Introduction: A non-invasive method for regional mapping of mechanical activation could be useful in the diagnosis of pathologies affecting cardiac contraction patterns. With the advent of high frame rate echocardiography, there is potential to uncover rapid events not seen by conventional imaging. Novel echo acquisition and signal processing methods were tested for the assessment of mechanical activation.
Purpose: To assess the feasibility of using high frame rate ultrasound imaging to determine spatio-temporal information about onset of mechanical activation in the left ventricle.
Methods: High frame rate ultrasound imaging (1000 to 1200 fps) was performed on 3 anesthetized open chest dogs during epicardial right ventricle (RV) and left ventricle (LV) free wall pacing. Combined sonomicrometry and electromyography (EMG) was recorded simultaneously.
The activation of the LV was mapped by tracking the propagation of the mechanical wave that occurred in the tissue after pacing. The wave propagation was estimated using Clutter Filter Wave Imaging (CFWI). CFWI was configured to highlight tissue moving at a velocity above 2.5 cm/s. An activation map showing the arrival times of the propagating activation wave, as estimated by CFWI, was computed for each pacing experiment.
The timing of mechanical activation from CFWI was compared to electrical activation and to mechanical activation in terms of strain rate measured by sonomicrometry.
Results: Figure 1a shows the mechanical activation map from pacing of the RV free wall. Early activation can be seen in the mid to apical septum, then spreading bilaterally with the latest activation in the basal lateral wall. The delays between activation of the basal septum and the lateral wall, measured using EMG and CFWI were 24.3±4.3 and 23.6±1 ms, respectively, with a difference of 0.7±4.4 ms. The difference between mechanical activation measured by sonomicrometry and CFWI was 1.7±6.7 ms.
Figure 1b shows the mechanical activation map from pacing of the LV lateral wall. Mechanical activation started in the mid lateral wall, then spreading bilaterally with the latest activation in the basal septum. The delays between activation of the basal septum and the lateral wall, measured using EMG and CFWI were 35.4±10.01 and 33.5±8.04 ms, respectively, with a difference of 1.9±12.8 ms. The difference between mechanical activation measured by sonomicrometry and CFWI was 3.4±4.1 ms.
Conclusion: This pilot study showed that mechanical activation measured by CFWI had good agreement with invasive measurements. Thus, this novel CFWI method shows potential as a non-invasive tool for LV mechanical activation mapping.