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Hypertrophic cardiomyopathy: Morphologic variants and the pathophysiology of left ventricular outflow tract obstruction

Hypertrophic cardiomyopathy: Morphologic variants and the pathophysiology of left ventricular outflow tract obstruction
Literature review current through: Jan 2024.
This topic last updated: Sep 06, 2022.

INTRODUCTION — Hypertrophic cardiomyopathy (HCM) is a genetically determined heart muscle disease most often (60 to 70 percent) caused by mutations in one of several sarcomere genes which encode components of the contractile apparatus. (See "Hypertrophic cardiomyopathy: Gene mutations and clinical genetic testing".)

HCM is characterized by left ventricular (LV) hypertrophy of various morphologies, with a wide array of clinical manifestations and hemodynamic abnormalities (figure 1). Depending in part upon the site and extent of cardiac hypertrophy, patients with HCM can develop one or more of the following abnormalities:

LV outflow obstruction (LVOT)

Diastolic dysfunction

Myocardial ischemia

Mitral regurgitation

These structural and functional abnormalities can produce a variety of symptoms, including:

Fatigue

Dyspnea

Chest pain

Palpitations

Presyncope or syncope

In broad terms, the symptoms related to HCM can be categorized as those related to heart failure (HF), chest pain, or arrhythmias. Patients with HCM have an increased incidence of both supraventricular and ventricular arrhythmias and are at an increased risk for sudden cardiac death. (See "Hypertrophic cardiomyopathy in adults: Supraventricular tachycardias including atrial fibrillation" and "Hypertrophic cardiomyopathy: Risk stratification for sudden cardiac death".)

A resting or exercise-provoked LVOT gradient is present in most patients with HCM (70 percent). Significant LVOT obstruction at rest, present in 20 to 30 percent, is an independent predictor of poor prognosis in patients with HCM. Four major approaches are available for treatment of LVOT obstruction in patients with HCM:

Pharmacologic therapy

Septal myectomy

Alcohol (ethanol) septal ablation

Dual-chamber pacing (which has only a limited role)

This topic will review the pathophysiology of the LVOT obstruction in HCM as well as the morphologic variants of HCM. The clinical manifestations, diagnosis, evaluation, natural history, and treatment of this disorder are discussed separately. (See "Hypertrophic cardiomyopathy: Clinical manifestations, diagnosis, and evaluation" and "Hypertrophic cardiomyopathy: Natural history and prognosis" and "Hypertrophic cardiomyopathy: Management of patients without outflow tract obstruction" and "Hypertrophic cardiomyopathy: Management of patients with outflow tract obstruction".)

PATHOPHYSIOLOGY AND EVOLUTION OF LVOT OBSTRUCTION — The identification of factors that contribute to the development of LVOT obstruction was initially facilitated by the advent of two-dimensional echocardiography. Subsequently, imaging findings from both echocardiography and cardiovascular magnetic resonance (CMR) imaging have been correlated with hemodynamic and cineangiographic findings. (See "Hypertrophic cardiomyopathy: Clinical manifestations, diagnosis, and evaluation", section on 'Cardiac catheterization'.)

Mechanism of LVOT obstruction — Subaortic (ie, LVOT) obstruction in HCM is due to systolic anterior motion (SAM) of the mitral valve contacting the ventricular septum in midsystole (movie 1). This creates mechanical impedance to blood flow as it exits the heart, resulting in a pressure gradient between the LV cavity and the aorta. Increased LV systolic pressures are recorded just below the level of the mitral valve leaflet-septal coaptation, while the systolic pressures above this point are similar to those in the aorta. The presence of SAM-septal contact at rest or with provocation will produce a pressure gradient of 30 mmHg or greater.

There are multiple morphologic alterations of the LVOT area and mitral valve that contribute to the development of SAM-septal contact, including:

Narrowed diameter of the LVOT due to increased septal wall thickness

Apically positioned papillary muscles that tether the mitral valve plane toward the ventricular septum

Elongated anterior leaflet of the mitral valve

As high-velocity blood is ejected from the LV during systole, the mitral valve is pulled or "dragged" toward the ventricular septum (Venturi effect), creating outflow tract obstruction [1]. SAM usually involves only the anterior mitral valve leaflet, but the posterior leaflet and chordal structures may also be involved. When SAM of the mitral valve occurs, a gap may be present between the anterior and posterior mitral leaflets, which often produces posteriorly directed mitral regurgitation (MR) and which may also contribute to symptoms. (See 'Development of mitral regurgitation' below and "Hypertrophic cardiomyopathy: Clinical manifestations, diagnosis, and evaluation", section on 'LVOT obstruction'.)

