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 (M(max)) occurred at 152+24 and 147+24 ms, respectively; p=0.66, intra-class correlation ICC 0.93). M(max) 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.