What does lung uptake in a nuclear stress test indicate?

Lung Uptake in Nuclear Stress Test: Indication of Left Ventricular Dysfunction and Coronary Artery Disease

Increased lung uptake in a nuclear stress test is primarily indicative of left ventricular dysfunction and is associated with more severe coronary artery disease. This finding represents a high-risk marker that warrants careful clinical attention.

Physiological Mechanism

• Increased pulmonary uptake of radiopharmaceuticals during stress testing occurs as a consequence of left ventricular failure, which leads to elevated left ventricular filling pressures 1
• The extraction fraction of thallium-201 by the lungs increases significantly with elevated left atrial pressure and prolonged pulmonary transit time 1
• Stress-induced myocardial ischemia can cause transient left ventricular dysfunction, resulting in increased pulmonary capillary wedge pressure and subsequent increased lung uptake of the radiotracer 2

Clinical Significance

• Lung uptake is considered one of the "nonperfusion high-risk markers" in nuclear myocardial perfusion imaging, along with ECG abnormalities, stress-induced wall motion abnormalities, reduced ejection fraction, and transient ischemic left ventricular dilation 3
• Increased lung uptake correlates directly with:
  • Left ventricular end-diastolic pressure 2
  • Pulmonary capillary wedge pressure 2
  • Extent of coronary artery disease 2, 1
• Lung uptake correlates inversely with:
  • Left ventricular ejection fraction 2
  • Arterial systolic blood pressure 2

Prognostic Implications

• Patients with multivessel coronary artery disease demonstrate significantly higher lung-to-heart ratios of radiotracer compared to those with single-vessel disease or no significant coronary disease 1
• Lung congestion in cardiac patients is associated with:
  • Increased pulmonary vascular resistance 4
  • Reduced pulmonary artery compliance 4
  • Right ventricular dilatation and dysfunction 4
  • Increased mortality, even after adjusting for other risk factors 4

Different Radiotracers

• While both thallium-201 and technetium-99m sestamibi can show lung uptake, their physiological characteristics differ 2
• Stress technetium-99m sestamibi lung uptake correlates with rest thallium-201 lung uptake in patients with known or suspected coronary artery disease 2
• The initial/final lung activity ratio increases proportionally with the extent of coronary artery disease, particularly in patients with multivessel disease 1

Clinical Application

• When interpreting nuclear stress tests, identification of increased lung uptake should prompt a thorough assessment for:
  • Multivessel coronary artery disease 1
  • Left ventricular dysfunction 2
  • Elevated left ventricular filling pressures 2
• This finding may warrant more aggressive diagnostic and therapeutic approaches, including consideration of cardiac catheterization to evaluate coronary anatomy and left ventricular end-diastolic pressure 3

Pitfalls and Caveats

• Image quality can affect assessment of lung uptake, particularly in obese patients or those with chronic lung disease 3
• Quantitative assessment of lung-to-heart ratio is more reliable than visual assessment alone 1
• Other conditions that can cause diffuse lung uptake include renal insufficiency, especially when combined with coronary artery disease or congestive heart failure 5
• Pulmonary congestion may be present even with only modestly elevated pulmonary artery wedge pressure, suggesting that other factors contribute to lung water accumulation 4

In summary, lung uptake on nuclear stress testing is an important finding that indicates left ventricular dysfunction, typically from significant coronary artery disease, and carries important prognostic implications that should guide clinical decision-making.