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With advances in high-performance, compact ultrasound diagnostic equipment, medical practitioners beyond ultrasound specialists are increasingly able to perform bedside ultrasound examinations. This technique has been incorporated into the curriculum for medical students at many universities worldwide . Cardiovascular point-of-care ultrasound (POCUS) is an ultrasound examination of the heart and vascular system performed at the bedside that is used to differentiate between clinical hypotheses. Typically, POCUS is administered to address a specific clinical question promptly, such as determining whether hypotension is due to cardiac tamponade. Consequently, POCUS has the potential to reduce reliance on traditional imaging modalities . Empirical evidence indicates that direct visual assessment with cardiovascular POCUS is more effective than cardiovascular auscultation for detecting cardiovascular diseases during routine bedside examinations. Given the widespread availability of POCUS and its use by clinicians with diverse specialties, who often have less ultrasound training than cardiologists, there are opportunities to enhance image quality and interpretation with artificial intelligence, remote learning and guidance, web-based operations, and other technological advancements. Nonetheless, despite these emerging capabilities, the adoption of cardiovascular POCUS remains in its early stages and is not yet universally implemented.

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POCUS is the utilization of ultrasound technology directly at the patient’s bedside, where it is incorporated into clinical reasoning to aid diagnosis, monitoring, risk stratification, and therapeutic intervention ^, . The term “POCUS” is broadly defined as “the acquisition, interpretation, and immediate clinical integration of ultrasonographic imaging performed by a treating clinician” ^, . Importantly, this term is not limited by the examination’s location, the imaging device’s capabilities, or the practitioner’s specialty. A basic cardiac POCUS examination includes the following elements, as adapted from the original definition of POCUS: 1) The ultrasound machine must be capable of at least B-mode (grayscale) imaging. 2) The following views must be acquired: parasternal long axis (PLAX), parasternal short axis (PSAX), apical four-chamber (A4C), and subcostal. 3) Clinical questions, particularly those concerning left ventricle (LV) and right ventricle (RV) size and function, intracardiac volume status, and the presence of pericardial fluid, are assessed qualitatively. 4) Structured documentation of the procedure and findings is recorded in the patient’s medical record. 5) The treating clinician routinely archives images, unless an archiving system is unavailable. The American Society of Echocardiography guidelines distinguish POCUS from comprehensive echocardiography. Comprehensive echocardiography, or “complete echocardiography,” is a systematic or comprehensive echocardiography approach usually performed by certified cardiologists . POCUS can be performed by clinicians after a short training period, even by medical professionals with limited knowledge or experience in specialized echocardiography, and the technique should be maintained through daily use. Conversely, performing comprehensive echocardiography requires extensive knowledge ranging from basic ultrasound engineering to the pathophysiology and treatment of various cardiac diseases. Various cardiac functions must be assessed using several echocardiographic techniques, including strain and tissue Doppler approaches. For comprehensive echocardiography, a high-end machine equipped with all options is necessary. However, POCUS can be performed with a portable device that has limited capabilities. Still, if high-end equipment is available at the bedside, POCUS can be performed using this type of machine .

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Cardiac POCUS has revolutionized bedside patient care by providing immediate, real-time imaging of the heart and surrounding structures. This non-invasive technique enables healthcare providers to rapidly assess cardiac function, identify abnormalities, and inform treatment decisions. By enabling rapid detection of pathologies like pericardial effusions, valvular disorders, or ventricular dysfunction, cardiac POCUS significantly enhances diagnostic accuracy and reduces the time needed to reach a definitive diagnosis . This timely information can be vital in emergency situations, potentially saving lives by facilitating prompt and appropriate treatment decisions. Additionally, cardiac POCUS improves patient safety by reducing the requirement for more invasive diagnostic procedures and minimizing the risk of complications associated with traditional imaging techniques. Unlike other imaging modalities, like computed tomography or X-rays, POCUS does not expose patients to ionizing radiation, making it especially valuable for frequent use or in vulnerable groups such as pregnant women or children . Furthermore, the portability and ease of use enable repeated examinations without requiring the movement of critically ill patients, thereby decreasing the complication rates associated with patient transport. Therefore, integrating cardiac POCUS into clinical practice has led to more efficient, safer, and patient-centered care across medical specialties.

