johnson2015

Internal Medicine Point-of-Care Ultrasound
Assessment of Left Ventricular Function
Correlates with Formal Echocardiography
Benjamin K. Johnson, MD,1 David M. Tierney, MD, FACP,1 Terry K. Rosborough, MD, FACP,1
Kevin M. Harris, MD, FASE,2 Marc C. Newell, MD2
1
Abbott Northwestern Hospital, Department of Medical Education, 800 East 28th Street, Minneapolis, MN 55407
Minneapolis Heart Institute, Minneapolis Heart Institute Foundation, 920 East 28th Street, Suite 300,
Minneapolis, MN 55407
2
Received 19 December 2014; accepted 1 April 2015
ABSTRACT:
Purpose. Although focused cardiac
ultrasonographic (FoCUS) examination has been
evaluated in emergency departments and intensive
care units with good correlation to formal echocardiography, accuracy for the assessment of left ventricular systolic function (LVSF) when performed by
internal medicine physicians still needs independent
evaluation.
Methods. This prospective observational study in a
640-bed, academic, quaternary care center, included
178 inpatients examined by 10 internal medicine
physicians who had completed our internal medicine
bedside ultrasound training program. The ability to
estimate LVSF with FoCUS as “normal,” “mild to
moderately decreased,” or “severely decreased” was
compared with left ventricular ejection fraction
(>50%, 31–49%, and <31%, respectively) from formal
echocardiography interpreted by a cardiologist.
Results. Sensitivity and specificity of FoCUS for any
degree of LVSF impairment were 0.91 (95% confidence interval [CI] 0.80, 0.97) and 0.88 (95% CI 0.81,
0.93), respectively. The interrater agreement between
internal medicine physician-performed FoCUS and
formal echocardiography for any LVSF impairment
was “good/substantial” with j 5 0.77 (p < 0.001), 95%
CI (0.67, 0.87). Formal echocardiography was classified as “technically limited due to patient factors” in
20% of patients; however, echogenicity was sufficient
in 100% of FoCUS exams to classify LVSF.
Conclusions. Internal medicine physicians using
FoCUS identify normal versus decreased LVSF with
high sensitivity, specificity, and “good/substantial”
interrater agreement when compared with formal
Correspondence to: D. M. Tierney
C 2015 Wiley Periodicals, Inc.
V
92
echocardiography. These results support the role
of cardiac FoCUS by properly trained internal medicine physicians for discriminating normal from
C 2015 Wiley Periodicals, Inc. J Clin
reduced LVSF. V
Ultrasound 44:92–99, 2016; Published online in Wiley
Online Library (wileyonlinelibrary.com). DOI: 10.1002/
jcu.22272
Keywords: internal medicine; point-of-care ultrasound; focused cardiac ultrasound; systolic function
INTRODUCTION
T
o evaluate and treat patients, internal medicine (IM) physicians rely on traditional
physical examination tools and techniques that
have not significantly changed in over 150
years. With these tools alone, the clinician’s
diagnostic ability is limited, especially with
respect to cardiac pathology.1,2 This is troubling
because the cardiac examination is one of the
more clinically important evaluations an IM
physician routinely performs. The point-of-care
sonographic device has become increasingly
available to physicians within the last 10 years
and has the potential to improve the accuracy
of the cardiac physical exam.3–5
Focused cardiac ultrasound (FoCUS) by emergency department physicians, intensive care
unit physicians, and cardiologists has shown
good correlation to formal echocardiography.6–9
The value of FoCUS extends to the IM patient,
where real-time knowledge of a patient’s left
JOURNAL OF CLINICAL ULTRASOUND
INTERNIST ASSESSMENT OF SYSTOLIC FUNCTION
ventricular systolic function (LVSF) can be helpful in determining the etiology of shock, hypotension, dyspnea, and other common syndromes.10–13
Prompt diagnosis of these entities among inpatients being cared for by IM physicians could lead
to more rapid and accurate treatment. In addition, FoCUS could provide ongoing follow-up on a
daily or hourly basis to monitor a patient’s physiology and tailor treatment in this patient population. Limited literature exists on FoCUS use by
IM physicians and residents, and additional verification among various training models and
patient populations is needed.14–17 This study
evaluates the agreement between assessment of
LVSF with FoCUS performed by IM physicians
and formal echocardiography in a technically difficult inpatient population.
