Cardiac Anatomy and Physiology: Chambers, Segments, and the Cardiac Cycle
Chamber anatomy and the segment model
Begin with the fibrous skeleton: the aortic valve sits centrally, the anterior mitral leaflet is continuous with the aortic root, and this relationship explains why root disease can produce mitral pathology. The LV is a truncated ellipsoid whose subendocardial fibers run longitudinally - they are the first to fail in ischemia, which is why longitudinal strain drops before ejection fraction does.
Candidates must map the 17-segment model (6 basal, 6 mid, 4 apical, plus the apical cap) to coronary territories. LAD supplies anterior, anteroseptal, and apical segments; LCx supplies anterolateral and inferolateral walls; RCA supplies inferior and inferoseptal segments in a right-dominant system.
Physiology questions favor the phases of the cardiac cycle - isovolumic contraction, rapid and reduced ejection, isovolumic relaxation, rapid filling, diastasis, atrial systole - and the pressure–volume loop, where the end-systolic pressure–volume relation indexes contractility, the end-diastolic relation indexes compliance, and loop area equals stroke work.
Normal values worth memorizing: LV ejection fraction 55–70%, LV end-diastolic dimension 3.5–5.6 cm, wall thickness up to 1.0 cm, LA volume index 22–34 mL/m², TAPSE ≥1.7 cm.
Traps: the moderator band and three tricuspid papillary groups identify the RV; the coronary sinus drains into the right atrium; apical segments are frequently lost to foreshortening.
Rule of thumb: when one segment is abnormal, name the supplying artery and inspect its paired segment - a wall motion abnormality that does not fit a coronary territory suggests artifact or a non-ischemic process.