Assessment of left ventricular ejection fraction using an ultrasonic stethoscope in critically ill patients.

Abstract

Assessment of cardiac function is key in the management of intensive care unit (ICU) patients and frequently relies on the use of standard transthoracic echocardiography (TTE). A commercially available new generation ultrasound system with two-dimensional imaging capability, which has roughly the size of a mobile phone, is adequately suited to extend the physical examination. The primary endpoint of this study was to evaluate the additional value of this new miniaturized device used as an ultrasonic stethoscope (US) for the determination of left ventricular (LV) systolic function, when compared to conventional clinical assessment by experienced intensivists. The secondary endpoint was to validate the US against TTE for the semi-quantitative assessment of left ventricular ejection fraction (LVEF) in ICU patients.
In this single-center prospective descriptive study, LVEF was independently assessed clinically by the attending physician and echocardiographically by two experienced intensivists trained in critical care echocardiography who used the US (size: 135×73×28 mm; weight: 390 g) and TTE. LVEF was visually estimated semi-quantitatively and classified in one of the following categories: increased (LVEF>75%), normal (LVEF: 50 to 75%), moderately reduced (LVEF: 30 to 49%), or severely reduced (LVEF<30%). Biplane LVEF measured using the Simpson's rule on TTE loops by an independent investigator was used as reference.
A total of 94 consecutive patients were studied (age: 60±17 years; simplified acute physiologic score 2: 41±15), 63 being mechanically ventilated and 36 receiving vasopressors and/or inotropes. Diagnostic concordance between the clinically estimated LVEF and biplane LVEF was poor (Kappa: 0.33; 95% CI: 0.16 to 0.49) and only slightly improved by the knowledge of a previously determined LVEF value (Kappa: 0.44; 95% CI: 0.22 to 0.66). In contrast, the diagnostic agreement was good between visually assessed LVEF using the US and TTE (Kappa: 0.75; CI 95%: 0.63 to 0.87) and between LVEF assessed on-line and biplane LVEF, regardless of the system used (Kappa: 0.75; CI 95%: 0.64 to 0.87 and Kappa: 0.70; CI 95%: 0.59 to 0.82, respectively).
In ICU patients, the extension of physical examination using an US improves the ability of trained intensivists to determine LVEF at bedside. With trained operators, the semi-quantitative assessment of LVEF using the US is accurate when compared to standard TTE.

Full text

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RESEARCH Open Access
Assessment of left ventricular ejection fraction using
an ultrasonic stethoscope in critically ill patients
Jean-Bernard Amiel1,2, Ana Grümann1, Gwenaëlle Lhéritier1, Marc Clavel1,2, Bruno François1,2, Nicolas Pichon1,2,
Anthony Dugard1,2, Benoît Marin3and Philippe Vignon1,2,4*
Abstract
Introduction: Assessment of cardiac function is key in the management of intensive care unit (ICU) patients and
frequently relies on the use of standard transthoracic echocardiography (TTE). A commercially available new
generation ultrasound system with two-dimensional imaging capability, which has roughly the size of a mobile
phone, is adequately suited to extend the physical examination. The primary endpoint of this study was to
evaluate the additional value of this new miniaturized device used as an ultrasonic stethoscope (US) for the
determination of left ventricular (LV) systolic function, when compared to conventional clinical assessment by
experienced intensivists. The secondary endpoint was to validate the US against TTE for the semi-quantitative
assessment of left ventricular ejection fraction (LVEF) in ICU patients.
Methods: In this single-center prospective descriptive study, LVEF was independently assessed clinically by the
attending physician and echocardiographically by two experienced intensivists trained in critical care
echocardiography who used the US (size: 135 × 73 × 28 mm; weight: 390 g) and TTE. LVEF was visually estimated
semi-quantitatively and classified in one of the following categories: increased (LVEF > 75%), normal (LVEF: 50 to
75%), moderately reduced (LVEF: 30 to 49%), or severely reduced (LVEF < 30%). Biplane LVEF measured using the
Simpson’s rule on TTE loops by an independent investigator was used as reference.
