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D. B. Loriaux et al.
The procedure was completed without complication and with resolution of the patient’s
symptoms (NYHA Class I).
Fig. 6 Post-ablation angiography showing 100% occlusion of septal branch. Post-ablation angiography in RAO
cranial projection showing 100% occlusion of rst septal
perforator artery with unchanged left anterior descending
artery (LAD) perfusion
Post procedural Assessment
The patient was transferred to the Cardiovascular
Intensive Care Unit for continued overnight monitoring for potential development of new atrioventricular block with the transvenous temporary
pacing wire in place. Review of her telemetry
showed normal sinus rhythm with no evidence of
high-grade block. Her post-ablation electrocardiogram showed new right bundle branch block
(Fig.7).
Note that although 12-lead ECG abnormalities such as localized or widespread repolarization changes, prominent precordial voltages, left
axis deviation, or deep inferior and lateral
Q-waves may be present on the baseline ECG for
patients with HCM, these changes are neither
sensitive nor specic. None of these abnormalities were present on the pre-ablation ECG for this
patient with chronic and severely elevated LVOT
gradient. On her post-ablation ECG a new right
bundle branch block (RBBB) is seen, which
occurs in 60% of patients undergoing ASA [3, 4].
RBBB develops because the septal branches supplying the region of hypertrophied septum also
Fig. 7 Pre and post-ablation electrocardiograms. (Left
panel) Pre-ablation electrocardiogram showing normal
sinus rhythm with narrow QRS complexes. (Right panel)
Post-ablation electrocardiogram showing normal sinus
rhythm with new right bundle branch block
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203
provide perfusion to the right bundle branch. The
development of new RBBB following ASA has
not been shown to adversely affect clinical outcomes [5].
On postoperative day 1, the temporary pacing wire was removed and the patient was
transferred to the cardiology stepdown unit.
She was discharged home on postoperative
day 3.
At the patient’s 1-week post-ablation follow up visit, she continued to report signicantly
improved symptoms (NYHA Class I). Follow-up
echocardiography performed 3-months postablation showed persistent normalization of her
LVOT gradient.
Key Points
• Transthoracic echocardiography is the
diagnostic study of choice for HCM.
• Alcohol septal ablation offers a safe,
effective, and minimally invasive treatment strategy for HCM.
• With less invasive nature, accelerated
recovery, and similar symptomatic
improvement compared with surgical
myectomy, alcohol septal ablation is currently the most commonly performed septal reduction therapy for obstructive HCM.
Introduction
Hypertrophic cardiomyopathy (HCM) is the
most common heritable cardiac disorder, affecting 0.2–0.5% of the general population, and a
leading cause of sudden cardiac death (SCD) in
younger patients [20, 21]. HCM is inherited in an
autosomal dominant pattern from pathogenic
variants in multiple genes encoding sarcomere
proteins [2, 22]. Sporadic cases without a family
history of HCM also occur. Partially due to considerable heterogeneity in genotypic and phenotypic presentation, HCM remains signicantly
underdiagnosed. It is estimated that up to 85% of
all HCM cases phenotypic expression remain
undiagnosed [3]. The signicant gap that continues to exist between conrmed and undiagnosed
HCM highlights the need for improved understanding of its presentation, diagnosis, and
widely available treatments. This chapter will
focus on interventional therapy for HCM, percutaneous alcohol septal ablation (ASA) , including
the history of HCM and ASA, recommended
approach to diagnosis, evolution of available
treatment strategies, complex management considerations, and the central role of cardiovascular
imaging in each stage of HCM diagnosis and
treatment.
Section 1—History
History ofHCM andASA:
TheGroundwork forModern
Diagnosis andTreatment
The current understanding and management of
HCM has been shaped by the historic work of anatomists, pathologists, geneticists, surgeons, and clinicians whose shared efforts have made it possible
to understand, diagnose, and treat the complex
pathophysiology that denes the disease.
The modern description of HCM is credited to
the English forensic pathologist Dr. Robert Teare.
