MRA reshapes Rx of renal transplant dysfunction
When a transplanted kidney stops functioning properly, MR angiography can not only uncover the problem but can also guide a change in clinical management in more than half of patients and prevent invasive procedures in more than one-third.
A survey conducted at the University of Wisconsin-Madison has found that MRA wields considerable influence on referring physicians' diagnoses and treatment of patients with suspected dysfunction in a transplanted kidney. The results of the survey were published in the September issue of the Journal of Vascular and Interventional Radiology.
When Dr. Reed Omary and colleagues analyzed the questionnaires, they found that diagnostic certainty increased by an average of 33% following MRA. In addition, MRA changed the initial diagnosis in 20 patients (65%). Immediate clinical management changed in 16 patients (52%), and invasive procedures were avoided in 12 patients (39%).
Fatty acid SPECT reveals hibernating heart tissue
Perfusion imaging with a radiolabeled fatty acid can identify patients with metabolically active but hibernating myocardium, and in doing so, help predict whether bypass surgery will be successful in improving depressed left ventricular function.
In a study of patients already scheduled for bypass surgery, researchers used single-photon emission computed tomography (SPECT) with iodine-123-iodophenylpentadecanoic acid (IPPA) to determine myocardial viability. They found that the presence of viable myocardium was the most important clinical and scintigraphic predictor of substantial improvement in left ventricular ejection fraction (LVEF). The results of the Multicenter IPPA Viability Trial were published in the August issue of the Journal of Nuclear Medicine.
Myocardial energy production relies on fatty acids. For this reason, fatty acid imaging may be useful for assessing myocardial hibernation. To test IPPA's potential in viability studies, a multicenter research team led by Dr. Mario S. Verani of Baylor College of Medicine studied 119 patients with abnormal left ventricular wall motion and an LVEF of less than 40%. All patients were already scheduled to have coronary artery bypass grafting (CABG) and underwent IPPA tomography (both resting and 30-minute redistribution imaging) and blood-pool radionuclide angiography within three days of the procedure. Radionuclide angiography was repeated six to eight weeks after CABG.
Before bypass surgery, 113 of 119 patients demonstrated abnormalities on IPPA SPECT. Of these, 71 showed tracer redistribution in the 30-minute images, suggesting the presence of viable but hibernating myocardium.
On average, the LVEF increased only modestly after CABG (from 32% to 36%), although the difference was highly statistically significant. Only 27 patients experienced a more clinically meaningful 10-percentage-point increase in LVEF after surgery-an outcome that researchers found could best be predicted by the presence of at least seven IPPA-viable myocardial segments (accuracy, 72%).
The research team concluded that only a minority of patients who have depressed LV function at the time of bypass surgery actually experience a substantial improvement after the procedure, and that IPPA SPECT may be helpful in identifying those fortunate few ahead of time.
3-D echo offers practical option for cardiac assessment
Being just a little more stingy in data collection can speed the calculation of left ventricular volumes and ejection fraction enough to make routine use of 3-D echo practical for this purpose. Research teams based in the Netherlands and Egypt have found that images acquired at 16 degrees intervals around the heart, rather than every 2 degrees , were sufficient for doing 3-D reconstructions and determining LV function.
Dr. Youssef Nosir and colleagues studied 21 subjects with MR and with precordial 3-D echo at 2 degrees acquisition intervals. Images were processed using data taken at 2 degrees , 4 degrees , 8 degrees , 16 degrees , 32 degrees , and 64 degrees intervals, by excluding images taken in between. Eight equidistant short-axis slices were generated from each data set. Left ventricular volumes and ejection fraction were calculated and the results compared with those obtained with MR.
The researchers found that LV short-axis images obtained at 16 degrees rotational intervals were sufficiently good in all cases to enable tracing of the LV endocardial border. In addition, they observed good correlation between LV end-diastolic and end-systolic volumes and ejection fraction calculated with 3-D echo and MR (r = 98, 99, and 99, respectively).
The researchers concluded that image acquisition at 16 degrees intervals would be sufficient for doing LV functional measurement, and this would reduce the acquisition time while maintaining enough accuracy for clinical decision-making. As a result, 3-D echo would become more practical as a routine method of calculating common measures of cardiac function. The study was published in the August issue of the Journal of the American Society of Echocardiography.
