Hypertrophic Cardiomyopathy

Meet the patient

A 19-year-old county-level sprinter collapses 200 metres into a race. He is back on his feet in seconds, but his coach noticed he was "pale and gone" for a moment. In the department he looks well; a rough ejection systolic murmur sits at the left sternal edge, and his ECG shows voltage criteria for left ventricular hypertrophy with lateral T-wave inversion.[1][4]

Two exam questions are now live, and the rest of the page exists to answer them: is this HCM or athlete's heart? (the murmur on Valsalva and the echo decide it), and if it is HCM, is he at risk of dying on the track? (the SCD cluster and the ICD decision decide it). Hold those two and the topic slots into place.[1][4]

What HCM is — and the 15-13-z2 wall-thickness rule

HCM is unexplained left ventricular hypertrophy in a non-dilated ventricle, once you have excluded every other cause that could produce that much wall. Hypertension, aortic stenosis, athletic remodelling and amyloidosis all thicken the wall; HCM is the diagnosis that remains when none of them explains it.[1][4]

The wall-thickness thresholds are a number rule worth memorising once:[1]

The 15-13-z2 rule. Fifteen millimetres or more in any LV segment in an adult; thirteen millimetres or more in a first-degree relative of a known case; a z-score of 2 or more in a child. Measure by echo, cardiac MRI or CT — the modality changes only the resolution, never the number.[1][2]

The disease has changed its name four times, and every name still surfaces in MCQ stems. HCM was hypertrophic obstructive cardiomyopathy (HOCM), then idiopathic hypertrophic subaortic stenosis (IHSS), then asymmetric septal hypertrophy (ASH). The modern unifier is HCM, qualified obstructive or non-obstructive — because the two halves diverge sharply in prognosis and treatment.[1]

Etymology for viva gold: sarcomere, from Greek sarx (flesh) plus meros (part) — the contractile unit of the myocyte; hypertrophy, from hyper (over) plus trophē (nourishment) — growth in size, not in number. HCM is a disease of the sarcomere that hypertrophies the wrong way.[1]

The clinical skill is not naming the disease. It is three judgements, in order: (1) is it HCM or a mimic (athlete's heart, hypertensive heart, amyloid); (2) what is the SCD risk; and (3) medical therapy, septal reduction, or ICD.[1]

Four axes — and the one that decides therapy is obstruction

Classify HCM along four axes, but only obstruction changes what you prescribe. The other three — morphology, genotype, phase — refine the picture; obstruction writes the script.[1]

[1]

Morphology runs from reverse-curve (asymmetric septal) — the classic, highest sarcomere yield, most obstruction — through neutral (concentric) and sigmoid septum (commonest in the elderly, often non-obstructive) to apical HCM (spade-shaped cavity, giant negative T waves in V2 to V6, common in Japan) and mid-cavitary obstruction with apical aneurysm in a minority.[1]

Genotype splits sarcomere-positive HCM — 40 to 60 percent of unselected cases and up to 70 percent in family studies; younger onset, more fibrosis, higher arrhythmia risk — from sarcomere-negative HCM, which is usually milder and later. MYH7 (beta-myosin heavy chain) and MYBPC3 (myosin-binding protein C) carry the majority of positive cases; TNNT2 is the rare one to remember, because it classically gives mild hypertrophy with disproportionate SCD risk.[1]

Clinical phase runs from the hyperdynamic or obstructive phase of most symptomatic young adults to the burned-out (dilated) phase — about 5 to 10 percent, over decades, develop LV dilation, wall thinning and systolic dysfunction (EF under 50 percent) that looks like DCM and is treated like it.[1]

The histology triad — disarray, fibrosis, small-vessel disease

Whatever the gene, every HCM heart shares one histology, and the three lesions map one-to-one onto the three clinical threats. Learn the triad as a cluster and the symptoms explain themselves.[4]

[1] [4]

