This study used LA-LV V-LOOPs to comprehensively analyze the left ventricular function of healthy adults of different ages. The main results can be summarized as follows: (1) With the increase of age, LA-LV V-LOOPs upwards shift. The results showed that the left atrial volume of healthy adults increased with age while no significant difference was found in left ventricular volume. (2) The left ventricular volume of female group throughout LV systole was smaller than that of male group, however, no remarkable difference between the Slopes of LV systole. (3) LA-LV V-LOOPs could synchronously reflected the left atrial-ventricular function in real time.
Left atrial volume
Studies had proved that the maximum left atrial volume was an important indicator of left ventricular diastolic function, and had clear value in assessing the severity of heart disease [12, 13].
Although most studies focus on the maximum left atrial volume, the minimum left atrial volume could not be ignored. Since the left atrium was continuously exposed to the left ventricle during mitral valve opening, the minimum left atrial volume may well reflect the left ventricular end diastolic pressure. Even in some studies, the minimum left atrial volume could better reflect the increase of left ventricular filling pressure and pulmonary wedge pressure than the maximum left atrial volume, which had greater prognostic value[14-16].
The evaluation of volume changes in the cardiac cycle can convey potential information reflecting pathophysiology[10, 17, 18]. In LA-LV V-LOOPs, the left atrial volume was included throughout the cardiac cycle. Whether it is the maximum volume of left atrium, the minimum volume of left atrium, or even the volume of every stage in the cardiac cycle, can be reflected in LA-LV V-LOOPs. Therefore, LA-LV V-LOOPs had the possible to reflect both left ventricular diastolic function and left ventricular end diastolic pressure at the same time.
In our study, the left atrial volume of the whole cardiac cycle showed an upward trend with the increase of age. This may indicate decreased diastolic function and increased left ventricular end diastolic pressure in the elderly, which was consistent with the results of traditional echocardiography and the reflection of left ventricular function in the elderly in previous studies[19].
Left ventricular volume
The evaluation of left ventricular (LV) volume and ejection fraction (EF) was very important for the practice of Cardiology [2, 20].The volume of the left ventricle depended on the load condition of the heart. Changes in left ventricular volume defined SV and cardiac output[21]. For a single cardiac cycle, LVEF was calculated as the difference between end diastolic volume (EDV) and end systolic volume (ESV) divided by EDV. Therefore, the change of left ventricular volume in cardiac cycle could evaluate left ventricular systolic function. In this study, the total systolic left ventricular volume in women was smaller than that in men while the difference of systolic left ventricular volume was not significant, which may indicate that women had higher ejection fraction. Previous studies had yielded similar results[7, 22, 23].Women's hearts may have better reserve function than men.
Atrial-ventricular coupling
LA-LV V-LOOPs could reflect this correlation of LA-LV in real time. Depending on the morphological changes of loop, the changes of atrial-ventricular volume in the whole cardiac cycle could be recognized at the same time. We tried to use the slope of loop, the ratio of left atrial and left ventricular volume difference, to express the overall function under atrial-ventricular coupling. As shown in Figure 5, the systolic slope was equal to the difference of left atrial volume divided by the difference in left ventricular volume. The difference of left ventricular volume could reflect the change of stroke volume. The left atrium plays a storage function in systole and existed as a reservoir. The change of its volume may be affected by three factors: the blood flow to the left ventricle, the blood flow from the pulmonary circulation and the structure of the left atrium. Therefore, the change of left atrial volume could reflect the changes of pulmonary circulation pressure, systemic circulation pressure and left ventricular contractility. In the elderly population, the increase of slope may reflect one or more combinations of decreased cardiac output, increased pulmonary circulation pressure, decreased systemic circulation pressure and decreased left ventricular contractility. In a word, ‘Slope’ may be associated with worse prognosis.
Further study
At present, our study only explored the changes of left atrial-ventricular volume by LA-LV V-LOOP in healthy adults. Previous studies have shown that the volume of left atrium and ventricle also has great diagnostic and predictive value for other heart diseases, such as hypertensive heart disease[24], sepsis cardiomyopathy[25], dilated cardiomyopathy[26], heart failure[27] and so on. Next, we plan to explore other heart diseases accordingly. LA-LV V-LOOPs had a certain ability to evaluate the volume change in different stages of the same cardiac cycle.
Limitation
The acquisition and analysis of three-dimensional images only used the machines and software of the same supplier, which was not generally applicable. We were not sure whether the machines of other manufacturers could get similar results. The distribution of age was not completely uniform. The elderly population was relatively small, and there may be some bias. Although the subjects were healthy adults and met the inclusion criteria, we could not rule out the possibility of subclinical coronary artery disease, especially in elderly subjects.