Echocardiography

Billing

With the growing use of point-of-care (POC) echocardiography in the ICU, the question of reimbursement has been a topic of ongoing discussion. Several components of the focused critical care echocardiographic examination differ from the classic comprehensive echocardiographic examination. Physicians not fully accredited in echocardiography often perform the focused echocardiographic examination in critically ill patients, and the liability of interpretation only extends to the specific focus of the assessment. Images commonly are not stored for further clinical use. In the United States, Medicare uses the Current Procedural Terminology (CPT) code for the reimbursement of medical, surgical, and diagnostic services. Currently, the CPT coding does not incorporate an individual code for focused critical care ultrasound examinations, and its components do not fulfill the requirements of the standard diagnostic TTE examinations or the limited/follow-up examination, as described in their coding system. TEE requires specific competence and is performed by physicians with advanced training. When performed in the ICU, these examinations are commonly accepted using existing CPT codes for TEE examinations.

POC echocardiography has the potential to reduce overall ICU costs considerably. By adding a noninvasive, less expensive diagnostic and monitoring technology, it can expedite and focus clinical management and decrease the risk to patients significantly. With standardization of critical care echocardiography training, its differentiation from the classic comprehensive training, and the increasing evidence of the benefits of POC echocardiography, a specific billing code for the focused examination is warranted.

Equipment

Typically, echocardiography equipment used in echocardiography laboratories and cardiac operating rooms features the newest and most advanced technologies. The most advanced equipment is not needed for use in a critical care setting. Several companies now offer machines with specific features geared toward use in emergency departments, trauma bays, or ICUs. These machines are used for the broad spectrum of critical care applications, including lung, vascular, and abdominal ultrasonography. The machines can be equipped with multiple software programs, including those useful for TTE and TEE. The ideal ICU ultrasound system is compact, portable, and durable. It requires minimal start-up time and has an easy-to-use operator interface. For routine daily use, it should have an extended battery life and internal storage capacity.

The transducers used for TTE and TEE examinations are typically phased-array transducers. They provide a frequency ranging from 1 to 10 MHz, which offers the optimal balance of penetration and resolution required to image the heart.

Knobology

Echocardiography machines have a collection of knobs and buttons to adjust image quality, use different modalities, and store images. As each manufacturer has a set arrangement of knobs, sliders, and buttons, it is essential for each operator to become familiar with the layout of the machine that he or she will use on a regular basis. The most important controls and their function are as follows:

• GAIN: Adjusts overall image brightness

• TIME-GAIN-COMPENSATION (TGC): Selectively adjusts sector image brightness

• DEPTH: Adjusts depth of view

• ZOOM: Selects specific image sector

• FOCUS: Adjusts focal zone

• DYNAMIC RANGE: Adjusts gray-scale to filter out background noise

Ultrasound modalities

More so than during the examination of anatomic structures other than the heart, the use of multiple ultrasound modalities is essential for echocardiography. The most commonly used modalities in the ICU are two-dimensional (2D) imaging, motion mode (M-mode), color flow Doppler (CFD), pulsed wave Doppler (PWD), and continuous wave Doppler (CWD). 2D remains the initial and most commonly used mode of anatomic imaging and qualitative assessment of gross pathologies in the ICU. A modality less frequently used is M-mode. M-Mode represents a one-dimensional image against time and has the advantage of excellent temporal resolution, which is useful for the imaging of fast-moving structures like valvular leaflets.

When assessing hemodynamic profiles, the use of Doppler echocardiography, in addition to classic 2D imaging, provides the information needed for quantitative measurements. CFD displays blood flow velocity and direction of flow by color mapping. It combines qualitative 2D imaging with semiquantitative information about blood flow. CFD is useful for diagnosing intracardiac shunts or valvular pathologies and for seeking evidence of obstructions to blood flow. When a quantitative assessment is needed for the calculation of stroke volume (SV), cardiac output (CO), and pulmonary artery pressures (PAP), PWD and CWD are the modalities of choice. Both modes provide information about blood flow direction and numeric estimates of blood flow velocity at the interrogated anatomic site. Whereas PWD measures blood flow velocity at the specific site of the sample volume and is limited by a certain velocity threshold called the Nyquist limit, CWD displays the maximum velocity along the whole interrogation beam without a velocity threshold. Both modalities require alignment of the interrogation beam with the direction of blood flow to minimize the underestimation of velocity caused by a suboptimal incidence angle. As with 2D imaging, several interventions can be applied to enhance Doppler quality and prevent artifacts as a result of the Nyquist limit. Most importantly, adjustment of the transducer location and frequency, sample volume depth, and movement of the baseline can maximize peak velocities with PWD. ^,

Image acquisition and optimization

Following a consistent order of image acquisition minimizes the risk of missing images and pathologies and facilitates learning. Clockwise positioning and rotation of the transducer provides a simple and logical approach to the focused examination ( Fig. 31.1 ).

