Diagnostic Electrophysiology & Ablation

The Role of Cardiac MRI in the Diagnosis and Risk Stratification of

Hypertrophic Cardiomyopathy
Ethan J Rowin and Martin S Maron

Hypertrophic Cardiomyopathy Institute, Division of Cardiology, Tufts Medical Center, Boston, MA; Chanin T. Mast
Center for Hypertrophic Cardiomyopathy, Morristown Medical Center, Morristown, NJ, USA

Abstract
Hypertrophic cardiomyopathy (HCM), the most common genetic cardiomyopathy, is a disease characterised by substantial heterogeneity.
Although the majority of patients with HCM remain asymptomatic with near-normal longevity, a small, but important, subset remain
at risk for a wide range of clinical outcomes including sudden death. Cardiovascular magnetic resonance (CMR), with its high spatial
resolution and tomographic imaging capability, has emerged as an imaging modality particularly well suited to characterise the phenotypic
expression of HCM. CMR helps in the diagnosis of HCM by identifying areas of hypertrophy not well visualised by echocardiography,
providing more accurate wall thickness measurements and differentiating HCM from other causes of left ventricular (LV) hypertrophy.
CMR has led to the identification of novel subgroups of patients with HCM, including those with LV apical aneurysms (a subgroup at
increased risk for ventricular arrhythmias and thromboembolic stroke), as well as abnormalities that contribute to LV outflow obstruction.
Additionally, contrast-enhanced CMR with late-gadolinium enhancement (LGE) has recognised patients with extensive LGE (≥15 % LV
myocardium) as individuals who may be at increased risk of sudden death, independent of other high-risk features, with implications on
management strategies including consideration for primary prevention implantable cardioverter defibrillator therapy. These observations
justify an expanded role of CMR in the routine clinical assessment of patients with HCM.

Keywords
hypertrophic cardiomyopathy, cardiovascular magnetic resonance, sudden death

Disclosure: The authors have no conflicts of interest to declare

Received: 13 January 2016 Accepted: 18 October 2016 Citation: Arrhythmia & Electrophysiology Review 2016;5(3):197–202. DOI: 10.15420/aer.2016:13:3
Correspondence: Ethan J Rowin, Tufts Medical Center, #70, 800 Washington Street, Boston, Massachusetts 02111, USA. E: erowin@tuftsmedialcenter.org

Hypertrophic cardiomyopathy (HCM), the most common genetic stratification of patients with HCM.14–18 Thereby, it is timely to discuss
cardiomyopathy, is present in one in 500 of the general population the specific areas that CMR contributes in the clinical evaluation and
and is caused by over 1,400 mutations in at least 11 genes encoding risk assessment of patients with HCM.
the cardiac sarcomere.1–4 Although the majority of patients with
HCM remain asymptomatic with near-normal longevity, a small, but Diagnosis
important, subset of patients are at increased risk for a wide range A diagnosis of HCM is made when unexplained LV hypertrophy
of clinical outcomes including development of advanced heart (range 13–60 mm; mean 22 mm) occurs in the absence of another
failure symptoms, atrial and ventricular arrhythmias, thromboembolic disease capable of producing a similar magnitude of hypertrophy.5,6
events, and even sudden death. 5–8 HCM is characterised by a Therefore, the clinical diagnosis is highly dependent on accurate
heterogeneous phenotypic expression with diverse range of extent non-invasive quantification of the LV wall thickness. Traditionally,
and pattern of hypertrophy (massive to minimal hypertrophy, 2D echocardiography has been the primary imaging modality used
that can occur at any location from the apex to the base), 4,9 in evaluation; however, the echocardiographic examination may
outflow obstruction (resting, provocable or nonobstructive),10 and provide measurements that appear to fall within the non-diagnostic
left ventricular (LV) systolic function (hyperdynamic to systolic range (i.e. normal or borderline increase).9 By virtue of its high
dyfunction).1 Cardiovascular magnetic resonance (CMR), a high- spatial resolution, CMR allows a more precise assessment of LV wall
resolution 3D tomographic imaging technique that provides sharp thickness and areas of hypertrophy. In fact, CMR has identified focal
contrast between the blood pool and myocardium, has emerged as and segmental areas of hypertrophy within the LV that is not reliably
an imaging technique that is particularly well suited to characterise identified by 2D echocardiogram, particularly in the anterolateral
the diverse morphological expression of this disease (see Figure 1), free wall, apex or posterior septum (see Figure 2).9,19 This is an
and is the imaging modality of choice when the diagnosis or important consideration as 20 % of patients with HCM have focal
morphological characteristic of HCM remains in doubt following areas of hypertrophy, confined to one or two LV segments.4 For these
echocardiography.1,2,11–13 In addition, contrast-enhanced CMR with reasons, when a clinical diagnosis of HCM is suspected due to clinical
late-gadolinium enhancement (LGE) has the capability to identify symptoms, electrocardiographic abnormalities or family history, and
areas of myocardial fibrosis/scarring with novel data demonstrating echocardiography is normal/non-diagnostic, additional testing with
that the extent of LGE by CMR may play an important role in risk CMR should be performed.5

