The complexity of surgical procedures, as well as the comorbidity of patients undergoing cardiac surgery (CS), is increasing. Early detection and treatment of postoperative complications are part of the success in reducing morbidity and mortality.

The main serious problems that can occur in the cardiac surgery immediate postoperative (IPO) are hemodynamic instability, severe respiratory failure, and/or states of low cardiac output (CO). Inappropriate or delayed management can lead to multiorgan dysfunction syndrome, the main cause of prolonged hospitalizations and morbidity and mortality.

The addition of the information provided regarding the surgical technique performed, perioperative events, preoperative imaging studies, along with clinical, semiological, analytical, and hemodynamic information at the time of evaluation, should help us identify the etiological cause, determine the patient’s hemodynamic profile, and the main component causing it, thus enabling the selection of initial treatment and assessing the degree of response to the decision made.

The introduction of ultrasound techniques1 (transthoracic echocardiography -TTE-, transesophageal echocardiography -TEE- and lung ultrasound -LU-) has been crucial in the cardiopulmonary, hemodynamic, and etiological assessment of critically ill patients, providing immediate, reliable, and sometimes conclusive information, allowing the clarification of many clinical situations without an acceptable therapeutic response.

Cardiac surgery post-operated patients (CPO) pose certain technical difficulties associated with patient mobilization limitations, dressings, drains, inability to use the subxiphoid approach, postoperative pain, intubation, ventilatory support, etc. (Fig. 1). The technical limitations that hinder image acquisition, along with the frequent presence of loculated clots or pericardial-pleural effusion, could complicate the interpretation of ultrasound studies, sometimes requiring the combination of other imaging modalities for proper study.

Figure 1.

A: AAL, anterior axillary line; PAL, posterior axillary line; PSL, parasternal line; 1: left upper anterior area, 2: left lower anterior area, 3: left upper lateral area, 4: left inferior lateral area.

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Since respiratory assessment is addressed in another chapter of this series, we will focus especially on the study of the most common cardiovascular complications detected in the IPO.2

The assessment of left ventricular (LV) function is one of the most important parameters in echocardiographic studies in most cases due to its prognostic, diagnostic, and therapeutic implications. However, evaluating the LV function is challenging because there is no single measure that provides us with the big picture of cardiac function. It often requires using various echocardiographic modalities to complete the assessment.

The factors that determine the LV function include preload, afterload, intrinsic contractility, ventricular size, contraction frequency, electrical uniformity, and mechanical contraction (ventricular synergy and interdependence) and the rate of myocardial relaxation (lusitropy).5

The most widely used echocardiographic parameter in the routine clinical practice is the left ventricular ejection fraction (LVEF), although it may not always adequately reflect ventricular function. Therefore, a comprehensive evaluation includes the analysis of diameters, volumes, geometry, mass, wall thickness, segmental contractility, diastolic function, and estimation of filling pressures. These aspects, however, go beyond the scope of this chapter (Table 1).6–10

Table 1.

Assessment of ventricular systolic function.