• Myocyte disarray is the histological hallmark — myocytes oriented obliquely and chaotically with abnormal intercellular connections, instead of the parallel array of normal myocardium. Disarray is the structural substrate for re-entry and ventricular arrhythmia.[4]
• Interstitial fibrosis is increased collagen that stiffens the myocardium (diastolic dysfunction) and shows as late gadolinium enhancement (LGE) on cardiac MRI. LGE exceeding 15 percent of LV mass predicts SCD and heart failure.[1]
• Intramural small-vessel disease — medial thickening of intramural coronary arterioles creates a demand-supply mismatch that drives microvascular ischaemia: angina with angiographically normal coronaries, progressive replacement fibrosis, and the scar that hosts arrhythmia.[1]

The one-line cluster: disarray kills, fibrosis stiffens, small vessels ache. Disarray is the arrhythmia substrate; fibrosis is the diastolic and scar substrate; small-vessel disease is the angina substrate.[1][4]

Why the septum pulls the mitral leaflet in — Venturi plus drag equals SAM

In obstructive HCM the hypertrophied basal septum narrows the outflow tract, and two coupled forces then drag the anterior mitral leaflet into it. That drag is systolic anterior motion (SAM), and SAM is the whole of the obstructive phenotype.[1]

Two mechanisms, working together:[1]

1. The Venturi effect — high-velocity flow through the narrowed LVOT generates a lateral suction on the leaflet.
2. Flow-drag (pushing) forces — the ejected bloodstream directly shoves the leaflet toward the septum; modern mechanical modelling weights this above Venturi.[1]

SAM has three consequences, and they explain every bedside sign: (1) it narrows the LVOT further (dynamic obstruction); (2) the leaflet cannot coapt, so a posteriorly directed jet of mitral regurgitation appears; (3) the obstruction becomes dynamic — it swings beat-to-beat with preload, afterload and contractility.[1]

That is the whole logic of the murmur. Anything that drops preload or afterload (Valsalva strain, standing, nitrates, dehydration) widens the gradient and makes the murmur louder; anything that raises them (squatting, passive leg raise, handgrip) shrinks it. And anything that boosts contractility (digoxin, dobutamine, exercise) does the same damage as a nitrate.[1]

The diastolic half of the disease matters just as much. Hypertrophy, fibrosis and abnormal calcium handling slow relaxation, raise LV end-diastolic pressure, and enlarge the left atrium — which is why atrial fibrillation is so poorly tolerated: the stiff ventricle depends on the atrial kick. Dyspnoea, orthopnoea and a raised JVP appear with a normal or hyperdynamic ejection fraction.[1]

Microvascular ischaemia supplies the third strand: thick myocardium outstrips its capillary bed, the arterioles are themselves diseased, and the patient gets exertional chest pain and dynamic ST changes with clean epicardial coronaries. Disarray plus scar plus ischaemia is the substrate for ventricular tachycardia and fibrillation — and so for sudden cardiac death.[1]

The single equation that links the Doppler velocity to the gradient is the simplification of Bernoulli: peak gradient (in mmHg) is four times the peak velocity squared. A velocity of 3 m/s gives a gradient of 36 mmHg. It is also why contractility up or preload down worsens the gradient, and why beta-blockade and volume loading shrink it.[1]

The murmur that moves with Valsalva — left sternal edge, louder on standing

The murmur of obstructive HCM is an ejection systolic sound at the left sternal edge, and it does the opposite of aortic stenosis on every manoeuvre. That single sentence is the most testable bedside fact in the disease.[1]

The murmur is rough, crescendo-decrescendo, heard at the left sternal edge and apex, and it does not radiate to the carotids — the obstruction is dynamic and subvalvular. A separate pansystolic, blowing mitral regurgitation murmur at the apex, radiating to the axilla often rides alongside it.[1]

The manoeuvre grid is the viva centrepiece — reproduce it exactly:[1]

[1]

One-line discriminator beneath the table: Valsalva louder and squatting softer means HCM; Valsalva unchanged or softer and squatting louder means aortic stenosis; a click that moves earlier on Valsalva means MVP. A small VSD rounds out the differential — a pansystolic murmur at the lower left sternal edge that rises with handgrip and ignores Valsalva, often with a thrill.[1]