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Diagnostic Electrophysiology & Ablation

Figure 1: Cardiovascular Magnetic Resonance Images Similarly, an overestimation of LV wall thickness may also occur with
in Six Patients with Hypertrophic Cardiomyopathy echocardiography. For example, when the crista supraventricularis,
Demonstrating Diverse Phenotypic Expression
a right ventricular muscle structure, is situated adjacent to the
ventricular septum; this structure may be inappropriately included in
A B C
the septal measurements by echocardiography, an overestimation of
wall thickness that can be avoided using CMR.13
*
LV
LV
RV RV LV
* Assessment of Family Members with
RV *
Hypertrophic Cardiomyopathy
Screening of all first-degree relatives of patients with HCM is
D E F indicated to identify those individuals with potentially unrecognised
Ao Ao
LA LA
disease.5,6 Screening should begin at the onset of adolescence, with
LA
RV repeat imaging performed annually (every 12–18 months) throughout
adolescence, and then every 5 years until the fourth decade of life,
LV
LV
as delayed-onset hypertrophy can also occur later in adulthood.
* LV While echocardiography has traditionally been the mainstay test
* used in screening, the realisation that CMR provides a more precise
delineation of LV hypertrophy has led to the increased use as part of
A–C: Short-axis CMR images demonstrating: (A) massive LV hypertrophy (wall thickness
of 31 mm) confined to the ventricular septum (asterisk), (B) massive LV hypertrophy the screening evaluations.20,21 This not only allows for more accurate
(wall thickness of 30 mm) in the inferior septum and inferior wall (asterisk) and (C) mild diagnosis, but also a benchmark for future studies to better define the
asymmetric hypertrophy of the septum (asterisk; wall thickness of 16 mm) in a patient with a
disease-causing sarcomere mutation in the myosin-binding protein C gene. D: Four-chamber potential progression of LV hypertrophy.
long-axis view demonstrating hypertrophy localised to the LV apex (asterisks). E: Three-
chamber long-axis view demonstrating muscular midcavitary obstruction attributable to the
insertion of anomalous anterolateral papillary muscle directly into anterior leaflet (arrow) The availability of genetic testing in clinical practice has resulted in
contacting the midventricular septum in systole (arrowheads). F: A 24-year-old genotype- the identification of family members with HCM who carry a disease-
positive phenotype-negative man with two deep, narrow myocardial crypts (arrows) in
the anterior septum, considered a morphological marker for affected status. Ao = aorta; causing sarcomere mutation (and therefore are at risk of developing
CMR = cardiovascular magnetic resonance; HCM = hypertrophic cardiomyopathy; LA = left phenotypic HCM), but without LV hypertrophy (i.e. genotype positive–
atrium; LV = left ventricle; RV = right ventricle.
phenotype negative [G+P−] patients).20–23 This led to the observation
with echocardiography that abnormalities of myocardial function
Figure 2: Cardiovascular Magnetic Resonance for
are present in G+P− patients, and the emerging principle that even
Hypertrophic Cardiomyopathy Diagnosis
in the absence of increased LV wall thickness these hearts may be
abnormal.21–23 CMR has added to these insights by demonstrating that
A
a number of additional morphological abnormalities may be present
including myocardial crypts (see Figure 1F), elongated mitral valve
leaflets, expanded extracellular space (with T1 mapping) and LGE.24–27
When genetic testing is negative or ambiguous (as in 60 % of patients),
or when not pursued due to financial or personal preference, CMR can
identify these abnormalities in the absence of LV hypertrophy, raising
suspicion for genotype-positive status among family members.2,21
B C
This should prompt continued close surveillance with serial CMR for
development of LV hypertrophy and conversion to clinical disease.
RV
RV Differentiation of Other Aetiologies of Left
Ventricular Hypertrophy
Athlete’s Heart
LV hypertrophy associated with systemic training (i.e. athlete’s heart)
LV
LV may be difficult to differentiate from HCM.28,29 The differentiation
between athlete’s heart and HCM is critical as HCM is an important
cause of sudden death in athletes, responsible for 6–36 % of
events.30–32 A variety of different morphological features on CMR may
An asymptomatic 36-year-old woman with a family history of HCM. A: Twelve-lead help distinguish HCM from athlete’s heart. Additionally, CMR can
electrocardiogram was abnormal with incomplete right bundle branch block and anterior
and inferior Q waves. B: 2D echocardiogram demonstrated normal LV wall thickness.
evaluate for other structural abnormalities that are also frequently
C: Given abnormal ECG, patient underwent CMR, which reveals an area of segmental implicated in sudden death of athletes including arrhythmogenic right
hypertrophy in the anterolateral LV wall (asterisk) consistent with a diagnosis of HCM.
CMR = cardiovascular magnetic resonance; HCM = hypertrophic cardiomyopathy;
ventricular cardiomyopathy and myocarditis.30–32 Thereby, a normal
LV = left ventricle; RV = right ventricle. CMR provides a further level of reassurance.

