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\begin{document}

\title{ECHOCARDIOGRAPHIC PARAMETERS OF CARDIAC STRUCTURE AND FUNCTION IN THE
DIAGNOSIS OF ACUTE MYOCARDITIS IN ADULT PATIENTS: A SYSTEMATIC REVIEW
AND META-ANALYSIS}



\author[1]{Shaun Khanna}%
\author[1]{Cindy Li}%
\author[1]{Anjalee T. Amarasekera}%
\author[1]{Aditya  Bhat}%
\author[1]{Henry H.L. Chen}%
\author[1]{Gary C.H. Gan}%
\author[1]{Timothy Tan}%
\affil[1]{Blacktown \& Mount Druitt Hospital}%


\vspace{-1em}



  
  \date{May 15, 2024}


\begingroup
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\selectlanguage{english}
\begin{abstract}
\textbf{Background:} Transthoracic echocardiography (TTE) plays a key
role in the initial work-up of myocarditis where the identification of
pathologic structural and functional changes may assist in its diagnosis
and management. The aim of this systematic review was to appraise the
evidence for the utility of echocardiographic parameters of cardiac
structure and function in the diagnosis of acute myocarditis in the
adult population. \textbf{Methods:} A systematic literature search of
medical databases was performed using PRISMA principles to identify all
relevant studies assessing TTE parameters in adult patients with
myocarditis (1995-2020; English only; PROSPERO registration
CRD42021243598). Data for a range of structural and functional TTE
parameters were individually extracted and those with low heterogeneity
were then meta-analysed using a random-effects model for overall effect
size, and assessed through standardized mean difference (SMD).
\textbf{Results:} Available data from up to six included studies
revealed that myocarditis can be reliably differentiated from healthy
controls using echocardiographic measures of left ventricular (LV) size
and systolic function, in particular LV end-diastolic diameter, LV
ejection fraction (LVEF) and LV global longitudinal strain (LV-GLS)
(p[?]0.01 for all). LV-GLS demonstrated the highest overall effect size,
followed by LVEF and LVEDD (SMD: \textbar{}0.46-1.98\textbar{}). Two
studies also demonstrated that impairment in LV-GLS was associated with
adverse cardiovascular outcomes in this population, irrespective of
LVEF. \textbf{Conclusions:} LV-GLS demonstrated the greatest overall
effect size and therefore ability to differentiate myocarditis
populations from healthy controls. GLS was also shown to be a predictor
of adverse cardiovascular outcomes, in this population.%
\end{abstract}%



\sloppy


\textbf{ECHOCARDIOGRAPHIC PARAMETERS OF CARDIAC STRUCTURE AND FUNCTION
IN THE DIAGNOSIS OF ACUTE MYOCARDITIS IN ADULT PATIENTS: A SYSTEMATIC
REVIEW AND META-ANALYSIS}

\textbf{Running Title:} Echocardiography in Myocarditis: A Systematic
Review and Meta-Analysis

\textbf{Shaun Khanna \textsuperscript{a,b} MBBS, Cindy
Li\textsuperscript{a} MBBS, Anjalee T. Amarasekera
\textsuperscript{a,b}BPharm, PhD, Aditya Bhat \textsuperscript{a, b, c}
MBBS, FRACP, Henry H.L. Chen \textsuperscript{a, d} MBBS, FRACP, Gary
C.H. Gan\textsuperscript{a, b, c} MBBS, FRACP, PhD, Timothy C.
Tan\textsuperscript{a, b, c, d} MBBS, FRACP, PhD}

\textbf{Affiliations:}

\textsuperscript{a} Department of Cardiology, Blacktown Hospital,
Sydney, NSW, Australia

\textsuperscript{b} Westmead Heart Rhythm Institute, Faculty of Medicine
and Health, University of Sydney, Sydney, NSW, Australia

\textsuperscript{c} University of New South Wales, Sydney, NSW,
Australia

\textsuperscript{d} University of Sydney, Sydney, NSW, Australia

\textbf{Corresponding Author:} Professor Timothy C. Tan

Department of Cardiology, Blacktown Hospital 18 Blacktown Road,
Blacktown, NSW 2148, Australia Phone: (+61) 402 075 550 Email:
timothy.tan9@gmail.com

\textbf{Sources of support:} None

\textbf{Conflicts of interest:} None

\textbf{Article Type:} Systematic Review and Meta-Analysis

\textbf{Keywords:} Myocarditis, Non-invasive cardiac Imaging,
transthoracic echocardiography, Speckle Tracking Echocardiography,
LVEDD, LVEF, LV-GLS

\textbf{Word count:} 4563

\textbf{References:} 38

\textbf{Figures/Tables:} 6

\textbf{Abbreviations}

CMR: cardiac magnetic resonance; TTE: Transthoracic echocardiography;
LV-GLS: left ventricular global longitudinal strain; STE: speckle
tracking echocardiography; 2D: two-dimensional; 3D: three-dimensional;
CI: confidence interval; SMD: standardized mean difference; LVEDD: left
ventricular end diastolic diameter; LVEF: left ventricular ejection
fraction; 3D: Three Dimensional; ICI: immune checkpoint inhibitor.

\textbf{HIGHTLIGHTS}

\textbf{What is already known on this subject?}

Myocarditis is a disease process that is often a diagnosis of exclusion,
as it frequently mimics other acute cardiac pathologies.

