Q. Describe Shunts?

Detection, localization and quantification of intracardiac shunts are one of the most important exercises in cardiac catheterization. In most cases a preliminary clinical evaluation will give us knowledge of the possible intracardiac shunt.

The pointers to the presence of a shunt are:

1) Unexplained arterial desaturation (arterial saturation < 95 per cent) suggestive of a right to left shunt and representing alveolar hypoventilation.

2) Unexpectedly high pulmonary artery saturation > 80 per cent-suggestive of a left to right shunt.

3) When data at catheterization does not confirm a particular lesion.

Detection of left to right intracardiac shunts-Measurement of blood oxygen saturation and content in the right heart (oximetry run) Oximetry run is a basic technique for detecting and quantifying intracardiac shunts.

The oxygen content or per cent saturation is measured in blood samples drawn sequentially from PA, RV, RA, SVC and IVC. A significant step-up is defined as an increase in the blood oxygen content or saturation that exceeds the normal variability that might be observed if multiple samples were drawn from that cardiac chamber. Oxygen content can be calculated from the knowledge of percentage saturation, the patient's hemoglobin concentration and an assumed constant relationship for oxygen carrying capacity of hemoglobin (1.36mL O₂/g hemoglobin).