Physiologic Intervention in Cardiovascular Nuclear Medicine

Homeostasis of cardiac output is maintained by a complex intergration of many physiologic responses, both central and peripheral, including pulse,the contractile state of the ventricle, and pre-and after load. In the abnormal ventricle at rest, any or all of the measurable parameters that define left ventricular function may be normal. However, in disease states, exercise can provoke abnormalities in these parameters indicating a reduction in myocardial reserve. Regional asynergy occurs in patients with significant ischemic heart disease during exercise reflecting a local supply-demand mismatch. Recently, radionuclide ventriculography has been combined with exercise techniques in attempts to elucidate details of the normal and abnormal ventricular response to stress noninvasively. The majority of data describe the response of the ventricle during graded supine bicycle exercise. The normal response is to increase myocardial contractility, reducing end-systolic volume, while end-diastolic volume remains constant. This results in an increase in ejection fraction. In ischemic ventricles, regional asynergy develops and ejection fractions may either fall or fail to rise. This appears to be accomplished by an increase or no change in the end-diastolic volume, with an increase in end-systolic volume, particularly in patients with angina during exercise. Radionuclide methods can be applied to large mumbers of patients providing informaton that is unobtainable by more invasive procedures. This review traces the development of knowledge of the ventricular response to exercise, emphasizing the role of radionuclide ventriculography. Although radionuclide angiography has the capacity for advancing the understanding of the ventricular response to exercise, the technical limitations of this technique in specific diagnostic conditions has yet to be defined adequately.