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Is there a component of coronary collateral flow which cannot be detected by radiolabelled microspheres?
M P Maxwell1, D J Hearse, D M Yellon
1Cardiovascular Research, Rayne Institute, St Thomas' Hospital, London.
Insights
This study investigated collateral blood flow to the ischemic myocardium in cats, rats, and rabbits. Results suggest a potential limitation in the microsphere technique for detecting all collateral flow, indicating a need for improved methods.
Area of Science:
- Cardiovascular Physiology
- Myocardial Ischemia Research
- Blood Flow Measurement Techniques
Background:
- Assessing collateral blood flow to ischemic heart tissue is crucial for understanding myocardial infarction.
- The radiolabeled microsphere technique is a common method, but its ability to detect all collateral flow is questioned.
Purpose of the Study:
- To investigate the possibility of a collateral flow component to ischemic myocardium undetectable by the radiolabeled microsphere technique.
- To compare blood flow measurements using 141Ce-labeled microspheres and 86Rubidium (86Rb) in animal models of myocardial ischemia.
Main Methods:
- Anesthetized cats, rats, and rabbits underwent coronary artery ligation to induce myocardial ischemia.
- Regional blood flow was assessed simultaneously using 141Ce-labeled microspheres and 86Rb.
- Perfused tissue was delineated with blue dye; hearts were processed to separate ischemic and non-ischemic fractions for radioactivity assessment.
Main Results:
- Significant differences in collateral flow measurements were observed between 86Rb and 141Ce microspheres across all species (p < 0.01).
- Uncorrected 86Rb measurements indicated higher collateral flow (e.g., cat: 21.6% vs. 12.4% for microspheres).
- Even after correcting 86Rb data for potential artifacts, significant discrepancies with microsphere measurements persisted.
Conclusions:
- The findings suggest either a component of collateral flow is insensitive to the microsphere technique or there are methodological limitations in one or both techniques.
- Further investigation into the limitations of both 86Rb and microsphere methods is warranted for accurate collateral flow assessment in ischemic myocardium.
Abstract:
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)