Normal asynchrony of left ventricular long and short axes: Their relationship with aortic hemodynamics

Abstract Background The relationship between left ventricular (LV) long and short axes, aortic pressure ( P ), flow velocity ( U ) and wave intensity is not well established. Methods Eleven dogs were anaesthetized and mechanically ventilated and LV long and minor axes shortening velocities were calculated using ultrasound crystals. P and U were measured in the ascending aorta using a high fidelity pressure catheter and ultrasonic flow transducer. Results Pre-ejection: The LV minor axis began to shorten as the long axis lengthened creating LV shape change. Early ejection: The aortic valve opened 83 ± 20 ms after the ECG Q-wave. Aortic P and U simultaneously increased; peak aortic velocity and maximum minor axis shortening velocity ( Mmax ) occurred at 152 + 24 and 147 + 24 ms, respectively; p = 0.66, intra-class correlation ICC 0.93). Mmax also corresponded to the time when the reflected compression wave arrived back to the heart (ICC 0.75). Late ejection: LV long axis reached its peak shortening velocity 28 + 21 ms later than the minor axis at 175 ± 33 ms, coinciding with peak LV pressure (187 + 25 ms; p = 0.77, ICC 0.65) and onset of the forward expansion wave (177 + 28 ms, p = 0.88, ICC 0.89). Both axes then continued to slow until 210 ± 30 ms when an increased rate of decline of shortening velocity corresponded with peak aortic pressure. Conclusion Long axis peak shortening velocity lagged consistently behind the minor axis, representing a degree of normal asynchrony. The arrival of the reflected wave appears to bring about the slowing down of the minor axis.