Eindhoven, the Netherlands - Dutch researchers have been able to measure, for the first time, volumetric blood flow in the coronary arteries of 35 patients [1]. Dr Wilbert Aarnoudse (Catharina Hospital, Eindhoven, the Netherlands) and colleagues report their findings online November 22, 2007 in the Journal of the American College of Cardiology.

Aarnoudse et al explain that absolute blood-flow measurements would be a great step forward for the diagnosis and understanding of microvascular disease and would be particularly important to better understand conditions such as heart transplantation, stem-cell therapy, and large transmural MIs.

They describe their success in determining absolute blood flow in selective coronary arteries in milliliters per minute using a new technique, adapted from traditional coronary sinus thermodilution, a method first proposed during the 1970s. "We believe this novel methodology for direct volumetric coronary flow measurement can be a valuable tool in clinical research on the coronary circulation," they say.

The researchers first validated their methodology in dogs and then tested its use during cardiac catheterization in 35 conscious patients referred for physiological assessment of a coronary stenosis or for percutaneous coronary intervention.

The technique employs thermodilution with continuous infusion of saline at room temperature and a standard sensor-tipped pressure/temperature guidewire. During the procedures, all measurements were continuously displayed on a corresponding interface, the RadiAnalyzer (Radi Medical Systems, Uppsala, Sweden), which uses specific software and makes calculations simple.

Coronary flow is measured, as is temperature, distal coronary pressure, and fractional flow reserve, the researchers explain. This in turn enables the resistance of the coronary artery to be calculated, they note, adding that the resistance of a specific myocardial territory can even be worked out. The latter will allow further studies in particular groups of patients in whom microcirculatory function is affected, such as after myocardial stem-cell therapy, MI, or heart transplantation.

"This methodology is fairly simple to perform, accurate, and very reproducible," they say.

However, the researchers do point out a number of limitations, including the fact that the instrumentation of the coronary artery is "somewhat more complicated than in regular diagnostic or interventional intracoronary procedures." This is because the pressure/temperature guidewire must be introduced first, after which the infusion catheter should be introduced using a second Y-connector connected to the pump.

Although these extra steps take only approximately 10 minutes, this additional work "will most likely limit the use of this method to investigational studies and specific groups of patients," they note.

Nevertheless, they believe this first direct volumetric blood-flow measurement "will facilitate pathophysiological studies of the coronary circulation."