Transthoracic echocardiography is traditionally the initial imaging
modality used for non-invasive structural assessment in populations with
myocarditis.

\textbf{What might this study add?}

This study demonstrates that left ventricular global longitudinal
strain, left ventricular ejection fraction and left ventricular
end-diastolic diameter can differentiate between myocarditis patients
and healthy controls.

LV-GLS demonstrated the greatest overall effect size when comparing
these two populations, in comparison to the other measures.

\textbf{How might this impact on clinical practice?}

This study demonstrates that assessment of myocardial deformation
indices allows for sensitive discrimination between myocarditis patients
from healthy controls.

Routine assessment of LV-GLS may serve as an important diagnostic tool
in the acute care setting.

\textbf{Structured Abstract (Word Count: 245)}

\textbf{Background:} Transthoracic echocardiography (TTE) plays a key
role in the initial work-up of myocarditis where the identification of
pathologic structural and functional changes may assist in its diagnosis
and management. The aim of this systematic review was to appraise the
evidence for the utility of echocardiographic parameters of cardiac
structure and function in the diagnosis of acute myocarditis in the
adult population.

\textbf{Methods:} A systematic literature search of medical databases
was performed using PRISMA principles to identify all relevant studies
assessing TTE parameters in adult patients with myocarditis (1995-2020;
English only; PROSPERO registration CRD42021243598). Data for a range of
structural and functional TTE parameters were individually extracted and
those with low heterogeneity were then meta-analysed using a
random-effects model for overall effect size, and assessed through
standardized mean difference (SMD).

\textbf{Results:} Available data from up to six included studies
revealed that myocarditis can be reliably differentiated from healthy
controls using echocardiographic measures of left ventricular (LV) size
and systolic function, in particular LV end-diastolic diameter, LV
ejection fraction (LVEF) and LV global longitudinal strain (LV-GLS)
(p[?]0.01 for all). LV-GLS demonstrated the highest overall effect size,
followed by LVEF and LVEDD (SMD: \textbar{}0.46-1.98\textbar{}). Two
studies also demonstrated that impairment in LV-GLS was associated with
adverse cardiovascular outcomes in this population, irrespective of
LVEF.

\textbf{Conclusions:} LV-GLS demonstrated the greatest overall effect
size and therefore ability to differentiate myocarditis populations from
healthy controls. GLS was also shown to be a predictor of adverse
cardiovascular outcomes, in this population.

\textbf{INTRODUCTION}

Myocarditis has been historically defined as an acute disease process
which results in myocardial inflammation and necrosis\textbf{(1).} The
often-resultant impairment in myocardial function increases the
predisposition to the development of a non-ischemic cardiomyopathy,
which has been shown to result in poor prognostic outcomes such as
chronic congestive failure, cardiac arrhythmias and sudden cardiac
death\textbf{(1).} Whilst the gold-standard investigation is cardiac
magnetic resonance (CMR), the initial non-invasive assessment typically
utilised is transthoracic echocardiography (TTE), as it is widely
available, easily accessible, and cost-effective within most healthcare
settings

\textbf{(2).}

The traditional TTE parameters assessed in myocarditis include left
ventricular (LV) regional or global dysfunction, presence of LV
dilatation, LV hypertrophy, right ventricular (RV) dysfunction,
bi-ventricular thrombi, pericardial effusions and diastolic
dysfunction\textbf{(2).} These findings however typically represent more
clinically significant disease with more substantial myocardial
injury\textbf{(1).} Early and subclinical myocardial dysfunction is
usually not often recognised by standard two-dimensional TTE,
particularly in the setting of normal LV systolic function as assessed
through traditional measures such as LV ejection fraction (LVEF). The
emergence of advanced echocardiographic imaging techniques such as
two-dimensional and three-dimensional myocardial strain, have allowed
for identification of subclinical myocardial dysfunction, and have been
shown to increase sensitivity of echocardiography in the diagnosis and
prognosis of the disease

\textbf{(3).}

The aim of this systematic review and meta-analysis was to identify key
echocardiographic parameters of LV structure and function based on
available published evidence which may allow for discrimination of adult
patients with myocarditis from healthy controls.

\textbf{METHODS}

\textbf{Search Strategy and Selection (move structure)}

The methods and results of this review have been done in accordance to
the Meta-analysis Of Observational Studies in Epidemiology and Preferred
Reporting Items for Systematic reviews and Meta-Analyses (PRISMA)
statement \textbf{(4, 5).} The review protocol is previously registered
on the International Prospective Register of Systematic Reviews
(PROSPERO) with Centre of Reviews and Dissemination (CRD) report number
of CRD42021243598. A number of medical databases were searched including
PubMed, Ovid Medline, EMBASE, Web of Science, Cochrane Central Register
of Controlled Trials (2005-2020), Scopus, Proquest, Science Direct and
grey literature using both free-text terms and Medical Subject Heading
(MeSH) terms for studies with English language and adult human studies
that reported standardized TTE indices. The search terms and key search
strategies are listed in \textbf{Supplementary Materials 1.} A grey
literature search identified additional studies that were not identified
in the initial search of the afore-mentioned medical databases. All
diagnostic cohort and case-control studies that measured and compared
echocardiographic parameters between myocarditis and adult control
populations were included. Studies which were not able to provide
sufficient data, those with pediatric populations or those that did not
compare the study populations involved in the analysis hypothesis were
excluded.