In 1958, while working at St. George’s Hospital
in London, Teare published a landmark description of asymmetrical myocardial hypertrophy
identied at the time of autopsy in eight patients
[23]. Massive cardiomegaly with disproportionate enlargement of the interventricular septum
was found on post-mortem examination of each
sudden death victim [24]. In his report, Teare
described the cardinal clinical and histopathological features of HCM: chest discomfort, palpitations, exertional dyspnea, and syncope in
patients with pathologic Q-waves on electrocardiogram and “myocyte disarray” with bre
hypertrophy on autopsy (Fig. 8) [23]. In an
addendum to this paper, Teare was also the rst to
suggest a hereditary cause when he reported the
sudden death of the 16-year-old brother of one of
the original eight cases. In a single communication, Teare united many unanswered pieces of
medical history into a single disease entity [25].
Building upon Teare’s description of HCM in the
British Heart Journal, the stage was set for discovery of an effective treatment for HCM, including the focus of this chapter: alcohol septal
ablation.
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D. B. Loriaux et al.
a
b
Fig. 8 Electrocardiographic, histopathologic, and anatomic features of HCM. (a) Classic electrocardiographic
features in hypertrophic cardiomyopathy (HCM) including sharp, “dagger” Q-waves (arrows), which may be seen
in the lateral (I, aVL, V5, V6) and/or inferior (II, III, aVF)
leads. (b) HCM histopathology demonstrating architec-
c
tural disarray of hypertrophied myocytes. (c) Characteristic
gross pathology for a patient with sudden cardiac death
who was diagnosed with HCM at the time of autopsy. A
cross section of the heart is shown with severe, asymmetric left ventricular hypertrophy
In the early 1960s at the National Institutes of
Health, Dr. Glenn Morrow pioneered transaortic
ventricular septal myectomy (Morrow procedure) as a method for relieving LV outow tract
obstruction. A small portion of myocardium
(3–10g) was resected from the proximal ventricular septum. His experience with this technique
was published in a report of 25 patients [26]. For
over 30 years, myectomy remained the only
proven septal reduction therapy for HCM.
It was not until the mid-1990s that alcohol
septal ablation (ASA) was introduced by Dr.
Ulrich Sigwart at the Royal Brompton Hospital
in the United Kingdom as a minimally invasive
alternative to surgical myomectomy [27, 28]. The
idea of producing septal infarction by catheterbased techniques as a treatment for HCM,
Sigwart states, “Was suggested by observations
that systolic and diastolic myocardial function of
selected areas in the left ventricle can be selectively suppressed by balloon occlusion of the
supplying artery during coronary angioplasty”
[27]. In this original description of the procedure,
Sigwart reported three patients with advanced
hypertrophic obstructive cardiomyopathy, all
between the ages of 60 and 70years, who underwent injection of “absolute alcohol into the rst
major septal coronary vessel” to produce septal
infarction. All three patients tolerated the procedure well and achieved striking symptomatic
improvement on the rst day after treatment [27].
As stated by Dr. Sigwart, “The attraction of the
procedure resides in its simplicity, minimal morbidity, and the fact that the outcome of the denite ablation can be estimated by temporary
occlusion of the target vessel” [27].
In the decades that have passed since the rst
septal ablation was performed by Sigwart, percutaneous procedures have revolutionized the management of structural heart disease. ASA has
proven to signicantly improve morbidity in
patients with HCM by decreasing the left ventricular outow tract (LVOT) gradient, reducing
mitral regurgitation, and alleviating heart failure
symptoms through a minimally invasive approach
with substantially shorter recovery times than
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surgery [29]. The efcacy and safety of alcohol
septal ablation is now well established, with
greater than 95% of patients free of recurrent CV
events at 15 years. The EURO-ASA registry,
which includes acute and long-term data from
1000 patients treated with ASA in 10 tertiary centers from 7 European countries, conrms the
safety and durable relief of LVOT obstruction in
patients with HCM who are treated with ASA
[30]. All consensus and guideline panels regard
ASA as an effective alternative treatment strategy
to SM in patients with obstructive HCM who are
sub-optimal surgical candidates (i.e. those with
extensive comorbidities, advanced age, multiple
prior sternotomies, or a strong aversion to surgery) [2]. The number of ASA procedures performed worldwide now greatly exceeds the
number of surgical myectomies each year [4].
