Mechanical Wave Analysis at High Frame-Rate Echocardiography: Feasibility, Determinants and Normal Ranges.

Background: High-frame-rate echocardiography can identify naturally-occurring mechanical waves (MW). As the velocity of MW is related to tissue properties, this methodology could solve a fundamental shortcoming of echocardiography. However, to be useful clinically, there would need to be limited overlap between the normal range of MW, and measurements associated with pathology such as LV dysfunction and ischemic heart disease.

Objectives: To evaluate the feasibility, key determinants, and normal ranges of MW in asymptomatic people, and patients with cardiac pathology.

Methods: Asymptomatic participants were recruited from a community-based heart failure surveillance program. Clinical evaluation, six-minute walk test, and echocardiography with specialized high-frame-rate imaging were performed. MW signals from atrial kick (AK), aortic valve closure (AVC), and mitral valve closure (MVC) were acquired from parasternal long-axis (PLAX) and apical four-chamber (A4C) windows. Measurements were averaged across three cycles using automated and manual methods, and outliers were removed (AVC and MVC >9 m/s, AK >7 m/s). Participants were classified into normal and abnormal groups based on echocardiographic and clinical parameters.

Results: Of the 239 participants, manual measurement was feasible in 80% for AK-, 77% for AVC- and 77% for MVC-MW in the PLAX view, and 91%, 85% and 62% from the apical view. Manual measurements were more feasible than automated measurements. Clinical and echocardiographic markers of hemodynamics and cardiac function had little or no association with MW velocities. There was poor agreement noted between apical and PLAX view MVC signals, especially with high velocity measurements. In 158 normal participants, MW velocities in PLAX for AVC, MVC and AK were 3.78±1.72, 3.36±1.75, 1.46±0.87 m/s. In A4C, these were 3.32±1.72, 4.14±1.98 and 1.23±0.49 m/s, respectively. Only AK measurements were significantly different between the patients with normal and abnormal echocardiograms. There was little bias within and between observers, but limits of agreement were wide for all measures.

Conclusion: MW measurement - especially AK - is a feasible adjunct to standard echocardiography. However, the normal ranges are wide, even among participants with otherwise normal studies. MW velocities do not seem to be abnormal in subclinical dysfunction.