Cardiovascular · Topic 12 of 48
Hypertrophic Cardiomyopathy
Cardiovascular · cardiomyopathy
Hypertrophic Cardiomyopathy
A thick, stiff ventricle whose outflow obstruction worsens with less preload or afterload: keep the patient full, slow and constricted — beta-blocker first, no vasodilators.
Key numbers
LV wall thickness 15 mm or morewall ≥ 15 mm
Obstructive: LVOT gradient ≥ 30 mmHgLVOT ≥ 30 mmHg
Major sudden-death risk factors favour an ICDmassive LVH ≥ 30 mm
01 · Defined byObstructive: LVOT gradient ≥ 30 mmHg
HCM is obstructive when the peak LVOT gradient is ≥ 30 mmHg at rest or with provocation; gradients ≥ 50 mmHg usually cause symptoms and are the threshold for advanced therapy.
02 · GiveFirst line: nonvasodilating beta-blocker
For symptomatic obstructive HCM, titrate a nonvasodilating beta-blocker (eg, metoprolol) to effect; substitute verapamil or diltiazem if it fails or is not tolerated. Slowing the rate lengthens filling and lowers the gradient.
03 · AvoidAvoid vasodilators, inotropes and dehydration
In obstructive HCM avoid what lowers preload or afterload or raises contractility: nitrates, dihydropyridine CCBs, ACE inhibitors/ARBs, high-dose diuretics, positive inotropes and digoxin — all worsen the outflow obstruction.
01
What it is
Core ideaSeptal bulge plus mitral SAM obstructs outflowObstruction comes from the hypertrophied basal septum plus systolic anterior motion (SAM) of the anterior mitral leaflet into the outflow tract, which also causes posteriorly directed mitral regurgitation.
02
Causes & risk factors
Why it happensExertional syncope signals sudden-death riskHCM is a common cause of sudden death in young athletes; unexplained or exertional syncope (arrhythmic or from obstruction) is an important sudden-death risk marker and needs full evaluation.
Major sudden-death risk factors favour an ICDA primary-prevention ICD is reasonable with ≥ 1 major risk factor: HCM sudden death in a relative ≤ 50 years, wall thickness ≥ 30 mm, arrhythmic syncope, LV apical aneurysm, or LVEF < 50%.
03
Presentation
What you'll seeMurmur louder with Valsalva or standingThe obstructive HCM murmur is a late-peaking systolic murmur at the left sternal border (3rd–4th intercostal space) that gets louder with Valsalva or squat-to-stand and softer with handgrip, squatting or passive leg raise.
Brisk bifid carotid pulse and an S4With LVOT obstruction the carotid pulse has a brisk upstroke, bifid peak and rapid downstroke (unlike the slow-rising pulse of aortic stenosis); an S4 is common from atrial contraction into a stiff ventricle.
04
Diagnosis & monitoring
Work-upLV wall thickness 15 mm or more must knowHCM is diagnosed by echo or cardiac MRI showing maximal end-diastolic LV wall thickness ≥ 15 mm with no other cause (hypertension, aortic stenosis, infiltration); 13–14 mm suffices with a family history or pathogenic variant.
Mavacamten: serial echo, interrupt if LVEF < 50%Cardiac myosin inhibitors can cause systolic heart failure: mavacamten is REMS-restricted, needs echo LVEF before and during therapy, is not started when LVEF is < 55%, and is interrupted if LVEF falls below 50%.
05
Do right now
In this orderFirst moves
1
→Hypotension: IV fluids, then phenylephrine
2
→Avoid vasodilators, inotropes and dehydration
3
First line: nonvasodilating beta-blocker
Why each step
Hypotension: IV fluids, then phenylephrineAcute hypotension in obstructive HCM is urgent: give IV fluid to restore preload; if unresponsive, give IV phenylephrine (a vasoconstrictor without inotropy), alone or with a beta-blocker. Do not give dobutamine or other inotropes.
Avoid vasodilators, inotropes and dehydrationIn obstructive HCM avoid what lowers preload or afterload or raises contractility: nitrates, dihydropyridine CCBs, ACE inhibitors/ARBs, high-dose diuretics, positive inotropes and digoxin — all worsen the outflow obstruction.
