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Effects of heart rate on myocardial thallium-201 uptake and clearance
J E Nordrehaug1, R Danielsen, H Vik-Mo
1Department of Clinical Physiology, University of Bergen, Haukeland Hospital, Norway.
Insights
Heart rate significantly impacts thallium-201 myocardial uptake and clearance. Higher heart rates during exercise increase initial uptake and clearance, with a linear relationship observed. Submaximal exercise may reduce clearance reproducibility.
Area of Science:
- Nuclear Cardiology
- Cardiovascular Physiology
- Medical Imaging
Background:
- Thallium-201 (201Tl) scintigraphy is a common tool for assessing myocardial perfusion.
- Exercise stress testing is frequently combined with 201Tl imaging to evaluate coronary artery disease.
- The influence of varying heart rates on 201Tl kinetics requires further elucidation.
Purpose of the Study:
- To prospectively investigate the effects of different heart rates on myocardial uptake and clearance of 201Tl.
- To determine the relationship between exercise intensity, heart rate, and 201Tl myocardial kinetics.
- To assess the impact of heart rate on the reproducibility of 201Tl clearance measurements.
Main Methods:
- Seven healthy men underwent bicycle exercise tests at maximal, 80%, and 60% of predicted maximal heart rate.
- Initial and delayed (3-hour) 201Tl myocardial images were acquired in three views.
- Myocardial uptake and clearance were quantified, and relationships with heart rate were analyzed.
Main Results:
- Initial myocardial 201Tl uptake was significantly higher at maximal heart rate compared to submaximal levels.
- A strong linear relationship (r=0.86) was observed between heart rate and initial myocardial uptake.
- Myocardial 201Tl clearance demonstrated a linear relationship with heart rate (r=0.80), increasing with higher heart rates, but the change per beat was modest (1.67 x 10%/bpm).
Conclusions:
- The observed linear relationship between heart rate and 201Tl clearance is primarily driven by changes in initial myocardial uptake.
- Submaximal exercise levels may decrease the reproducibility of 201Tl clearance estimation.
- The effect of heart rate on myocardial 201Tl clearance appears less pronounced than previously suggested.
Abstract:
The effects of heart rate on the myocardial uptake and clearance of 201Tl were studied prospectively in seven healthy men, mean age 43 +/- 7 (s.d.) yr. Initial and delayed (3 hr) thallium images were obtained in three views after three bicycle exercise tests: to maximal, 80% and 60% of predicted maximal heart rate. The mean of three views initial myocardial 201Tl uptake was higher at maximal than at both 80% and 60% of predicted maximal heart rate, being 81% (p less than 0.01) and 60% (p less than 0.01) of maximal activity, respectively. The myocardial activity in the delayed images was identical. There was a linear relationship between heart rate and the initial myocardial activity, r = 0.86 (p less than 0.001). The mean (range) 201Tl clearance was 58% (51-65), 47% (34-56), and 34% (22-49) (all differences p less than 0.01), respectively. Concordance among the three individual views in estimating clearance was best for the highest exercise level. There was a linear relationship between heart rate and clearance, r = 0.80 (p less than 0.001). Clearance was altered by only 1.67 x 10%/heart bpm (0.024 hr/heart beat). Clearance in the liver, spleen and lungs increased at submaximal exercise levels. Thus, a linear relationship between heart rate and clearance is the result of changes in the initial exercise myocardial 201Tl activity. Submaximal exercise may reduce reproducibility of clearance estimation, and the change of myocardial clearance with heart rate seems less than previously suggested.