Genetic LVH (often asymmetric septal) with dynamic LVOT obstruction — leading cause of SCD in young athletes.
Also known as: HCM, hypertrophic cardiomyopathy, HOCM, IHSS, asymmetric septal hypertrophy
Overview
Primary myocardial disease defined by unexplained left ventricular hypertrophy (wall thickness ≥15 mm, or ≥13 mm with family history) in the absence of another cardiac or systemic cause. Often features dynamic left ventricular outflow tract obstruction from systolic anterior motion (SAM) of the mitral valve.
Epidemiology
Prevalence ~1 in 500. Autosomal dominant inheritance in most familial cases. Most common cause of sudden cardiac death in young athletes in the US.
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Sarcomere mutations produce myocyte hypertrophy, disarray, and interstitial fibrosis. Asymmetric septal hypertrophy narrows the LVOT, and during systole the anterior mitral leaflet is pulled into the septum (SAM), creating dynamic obstruction and posteriorly-directed mitral regurgitation. Diastolic dysfunction is universal. The disorganized myocardium serves as a substrate for ventricular arrhythmia.
Clinical presentation
Symptoms
Often asymptomatic; HCM detected on screening or after sudden death of a family member
Sudden cardiac death may be the first manifestation
Signs / physical exam
Brisk, bisferiens carotid pulse (spike-and-dome)
Sustained, displaced apical impulse with palpable presystolic component (S4)
Harsh systolic ejection murmur at LLSB — INCREASES with Valsalva strain and standing (decreased preload), DECREASES with squatting or handgrip (increased afterload/preload)
Holosystolic apical murmur of MR from SAM
S4 gallop from forceful atrial contraction into stiff LV
Differential diagnosis
Aortic stenosis — Fixed obstruction — murmur DECREASES with Valsalva; calcified valve on echo
Athlete's heart — Symmetric hypertrophy ≤13 mm, regresses with detraining, normal diastolic function, larger LV cavity
Hypertensive LVH — Symmetric concentric LVH in patient with chronic HTN; usually wall thickness <15 mm
Cardiac amyloidosis — Thickened walls but LOW voltage on ECG, granular sparkling myocardium, pseudo-Q waves; confirm with PYP scan or biopsy
Mitral valve prolapse — Mid-systolic click; murmur shifts with Valsalva but no LVH
Diagnostic workup
Diagnostic criteria
Adult: maximum LV wall thickness ≥15 mm unexplained by loading conditions, or ≥13 mm with affected family member or positive genetic testing. LVOT gradient ≥30 mmHg at rest or ≥50 mmHg with provocation defines obstructive HCM.
Labs
Basic labs; consider genetic testing in proband and cascade screen of first-degree relatives
BNP/NT-proBNP for severity assessment
Cardiac enzymes if chest pain
Imaging
Transthoracic echo — diagnostic; document septal thickness, LVOT gradient at rest and with provocation (Valsalva, exercise), SAM, MR
Cardiac MRI with late gadolinium enhancement — extent of fibrosis and SCD risk stratification, mass quantification, apical HCM identification
ECG — LVH with strain, deep narrow Q waves (septal hypertrophy), giant precordial T-wave inversions in apical HCM (Yamaguchi)
Holter monitor — screen for non-sustained VT (SCD risk factor)
Exercise stress echo to provoke LVOT gradient
Diagnostic algorithm
Maneuver
Preload / Afterload
HCM murmur
Aortic stenosis murmur
MVP click-murmur
Valsalva (strain)
↓ Preload
LOUDER
Softer
Click earlier, murmur longer
Standing from squat
↓ Preload
LOUDER
Softer
Click earlier, murmur longer
Squatting
↑ Preload, ↑ Afterload
Softer
Louder
Click later, murmur shorter
Sustained handgrip
↑ Afterload
Softer
Softer
Click later, murmur louder if MR
Passive leg raise
↑ Preload
Softer
Louder
Click later, murmur shorter
Bedside maneuvers help distinguish HCM from AS and MVP.
Treatment
First-line
Avoid dehydration, alcohol, sudden standing, and intense competitive athletics (per 2020 ACC/AHA — shared decision-making for participation)
Symptomatic obstructive HCM: non-vasodilating beta-blocker (metoprolol, atenolol, propranolol) titrated to symptoms and HR
Non-dihydropyridine CCB (verapamil, diltiazem) if beta-blocker not tolerated
Septal reduction therapy — surgical septal myectomy (preferred in young patients, experienced center) or alcohol septal ablation — for refractory symptoms with LVOT gradient ≥50 mmHg despite optimal medical therapy
ICD placement — Class I for survivors of cardiac arrest or sustained VT; Class IIa for ≥1 major risk factor (family history of SCD, unexplained syncope, LV thickness ≥30 mm, non-sustained VT on Holter, abnormal BP response to exercise, extensive LGE on MRI)
Family screening — first-degree relatives by ECG and echo every 1-3 years from childhood; genetic testing if a pathogenic variant is identified in proband
Heart transplant for end-stage HCM with refractory heart failure
Complications
Sudden cardiac death (annual risk ~1% overall, higher in those with risk factors)
Atrial fibrillation with embolic stroke
Heart failure (obstructive and end-stage burnout/dilated phase)
Infective endocarditis (rare)
Conduction disease after septal ablation/myectomy
PANCE pearls
HCM murmur INCREASES with Valsalva or standing (decreased preload) — opposite of most systolic murmurs.
Mavacamten (EXPLORER-HCM) reduces LVOT gradient and improves symptoms in obstructive HCM.
First-degree relatives need cascade screening — even asymptomatic carriers may carry SCD risk.
Avoid dihydropyridine CCBs (nifedipine, amlodipine), ACE inhibitors, nitrates, and digoxin in obstructive HCM — they worsen LVOT gradient.
Apical (Yamaguchi) HCM: giant precordial T-wave inversions and spade-shaped LV cavity on echo/MRI — Japanese predominance, generally favorable prognosis.
References
AHA/ACC 2020 HCM — 2020 AHA/ACC Guideline for the Diagnosis and Treatment of Patients With Hypertrophic Cardiomyopathy (Ommen et al., Circulation 2020)
ESC 2023 HCM — 2023 ESC Guidelines for the Management of Cardiomyopathies (Arbelo et al., Eur Heart J 2023)
EXPLORER-HCM — Mavacamten for Treatment of Symptomatic Obstructive HCM (Olivotto et al., Lancet 2020)
VALOR-HCM — Mavacamten in Patients with Obstructive HCM Referred for Septal Reduction (Desai et al., JACC 2022)
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