The pulse and apex finish the bedside picture:[1]

• Pulse — jerky, brisk upstroke; a bisferiens pulse (double systolic impulse) may be felt in obstruction. Volume is normal, unlike the pulsus parvus et tardus of aortic stenosis.
• Apex — classically a double or triple apical impulse: a pre-systolic outward movement (vigorous atrial contraction into the stiff ventricle — the palpable S4) followed by the systolic thrust.
• Heart sounds — an S4 gallop is common (stiff ventricle); a paradoxically split S2 may appear from prolonged LV ejection in severe obstruction.
• Thrill — a systolic thrill at the left sternal edge in severe obstruction.[1]

[1]

Athlete or disease? The 12-to-13 mm grey zone and the amyloid trap

A systolic murmur with LVH on ECG is not always HCM, and the two traps that end careers — or end patients — are athlete's heart and cardiac amyloidosis. Get these right first; everything else is a refinement.[1][4]

The athlete's-heart grey zone is 12 to 13 mm of wall thickness. Below it, physiological remodelling is far more likely; above 15 mm, HCM dominates. Between 12 and 13 mm is where careers are won and lost, and six discriminators settle it:[1]

• LV size — athlete's heart has a mildly enlarged LV (end-diastolic diameter over 54 mm in men); HCM keeps the cavity small.
• LA size — normal in the athlete; enlarged in HCM.
• ECG — bradycardia and early repolarisation in the athlete; pathological T inversion, Q waves, strain pattern in HCM.
• LGE on MRI — absent in athlete's heart; replacement fibrosis in HCM.
• Deconditioning — athlete's wall regresses in 6 to 12 weeks off training; HCM does not regress.
• Family history — none in athlete's heart; HCM or SCD in the family in HCM.[1]

The classic trap: mislabelling an athlete ends a career for nothing. Decondition for 6 to 12 weeks and repeat the echo and MRI before you sign the disqualification.[1]

[1]

Round out the LVH differential with three more: hypertensive heart disease (concentric LVH that regresses with blood-pressure control, no family history), aortic stenosis (concentric LVH with a fixed valvular gradient, not a dynamic subaortic one), and Fabry disease — X-linked and treatable with enzyme replacement, suspected in men with concentric LVH and negative T waves in the inferolateral leads.[1]

[1]

How common, and why the young athlete dies first

HCM has a population prevalence of about 1 in 500 — the commonest monogenic cardiac disorder and the commonest inherited heart-muscle disease. It is roughly equal across sex and ethnicity, but women are diagnosed later and present more often with heart failure — a recognised care gap.[4][1]

It is also the commonest medical cause of sudden cardiac death in young athletes and competitive sportspeople in the United States and many other regions — even though the absolute annual risk across the whole HCM population is modest. That paradox is the whole rationale for pre-participation screening and for sport restriction once the diagnosis is made.[4]

The SCD risk modifiers for penetrance and severity cluster as a named list:[1]

• Family history of HCM or of sudden death under 50 in a first-degree relative.
• Pathogenic sarcomere mutation — especially compound or double heterozygotes, and certain high-risk alleles (some MYH7 and TNNT2; TNNT2 classically gives mild hypertrophy with disproportionate SCD risk — a viva favourite).
• Massive LVH — maximal wall thickness over 30 mm.
• Early age at diagnosis — childhood and adolescent onset carry higher SCD rates.
• Male sex and intense competitive sport — they surface latent disease.[1]

The clinical symptom triad is dyspnoea (commonest, from raised LV end-diastolic pressure, worsened by atrial fibrillation), angina (microvascular, with clean coronaries), and syncope or pre-syncope (LVOT obstruction, neurally mediated vasodilation, or arrhythmia). And in young patients the first presentation may be sudden cardiac death during or just after exertion — the single most feared event in the disease.[1][4]