MATERIALS AND METHODS
This prospective observational study took place at a
640-bed, academic, university-affiliated, quaternary care center with approximately 40,000 inpatient admissions annually. The IM residency
program has 33 residents, 22 full-time IM faculty,
and 45 teaching hospitalists. The present study was
approved by our institutional review board (Schulman Associates IRB, Inc., which has no affiliation
with FujiFilm SonoSite, the manufacturer of the
sonographic devices used in this study; Approval
No. 201401371).
Training
The residency program instituted an internal medicine bedside ultrasound (the IMBUS program)
curriculum in 2011. IM residents in their first year
of training and faculty take part in a 1-week (40hour) training course focused on incorporation of
bedside ultrasound into their physical exam,
including pulmonary, cardiac (18 hours), abdominal, HEENT (head, eyes, ears, nose, and throat),
musculoskeletal, and soft tissue ultrasound. The
cardiac portion of the curriculum not only trained
the user to characterize LVSF as mildly, moderately, or severely reduced based on visual estimation but also to identify volume status, pericardial
disease, valvular disease, and structural heart disease. Following the IMBUS course, the resident is
mentored at the bedside by a certified faculty
member for all patient exams until the learner is
certified to perform exams independently.
Certification
Certification within the FoCUS portion of the
IMBUS curriculum requires (1) completion of
VOL. 44, NO. 2, FEBRUARY 2016
the initial course, (2) completion of a minimum
quantity of mentored FoCUS exams, followed by
(3) a one-on-one assessment by the IMBUS program director using a checklist of criteria pertaining
to
technical
image
acquisition,
interpretation, and appropriate clinical integration of findings. When all three of these mastery
learning18,19 components are achieved, a physician receives FoCUS certification. The number
of completed examinations performed by a physician at the time of certification in any given
area such as “LVSF assessment” is variable but
always above a set minimum.
The mean number of cardiac exams for LVSF
performed by certified mentors achieving their
IMBUS cardiac certification prior to the initiation of the study was: total focused cardiac
exams involving three to four views (parasternal long/short axis, apical 4/5 chamber, apical
long axis, apical two-chamber, subxyphoid fourchamber) 5 44.4 exams (SD 5 2.0), exams with
“normal” LVSF 5 20.3 (SD 5 1.8), exams with
“mild/moderate” LVSF impairment 5 16.4 (SD 5
2.2), and exams with “severe” LVSF impairment 5
7.8 (SD 5 0.7).
FoCUS Exams
The FoCUS examination is a routine part of our
inpatient care among patients admitted to the
IM resident service. Patients included in the
study consisted of a daytime convenience sample of patients with a broad range of comorbidities admitted to the IM resident service with
clinical questions related to cardiac physiology
who also underwent formal echocardiography
within 48 hours. The FoCUS exams used in this
study were on patients who already had a formal echo ordered or would have had a formal
echo performed regardless of the FoCUS findings. Therefore, the FoCUS results did not
influence the decision to order a formal echocardiogram. The patients had varying levels of acuity and were located throughout all parts of the
hospital, including the general medical ward,
intensive care unit, and telemetry units. The
residents performing the FoCUS were blinded
to results from any prior and current formal
echocardiography. Of note, the physicians performing/interpreting the FoCUS were not
blinded to the patient’s current clinical presentation. This is similar to a typical use environment for FoCUS, wherein the provider is aware
of the clinical specifics around the examination.
All of the residents who participated in the
IMBUS program were informed that their work
93
JOHNSON ET AL
TABLE 1
Patient’s Characteristics and Formal Echocardiography
Findings
Patient Characteristic
Mean age (y)
Age > 60 (%)
Age range (y)
Male sex (%)
Obese (BMI > 30) (%)
COPD (%)
Median duration between FoCUS and
formal echo (hours)
Echo quality reported as technically
limited (%)
Formal echo LVEF findings (%)
30%
31–49%
50%
n 5 178
70
77
21–100
51
34
19
19
20
15
17
68
Abbreviations: BMI, body mass index; COPD, chronic obstructive
pulmonary disease; FoCUS, focused cardiac ultrasound; LVEF, left
ventricular ejection fraction.
would be evaluated and used for research
purposes.
All FoCUS exams included in this study had
one of 10 IMBUS-certified IM physicians present at the bedside. This certified physician was
responsible for providing mentoring to ensure
appropriate image acquisition and interpretation by the performing, noncertified resident.
The physician’s ability to estimate LVSF with
FoCUS as “normal,” “mild to moderately
decreased,” or “severely decreased” was compared with formal cardiologist-interpreted echocardiography. The cardiologist-interpreted LVSF
was reported as ejection fraction in percentage
form. To compare this continuous data to the
ordinal data obtained from FoCUS, the following scale, utilized by our echocardiography laboratory, was used: ejection fraction greater than
or equal to 50% on formal echo was considered
“normal”; ejection fraction of 31–49% was considered “mild to moderately reduced”; and ejection fraction less than or equal to 30% was
considered “severely reduced.” Physicians performing the FoCUS exams were aware of the
ejection fraction correlates to these three classification categories of LVSF.