Following the introduction and widespread utilization of ASA, novel percutaneous options for
SRT in HOCM have been described including
coil embolization, radiofrequency ablation, and
transcatheter electrosurgical myotomy [31, 32].
However, these alternative SRT methods have
been studied in a limited number of patients and
without long-term outcomes.
The success of ASA as a treatment for HCM is
contingent upon careful preprocedural evaluation
and assessment of patient candidacy involving a
multidisciplinary heart team evaluation including
a cardiac surgeon experienced in surgical myomectomy. The focus of the remaining sections of
this chapter will be on the cardiovascular imaging modalities that play a central role in guiding
ASA patient selection, procedural intervention,
and post-procedural monitoring.
Section 2: Pre-procedural
Assessment ofHCM
Clinical Presentation andDiagnosis
ofHCM
HCM has potential for clinical presentation in all
phases of life, from infancy to old age [1]. Early
diagnosis and accurate risk stratication promotes
timely intervention and a signicant reduction in
disease related morbidity and mortality [33]. With
efcient diagnosis and treatment, a new diagnosis
of HCM is compatible with normal life expectancy and little or no disability for the majority of
patients [2]. Effective clinical screening for HCM
must include a three- generation family history,
comprehensive physical examination, and electrocardiogram [1]. When the clinical features of
HCM are present, further evaluation with comprehensive 2D echocardiography is indicated.
Echocardiography is the cornerstone of screening,
diagnosis, and prognostication for HCM [13, 34].
A comparison of imaging modalities for the
assessment of HCM is shown in Table 4. The
diagnostic features of HCM on 2D echocardiography are summarized in Table5.
Table 4 Multimodality imaging comparison
Modality HCM application Advantages Limitations
TTE
• For patients undergoing ASA,
TTE or intraoperative TEE
with intracoronary ultrasoundenhancing contrast injection of
the candidate’s septal
perforator is recommended
(class I, LOE B-NR) [2]
• Recommended 3–6months
following SRT to evaluate
procedural results (class I,
LOE B-NR) [2]
• Myocardial contrast echo
enhances endocardial
denition and denes
myocardial perfusion
territories to guide alcohol
septal ablation
• Availability and cost
• Preferred method for
assessment of diastolic
function
• Superior to CMR in
quantication of outow tract
gradient
• Able to provoke physiological
gradients with exercise in
patients who have a resting
LVOT gradient less than
30mmHg at rest
• Contrast echocardiography is
able to reliably delineate
location and extent of septal
perfusion territory prior to
ASA
• Doppler-specic angle
dependence in assessing LVOTG
• Less precise differentiation of
endocardial borders and blood
pool relative to CMR
• Less reliable in distinguishing
epicardial fat, pericardium, and
trabeculations relative to CMR
• More likely to underestimate
magnitude of hypertrophy [6]
(continued)
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Table 4 (continued)
Modality HCM application Advantages Limitations
TEE
CMR
Comparison of the clinical applications, advantages, and disadvantages of common diagnostic imaging modalities for
hypertrophic cardiomyopathy
ASA alcohol septal ablation, CMR cardiac magnetic resonance imaging, HCM hypertrophic cardiomyopathy, LV left
