent foramen ovale etc.

- persistent superior vena cava

- calculation of RV and PA pressure ratios

- complex congenital heart defects

- Control during and after catheter intervention (Wilkenshoff 2008)

- Indications for left heart contrast echocardiography include:

- Differentiation of structures in the LV apex such as thrombi

- Amplification of Doppler signals in the left heart

- Imaging of the left ventricle (Wilkenshoff 2008)

Contraindications of transesophageal echocardiography:

- esophageal varices

- relevant coagulation disorder with e.g. a quick value < 20 % or platelets < 30,000 / µl

- Tumors in the upper digestive tract such as larynx, pharynx, esophagus, stomach

- clinically relevant bleeding in the upper digestive tract (Striebel 2014)

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