High frame rate strain rate imaging of the interventricular septum in healthy subjects

Objective: In the present study the feasibility was assessed of a new strain rate imaging method with a very high frame rate of around 300 frames per second. Methods: Digital radio-frequency (RF) data were obtained in nine healthy subjects using a sector of 20-30° in an apical four chamber view. The RF data were analysed using a dedicated software package that displays strain rate images and profiles and calculates strain rate values. With the new method, it is possible to study events and spatial-temporal differences in the heart cycle with duration down to 3.5-3 ms, including the pre-ejection period and the isovolumic relaxation period. Since the interventricular septum (IVS) is of crucial importance for the left and right ventricular function, we assessed changes through the heart cycle of the strain rate in the IVS. Results: Mean peak systolic strain rate in the healthy subjects was -1.65±0.13 s^-1. Mean peak diastolic strain rate during early filling was 3.14±0.50 s^-1 and during atrial systole 0.99±0.09 s^-1. We found individual differences in the strain rate patterns, but in all subjects, the ventricular contraction started simultaneously in all parts of the septum. After the ejection period, the elongation started before aortic valve closure, in the midinferior septum and propagated towards the apex. Conclusion: High frame rate strain rate imaging makes it possible to study rapid deformation patterns in the heart walls.