\emph{Inclusion Criteria}

Studies that (a) compared myocarditis and healthy control adult patients
(age of [?] 18 years) (b) included patients who had a comprehensive TTE
(c) reported their results with means and standard deviations to allow
measurement of standardized mean difference (SMD) were included.

\emph{Exclusion Criteria}

Studies were excluded if they were (a) only in abstract form, (b) did
not compare myocarditis patients to controls, (c) reported medians and
interquartile ranges, or (d) had missing data.

\textbf{Data Extraction}

Two investigators (S.K and A.A) independently screened records retrieved
from the search by title and abstract. Details such as first author,
year of publication, study design, participant characteristics, age,
sample size, sample stratification, outcome measures, results and
author's conclusion were collated and examined. Selected records were
further screened for eligibility in full text by the same investigators
(S.K and A.A). Data collection was performed independently by two
investigators (S.K and C.L) using the same pre-determined template.
Discrepancies at any stage of selection were arbitrated by the senior
author (T.C.T) if discussion between all three reviewers failed to
achieve a consensus (S.K, A.A, and C.L).

\textbf{Quality Appraisal of the selected studies for the review}

The quality of included studies and risk of bias was assessed by two
investigators (S.K and A.A) using the Joanna Briggs Institute Critical
Appraisal tools for use in Analytical Cross-Sectional Studies (JBI
tool)\textbf{(6).} See \textbf{Supplementary Table 3.} This process
afforded increased methodological rigor and evaluated potential bias and
threats to validity. Publication bias was assessed by visual analysis of
funnel plots and using Egger methods\textbf{(7, 8).} Both reviewers were
trained in the use of the appraisal tool prior to this process. In
brief, the quality assessments of the checklist included eight questions
to assess the methodological quality of a study and to determine the
extent to which a study has addressed the possibility of bias in its
design, conduct and

analysis. This criterion is available in \textbf{Supplementary Materials
3.}

\textbf{Statistical analysis}

For individual TTE measures of interest, a meta-analysis was only
performed if studies reported continuous variable indices as means and
standard deviations. All indices were meta-analyzed with random-effects
modeling for overall effect size through SMD. The observational design
of the selected studies was considered, and the methodological
differences potentially responsible for a significant component of the
variance within the measures of interest. Pooled estimates were obtained
through a random-effect model. Articles were required to report on a
quantitative estimation including mean, confidential interval (CI), and
standard deviation. 95\% confidence intervals (CIs) were calculated for
all indices. Lack of heterogeneity (magnitude of inconsistency) within
the pooled studies was tested using the I\textsuperscript{2} statistic
and deemed significant if [?]50\%. Potential publication bias was assessed
visually from funnel plots (supplementary materials). All statistical
analysis was performed using the Metan package included in the STATA
version 16.1 statistical software. A p value \textless{}0.05 was
considered statistically significant for all analyses.

\textbf{RESULTS}

\textbf{Search Results}

The initial literature search yielded 1276 studies from various
literature sources, including grey literature. After removing
duplicates, 1058 records were screened by title and abstract of which
558 studies were initially excluded, as they included non-myocarditis
populations or were in supplementary format. The remaining 500 records
were reviewed by title and abstract screening by two reviewers (SK and
AA). A total of 110 peer-reviewed studies were assessed by full text for
eligibility of which 14 studies were shortlisted for inclusion in this
study. Studies that did not have a direct comparison between myocarditis
patients and controls, those that included pediatric populations and
those that did not report results as means and standard deviations were
excluded (n=8). Data from 6 studies with publication dates ranging from
Jan 2010--Jan2020 was extracted and meta-analyzed, and is shown
in\textbf{Table 1.} A detailed flow diagram with the study selection
process and various reasons for exclusion is shown in \textbf{Figure 2.}

\textbf{Study Quality and Characteristics}

Four of the six included studies were assessed to be of fair quality and
two of good quality using the JBI Tool, indicating a good selection of
studies. \textbf{See Supplementary Materials 3.} Four of the included
studies were retrospective analyses and the other two were prospective
studies. There was a pooled total of 269 myocarditis patients and 240
control patients included in this meta-analysis.

\textbf{Diagnosis of Myocarditis}

The diagnosis of myocarditis as per the European Society of Cardiology
Working Group on Myocardial and Pericardial Diseases, requires
fulfillment of [?]1 clinical presentation and [?]1 diagnostic criteria.
These criteria have to be fulfilled in the absence of coronary artery
disease as detected by coronary angiography, and absence of pre-existing
cardiovascular disorder that can otherwise explain the
presentation\textbf{(9).} All studies included in the meta-analysis made
a clinical diagnosis of myocarditis that fulfilled international
criteria as per European Society of Working Group on Myocardial and
Pericardial diseases. Whilst the majority of studies used CMR diagnostic
criteria (non-ischemic late gadolinium enhancement and/or Lake Louise
Criteria) \textbf{(10)} , others used echocardiography and/or
endo-myocardial biopsy for diagnosis.