Areas of LV hypertrophy may similarly be underestimated by CMR can help differentiate athlete’s heart from HCM by identification
echocardiography, with more accurate measurements made by CMR. of focal pattern of hypertrophy, a finding supportive of a diagnosis
This has important management implications as massive hypertrophy of HCM. In addition, forced deconditioning of an athlete may serve
(wall thickness ≥30 mm) is an independent risk factor for sudden as a useful strategy to resolve diagnosis, with CMR well suited to
death in HCM, and in some patients may only be recognised by CMR.2 compare maximum LV wall thickness measurements before and after

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 Cardiac MRI in Hypertrophic Cardiomyopathy

a period of systemic deconditioning. In this regard, a patient whose Figure 3: Cardiovascular Magnetic Resonance for
wall thickness regresses by more than 2 mm supports a diagnosis Differentiation of Aetiology of Left Ventricular Hypertrophy
of athlete’s heart, while hypertrophy that remains present despite
Amyloid Fabry’s Disease Danon Disease
deconditioning supports a diagnosis of HCM.33
A C E

Contrast-enhanced CMR with LGE, provides the opportunity to aid in

the differentiation between HCM and athlete’s heart given the ability to LV * LV
* * LV
non-invasively provide tissue characterisation by means of identifying
*
focal areas of replacement fibrosis and expanded extracellular space. RV RV *
RV
While LGE is present in about half of individuals with HCM, LV
remodelling associated with athlete’s heart should not result in focal
areas of myocardial scarring/fibrosis, especially in younger individuals.33 B D F
Therefore, in an athlete suspected to have HCM, the presence of LGE
on contrast-enhanced CMR favours a diagnosis of HCM. In contrast,
the absence of LGE cannot be used to reliably exclude the possibility of
HCM as this is found in half of patients with a clinical diagnosis of HCM.13

