Syncope in a Young Athlete With Dynamic Outflow Obstruction

No - in hypertrophic cardiomyopathy the gradient is dynamic and load-dependent, varying with preload, afterload, contractility, and heart rate. A resting gradient below 30 mmHg does not exclude severe provocable obstruction, and this patient's syncope during maximal exertion is exactly the setting in which the gradient would be highest.

Provocation:

• Valsalva (strained phase) in the semi-recumbent or standing position - reduced preload increases the gradient and SAM.
• Standing from supine, which drops preload rapidly.
• Symptom-limited exercise echocardiography - the preferred test for a symptomatic patient because it reproduces the physiology of the event (tachycardia, reduced afterload, dehydration) and also captures the BP response and arrhythmia. Measure the gradient immediately post-exercise, not after a recovery pause.

What not to use: dobutamine. In obstructive HCM with SAM, dobutamine raises contractility and lowers afterload with little preload dependence, which can produce profound obstruction and hypotension. It reproduces a laboratory artifact rather than the patient's physiology.

Threshold context: a provoked gradient ≥50 mmHg in a symptomatic patient is the accepted trigger for considering septal reduction therapy - which is why a resting 18 mmHg must not close the question.

It is SAM-related MR. As the anterior leaflet is dragged into the LVOT, it fails to coapt normally with the posterior leaflet, and the resulting regurgitant jet is directed away from the septum - posteriorly and usually late-peaking and dynamic.

Why it matters:

• It is a marker that the mechanism of MR is outflow obstruction, not intrinsic valve disease. Relieving the obstruction (myectomy or alcohol septal ablation) usually relieves the MR as well - so the surgeon should not plan a mitral repair for a valve that is structurally normal.
• Conversely, if the jet were anteriorly directed, or you found prolapse, flail, or chordal thickening, you would be dealing with intrinsic degenerative disease that needs its own repair, and the operative plan changes.
• The MR is dynamic: it varies with loading. Grade it in the same hemodynamic state as the gradient measurement, and describe the variability rather than giving a single number.
• Sample the LVOT gradient with continuous-wave, not pulsed, Doppler - velocities exceed the pulsed Nyquist limit and a PW tracing will alias or truncate, giving a falsely low gradient.

What to report:

• Maximum LV wall thickness and its location - 26 mm. The conventional high-risk marker is ≥30 mm, so he is below the classic threshold, but thickness is a continuous risk variable and 26 mm in a 29-year-old is substantial.
• Apical aneurysm - screen for it explicitly, including contrast if the apex is not seen; an apical aneurysm with akinetic walls is an additional risk marker.
• LVOT gradient at rest and provoked.
• LVEF and LA size, MR severity, and filling pressures.
• Symptoms/context you can document: exertional syncope is one of the major risk markers; his brother's sudden death at 24 is another.

Limits:

• Echocardiography supplies only part of the risk profile. It cannot see fibrosis, does not provide the ambulatory Holter (nonsustained VT) or the exercise BP response, and cannot make the ICD decision.
• The right output is a report that lays out the risk-relevant echo features plus a statement that the patient needs specialist HCM evaluation with exercise testing, ambulatory monitoring, and shared decision-making about an ICD - not a report that implies a 26 mm septum is "low risk." Also flag exercise restriction as part of the counselling message to the referring clinician.