Is there a component of coronary collateral flow which cannot be detected by radiolabelled microspheres?

The possibility of a component of collateral flow to the ischaemic myocardium that cannot be detected by the radiolabelled microsphere technique was examined in the cat, rat, and rabbit in vivo. Animals were anaesthetised and a coronary artery ligated. The regional distribution of blood flow was assessed by the simultaneous injection of 141Ce labelled microspheres and 86Rb. Blue dye was injected into the circulation to delineate the perfused tissue and the heart removed, frozen, and lyophilised, after which tissue was separated into ischaemic and non-ischaemic fractions and the radioactivity of each assessed. Flow to the ischaemic zone, expressed as a percentage of that in the non-ischaemic tissue, for 86Rb based assessments and 141Ce measurements was: for the cat 21.6(3.9)% and 12.4(1.4)% (n = 12 hearts); the rat 13.2(2.6)% and 5.2(1.8)% (n = 9); and the rabbit 7.2(0.8)% and 1.9(0.8)% (n = 5) respectively. In all species there was a statistically significant difference (p less than 0.01) between the results for the two markers. These results suggest either a microsphere insensitive component of collateral flow or some methodological inadequacy of one of the assessment techniques. The 86Rb data were corrected for possible artefacts due to the flow rate dependent extraction of the isotope. The new 86Rb values for collateral flow in the cat, rat, and rabbit were 15.2(2.9)% (NS vs microspheres), 9.5(1.9)% (p less than 0.05), and 5.2(0.5)% (p less than 0.05) respectively. Although these values were closer to the 141Ce microsphere values, significant differences between the two results still remained, possibly owing to other limitations of the 86Rb method.(ABSTRACT TRUNCATED AT 250 WORDS)