Results: A total of 94 consecutive patients were studied (age: 60 ± 17 years; simplified acute physiologic score 2:
41 ± 15), 63 being mechanically ventilated and 36 receiving vasopressors and/or inotropes. Diagnostic
concordance between the clinically estimated LVEF and biplane LVEF was poor (Kappa: 0.33; 95% CI: 0.16 to 0.49)
and only slightly improved by the knowledge of a previously determined LVEF value (Kappa: 0.44; 95% CI: 0.22 to
0.66). In contrast, the diagnostic agreement was good between visually assessed LVEF using the US and TTE
(Kappa: 0.75; CI 95%: 0.63 to 0.87) and between LVEF assessed on-line and biplane LVEF, regardless of the system
used (Kappa: 0.75; CI 95%: 0.64 to 0.87 and Kappa: 0.70; CI 95%: 0.59 to 0.82, respectively).
Conclusions: In ICU patients, the extension of physical examination using an US improves the ability of trained
intensivists to determine LVEF at bedside. With trained operators, the semi-quantitative assessment of LVEF using
the US is accurate when compared to standard TTE.
Introduction
In intensive care unit (ICU) settings, several studies have
long shown that physical examination was inaccurate in
predicting the hemodynamic status of patients with circu-
latory or respiratory failure, even when performed by
experienced intensivists [1,2]. Specifically, the range of car-
diac index (low, normal or high) has been shown to be
adequately predicted by the physical examination in only
44 to 51% of ICU patients who were evaluated using right
heart catheterization [1-3]. Ejection fraction (EF) is the
most commonly used parameter of left ventricular (LV)
systolic function on clinical grounds [4]. This parameter is
altered not only by LV contractility (and inotropes), but
also by LV volumes, preload, afterload (and vasopressors)
and valvular function [5]. Nevertheless, LVEF has the
advantage of internally normalizing the stroke volume by
LV end-diastolic volume and, therefore, can be used as a
parameter of LV systolic function that is independent of
* Correspondence: philippe.vignon@unilim.fr
1Medical-surgical Intensive Care Unit, Dupuytren Teaching Hospital, Avenue
Martin Luther King, 87000 Limoges, France
Full list of author information is available at the end of the article
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© 2012 Amiel et al.; licensee BioMed Central Ltd. This is an open access article distributed under the terms of the Creative Commons
Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in
any medium, provided the original work is properly cited.

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the size of the patient or the ventricle [6]. Although LVEF
fails to directly reflect systolic flow or the overall circula-
tory state, the determination of cardiac pump function is
key in the management of ICU patients with cardiore-
spiratory compromise.
Standard transthoracic echocardiography (TTE) is cur-
rently the first-line imaging modality recommended for
the measurement of LVEF [4]. Miniaturized, battery-
operated systems have been successfully used in ICU
patients [7,8]. The recent emergence of commercially
available pocket-size miniaturized ultrasound devices
virtually enables physicians to extend the physical exam-
ination with an ultrasonic stethoscope (US) [9]. This
approach has been validated for the qualitative evalua-
tion of LVEF in cardiology patients [10], but not yet in
the ICU settings. Accordingly, the primary endpoint of
this study was to evaluate the additional value of an US
for the determination of LV systolic function, when
compared to conventional clinical assessment by experi-
enced intensivists. The secondary endpoint was to vali-
date the US against TTE for the semi-quantitative
assessment of LVEF in ICU patients.
Materials and methods
Patients
This single-center prospective descriptive study was
approved by our institutional Ethical Committee, which
waived the need for informed consent. During a six-week
period, all patients hospitalized in our medical-surgical
ICU underwent, systematically, a clinical and echocardio-
graphic assessment of LVEF using standard TTE and a
new generation US within the first 12 hours of admission.
The presence or absence of congestive heart failure was
clinically evaluated by the attending physician (senior
intensivist with at least five-years’ experience in critical
care medicine) based on medical history, physical exami-
nation and admission chest X-ray as previously described
[11], or on any other available information, including pre-
viously measured LVEF. In each patient, the clinically or
echocardiographycally estimated LVEF was classified in
one of the following categories: increased (LVEF > 75%),
normal (LVEF: 50 to 75%), moderately reduced (LVEF: 30
to 49%), or severely reduced (LVEF < 30%). Hypotension
was defined as a systolic blood pressure < 90 mmHg or a
mean blood pressure < 65 mmHg. Shock was defined as
the presence of clinical signs of tissue hypoperfusion con-
firmed by a metabolic acidosis, high lactate level or a
decreased ScvO2associated with a sustained hypotension,
or not [12]. Patients were not studied when < 18 years or
when one of the investigators was not available.
