Diagnostic Procedures

Intracoronary Diagnostics

Intravascular Ultrasound (IVUS)

This is one of many examples of interventional techniques pioneered by Stanford researchers. IVUS is an imaging technique that has become the international gold standard for detection and evaluation of coronary artery disease. Designed to provide data about lesion characteristics, IVUS is used to improve decision-making regarding coronary intervention for patients. IVUS refers to a catheter or tube that has an ultrasound probe near its tip. An IVUS catheter can be placed in a coronary artery to look from the inside at the artery. It provides very detailed pictures of the inside of the artery and often provides more information than a standard angiogram alone.

Optical Coherence Tomography (OCT)

OCT is another catheter-based imaging technique that is analogous to IVUS, but uses light waves instead of sound waves. Because of this, OCT has much greater resolution than IVUS, making it able to visualize tiny details within the coronary artery. Stanford physicians are studying ways to apply this novel technology to improve patient care.

Fractional Flow Reserve (FFR)

FFR is an index that can be measured with a coronary pressure wire in a patient with a moderate narrowing of unclear significance. The coronary pressure wire is a small wire with a pressure sensor near its tip that can be placed beyond the moderate narrowing. FFR is the ratio of the coronary pressure beyond the narrowing compared to the pressure before the narrowing. Measuring FFR provides more information than a standard angiogram alone about the significance of moderate coronary narrowings and its use improves patient outcomes. Stanford physicians have been world leaders in developing and validating this technique.

Index of Microcirculatory Resistance (IMR)

IMR is an index first described at Stanford which can be measured to determine the status of the small branches of vessels that supply blood to the heart, but which are poorly visualized by the standard coronary angiogram. IMR is determined by using a small wire that can measure the pressure and flow of blood into the small vessels. Patients who have chest pain, but normal appearing coronary arteries and no evidence of coronary spasm, may have abnormal flow in the small vessels (abnormal IMR), which when detected can be treated with certain medications.

Acetylcholine challenge

Patients with normal appearing coronary arteries sometimes develop symptoms because of episodes of coronary spasm. Spasm refers to temporary constriction of an artery which results in decreased blood flow to the heart. Spasm can occur if the lining of the artery, called the endothelium, is not functioning properly. Acetylcholine is a medicine that temporarily triggers spasms in patients who have abnormal endothelium. It can be given safely in the cardiac catheterization laboratory to help determine if spasm is the cause of a patient's symptoms.

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