Whether with TTE or TEE, standardized views are based on anatomic landmarks, which can be obtained at defined acoustic windows with specific transducer positions and angles. To avoid inadequate imaging and the risk of misinterpretation, knowledge of the specific anatomic landmarks defining each view is pertinent. In addition, the following techniques should always be used to optimize imaging. Body position: Extension of the left arm opens up the parasternal windows, and a slight left-side tilt can bring the cardiac apex closer to the chest wall. Flexing the legs at the hip facilitates the acquisition of subcostal windows. Image acquisition: Small changes in transducer position and angle, a change in the intercostal space above or below, and the use of TEE can provide improved imaging. Machine setting: Aside from adjusting gain, TGC, and dynamic range, precisely adjusting the focus and depth to the region of interest (ROI) is critical. In addition, using the zoom feature can be helpful. Especially in Doppler modes, these adjustments can improve measurements and avoid Doppler aliasing. Another option for improving image quality is contrasted echocardiography. Even though not commonly used by intensivists when performing focused ICU examinations, injection of contrast media can significantly enhance opacification of the right and left ventricular chambers and enhance the definition of the endocardial border.

Transthoracic echocardiography

In TTE, three standard acoustic windows are used: the parasternal, apical, and subcostal positions (see Fig. 31.1 ). A fourth position called suprasternal is additionally used during comprehensive examinations and in the pediatric population.

Standard transthoracic views

The focused echocardiographic examination in the ICU commonly includes five major views: (1) the parasternal long-axis (PS LAX), (2) the parasternal short-axis (PS SAX), (3) the apical four-chamber (A4CH), (4) apical five-chamber (A5CH), and (5) the subcostal long-axis (SC LAX) ( Table 31.3 ). ^,

PS LAX is obtained by positioning the transducer in the left third or fourth intercostal space (ICS), along the anterior midclavicular line, with the transducer marker directed toward the right shoulder (see Fig. 31.1 ). This view is primarily used to evaluate LV and right ventricle (RV) size and systolic function and to obtain quantitative measurements of ventricular size and wall thickness by the M-mode. The mitral valve (MV) and aortic valve (AV), including the left-ventricular outflow tract (LVOT) and aortic root, can be assessed with 2D and CFD for regurgitation, stenosis, or dynamic outflow obstruction. Additionally, this view can be used for the visualization of pericardial pathologies.

PARASTERNAL SHORT-AXIS VIEWS are obtained in the same transducer position as the parasternal long-axis view, with the transducer rotated 90 degrees clockwise and the marker directed toward the left shoulder (see Fig. 31.1 ). Within this view, multiple planes of the heart can be imaged depending on the tilt of the transducer. When tilting the probe from superiorly to inferiorly, visualization starting with the short axis of the AV over the basal and mid-SAX of the LV down to the apical segment of the LV is possible. This view is best used for the evaluation of LV size and systolic function. It is optimal for describing regional wall motion abnormalities, as all territories of coronary perfusion can be visualized simultaneously. In addition, the basal AV SAX view can provide information about the tricuspid valve (TV), including measurements of right ventricular systolic pressure (RVSP) by CWD.

APICAL VIEWS provide images of all four chambers (see Fig. 31.1 ). Most commonly used in the ICU are the A4CH and A5CH views. With the transducer positioned at the apex of the heart, commonly in the sixth or seventh ICS along the anterior axillary line, the probe marker is directed toward the left axilla. With tilting of the probe superiorly, the 4CH and 5CH views are obtained.

The 4CH view is used for the assessment of atrial and ventricular chamber sizes, biventricular systolic function, and regional wall motion abnormalities. Because of the optimal incidence angle and visualization of the TV, MV, and AV in the 4CH and 5CH views, quantitative measures by M-mode, CFD, CWD, and PWD are best obtained from the apical position. These views are mostly used by intensivists for quantitative evaluation of RV function and RVSP, LV cardiac output, and diastolic function, in addition to the evaluation of valvular pathologies by spectral-Doppler echocardiography.

From the 4CH position, a counterclockwise rotation of the transducer by 90 and 110 degrees will visualize the apical two-chamber (A2CH) and three-chamber views (A3CH), which completes the visualization of all LV wall segments when combined with the 4CH view.

SUBCOSTAL VIEWS are obtained by positioning the transducer in the subxiphoid or subcostal position while maintaining the marker directed toward the left lateral side of the patient. Aiming the probe toward the left shoulder and maintaining it flat on the abdomen, the heart is cut in a horizontal plane, showing all four chambers and particularly the RV free wall (see Fig. 31.1 ). A 90-degree rotation of the transducer counterclockwise while slightly aiming the probe toward the right shoulder will visualize the inferior vena cava (IVC) and its junction into the RA. These views can provide information about pericardial pathologies, such as pericardial effusion and tamponade. When angled slightly toward the right and caudad, global volume status can be assessed by measuring IVC diameter and dynamic collapse with respiratory variation (see Fig. 31.1 ).