Hypertrophic cardiomyopathy
Wall thickness, obstruction at rest and on provocation, the mitral apparatus, and the SCD risk inputs.
Numbers to remember
- ≥15 mm maximal wall thickness in any segment (≥13 mm in a first-degree relative) [13,14]
- ≥30 mmHg LVOT gradient = obstruction; ≥50 mmHg = haemodynamically important, the threshold for septal reduction [13]
- ≥30 mm wall thickness = major SCD risk marker [13,127]
- LVEF <50% = end-stage (hypokinetic) HCM [13]
- Provoke every patient with a resting gradient <50 mmHg [13,126]
Questions echo must answer
Hypertrophic cardiomyopathy is defined by LV wall thickness ≥15 mm in any segment (≥13 mm in a first-degree relative, or with a positive genotype) that is not explained by abnormal loading conditions [13,14]. About two-thirds of patients have LV outflow tract obstruction at rest or with provocation [129], and a resting gradient ≥30 mmHg roughly doubles the risk of HCM-related death and markedly increases progression to NYHA III–IV [128]. Echo therefore has five jobs:
- PhenotypeWhere is the hypertrophy and how thick is the thickest segment? This includes asymmetric septal, apical, mid-ventricular and concentric patterns.
- ObstructionIs there a gradient at rest, and what is it with Valsalva, standing and exercise? At what level is it: LVOT or mid-cavity?
- MechanismLook for SAM, leaflet elongation, anomalous papillary muscles, and the direction of the MR jet.
- RiskRecord maximal wall thickness, LA diameter, maximal gradient, LVEF and apical aneurysm. These are the inputs to SCD risk [13,127].
- DifferentialRule out phenocopies: hypertension, athlete's heart, amyloidosis, Fabry disease and AS.
Key pointA normal resting gradient does not mean non-obstructive HCM. Guidelines require provocation, meaning Valsalva, standing and ideally exercise echo, before that label is applied [13,126].
Acquisition protocol
- PLAXMeasure IVSd and PWd at end-diastole, perpendicular to the long axis, excluding RV trabeculations and the moderator band. Look for SAM and chordal SAM. Measure the LA AP diameter, which is an HCM Risk-SCD input [127].
- PSAX sweepMeasure the thickest segment at basal, mid and apical levels. In the 2D short axis the maximal thickness is often anterior septal or anterolateral and is missed in PLAX [126].
- M-modeRecord SAM timing and duration (septal contact) and mid-systolic aortic valve closure.
- A4C / A2C / A3CAssess apical hypertrophy (spade shape), mid-cavity obstruction, apical aneurysm and thrombus. Use contrast if the apex is not clearly seen [126].
- A5C / A3C colourFind the site of flow acceleration: LVOT or mid-cavity. Then take CW with the late-peaking "dagger" envelope, and PW mapping from apex to LVOT if the level is uncertain.
- ProvocationRepeat CW during the Valsalva strain phase, then after standing. In symptomatic patients with a resting and Valsalva gradient <50 mmHg, perform exercise echocardiography [13,28].
- MitralMeasure anterior leaflet length. Look for papillary muscle insertion directly into the anterior leaflet. Record MR jet direction and severity (a posterior jet is typical of SAM). Look for primary leaflet disease.
- DiastolicRecord mitral inflow, septal and lateral e′, E/e′, LAVI, TR velocity and LA strain [2,32].
- FunctionRecord LVEF (biplane), GLS and RV wall thickness.
- Maximal wall thickness and its segment
- Resting LVOT gradient
- Valsalva gradient
- Standing or exercise gradient
- SAM and septal contact
- MR mechanism, jet direction and severity
- LA diameter and LAVI
- LVEF, GLS
- Apical aneurysm or thrombus excluded (contrast if needed)
- RV thickness, TR velocity
Diagnosis & severity
| Item | Threshold | Meaning |
|---|---|---|
| Maximal LV wall thickness | ≥15 mm (≥13 mm in relatives) | Diagnostic of HCM when not explained by loading [13,14] |
| Maximal wall thickness | ≥30 mm | Major SCD risk marker [13] |
| LVOT peak gradient (rest or provoked) | ≥30 mmHg | Obstructive physiology [13] |
| LVOT peak gradient | ≥50 mmHg | Haemodynamically important; septal reduction if symptomatic despite drugs [13,14] |
| LVEF | <50% | End-stage HCM; major SCD risk marker [13] |
| Apical aneurysm | Any thin-walled dyskinetic segment | SCD and thromboembolic risk marker [13,181] |
| LA diameter (PLAX) | Continuous input | HCM Risk-SCD model [127] |
SCD risk: the echocardiographic inputs
The ESC HCM Risk-SCD model uses age, maximal wall thickness, LA diameter, maximal LVOT gradient (rest or Valsalva), family history of SCD, NSVT and unexplained syncope. An ICD should be considered at a 5-year risk ≥6% and may be considered at 4–6% [14,127]. The 2024 AHA/ACC guideline adds LVEF <50%, apical aneurysm and extensive LGE (≥15% of LV mass) as major markers [13].
Practical tipEnter the maximal gradient from either rest or Valsalva. Exercise gradients were not used to derive the model [127].
Thresholds that change management
- Symptomatic with a gradient ≥50 mmHg (rest or provoked) despite a beta-blocker or non-dihydropyridine calcium-channel blocker → consider a cardiac myosin inhibitor (mavacamten) or septal reduction therapy at an experienced centre [13,14,72].
- Mavacamten monitoring is echo-driven. Measure LVEF and the Valsalva LVOT gradient at baseline and during titration. Interrupt treatment if LVEF falls below 50% [13,72]. In EXPLORER-HCM, mavacamten reduced LV mass and LA volume on CMR [73].
- Avoid vasodilators, high-dose diuretics and inotropes when there is obstruction, because they increase the gradient [13].
- Apical aneurysm → consider an ICD and anticoagulation according to guideline risk assessment [13,181].
- Surveillance. Repeat echo every 1–2 years in stable patients, and at any change in symptoms. Screen first-degree relatives with ECG and echo [13,14].
Pitfalls & mimics
PitfallMR contamination of the LVOT signal. The MR jet starts at mitral closure (with isovolumic contraction), peaks early and is higher (often >6 m/s). The LVOT envelope starts after aortic opening and peaks late. Sweep the CW cursor slowly between the two, and calculate the gradient only from the dagger-shaped envelope.
- Overestimated septal thickness from RV trabeculations, the moderator band or an oblique cut. Zoom and use the PSAX to confirm.
- Sigmoid septum in older hypertensive patients: a localised basal bulge with a normal remaining wall. It is not HCM unless other features are present.
- Athlete's heart: wall thickness usually ≤15 mm, with a dilated, normally relaxing LV, normal e′ and regression with detraining [150].
- Phenocopies: amyloidosis (low voltage, apical sparing, thick valves and interatrial septum, pericardial effusion) [30]; Fabry disease; Danon disease; mitochondrial disease; AS and hypertension (concentric hypertrophy with loading).
- Apical HCM is missed without contrast or careful off-axis imaging. The spade-shaped cavity and giant negative T waves are clues [126].
- Dehydration or hypovolaemia exaggerates the gradient. A normovolaemic state is needed for decisions.