Late-onset and atypical forms deserve a line each: elderly HCM often has a sigmoid septum and hypertension overlap (with amyloid lurking); apical HCM gives giant negative T waves in V2 to V6 and a spade-shaped cavity; the burned-out phase (5 to 10 percent) progresses to systolic HF with EF under 50 percent; and women are under-represented in trials and diagnosed late.[1]

Read the workup like the echo report — the investigations that earn marks

Five investigations carry the weight in HCM: the ECG, the transthoracic echo, the cardiac MRI, the Holter, and the exercise test. Genetic testing and coronary angiography are selective. Run them in that order and the picture completes itself.[1][4]

The ECG is abnormal in about 90 percent and may be the first clue in an asymptomatic athlete:[1]

• LV hypertrophy by voltage (Sokolow-Lyon SV1 plus RV5 or RV6 over 35 mm; Cornell).
• LV strain pattern — ST depression and deep T inversion in I, aVL, V5 to V6.
• Lateral or precordial pathological Q waves (septal depolarisation through the hypertrophied septum) — a mimic of old MI.
• Apical HCM — giant (over 10 mm) deep T inversion in V2 to V6 with high R waves — virtually pathognomonic.
• Left atrial enlargement, PR shortening, conduction disease. A normal ECG does not exclude HCM, but a normal ECG plus a normal echo in a relative makes disease unlikely.[1]

The chest X-ray is non-specific — cardiomegaly, left atrial enlargement (double shadow, splayed carina), pulmonary venous congestion in failure — useful only to exclude alternatives.[1]

Transthoracic echocardiography is the first-line and central test, answering five questions at once: (1) is hypertrophy present and where; (2) is there LVOT obstruction and what is the gradient; (3) is there SAM and mitral regurgitation; (4) what is the diastolic function; (5) are there associated lesions. The diagnostic and quantification thresholds, reproduced verbatim from AHA/ACC 2020:[1]

[1]

Cardiac MRI is the reference standard for wall thickness in every segment (especially the apex, missed on TTE), LV mass, and — critically — late gadolinium enhancement, the focal replacement fibrosis. LGE exceeding 15 percent of LV mass independently predicts SCD and increasingly tips a borderline ICD decision toward yes.[1]

Holter monitoring — 24 to 48 hours, ideally 7 days — is mandatory in the SCD workup, because non-sustained VT is a major risk modifier and may be entirely silent.[1]

Exercise testing (symptom-limited treadmill or bicycle with continuous BP) finds provocable gradients, exercise-induced symptoms, and the blood-pressure response: a fall of over 10 mmHg, or failure to rise by over 20 mmHg during effort, is an SCD risk modifier in patients under 40.[1]

Cascade genetic testing of the index and first-degree relatives is recommended. Genotype-positive, phenotype-negative relatives get serial surveillance (echo, ECG, MRI annually in children and adolescents, every 2 to 5 years in adults); genotype-negative relatives are discharged from surveillance.[1]

Coronary angiography or CT coronary is reserved for angina with significant pre-test probability of epicardial CAD, or before septal reduction. Microvascular angina is common with angiographically normal coronaries.[1]

The classic trap — the obstructed ventricle that nitrates kill

HCM rarely arrives as a resuscitation emergency the way an MI does, but two scenarios are time-critical, and the second is the one that ruins careers.[1]

Cardiac arrest (VF or pulseless VT) gets immediate defibrillation at 200 J biphasic and standard advanced life support. After recovery, an ICD is indicated for secondary prevention regardless of the risk score — survival itself is the indication.[1]

Haemodynamic collapse with severe LVOT obstruction is the classic trap. The obstructed HCM ventricle is hypercontractile, underfilled, and exquisitely load-dependent — and the standard "cardiac" drugs are exactly the ones that kill it.[1]

[1]

The one-line rule for the trap: empty and fast kills HCM; full and slow saves it. Volume, beta-blockade, phenylephrine — in that order.[1]

Beta-blocker first, never nitrates, ICD for the high-risk few

Four parallel tracks run together — lifestyle and screening, symptom control, septal reduction, and SCD risk management. Hold all four in your head or you will miss one.[1][2]