ventricle, LVOT left ventricular outow tract, LVOT G left ventricular outow tract gradient, SCD sudden cardiac death,
TEE transesophageal echocardiography, TTE transthoracic echocardiography, VSD ventricular septal defect
• Can be considered in patients
with inconclusive TTE or as an
alternative or complementary
investigation to CMR
• Can be useful in excluding
subaortic membrane or mitral
regurgitation secondary to
structural abnormalities of the
mitral valve apparatus, or in
the assessment of the
feasibility of ASA (class 2a,
LOE B-NR) [2]
• Used perioperatively for
surgical myectomy to guide
surgical approach, monitor for
complications, and assess
residual gradient (class I, LOE
B-NR) [2]
• CMR is indicated for
diagnostic clarication in cases
of suspected HCM when
echocardiography is
inconclusive (class I, LOE
B-NR) [2]
• CMR is indicated to inform
selection and planning of SRT
for patients with HOCM in
whom the anatomic
mechanism of obstruction is
inconclusive on
echocardiography (class I,
LOE B-NR) [2]
• CMR is useful for patients
with LVH in whom there is a
suspicion of alternative
diagnoses such as inltrative
or glycogen storage diseases,
athlete’s heart, etc. (class I,
LOE B-NR) [2]
• For patients who are not
identied as high-risk for
SCD, CMR is benecial to
assess for maximum LV wall
thickness, LVEF, LV apical
aneurysm, and extent of
brosis with LGE (class I,
LOE B-NR) [2]
• Particularly useful for
assessing mitral valve
apparatus in patients with
signicant LVOTO and
unclear mechanism of
obstruction
• Superior endocardial
visualization relative to TTE
• Enhanced spatial resolution
relative to TTE
• In patients undergoing SM,
TEE should be used to guide
surgical intervention and
monitor for intraoperative
surgical complications (i.e.
VSD, acute aortic
regurgitation, residual
LVOTO)
• Following SM, TEE can
conrm adequacy of
myectomy [7]
• Superior endocardial
visualization with excellent
demarcation between
myocardium and blood pool
[8]
• Enhanced spatial resolution
and image quality, enabling
identication of morphologic
HCM variants that are more
likely to be missed on TTE
[8–10]
• Superior to 2D echo in
measurement of LV mass,
detection of myocardial crypts,
papillary muscle pathology,
LV apical and anterolateral
hypertrophy, aneurysms, and
thrombi [11, 12]
• Reproducibility; less inter-user
variability relative to
echocardiography
• Particularly helpful for
treatment planning in the
setting of multiple areas of LV
obstruction and/or
accompanying RV obstruction
• Enables quantication of
septal brosis [13]
• Prognostication value; the
presence of LGE has been
correlated to increased CV
mortality, heart failure, and
arrythmias [14–19]
• Doppler-specic angle
dependence in assessing LVOTG
• Invasive procedure
• Less precise differentiation of
endocardial borders and blood
pool relative to CMR
• Less reliable in distinguishing
epicardial fat, pericardium, and
trabeculations relative to CMR
• More likely to underestimate
magnitude of hypertrophy [6]
• Unable to provoke physiological
gradients with exercise in
patients who have a resting
LVOT gradient less than
50mmHg
• Higher cost
• Less widely available
• Longer duration study
• Institutional differences in
magnetic resonance hardware
and software, inconsistent
optimization of inversion times,
improperly nulled LV
myocardium, different types and
dosage protocols for gadolinium
contrast, and diverse LGE
protocols may all signicantly
impact study interpretation [6]
