left ventricular outflow tract obstruction

Blood leaving the left ventricle passes through a short channel — the left ventricular outflow tract — on its way to the aorta, like water funnelling through a doorway before reaching the hall. Left ventricular outflow tract obstruction is a narrowing of that doorway during contraction, so the heart must generate extra pressure to push blood through, and less blood reaches the body.

The classic cause is hypertrophic cardiomyopathy: a thickened septum narrows the outflow tract, and during ejection the mitral valve leaflet is drawn forward into the stream (systolic anterior motion), worsening the blockage. The obstruction is often dynamic — it varies with the heart's filling and squeezing, so it can be mild at rest yet severe after standing up, exertion, or dehydration, which is why some patients faint with exercise.

Symptoms include breathlessness, chest pain, palpitations, and fainting, and a characteristic murmur that gets louder when the ventricle is less full. Because the obstruction is dynamic, treatment often aims to slow and relax the heart and keep it well filled, sometimes with medication; severe, drug-resistant cases may be relieved by septal myectomy or alcohol septal ablation. It differs from fixed outflow narrowing such as aortic stenosis at the valve.