Basic Cardiac Anatomy
Left Ventricle
Pumps oxygenated blood to the body (systemic circulation) and accounts for 3/4 of the heart's total mass. The Left Ventricular Ejection Fraction (LVEF) is a term used to described the amount of blood pumped out each time the heart contracts.
LVEF = (Stroke Volume / End Diastolic Volume) x 100
Right Ventricle
Pumps deoxygenated blood to the pulmonary artery where it is delivered to the lungs for oxygenation. It is the most anterior chamber of the heart and is more trabeculated than the left ventricle, including a distinct muscular band called the "moderator band”
LV Function Measurements
Single plane dimension: The left ventricular size dimension is measured at end-diastole (largest) and end-systole (smallest) in the parasternal long axis view through the mitral leaflet tips.
Biplane Simpson’s Method of Discs: The left ventricular volumes are measured at end-diastole and end-systole in the apical 4 chamber and apical 2 chamber views from mid mitral annulus to cardiac apex. The difference in LV length between the two views should be <10%.
3D: Provides a more accurate assessment of end-diastolic and end-systolic volumes because ultrasound systems don’t make assumptions about the heart’s shape. Limited by image quality but can be more reproducible.
Visual estimation: Multiple views used to assess contractility and size in comparison to surrounding chambers (qualitative).
RV Function Measurements
TAPSE: Tricuspid annular plane systolic excursion (M-mode, abnormal <17mm)
TDI: Tissue Doppler Imaging (S’ peak velocity at the lateral tricuspid annulus, abnormal <9.5cm/s)
FAC: Fractional area change (abnormal <35%)
RV strain: Global longitudinal strain (abnormal is <20%)
Visual estimation: Multiple views used to assess contractility and size in comparison to surrounding chambers (qualitative).
Left Atrium (LA)
The left atrium receives oxygen-rich blood from the four pulmonary veins during systole, when the mitral valve is closed. Assessing the size of the left atrium is important, and volume measurements are preferred over single linear dimensions because the chamber often enlarges asymmetrically. These volumes are typically measured at end-systole using apical 4-chamber and apical 2-chamber views. Left atrial enlargement is a key marker of diastolic dysfunction and should be carefully evaluated during routine echocardiographic exams.
Right Atrium (RA)
The right atrium receives deoxygenated blood from the inferior and superior vena cava during systole, when the tricuspid valve is closed. Assessing the size of the right atrium can be done by volume and/or area at end-systole when it is the largest.
There are a few normal anatomical structures inside of the right atrium: eustachian valve, crista terminalis, Chiari network, and pectinate muscles.
Interventricular Septum (IVS)
The muscular and membraneous wall that divides the left ventricle and right ventricle. It provides structural support and contains specialized fibers that help transmit electrical signals, ensuring that the ventricles contract synchronously.
Echocardiography is used to assess the motion, thickness, and morphology of the IVS as pressures and volumes change in the heart from various pathologies.
Interatrial Septum (IAS)
A thin wall of tissue that separates the two atria. It includes the secundum portion, the primum portion, and the sinus venosus portion. A hole in this wall, a patent foramen ovale, is present in 25% of the population and can be detected with an agitated saline bubble study using echocardiography. This wall may bow in one direction indicating increased pressures.