EchoCG Monitoring of oHCM on Mavacamten: BSE 2025 Protocol
Clinical Task of the BSE 2025 Protocol
The British Society of Echocardiography 2025 guideline describes transthoracic EchoCG monitoring of adult patients with obstructive hypertrophic cardiomyopathy receiving myosin inhibitor therapy. In the practical UK context, this primarily refers to mavacamten, as it is the licensed drug of this class. The protocol's goal is not to re-phenotype HCM at each visit but to safely manage therapy, where decisions depend on two echocardiographic values: LV contractile function and the degree of dynamic LVOT obstruction.
The main risk of monitoring is missing excessive negative inotropic effects. Therefore, LVEF in the report must be quantitative, reproducible, and comparable to previous studies. The second risk is incorrectly measuring the LVOT gradient, especially confusing it with the mitral regurgitation signal or underestimating provoked obstruction.
Who Undergoes Surveillance EchoCG
The protocol applies to adult patients with obstructive HCM who have been prescribed or are planned to be prescribed a myosin inhibitor. The baseline study before starting therapy should confirm the phenotype, degree of hypertrophy, presence of systolic anterior motion of the mitral valve, mitral regurgitation, chamber sizes, LVEF, and LVOT gradient at rest and during provocation.
Subsequent follow-up studies should be focused. The ultrasound diagnostician must provide numerical values suitable for the medication algorithm: LVEF, peak LVOT gradient at rest, and maximum provoked gradient, usually during the Valsalva maneuver. Descriptive formulations without numbers—"gradient decreased," "contractility satisfactory"—are insufficient for this pathway.
When to Monitor: Frequency of Studies
BSE emphasizes that the new class of drugs requires frequent standardized EchoCG surveillance. In UK practice, related to NICE requirements and the mavacamten medication algorithm, monitoring is usually conducted every 4 weeks during the initiation and titration phase, then every 12 weeks on maintenance therapy. Additional studies are required when changing doses, temporarily discontinuing, the onset of heart failure symptoms, intercurrent illness, or clinical suspicion of LVEF drop.
For the EchoCG office, this means the study should be short but technically rigorous. The priority is to obtain the same key slices and Doppler positions so that changes between visits reflect treatment effects rather than methodological variability.
Mandatory Numerical Thresholds
| Indicator | Threshold | Practical Significance in the Report |
|---|---|---|
| LVEF before starting mavacamten | ≥55% | Value at which therapy can be considered according to the medication pathway; therapy is not initiated if LVEF is lower. |
| LVEF during therapy | <50% | Critical safety threshold: requires urgent indication in the conclusion and communication with the prescribing team, as the drug is temporarily discontinued according to the algorithm. |
| Peak LVOT gradient | ≥30 mmHg | Echocardiographic criterion for LVOT obstruction in HCM. |
| Peak LVOT gradient | ≥50 mmHg | Hemodynamically significant obstruction; key threshold for selection and assessment of response to therapy. |
How to Measure LVEF
LVEF should be measured quantitatively, preferably using the same method during serial visits. The main approach is apical two- and four-chamber views with biplane method calculation if endocardial contour quality permits. In difficult visualization, available methods to enhance the endocardial border should be used, as incorrect classification of LVEF around the 50% threshold directly affects the continuation or discontinuation of treatment.
In the report, it is important not only to note the LVEF number but also the context: visualization quality, calculation method, presence of regional abnormalities, changes in LV end-sizes compared to the previous visit. In HCM, a small LV cavity, pronounced hypertrophy, and hyperdynamic kinetics can create a subjective impression of "very good" contractility; therefore, visual assessment without calculation should not replace quantitative LVEF.
How to Measure LVOT Gradient
The LVOT gradient is measured using continuous-wave Doppler aligned with the flow. The peak velocity should be recorded, and the peak instantaneous gradient calculated. The minimum set for a surveillance study is the gradient at rest and the maximum provoked gradient, most often during the Valsalva maneuver. If the maximum gradient was previously obtained from another position, it should be repeated for comparability.
The main technical error is recording the mitral regurgitation jet instead of the LVOT signal. The dynamic obstruction signal usually has a late systolic rise, whereas mitral regurgitation often starts earlier, has higher velocities, and a different spectral shape. In case of doubt, color Doppler, pulse Doppler for localization of acceleration, and several acoustic windows should be used.
What Else to Include in the Follow-up Study
Although the medication decision is tied to LVEF and gradient, the report should not ignore the mechanism of obstruction. Systolic anterior motion of the mitral valve leaflets, contact with the interventricular septum, the nature and degree of mitral regurgitation, sizes of the left atrium and LV, and other findings that may alter clinical tactics should be described. In pronounced mitral regurgitation, it is especially important to separate its Doppler signal from the LVOT signal.
For the baseline study, the set is broader: hypertrophy morphology, maximum wall thickness, diastolic function, pulmonary artery pressure if a correct tricuspid regurgitation signal is present, valve pathology, and alternative causes of hypertrophy. In subsequent frequent visits, the focus shifts to safety and response dynamics.
Conclusion Format
The optimal conclusion should be tabular or structured. The first line should include the current and previous LVEF. The second line should include the LVOT gradient at rest. The third line should include the maximum provoked gradient with the maneuver indicated. Then, SAM, mitral regurgitation, and technical limitations should be noted. If LVEF is <50%, this should be highlighted at the beginning of the conclusion as a critical value.
The formulation might be: "LVEF 48% by biplane method; value below safety threshold for mavacamten therapy. Peak LVOT gradient 18 mmHg at rest and 24 mmHg during Valsalva. Urgent notification of the team managing myosin inhibitor therapy is recommended." Such a structure immediately answers the cardiologist's question: continue, change, or temporarily discontinue the drug.
Practical Pitfalls
- No Provocation. A normal gradient at rest does not exclude clinically significant dynamic obstruction; a provoked gradient is needed.
- Visual LVEF Only. For mavacamten, the 50% threshold is a medication trigger, so quantitative assessment is required.
- Mixing MR and LVOT. In HCM with SAM, mitral regurgitation often coexists with obstruction and can mimic a high gradient.
- Non-comparable Visits. Changing the window, LVEF calculation method, or provocation test can create false dynamics.
- Lack of Urgent Communication. With LVEF <50%, a single record in the protocol is insufficient; BSE considers this a result significant for immediate therapy management.
Frequently asked questions
What is the main safety figure for mavacamten?
LVEF. Therapy is not initiated if LVEF is <55%, and if LVEF decreases to <50% during treatment, immediate notification to the treating team and temporary discontinuation of the drug according to the algorithm is required.
What LVOT gradient is considered obstruction in HCM?
A peak LVOT gradient ≥30 mmHg corresponds to obstruction, and ≥50 mmHg is considered a hemodynamically significant threshold for selection and assessment of response to treatment.
Is it sufficient to measure the gradient only at rest?
No. For monitoring, it is necessary to indicate the gradient at rest and the maximum provoked gradient, usually during the Valsalva maneuver, ensuring that the Doppler signal pertains to the LVOT and not to mitral regurgitation.