Lung uptake of Thallium-201 during atrial pacing stress: Hemodynamic determinants

Increased lung activity on Thallium-201 imaging during exercise stress testing has been shown to be related to left ventricular dysfunction in patients with coronary artery disease (CAD). This study was undertaken to more fully define the hemodynamic determinants of Thallium-201 lung uptake. In this investigation, 21 patients (6 normal, 15 CAD) were studied during graded tachycardia induced by atrial pacing with continuous hemodynamic monitoring. At peak pacing (end-point=85% predicted maximal heart rate or development of angina) 2.0 mCi Thallium-201 was injected IV and imaging initiated within 5 minutes. Lung activity was expressed as a percent of peak myocardial counts on the anterior image (lung Thallium-201 index). The influence of rest, peak, and post-pacing hemodynamic parameters, including pulmonary capillary wedge pressure (PCWP), cardiac index (CI), heart rate, and aortic pressure on lung Thallium-201 index was examined using step-wise multiple regression analysis. This study concludes that lung uptake of Thallium-201 during atrial pacing stress appears to depend on; hydrostatic pressure in the pulmonary capillary bed, and changes in cardiac output which may determine tissue contact time and influence extraction efficiency