What are the left ventricular outflow tract (LVOT) obstruction gradients as seen on echocardiogram?

From the Guidelines

Left ventricular outflow tract (LVOT) obstruction gradients on echocardiography are considered significant if they are ≥30 mmHg at rest, with severe obstruction defined as ≥50 mmHg, as stated in the 2024 AHA/ACC/AMSSM/HRS/PACES/SCMR guideline for the management of hypertrophic cardiomyopathy 1.

Key Points to Consider

• LVOT gradients are dynamic and sensitive to ventricular preload, afterload, and contractility, and thus vary with heart rate, blood pressure, volume status, activity, medications, food, and alcohol intake 1.
• Provocative maneuvers such as standing, Valsalva strain, or exercise with simultaneous auscultation or echocardiography are recommended if minimal gradients (ie, <30 mmHg) are observed at rest 1.
• The site and characteristics of obstruction should be identified, as management will change depending on whether the obstruction is deemed to be valvular, dynamic LVOTO, fixed subvalvular, or midcavitary due to hypertrophied/anomalous papillary muscles and/or hyperdynamic LV function with systolic cavity obliteration 1.

Management and Treatment

• First-line medical therapy for patients with significant gradients includes beta-blockers or non-dihydropyridine calcium channel blockers, which reduce contractility and heart rate, thereby decreasing LVOT obstruction.
• Patients should avoid dehydration, excessive alcohol, and vasodilators which can worsen obstruction.
• If medical therapy fails, invasive options include septal reduction therapy (alcohol septal ablation or surgical myectomy) 1.

Monitoring and Follow-up

• Serial echocardiographic assessment is essential to monitor gradient changes over time and evaluate treatment response, with follow-up typically recommended every 1-2 years for stable patients or more frequently when symptoms change 1.

From the Research

Echo LVOT Obstruction Gradients

• LVOT obstruction gradients can be measured using transesophageal echocardiography (TEE) and Doppler techniques, providing detailed information on the site, mechanism, and severity of the obstruction 2.
• Studies have shown that intraoperative TEE is useful in defining the level and nature of LVOT obstruction, directing the surgical approach, and detecting surgical complications 2.
• The causes of LVOT obstruction are diverse, including hypertrophic obstructive cardiomyopathy (HOCM), hypertensive left ventricular hypertrophy, post-open heart surgery, sigmoid septum, and discrete subaortic membrane 3.
• LVOT obstruction gradients can be improved or reduced with medications and transcatheter procedures, with significant improvement observed in 93% of cases at follow-up echocardiography 3.
• Management of HOCM with obstruction involves activity restriction, prevention of sudden cardiac death, control of symptoms, and screening of relatives, with pharmacologic treatment consisting of negative inotropic drugs and nondihydropyridine calcium channel blockers 4.
• Septal reduction therapy, including septal myectomy and alcohol septal ablation, may be considered for patients with intolerable symptoms despite optimal conservative therapy 4.
• LVOT obstruction may cause false-positive dobutamine stress echocardiograms, highlighting the importance of considering alternative diagnoses in patients with suspected coronary artery disease 5.
• The mechanism of obstruction in HOCM involves muscular hypertrophy encroaching on the ventricular chamber, reducing chamber area and volume, with obstruction at the mitral valve level 6.