Hypertensive Cardiomyopathy
The differentiation of LV hypertrophy due to systemic hypertension from Three different patients referred for evaluation of HCM; CMR in each raised concern for
alternative aetiology of LV hypertrophy. A: Pre-contrast short-axis CMR image in a 64-year-
HCM has historically been challenging. CMR can help in differentiation old man with increased LV wall thickness in both septum and lateral wall (maximum wall
by examining the pattern of hypertrophy, with longstanding systemic thickness of 18 mm in septum and 14 mm in lateral wall). B: Post-contrast images in the
same patient demonstrates early contrast washout with epicardial LGE in septum (arrows)
hypertension resulting in more concentric hypertrophy (near-identical and global subendocardial LGE (arrowheads) leading to concern for amyloidosis. Patient
hypertrophy in septum and lateral wall), while LV wall thickening in underwent cardiac biopsy confirming a diagnosis of amyloidosis. C: Pre-contrast short-axis
CMR image in a 44-year-old woman with increased LV wall thickness in both septum and
HCM is more commonly asymmetric.11–13 This asymmetric pattern lateral wall (maximum wall thickness of 16 mm in septum and 13 mm in the lateral wall).
favours a diagnosis of HCM over hypertension; however, it should D: Post-contrast images in the same patient demonstrate LGE confined to the basal inferolateral
wall leading to concern for Fabry’s disease. Patient underwent genetic testing, which
be noted that in some patients with HCM the pattern of hypertrophy revealed a pathogenic mutation in the galactosidase alpha gene confirming the diagnosis.
may also be symmetrical.11–13 Additionally, presence of LV outflow E: Pre-contrast short-axis CMR image in a 21-year-old man demonstrated massive LV
hypertrophy (wall thickness of 32 mm) confined to the ventricular septum (asterisk). F: Post-
obstruction due to typical systolic anterior motion of the mitral valve contrast images in the same patient demonstrated transmural LGE throughout the anterior
will help sway a diagnosis towards HCM, as this finding is present in and lateral walls with mid-myocardial LGE throughout the septum in a pattern atypical for
HCM and thereby raising concern for Danon Disease. Genetic testing was thereby sent and
over two-thirds of patients with HCM and rarely seen in hypertensive revealed a pathogenic mutation in the lysosomal-associated membrane protein 2 gene
cardiomyopathy.11–13 CMR can also be helpful in the detection of confirming the diagnosis. CMR = cardiovascular magnetic resonance; HCM = hypertrophic
cardiomyopathy; LGE = late-gadolinium enhancement; LV = left ventricle; RV = right ventricle.
changes in serial measurements of LV wall thickness after aggressive
treatment with antihypertensives, in which a regression of hypertrophy
would favour a diagnosis of hypertensive cardiomyopathy. CMR sequences, has potential to help in the further differentiation
of HCM from these infiltrative cardiomyopathies.38,39 Although CMR
Infiltrative Cardiomyopathy findings may be suggestive of a phenocopy in a patient undergoing
Infiltrative cardiomyopathies, including amyloidosis or glycogen/ evaluation for HCM, CMR findings in themselves are not diagnostic and
lysosmal storage diseases (such as Fabry’s or Danon disease) can must be considered within the clinical contest of an individual patient.
mimic clinical HCM as they can produce increased wall thickness Therefore. confirmation with either laboratory testing, molecular
as part of their phenotypic expression (see Figure 3).34–36 Although genetic analysis or biopsy (either cardiac or another affected tissue) is
these diseases may have non-cardiac signs and symptoms, disease often ultimately required to make a definitive diagnosis.5,6
expression can also be confined only to the heart. The accurate
differentiation of these ‘phenocopies’ is critical as treatment strategies Phenotype Characterisation of HCM
and prognosis differs compared with HCM. In amyloidosis, CMR Left Ventricular Apical Aneurysms
identification of increased LV wall thickness in both the lateral wall Increasing penetration of CMR into routine cardiovascular practice
as well as the septum combined with global subendocardial LGE is has resulted in more frequent identification of a subset of patients
suggestive of cardiac amyloidosis and not typical in HCM.34 Suspicion with an unusual phenotype of HCM with thin-walled, scarred LV apical
of Fabry’s disease, an X-linked storage disease in which mutations aneurysms (see Figure 4). This important group of patients had been
in the alpha-galactosidase A gene leads to cellular accumulation underdiagnosed prior to the application of CMR to HCM, largely based
of glycosphingolipids in multiple organs including the heart, and on small- to moderate-sized aneurysms not reliably identified by
potentially treatable with enzyme replacement therapy, can be raised echocardiography.40 Contrast-enhanced CMR has demonstrated that
by increased LV wall thickness in both the lateral wall and septum with the aneurysm rim in these patients is composed predominantly of
LGE confined to the basal inferolateral wall.35 Danon disease, which fibrosis that extends from the aneurysm rim into the septum and free
is due to mutations in genes that encode the lysosomal-associated wall and serves as nidus for ventricular tachycardia. These changes
membrane protein 2, leads to accumulation of intracellular vacuoles may place in patients at increased risk of arrhythmic sudden death
and is a profound and accelerated disease process with rapid clinical and thromboembolic stroke (secondary to LV thrombus formation
deterioration leading commonly to advanced heart failure and sudden in the aneurysmal cavity).40 Thereby, the identification of LV apical
death at a young age (commonly <25 years old).36 CMR can be aneurysms may raise important management implications with
suggestive of the diagnosis in the setting of massive LV hypertrophy consideration for implantable cardioverter defibrillator (ICD) therapy
with extensive diffuse and often transmural LGE.37 T1 mapping, a novel as well as systemic anticoagulation for stroke prevention.1,5