Echocardiographic assessment of LVEF
The tested US was a new generation (VScan™, Gen-
eral Electrics Healthcare) miniaturized (size: 135 × 73
× 28 mm; weight: 390 g), battery-operated (total scan
time of one hour) device with a broad-band width (1.7
to 3.8 MHz) phased array probe (120 × 33 × 26 mm).
This system can store digital still-frames or image
loops, uses a color-coded overlay for real-time blood
flow imaging, and allows distance measurements using
integrated electronic calipers, but has neither spectral
nor tissue Doppler capability (Figure 1). TTE studies
were performed with a full-feature system (CX50, Phi-
lips Healthcare).
The two echocardiographic examinations were per-
formed independently, and randomly according to the
availability of investigators and ultrasound systems, but
within the same hour. Operators were experienced
intensivists highly trained in critical care echocardiogra-
phy [13]. The following TTE views were systematically
screened in each patient: parasternal short-axis view,
apical four- and two-chamber views and subcostal four-
chamber view. In each TTE view, imaging quality was
graded as 0 (no image), 1 (less than 50 percent of endo-
cardial border well delineated), 2 (more than 50 percent
of endocardial border well delineated) and 3 (entire
endocardial border well delineated) [7]. An overall qual-
ity score was calculated by adding imaging quality
grades of all four studied TTE views (range: 0 to 12).
Three digital loops were recorded during TTE at end-
expiration in the apical four- and two-chamber views
for further analysis. The time required to perform the
examination purposely focused on the visual estimation
of LVEF (from the first image obtained to the end of
examination) was recorded.
The investigators assessed semi-quantitatively LVEF
using TTE or the US in the apical four- and two-cham-
ber views, with the same four-subset classification than
that used for the clinical evaluation. The echocardiogra-
phers and the front-line intensivists who clinically
assessed LVEF had access to the same information but
were not allowed to communicate until individual clini-
cal research forms had been independently fulfilled at
the patient’s bedside. LVEF was then measured off-line
by two independent intensivists with an ASE level 3
competence in echocardiography [14]. LV end-diastolic
volume (LVEDV) and LV end-systolic volume (LVESV)
were measured in the apical four- and two-chamber
views using the Simpson’s method, according to current
recommendations [15]. LV volumes were measured on
three non-consecutive cardiac cycles and averaged.
LVEF was conventionally calculated as the stroke
volume (LVEDV-LVESV) normalized by LVEDV [5].
Values derived from both the apical four- and two-
chamber views were then averaged to obtain individual
biplane LVEF, unless image quality of the apical two-
chamber view was not suitable for LV volume measure-
ments. TTE-derived LVEF values were used to
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determine the reference category of individual systolic
cardiac function.
Statistical analysis
Results are expressed as means ± standard deviations or
frequencies and percentages. Paired comparisons were
performed using the paired Student t-test for continuous
variables and with the Mac Nemar Chi-2 test for quali-
tative variables. Percent comparisons were performed
using Pearson’s Chi-2 test. Interobserver variability of
LVEF measurement was computed as the absolute dif-
ference between the two sets of measurements divided
by the mean of the two values and expressed as a per-
centage of error. Diagnostic concordance for the semi-
quantitative evaluation of LVEF at patient’s bedside was
assessed using a weighted Kappa test with 95% confi-
dence intervals (CI) as follows: clinical evaluation vs.
measured LVEF, visual assessment using the US and
TTE vs. measured LVEF, and visual assessment using
the US vs. visual assessment using TTE. A P-value <
0.05 was considered statistically significant.
Results
Among the 122 patients admitted to our ICU during the
study period, 33 were excluded due to the unavailability of
one investigator (n = 26), or an age < 18 years (n = 2).
Finally, 94 patients were studied (mean age: 60 ± 17 years;
men: 71; mean simplified acute physiologic score (SAPS
2): 41 ± 15). Reasons for admission to the ICU were pre-
dominantly a circulatory failure (n = 56) or an acute
respiratory failure (n = 26). Sixty-three patients (67%) were
mechanically ventilated and 36 patients (38%) received
vasopressors and/or inotropes (Table 1). Mean duration of
echocardiographic examination was significatively shorter
when using the US (241 ± 107 vs. 300 ± 131 s: P = 0.0014)
but its overall mean image quality was inferior to that of
TTE (5.9 ± 3.7 vs 6.9 ± 3.7: P = 0.0009). Noticeably, the
proportion of good-to-excellent image quality grade in the
apical four-chamber view used to visually assess LVEF was
not significantly different with the US and TTE (grades 2
and 3: 54/94 vs 61/94; P = 0.37), and LVEF was not
visually evaluable in a similar proportion of patients (12/
94 vs 10/94: P = 0.50).