Track 1 — lifestyle and family screening. Competitive sport is contraindicated in clinically diagnosed HCM (Class 3 in AHA/ACC 2020 — should not participate); recreational low-intensity activity is encouraged. Avoid dehydration and hot environments, where preload-dependent obstruction worsens. Screen first-degree relatives with ECG and echo, plus or minus cardiac MRI and genetic testing — every 1 to 2 years in children and adolescents, every 2 to 5 years in adults. Endocarditis prophylaxis is reserved for prosthetic valves, prior endocarditis, and certain congenital disease — not routine for native HCM valves.[1]

Track 2 — symptomatic drug therapy runs in four steps, in order:[1][2]

Step 1 — beta-blocker (first-line). Propranolol (long-acting, 160 to 240 mg orally daily in divided doses, up to 320 mg a day), metoprolol succinate (100 to 200 mg daily), bisoprolol (5 to 10 mg daily), atenolol (50 to 100 mg daily), nadolol (40 to 80 mg daily). In acute settings, esmolol intravenously (loading 500 micrograms/kg over 1 minute, then 50 to 200 micrograms/kg/minute) for its short half-life. Titrate to a resting heart rate of 60 to 65 per minute. Mechanism: lower rate (longer diastole, better filling), lower contractility (less SAM, smaller gradient), blunted exertional surges.[1][2]

Step 2 — add disopyramide, or switch to a non-dihydropyridine CCB. Disopyramide 100 to 200 mg orally three to four times daily (controlled-release 250 mg twice daily where available), titrated — its negative inotropy shrinks SAM and the gradient without dropping preload; combine with a beta-blocker for synergy, monitor the QTc, and avoid in long QT. Verapamil 240 to 480 mg orally daily (sustained release), or diltiazem 180 to 360 mg daily — but never combine disopyramide with verapamil (combined negative dromotropy and inotropy can cause complete heart block and shock), and avoid verapamil in obstruction with conduction disease, severe HF, or hypotension.[1][2]

Step 3 — cardiac myosin inhibitors. Mavacamten, first-in-class and FDA-approved for symptomatic obstructive HCM (NYHA class II to III), reduces actin-myosin cross-bridges, lowering hypercontractility, the gradient and filling pressures. Dose 2.5 to 15 mg orally once daily, titrated to LVOT gradient and LVEF (interrupt if LVEF falls below 50 percent); EXPLORER-HCM showed improved peak VO2, NYHA class, gradient and quality of life versus placebo. Aficamten, next-in-class with a shorter half-life, improved exercise performance versus metoprolol in MAPLE-HCM. Both sit before or instead of invasive septal reduction; their place relative to myectomy and ASA is still evolving.[3][5]

Step 4 — septal reduction therapy, for NYHA class III to IV symptoms (or class II with exertional syncope) with an LVOT gradient of 50 mmHg or more despite maximally tolerated drugs:[1]

[1]

The SCD risk cluster — and where ESC and AHA/ACC disagree

The ICD is the only therapy proven to prevent sudden cardiac death in HCM, so the entire art is deciding who gets one. Two frameworks divide the world, and they diverge exactly on the borderline patient.[1][2]

Secondary prevention needs no score: prior cardiac arrest, spontaneous sustained VT, or sustained VF — ICD regardless.[1]

For primary prevention, the ESC 2014 HCM Risk-SCD equation computes a 5-year SCD probability from age, maximal LV wall thickness, left atrial diameter, LVOT gradient, family history of SCD, NSVT, and unexplained syncope. ICD when the 5-year risk is 6 percent or more (consider at 4 to under 6; generally not below 4).[2]

The AHA/ACC 2020 approach instead weighs major SCD risk modifiers — the presence and magnitude of each tilting the decision:[1]

[1]

The cluster of six, for the viva: family history of SCD under 50, massive LVH over 30 mm, NSVT on Holter, unexplained syncope, abnormal BP response on exercise under 40, and extensive LGE over 15 percent on MRI.[1]

