Nuclear cardiology approaches to defining normal and abnormal cardiovascular aging

The application of thallium-201 myocardial perfusion scintigraphy to asymptomatic adults has refined the prevalence and prognostic significance of exerciseinduced silent myocardial ischemia. The relatively high occurrence of silent ischemia in both sedentary and athletic older men is noteworthy. A cost-effective intervention to treat these apparently healthy subjects could have major economic implications. The similarity of risk factors for silent ischemia and clinical CAD reinforces efforts at early risk-factor modification to prevent the progression from silent to symptomatic status. Many studies that used radionuclide ventriculography have documented a reduced left ventricular ejection fraction response to maximal cycle ergometry with age. In addition we have observed that the stroke volume increase with exercise in older adults is accomplished by a greater left ventricular dilatation (ie, the Frank-Starling mechanism) than in the young. The blunted exercise-induced increase in ejection fraction in healthy older subjects, especially women, must be considered when exercise radionuclide ventriculography is used as a diagnostic tool for CAD. The increase in peak diastolic filling rate during exercise is also attenuated with age. An attractive explanation for the age-associated reduction in the left ventricular systolic and diastolic responses to strenuous aerobic exercise is a diminution of β-adrenergic responsiveness with aging.