LVEF was measured off-line in 84 patients (89%) in the
apical four-chamber view and in 44 patients (47%) in the
apical two-chamber view. Interobserver variability for
LVEF measurement was 9 ± 7%. Mean LVEF was 54 ±
19%. According to TTE-derived LVEF values, 8 patients
had an increased LVEF, 51 patients had a normal LVEF,
14 patients had a moderately reduced LVEF and the
remaining 11 patients had a severely reduced LVEF. Diag-
nostic concordance between the clinically estimated LVEF
by the attending physicians and the measured LVEF was
poor (Kappa: 0.33; 95% CI: 0.16 to 0.49), and only slightly
improved by the knowledge of a previously determined
LVEF value (n = 21; Kappa: 0.44; 95% CI: 0.22 to 0.66).
The sensitivity and specificity of the clinical judgement to
identify a decreased LVEF (that is, < 50%) was 60% (95%
CI: 39 to 79) and 83% (95% CI: 71 to 92), respectively.
In contrast, the diagnostic agreement was good between
the visually assessed LVEF using the US and TTE (Kappa:
0.75; CI 95%: 0.63 to 0.87). Similarly, the visually assessed
Figure 1 New generation miniaturized ultrasound system the size of a smartphone used in the current study.
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LVEF using the US and TTE was in agreement with the
measured reference values (Kappa: 0.75; 95% CI: 0.64 to
0.87 and Kappa: 0.70; 95% CI: 0.59 to 0.82, respectively).
When compared with the reference LVEF, the visual
assessment using the US overestimated LVEF in nine
patients and underestimated LV systolic function in a sin-
gle patient (Table 2). Similarly, TTE led to visually overes-
timate LVEF in 12 patients and to underestimate LV
systolic function in 8 patients when compared to reference
measurements (Table 3). When the reference LVEF was in
the normal or increased range of values, LV systolic dys-
function was erroneously identified in only three patients.
Regardless of the ultrasound system used, most inaccurate
visual assessments of LVEF were related to an inadequate
evaluation of the severity of LV systolic dysfunction or to
the erroneous distinction between a normokinetic and a
hyperkinetic LV (Tables 2 and 3).
Discussion
In this study, LVEF could not be accurately predicted in
ICU patients by the sole physical examination and the
knowledge of a previously determined LVEF value failed
to significantly improve the clinical judgement of the
front-line intensivist. In contrast, the herein tested new
generation US allowed an accurate semi-quantitative
assessement of LVEF when compared with standard
TTE, during a focused, rapid-to-perform examination.
Previous studies have long shown that physical exami-
nation was inaccurate in predicting the hemodynamic
status of ICU patients (for example, cardiac index, car-
diac filling pressures, systemic vascular resistance) when
using right heart catheterization as a reference. In these
series, the cardiac index was adequately graded as low,
normal or high in only approximately half of the cases
when compared to measurements obtained by the ther-
modilution technique [1,2]. Similarly, front-line intensi-
vists adequately predicted LVEF in only 64 of our
patients (68%), as reflected by a poor diagnostic agree-
ment between the clinical assessment and the reference
LVEF value. Importantly, the use of an US as an exten-
sion of the physical examination markedly improved the
clinical evaluation of cardiac function. In a systematic
review of the literature, Badgett et al. [11] reported that
the performance of the physical examination for detect-
ing a decreased LVEF or increased LV filling pressure
was fairly poor in ICU patients, with an overall sensitiv-
ity and specificity of 54% and 69%, respectively. In the
present study, the sensitivity and specificity of the clini-
cal examination to identify a decreased LVEF were
slightly higher (60% and 83%, respectively). Interestingly,
the knowledge of a previous LVEF value failed to signifi-
cantly improve the clinical judgement in our patients.
This result is presumably related to the frequency of
transient LV systolic dysfunction in ICU patients who
sustain acute insults [16,17] and to the beneficial effects
of ongoing inotropic support which may have variously
improved LV systolic function.
