Idiopathic Hypertrophic Subaortic Stenosis (IHSS)

From: 5 minutes consult

Description
Marked ventricular hypertrophy causing variable degree of dynamic outflow tract obstruction
System(s) affected: Cardiovascular
Synonym(s): Hypertrophic obstructive cardiomyopathy (HOCM); Muscular subaortic stenosis

Epidemiology
Predominant age: Most commonly presents in 3rd decade (disease of young adulthood), but occurs from newborns to elderly
Predominant sex: Male = Female
Apical HOCM is a variant seen more often in Japan
Outflow obstruction (defined by echo Doppler) is a strong independent predictor of disease progression to death or severe symptoms.PrevalenceUncommonALERTGeriatric Considerations
Occurrence more frequent with increasing age
Female prevalence greater in this age groupPediatric ConsiderationsMost common cause of sudden death in young athletes

Risk Factors
Sudden death:
Family history of hypertrophic cardiomyopathy (HCM) with premature sudden death
Cardiac arrest (ventricular fibrillation)
Sustained or nonsustained ventricular tachycardia
Unexplained syncope
LV thickness >30 mm
Abnormal exercise BPGenetics
Autosomal dominant (mutations in any 1 of 10 genes) with >50% penetrance
Evidence of disease (usually milder) found in 25% of 1st-degree relatives. Relatives usually do not have outflow obstruction, exhibit only localized hypertrophy, and are asymptomatic.

General Prevention
Avoid strenuous exercise, especially competitive sports, and heavy lifting that induce Valsalva maneuver.
Maintain hydration to avoid volume depletion.
Avoid rapid standing.
Avoid inotropic drugs and diuretics.
Use antitussives for infections accompanied by cough.
ICD recommended for patients at high risk for sudden cardiac death (1)[C].

Pathophysiology
Etiology characterized by systolic anterior motion of mitral valve leaflets with dynamic pressure gradient in subaortic area leading clinically to mitral regurgitation:
Causes diastolic dysfunction with impaired ventricular filling and elevated atrial filling pressures, producing dyspnea.
Eventually, systolic dysfunction with limited cardiac output with exercise, exertional syncope, and secondary left ventricular (LV) hypertrophy
Thickened septum impinging on anterior mitral-valve leaflet during systole, causing outflow obstruction

Commonly Associated Conditions
Mitral regurgitation
Essential HTN
Mitral valve prolapse
Angina pectoris
Atrial fibrillation
Ventricular arrhythmias

[General]
Dyspnea (mainly result of diastolic dysfunction; onset initially exertional): 50–90%
Angina pectoris: 50–90%
Syncope (exertional): 50–90%
Presyncope (exertional): 50–90%
Fatigue: 50–90%
Palpitations: 50–90%
Paroxysmal nocturnal dyspnea: 50%
Double apical impulse owing to prominent atrial system and systolic thrill
Point of maximal impulse displaced laterally
Rapidly rising bifid carotid pulse
Prominent S4 and frequent S3
S2 variable, usually paradoxic, splitting (depending on degree of outflow obstruction)
Harsh systolic crescendo/decrescendo murmur best heard between apex and left sternal border
Murmur: Increases and lengthens with Valsalva maneuver, standing, amyl nitrite inhalation; decreases with sudden squatting, lying down, passive leg raising, isometric handgripALERTPediatric ConsiderationsChildren may be asymptomatic. Evaluation of a heart murmur may disclose IHSS.

Diagnostic Tests and Interpretation
EKG: Common findings (50–90%):
Nonspecific ST-T wave abnormalities
LV hypertrophy
EKG: Less common findings (<50%):
Prominent and abnormal Q waves in anterior precordial and lateral limbs lead, simulating myocardial infarction
P-wave abnormalities indicating left atrial enlargement
Short PR interval with QRS morphology suggesting preexcitation without clear evidence of preexcitation (rare)
Holter findings: Frequent ventricular arrhythmias with up to 25% revealing ventricular tachycardia.
Atrial fibrillation: Late finding, especially older age; sign of poor prognosisImaging
CXR: Variable from normal cardiac size to cardiomegaly, nondiagnostic
ECG:
Asymmetric septal hypertrophy with septal-to-free-wall ratio >1.3:1
Abnormal systolic anterior leaflet motion of mitral valve
LV hypertrophy (especially LV wall thickness >15 mm)
Left atrial enlargement
Small ventricular chamber with hypercontractility
Partial systolic closure of aortic valve in mid systole
Mitral regurgitation/prolapse by Doppler
Continuous-wave Doppler best measures significant dynamic outflow obstruction at rest, >30 mm Hg (2.7 m/s) or provocable (Valsalva maneuver or amyl nitrite) to >30 mm Hg, or nonobstructive ≤30 mm Hg (basal and provocable).
MRI imaging of LV is useful if echo images suboptimal or LV segmental hypertrophy is in unusual location.
Radionuclide: Thallium scintigraphy with stress may reveal positive defects in setting of arteriographically normal coronary arteries.
Cardiac cath/angiocardiography usually is not needed unless other anomalies are suspected (e.g., intrinsic valvular disease or coronary disease).Pathological Findings
Distinctive pattern of LV hypertrophy without anatomic evidence of pressure overload
Dilated atria
Increased LV mass and small chamber sizes
Mural plaque of LV outflow tract
Mitral valve thickening
Fibrosis
Anatomic variants:
Apical form: Not associated with intraventricular gradients
Localized midventricular obstructive form
Disorganization and disarray septal muscle bundles
Abnormal intramural coronary arteries