The named divergence: a patient with two modifiers but a low ESC equation score is handled differently in Boston (AHA/ACC — the modifiers carry the decision) than in London (ESC — the 6 percent equation governs). Name the framework you are using before you recommend the box. LGE over 15 percent of LV mass is the modifier that increasingly tips a borderline score toward ICD in both systems.[1][2]

Comorbidities, subtypes, and special populations

Four situations flip at least one rule you learned above: atrial fibrillation, the burned-out phase, pregnancy, and non-cardiac surgery. Each deserves a named paragraph.[1]

Atrial fibrillation is common and poorly tolerated — the stiff ventricle cannot afford to lose the atrial kick. Rhythm control is preferred: amiodarone 200 mg orally daily is the usual first agent (sotalol, disopyramide or quinidine as alternatives). Anticoagulate every HCM patient with AF regardless of the CHA2DS2-VASc score — warfarin traditionally, DOACs now acceptable on observational data. Acute haemodynamic instability gets urgent electrical cardioversion. Consider AF ablation or surgical left-atrial appendage exclusion at myectomy.[1]

The classic pitfall: reaching for the CHA2DS2-VASc score in HCM. HCM is itself an anticoagulation indication in AF — the score is irrelevant.[1]

Burned-out or dilated phase (EF under 50 percent) — about 5 to 10 percent, over decades. Switch to guideline-directed HFrEF therapy: ACE inhibitor, ARB or ARNI; a beta-blocker (bisoprolol, carvedilol or metoprolol succinate); an MRA; an SGLT2 inhibitor; and diuretics as needed — preload dependence is no longer a concern once EF has fallen. Transplant evaluation in advanced disease.[1]

Apical HCM — spade-shaped cavity, giant T inversions, no LVOT obstruction, so beta-blockade for symptoms and screen for apical aneurysm and thrombus (anticoagulate if present); SCD risk is generally lower. Mid-cavitary HCM — gradient at the mid-ventricle, apical aneurysm in a minority; treat the gradient with a beta-blocker plus or minus a myosin inhibitor, rarely a surgical apical myectomy.[1]

Pregnancy in chronic stable HCM is generally well tolerated — the higher heart rate and lower systemic vascular resistance partly offset the gradient. Counsel pre-pregnancy on symptoms, gradient and SCD risk. Continue beta-blockers through pregnancy and labour if previously needed (watch for fetal bradycardia and growth restriction). Avoid IVC compression (left lateral in labour); vaginal delivery preferred, caesarean for obstetric indications or severe symptoms. Regional anaesthesia (low-dose epidural) is preferred for operative delivery but avoid sudden afterload drops; use phenylephrine, not beta-agonist sympathomimetics, and avoid ergometrine. High-risk patients — recent syncope, severe obstruction, EF under 50 percent — are counselled against pregnancy.[1]

Non-cardiac surgery — the obstructed HCM patient is high-risk for anaesthetic collapse. Maintain preload (avoid hypovolaemia, careful fasting, IV fluids), maintain sinus rhythm and a controlled rate (continue beta-blockade peri-operatively), maintain afterload (no vasodilators or abrupt sympathetic blockade; favour phenylephrine over ephedrine), and avoid hypercontractility (no high-dose ketamine, no pure beta-agonists). Spinal anaesthesia can precipitate collapse from sudden afterload loss — caution or avoid.[1]

Children and the elderly: in children, a z-score of 2 or more defines disease, SCD rates are higher, and the HCM Risk-Kids calculator (not the adult equation) is used; in the elderly, sigmoid morphology and hypertension overlap dominate, beta-blockade is tolerated less well (start low), and amyloid must be excluded.[1]

Complications, pitfalls, prognosis, and disposition

The complications of HCM are the disease in a different order: sudden death, atrial fibrillation, heart failure, syncope, and thromboembolism. Learn them as one list — the same five threats threaded through the topic.[1][4]