A substantial body of echocardiographic, hemodynamic, and cineangiographic evidence in patients with a resting LVOT gradient >50 mmHg associated with SAM and MR has yielded the following [1]:

The magnitude of LVOT pressure gradient measured at cardiac catheterization correlates well with Doppler velocities and with the duration of SAM-septal contact. For this reason, there is usually no compelling rationale for patients to undergo catheterization to assess outflow tract gradients, unless the measurements on echocardiographic assessment are ambiguous. (See "Hypertrophic cardiomyopathy: Clinical manifestations, diagnosis, and evaluation", section on 'Diagnostic evaluation'.)

LVOT obstruction can occur associated with any septal wall thickness. In patients with normal or mild increases in septal wall thickness, the mechanism for outflow obstruction is usually due to elongated anterior mitral valve leaflet. This is clinically relevant since those patients who are symptomatic despite drug therapy with elongated mitral valve leaflet should be considered for surgical myectomy with limited septal resection with mitral valve repair (ie, plication), rather than percutaneous approach with alcohol septal ablation [2]. (See "Hypertrophic cardiomyopathy: Management of patients with outflow tract obstruction".)

There is often an area of scarring at the site of repetitive SAM mitral-septal contact (contact lesion).

Although some patients with LVOT gradients of >50 mmHg have mild or no symptoms, in most patients, the magnitude of the gradient relates to symptoms and exercise limitation, which provides the rationale for treatments aimed at gradient reduction. Factors that aggravate LVOT obstruction may increase or induce symptoms of exercise limitation, syncope, and/or ischemic chest pain [3]. Conversely, therapies that reduce LVOT obstruction alleviate symptoms.

Development of mitral regurgitation — In addition to producing subaortic obstruction, SAM of the mitral valve also results in varying degrees of posteriorly directed MR due to a gap between the mitral leaflets. There are several variables which influence MR, resulting in great interindividual differences in MR at comparable degrees of SAM of the mitral valve; nonetheless, there is a correlation between the severity of MR and the LVOT gradient.

In a study of 23 patients with obstructive HCM undergoing surgery, differences in mitral valve leaflet length and mobility appeared to influence the extent of MR [4]. SAM produced greater MR if the posterior leaflet was limited (by its chordal and papillary muscle connections) in its ability to move anteriorly and participate in SAM and to coapt effectively (figure 2).

In one study of 93 patients without independent mitral valve disease, the mean LVOT gradient in those with trivial, mild, moderate, and severe MR was 23, 44, 70, and 104 mmHg, respectively [5].

In contrast to posteriorly directed MR, the presence of a central or anteriorly directed MR jet suggests the presence of intrinsic mitral valve disease and should be evaluated further with transesophageal echocardiography, particularly if the patient is a candidate for invasive septal reduction therapy, since this may require repair of the mitral valve at the time the outflow tract gradient is relieved.

DYNAMIC NATURE OF LVOT OBSTRUCTION — There can be significant variability in the degree of LVOT obstruction in HCM. LVOT obstruction at rest is a consistent finding in some patients with HCM (waveform 1 and waveform 2) [1]. In others, there is no evidence of LV outflow obstruction at rest, but outflow tract obstruction which develops with certain provocative conditions (waveform 3).

A variety of maneuvers and medications can result in either induction/increase or reduction/elimination of LVOT obstruction.

Inducing/increasing LVOT obstruction – LVOT obstruction can be induced or increased by maneuvers that reduce preload (chamber size), decrease afterload, or increase LV inotropy.

Preload is reduced by dehydration, sudden adoption of the upright posture, the Valsalva maneuver, and certain medications (eg, diuretics, dihydropyridine calcium channel blockers, etc).

