Left ventricular (LV) dysfunctions (systolic and diastolic) are common in the critically ill patient. They may be due to preexistent disease (e.g., coronary artery disease [CAD]) or acquired as a part of a clinical syndrome responsible for the intensive care unit (ICU) admission (e.g., septic cardiomyopathy). Clinical examination alone or in combination with chest radiography may be insufficient for assessing LV function in the ICU. Echocardiography will provide crucial information; thus, echocardiographic assessment of LV function is necessary in nearly all ICU patients. Other technologies, such as bioreatance (NICOM) and thermo or marker dilution (LiCO, PICO), may provide additional information that can also be useful. Indwelling Doppler devices assessing aortic blood flow have been utilized with variable degree of success. Finally, carotid artery blood flow measured ultrasonographically has been recently suggested as an alternative to more technically challenging analysis of the transaortic stroke volume (SV) (cardiac output [CO]). All of these methods assist in assessing the LV.

Transthoracic Echocardiography Versus Transesophageal Echocardiography—Hand-Held Devices


Transthoracic echocardiography (TTE) is the modality most frequently utilized in the ICU. In spite of being operator dependent TTE will usually provide clinically useful information that alters the plan of care in nearly 50% of critically ill patients. It is noninvasive, has virtually no contraindications, can be repeated as often as necessary to reevaluate cardiac function after therapeutic interventions (volume resuscitation, inotropic support, vasoconstrictors), and usually requires no more then 5 min to acquire clinically relevant information about cardiac function by the experienced operator.1 Moreover, it is easy to train intensivists in TTE. Newer generations of the handheld, pocket sized, battery-powered devices are now available and are simple and convenient to operate. They can provide a focused qualitative assessment of the LV systolic function. Handheld devices can be also valuable in ultrasound-guided thoracentesis, paracentesis, and abdominal examination. The role and utility of these devices in the assessment of the hemodynamically unstable ICU patient is still evolving.

Transesophageal echocardiography (TEE) is often considered superior to TTE in the ICU. TTE frequently provides poorer image quality in postoperative patients due to mechanical ventilation (positive end-expiratory pressure [PEEP] >15 cm of H2O), inability to position the patient, lack of patient cooperation, chest wall edema and obstructed views due to wound dressings, chest tubes, drains, and an open chest or abdomen. In the critical care setting, TTE leads to a successful examination in 50% of attempts,2,3 in contrast to 90% with TEE.4,5 There are, however, challenges to the routine performance of TEE in the ICU. The TEE examination requires additional time and expertise when compared with the TTE examination. There is a small, but definite list of absolute and relative contraindications (Chapter 8). Insertion of the probe into the esophagus carries with it a risk of loss of the airway. Additionally, TTE carries with it a small but real risk, in the order of 0.01%, of significant complications such as esophageal perforation.

Regardless of what modality is used to perform the examination, it is important that the examination be as complete as the training of the practitioner allows. If the initial point of care examination is technically limited or there is doubt as to the findings, the examination should be followed as soon as possible with a comprehensive examination by a more experienced operator. A comprehensive examination is less likely to miss an unexpected diagnosis. With practice, a complete examination may be performed in minutes. A reasonable strategy is to first focus on the areas or structures of interest as directed by the clinical presentation. Once the immediate question is answered, this should be followed by a complete examination. Items of lesser interest may then be reexamined in a more leisurely manner. Guidelines exist that standardize the images captured on both the TTE and TEE examinations.6 These are important in assuring that all structures are viewed from multiple angles, allowing each individual structure to be completely and accurately assessed and documented as needed. The standardized views also assure that no structure is missed in the examination and provide the common language that allows practitioners to communicate their findings with each other and all members of the treatment team.

LV Systolic Function


Not less than 36% of all critically ill patients have reduced LV systolic function during their ICU stay. In the past, systolic function and particularly assessment of LV ejection fraction (LVEF) was overstated at the expense of diastolic function and volume responsiveness. This was partially due to historical connection of the bedside ultrasonography of the heart to classical cardiac echocardiography and the statistical importance of CAD to the latter. Recently, diastolic function, venous return and right ventricular function are increasingly recognized as major contributors to hemodynamic stability (see below). Nonetheless, LVEF assessment is still an important pert of the point of care cardiac evaluation. Thus, assessment of LV systolic function and its changes over time are quite helpful in therapeutic decision-making for the critically ill patient. Global LV systolic function is important because many diseases of the critically ill, and in particular sepsis, may lead to global rather than focal ventricular dysfunction. The presence of focal or regional wall motion abnormalities during the initial evaluation may indicate preexistent CAD, while the appearance of new or worsening wall-motion abnormalities may be indicative of the ischemic changes due to hypoxia or superimposition of myocardial infarction. Regardless, information on global and regional LV function is of critical importance in the clinical decision making throughout the ICU stay and may be useful in both early and later stages where challenging liberation from mechanical ventilation or inotropic medication may be explained and a causative lesion appropriately treated.