\textbf{Diagnostic Discrimination of Parameters Assessed}

Data on a range of echocardiographic parameters was assessed, although
only indices which were reported in [?]4 studies were meta-analyzed in
this study. Three echocardiographic parameters i.e. LV end diastolic
diameter (LVEDD), LVEF and LV global longitudinal strain (LV-GLS) were
meta-analyzed from available data from 6 included studies. All TTE
measurements were able to discriminate between adult myocarditis and
control populations (p[?]0.01), but with variable effect sizes.
See\textbf{Figures 3-5.} None of the included studies, as visually
assessed by Funnel Plots, demonstrated to be high risk for publication
bias. See\textbf{Supplementary Material 4.} Meta- Analysis Forest plots
for LVEDD, LVEF and LV-GLS are demonstrated in \textbf{Figures 3-5.} A
summary of the meta-analysis results is displayed in \textbf{Table 2.}

\textbf{Measurement of Left Ventricular Indices}

In terms of the methodology for echocardiographic imaging, the majority
of studies followed recommendations from the American Society of
Echocardiography \textbf{(11),} with two studies following
recommendations from the European Association of Cardiovascular Imaging
\textbf{(12),} for two-dimensional echocardiographic measurements
including LVEDD and LVEF. LV-GLS was measured using software from
different vendors including TomTec Imaging systems, GE Echopac
workstation, X-Strain and Syngo Vector Imaging which increased the
variability of absolute strain values. All studies had reported mean
LV-GLS values derived from offline measurements made in the standard
three apical views by at least two operators. Despite different software
used, all algorithms for strain assessment appeared to utilise similar
approaches where the endocardial borders were manually traced throughout
the cardiac cycle. Longitudinal strain was assessed in all 17
longitudinal LV segments, and the segmental values were averaged to give
the mean LV-GLS.

\textbf{Parameters of left ventricular size}

\emph{Two-dimensional Left Ventricular End-Diastolic Diameter}

LVEDD had the lowest overall effect size with a standard mean difference
of 0.47 (95\%CI; 0.11-0.81, p[?]0.01), with no significant heterogeneity
(54\%). Fifty percent of the studies individually demonstrated
statistically significant differences in LVEDD between myocarditis
populations and controls, whilst the other half did not. Importantly the
two studies that demonstrated this difference, also showed a significant
difference in LVEF \textbf{(13, 14).}

\emph{Two dimensional Left Ventricular Volumes}

Only three out of the six included studies reported standard
two-dimensional LV end-systolic and end-diastolic volumes, hence a
meta-analysis was not performed. All volumes were calculated using
Simpson's Biplane method from the standard three apical views. Only one
study indexed two-dimensional volumes to body surface area\textbf{(15).}
In this study, indexed LV-EDV (ml/m\textsuperscript{2}) was
significantly higher in myocarditis patients when compared to controls
(59\selectlanguage{ngerman}±13 vs 57±14, p=0.03). Overall, there was no significant differences
between non-indexed volumes in each of the other individual studies.

\emph{Three-Dimensional Left Ventricular mass and volume}

Only one published study evaluated three-dimensional left ventricular
structure and function, hence a meta-analysis was not performed to
assess these parameters. In this study, echocardiography images were
obtained using a Vivid S9 Ultrasound Machine and analysis was done
offline using EchoPAC v113 software. Only three-dimensional LV
end-diastolic volume (3D LVEDV, ml/m\textsuperscript{2}) and
three-dimensional LV mass indexed (g/m\textsuperscript{2}) were
reported. Interestingly, 3D LVEDV (60.3±13.5 vs 57±10, p=0.219) and 3D
LV mass (66.7±6.9 vs 67.8±9.1, p=0.54) were not significantly different
between myocarditis populations and controls.

\emph{Wall Motion Index Score}

The wall motion score index was calculated by sum of all segment scores
divided by the number of segments assessed. 16 segments were assessed
with scores as followed: 1 = normal, 2 = hypokinesis, 3 = akinesis, 4 =
dyskinesis and 5 = aneurysmal \textbf{(11).} Two of the three studies
that assessed for wall motion score index demonstrated normal values in
myocarditis and control populations, particularly as they only included
patients with a normal left ventricular ejection fraction. One study
showed that the myocarditis population had a higher wall motion score
index compared to controls (1.6±0.7 vs 1, p\textless{}0.01)

\textbf{(13).}

\textbf{Parameters of left ventricular systolic function}

In our study, functional parameters such as LVEF and LV-GLS proved to
have a higher overall effect size between myocarditis and control
populations.

\emph{2D Left Ventricular Ejection Fraction}

LVEF had a higher overall effect size compared to LVEDD, with a standard
mean difference of \textbar{}0.77\textbar{} (95\% CI:
\textbar{}0.26\textbar{} - \textbar{}1.28\textbar{}, p\selectlanguage{english}[?]0.01), with a
higher degree of heterogeneity at 86\%. Four out of the six studies
demonstrated a statistically significant difference in LVEF between
those with acute myocarditis when compared to controls. Importantly,
Hsaio et al. demonstrated a significantly lower LVEF in myocarditis
patients compared to controls (LVEF (\%): 49+-12 vs 64+-4,
p\textless{}0.01), with a large proportion with impaired systolic
function and significantly higher wall motion index score\textbf{(13).}
Furthermore, a subgroup analysis in this study for myocarditis patients
with preserved LV function, also demonstrated significant difference in
comparison to control populations (LVEF (\%): 59+-6 vs. 64+-4;
p=0.002)\textbf{(13).} Three other studies also demonstrated similar
findings with statistically significant differences in LVEF, despite
normal-range values\textbf{(14-16).} Two studies (Di Bella et al. 2018
and Caspar et al. 2017) demonstrated no significant differences in LVEF
between myocarditis and control populations (61+-4 vs 62+-3, p=0.78 and
62.1+-3.7 vs 63.5+-3.8, p=0.099, respectively). Importantly, these studies
did show significantly different LV-GLS values between these populations

