Muscle dynamics in hypertrophic cardiomyopathy

Area of Science:

• Cardiology
• Cardiovascular Physiology
• Echocardiography

Background:

• Hypertrophic cardiomyopathy (HCM) is often associated with prolonged isovolumic relaxation period (IRP), indicating impaired left ventricular pressure decline.
• Previous studies suggest IRP is a key indicator of diastolic dysfunction in HCM.

Purpose of the Study:

• To investigate the variability of IRP in a cohort of hypertrophic cardiomyopathy patients.
• To identify subgroups within HCM patients based on IRP measurements.
• To explore the relationship between short IRP and hemodynamic characteristics, including outflow tract obstruction.

Main Methods:

• Simultaneous recordings of echocardiogram, apexcardiogram, phonocardiogram, and ECG were performed.
• Eighty-four patients with proven HCM and 31 normal subjects were studied.
• Isovolumic relaxation period (IRP) was measured and analyzed across different subgroups.

Main Results:

• Normal subjects had a mean IRP of 61 ± 11 ms.
• HCM patients exhibited a wide range of IRP values (0–160 ms).
• Three subgroups were identified: prolonged IRP (sinus rhythm), normal IRP (atrial fibrillation), and short IRP (0–45 ms).
• The short IRP subgroup showed signs of outflow tract systolic pressure gradient, aortic valve abnormalities, and mitral valve motion abnormalities.
• Short IRP was linked to delayed aortic valve closure, questioning the reliability of the A2-Mo interval as a measure of ventricular relaxation.

Conclusions:

• Isovolumic relaxation period (IRP) shows significant variability in hypertrophic cardiomyopathy (HCM).
• A subset of HCM patients with short IRP may present with dynamic outflow tract obstruction.
• The non-invasive A2-Mo interval may not consistently reflect left ventricular relaxation in all HCM patients, especially those with short IRP.