Echocardiography is largely a two-dimensional (2D) method of viewing a three-dimensional (3D) structure. A minimum of two orthogonal views should be performed for each structure of interest before making a diagnostic or a therapeutic decision. This is specifically mandated for a quantitative LVEF calculation by a biplane Simpson’s method where evaluation in the apical four-chamber and two-chamber (perpendicular) views is mandatory.

Ventricular systolic function depends on both preload and afterload. Estimates of systolic function should be performed under different loading conditions to ascertain the true function. Once again, this demonstrates the importance of obtaining serial assessments rather than single snapshot views. Responses to passive leg raising or volume challenge are two methods of determining LV contractility relation to loading conditions (see Chapter 10).

Segmental wall-motion abnormality assessment and regional LV function should be performed using visual identification with a standardized 17-segment model simultaneously with global LV function evaluation. Qualitative, semi-quantitative and quantitative measures are used for assessing global LV systolic function. LVEF by visual assessment or biplane Simpson’s methods, and linear M-mode measurements (i.e., fractional shortening) can be evaluated by TTE in initial stages or adopting ultrasonography into clinical ICU practice. Once Doppler techniques become familiar to the operator velocity–time integral (VTI) can be included and provide additional information on SV and CO independent of LVEF measurements. All of the methods, once integrated into clinical practice will provide a reliable set of tools with low-variability and high-quality bedside information. The most commonly used methods will now be discussed. It is incumbent upon the intensivist echocardiographer to be familiar with the advantages and limitations of all methods used in the assessment of LV systolic function.

Qualitative Assessment of LV Systolic Function


The most important and commonly used method of assessing LV global and focal wall motion is by a qualitative assessment in multiple views. This method is extremely effective, rapid, and consistent with nuclear scanning studies when done by an experienced echocardiographer. The result is both an assessment of regional wall motion and an overall assessment of LV function usually expressed in terms of an estimated ejection fraction (EF). To help interpret LV systolic function, several questions should be asked:

  • Is the ventricle adequately filled? (See chapter 10)

  • Is the ventricle’s contractile function adequate?

  • Is the ventricular contractility uniform throughout the coronary artery distributions and if present can regional wall motion abnormalities be attributed to the specific coronary artery.

Qualitative LV systolic function can be adequately performed with portable and pocket size ultrasound systems.

Visual Assessment with a Standard 17-Segment Model

In an effort to have a uniform nomenclature for the LV function derived from multiple assessment modalities such as cardiac magnetic resonance imaging (MRI), echocardiography, nuclear scanning, and angiography, the American Heart Association produced a consensus statement suggesting that the LV be divided into 17 different segments.7 The LV is divided into basal, midcavity, and apical segments along the long axis of the heart. Each segment is then further divided into six in the basal, six in the midcavity, and four in the apical segments, and an apical cap is included as the 17th segment. The corresponding coronary arterial distribution is shown in Figure 9-1.

Figure 9-1

(A) Four-chamber view showing the coronary artery distribution and the corresponding LV segments. The septal wall (anterior 1/3) is supplied by the left anterior descending (LAD) artery; lateral wall is supplied by the circumflex artery (Cx). (B) Two-chamber view showing the coronary artery distribution and the corresponding left ventricular segments. The base, mid, and apical segments of anterior wall are supplied by the LAD artery and the inferior wall is supplied by the right coronary artery. (C) Oblique view of the LV showing the anteroseptal and posterior segments. The base, mid, and apex of the anteroseptal wall and posterior wall are supplied by the LAD and left circumflex (Cx) arteries, respectively. (D) Midpapillary short-axis view of the left ventricle (LV) showing the three arterial distribution and corresponding segments. This is the midpapillary transgastric short-axis view of the LV showing the LAD supplying the midanterior and anteroseptal segments, Cx supplying midlateral and posterior segments of the lateral wall, and RCA supplying midseptal and inferior segments of the LV. Cx, left circumflex coronary artery; LAD, left anterior descending artery; RCA, right coronary artery. (Reproduced with permission from Dr. Martin London’s Web site