\textbf{(15, 17).}

\emph{2D Left Ventricular Global Longitudinal Strain}

LV-GLS had the highest overall effect size compared to LVEDD and LVEF
with a SMD of \textbar{}1.98\textbar{} (95\% CI:
\textbar{}1.51\textbar{} - \textbar{}2.45\textbar{}, p\textless{}0.01),
with no significant heterogeneity (76\%). All six studies demonstrated
statistically significant differences in LV-GLS between myocarditis
populations and controls, irrespective of baseline LVEF. Interestingly,
Caspar et al. demonstrated that two-dimensional LV-GLS was impaired in
patients with myocarditis (-17.8\% vs -22.1\%, p\textless{}0.01) as were
2D layer-specific sub-epicardial GLS (-15.4\% vs -19.7\%,
p\textless{}0.01) and sub-endocardial GLS (-20.7\% vs -25.1\%,
p\textless{}0.0001), even two years after the initial myocarditis
event\textbf{(17).} Di Bella et al. demonstrated that longitudinal
strain was significantly lower in areas of late gadolinium enhancement
(p=0.04), and that GLS was shown to have a moderate predictive value of
distinguishing the two groups with an AUC of 0.73 (95\% CI: 0.66-0.79)

\textbf{(13).}

\emph{Three-Dimensional Measure of Left Ventricular Function}

Unfortunately, there were no studies which compared 3D LVEF between
patients with myocarditis and controls. Only one published study
assessed 3D strain (3D STE) hence a meta-analysis was not performed to
assess this parameter. In this study, 3D-STE was measured using the
Vivid E9 (GE-healthcare) echocardiographic system\textbf{(17).}
Acquisitions were performed with the highest possible frame rate and
then analysed offline using EchoPAC v113 for 3D STE LV myocardial
deformation. 3D LV-GLS, global area strain (GAS) and global radial
strain (GRS) was calculated using average of 17 myocardial segments. 3D
LV-GLS, GCS, GAS and GRS were lower in magnitude in the myocarditis
group compared to controls (-11.80\% vs -14.98\%, p\textless{}0.0001;
-12.57\% vs -15.12\%, p\textless{}0.001; -22.28\% vs -25.87\%,
p\textless{}0.001; and 31.47\% vs 38.06 \%, p\textless{}0.0001,
respectively). ROC curve analysis identified diagnostic values of 3D
GLS, GCS, GAS and GRS for the diagnosis of myocarditis with AUC values
of 0.78, 0.71, 0.73 and 0.70 respectively.

\textbf{Parameters of right ventricular size and systolic function}

Only one published study was identified to have assessed parameters of
RV size and systolic function in patients with acute myocarditis
compared to controls and therefore none of the RV parameters of size and
systolic function were meta-analysed\textbf{(17).} This study by Caspar
and colleagues assessed standard measures of RV size and systolic
function in the apical four-chamber view with an average of the six
segments (including the RV free wall and septum). The right ventricular
parameters assessed included RVS' (13.2+-2 vs 14.2+-2.1, p=0.028), RV
global strain (-20.6+-3.5 vs -22.9+-3.3, p=0.003) and RV free wall strain
(-24.6+-5.4 vs -27.2+-4.3, p=0.023), were all significantly lower in the
myocarditis population when compared to healthy controls.

\textbf{DISCUSSION}

This study seeks to examine the evidence for the utility of 2D and 3D
echocardiographic parameters of cardiac chamber size and systolic
function in differentiating between adult patients with acute
myocarditis and controls. Our study identified three echocardiographic
parameters (LVEDD, LVEF and LV-GLS) to be useful in the differentiation
between myocarditis and control populations, but with different overall
effect sizes. This study also highlights the application and value of
echocardiography as first line imaging in the clinical setting for
differentiation of patients with acute- and sub-acute phases of
myocarditis. As this disease entity manifests in a heterogeneous manner,
with a known preponderance to LV impairment (due to greater quantity of
myocardium), assessment of the LV systolic function may provide greater
sensitivity to clinical and subclinical changes to the myocardium.
Patients presenting with myocarditis, both acute and recurrent,
typically undergo echocardiography for an initial assessment of
ventricular size and function, along with assessment of regional
wall-motion abnormalities \textbf{(18).}More sensitive measures of LV
systolic function such as LV-GLS have been found to be useful in several
cardiac pathologies, both for diagnosis and prognostication. Similarly,
these measures have also demonstrated the greatest ability to identify
earlier phenotypes of myocarditis, especially those where baseline LV
systolic function is preserved

