How Is a Fractional Flow Reserve Measured?

A fractional flow reserve (FFR) estimates the degree of blockage in the coronary arteries. 

A fractional flow reserve (FFR) is a procedure done during cardiac catheterization to estimate the degree of blockage in the coronary arteries. It is a guide wire-based procedure that determines the ratio between the maximum achievable blood flow in a diseased blood vessel (coronary artery) and normal maximum flow. 

An FFR of one is accepted as normal, whereas values lower than 0.75 generally indicate a heart attack.

An FFR is measured at the time of coronary angiogram or cardiac catheterization using a pressure wire. If an FFR does not reveal any significant obstruction, the physician will prefer medical therapy. 

In short, an FFR may be used to determine the course of therapy in patients with abnormal narrowing of the coronary artery (coronary stenosis).

A fractional flow reserve measurement is indicated:

• To identify the extent of coronary stenosis (the narrowing of blood vessels)
• To identify the culprit block in the multiple blood vessels
• To identify the exact location of the block in the case of an unclear angiographic image
• To determine if a particular obstruction requires an angioplasty or a coronary bypass graft (CABG)

However, individuals with asthma should avoid undergoing the fractional flow reserve procedure.

Before the procedure

• The physician will explain the risks and benefits of the procedure to the patients.
• You need to sign an informed consent before the procedure.
• You should clarify all your concerns with the physician regarding the procedure.
• The physician may perform a cardiac catheterization to identify the need for a fractional flow reserve.
• There are some potential discomforts associated with the procedure such as
  • Shortness of breath,
  • Chest pain,
  • Warmth in the area,
  • Abnormal sweating and
  • Racing heart.
• Blood thinners would be given to you before the surgery.
• Your physician would ask you to stop medications such as theophylline 12 hours before the surgery.

During the procedure

• The physician performs a fractional flow reserve under sedation.
• You will lie flat on the operating table, then the physician inserts a thin guide wire through a catheter during an angiogram.
• Once the special guide wire crosses the block, the physician infuses a medicine such as adenosine into the blood vessel that increases blood flow (hyperemic). This will measure the flow and pressure of the blood. 
• The fractional flow reserve value is displayed on the monitor attached. The higher the fractional flow reserve value, the lower the chances of any abnormality.
• Usually, a fractional flow reserve value of one is accepted as normal, whereas values lower than 0.75 generally indicate a heart attack.

The risk associated with a fractional flow reserve is low, but complications are associated with cardiac catheterization. These include

• Coronary vessel perforation (hole in the blood vessels)
• Embolism (diffused blood clots in the blood vessels)
• Infection in the site
• Spasm of the blood vessel
• Kidney failure
• Heart attack
• Stroke
• Serious arrhythmias (irregular heartbeat)
• Death