• Unable to provoke physiological
gradients with exercise in
patients who have a resting
LVOT gradient less than
50mmHg
• CMR is less reliable than TTE in
assessing LVOT hemodynamics
• Turbulent LVOT ow can result
in signicant CMR artifacts
D. B. Loriaux et al.
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Diagnostic features of HCM on echocardiography
Table 5
Variable HCM features and signicance Sample imaging
LVH
SAM • 33% prevalence of SAM in HCM on rest
BBM • Echocardiographic analogue of the
• Unexplained maximal wall thickness
>1.4cm in any myocardial segment at
end-diastole [35]
• Maximal wall thickness >1.2in patients
with family history of HCM or positive
genetic testing [35]
• Measurement in M-mode should be
avoided to prevent overestimation by
oblique cut
• Maximal LV wall thickness 3.0cm or
greater (right) is associated with increased
risk for SCD
images [13]
• Additional 30–40% prevalence of
provocable LVOT gradient >30 mmHg with
maneuvers that alter loading conditions and
contractility [13, 36]
• SAM nearly always results in failure of
normal leaet coaptation and MR
• SAM-related MR is inherently dynamic in
nature; its severity varies with degree of
LVOTO
• MR jet appears in mid-late systole and has
posterior orientation
– Note that a central or anteriorly oriented
jet raises suspicion for intrinsic mitral
valve pathology and should prompt
further assessment with TEE
• M-mode (right) is frequently used to
conrm SAM
Brockenbrough–Braunwald–Morrow Sign:
a paradoxical decrease in arterial pulse
pressure during the post-PVC beat seen in
patients with HCM [37, 38]
• Severe AS can also translate to signicantly
increased CW Doppler gradient following a
PVC.To carry diagnostic value in HCM,
this nding must occur in the absence of
severe AS
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Table 5 (continued)
Variable HCM features and signicance Sample imaging
LVOTO
Diagnostic features of hypertrophic cardiomyopathy by transthoracic echocardiography. (Top panel) Severe left ventricular hypertrophy (LVH) involving the basilar interventricular septum (3.3 cm). (Second panel) M-mode showing
systolic anterior motion (SAM) of the anterior mitral leaet (yellow arrows). (Third panel) Echocardiography equivalent of the Brockenbrough–Braunwald–Morrow (BBM) Sign: increased left ventricular outow tract gradient corresponding to a decreased arterial pulse pressure following a premature ventricular contraction (yellow arrow). (Bottom
panel) Left ventricular outow tract obstruction shown at rest and with valsalva in an apical three-chamber window
IVSd interventricular septal diameter, LV left ventricle, LVOTO left ventricular outow tract obstruction, MR mitral
regurgitation, PVC premature ventricular contraction, SCD sudden cardiac death, SRT septal reduction therapy
• Dened as a peak instantaneous gradient
³30 mmHg [2]
– 70% of patients with HCM have LVOTO
³30 mmHg either at rest or with
provocation [39]
• Late peaking “dagger shape” Doppler
prole
• Pulse wave Doppler is recommended to
localize obstruction (apical, mid-cavitary,
or outow tract)
• Doppler of MR jet for direct comparison
with LVOT doppler waveform is
recommended to ensure that MR is not
mistaken for LVOT velocity
– Doppler should be performed in
multiple views (especially apical 5 and
apical 3) to align Doppler signal and
avoid MR
• Treatment threshold (SRT) ³50 mmHg [2,
40]
– Peak instantaneous LVOT gradient, not
mean gradient, dictates treatment
decisions
– When resting gradient is <50 mmHg in a
patient with suspected HCM, it is
essential to perform provocative
maneuvers (Valsalva, squat-to-stand,
upright exercise) to uncover a signicant
LVOTO [41]
• Exercise stress echo is recommended in
symptomatic patients when bedside
maneuvers fail to induce LVOTO ³50
mmHg
– Pharmacologic provocation with
dobutamine is not recommended unless
the patient is unable to exercise
D. B. Loriaux et al.
If a segment of the LV cannot be adequately
visualized using chest wall echocardiography, it
is recommended that enhanced imaging with
ultrasound contrast agents, transesophageal
echocardiography, and/or cardiovascular magnetic resonance imaging (CMR) be considered
[13, 42]. CMR provides detailed information
about cardiac morphology, function, and myo-
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cardial characteristics in an innite number of
planes with high-resolution images that enable
precise quantication of myocardial thickening,
ow, and extent of brosis [43–45]. Data acquired
from CMR is often complementary to echocardiography. The diagnostic features of HCM using
CMR are presented in Table6.