Conditions associated with increased inotropy include fever, exercise, isoproterenol/dobutamine infusion, or postextrasystolic potentiation (ie, increased inotropy after an extrasystolic beat). The increased LVOT gradient and reduced aortic pulse pressure caused by postextrasystolic potentiation is known as the Brockenbrough sign. (See "Hypertrophic cardiomyopathy: Clinical manifestations, diagnosis, and evaluation", section on 'Cardiac catheterization'.)

Reducing/eliminating LVOT obstruction – LVOT obstruction can be reduced or eliminated by maneuvers that increase chamber size or medications which reduce inotropy.

Squatting or laying supine with legs elevated will increase venous return and preload, whereas isometric handgrip exercise will increase afterload; all of these maneuvers result in an increased LV cavity size and reduced LVOT obstruction.

Drugs that reduce inotropy (eg, beta blockers, nondihydropyridine calcium channel blockers [specifically diltiazem and verapamil], and disopyramide) also diminish obstruction.

Notably, LVOT gradients in HCM are dynamic, characterized by marked spontaneous changes under basal conditions, which can result in varying gradients from zero to very high values. LVOT gradients are also influenced by a variety of factors that alter LV contractility and loading, including exercise, level of hydration, ingestion of alcohol, or heavy meals (waveform 4) [6-8].

HCM VARIANTS — In addition to the classic description of HCM with or without LVOT obstruction, a variety of other HCM variants exist, some of which are managed quite differently than classic HCM.

Midcavity obstructive HCM — Midcavity (ie, midventricular) obstruction is an important morphologic variant of HCM, which arises from different anatomic and hemodynamic circumstances [9,10]. Perhaps the most common HCM morphology associated with midcavitary obstruction occurs due to the apposition of septum and lateral wall in the context of a small, hyperdynamic cavity. In these patients the intracavitary "gradient" does not usually produce clinically significant symptoms, although beta blockers appear to be the most reasonable therapy in symptomatic patients.

Midcavity obstruction in HCM can also be due to the systolic apposition of hypertrophied papillary muscle and lateral wall at the level of the mid-LV, producing two distinct LV chambers (ie, proximal and distal with an "hour glass" shape LV), and associated with an LV apical aneurysm of varying size [10]. This phenotypic subgroup of HCM patients is uncommon, presenting in approximately 2 percent of patients with HCM [11]. (See 'Midcavity obstruction with LV apical aneurysm' below.)

Another cause of midcavitary obstruction is anomalous insertion of the anterolateral papillary muscle directly into the anterior leaflet of the mitral valve (in the absence of chordae tendineae). In this morphologic abnormality, the anomalous papillary muscle is often apically displaced and along with the anterior leaflet makes contact with the septum at midsystole to produce midcavitary obstruction [11,12]. In this situation, patients may have limiting symptoms similar to patients with typical isolated LVOT obstruction. Clinical examination reveals the typical signs of dynamic obstructive HCM (eg, a systolic murmur that accentuates with exercise or a change to an upright posture). (See 'Dynamic nature of LVOT obstruction' above and "Hypertrophic cardiomyopathy: Clinical manifestations, diagnosis, and evaluation" and "Auscultation of cardiac murmurs in adults" and "Physiologic and pharmacologic maneuvers in the differential diagnosis of heart murmurs and sounds" and 'Midcavity obstruction with LV apical aneurysm' below.)

The diagnosis of midcavity obstructive HCM can be made with echocardiography, left ventriculography, or cardiovascular magnetic resonance (CMR) [13]. Imaging in isolated midcavity HCM shows absence of systolic anterior motion of the mitral valve and a narrowed mid-LV cavity with or without an LV apical aneurysm. High Doppler velocities, indicating a midcavity gradient, are recorded at the level of the papillary muscle. Color Doppler demonstrates a mosaic pattern at this level, confirming that the level of obstruction is below the mitral valve leaflets. In some patients, the midcavity obstruction is associated with an apical LV aneurysm, which may be the site of origin of a rapid monomorphic ventricular tachycardia and clot formation (image 1).

