In the normal heart, blood returns to the right heart chambers and is then pumped through the lungs to receive oxygen. Oxygenated blood from the lungs enters the left side of the heart and is then pumped to the brain and body.

Abnormal communications between the heart chambers (atrial and ventricular septal defects, patent foramen ovale) may result in blood flow directly between the chambers. This abnormal flow of blood is SHUNTING

Shunting from the left heart to the right heart (left-to-right shunt) results in blood carrying oxygen returning and re-circulating through the lungs. See our ASD page.

Shunting from the right heart to the left heart results in non-oxygenated blood bypassing the lungs and mixing with oxygenated blood. Right-to-left shunting is associated with risk of stroke, migraine headache, reduced blood oxygen, and risk for scuba divers. See our PFO page. See our MIGRAINE page.

A heart ultrasound or echocardiogram (echo for short) is important in diagnosing shunt because all heart structures can be seen and evaluated.

Microscopic bubbles can be safely and easily injected through an IV in the arm. When these bubbles enter the heart they are easily seen by echo as small specks. When these specks appear in the left atrium, a right-to-left shunt is diagnosed because the bubbles have bypassed the filtering of the lungs.

Heart ultrasound or echo can be performed from the chest surface or from a probe placed in the esophagus (TEE). These methods are good for defining heart structures but are less reliable for detecting and quantifying the amount of shunt.

Trans-Cranial Doppler (TCD) is a new test which measures brain artery blood flow by using safe ultrasound echo probes placed on the surface of both sides of the head. If microscopic bubbles injected through an IV shunt past the lungs to the left heart, TCD detects and counts each bubble as it appears in the brain arteries.

The problems which occur due to right-to-left shunt are primarily related to the amount of blood flow shunting to the left heart. The risk of stroke, chance of reduced oxygen, migraine headache, and the risk of decompression illness (“the bends”) and abnormal brain scans in scuba divers—all are associated with higher levels of shunting.

TCD is not only the most sensitive way to diagnosis right-to-left shunt, it is the best way to quantify shunt.

The best TCD test for shunt is a new type of trans-cranial doppler called Power M-mode TCD.