• Sudden cardiac death (VF) — the cardinal and most feared, above all in the young and during exertion.
• Atrial fibrillation — embolic stroke, haemodynamic collapse, heart failure.
• Heart failure — diastolic in the classic phase; systolic in the burned-out phase.
• Syncope and injury — from obstruction or arrhythmia.
• Infective endocarditis on the SAM-damaged mitral apparatus (small absolute risk) and thromboembolism from AF or an apical aneurysm.[1]

Complications of septal reduction: complete heart block needing a permanent pacemaker (more after ASA, 10 to 20 percent, than myectomy, 2 to 5 percent); ventricular septal defect (myectomy, rare); coronary dissection, LAD injury, or large anterior infarct (ASA); residual or recurrent obstruction.[1]

The classic pitfalls examiners love:[1]

• Mislabelling an athlete — decondition and MRI before ending a career.
• Missing cardiac amyloidosis in the elderly look-alike — different management, dangerous drugs.
• Giving nitrates for chest pain in undiagnosed HOCM — collapses the patient.
• Withholding a beta-blocker for mild symptoms — it is first-line for a reason.
• Missing NSVT by skipping the Holter in the SCD workup.
• Combining disopyramide with verapamil — heart block and shock.
• Using digoxin in obstructive HCM — more contractility, worse gradient.
• Anticoagulating by CHA2DS2-VASc in HCM with AF — anticoagulate all regardless.[1]

Prognosis in a specialist clinic is an annual HCM-related mortality of about 1 to 2 percent — dramatically lower than the 4 to 6 percent of older tertiary-referral series, a difference that reflects ascertainment bias (modern cohorts catch many mild, family-screened cases), not a change in the disease. SCD runs about 1 percent a year overall, stratified from under 0.5 percent (low risk) to over 3 to 5 percent (high risk, multiple modifiers), commonest in adolescents and young adults; about 5 to 10 percent progress to the burned-out phase over decades. After septal reduction, symptom relief is excellent and durable; after ICD, appropriate shock rates run 3 to 5 percent per year in primary prevention.[4][1]

Disposition: genotype-positive, phenotype-negative relatives live in a specialist HCM clinic under serial surveillance; symptomatic obstructive disease is managed medically and escalated to a centre of excellence for myosin inhibitor, myectomy or ASA evaluation; high-risk patients are referred for ICD; the burned-out phase enters a heart-failure or transplant pathway; and acute collapse with obstruction goes to critical care with HCM-aware anaesthesia.[1]

The guidelines and the trials — name them in the viva

Two guidelines and two trials carry the HCM viva; name them by author and year.[1][2]

The 2020 AHA/ACC Guideline (Ommen et al., Circulation 2020) is the current North American standard — it brought mavacamten into the algorithm, emphasised shared decision-making for ICD and sport, and codified the major SCD risk-modifier approach over a single equation. The 2014 ESC Guideline (Elliott et al., European Heart Journal 2014) is the European standard and the origin of the HCM Risk-SCD 5-year equation with the 6 percent cut-off.[1][2]

The trials: EXPLORER-HCM (Olivotto et al., Lancet 2020, PMID 32871100) — mavacamten improved peak VO2, NYHA class, LVOT gradient and quality of life versus placebo in symptomatic obstructive HCM. MAPLE-HCM (Lewis et al., JAMA Cardiology 2026, PMID 42307914) — aficamten improved exercise performance versus metoprolol in obstructive HCM.[3][5]

[1]

Regional delta to name: the AHA/ACC major-modifier approach and the ESC HCM Risk-SCD equation diverge for the borderline case — a patient with two modifiers but a low equation score is handled differently in the US and Europe. Genetic testing uptake and mavacamten or aficamten availability vary by health-system funding; in resource-limited settings rheumatic and hypertensive heart disease dominate and HCM is under-diagnosed.[1]

Key thresholds examiners reward: wall thickness 15 mm (adult), 13 mm (relative), z-score 2 (child); LVOT gradient 30 mmHg (obstruction), 50 mmHg (intervention); HCM Risk-SCD 6 percent 5-year cut-off; massive LVH over 30 mm.[1]