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Cardiac POCUS is not defined by the type of machine employed, but it is generally carried out using ultrasound devices with limited image optimization capabilities. Ultrasound machines that are readily available, portable, and simple to operate at the bedside, with all essential features for performing a cardiac exam, are preferred. POCUS machines should be equipped with B-mode imaging, M-mode, and color-Doppler mode capabilities. The machine settings should include depth, gain, and focus adjustments. For optimal cardiac POCUS imaging, a phased array probe is recommended, particularly for adult patients . This probe operates within a frequency range of 2–5 MHz, providing an ideal balance between penetration depth and image resolution for cardiac structures. The phased array design enables a broader field of view at depth, which is critical for visualizing the entire heart through the limited acoustic windows available in the chest. The highest possible frequency should be used for imaging throughout the examination. Each probe is equipped with a marker on one side that corresponds to a marker on the screen. Conventionally, the probe marker is positioned on the left. However, it is conventional to place the probe marker on the right of the screen when performing a cardiac ultrasound Fig. 1 .

An ultrasound machine equipped with a transthoracic probe. On the probe, the marker is typically a notch or a light. In the ultrasound image, the marker is usually visible at the top of the screen and can be positioned on the left or right, depending on the preset and the transducer used. By convention, the marker is placed on the right of the screen when performing a cardiac ultrasound.

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Understanding a standardized transthoracic echocardiography (TTE) examination is fundamental to all echocardiographic practice. Many practitioners initially engage in goal-directed, focused, limited examinations, and it may be tempting to concentrate solely on the primary clinical question, conducting the study in a disorganized and variable manner. However, it is strongly advised that those learning TTE develop a standardized examination sequence to ensure that potentially significant findings are not overlooked. As practitioners gain experience and perform more comprehensive examinations, they will have already established sound habits. They can expand upon existing examinations rather than having to learn an entirely new sequence. Acquiring different images involves obtaining four primary heart perspectives: the subcostal, A4C, PSAX, and PLAX views Fig. 2 .

The locations and views for the cardiac scan. PSAX Parasternal Short Axis; PLAX Parasternal Long Axis; A4C Apical Four Chamber; SC4C SubCostal Four Chamber.

Each view provides unique insights into cardiac structure and function, facilitating rapid assessment in various clinical scenarios. Mastery of these views is essential for clinicians using POCUS in cardiac evaluations, as they provide complementary information vital to accurately diagnose and manage cardiac conditions .

During the patient examination, it is advisable to apply gel to enhance the contact between the probe and the tissue. Additionally, the probe should be stabilized by ensuring continuous contact between the hand holding the probe and the patient’s body. The probe has four fundamental movements: sliding, tilting, rotating, and rocking. The appropriate manipulation or combination of these movements yields the desired image.

Sliding is moving the probe across the chest to scan anatomical structures. Rocking refers to the forward and backward motion that aligns the body orientation with the monitor. Rotating entails turning the probe like a dial to transition between the long-axis and short-axis views. Tilting involves angling the probe up or down to visualize structures at various depths Fig. 3 .

The probe has four fundamental movements: sliding, tilting, rotating, and rocking. The appropriate manipulation or combination of these movements yields the desired image.

5.2

Standard windows for cardiac POCUS

Four standard windows should be used in every comprehensive or diagnostic examination: the PLAX, PSAX, A4C, and subcostal views . In practice, not all windows may be available for TTE because the patient cannot be optimally positioned, or there are patient factors such as obesity, hyperinflated lungs, or poor access to window views. During a laparotomy, the patient is supine, and neither the apical nor the subcostal windows are likely to be accessible as they are in the surgical field. In an arrest situation, the only (and often the best) access is likely through the subcostal window, particularly when external cardiac massage is being conducted. In many patients, one or more windows may provide poor images. For instance, in patients with chronic lung disease, the parasternal window may be difficult to scan. Therefore, in a focused examination, it may be appropriate to proceed from the parasternal window to another view if there are inadequate images . The following sections describe the components of basic TTE examinations.

5.2.1

The subcostal view

The subcostal window is first identified by positioning the probe immediately inferior to the xiphoid process of the sternum, angling it upwards and slightly towards the left. A hand should be placed on top of the probe to avoid obstructing its optimal positioning. The probe’s marker should be oriented towards the patient’s left side . This view is optimally obtained with the patient in a supine position with knees bent. This imaging window is positioned at a greater distance compared to the apical and parasternal views, necessitating an increased depth of field to visualize the heart adequately. This is particularly advantageous for evaluating pericardial effusions. Moreover, this window is the most beneficial during emergencies, such as cardiopulmonary resuscitation. It is often the most effective in cases involving hyperinflated lungs due to airway disease or positive end-expiratory pressure .

By angling the probe to the right from the subcostal short-axis (SAX) view and rotating it 90° with the probe oriented towards the patient’s head, the inferior vena cava (IVC) and the liver can be visualized. The hepatic veins drain into the vena cava. Furthermore, the portal veins are visible in this view, distinguished by their increased echogenicity, which presents as a white sclerotic appearance around the venous chambers compared to the hepatic veins Fig. 4 .

