Ventricular Pacing Alters Twisting Synchrony of the Left Ventricle ABSTRACT Background: Normal cardiac motion is a coordinated sequence of apex to base and circumferential shortening along with a simultaneous twisting component. The normal atrioventricular conduction coordinates this sequential motion of normal heart. Bypassing the normal conduction pathway disturbs this coordination between different components of cardiac motion, which could affect overall cardiac function. We studied the impact of ventricular pacing on the twisting dynamics of left ventricular (LV) function. Methods: Three pigs (2-3kg) were lightly anesthetized and the heart exposed after median sternotomy. We used a 10 MHz sector probe and a 13 MHz linear probe placed lightly on the surface of the heart to acquire 2D and tissue Doppler images on a GE VIVID 7 Dimensions ultrasound system at frame rates >150/sec. The study was conducted at three states including sinus rythem, RA-LV and RA-RV pacing. High fidelity aortic pressure was recorded simultaneously. Acquired data was later analyzed offline in EchoPac® for motion analysis of LV walls using tissue Doppler based and 2D speckle tracking based method. Results: Right ventricular (RV) pacing distorted the twisting synchrony of LV with a simultaneous drop in systolic pressure from 60-70 mmHg to 40-50 mmHg recorded by a catheter in the change with ventricular pacing. DISCUSSION The twisting component of cardiac motion has been described in a mathematical model of LV mechanics by Arts et al., and the mechanical model of helical heart hypothesis by Torrent-Guasp. Cardiac twist effictively adds force to ejection by producing intersegmental torsion. A coordinated sequence of apex to base and circumferential shortening, along with simultaneous twisting, is essential for effective dynamic cardiac function. Bypassing the normal conduction pathway disturbs this coordination between different components of cardiac motion, which yield coordinated twisting. Thus it may be important to evaluate segmental twist and torsion during, before and after CRT. Limitations High-resolution and high frame rate image acquisition that was made possible due to epicardial scanning in this study, may be difficult to obtain in clinical exams through poor acoustic windows. CONCLUSIONS Twisting synchrony in ventricular walls correlates well with ejection pressure and dynamic function of heart. Tracking regional twist could be a reliable parameter of ventricular synchrony and cardiac function during CRT. DISCLOSURES No relationships to disclose: Muhammad Ashraf, MD Xiao Kui Li, MD Ling Hui, MD, PhD Edward Hickey, MD Occasional consultant to GE Medical Systems: David J. Sahn, MD This work was supported in part by the NIH Bioengineering Research Partnership grant HL67647. based methods. We sought to study the effect of ventricular pacing on segmental twisting and relate this to hemodynamic variables, using the new speckle tracking based method. METHODS Three piglets (2-3kg) were lightly anesthetized and the heart exposed by median sternotomy. Cardiac motion was scanned from the surface of the heart using a 10 MHz sector probe and a 13 MHz linear probe to acquire 2D grayscale and tissue Doppler images on a GE Vivid 7 Dimension ultrasound system at frame rates >150/sec. The study was conducted at three states including sinus rhythm, synchronous RA-LV and RA-RV pacing. High fidelity aortic pressure was Ventricular Pacing Alters Twisting Synchrony of the Left Ventricle Muhammad Ashraf, MD, Xiao Kui Li, MD, Ling Hui, MD, PhD, Edward Hickey, MD, David J. Sahn, MD Oregon Health & Science University, Portland, OR recorded simultaneously. Acquired data was later analyzed offline in EchoPac® for motion analysis of LV walls. RESULTS Ventricular pacing distorted the twisting synchrony of the LV with a simultaneous drop in systolic pressure from 60-70 mmHg to 40-50 mmHg recorded by a catheter in the descending aorta. Amplitude of twist was reduced in all segments of the LV walls (clockwise from 5°-7° to 1°-3° at basal level, and counter-clockwise from 7°-9° to 2°-4° at apical level) along with loss of synchrony. These effects were more prominent with LV pacing. Tissue Doppler based strain analysis had not clearly defined twist, nor showed any consistent pattern of descending aorta. Amplitude of twist was reduced in all segments of LV walls (clockwise from 5°-7° to 1°-3° at basal level, and counter-clockwise from 7°-9° to 2°-4° at apical level) along with loss of synchrony. These effects were more prominent with LV pacing. Conclusion: Tracking regional twist could be a reliable indicator of synchrony and cardiac function during CRT. BACKGROUND It has been shown that LV mechanical dyssynchrony, as compared to EKG changes, is a more important determinant of response to cardiac resynchronization therapy (CRT). Various techniques to detect and quantify LV mechanical dyssynchrony are currently under investigation. Echocardiography, and in particular tissue Doppler motion detecting methods, have shown significant promise in this regard. An array of echocardiographic parameters has been developed to identify mechanical dyssynchrony based on the onset, peak, or end-systolic motion of the different segments of the ventricular wall. However, the correlation between these parameters and hemodynamic variables has not been demonstrated yet. Recently a new motion detecting method has been introduced which lacks the angle dependency inherent to Doppler Sinus Rhythm RA-LV Pacing RV Pacing RA-RV PACING RA-RV Pacing