Table 6 Diagnostic features of HCM on CMR
Variable HCM features and signicance Sample imaging
HCM
anatomy
• Basal asymmetric hypertrophy
accounts for 60–70% HCM cases
(Panel A)
• CMR particularly useful for detecting
less common patterns of hypertrophy:
apical HCM variants (Panel B) or
obstruction arising secondary to
thickened chordal apparatus and/or
abnormal papillary muscles (Panel C)
The presence of LVH and signicant LVOTO
on echocardiography or CMR is not pathognomonic for HCM.A diagnosis of HCM relies on
these ndings in the absence of another cardiac
or systemic disease capable of producing the
magnitude of hypertrophy characteristic of
HCM [2]. As there are many systemic disorders
a
b
c
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Table 6 (continued)
Variable HCM features and signicance Sample imaging
LVOTG and
Mechanism
of
Obstruction
T1 and T2
mapping
• Cine phase contrast MR imaging can
be used to quantify blood ow
through the LVOT
• CMR planimetry- derived LVOT area
of 2.7cm2 or less identies signicant
LVOT obstruction in patients with
HCM with 100% accuracy [46]
• LVOT/Ao diameter ratio less than
0.45 is an accurate and reproducible
method for predicting severity of
LVOT obstruction [47]
• Identication of atypical mechanisms
for LVOT obstruction (i.e. papillary
muscle hypertrophy, mitral valve
apparatus) is essential in determining
candidacy for ASA
• T1 and T2 mapping enables
identication of myocardial injury
without gadolinium-based contrast
agents
• T1 mapping identies regions of
myocardial scarring as well as
interstitial brosis
• T2 mapping serves as a marker of
myocardial edema or inammation
• Native T1 values in segments of
severe hypertrophy (highlighted
region, top panel) demonstrate
signicantly higher T1 values than
segments of mild or moderate
hypertrophy [48]
• Mean T2 values of segments with
moderate or severe hypertrophy
(highlighted region, bottom panel) are
signicantly higher than those of mild
hypertrophy [48]
• In patients with HCM, T1 and T2
remodeling precedes morphological
and functional remodeling in HCM
[48]
D. B. Loriaux et al.
LGE • Marker of myocardial brosis
• Valuable indicator for risk
• Usually identied at hypertrophied
• LGE valuable in identifying end-stage
stratication of SCD (HCM patients
with ≥15% LGE relative to LV mass
have been found to have increased risk
of sudden cardiac death events)
insertion points of the interventricular
septum
HCM: reduced LVEF (<50%),
coexistence of myocardial
hypertrophy and thinning, and
extensive LGE reecting diffuse
myocardial scarring
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Table 6 (continued)
Variable HCM features and signicance Sample imaging
Assessment
of ASA
• LGE identies region of ablated
hypertrophied septum
• Location and extent of LGE induced
by ASA is predictive of success rate
[49]
• CMR is useful both in planning and in
follow-up for ASA; infarction size and
location correlates with total septal
mass reduction and LVOTG
alleviation [49]
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Diagnostic features of hypertrophic cardiomyopathy (HCM) on cardiac magnetic resonance imaging (CMR). Features
highlighted include patterns of hypertrophy (top panel), mechanisms for left ventricular outow tract obstruction (second panel), T1 and T2 mapping to identify areas of myocardial brosis or edema without the use of gadolinium contrast
agents (third panel), patterns of late gadolinium enhancement (LGE) pre-ablation (fourth panel) and post-ablation (bottom panel)
Ao aorta, ASA alcohol septal ablation, IVS interventricular septum, LA left atrium, LV left ventricle, LVOT left ventricular outow tract, LVOTG left ventricular outow tract gradient, MV mitral valve, RV right ventricle
and secondary causes of LVH, it is crucially
important to consider a full differential including glycogen or lysosomal storage diseases,
mitochondrial myopathies, inltrative processes, amyloid, sarcoid, and other heritable
cardiomyopathies [2]. Carefully differentiating
the unique etiologies for LVH and LVOTO
using diagnostic criteria and appropriate cardiovascular imaging is essential as management
varies signicantly with each of these cardiovascular conditions [2, 35].
Dynamic outow tract obstruction in HCM is
most commonly related to systolic anterior
motion (SAM) of the mitral valve [50, 51]. SAM
in HCM is a result of narrowing of the LVOT
causing increased ow velocity and decreased
pressure above the anterior mitral leaet (Venturi
effect) [51]. In addition to the Venturi effect,
patients with SAM have primary structural abnormalities of the mitral apparatus including anterior
displacement of the papillary muscles, inward
displacement of the papillary muscles toward one
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