Abstract 14214: Visualization and Quantification of Autogenic Cardiac Mechanical Waves

Introduction: We have developed a visualization technique, High Speed Difference Imaging (HSDI) that has revealed many rapidly propagating phenomena throughout the cardiac cycle. We observed diastolic and systolic waves in adult volunteers and measured their velocities to determine the nature of the waves. We hypothesize from these early observations that these waves are autogenic shear waves that will propagate at higher velocities in systole. Methods: High frame rate ultrasound images were acquired using the T5 System with synchronous EKG. T5 is the Duke University Phased Array Research Ultrasound Scanner that can be configured to acquire real time, live images at rates up to 1000 B-Modes per second for adult cardiac applications. HSDI were generated in 10 volunteers in the AP4 view. A late diastolic shadow that propagated from apex to base in the lateral wall was characterized in all volunteers. A distinct early systolic shadow was able to be isolated in the lateral wall of five volunteers. The velocity of these shadows was calculated by measuring the length of the lateral wall along during its appearance and by counting calibrated timed frames while the shadow was visible. Results: The diastolic propagating shadow was observed in all ten volunteers in multiple cardiac cycles. The late diastolic shadow was measured propagating apex to base at an average velocity of 2.5 ± 0.5 m/sec. In the five volunteers with distinct systolic shadows, the propagating velocity was measured to be 4.8 ± 0.7 m/sec. The average ratio of systolic shadow propagation velocity to diastolic in the five patients was 1.95. These propagation velocities are comparable to published myocardial shear wave velocities in humans. Conclusions: The propagation velocity of these waves doubles in systole when the myocardial tissue is stiffened, and the velocities measured are within the range of reported shear wave velocities in myocardium. We conclude that high frame rate ultrasound imaging may allow for the visualization and quantification of autogenic cardiac shear waves.