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

Abstract

Background: High-frame rate echocardiography can identify naturally occurring mechanical waves (MWs). As the velocity of MWs 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 MWs and measurements associated with pathology such as left ventricular dysfunction and ischemic heart disease.

Objectives: This study aims to evaluate the feasibility, key determinants, and normal ranges of MWs in asymptomatic people and in patients with cardiac pathology.

Methods: Asymptomatic participants were recruited from a community-based heart failure surveillance program. Clinical evaluation, 6-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 4-chamber (A4C) windows. Measurements were averaged across 3 cycles using automated and manual methods, and outliers were removed (AVC >9 m/s, MVC >9 m/s, and AK >7 m/s). Participants were classified into normal and abnormal groups on the basis of echocardiographic and clinical parameters.

Results: Of the 239 participants, manual measurement was feasible in 80% for AK, 77% for AVC, and 77% for MVC MWs in the PLAX view and in 91%, 85%, and 62% in the A4C view. Manual measurements were more feasible than automated measurements. Clinical and echocardiographic markers of hemodynamic status and cardiac function had little or no association with MW velocities. Poor agreement was noted between A4C and PLAX MVC signals, especially with high-velocity measurements. In 66 participants without overt CVD, MW velocities in the PLAX view for AVC, MVC, and AK were 3.91 ± 1.82 m/s, 3.58 ± 1.67 m/s, and 1.77 ± 1.10 m/s. In the A4C view, these were 4.09 ± 1.54 m/s, 5.63 ± 1.61 m/s, and 1.24 ± 0.38 m/s, respectively. These values were generally slightly higher in 103 asymptomatic people with subclinical dysfunction. Only AK measurements were significantly different between patients with normal and abnormal findings on echocardiography. There was little bias within and between observers, but limits of agreement were wide for all measures.

Conclusions: 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.

Keywords: aortic valve closure; atrial kick; mechanical waves; mitral valve closure.