NEW DEVELOPMENTS IN X-RAY DENSITOMETRIC E VALUATION OF MYOCARDIAL PERFUSION DURING CARDIAC-CATHETERIZATION

X-ray densitometric evaluation of digital subtraction coronary arterio grams allows a qualitative and quantitative detection of contrast medi um propagation through the epicardial coronary arteries, the capillary system and the coronary venous system. So-called ''time-density-curve s'' (TDCs) can be generated following Lambert-Beer's law similar to in dicator dilution curves by using contrast medium as the indicator. Sev eral time and density parameters can be derived from these TDCs, which are related to local myocardial perfusion. Different animal validatio n studies have shown the applicability of this concept for in-vivo eva luation of coronary blood flow and myocardial perfusion. Nevertheless, absolute measurement of volumetric coronary blood flow or myocardial perfusion failed. Therefore, relative changes in coronary blood flow o r myocardial perfusion in response to pharmacologically induced maximu m hyperemia were measured and coronary or myocardial perfusion reserve was calculated as the ratio of hyperemic flow or perfusion devided by baseline values. Despite theoretical attractions for an application d uring routine cardiac catheterization, this densitometric approach did not get a wide acceptance. Primary reason for this limited use in spe cialized centers was the time consuming process of densitometric evalu ation of the subtraction coronary arteriograms, which require digital cine angiography and necessitates enormous computer hard ware. This ma in limitation has been overcome since more powerful computer hard ware (processor speed, hard disk space, digitization boards) has become ra pidly available during the last years at more moderate pricing and dig ital techniques today are state of the art in cardiac catheterization laboratories. In addition, soft ware program packages allowed an autom atization of the digitization and densitometric evaluation process. Th ese programs include ECG triggered cine image digitization with improv ed temporal resolution, semiautomatic definition of regions-of-interes t including definition of reference regions-of-interest for the detect ion of background density changes and quality-controlled densitometric parameter analysis. This progress made an application during routine cardiac catheterization feasible. In animal validation studies this im proved X-ray densitometric approach for evaluation of local myocardial perfusion was validated versus colour-coded microsphere techniques. T he time parameter ''rise time'', defined as the time from the start of local contrast medium induced density change to its maximum, revealed a close correlation (r(2) = 0,965) to the results of the microsphere technique over a wide range of perfusion. We have applied this techniq ue before and after coronary interventions such as balloon angioplasty and stenting. Results documented an improvement of poststenotic myoca rdial perfusion reserve immediately after coronary balloon angioplasty and an additional improvement after adjunct coronary stenting. Only a fter stenting but usually not after coronary balloon angioplasty alone poststenotic myocardial perfusion reserve gained the intraindividual reference level, measured in a perfusion bed supplied by an epicardial coronary artery without stenoses. These results documented the functi onal benefit of coronary stenting on poststenotic myocardial perfusion in addition to the well known morphologic benefit with the creation o f a larger and more circular conduit.