\textbf{(19).}

\textbf{2D Parameters of Left Ventricular Size}

This meta-analysis demonstrated that half of the studies featured
quantifiable changes in LV end-diastolic diameter, a marker of
structural myocardial remodeling, thus potentially useful as a
discriminator between myocarditis and control populations although not
strong. Measurement of LV diameter was demonstrated to have the lowest
overall effect size when compared to the parameters of LV function which
was consistent with the notion that measures of LV function being more
sensitive for the detection of underlying myocardial pathology compared
to measures of LV structural change\textbf{(20).} Identification of
increased LV diameter may also be reflective of the chronicity of
disease hence effective in distinguishing more chronic or fulminant
myocarditis, which would also be more likely to have other
echocardiographic abnormalities such as regional wall motion
abnormalities and impaired LV systolic function, as demonstrated in two
of the included studies \textbf{(13, 14).}

Only four out of the six studies included in this systematic review
reported LV volumes with only one study reporting significant
differences in indexed volumes. The heterogeneity in the methodology for
the assessment of LV volumes did not allow for meta-analysis of this
parameter although it is postulated that LV volume changes would provide
a more accurate reflection of LV structural change compared to linear
measurements of LV size changes. Moreover, current guidelines do not
recommend use of LVEDD for routine quantification of LV size but indexed
volumes instead. Whilst LV dilatation has been hypothesized to be
associated with an increased risk of heart failure, LV volumes have been
shown to more accurately reflect LV remodeling, in comparison to single
dimensional assessment \textbf{(21, 22).} One study did demonstrate that
indexed left ventricular end-diastolic volumes were greater in their
cohort of myocarditis patients compared to controls consistent with
expectations. However, the remaining studies reporting non-indexed LV
volumes did not demonstrate any significant differences between
myocarditis populations and controls. This finding is largely thought to
be attributed to the non-indexation of LV volumes, limiting its
precision and accuracy.

\textbf{Left Ventricular Systolic Function}

The importance of a baseline echocardiogram during the acute-phase of
myocarditis is important as it allows for appropriate classification
between severe and non-severe myocarditis, based on preservation of
LVEF. This is important as these populations exhibit different
pathologic changes, disease states and clinical outcomes\textbf{(23).}
Impairment in LV systolic function in patients with myocarditis is
attributed to a greater percentage of myocardial involvement secondary
to an inflammatory myopathic process, which is consistent with the
immune checkpoint inhibitor (ICI) myocarditis\textbf{(24).} As a result,
there is development of regional and/or global systolic dysfunction,
which is typically seen in more severe forms of myocarditis, such as
immune-mediated myocarditis. Two of the included studies in this
meta-analysis demonstrated no significant differences in LVEF between
myocarditis and control populations, both in the initial
phase\textbf{(17),} and on a follow-up at a mean period of 22 months,
highlighting the heterogeneous nature of this disease process
\textbf{(15).}Interestingly, the majority of patients with myocarditis
in this systematic review had a normal LVEF. Only one study demonstrated
an impaired mean LVEF in the myocarditis population. This study focused
on patients with ICI myocarditis secondary to checkpoint inhibition
chemotherapy \textbf{(13).}

This study also reinforces the value of LV-GLS in differentiating cases
of both severe and non-severe myocarditis in both the acute- and
sub-acute disease states. All included studies clearly demonstrated
significantly lower LV-GLS values in myocarditis populations, compared
to controls suggesting that LV-GLS may be a more sensitive marker of LV
systolic function compared to LVEF. LV-GLS was shown to be directly
associated with degree of myocardial inflammation, and diagnostic of
regional myocardial fibrosis, when correlated with CMR\textbf{(16).} In
some longitudinal studies, LV-GLS was shown also shown to remain
impaired on follow-up\textbf{(17)} , which highlights the value of
LV-GLS as a potential marker for monitoring and diagnosing chronic
myocarditis or response to treatment.

The main advantages of LV-GLS compared to standard echocardiographic
parameters in assessment of myocarditis, are the signal-to-noise ratio,
angle independence and ability to differentiate between active and
passive myocardial segmental motion\textbf{(25).} LV-GLS has recently
emerged as a measure of cardiac function which is sensitive in detecting
subclinical cardiac injury relative to LVEF and has been shown to have
prognostic value in multiple pathologies

\textbf{(14, 26).}

Additionally, the sub-endocardial layers of the myocardium with a
predominance of longitudinal myocardial fibers are typically impacted in
myocarditis. Hence the longitudinal left ventricular contractile
function is expected to be most impaired in acute myocarditis (27, 28).
These are consistent with results from the study which demonstrated the
endo-GLS to be more impaired compared to mid- and
epicardial-GLS\textbf{(29).} The distribution of LV-GLS impairment in
studies examining regional systolic dysfunction which match areas of
inflammatory response further strengthens the value of measuring LV-GLS
in the clinical setting.