The left anterior descending (LAD) coronary artery supplies the anterior wall of the heart and anterior two thirds of the interventricular septum. The left circumflex artery (LCx) supplies the lateral wall of the LV. The right coronary artery (RCA) supplies the posterior third of the interventricular septum and inferior wall of the LV. A semiquantitative assessment can be performed using a wall-motion score or index. The LV contractility is dependent on movement of the base toward the apex, thickening of the wall segments, and a spiral squeeze or rotational movement of the LV. Thickening of the wall segments and the endocardial excursion of the LV segment are important to assess the wall motion. The wall-motion score is described here:

  1. Normal (>30% endocardial excursion and >50% wall thickening)

  2. Mild hypokinesis (10–30% endocardial excursion and 30–50% wall thickening)

  3. Severe hypokinesis (<20% endocardial excursion and <30% wall thickening)

  4. Akinesis (no endocardial excursion and <10% wall thickening)

  5. Dyskinesis (moves paradoxically-outwards during systole)

The wall-motion score index is defined as the wall-motion score/number of segments. This is a subjective assessment and does not have a true linear relationship. A stunned myocardium without a perfusion defect can exhibit wall-motion abnormality. Multiple views must be obtained to truly define the degree of LV impairment and the arterial distribution involved. Endocardial excursion alone may be due to tethered myocardium, and a change in wall thickness is a precise indicator of ischemia.8 The reproducibility of wall thickening measurements was evaluated, which led to the following conclusions:

  1. It is difficult to obtain consistent data on wall thickening in the longitudinal plane.

  2. Multiple measurements are necessary to reduce variability.

  3. It is necessary to ensure that borders, locations, and angles are carefully defined.9

Quantitative Assessment of LV Systolic Function with Echocardiography


Quantitative techniques of ventricular assessment allow for a more measurable and arguably less biased assessment of the ventricle. These techniques have their advantages and their limitations.

Volumetric Ejection Fraction, SV, and CO by Biplane Simpson’s Method

SV is obtained by calculating the difference between the end-diastolic volume (EDV) and end-systolic volume (ESV). SV = ESV/EDV. EF is defined as SV divided by the EDV. EF = SV/EDV %. CO can be quantified by multiplying SV by the heart rate (HR). CO = SV × HR. The American Society of Echocardiography (ASE) recommends the modified Simpson’s method.10 This method calculates ESV, EDV, SV, and EF in two planes and averages them. With TTE apical four- and two-chamber views are utilized as located in the planes perpendicular to each other (Videos 9-1 and 9-2). Endocardial borders need to be well visualized to trace them out. Representative frames are chosen at the end of systole (Figures 9-2 and 9-3) and diastole (Figures 9-4 and 9-5) and endocardial borders traced. End systole and end diastole are identified by the position and motion of mitral valve leaflets in two subsequent frames or less reliably by the EKG or the LV visible cavity size (smallest vs. largest) (Table 9-1). When using TEE, the midesophagus four-chamber, and two-chamber planes can be used for the same purpose (Figure 9-6). Most ultrasound systems will automatically calculate EDV, ESV, and EF. The CO can be calculated manually if not so provided.

Figure 9-2

Endocardial borders are traced in systole in apical two-chamber view.

Figure 9-3

Endocardial borders are traced in systole in apical four-chamber view. Note that ejection fraction is automatically calculated by the ultrasound system.

Figure 9-4

Endocardial borders are traced in diastole in apical two-chamber view.

Figure 9-5

Endocardial borders are traced in diastole in apical four-chamber view. Note that Left ventricular diastolic volume is automatically calculated by the ultrasound system.

Figure 9-6

Simpson’s method of left ventricular ejection fraction assessment. (A) TEE midesophageal four-chamber end-diastolic frame: LV at end-diastole frame is frozen. The endocardial border is traced out to get the end-diastolic dimension. (B) Midesophageal four-chamber end-systolic frame: the LV frame at end-systole is frozen. The endocardial border is tracked in the machine. (C) Midesophageal oblique two-chamber end-diastolic frame: the LV frame at end-diastole is frozen in this oblique view, adding another dimension to the previous measurements. The endocardial border is tracked in the machine. (D) Midesophageal oblique two-chamber end-systolic frame: the LV frame at end-systole is frozen. The endocardial border is tracked in the machine in this two-chamber view, giving an added dimension to the previous calculation. LV, left ventricle.

Only gold members can continue reading. Log In or Register to continue

Premium Wordpress Themes by UFO Themes