Physiology of the left heart
The left ventricle (LV) is a pressurized chamber with a definite myofiber architecture. The normal left ventricle is cone shaped, posterior to and ‘hugged’ by the right ventricle (RV) and comprises an inlet portion containing the mitral valve apparatus, an overlapping outlet portion leading to the aortic valve, and a rather smooth apical portion containing fine crisscross trabeculations25. Anatomically, the LV is narrower and longer than the RV. Regarding the myoarchitecture, the LV wall contains three layers from the subepicardium to the subendocardium with a counterdirectional helical arrangement of muscle fibers that is energetically efficient and important for equal redistribution of stresses and strain in the heart26. Furthermore, there is a gradual thinning of the LV wall that is observed toward the apical segments. In contrast to the RV, there are two papillary muscles that originate from the LV free wall and are attached to the mitral valve chordae tendinae. During contraction, the base and apex of the LV rotate in opposite directions. The left and right ventricles are also subjected to the same filling pressure, and their combined ventricular output perfuses the fetal system. The LV primarily perfuses the coronary and cerebral circulations through the ascending aorta, and the RV perfuses the lower body and placental circulation through the ductus arteriosus and descending aorta. Postnatally, after programmed closure of the fetal shunts, the LV pumps blood at higher pressures than other cardiac cavities as it faces a much higher workload and mechanical afterload. Recent findings from the study by Junno et al. suggest that the fetal left ventricle seems to be more sensitive to progressively worsening hypoxemia and acidemia than the right ventricle27. As stated by Sengupta and colleagues, understanding the cardiac structure–function relationship of both the left and right heart is essential and constitutes the basis of a comprehensive and structured assessment of cardiac anatomy26. The advent of high temporal resolution imaging methods, volumetric approaches and the recently introduced novel semiautomatic algorithms for standardized reconstruction of cardiac geometry might contribute to an improvement of prenatal detection rates for more than just left-sided lesions. The potential of these volume-based technologies to provide profound insights into global anatomic changes of left heart anomalies will be discussed below.