GLOBAL SYSTOLIC FUNCTION
	Visual estimation is the most widely used method to study the systolic function. While this method has acceptable correlation with ventriculography-determined function when performed by experienced observers, its accuracy decreases with less experience, as well as in cases of ventricles with abnormal morphology, non-homogeneous contraction, segmental contractility abnormalities, or in the presence of asynchrony.
A.	LINEAR MEASUREMENTS (M-mode)
	The presence of segmental contractility abnormalities, prior necrosis, spherical ventricles, or asynchrony limits its utility. The high temporal resolution of M-mode, along with 2D echocardiography of better spatial resolution allows us to measure the diameters of the ventricular cavity by performing 2D echocardiography-guided M-mode cuts. This helps avoid obliquity.
	A1. Left ventricular ejection fraction (LVEF) (Teichholz)
	Although this parameter is still being used in the routine clinical practice, it is based on the assumption that the geometric shape of the left ventricle is fixed (elongated ellipsoid). This parameter is ill-advised in cases of segmental motility disorders, greatly dilated ventricles, ventricular asynchrony, etc.
	A.2. Shortening fraction (SF)
	The SF is a surrogate parameter for the EF (Teichholz) to study the LVEDD and the DLVOT. It has the same limitations as those mentioned in the estimation of the LVEF by Teichholz.
	A.3. Left ventricular end-systolic diameter (LVESD):
	The assessment of LVESD is a parameter that can warn us of a possible ventricular dysfunction despite having a normal EF due to an increased preload, as is the case with aortic and mitral regurgitation.
	A.4. The E-Septal wall distance:
	A decrease in the left ventricular systolic function tends to increase it, as it is also the case with significant aortic regurgitation and mitral stenosis.
	A.5 Mean circumferential shortening velocity
	When assessing velocity rather than the magnitude of shortening, it has been described as an earlier parameter of systolic function less dependent on preload than shortening fraction (SF).
	A.6. Mitral annular plane systolic excursion (MAPSE):
	The MAPSE is the index of longitudinal shortening of the left ventricle and is related to the global systolic function. It is an angle-dependent echocardiographic parameter, and acquisitions should be made perpendicular to the mitral plane.
B.	VOLUMETRIC MEASUREMENTS (2D echocardiography):
	B1. Simpson biplane: Estimating the EF by 2D echocardiography is the most widely used method in the routine clinical practice to assess ventricular function. Its high spatial resolution overcomes the limitations of the M-mode technique. Also, the improved equipment, acquisition of the second harmonic, and use of contrast agents facilitate the appropriate endocardial definition in most patients. Despite being the most widely used technique, in some cases, especially in the postoperative of cardiac surgery, it may entail additional technical complexity due to difficulty in obtaining a correct plane or properly identifying the endocardial border. Furthermore, its quantification, as it is the case with other parameters, is influenced by preload and afterload conditions.
	B.2. Area-Length Method: it is applicable in symmetric ventricles. An alternative method to calculate left ventricular volumes in cases with poor endocardial definition in apical views (especially laterally). The volumes are more representative of the true dimensions of the ventricular cavity and are also better suited for ventricles with abnormal morphology.
C.	Doppler:
	C1. Stroke volume and cardiac output: The assessment of the global systolic function can be complemented by assessing the stroke volume and the cardiac output. Interobserver variability is high, mainly due to measurements of the outflow tract. Small variations in the measurement of LVOT can lead to variations in the calculation of the stroke volume of up to 20%. Nonetheless, the VTI value in the LVOT can give us an initial approximation of cardiac output assessment (normal values between 18 cam and 22cm).
	C2. Pre-ejection parameters: These methods study the pre-ejection period. They are, by definition, more independent of load and more related to the intrinsic contractility of the myocardium.
	C.2.1. dP/dt: The rate of ventricular pressure change with respect to time (dP/dt) is a parameter more widelu used during left ventricular cardiac catheterization. On the echocardiography, although we cannot measure it, in the presence of mitral regurgitation, we can estimate the ratio of the velocity of its curve (dV/dt). It should not be used in cases of acute mitral regurgitation, significant aortic stenosis, high blood pressure, or overt asynchrony, where decreased values do not imply myocardial dysfunction.
	C.2.2. Tei index or myocardial performance index (MPI): it allows for a comprehensive estimation of both ventricular (right or left) systolic and diastolic functions. It is based on the relationship between the ejection and non- ejection work of the heart. It is defined as the ratio of the sum of isovolumetric relaxation time and isovolumetric contraction time, divided by the ejection time (Tei Index=IVRT+IVCT)/ET). This prognostic index is not widely used in the routine clinical practice but tends to increase in cases of systolic and/or diastolic ventricular dysfunction.
	It is a simple, reproducible method, independent of the heart rate and blood pressure, to estimate the severity and prognosis of myocardial involvement and as a predictor of postoperative left ventricular dysfunction in patients with mitral regurgitation with apparently normal ejection fraction (EF). A preoperative Tei index > 0.5 predicts postoperative LV dysfunction in patients with mitral regurgitation and apparently normal EF. We can measure it using Doppler tissue imaging (DTI) at the level of the mitral annulus (A) or the pulsed-wave spectral DTI by placing the wide sample volume between the LVOT and the mitral valve (B). The DTI can also be used to measure the Tei Index of the RV, keeping in mind that RV IVRT is virtually non-existent in the normal RV. This parameter is unaffected by heart rate or preload and has shown correlation with the severity and prognosis of various conditions affecting the RV. Its normal value according to the DTI is 0.39, and it is considered pathological when it is > 0.55.
	C.3. Doppler tissue imaging (DTI): The velocity of the mitral annulus or basal myocardium measured by DTI can be a simple approach to quantify the longitudinal ventricular function and is less dependent on loading conditions. However, it is not applicable in cases associated with mitral valves, mitral annuloplasty, or severe annular calcification. An S wave with a velocity < 8cm/sec calculated by pulsed-wave spectral DTI at various sites around the mitral annulus (septal, lateral, and posterior) has a 94% sensitivity rate, a 93% specificity rate, and a 94% accuracy for the detection of EF<40%.
D.	Regional systolic function
	The proper assessment of regional function requires good endocardial definition, visualization of all walls in various views, and confirmation that segmental abnormalities seen in one view are confirmed in a different view. Situations in which abnormal motility is accompanied by normal thickening (left bundle branch block, pacemaker rhythm, post-cardiac surgery, pericardial constriction) should be distinguished from ischemic changes, where abnormal motility is accompanied by changes to myocardial thickness.