Patients with HCM and midcavitary obstruction from anomalous papillary muscle insertion, with or without associated LVOT obstruction, and who have advanced HF symptoms refractory to atrioventricular (AV) nodal blocking agents (ie, beta blockers and nondihydropyridine calcium channel blockers), should be evaluated for invasive septal reduction therapy. In most cases, the identification of anomalous papillary muscle insertion sways the decision toward surgical myectomy rather than alcohol septal ablation, since only surgery can address the morphologic abnormality of midcavitary obstruction. In addition, advance knowledge of the anomalous papillary muscle insertion is crucial as knowing this information may change operative strategy to an extended myectomy and adjunctive papillary muscle shaving in order to provide the patient complete relief of outflow tract obstruction. (See "Hypertrophic cardiomyopathy: Management of patients with outflow tract obstruction".)

Midcavity obstruction with LV apical aneurysm — Some patients with HCM and midcavity obstruction develop thin-walled scarred LV apical aneurysms. These patients represent a different phenotype than apical HCM in which the apex is the primary site of LV hypertrophy. (See 'Apical HCM' below.)

Patients with HCM and LV apical aneurysms are at increased risk of ventricular arrhythmias (including sudden cardiac death [SCD]), thromboembolic events, and advanced HF. The junction of the thin-walled scarred apical aneurysm and the LV myocardium provides a nidus for ventricular tachyarrhythmias and thrombus formation. For this reason, patients with HCM and an apical aneurysm appear to be at increased risk for sudden death events and stroke. There is no evidence that these apical aneurysms rupture or expand in size over time. In addition, these patients can also experience limiting HF symptoms, although this is often a result of developing systolic dysfunction rather than a consequence of midcavitary obstruction. Rarely, patients with HCM and an apical aneurysm will also have coexistent subaortic obstruction due to SAM-septal contact; in such patients, the clinical examination will demonstrate typical signs of dynamic obstructive HCM (eg, a systolic murmur that accentuates with exercise or a change to upright posture).

The diagnosis of midcavity obstruction with apical aneurysm is typically made with echocardiography, left ventriculography, or CMR [13,14]. In one series, echocardiography detected an apical aneurysm in only 16 of 28 (57 percent) patients with apical aneurysm, but CMR detected the aneurysm in all 28 patients [15].

In one series of 93 patients with HCM with apical aneurysm followed for a mean of four years, 20 experienced an SCD event rate of 4.7 percent per year and a nonfatal embolic event rate of 1.1 percent per year. HCM-related deaths and life-threatening events due to apical aneurysm occurred at a rate of 6.4 percent per year, which was three times greater than the rate in patients with HCM without aneurysms [16].

In a recent series of 160 patients with HCM with apical aneurysm followed for a mean of six years, 9 percent experienced an SCD event (1.7 percent per year), and 24 percent of patients had stroke or thrombus identified in the apical aneurysm. When compared with patients who had an aneurysm <2 cm, patients with an aneurysm ≥2 cm had a higher risk of SCD and stroke events [17].

For these reasons, identification of this unique HCM phenotype with LV apical aneurysm should prompt consideration for primary prevention implantable cardioverter-defibrillator (ICD) and anticoagulation for stroke prophylaxis. Catheter ablation has been used successfully to mitigate or eliminate ventricular tachycardia in patients with HCM and an apical aneurysm who have experienced multiple episodes of sustained ventricular arrhythmias [16,18]. Ultimately, management recommendations should be carried out implementing a shared decision-making strategy with the patient and the managing cardiologist, with an understanding of the inherent limitations of risk stratification applied to an uncommon cohort of patients. (See "Hypertrophic cardiomyopathy: Risk stratification for sudden cardiac death", section on 'Established major risk markers'.)

Apical HCM — Apical HCM is another uncommon morphologic variant of HCM in which the hypertrophy of the myocardium predominantly involves the apex of the LV [19,20]. The majority of these patients do not have subaortic LVOT obstruction but may have midcavity obstruction [15,20]. (See 'Midcavity obstructive HCM' above.)

The prevalence of apical HCM has been difficult to quantify. Some data suggest significant regional variation, though the data are not compelling [15,21-25].