Rotating the probe from the SC4C by 90° will reveal the IVC, which runs through the liver (brown color) toward the RA. RA Right Atrium; # Portal Vein; ∗ Hepatic Vein. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)

This view of the right atrium, IVC, and liver allows assessment of IVC size and collapse with respiration . Based on these measurements, the right atrial pressure (RAP) can be estimated. This has only been validated in patients who are spontaneously breathing. The IVC is commonly dilated and may not collapse in patients on ventilators, so it should not be used in these cases to estimate RA pressure.

5.2.2

The A4C view

Typically, the apical window is located at the fifth intercostal space along the midclavicular line, with the orientation marker pointed towards the patient’s left side when in a supine position . However, this window may shift towards the axillary line when the patient is in the left lateral decubitus position. In cases with cardiac enlargement, this displacement may be further accentuated, extending downward towards the sixth intercostal space. A similar downward shift can occur when there is airflow obstruction, in which enlarged lungs displace the heart. Optimal identification of the window involves initially positioning the probe below the apex and then sliding it upwards until the heart is visualized. Subsequently, the probe should be adjusted to position the apex at the top of the sector scan.

During systole, the apex of the downward ventricle exhibits minimal movement, whereas the base of the heart shifts toward the apex. When the ultrasound probe is accurately positioned over the heart’s apex, the apex remains stationary on the screen. If there is notable movement of what appears to be the apex with each heartbeat, the probe is likely positioned over the LV wall and is closer to the base than is optimal. This foreshortening can be rectified by obtaining an image from a rib space one level lower. Positioning the patient on their left side is often helpful for acquiring optimal apical windows.

The A4C view in radiological imaging typically displays the LV on the right side of the screen and the RV on the left side. To optimally visualize both the RV and LV simultaneously, a slight clockwise or counterclockwise rotation from this position may be necessary. Additionally, the tricuspid and mitral valves (MV) can be observed in the image.

When the probe is angled excessively upwards towards the sternum, transitioning from a four-chamber to a five-chamber view is possible. This view is particularly valuable to examine the LV outflow tract and the aortic valve, which are not observable in the standard four-chamber view. Conversely, angling the probe too low towards the patient’s back will visualize the coronary sinus Fig. 5 .

A/A4C view. B/Tilting the probe upwards towards the sternum will show a five-chamber view which includes the LVOT. C/Angling the probe too low towards the patient’s back will visualize the coronary sinus. LVOT Left Ventricular Outflow Tract; A4C Apical Four Chamber.

5.2.3

The parasternal views

The parasternal window is more accurately referred to as the left parasternal window. It is located around the third or fourth intercostal space, between the nipple line and the sternal ridge, just lateral to the sternum’s border . The exact location depends on the patient’s position and the position of their heart within the chest. Various pathologies, particularly lung disease, may affect the precise position and alignment of the probe, which can vary from patient to patient.

The PLAX (of the LV) can be found by ensuring that the index marker of the probe is pointed towards the right shoulder. A long-axis view of the LV has both the aortic valve and the MV in view simultaneously. In this view, the left atrium and a short section of the ascending aorta can also be visualized.

By rotating the transducer approximately 90° from the PLAX view until the index marker of the probe is aimed towards the left shoulder, a short-axis view can be obtained. Depending on the angulation of the probe, a series of short-axis views can be obtained. Angling the probe towards the head cuts the RV and aortic valve, producing an inflow-outflow view of the RV and a “Mercedes-Benz” view of the aortic valve. By angling the probe down towards the left hip, both the MV and the LV can be seen in short axis in the basal, mid, and apical planes. Fig. 6 .

Different angulations of the probe at the level of the PSAX.

1/P-SAX AV: Parasternal Short Axis Aortic Valve level

2/P-SAX MV: Parasternal Short Axis Mitral Valve level

3/P-SAX PM: Parasternal Short Axis Papillary Muscle level

4/P-SAX Ap: Parasternal Short Axis Apical level.

In a POCUS examination, the short-axis view of the LV is utilized, which can be identified by the presence of papillary muscles within the LV chamber.

6

Integrating POCUS with other hemodynamic monitoring modalities can significantly enhance diagnostic accuracy ^, . The use of bedside ultrasound in hemodynamic monitoring enables clinicians to identify vital hemodynamic features that are compromised in various states of shock.