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Diagnostic Electrophysiology & Ablation

Figure 4: Left Ventricular Scarring Associated with Apical by echocardiography yet are critical as they potentially alter the septal
Aneurysm Formation in a Patient with Hypertrophic reduction strategy in favour of surgical myectomy, as alcohol septal
Cardiomyopathy
ablation is unable to address these additional abnormalities.43,44

A B Risk Stratification
Sudden Death
LA Since the initial descriptions of HCM, sudden death has been a highly
P
visible and devastating disease consequence. Fortunately, sudden death
D
is confined to a small subset of patients with HCM within the broad
disease spectrum.7,8 Sudden death events occur unpredictable, often
without warning signs or symptoms and is most common in young
A: Cine steady state-free precession non-contrast two-chamber long-axis CMR image in
systole of a thin-walled LV apical aneurysm (arrowheads) with maximal LV wall thickness
people through mid-life.1 The application of ICD for primary prevention
at midventricular level with muscular apposition of the septum and LV free wall producing of sudden death in HCM has created the opportunity to prevent these
distinct proximal (P) and distal (D) chambers. B: Two-chamber end-diastolic images from the
same patient after injection of gadolinium contrast showing transmural LGE of the aneurysm
catastrophic events.45 This has placed increased importance on risk
rim (arrowheads) with extension into the contiguous anterior and inferior walls (thick arrows). stratification to help identify individuals who may benefit from device
A and B: The LV apical aneurysm contains a sizable intracavitary thrombus attached to
the rim of the aneurysm (narrow arrow). CMR = cardiovascular magnetic resonance;
therapy for primary prevention. The current American College of
HCM = hypertrophic cardiomyopathy; LGE = late-gadolinium enhancement; LA = left Cardiology (ACC) and American Heart Association (AHA)-based HCM risk
atrium; LV = left ventricle.
stratification algorithm has relied on five major risk markers (see Figure
5) and has been highly effective in identifying many patients with HCM
Figure 5: Pyramid Profile of Risk Stratification Model who will benefit from ICD therapy.5 While this has been instrumental in
Currently Used to Identify Patients at the Highest Risk of
decreasing rates of sudden death and HCM-related mortality to 0.5 %/
Sudden Death Who May be Candidates for ICD for Sudden
Death Prevention year, some patients without conventional risk markers nevertheless
remain at risk of sudden death.7,8 These limitations have led to an
interest in additional strategies to improve the current risk model. In this
2° Prevention: regard, attention has focused on contrast-enhanced CMR with LGE to
Cardiac arrest/sustained VT
non-invasively identify myocardial fibrosis, the potential arrhythmogenic
1° Prevention:
substrate in HCM.14–18 Early studies demonstrated that patients with HCM
Familial history of HCM-SD ICD
Unexplained syncope and evidence of LGE on CMR have increased rates of non-sustained
Multiple-repetitive NSVT Highest
Abnormal exercise BP response
ventricular tachycardia on ambulatory Holter monitoring compared with
Massive LVH ≥30 mm patients without LGE, raising the concept that LGE represents a substrate
LGE ≥15 % of LV mass*
for generation of malignant ventricular arrhythmias.14
Rare subgroups: Intermediate