Most patients with apical HCM present with no or mild symptoms, although presentation with angina, HF, myocardial infarction, atrial fibrillation (AF), or ventricular fibrillation has been reported [15,20]. AF has been reported in 12 to 25 percent of patients with apical HCM, similar to the rate in general cohorts of patients with HCM [20,26]. Symptoms are often mild, but a minority of patients have refractory symptoms of dyspnea, angina, and presyncope or syncope due to diastolic dysfunction and low cardiac output. Apical myectomy has been reported as a potential option in select patients with low stroke volume (low output HF) due to very small LV cavity from extensive distal hypertrophy. (See "Hypertrophic cardiomyopathy: Management of patients with outflow tract obstruction".)

Typical features of apical HCM include [21]:

Audible or palpable "fourth heart sound," reflecting impaired LV relaxation

"Giant" negative T waves on electrocardiogram, particularly in the left precordial leads

"Spade-like" configuration of the LV cavity at end-diastole on imaging

Associated apical wall motion abnormalities which may include hypokinesis and aneurysm formation [20]

The diagnosis of apical HCM can be made with echocardiography, left ventriculography, computed tomography, or most accurately with CMR [15,27,28]. Multimodality imaging with several of the available techniques can provide the most accurate assessment of the phenotypic anatomy [29].

The approach to the management of apical HCM is the same as for most patients with HCM. Symptomatic patients are initially treated with medical therapy; however, since nearly all patients with apical HCM do not have evidence of LVOT or midcavity obstruction, septal reduction therapy is almost never an option in those patients [21]. Risk stratification for ventricular tachyarrhythmias and SCD is the same as for other patients with HCM, but apical HCM is typically associated with a low risk and almost never requires ICD placement for primary prevention [30]. (See "Hypertrophic cardiomyopathy: Management of patients with outflow tract obstruction".)

The apical variant has a better mortality prognosis than other forms of HCM but is still associated with a relatively high rate of important cardiac events. In one series of 105 patients with apical HCM (mean age 41 years) followed for a mean of 13.6 years at a referral center in Canada, the total cardiovascular mortality rate was 1.9 and overall estimated survival was 95 percent at 15 years [20]. However, 30 percent of patients experienced a serious cardiac complication, most commonly AF (12 percent) or a myocardial infarction (10 percent). In a different cohort of 306 Korean patients with apical HCM, AF was seen in 77 patients (25 percent) [26]. (See "Hypertrophic cardiomyopathy: Natural history and prognosis".)

Right ventricular obstruction — A very small number of HCM patients demonstrate obstruction to flow on the right ventricular (RV) outflow tract. This is usually a result of midsystolic contact of prominent right ventricular muscle bundles located in the RV outflow tract region (figure 1). RV obstruction in HCM is very uncommon but can be identified using echocardiography with 2D and Doppler pulse wave through the RV outflow tract. If present, RV obstruction can be a cause of symptoms such as exertional dyspnea similar to left-sided obstruction. The approach to treatment is similar to the standard approach to treatment for patients with HCM and LVOT obstruction. Patients who remain symptomatic after a trial of medical therapy with AV nodal blocking agents can be considered for surgical intervention to relieve right-sided obstruction, usually by resection of accessory RV muscle bundles in the outflow tract area [31,32]. (See "Hypertrophic cardiomyopathy: Management of patients without outflow tract obstruction" and "Hypertrophic cardiomyopathy: Management of patients with outflow tract obstruction".)

Obstructive HCM in older adults — Although the majority of patients with HCM patients are diagnosed at a relatively young age (average 44 years old), HCM can also be diagnosed initially in patients of advanced age. Regardless of the age at diagnosis, patients with increased LV wall thickness and LVOT obstruction may develop symptoms. The approach to the treatment of symptomatic LVOT obstruction is the same regardless of age (ie, initial medical therapy, followed by septal reduction therapy if symptoms persist), although older patients are more likely to have comorbidities (eg, coronary heart disease, aortic stenosis, etc) that may also require treatment. (See "Hypertrophic cardiomyopathy: Management of patients without outflow tract obstruction" and "Hypertrophic cardiomyopathy: Management of patients with outflow tract obstruction".)

