Spotting Obstructive HCM and Knowing When to Escalate Therapy

Key Takeaways

• A resting echocardiogram can miss dynamic obstruction; provocative maneuvers are needed to reveal the gradients that actually drive symptoms.
• Nonvasodilating beta-blockers, then non-dihydropyridine calcium channel blockers, remain first-line – while pure vasodilators and high-dose diuretics can worsen a dynamic gradient.
• Cardiac myosin inhibitors give a targeted next step for persistent symptomatic obstruction, but require serial echocardiographic left ventricular ejection fraction (LVEF) monitoring and REMS-governed dispensing.

Left ventricular outflow tract (LVOT) obstruction is one of the principal determinants of symptoms and complications in hypertrophic cardiomyopathy (HCM), yet it is easy to underdetect. Obstruction is dynamic – it varies with heart rate, blood pressure, volume status, activity, and even meals – so a single resting gradient can substantially understate a patient's true hemodynamic burden.¹

Provocation is not optional

Obstruction is defined as a peak LVOT gradient of at least 30 mm Hg, at rest or with provocation. In a symptomatic patient whose resting study is unrevealing, the diagnosis is confirmed by provoking the gradient.¹

Transthoracic echocardiography should be performed both at rest and with maneuvers – Valsalva strain and standing from a squat at the bedside – and, when those are non-diagnostic, exercise stress echocardiography, which is the most physiologic form of provocation. Skipping provocation is the most common way a symptomatic obstructive patient gets labeled nonobstructive and steered away from obstruction-directed therapy.¹

First-line therapy, and what to stop

For symptoms attributable to obstruction, guideline-directed medical therapy begins with a nonvasodilating beta-blocker titrated to symptom benefit or maximally tolerated dose. When beta-blockers are ineffective or not tolerated, a non-dihydropyridine calcium channel blocker (verapamil or diltiazem) is substituted.¹

Equally important is subtracting agents that aggravate a dynamic gradient: Pure vasodilators – angiotensin-converting enzyme (ACE) inhibitors, angiotensin receptor blockers, and dihydropyridine calcium channel blockers – and high-dose diuretics can worsen obstruction and should be reconsidered.¹

Verapamil is potentially harmful in patients with severe resting dyspnea, hypotension, or very high resting gradients (for example, above 100 mm Hg).¹

When symptoms persist: Escalation

For patients who remain symptomatic despite adequate first-line therapy, the guideline endorses 3 parallel options, chosen through shared decision-making:¹

• Adding a cardiac myosin inhibitor (adults only),
• Adding disopyramide in combination with an atrioventricular nodal blocking agent, or
• Referral for septal reduction therapy at an experienced center

Cardiac myosin inhibitors target the disease mechanism directly, reducing the excess actin-myosin cross-bridge formation that drives hypercontractility and obstruction.²

In the phase 3 SEQUOIA-HCM trial, a selective cardiac myosin inhibitor improved peak oxygen uptake versus placebo (least-squares mean between-group difference 1.7 mL/kg/min; 95% CI 1.0-2.4; P<0.001), with significant improvement across all 10 prespecified secondary endpoints and an adverse-event rate similar to placebo.²

A selective cardiac myosin inhibitor in this class was approved by the US Food and Drug Administration (FDA) for symptomatic obstructive HCM in December 2025.³

Monitoring changes once a myosin inhibitor is on board

The trade-off for that targeted efficacy is a predictable, dose-related reduction in LVEF, which can produce heart failure from systolic dysfunction. Class labeling reflects this:³

• Echocardiographic LVEF assessment is required before and during treatment
• Initiation is not recommended below an LVEF of 55%
• Dose reduction or interruption is directed as LVEF falls

Because of the heart-failure risk, these agents are dispensed only through a Risk Evaluation and Mitigation Strategy (REMS) requiring prescriber, pharmacy, and patient enrollment. LVEF reductions seen in trials were reversible after stopping.^2,3

Drug interactions matter – metabolism runs largely through CYP2C9, so strong CYP2C9 inhibitors and certain azoles raise exposure and heart-failure risk, and concomitant rifampin is contraindicated.³

The practical message for clinicians treating HCM patients: Confirm obstruction with provocation before concluding a symptomatic patient is nonobstructive, optimize and rationalize first-line therapy, and – when symptoms persist – escalate deliberately, matching the added echocardiographic surveillance and REMS logistics of cardiac myosin inhibition to the patient in front of you.^1,3