A board-certified cardiologist with a minimum
of adult cardiovascular medicine core cardiology
training (COCATS) Level II for echocardiography, in a lab with a Level III director, interpreted all formal echocardiograms and was
blinded to the results of the FoCUS examination. The cardiologist reading the formal echocardiogram classified the formal study as
technically “excellent/good,” “fair,” or “limited.”
94
Technology
The FoCUS exams were performed with SonoSite NanoMaxx or SonoSite EDGE portable
ultrasound systems equipped with a P21 (1–5MHz) phased-array transducer (FujiFilm SonoSite Inc., Bothell, WA). The formal echocardiograms were obtained using one of the following
five devices: Siemens C512 Sequoia with 4V1c
(2.25–4.25-MHz) transducer (Erlangen, Germany), Siemens SC2000 with 4V1c (2.25–4.25MHz) transducer, Philips IE33 with S5–1 or
X5–1 (2.25–4.25-MHz) transducer (Amsterdam,
Netherlands), GE Vivid I with 3S-RS (2.25–
4.25-MHz)
transducer
(Buckinghamshire,
United Kingdom), or GE Vivid 7 with M4S
(2.25–4.25-MHz) transducer.
Statistics
Sensitivity and specificity for FoCUS compared
with the gold-standard formal cardiologistinterpreted echocardiography assessment of
LVSF were calculated. Because of the high rate
of agreement due to chance, Kappa (j) statistics
were determined for LVSF assessment between
FoCUS and formal echocardiography interpretation of “normal” versus “any LVSF impairment.”
Agreement using j with linear weighting was
also performed for assessment of LVSF between
FoCUS and formal echocardiography in the individual categories of “normal,” “mild/moderately
reduced,” and “severely reduced” LVSF (JMP,
Version 10, SAS Institute Inc., Cary, North Carolina). As total disagreement about LVSF categories is clinically more important than
disagreeing in small degrees, a linear weighted j
measurement was also used to assess agreement
between individual categories of LVSF and formal echocardiography.
RESULTS
There were 209 patients who underwent FoCUS
and formal echocardiography over a 6-month
study period. Thirty-one patients had formal
echocardiograms that were performed more than
48 hours after FoCUS and were excluded. Therefore, 178 patients were included in the final
analysis. Baseline characteristics for the 178
patients are shown in Table 1. The median time
between FoCUS and formal echocardiography
exams, as defined by completion time of FoCUS
exam and start of formal echocardiogram, was
19 hours (interquartile range: 3–24 hours, range:
5 minutes to 47 hours). A significant proportion
(20%) of the included exams were reported as
“technically limited in quality secondary to
JOURNAL OF CLINICAL ULTRASOUND
INTERNIST ASSESSMENT OF SYSTOLIC FUNCTION
FIGURE 1. Internal medicine bedside ultrasound qualitative assessment of left ventricular systolic function (LVSF) compared with formal echocardiography left ventricular ejection fraction (LVEF) (n 5 178). Formal echocardiography LVEF cutoffs (horizontal gray lines) were set as “normal
50%,” “mild/moderate dysfunction 31–49%,” “severe dysfunction 30%.” White data points represent “technically limited” formal studies per
cardiologist interpretation. FoCUS, focused cardiac ultrasound.
patient characteristics” on the formal echocardiogram report. The technical difficulty of FoCUS
exams was not recorded; however, no patients
were excluded because of an inability to assess
LVSF with the FoCUS machine.
The agreement and disagreement between
FoCUS and formal echocardiography for
each patient exam are graphically depicted in
Figure 1. Sensitivity and specificity of FoCUS
when compared with formal echocardiography
for any LVSF impairment were 0.91 (95% confidence interval [CI] 0.80, 0.97) and 0.88 (95% CI
0.81, 0.93), respectively (Table 2). Agreement (j)
between FoCUS exams and formal echocardiography for any LVSF impairment was “good/substantial”20,21 with j 5 0.77 (p < 0.0001, 95% CI
[0.67, 0.87]). Agreement between individual categories of LVSF and formal echocardiography
was also “good/substantial” with j 5 0.77
(p < 0.001, 95% CI [0.67, 0.87]). Agreement
between FoCUS and formal echocardiography
did not worsen with increasing duration
between FoCUS and formal echocardiography
when divided into quartiles of time between
studies (Q1 [<3 hours]: j 5 0.74 [0.53, 0.96]; Q2
[3–19 hours]: j 5 0.64 [0.41, 0.87]; Q3 [19–24
hours]: j 5 0.78 [0.59, 0.96]; Q4 [>24 hours]:
j 5 0.93 [0.8, 1.0]).