LV apical aneurysms
End-stage HCM (EF <50 %) This notion led to several outcome studies, each with relatively
small patient cohorts, evaluating the presence of LGE on CMR and
B
demonstrating that patients with HCM with LGE were at increased
Lowest risk of cardiovascular mortality.16–18 However, LGE is fairly common in
LV
patients with HCM, with a prevalence of >50 %, and thereby the use
of presence of LGE alone as a sudden death risk marker would lead to
RV over-implantation of ICD for primary prevention.2

Major risk markers appear in boxes at the upper left. *Extensive LGE is a potential
novel primary risk marker that can also be used as an arbitrator when conventional risk Conversely, a large multicentre study with almost 1300 patients with
assessment is ambiguous. B. Example of a patient with extensive LGE throughout the septum
HCM demonstrated that LGE extent is capable of identifying patients
(arrows) occupying 17 % of LV mass, and without other traditional risk markers. Based on
extensive LGE, the patient had ICD placed for primary prevention of sudden death with at increased sudden death risk and deserving of consideration of ICD
appropriate ICD discharge for VF 1 year later. EF = ejection fraction; HCM = hypertrophic
placement.15 Extensive LGE, occupying ≥15 % of LV mass, is equivalent
cardiomyopathy; ICD = implantable cardioverter defibrillator; LGE = late gadolinium
enhancement; LV = left ventricular; LVH = left ventricular hypertrophy; NSVT = non-sustained to a twofold sudden death risk as compared with no LGE. This increased
ventricular tachycardia; RV = right ventricle; SD = sudden death; VT = ventricular tachycardia.
sudden death risk is present even among patients without other
established risk markers and who would otherwise be considered at
Outflow Obstruction low risk. Furthermore, when data from this study was pooled with data
Mechanical impedance to LV outflow due to systolic anterior motion of from a study by Ismail et al.,46 the only other study to report adjusted
the mitral valve is perhaps the most important cause of limiting heart hazard ratio for the extent of LGE in HCM, the amount of LGE remains
failure symptoms in HCM.10 The identification of LV outflow obstruction independently associated with sudden death risk (adjusted hazard
in the setting of drug-refractory severe symptoms is critical as it ratio 1.4 for every 10 % increase in LGE of LV mass; and adjusted hazard
alters management strategies towards invasive septal reduction ratio of 1.6 for 15 % LGE).47 Based on these data, it may be reasonable
therapy with either surgical myectomy or alcohol septal ablation.5,6 to consider that patients with HCM with extensive LGE (≥15 % LV
CMR allows for precise evaluation of the left ventricular outflow tract myocardium) at increased risk, independent of other high-risk features,
(LVOT) and anomalies contributing to outflow obstruction, including with implications on management strategies including consideration
anomalous insertion of the anterior papillary muscle directed into the for primary prevention ICD therapy (see Figure 5).2,15
mitral leaflet (see Figure 1e), elongated mitral valve leaflet lengths and
muscle bundles that extend from the apex and attach into the basal Extensive LGE also helps resolve decision making regarding ICD in
anterior septum.41,42 The identification of these features may be missed complex situations when sudden death risk remains ambiguous after