As previously reported using the same US [18], a fairly
good two-dimensional imaging quality was obtained in
most of our ICU patients, of which the majority was
mechanically ventilated. Accordingly, the diagnostic con-
cordance between the US and TTE was good for the
semi-quantitative assessment of LVEF. This result is in
keeping with those of previous studies performed in
other medical settings which reported a high concor-
dance for the diagnosis of decreased LVEF using the
herein tested US and TTE as a reference [10,19]. Inter-
estingly, the number and nature of LVEF misclassifica-
tions were similar using the two TTE approaches in our
patients and were predominantly related to the distinc-
tion between moderately and severely reduced LVEF,
and between normal and hyperkinetic LV wall motion.
Other commercially available US appear promising in
providing accurate information on cardiac chamber size
Table 1 Characteristics of the study population
Descriptive parameters
Age, yr
Men, n
SAPS II
Invasive mechanical ventilation, n
Reason for admission, n*:
shock
hypotension
cardiac arrest
acute respiratory failure
systematic assessment
Hemodynamic management*:
fluid loading, mL
vasopressor support, n
inotropes, n
Blood pressure, mmHg:
systolic
diastolic
mean
Heart rate, bpm
Central venous pressure, mmHg
VT, mL
Plateau pressure, cmH2O
PEEP, cm H2O
PaO2/FiO2
Lactates, mmol/L
Creatinin, μmol/L
ALAT, IU/L
Hemoglobin, g/dL
60 ± 17
71 (74%)
41 ± 15
63 (66%)
35
16
5
26
28
478 ± 967
26 (28%)
10 (11%)
120 ± 27
68 ± 15
84 ± 19
91 ± 24
9 ± 4
460 ± 63
19 ± 4
7 ± 3
251 ± 112
4.04 ± 3.92
143 ± 158
93 ± 196
9 ± 2
*: a single patient may fulfill several criteria
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and function, but have yet been only scarcely tested in
cardiology patients [20].
Visual assessment of LV systolic function using TTE
has been shown to be reliable when performed by
trained operators [21]. In the ICU settings, we [22,23]
and others [24] have recently reported that a tailored
training program allowed residents without previous
experience in ultrasound to accurately assess semi-quan-
titatively global LV systolic function as normal or
increased, reduced or severely reduced. Interestingly, the
diagnostic agreement between the trained residents and
the experienced intensivists or cardiologists was good to
excellent in all these studies (Kappa: 0.76 (CI 95%: 0.59
to 0.93); Kappa: 0.84 (CI 95%: 0.76 to 0.92); Kappa: 0.68
(CI 95%: 0.48 to 0.88)) [22-24]. A recent study per-
formed in ambulatory patients showed that residents of
internal medicine who received a 15-hour training pro-
gram adequately assessed LVEF using the same US than
that used in the present study (Kappa: 0.87) [19].
Whether the new generation of US will allow trainees
who are novice in ultrasound to be reliable when per-
forming basic level critical care echocardiography
remains to be determined [13].
Taken together, these results suggest that the tested
US is reliable to semi-quantitatively assess LVEF during
a short, focused examination in ICU patients. Impor-
tantly, the European Association of Echocardiography
recently stated that current pocket-size imaging devices
should only be considered as screening tools or used to
complement the physical examination in various clinical
settings, including in ICUs [25]. The range of indica-
tions is limited and the results of US should be reported
as part of the physical examination. Finally, a specific
training and certification is recommended for all users
and the patient has to be informed that pocket-size ima-
ging systems fail to replace standard TTE [25]. In addi-
tion to the semi-quantitative evaluation of LVEF, the US
appears promising to quickly evaluate in ICU patients
the right ventricular size and function, the presence and
volume of pericardial and pleural effusions as well as
the size and respiratory variations of the inferior vena
cava, due to its two-dimensional imaging quality.
The present study has several limitations. Although
technically possible, LVEF has not been measured off-
line on images obtained with the US. Nevertheless, the
concept of US is based on a target-oriented (for exam-
ple, LVEF assessment), rapid evaluation to obtain infor-
mation which is not accessible to physical examination.