Whilst the majority of the included studies included patients with acute
inflammatory myocarditis, one study included patients with immune
checkpoint inhibitor (ICI) myocarditis\textbf{(14),} an entity that is
more complex and multi-faceted than inflammatory myocarditis, despite
similar diagnostic criteria \textbf{(30).}Patients with ICI myocarditis
may possibly have a greater impairment in LV-GLS and LV systolic
function compared to other subtypes, particularly with the presence of
confounding factors such as para-neoplastic cytokines, and other
mechanisms of treatment mediated toxicity

\textbf{(31).}

\textbf{Three dimensional Parameters of Cardiac Structure and Function}

Current guidelines recommend the use of 3D volumes in the quantification
of LV size. This is due to several advantages of 3D over 2D imaging
including minimal foreshortening and more accurate volumetric
quantification \textbf{(32).} Of the included studies, only one study
assessed 3D LVEDV and 3D LV mass, showing no significant difference
between myocarditis populations and controls \textbf{(17).} The proposed
reason for this negative finding is again likely due to the absence of
chronicity and the acute pathogenesis of myocarditis and its effect on
the myocardium \textbf{(1).} The other reason could relate to the
inclusion of only populations with preserved LV systolic function,
highlighting a non-severe myocarditis process in this cohort.
Unfortunately, none of the included studies compared 3D left ventricular
ejection fraction in myocarditis populations vs controls. The lack of
any studies examining changes in 3D LVEF is not surprising since 3D
echocardiography has only been studied in a handful of cardiac
pathologies to date largely due to inter-vendor differences, lack of
standardization and unclear feasibility or added clinical value

\textbf{(33).}

Three-dimensional speckle tracking echocardiography is an advanced echo
imaging technique that is postulated to provide a comprehensive
assessment of LV function with additional advantaged over 2D
imaging\textbf{(34),} i.e. simultaneous speckle tracking in more than
one direction allowing for assessment of longitudinal, circumferential
and radial strain simultaneously, and requirement for a single apical
acquisition, which in turn, may make assessment of LV strain more time
efficient and thus more applicable in a busy clinical setting
\textbf{(34).}The utility of 3D-LVS has been demonstrated in several
pathologies including ischemic heart disease, cardio-oncology, valvular
heart disease, left ventricular hypertrophy hence certainly applicable
for myocarditis. Furthermore, 3D-LVS has successfully been used to
identify subclinical LV dysfunction \textbf{(35),}and shown to be
non-inferior to 2D STE in patients with aortic stenosis\textbf{(36).} Of
the included studies, one study did demonstrate that patients with acute
myocarditis in comparison to controls had lower 3D LV-GLS values. This
study also highlighted that there was a good correlation between 2D- and
3D- GLS measurements in this study (r=0.84, p\textless{}0.01). These
findings are also in keeping with pooled results on 2D LV-GLS from the
meta-analysis in our study. Nonetheless, 3D-STE is still currently used
primarily in the research settings and not in routine clinical practice
given its high image and operator dependency. Some of the disadvantages
of 3D STE which may still serve as barriers for application in routine
clinical use, include the requirements for a stable regular heart rhythm
during image acquisition and analysis, optimal LV images and with good
temporal resolution and a high frame rate. Nonetheless, 3D-LVS may still
have a useful role in the diagnostic work-up in myocarditis

\textbf{(35).}

\textbf{Right Ventricular Systolic Function}

Whilst there have been several case reports on isolated RV involvement
in myocarditis, there is only one published study that fulfilled our
search criteria assessed RV systolic functional parameters in a cohort
of patients with myocarditis\textbf{(17).} This study demonstrated that
both traditional echocardiographic measures of RV size and systolic
function including RV strain parameters are both impaired in patients
with myocarditis. The prognostic significance of RV impairment has been
established in several cardiac pathologies, particularly non-ischemic
dilated cardiomyopathy, a known complication of
myocarditis\textbf{(37).} RV systolic dysfunction is a known independent
predictor of transplant-free survival and adverse heart failure outcomes
in dilated cardiomyopathy\textbf{(37).} Therefore, the there is
definitely some value in assessing RV size and function in patients with
myocarditis, as these parameters may not only assist in the diagnostic
process, but may also provide prognostic information

\textbf{Clinical Outcomes}

Two of the studies included in this systematic review assessed primary
and secondary longitudinal cardiovascular events in these
populations\textbf{(13, 14).} In patients with myocarditis, every 1\%
decline in longitudinal strain increased hazard ratios by 1.26 (95\% CI:
1.10--1.47) for primary cardiovascular MACE events\textbf{(13).}
Similarly, in patients with ICI myocarditis, after adjustment for LVEF,
each 1\% reduction in GLS was associated with a 1.5-fold increase in
cardiovascular MACE among patients with impaired systolic function (HR:
1.5; 95\% CI: 1.2-1.8) and a 4.4-fold increase with a preserved systolic
function (HR: 4.4; 95\% CI: 2.4-7.8) \textbf{(14).} These results
highlight the value of LV-GLS in the diagnosis and prognostication of
patients with acute inflammatory and ICI myocarditis, independent of
two-dimensional LVEF.

\textbf{Study Limitations}

There were some limitations identified in this systematic review and
meta-analysis. Firstly, the severity of the disease in the patients
included from the included studies were variable which may potentially
impact test performances. Secondly, strain assessment reported in the
included studies were all acquired using four different vendor-specific
software, which may potentially also impact the external validity of 2D
LV-GLS across different settings. Thirdly, different aetiologias of
myocarditis were included which can also bias the overall results.
Lastly, the included studies were all single-centre studies, which are
typically limited by greater inherent bias due to the greater variation
and generalisability between diagnostic work-up and protocols between
different centres in different studies. However, we did assess for
potential small-study effects on the individual parameters studied using
Egger's tests which did not demonstrate any evidence of small study
effects confounding the results.