Regarding the assessment of right ventricular (RV) function, which is discussed in a different chapter of this series, the tricuspid annular plane systolic excursion (TAPSE) and the peak systolic velocity (PSV)7,11,12 are the most widely used parameters because they are easy to estimate and because they have a low interindividual variability. Similarly, these parameters are influenced by preload and afterload,13 and should not be used in cases of tricuspid annulus implantation or prosthesis or severe annular calcification.

It is recommended that systolic functional assessment of the RV should be performed by changing fractional area (FA), with TAPSE and PSV serving as additional parameters.14

When there are difficulties to quantitatively assess the LVEF, visual estimation is the most widely used method to study the systolic function. While this method shows an acceptable correlation with ventriculography when performed by experienced observers, its accuracy decreases with less experience and, in the case of ventricles of abnormal morphology with non-homogeneous contraction, segmental contractility abnormalities, or the presence of asynchrony.15

Echocardiography has gained special relevance thanks to its accessibility at the bedside, non-invasiveness (in the case of TTE), and ability to provide anatomical and functional information.16

The process of hemodynamic resuscitation aims primarily at achieving adequate tissue perfusion pressure to restore proper oxygen supply to the cells. In addition to optimizing hemoglobin and blood oxygenation, it is essential to optimize the cardiac output (CO). This optimization should be guided by goals and the therapeutic response monitored to prevent or, at least, minimize the deleterious effects of these measures. Echocardiography provides relevant information about on the CO and its determinants, allowing us to assess the response to the therapeutic measures implemented.

Sistolic volume (SV) assessment (Fig. 2)

It can be performed using the velocity time integral (VTI) and the diameter of the left ventricular outflow tract (LVOT).

Figure 2.

Estimation of systolic volume (SV) and cardiac output (CO) through the velocity time integral (VTI) and radius (r) of the left ventricular outflow tract (LVOT). A: left parasternal view of the left ventricle in systole. B: zoomed LVOT. C: pulsed-wave Doppler LVOT 5C apical. D: calculations.

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VTI LVOT<11cm is correlated with a cardiac index<2L/min.17,18

At the CPO there is a high risk of developing respiratory failure after the surgical procedure due to a reduced respiratory reserve caused by inflammatory factors following extracorporeal circulation, mechanical and hemodynamic factors.21,22

It is associated with high morbidity and mortality rates,23 making it necessary to optimize perioperative respiratory care to improve outcomes after CS.

