Clinical application of monitoring techniques: Radioisotopic methods

The availability of mobile gamma cameras or the nearness of nuclear medicine devices to the coronary care unit make the assessment of transient myocardial ischemia by radioisotopic techniques practical. Nuclear cardiology provides information on the presence, site and extent of ischemia and helps the clinician in the evaluation of myocardial functional impairment and recovery. Monitoring of myocardial wall motion by radionuclide ventriculography demonstrates that during angina at rest: 1) global ejection fraction is not always sensitive to regional ischemia; 2) episodes of angina with undetectable electrocardiographic signs of ischemia can be associated with severe myocardial dysfunction; 3) separate left and right phase analysis of radionuclide ventriculography is a sensitive tool to assess segmental dyssynergy localized to the left or the right ventricle; 4) a prevalent right ventricular impairment during ischemia, not measurable by Thallium scintigraphy, is possible; 5) the recovery of function after ischemia is usually fast and apparently complete. In addition, useful diagnostic information can be derived by left ventricular injection of radioactive microspheres during cadiac catheterization followed by gated acquisitions of the intramyocardial radioactivity. Gated microsphere acquisitions, providing diastolic and systolic images, avoid blurring of images due to cardiac motion and enhance contrast between myocardium and background: the overall result is an improved detection and definition of small perfusion defects. Furthermore, this technique permits simultaneous assessment of regional perfusion and wall motion. An appraisal of potential mismatches between flow and function after revascularization procedures can be recognized by this approach. The development of technology is improving the performance of nuclear medicine instrumentation, hampered, at present, by limited spatial and temporal resolution. Overcoming these problems will result in new capability of nuclear techniques, by separating spatial (transmural extent) and temporal (trend on-off) distribution of the ischemic event.