The power of the left atrioventricular coupling index in cardiovascular disease

Figures

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  Figure 1. Functional roles of the LA during the cardiac cycle. (A) Reservoir phase: The LA serves as a reservoir, receiving blood from the pulmonary veins while the mitral valve is closed. During this phase, the LA expands to its maximal volume, while the LV ejects blood into the aorta through the open aortic valve. (B) Conduit phase: The mitral valve opens, and the LA functions as a passive conduit, allowing blood to flow from the pulmonary veins through the LA into the LV. This phase leads to LV expansion and filling, with minimal active involvement from the LA. (C) Booster pump phase: The LA contracts actively, functioning as a booster pump to enhance LV filling. This active contraction increases LA emptying volume, optimizing LV preload and priming the LV for systole. LA, left atrium; LV, left ventricle.

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  Figure 2. Hemodynamic changes in the LA and LV during different phases of the cardiac cycle. (A) Systole: The LA acts as a reservoir, receiving blood from the pulmonary veins while a weak vortex (↺, red rotating arrow) forms parallel to the closed mitral valve. The LV contracts, ejecting blood toward the aorta (↓↓↓, red downward arrows; aorta not shown), leading to LA expansion and LV volume reduction. (B) Early diastole: The mitral valve opens, allowing passive blood flow (→, red horizontal arrow) from the LA into the LV. A strong vortex (↻↻, red rotating arrows) forms in the LV, aiding its expansion, while LA volume decreases slightly. (C) Late diastole: The LA contracts actively, functioning as a booster pump to enhance LV filling (⇒, red double horizontal arrow). The LV vortex strengthens (↻↻↻, red rotating arrows), and LV volume reaches its maximum, while LA volume decreases further. LA, left atrium; LV, left ventricle.

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  Figure 3. The method to assess LACI by CMR. LACI is calculated as the ratio of LA end-diastolic volume to LV end-diastolic volume. LA end-diastolic volume (green volume) is shown in the 2-chamber panel (A) and 4-chamber panel (C) views during end-diastole. LV end-diastolic volume (yellow volume) is shown in the 2-chamber panel (B) and 4-chamber panel (D) views. LACI, left atrioventricular coupling index; CMR, cardiovascular magnetic resonance; LA, left atrium; LV, left ventricle.

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  Figure 4. The method to assess LACI by echocardiography. LACI is calculated as the ratio of the minimum LA volume at end-diastole to the LV end-diastolic volume. The Simpson's biplane method is used to integrate measurements from apical two- and four-chamber views: panel (A) shows LVEDV in the apical 4-chamber view, panel (B) shows LAEDV in the apical 4-chamber view, panel (C) shows LVEDV in the apical 2-chamber view, and panel (D) shows LAEDV in the apical 2-chamber view. LACI, left atrioventricular coupling index; LA, left atrium; LV, left ventricle; LVEDV, left ventricular end-diastolic volume; LAEDV, left atrial end-diastolic volume.