It is well-known that the diagnostic performance of lung ultrasound exceeds that of chest x-rays in the diagnosis of lung consolidation, lung collapse, pleural effusion, pulmonary edema, and pneumothorax.24 Lung ultrasound is also highly beneficial for etiological evaluation and diaphragmatic functional assessment.25

Due to space limitations and the fact that this topic is covered in another chapter of this series, we refer the reader to chapters number 3 and 4 of this series for further information.

Determining factors such as preexisting ventricular dysfunction, associated valvular heart disease, left ventricular hypertrophy, basal septal hypertrophy, pulmonary vascular disease/pulmonary hypertension (PH), or arrhythmias can not only impact accurate assessments but also the appropriate interpretation of echocardiographic findings.

Volume status assessment and dynamic gradient (video 1 of the supplementary data)

Volume status assessment using ultrasound is complex and requires being integrated with clinical examination. At the CPO, certain classical volume responsiveness concepts are not applicable due to the high incidence of arrhythmias, ventricular dysfunction, PH, chronic cor pulmonale, vascular diseases, and valve replacement procedures. However, echocardiography adds value to other devices, especially to assess the left ventricular end-diastolic area, transmitral Doppler inflow and LVOT variation, and inferior vena cava collapsibility (Table 2).

One of the most challenging clinical scenarios to manage in the CPO setting is mitral regurgitation due to abnormal systolic anterior motion (SAM), generating a pressure gradient in the LVOT or mesoventricular region, dragging and sucking the mitral anterior leaflet (Fig. 3). This should be suspected in cases with concentric hypertrophy, myectomy, or large post implantation toward the LVOT, states of hypovolemia, and/or need for ascending vasoactive support without an appropriate tensional response.

Figure 3.

Coronary artery bypass graft (CABG) in a patient with concentric LV hypertrophy: dynamic obstruction of LVOT due to excessive inotropic support and postoperative hypovolemia, leading to severe mitral regurgitation due to anterior septal motion (SAM). Note the progressive acceleration flow on the continuous-wave Doppler.

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Echocardiography is highly useful to assess the size of pericardial effusion (PE) and the degree of hemodynamic compromise. Sometimes, a simple transthoracic 4-chamber view is enough to assess PE, along with a subxiphoid long-axis view if dressings allow it.

Risk factors are advanced age, the need for emergent surgery in patients with prior anticoagulant or antiplatelet therapy, aortic root surgery, complex surgery, or poorly controlled anticoagulation in the perioperative period.

The diagnosis of cardiac tamponade is clinical and totally challenging in the CPO setting. Because the pericardium is open with drains in both the retrosternal and retropericardial spaces, it complicates its diagnosis with transthoracic echocardiography significantly. In the immediate CPO, PEs tend to be loculated, asymmetric, and located posteriorly in the atrioventricular groove and RV lateral wall. PEs are often associated with factors that change classic clinical and echocardiographic findings of tamponade, such as mechanical ventilatory support, PH, or pre-existing RV dysfunction.

In these circumstances, waiting for the onset of classic clinical and echocardiographic signs of tamponade often leads to delayed surgeries or inappropriate therapies.

In contrast, PEs that occur 72h after cardiac surgery are often larger and exhibit classical signs of cardiac tamponade.

The posterior location of PEs may require transesophageal studies to be able to see small loculated effusions causing atrial collapse (mid-esophageal 4- and 2-chamber views).

In a preliminary assessment using TTE we should pay special attention to the appearance, opening and closing of valve leaflets or occluders, the presence of leaflet calcifications, abnormal echogenic density adhered to the annulus suture, the occluder, the leaflets, the stents, or the cage. Also, we should be aware of any abnormal rocking motion occurring during the cardiac cycle. Completing the assessment with TEE is required for thorough evaluations.