First line: nonvasodilating beta-blockerFor symptomatic obstructive HCM, titrate a nonvasodilating beta-blocker (eg, metoprolol) to effect; substitute verapamil or diltiazem if it fails or is not tolerated. Slowing the rate lengthens filling and lowers the gradient.
06
Management
OrdersICD after cardiac arrest or sustained VTAn ICD is recommended (secondary prevention) for any patient with HCM who has survived cardiac arrest or had sustained ventricular tachycardia.
Refractory obstruction: myosin inhibitor, disopyramide or septal reductionIf symptoms from obstruction persist despite a beta-blocker or verapamil/diltiazem, add a cardiac myosin inhibitor (mavacamten, aficamten), or disopyramide with an AV-nodal blocker, or refer for septal reduction.
AF in HCM: anticoagulate regardless of CHA₂DS₂-VAScAtrial fibrillation is common and poorly tolerated in HCM; anticoagulate every patient with clinical AF regardless of CHA₂DS₂-VASc score — a DOAC first line, warfarin second.
Myectomy preferred; alcohol ablation if high surgical riskSurgical septal myectomy at an experienced center is preferred for suitable candidates; alcohol septal ablation is the alternative for older or high-risk patients but causes more complete heart block and repeat procedures.
Screen first-degree relatives with ECG and echoHCM is usually autosomal dominant: offer genetic testing and screen first-degree relatives with history, exam, ECG and echocardiogram — adults at diagnosis, then every 3–5 years if not cleared genetically.
07
Red flags & don'ts
Avoid harmVerapamil harmful: rest dyspnea, hypotension, huge gradient avoidVerapamil is potentially harmful in obstructive HCM with severe dyspnea at rest, hypotension or a resting gradient of 100 mmHg or more (and in infants under 6 weeks), because its vasodilation can precipitate collapse.
08
HCM or aortic stenosis murmur?
Commonly confused| Valsalva or standing | Louder |
|---|---|
| Squatting or leg raise | Softer |
| Carotid pulse | Brisk upstroke, bifid peak |
| Murmur location | Left sternal border, 3rd–4th intercostal space |
09
More detail
ReferenceShow 6 reference facts
About 6–8% progress to a burnt-out phase with LVEF ≤ 50%: stop negative inotropes (verapamil, diltiazem, disopyramide, myosin inhibitors), start HFrEF guideline-directed therapy and refer for advanced HF care or transplant.
Athlete's heart can thicken the wall to 12–15 mm; HCM is favoured by a small LV cavity, ECG and MRI findings (late gadolinium enhancement), and no regression with detraining.
Nonobstructive HCM: beta-blockers or verapamil/diltiazem for symptoms, cautious low-dose diuretics for congestion (the volume window is narrow); valsartan may be considered at age ≤ 45 with a sarcomeric variant.
Universal exercise restriction is no longer advised: mild-to-moderate recreational exercise is encouraged, and competitive sport is a shared decision with an HCM specialist.
The aortic stenosis murmur behaves oppositely: softer with Valsalva, louder with squatting or leg raise, heard best at the upper sternal borders radiating to the carotids, with a slow-rising carotid pulse.
HCM affects about 1 in 200–500 adults and is usually caused by sarcomere gene variants (most often MYH7 and MYBPC3); asymmetric septal hypertrophy is the classic pattern, apical HCM a nonobstructive variant.
Anything that empties or relaxes the ventricle — Valsalva, standing, dehydration, nitrates, inotropes — makes the obstruction and the murmur worse.
Sources · Merck Manual Professional — Hypertrophic Cardiomyopathy (rev. Sept 2026) · Merck Manual Professional — Hypertrophic Cardiomyopathy Arrhythmias · Ommen SR et al. 2024 AHA/ACC/AMSSM/HRS/PACES/SCMR Guideline for the Management of Hypertrophic Cardiomyopathy. J Am Coll Cardiol 2024;83:2324–2405 · Merck Manual Professional — Aortic Stenosis · Camzyos (mavacamten) prescribing information — DailyMed (rev. 9/2026) · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).