6.2

Echocardiographic measurements

6.2.1

LV measurements

6.2.1.1

LV end-diastolic dimension

The most common method for assessing LV dilatation is through the PLAX view, in which the LV internal dimension in diastole is measured. End diastole can be identified using several criteria: 1) the frame in which the LV is at its maximum size; 2) the frame following MV closure; and 3) the onset of the QRS complex. Measurements are taken using calipers from the endocardial border of the septal wall of the LV to the endocardial border of the posterior free wall of the LV. This measurement is taken during systole, at the level located below the tips of the MV leaflets during diastole. M-mode echocardiography can be used to precisely measure the distance within the boundaries of the LV. The range of normal values may differ between the sexes and among populations; however, a threshold of 5.5 cm distinguishes between a normal and dilated LV . It is recommended that the measurements be indexed to the LV end-diastolic diameter (LVEDD) relative to the patient’s body surface area (BSA). Generally, the normal indexed range is < 3.2 cm/m ² Fig. 7 .

Measurement of the LV dimension and area at end-diastole. On the left side, a normal-sized LV and on the right, a dilated LV. The LV EDD and EDA are significantly larger in the dilated LV compared to the normal. LV Left Ventricle; EDD End Diastolic Diameter; EDA End Diastolic Area.

6.2.1.2

LV end-diastolic area

Assessing the LV end-diastolic area (LVEDA) is the most frequently used visual and quantitative method for evaluating preload. Evaluating the filling and function of the LV in the PSAX view, particularly at the mid-LV level where the papillary muscles are visualized, is well-known among echocardiography practitioners and is recommended for serial assessment of preload. To measure the end diastolic area (EDA), the EDA of the LV, including the papillary muscles, is traced. A normal value will depend on the patient’s size; a smaller patient is likely to have a smaller EDA than a larger patient. As a general guideline, an LVEDA of <10 cm ² (or an indexed value of <6 cm ²/BSA) is indicative of hypovolemia, whereas a value > 20 cm ² (or an indexed value of >12cm ²/BSA) suggests a hypervolemic or dilated LV Fig. 7 .

6.2.1.3

LV function

To conduct a fundamental hemodynamic evaluation, estimates of ejection fraction (EF), such as visual assessment, fractional shortening (FS), fractional area change (FAC), mitral annular plane systolic excursion (MAPSE), or E-point septal separation (EPSS) are used. An overview of LV measurements is shown in Table 1 .

• o

  Eyeballing using the PSAX view

Table 1

Summary of LV measurements.

LV size	Reduced	Average normal	Increased
LV EDD mm	<40∗	<55	>55
LV area cm 2	<10	15	>20
LV function	Normal	Reduced LVEF	LVEF < 30 %
FS %	>25	<25	<15
FAC %	>35	<35	<20
EPSS mm	<8	>8	>18
MAPSE mm	>11	<11	<6

LV, left ventricle; EDD, end-diastolic diameter; FS, fractional shortening; FAC, fractional area change; EPSS, E-point septal separation; MAPSE, mitral annular plane systolic excursion; LVEF, left ventricular ejection fraction. ∗Value below the average normal limits of LV diameter.

This assessment entails a comprehensive evaluation of LV function by visually estimating the EF. A primary observation of LV contraction is typically conducted using the PSAX view; however, alternative views such as the A4C view may also be used. This evaluation is based on wall thickening and the endocardial motion of the LV myocardial segments towards the center of the LV. To assess hemodynamic status, classifications can be simplified into the following categories: normal, reduced, and increased. Due to its simplicity and rapid implementation, visual EF estimation may be employed in routine echocardiography. However, it is important to note that the LVEF is often underestimated when using visual estimation compared to quantitative assessment .

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  Fractional shortening

FS quantifies the percentage change in the LV cavity dimension during systole. The LVEDD and the LV end-systolic dimension (LVESD) are typically measured using an M-mode echocardiographic cut through the PLAX or PSAX view at the midpapillary level.

End systole is optimally defined as the frame immediately preceding MV opening or the point in the cardiac cycle at which the cardiac dimension is smallest in a normal heart. Measurements can also be derived from two-dimensional images from the PLAX or PSAX view at the base of the heart. The formula for calculating the percentage of FS is as follows: FS (%) = (LVEDD- LVESD/LVEDD) × 100 . A limitation of this method is that it may not accurately reflect global LV function when there are significant wall motion abnormalities, since measurements taken at the ventricular base may not represent the contraction of the entire ventricle. FS serves as a practical indicator of cardiac function, since it is easily obtainable and useful for categorizing systolic function in assessing hemodynamic states. It is also applicable for evaluating LV function during treatment. A reduced FS value is defined as <25 %, an increased FS value is >45 %, and a normal FS value ranges from 25 % to 45 % ^, Fig. 8 .

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  Fractional area change

FS of the LV which is typically measured using M-mode through the PLAX or PSAX view at the midpapillary level. Both the EDD and ESD are measured to calculate the FS. FS Fractional Shortening; PLAX Parasternal Long Axis; PSAX Parasternal Short Axis; EDD End Diastolic Diameter; ESD End Systolic Diameter.

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