• •

  The thickening of the aortic root due to the presence o hematoma or edema after valve implantation can be mistaken for the presence of perianular abscesses.27

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  The rocking motion of a valve is a sign of aortic position dehiscence. For the mitral position, when the entire native valve has been removed, an increased motion of a normal valve can be seen. The differential diagnosis will be based on the presence of a regurgitant jet.28

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  The appearance of paravalvular leak is always pathological,29,30 being more common in valve reinterventions, elderly patients, annular calcium debridement, and aortic or mitral reconstructions. The percentage of annular circumference damaged determines the severity of paravalvular leak and can be a sign of endocarditis in a later stage.

All prosthetic valves create a certain degree of obstruction compared to native valves depending on their design, size, and annular position (intra/supra), resembling stenosis. It is advisable to consult expected gradients for the diameter and model of the prosthesis (appendices 1 and 2).31–35 Therefore, it can be difficult to differentiate hemodynamic obstruction from a mild pathological dysfunction and prosthesis-patient mismatch (PPM) or mismatch (Table 3, Fig. 4, video 4 of the supplementary data).36

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  Elevated gradients can be observed in normally functioning small-sized valves, in hyperdynamic states, or increased SV, post-valvular pressure recovery phenomena, PPM, and stenosis.

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  In the presence of LV dysfunction, low gradients can be found with significant stenosis.

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  In the aortic position, the triangular morphology of the Doppler velocity contour with a short acceleration time provides us with information of normal functioning. As obstruction progresses, the Doppler velocity contour will become more rounded, until it reaches a delayed peak flow (Fig. 4).

  
  

  Figure 4.

  * Pulsed-wave Doppler sample volume very close to the prosthesis. # Stenosis additionally confirmed by the EOA compared with reference values if valve type and size are known. ** Pulsed-wave Doppler sample volume distant (apical) from the prosthesis. AT, acceleration time; DLVOT, diameter of the LVOT; DVI, Doppler velocity index or nondimensional functional index; EOA, effective orifice area; indexed EOA, EOA divided by body surface area; LVOT, left ventricular outflow tract; PPM, prosthesis-patient mismatch; VTI, velocity-time integral.

  Modified from Zoghbi WA, et al.

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  In the mitral position, along with an elevated mean gradient, an elongated hemi-pressure time will be present.

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  In addition to valvular gradients, it is of paramount importance to obtain flow-independent parameters of the prosthetic valve function, such as the effective orifice area (EOA) and the Doppler velocity index (DVI) or the dimensionless index (DI) (Table 3). The DVI value obtained in the early postoperative phase can serve as a control value or “valve footprint” for future studies. As long as the prosthetic valve function is normal, the DVI will remain constant even in the presence of SV changes.

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  The combined assessment of the parameters described will establish the degree of prosthetic obstruction (Table 3).37

DE, the TEE in particular, initially provides us with the necessary information for decision-making (the need for a device and the type or types of devices that should be implanted), and the identification of conditions that may contraindicate or complicate implantation (aortic valve disease, presence of a patent foramen ovale, thrombosis, dissection, arterial vascular disease, hypertrophic cardiomyopathy, etc.).

Once the type of device that should be implanted has been selected, the insertion process, exact positioning of the cannulas, detection of complications, assessment of the effectiveness of the device implanted, and the weaning process are extremely helpful.

Orthotopic heart transplant is the most common type of transplant, and the surgical technique can be either biatrial or bicaval. For echocardiographic evaluation purposes, the donor heart should be normal size, and the space left by the recipient's heart should be larger, tending to rotate clockwise and locate more medially in the mediastinum. Table 5 illustrates the general considerations in the evaluation of the transplanted heart44 (video 7 of the supplementary data).

Taking this into consideration, echocardiography helps us rule out the most common causes of hemodynamic instability that can occur in any post-cardiac surgery patient, as described earlier. Once these have been ruled out, we should focus on the more specific complications of heart transplantation:

None declared.

None declared.