Differential Diagnosis
Fixed-outflow obstruction: Aortic stenosis
Hypertensive heart disease, especially in elderly
Athletic heart
Amyloid (can diagnose with LV MRI)

Medication (Drugs)
First Line
β-Blockers (atenolol, nadolol, or sustained release metoprolol or propranolol). Disopyramide is added if outflow obstruction is ≥30 mm Hg (2)[B]:
Often decrease outflow obstruction at rest and especially if exertional; no clear evidence that they reduce incidence of sudden death
1/3–2/3 of patients experience symptomatic improvement.
May titrate up to 480 mg/d of propranolol equivalent to obtain clinical effect, provided patient tolerates dose
Disopyramide (1,3)[B]:
If β-blockers do not reduce outflow obstruction to <30>50% gradient reduction and 70% symptomatic improvement with 70% patients on β-blocker at doses of 400–600 mg/d.
Contraindications:
The anticholinergic side effects are dose-related and may limit use.
Can accelerate AV nodal conduction; may increase ventricular rate if atrial fibrillation or flutter develops. This is another reason to continue the β-blocker.
Verapamil, a calcium-channel blocker, may have better effect on exercise performance, may decrease outflow gradient due to depression of cardiac contractility, but vasodilation may counter this. Thus, use cautiously if resting outflow obstruction:
Also improves diastolic relaxation and relieves myocardial ischemia if it decreases contractility.
Contraindications to verapamil:
Major side effects include depression of impulse formation and A-V block, negative inotropism, and vasodilatation, all of which can result in hypotension, shock, pulmonary edema, and death.
Relatively contraindicated for use in patients with increased LV end diastolic pressure, paroxysmal nocturnal dyspnea, orthopnea, and/or sinus node disease and A-V block (unless an appropriate pacing device is present).
Digitalis glycosides are contraindicated except for atrial fibrillation with uncontrolled response.
Amiodarone is preferred for atrial fibrillation because it can control ventricular rate and convert it to sinus rhythm.
Nitrates and sympathomimetic amines (e.g., isoproterenol) are contraindicated except with concomitant coronary heart disease.
Diuretics are relatively contraindicated because they decrease ventricular volume.Second LineDiltiazem may provide benefits similar to those of verapamil, but practitioners have less experience of its use.

Additional Treatment
General Measures
Therapy based on pathophysiology; reduce ventricular contractility and outflow tract obstruction and increase ventricular volume, ventricular compliance, and outflow-tract dimensions
For drug-refractory patients with LV outflow tract obstruction (rest or provocation), probable need for surgical septal myectomy; consider percutaneous alcohol septal ablation or dual-chamber pacing

Surgery/Other Procedures
Ablation or dual-chamber pacing: LV myomectomy is the gold standard (1,2)[B]:
Only in setting of severe symptoms refractory to medical therapy (especially in younger patient) or sequential pacing in those patients with outflow gradient >50 mm Hg (<6.65 kPa), either at rest or with provocation
95% successful in abolishing gradient, with 70% of patients having marked symptomatic improvement for ≥5 years
Alcohol septal ablation can be very successful for gradient reduction to <25 class="doclink" href="http://www.5mcc.com/5mcc/ub/view/5-Minute-Clinical-Consult/116880/all/ub/view/5-Minute-Clinical-Consult/116880/all/Idiopathic_Hypertrophic_Subaortic_Stenosis__IHSS_#6">2).
Dual-chamber pacing in 2 randomized, cross-over trials showed only 25–40% reduction in outflow gradient and 0% reduction in another. Failure to achieve gradient reduction with temporary pacing suggests that permanent pacing is probably not indicated (2).

Follow-Up Recommendations
Intense competitive sports should be restricted in young patients because of the risk of sudden cardiac death (1)[C].
Heavy lifting and intense bursts of activity should be discouraged.ALERT
Sports participation not permitted if any of following are present:
Marked LV hypertrophy
Significant outflow gradient (rest or exercise)
Significant supraventricular and/or ventricular arrhythmias
History of sudden death in relative(s) with hypertrophic cardiomyopathyPatient MonitoringYearly, if symptoms and medical regimens stable

Diet
Control cardiovascular risk factors and normal BMI

Patient Education
Refer for psychosocial counseling if appropriate. (Patient and family may suffer from problems associated with restricted lifestyle and chronic disease.)
Recommend that family learn CPR
Genetic counseling may be appropriate.

Prognosis
Annual mortality rate: 4%/year (sudden death most common reason) in tertiary centers and 1%/year for total patients at non tertiary centers (1).
Chronic illness with restricted lifestyle

Complications
Sudden death
CHF
Arrhythmia
Atrial fibrillation with mural thrombosis formation
Infective mitral endocarditis

ICD-9
425.1 Hypertrophic obstructive cardiomyopathy

SNOMED
360465008 idiopathic hypertrophic subaortic stenosis (disorder)

AUTHOR
Jennifer Lynds, MDJames Chesebro, MD

BIBLIOGRAPHY
Maron BJ, et al. A report of the American College of Cardiology Foundation Task Force on Clinical Expert Consensus Documents and the European Society of Cardiology Committee for Practice Guidelines. J Am Coll Cardiol 2003;42:1687. [PMID:14607462]
Maron BJ. Hypertrophic cardiomyopathy: A systematic review. JAMA 2002;287:1308. [PMID:11886323]
Sherrid MC, et al. Multicenter study of the efficacy and safety of disopyramide in obstructive hypertrophic cardiomyopathy. J Am Coll Cardiol 2005;45(8):1251–1258. [PMID:15837258]

Idiopathic Hypertrophic Subaortic Stenosis (IHSS)
Last updated: November 20, 2009