In data from the Framingham Heart Study, among 1862 unrelated individuals of advanced age (mean 60 years old) who did not have hypertension or aortic valve disease, 3 percent had unexplained increase in LV wall thickness [33]. Sarcomeric contractile protein gene mutations were found in only 18 percent of these individuals. In another study of 31 individuals with late-onset HCM, who first developed symptoms at an average age of 60 years, mutations in cardiac myosin binding protein-C, troponin I, and alpha cardiac myosin heavy chain genes caused onset of HCM later in life, in contrast to familial early-onset HCM which results more commonly from defects in cardiac beta-myosin heavy chain, cardiac troponin T, and alpha tropomyosin genes [34]. In addition, the likelihood of identifying a mutation may be lower in late-onset HCM than in earlier onset HCM [35,36]. (See "Hypertrophic cardiomyopathy: Natural history and prognosis", section on 'Late onset disease'.)

The following clinical features have been noted [37-40]:

In comparison to younger patients, individuals with late onset disease tend to have milder hypertrophy that is localized to the anterior interventricular septum, and an ovoid or ellipsoid (rather than crescentic) LV cavity. Hypertension is more frequent than in younger subjects, but its role in triggering the development of hypertrophy is unclear.

Systolic anterior motion of the mitral valve and LVOT gradients in older patients tend to be associated with very narrow LVOTs, anterior displacement of the entire mitral valve apparatus, and a larger area of contact between the mitral valve leaflet and the septum than in younger subjects with HCM.

Obstructive HCM in older adults is sometimes complicated by aortic sclerosis or stenosis. Severe aortic stenosis may mask underlying LV obstruction. As a result, echocardiography may show calcific aortic stenosis in association with a markedly hypertrophied and asymmetric LV. (See "Aortic valve sclerosis and pathogenesis of calcific aortic stenosis".)

A characteristic feature of some cases of late onset disease is increased angulation of the aorta with respect to the long axis of the LV. This may reflect age-related "shrinkage" of the heart resulting in an upper septal bulge (sigmoid septum) and narrowing of the LVOT. These changes occur in older adults with and without HCM. This sigmoid septal morphology is less commonly associated with a mutation than other HCM morphologic variants.

The clinical outcome of patients diagnosed with HCM at advanced age appears to be similar to outcomes in the general population. In a study of 428 older patients with HCM (presenting for clinical evaluation at ≥60 years of age) who were followed for close to five years, the risk for disease-related morbidity and mortality, including sudden death, even with conventional risk factors was very low. In this population, non-HCM comorbidities appear to have a greater impact on survival [41]. (See "Hypertrophic cardiomyopathy: Natural history and prognosis".)

Sigmoid septal morphology — A sigmoidal configuration to the basal septum is observed with increased frequency in older individuals and may occur as part of the cardiac remodeling associated with aging [42]. However, a sigmoid shaped septum is still compatible with a diagnosis of HCM but only if the basal septal wall thickness measurement is increased. [36]. Additionally, the presence of systolic anterior motion with septal contact resulting in an LVOT gradient (ie, subaortic obstruction) strongly suggests a diagnosis of HCM in patients with is isolated sigmoid septal hypertrophy [42].

Among patients with HCM, this morphologic subtype appears to be less commonly associated with a mutation than other morphologic variants. Among 382 unrelated patients with HCM, a sigmoid septum was observed in 67 percent of the 126 patients diagnosed at or after 50 years of age as compared with 38 percent of younger patients. Only 23 percent of older patients had an identifiable mutation as compared with 44 percent of younger patients. Among 181 patients with a sigmoid septum, only 8 percent were genotype positive as compared with 79 percent of 131 patients with reverse curvature HCM.

End-stage hypertrophic cardiomyopathy — Progressive LV wall thinning occurs in approximately 5 to 15 percent of patients with HCM [43-46]. This is associated with deterioration in LV diastolic and systolic function, which is initially presaged by loss of long-axis contractile function prior to more generalized decrease in LV function and dilation. When wall thinning is marked, it is usually associated with replacement fibrosis and a significant decrease in systolic function. This stage has been termed "end-stage" or "burned out" HCM and is seen in up to 5 percent of patients from large cohorts (figure 3). End-stage HCM patients are at increased risk for HF progression and sudden death risk, raising important management considerations in these patients including close longitudinal follow-up with earlier consideration to advanced HF therapies and ICD for primary prevention. (See "Hypertrophic cardiomyopathy: Natural history and prognosis", section on 'HCM with LV systolic dysfunction (ejection fraction <50 percent)'.)

INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.

Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)

Basics topic (see "Patient education: Hypertrophic cardiomyopathy in adults (The Basics)")

Beyond the Basics topic (see "Patient education: Hypertrophic cardiomyopathy (Beyond the Basics)")

SUMMARY AND RECOMMENDATIONS

Prevalence of outflow tract obstruction – Left ventricular outflow tract (LVOT) obstruction (≥30 mmHg) at rest is present in up to 30 percent of patients with hypertrophic cardiomyopathy (HCM), while an additional 30 percent have no evidence of LVOT obstruction at rest but develop outflow tract obstruction with provocation. LVOT obstruction is a dynamic process and can be induced or increased by maneuvers that reduce preload (chamber size), decrease afterload, or increase LV inotropy. (See 'Introduction' above and 'Dynamic nature of LVOT obstruction' above.)

Typical mechanism of outflow tract obstruction – Subaortic obstruction in HCM is due to systolic anterior motion (SAM) of the mitral valve with ventricular-septal contact occurring in midsystole. The high velocity of blood flow out of the LV during systole pulls the mitral valve leaflet toward the ventricular septum (Venturi effect), creating mechanical impedance to blood flow and a pressure gradient between the LV and aorta as well as posteriorly directed mild to moderate mitral regurgitation (MR). A combination of morphologic factors contribute to SAM-septal contact, including narrow outflow tract area, abnormal positioning of the mitral valve plane toward the septum, and elongated anterior mitral valve leaflet. (See 'Mechanism of LVOT obstruction' above.)

Morphologic variants

Midcavity obstruction – Midcavity (ie, midventricular) obstruction is an uncommon morphologic variant of HCM, typically due to the systolic apposition of hypertrophied papillary muscle and lateral wall at the level of the mid-LV, in the setting of a small cavity and hyperdynamic function. Some patients develop midcavity obstruction due to anomalous papillary muscle insertion directly into the mitral valve, which will make contact with septum and lateral wall during midsystole. Patients with HCM and midcavity obstruction due to anomalous papillary muscle insertion who develop medically refractory heart failure (HF) symptoms should be evaluated for myectomy rather than alcohol septal ablation, since only surgery can address this unique morphologic issue. (See 'Midcavity obstructive HCM' above.)

-Apical aneurysm Some patients with HCM and midcavity obstruction develop thin-walled scarred LV apical aneurysms, a high-risk phenotype, associated with increased risk for sudden death events, thromboembolic events, and advanced HF symptoms. Identification of this unique HCM phenotype with LV apical aneurysm should prompt consideration for primary prevention implantable cardioverter-defibrillator (ICD), anticoagulation for stroke prophylaxis, and, in select patients, catheter ablation to treat recurrent sustained episodes of ventricular tachycardia. (See 'Midcavity obstruction with LV apical aneurysm' above.)

Apical hypertrophy – Apical HCM is another uncommon morphologic variant of HCM in which the hypertrophy of the myocardium predominantly involves the apex of the LV. These patients do not have subaortic LVOT obstruction but may have midcavity obstruction from apposition of septum and lateral wall in the setting of a small hyperdynamic cavity. The approach to the management of apical HCM is the same as for most patients with HCM. (See 'Apical HCM' above.)

Hypertrophic cardiomyopathy in older adults – Although the majority of HCM patients are diagnosed at a relatively young age (average 44 years old), HCM can also be diagnosed initially in patients of advanced age. Regardless of the age at diagnosis, patients with increase LV wall thickness and LVOT obstruction may develop symptoms. The approach to the treatment of symptomatic LVOT obstruction is the same regardless of age (ie, initial medical therapy, followed by septal reduction therapy if symptoms persist), although older patients are more likely to have comorbidities (eg, coronary heart disease, aortic stenosis, etc) that may also require treatment. (See 'Obstructive HCM in older adults' above.)

End-stage hypertrophic cardiomyopathy – End-stage HCM is characterized by thinning of the ventricular walls and deterioration in LV diastolic and systolic function. (See 'End-stage hypertrophic cardiomyopathy' above.)

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Topic 4947 Version 33.0

References

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