The mantra

Left sternal edge, louder with Valsalva, beta-blocker first, never nitrates, ICD for the high-risk few.[1][2]

Ward-round test — three stems

Stem 1 — the athlete who collapsed on the track (answer)

A 19-year-old sprinter collapses 200 metres into a race, recovers in seconds, and is found to have LVH on ECG with lateral T inversion. What is your first move, and what will the murmur do on Valsalva? Model: Restrict him from sport now — pre-participation suspicion of HCM is a no-play-until-cleared decision. Order a transthoracic echo (wall 15 mm or more, septum-to-free-wall ratio 1.3 or more, LVOT gradient, SAM) and a cardiac MRI for wall thickness and LGE. At the bedside expect an ejection systolic murmur at the left sternal edge that increases on Valsalva strain and on standing, and decreases on squatting — the mirror image of aortic stenosis. Family history of SCD under 50 and collateral from the coach and relatives complete the picture; genotype testing follows the phenotype.[1][4]

Stem 2 — the obstructive HCM that collapsed after the GTN (answer)

A 52-year-old with known obstructive HCM is given sublingual GTN on the ward for chest pain and becomes hypotensive and confused within minutes. What happened, and what do you do now? Model: The nitrate dropped preload, widened the LVOT gradient, and worsened SAM and the obstruction — the classic trap. Stop the nitrate. Give volume in small crystalloid boluses, a beta-blocker (esmolol intravenously — short-acting and titratable), and a pure alpha-agonist — phenylephrine 100 to 200 micrograms intravenously, titrated — to raise afterload without boosting contractility. Treat any tachyarrhythmia. Never reach for nitrates, diuretics, vasodilators, digoxin, pure beta-agonists, or an intra-aortic balloon pump in this ventricle. The chest pain was microvascular, not nitrate-responsive.[1]

Stem 3 — the elderly HCM with low voltages and carpal tunnel (answer)

A 78-year-old man is labelled HCM on a concentric-LVH echo, but his ECG voltages are tiny and he has bilateral carpal tunnel syndrome. What must you exclude before treating him as HCM? Model: This is the amyloid trap — voltage-mass discordance (a thick wall with low ECG voltages) plus bilateral carpal tunnel and a disproportionately raised troponin and BNP point to cardiac amyloidosis, not HCM. Confirm with an apical-sparing LGE pattern on cardiac MRI and a 99mTc-PYP scan for ATTR, plus serum and urine free light chains for AL. Get it right because the treatments collide — digoxin and calcium-channel blockers are dangerous in amyloidosis, and tafamidis may change the ATTR course. Exclude amyloid before you label any elderly HCM.[1]

References

1. [1]Ommen SR, Mital S, Burke MA, et al. 2020 AHA/ACC Guideline for the Diagnosis and Treatment of Patients With Hypertrophic Cardiomyopathy: Executive Summary: A Report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines Circulation, 2020.PMID 33215938
2. [2]Elliott PM, Anastasakis A, Borger MA, et al. 2014 ESC Guidelines on diagnosis and management of hypertrophic cardiomyopathy: the Task Force for the Diagnosis and Management of Hypertrophic Cardiomyopathy of the European Society of Cardiology (ESC) Eur Heart J, 2014.PMID 25173338
3. [3]Olivotto I, Oreziak A, Barriales-Villa R, et al. Mavacamten for treatment of symptomatic obstructive hypertrophic cardiomyopathy (EXPLORER-HCM): a randomised, double-blind, placebo-controlled, phase 3 trial Lancet, 2020.PMID 32871100
4. [4]Maron BJ. Hypertrophic cardiomyopathy: a systematic review JAMA, 2002.PMID 11886323
5. [5]Lewis GD, Garcia-Pavia P, Masri A, et al. Exercise Performance With Aficamten vs Metoprolol in Obstructive Hypertrophic Cardiomyopathy: The MAPLE-HCM Randomized Clinical Trial JAMA Cardiol, 2026.PMID 42307914