\textbf{CONCLUSIONS}

This systematic review and meta-analysis demonstrated the discriminatory
value of a range of echocardiographic parameters, particularly with
LV-GLS, in discriminating acute myocarditis from normal controls and
highlights the potential value of early TTE in suspected cases of
myocarditis. However, there is also clearly a need for further large
multi-centre studies or randomized controlled trials to further
characterize the sensitivity and specificity of each of the individual
parameters assessed. Nonetheless, these results support the importance
of echocardiography as an initial non-invasive diagnostic tool for the
work-up of such populations.

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\emph{}

\emph{Figure 1: Graphical Abstract}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

\textbf{Figure 1:} Graphical Abstract showing the utility of
Echocardiography in the Diagnosis of Acute Myocarditis. Left ventricular
global longitudinal strain (three stars) showed the largest overall
effect size, followed by left ventricular ejection fraction (two stars)
and left ventricular end-diastolic diameter (one star).

\emph{Figure 2: PRISMA Flow Diagram}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}

\textbf{Figure 2:} PRISMA flow diagram showing screening, identification
and inclusion of studies in the meta-analysis.

\emph{Table 1: Study Summary}\selectlanguage{english}
\begin{longtable}[]{@{}llllll@{}}
\toprule
\begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
\textbf{First Author}\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
\textbf{Year Published}\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
\textbf{Study Design}\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
\textbf{Myocarditis Subjects (n)}\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
\textbf{Control Subjects (n)}\strut
\end{minipage} & \begin{minipage}[b]{0.14\columnwidth}\raggedright\strut
\textbf{Parameters Assessed by Study}\strut
\end{minipage}\tabularnewline
\midrule
\endhead
\begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
Di Bella et al \textbf{(38)}\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
2010\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
Retrospective\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
13\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
13\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
LVEDD, LVEF, LV-GLS\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
Hsaio et al \textbf{(13)}\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
2013\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
Retrospective\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
45\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
83\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
LVEDD, LVEF, LV-GLS\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Caspar et al \textbf{(17)}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2017\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Retrospective\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
50\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
50\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
LVEF, LV-GLS\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
Kostakou et al \textbf{(16)}\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
2018\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
Prospective\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
25\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
19\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
LVEDD, LVEF, LV-GLS\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Di Bella et al \textbf{(15)}\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
2018\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
Prospective\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
35\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
25\strut
\end{minipage} & \begin{minipage}[t]{0.14\columnwidth}\raggedright\strut
LVEF, LV-GLS\strut
\end{minipage}\tabularnewline
\begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
Awadalla et al \textbf{(14)}\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
2020\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
Retrospective\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
101\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
50\strut
\end{minipage} & \begin{minipage}[t]{0.16\columnwidth}\raggedright\strut
LVEDD, LVEF, LV-GLS\strut
\end{minipage}\tabularnewline
\bottomrule
\end{longtable}

\textbf{Table 1:} Summary of Studies. LVEDD: Left Ventricular
End-Diastolic Diameter; LVEF: Left Ventricular Ejection Fraction;
LV-GLS: Left Ventricular Global Longitudinal Strain

\emph{Table 2: Echocardiographic Indices Summary}\selectlanguage{english}
\begin{longtable}[]{@{}lllllllll@{}}
\toprule
\textbf{Echo indices} & \textbf{Number of Studies} & \textbf{Number of
Myocarditis Patients} & \textbf{Number of Control Patients} &
\textbf{Overall Effect Size (SMD)} & \textbf{95\% CI} & \textbf{p} &
\textbf{I\textsuperscript{2}} & \textbf{z}\tabularnewline
\midrule
\endhead
\textbf{LVEDD} & \textbf{4} & \textbf{184} & \textbf{165} &
\textbf{0.46} & \textbf{0.11, 0.81} & \textbf{0.01} & \textbf{54} &
\textbf{-1.87}\tabularnewline
\textbf{LVEF} & \textbf{6} & \textbf{269} & \textbf{240} &
\textbf{-0.77} & \textbf{-1.28, -0.26} & \textbf{\textless{}0.01} &
\textbf{86} & \textbf{-0.20}\tabularnewline
\textbf{LV-GLS} & \textbf{6} & \textbf{269} & \textbf{240} &
\textbf{-1.98} & \textbf{-2.45, -1.51} & \textbf{\textless{}0.01} &
\textbf{76} & \textbf{2.48}\tabularnewline
\bottomrule
\end{longtable}

\textbf{Table 2:} Summary of Meta-Analysis results. LVEDD: Left
Ventricular End-Diastolic Diameter; LVEF: Left Ventricular Ejection
Fraction; LV-GLS: Left Ventricular Global Longitudinal Strain; SMD:
Standardized Mean Difference; I\textsuperscript{2} assess degree of
heterogeneity; z reflects Egger's values

\emph{Figure 3: Meta-Analysis of Studies with LVEDD}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

\textbf{Figure 3:} Forest Plot for LVEDD. LVEDD: Left Ventricular
End-Diastolic Diameter

\emph{Figure 4: Meta-Analysis of Studies with LVEF}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

\textbf{Figure 4:} Forest plot for LVEF. LVEF: Left Ventricular Ejection
Fraction

\emph{Figure 5: Meta-Analysis of Studies with LV-GLS}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

\textbf{Figure 5:} Forest Plot for LV-GLS. LV-GLS: Left Ventricular
Global Longitudinal Strain

\selectlanguage{english}
\FloatBarrier
\end{document}

