What is happening in the heart
In hypertrophic cardiomyopathy, the muscle of the left ventricle becomes abnormally thickened — usually most prominently in the septum, the wall that divides the two ventricles. The thickening is caused by mutations in the proteins that make the muscle contract; the muscle cells themselves are also disorganized at the microscopic level, a finding we call “myocyte disarray.” That disarray is part of why HCM carries an arrhythmia risk that simple wall thickness alone wouldn’t predict.
The consequences fall into three buckets:
- Obstruction. When the septum is thick enough, it crowds the outflow tract — the path blood takes as it leaves the left ventricle. Combined with abnormal motion of the mitral valve, this can dramatically reduce forward blood flow, especially during exertion. We call this obstructive HCM, or HOCM.
- Diastolic dysfunction. The thickened, stiff muscle has trouble relaxing and filling, even when it pumps fine. This drives shortness of breath, fatigue, and exercise limitation.
- Arrhythmia risk. The disorganized muscle can be a substrate for both atrial fibrillation and ventricular tachycardia — and HCM remains one of the leading causes of sudden cardiac death in young people, including athletes.
Obstructive versus nonobstructive
About two-thirds of patients have obstructive HCM — either at rest or only when provoked by exercise. The obstruction is dynamic: it gets worse with dehydration, with vasodilators, and with anything that makes the heart squeeze harder against an empty chamber. Nonobstructive HCM accounts for the other third and is driven primarily by the stiff, poorly relaxing ventricle.
The distinction matters because most procedural therapies — myectomy, alcohol ablation, and mavacamten — were developed specifically to relieve obstruction.
Why it matters
Most patients with HCM have a normal life expectancy. The two main reasons we follow patients carefully are:
- Symptoms from obstruction — shortness of breath, chest pain, presyncope on exertion, and exercise intolerance.
- Sudden cardiac death risk — small in absolute terms for most patients, but devastating when it happens, and concentrated in young people.
How we diagnose it
- Echocardiogram is the cornerstone. We measure wall thickness, look for obstruction at rest and with provocation, evaluate the mitral valve, and assess function.
- Cardiac MRI adds detail — particularly identifying late gadolinium enhancement, which marks fibrosis and is one of the strongest predictors of arrhythmia risk.
- ECG is almost always abnormal, even before the echo shows striking thickening.
- Holter or longer-term monitoring looks for runs of nonsustained VT — an important risk marker.
- Exercise testing to measure the blood pressure response and unmask provocable obstruction.
- Genetic testing and family screening — once a mutation is identified in a patient, first-degree relatives are screened.
Sudden-death risk stratification
We use the major risk factors together to decide whether a primary-prevention ICD is warranted:
- Family history of sudden cardiac death in a close relative
- Unexplained syncope (fainting), especially recent or recurrent
- Massive left ventricular wall thickness (typically 30 mm or more)
- Nonsustained ventricular tachycardia on monitoring
- Abnormal blood pressure response to exercise
- Extensive late gadolinium enhancement on MRI
- A left ventricular apical aneurysm
- An ejection fraction that has dropped below 50%
A single strong risk factor is often enough; multiple weaker ones add up. The conversation about an ICD is highly individualized.
How we treat it
Medications
- Beta-blockers are first-line for most symptomatic patients — they slow the heart, give it more time to fill, and reduce dynamic obstruction.
- Non-dihydropyridine calcium channel blockers (verapamil, diltiazem) are alternatives.
- Disopyramide is added when beta-blockers and calcium blockers don’t relieve obstruction.
- Mavacamten is a newer drug developed specifically for obstructive HCM. It directly reduces the excess contractility that drives obstruction; in trials, it meaningfully lowers gradients and improves symptoms. It requires periodic echocardiograms to monitor for over-suppression.
- We avoid vasodilators (some blood-pressure medications, nitrates) in obstructive HCM because they make the gradient worse.
Septal reduction therapy
When symptoms persist despite medications, we reduce the thickness of the septum directly:
- Surgical myectomy — open-heart surgery in which a strip of muscle is removed from the septum. In experienced centers, it has excellent long-term results and is the gold standard for many patients, particularly younger ones.
- Alcohol septal ablation — a catheter procedure that injects alcohol into a small artery feeding the septum, creating a controlled localized infarction that thins the muscle over weeks. Less invasive than surgery and a good choice for older patients or those at high surgical risk.
ICD decisions
When risk factors point to elevated sudden-death risk, a primary-prevention ICD is offered. Choice between transvenous and subcutaneous ICD depends on whether pacing is needed and on patient age and anatomy.
What to expect at your visit
We’ll review your echo, MRI, ECG, and family history together, and walk through your individual sudden-death risk. We’ll talk about symptoms — especially exertional shortness of breath, chest pain, and any fainting — and figure out whether obstruction is the driver. From there we build a plan that may include medications, a procedural therapy, an ICD, and a screening plan for your family.