Background: Inhomogenous left ventricular activation-inactivation has been suggested to play a role in the genesis of segmental early relaxation and in turn of isovolumic relaxation flow (IRF). The spatial distribution of conduction system in the left ventricle leads to heterogenous activation sequence even in healthy subjects. This study was conducted to evaluate our hypothesis that IRF should be ubiquitous in healthy subjects.
Methods: This prospective study included 126 healthy subjects (aged 15-81 years) free of acute or chronic illness by history and physical examination. No significant abnormality appeared in the resting 12-lead electrocardiogram or transthoracic echocardiogram. With the pulsed-wave Doppler echocardiography, the sample volume was placed at the mid-ventricle to detect the IRF.
Results: An apically directed IRF, with the velocity 17-101 cm/sec and the duration 57-145 ms, could be detected in all the study subjects. There was no inter-sex difference in such characteristics of IRF. However, its duration and velocity got longer and higher with aging. The fractional shortening of the left ventricle and the interventricular septal thickness were stepwisely selected as the determinants of the IRF velocity, and the transmitral E-to-A wave velocity ratio, the left ventricular inflow propagation velocity, and the interventricular septal thickness as the determinants of the IRF duration.
Conclusions: IRF is ubiquitous in healthy subjects. Both the duration and the velocity of IRF present an aging trend and may be mainly related to left ventricular diastolic and systolic performance, respectively.