8th March 2024

Cardiac Haemodynamic Assessment

The heart has a dual circulation with deoxygenated blood received via the SVC/IVC into the right atrium, down the AV valve into the RV, and to the lungs via the pulmonary arteries. Once oxygenated, the blood travels to the left atrium via pulmonary veins. This process prevents mixing of oxygen depleted blood from oxygenated blood. The differences in oxygen saturations are shown below.

Image Source: Wikimedia Commons (2016). Diagram of the human heart_(cropped, Licensed under a creative commons licence. Available for free at: https://commons.wikimedia.org/wiki/File:Diagram_of_the_human_heart_(cropped).svg (Accessed: 26 January 2024).

Cardiac catheterisation with oxygen studies is useful to identify and localise intracardiac shunts by detecting differences in oxygen saturation values. The normal values for oxygen saturation and pressures at different cardiac sites are presented in Table 2. A left to right shunt is considered if there is a significant increase (>75%) in blood oxygen saturation higher than normal values.  Left heart saturations < 94% are suggestive of a right to left shunt. 

Table 2: Normal oxygen saturations and pressures at different cardiac sites. Cited from Braunwald’s Heart Disease: A Textbook of Cardiovascular Medicine (Bonow et al, 2022)

Intracardiac shunts can be quantified using the ratio of pulmonary flow (Qp) and total systemic (Qs) blood flow (Table 2).

Table 3. Quantification of intra cardiac shunts using pulmonary blood flow (Qp) and total systemic blood flow (Qs)