Accordingly, off-line measurement of LV volumes using
the specific software provided with US is not clinically
relevant. Both the order of echocardiographic examina-
tions and allocation of ultrasound systems were not ran-
domized, but rather depended on the availability of
devices and investigators. Nevertheless, this potential
methodological bias should have a minor impact on the
observed results since surface echocardiography has
long been used in our ICU by highly trained operators
[26]. Accordingly, the present results cannot be general-
ized to less experienced operators. Additional informa-
tion provided by the US was purposely not analyzed,
especially that related to the use of color Doppler map-
ping. Accordingly, the present study failed to validate
the tested US to perform basic critical care echocardio-
graphy [13]. Finally, the therapeutic impact related to
the use of an US as an extension of physical examina-
tion in the ICU settings remains to be determined.
Table 2 Visual assessment of left ventricular ejection fraction (LVEF) using the ultrasound stethoscope*
Visual assessment of LVEF with the ultrasound stethoscope
Reference LVEFIncreased
LVEF > 75%
4
1
0
Normal
LVEF: 50 to 75%
4
47
3
Moderately depressed
LVEF: 30 to 49%
0
1
11
Severely depressed
LVEF < 30%
0
0
0
Increased
Normal
Moderately depressed
Severely depressed0146
*: Biplane LVEF measured off-line with the Simpson’s rule using an upper-end system was used as a reference.
Table 3 Visual assessment of left ventricular ejection fraction (LVEF) using the full-feature ultrasound system*
Visual assessment of LVEF with the full-feature system
Reference LVEFIncreased
LVEF > 75%
3
6
0
Normal
LVEF: 50 to 75%
5
43
2
Moderately depressed
LVEF: 30 to 49%
0
2
11
Severely depressed
LVEF < 30%
0
0
1
Increased
Normal
Moderately depressed
Severely depressed0047
*: Biplane LVEF measured off-line with the Simpson’s rule using the same ultrasound system was used as a reference.
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Conclusions
In ICU patients, the extension of physical examination
using an US improves the ability of trained intensivists
to determine LVEF at the bedside. With trained opera-
tors, the semi-quantitative assessment of LVEF using the
US is accurate when compared to standard TTE.
Key messages
• In the present study, the pocket-size device used as an
ultrasonic stethoscope (US) by intensivists trained in cri-
tical care echocardiography improved the clinical evalua-
tion of left ventricular ejection fraction (LVEF) in
intensive care unit (ICU) patients
• In this setting, the tested US was accurate for the
semi-quantitative evaluation of LVEF when using stan-
dard transthoracic echocardiography (TTE) as a
reference
• The concordance of visually estimated LVEF using
the US and TTE on the one hand, and the biplane
LVEF value on the other hand, were similar in our ICU
patients
• These results should not be extrapolated to other
indications of echocardiography and to less experienced
examiners. The design of the present study does not
allow us to validate the use of this US to perform basic
critical echocardiography.
Abbreviations
CI: confidence interval; EF: ejection fraction; ICU: intensive care unit; LV: left
ventricle; LVEDV: left ventricular end-diastolic volume; LVESV: left ventricular
end-systolic volume; TTE: transthoracic echocardiography; SAPS: simplified
acute physiologic score; US: ultrasonic stethoscope
Author details
1Medical-surgical Intensive Care Unit, Dupuytren Teaching Hospital, Avenue
Martin Luther King, 87000 Limoges, France.2CIC-P 0801, Dupuytren Teaching
Hospital, Avenue Martin Luther King, 87000 Limoges, France.3Unité
Fonctionnelle de Recherche Clinique et Biostatistique, Dupuytren Teaching
Hospital, Avenue Martin Luther King, 87000 Limoges, France.4University of
Limoges, 2 Avenue Dr Marcland, 87000, Limoges, France.
Authors’ contributions
JBA, GL, AD, MC, BF, NP and PV participated in the acquisition of data. BM,
AG and PV participated in the analysis and interpretation of data. JBA and
PV contributed to the conception and design of the study and were
involved in the drafting and revision of the manuscript. All authors read and
approved the version of the manuscript to be submitted.
Competing interests
The authors declare that they have no competing interests.
Received: 3 October 2011 Revised: 5 November 2011
Accepted: 15 February 2012 Published: 15 February 2012
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doi:10.1186/cc11198
Cite this article as: Amiel et al.: Assessment of left ventricular ejection
fraction using an ultrasonic stethoscope in critically ill patients. Critical Care
2012 16:R29.
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