ASSESSMENT OF LEFT-VENTRICULAR DYSFUNCTION BY NUCLEAR CARDIOLOGY

Nuclear cardiology techniques may be of help in evaluating the patient with symptoms of congestive heart failure and ventricular dysfunction in two respects: quantification of functional parameters by radionucl ide angiography, and differentiation of viable from nonviable myocardi um by perfusion and metabolic imaging. Left ventricular ejection fract ion and volumes can be accurately assessed by equilibrium radionuclide angiography with a count-based method without any geometric assumptio ns. Indeed, because of its high reproducibility, this method is partic ularly suited for making sequential measurements in the same patient. The distinction between viable or reversible and scarred or irreversib le dysfunctional myocardium can be made on the basis of myocardial per fusion, cell membrane integrity, and metabolic activity. Thallium myoc ardial imaging is used clinically to assess the first two parameters b ased on experimental data. Two clinical methods may be applied to the detection of viability: stress-redistribution-reinjection imaging or r est-redistribution imaging. In both of these, the severity of the redu ction in thallium activity should be assessed to discriminate viable f rom nonviable myocardium. Stress-redistribution-reinjection thallium i maging should be the first approach, if possible, because inducible is chemia is a much more significant clinical variable in a patient with ventricular dysfunction in terms of management and risk assessment tha n is knowledge of myocardial viability. Positron emmission tomography (PET) provides enhanced image resolution and correction for body atten uation, thereby overcoming the two major limitations of thallium imagi ng. In addition, it provides the capacity to quantitate regional blood flow and to assess regional metabolic activity independent of flow. O verall, the accuracies of thallium imaging (around 70%) and PET imagin g (around 82%) are similar for the prediction of segmental changes aft er revascularization. However, in patients with poor global left ventr icular function, the accuracy of PET seems to be better. Further studi es are needed in a large number of patients evaluated for regional and global function to establish algorithms using thallium and PET imagin g in dysfunctional myocardium. Dobutamine echocardiography should also be evaluated in these algorithms.