On-line assessment of myocardial flow reserve

Abstract

Listen

Translate article

Myocardial blood flow is determined by two variables, namely, the resistance of the myocardial perfusion bed and the perfusion pressure. Maximal myocardial flow at any given pressure is a function of the total cross-sectional area of the coronary resistance vessels. Myocardial flow reserve at any given pressure is thus a function of the resistance of the myocardial perfusion bed. Because flow reserve depends, among others, on perfusing pressure and basal coronary flow, it is variable and a large range of normal values have been reported. Therefore, MFR measurements in patients must be interpreted cautiously. Despite these limitations, it may be useful to calculate myocardial flow reserve in individual patients to evaluate the severity of coronary artery stenoses in addition to routine selective coronary arteriography, to study microvascular pathology in patients with evidence of small vessel disease and to evaluate the effects of left ventricular hypertrophy on myocardial perfusion. In this paper a radiographic technique for assessing regional coronary blood flow, based on the indicator dilution theory is described. Relative flow was represented by the ratio of maximal contrast density and appearance time of contrast. By computing the ratio of hyperemic flow and basal flow, myocardial flow reserve can be determined. Until recently the densitometric assessment of MFR was a time-consuming technique which included several potential sources of errors. A major problem concerned the difficulties in controlling the densitometric aspects which are related to the use of cinefilm. The introduction of digital image processing techniques enables the on-line assessment of myocardial flow reserve in routine clinical practice and eliminates the potential photographic source of error. Despite the theoretical limitations inherent to the method, at this time densitometric flow measurement is still one of the most useful techniques to study regional myocardial perfusion. The results of our validation study corroborate this perception.