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 Cardiac MRI in Hypertrophic Cardiomyopathy

standard risk stratification, as it can serve as an arbitrator towards Conclusion

ICD placement.15 In contrast, the absence of LGE is associated Over the last decade, contrast-enhanced CMR has emerged as a
with lower risk for sudden death and should provide a measure of powerful imaging tool uniquely suited for the characterisation of
reassurance.2,15 Therefore, LGE has emerged as a potentially powerful the heterogeneous phenotypes in HCM.9–13 CMR provides relevant
tool to strengthen the ACC/AHA risk stratification model. diagnostic and prognostic information not identifiable with traditional
echocardiography.15–19 CMR impacts a variety of clinical management
Systolic Dysfunction issues ranging from diagnosis and family screening to procedural
Extensive LGE can also be predictive of progression to the end-stage planning for septal reduction therapy.20,25,38–41 Newer data demonstrate
phase of HCM, characterised by LV remodelling with ventricular cavity that extensive LGE, occupying ≥15 % LV myocardium, identifies
dilation, wall thinning secondary to scarring and systolic dysfunction patients at an increased sudden death risk and these patients may
(ejection fraction <50 %).48 Extensive LGE, comprising ≥15 % of total ultimately benefit from ICD placement for primary prevention.2,15 These
LV mass, also prospectively identifies patients with preserved systolic observations help to justify an expanded role of CMR in the routine
function who are at risk of heart failure progression due to systolic assessment of patients with HCM. ■
dysfunction and may require future heart transplantation.15 This
recognition can alter management strategies including consideration
for altered medical therapy, prophylactic ICD and timely evaluation for Clinical Perspective
heart transplantation once symptoms develop.48 • Contrast-enhanced CMR has emerged as a power imaging tool
uniquely suited for the characterisation of the heterogeneous
Future Direction: T1 Mapping phenotypes in HCM.
T1 mapping is a novel and promising CMR technique that provides • CMR helps to diagnose HCM given its abilities to identify areas
assessment of the total extent of expanded extracellular space, rather of hypertrophy that is not well visualised by echocardiography,
than the detection of regional areas of myocardial fibrosis identified by to provide more accurate wall thickness measurements and to
traditional LGE imaging.49 It has been postulated that T1 mapping may differentiate other aetiologies of LV hypertrophy.
emerge as a diagnostic imaging marker in differentiating pathological • Contrast-enhanced CMR with LGE has identified patients
cardiovascular diseases such as HCM from that of other forms of LV with extensive LGE, occupying ≥15 % LV myocardium. Based
hypertrophy (such as Fabry’s disease39 or amyloidosis38) and that this on data from a recent large multicentre study, it may be
technique may prove to be superior to LGE for risk stratification in reasonable to consider that these patients are at increased
HCM. However, to date, there has been no link between T1 mapping risk of sudden death, independent of other high-risk features,
and cardiovascular outcomes within HCM. In addition, conflicting data with implications on management strategies including
exist regarding T1 mapping values in G+P– patients, and if this value consideration for primary prevention ICD therapy.
can indeed differentiate G+P– patients to normal controls.24,50 Thereby, • These observations help to justify an expanded role of CMR in
continued investigations applying T1 mapping to HCM is necessary to the routine clinical assessment of patients with HCM.
better to define the role of this technique.

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