Rapid activation between the mid-free wall of the right ventricle (RV) and the right interventricular septum (IVS) take place via the moderator band.1 The inside corner between the septum and the right anterior ventricular wall exhibits the deep pits called the interventricular sinuses. The opening of the interventricular vein (IV) (kuuselian vessel) is located in the interventricular sinus between the medial walls of the expanding fetal RV and left ventricle (LV). The IV is a slit between the fibers of the muscle leading to the outer layer of the left central muscular part of the IVS and runs into the LV at an angle of about 90° through the left IVS surrounded by the interventricular sphincter (ISP). Hypoxia may be the physiological factor that recruits the IV of the fetal heart and augments the flow of the oxygenated blood from right to left. The ISP and the IV may become patent by relaxing and widening the helical heart at the end of the fetal diastole. The sinoatrial node activates the right atrium, followed by activation of the left atrium. Left to right communication does not result because the earliest ventricular activation contracts the right IVS and the ISP in this order.
Clockwise rotation of the ventricular base at the very beginning of the diastole stretches the relaxing right IVS of the healthy heart after birth and keeps the IV closed between the right and the left muscular IVS as the heart is widening at the diastole. Stiff right IVS does not stretch enough but expands toward the right by plentiful right atrial filling volume as the stiff free wall of the RV and stiff moderator band pull the right IVS recruiting the IV. Right atrial systole pumps venous flow from right to left into the LV. This venous flow generates the fourth heart sound common in hypertrophy of systemic hypertension and in ischemic heart disease.2,3
Footnotes
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References
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