DISCUSSION
Real-time knowledge of a patient’s LVSF is clinically valuable information in many scenarios
VOL. 44, NO. 2, FEBRUARY 2016
encountered by IM physicians. Formal echocardiography may not always be quickly available,
nor are the cost and resources spent on a full
echocardiogram always necessary to answer
focused questions. Traditional physical exam
techniques to assess cardiac function, intravascular volume, and fluid responsiveness lack significant sensitivity and specificity even among
expert diagnosticians.22–26 The steady decline
of the traditional physical exam in recent years
is attributable to various causes including
decaying physician exam skills, increasing
patient obesity, and with the routinely available correlation to echocardiography and CT
scans, an increasing realization that the traditional physical exam is inadequate.1,27–29 Thus,
an immediately available and interpretable cardiac FoCUS exam, performed by the physician
who can integrate the findings with other clinical information, with better test characteristics
than traditional physical exam techniques
improves the diagnostic ability of the IM
physician.
Alexander et al showed that IM residents
who completed a brief, 3-hour training course in
echocardiography could use FoCUS to assess
LVSF with moderate accuracy (j5 0.51) when
compared with formal echocardiography.14 Croft
et al showed that after a 15-hour training
course in echocardiography, IM residents using
a hand-carried FoCUS device could significantly
improve their ability to assess LVSF compared
with their traditional physical exam skills alone
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JOHNSON ET AL
TABLE 2
Test Characteristics of Internal Medicine Bedside Cardiac Ultrasound Compared with Formal Cardiologist Interpreted
Echocardiography
Left Ventricular Systolic Function
(Ejection Fraction %)
Normal (50%)
Mild/moderate LV dysfunction (31–49%)
Severe LV dysfunction (30%)
Any LV dysfunction (<50%)
Exams (n 5 178)
Sensitivity
Specificity
111
44
22
67
0.88 (95% CI 0.81, 0.93)
0.70 (95% CI 0.51, 0.84)
0.72 (95% CI 0.50, 0.88)
0.91 (95% CI 0.80, 0.97)
0.92 (95% CI 0.80, 0.97)
0.86 (95% CI 0.79, 0.91)
0.97 (95% CI 0.92, 0.99)
0.88 (95% CI 0.81, 0.93)
Abbreviation: LV, left ventricular.
(18% improvement). The gold standard used by
Croft et al was a trained, noncardiologist echocardiography technician.15 Decara et al showed
that after a 20-hour training course in echocardiography, IM residents could identify decreased
LVSF with a moderate sensitivity and high
specificity when compared with experienced
cardiologists.16 Lucas et al showed that after a
27-hour cardiac FoCUS training program,
board-certified IM physicians could identify
decreased LVSF with good sensitivity (84%) and
specificity (85%) when compared with formal
echocardiography.17
Our study demonstrates that after completing
the IMBUS training course and a mastery learning18,19 pathway, IM physicians could identify
decreased LVSF with high sensitivity, specificity,
and excellent agreement (j) when compared with
formal cardiologist-interpreted echocardiography. Further subcategorization at the extremes
of “normal” or “severely reduced” LVSF remains
highly accurate as does the ability to differentiate normal from any abnormal function. The
increased difficulty in accurately characterizing
LVSF with FoCUS in the “mild-moderately
reduced” category is a problem commonly recognized among cardiologists as well.30 This supports the need for a required distribution of
LVSF impairment categories among the experience of a physician who is considered competent
in FoCUS.
The gold standard of formal echocardiography
used in this study has limitations in that there
is inherent interobserver variability and therefore sensitivity/specificity of the comparative
test can never be 100%. The observed agreement between FoCUS and formal echocardiography in this study is similar to the published
literature values for cardiologist interobserver
variability of LVSF. Two studies reported a j of
0.63 14,31 and another reported a q (intraclass
correlation coefficient) of 0.65.32 The intraobserver variability in our echocardiography
96
laboratory has previously been published with
j 5 0.78 for measurement of LVSF.33
The patient population included in the study
is unique in that it was a real-life clinical inpatient population with complex diseases, multiple
comorbidities contributing to difficult cardiac
sonographic exams (chronic obstructive pulmonary disease 19%, obesity 34%), and a high
prevalence of technically limited formal exams
(20%). The rationale for not excluding these
technically difficult patients from the study was
to try and assess the true clinical test characteristics of IM cardiac FoCUS in the inpatient
settings where the exam is often most needed
and its information most valuable. The same
patient and clinical characteristics that make
cardiac echocardiography technically difficult
also make traditional physical exam techniques
difficult to assess. Thus, an especially useful
role of FoCUS for IM physicians may be in the
technically difficult-to-assess patient population.
Despite 20% of patients having formal echocardiograms that were “technically limited due to
patient factors,” echogenicity of FoCUS exams
was technically adequate to at least categorize
LVSF 100% of the time.
There is significant work currently in the area
of FoCUS to quantify the scope and training
required
for
various
providers
to
be
“credentialed” or “proficient” in an area and
application of FoCUS. Kimura et al developed
and implemented a FoCUS curriculum within
their IM residency program and concluded that
it is feasible to teach IM residents FoCUS.34
Based on the available literature, guidelines
have been published from organizations such as
the American Society of Echocardiography,
American College of Emergency Physicians for
emergency cardiac sonographic examinations,
and the Society of Critical Care Medicine.35–40
However, the recommendations for FoCUS training and certification will undoubtedly differ
among various physician groups and various
applications. Our IMBUS program incorporates
JOURNAL OF CLINICAL ULTRASOUND
INTERNIST ASSESSMENT OF SYSTOLIC FUNCTION
an intensive educational and mastery learning
and certification process that not only utilizes a
minimum quantity of exams by the IM physician
but also fully evaluates the complete use of
FoCUS, including image acquisition, image interpretation, and appropriate clinical integration of
findings. Such an intensive certification approach
is not necessarily feasible for all programs, but
adds another training methodology to the small
amount of available literature on training and
utility of FoCUS among IM physicians.
There are some limitations to our study. We
acknowledge that this study is looking only at
the ability of FoCUS to evaluate the presence of
LVSF impairment and is not addressing the
50% of patients hospitalized with heart failure
and preserved LVSF.41 LVSF and its visual
assessment are a dynamic process dependent on
the current cardiac loading conditions, rhythm,
and myocardial contractility. The potential time
between FoCUS and formal echocardiography
(median 19 hours) is one of the limitations of
this study as it allows for potential changes in
these variables thus affecting LVSF in the acute
and dynamic inpatient environment. A patient
receiving fluid resuscitation for hypovolemia
may move across the LVSF spectrum from
hyperdynamic to normal or reduced function.
Thus, if such interventions are made between
the time of the FoCUS exam and formal echocardiogram, the assessments of LVSF may not
correlate. However, the lack of an inverse relationship between interrater agreement and
duration of time separating FoCUS and formal
echocardiography exams (exam quartiles: <3
hours, 3–19 hours, 19–24 hours, and >24 hours)
would suggest that this is not a significant confounder. Given that patients included in this
study were also undergoing formal echocardiography, we cannot exclude that selection bias
played a role in the outcome of the study. However, since 68% of the exams had normal LVSF,
this is likely not a significant confounder to the
calculated sensitivity and specificity.
The physicians performing the FoCUS studies,
although blinded to prior and current formal
echocardiography data, were not blinded to the
clinical scenario at the time of the FoCUS exam.
Therefore, knowledge of information, such as
b-type natriuretic peptide level, medication
usage (eg, angiotensin converting enzyme inhibitors, beta-blockers, aldosterone antagonists,
etc.), and prior implantation of an implantable
cardioverter defibrillator or biventricular pacemaker, may have influenced interpretation of
LVSF. In practice, the clinical knowledge of
VOL. 44, NO. 2, FEBRUARY 2016
a patient’s symptoms and clinical data is an
important contributor to the overall interpretation of FoCUS. The results of this study would
not reflect the real application of FoCUS if physicians had been blinded to this clinical knowledge
when performing and interpreting the study. The
physicians were not asked to give a clinical
assessment of the cardiac function prior to the
FoCUS exam. Thus, we were unable to compare
the physician’s presonographic clinical diagnosis
with the FoCUS findings.
IM physicians with rigorous bedside sonographic training within a mastery learning
environment can use FoCUS in technically difficult hospitalized patients to identify decreased
LVSF with high sensitivity, specificity, and
strong agreement with formal cardiologistinterpreted echocardiography. This study suggests that cardiac FoCUS is most accurate at
the extremes of the LVSF spectrum (normal
and severely reduced), or in simply differentiating normal from abnormal LVSF.
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