CAPTOPRIL-ENHANCED SCINTIGRAPHY USING THE METHOD OF THE EXPECTED RENOGRAM - IMPROVED DETECTION OF PATIENTS WITH RENIN-DEPENDENT HYPERTENSION DUE TO FUNCTIONALLY SIGNIFICANT RENAL-ARTERY STENOSIS

Purpose and design of study. Asymmetric-induced changes of the renogra m under angiotensin-converting enzyme inhibition (ACE-i), i.e. lateral ization, is probably the most distinctive finding for the detection of haemodynamically significant renal artery stenosis (RAS) in compensat ed kidney, since bilateral and symmetric patterns are non-specific. In the Consensus statement of diagnostic criteria of renovascular hypert ension with captopril renography (Am J Hypertens 1991; 4: 749-755S) AC E-i-induced asymmetry of renograms for the left and right kidney was v iewed as vitally important. However, detection of change in split func tion is a reliable parameter only when using a glomerular tracer, i.e. Tc-99m-DTPA. No indication regarding a more widely used tubular trace r such as Tc-99m-mercaptoacetyltriglycine (Tc-99m-MAG3) has been given . Methods and results. The theoretical contralateral curve, called 'ex pected renogram', was calculated frame by frame from renal curves obta ined under ACE-i and one of two baseline curves. The expected renogram was compared with the recorded ipsilateral curve. More than +/-2 SD d ifference between expected and recorded renograms was assumed as sugge stive of monolateral or bilateral RAS. Twenty-nine patients with angio graphically proven RAS (bilateral in 12) and 20 patients without arter iographic evidence of stenosis were evaluated by post-captopril/baseli ne Tc-99m-MAG3 renography. Results obtained with the expected renogram analysis were compared with those obtained by standard criteria which included: improvement of peak time under baseline conditions, wash-ou t (75%) time, and monolateral or bilateral residual cortical activity >10%, but asymmetrical, i.e. with >5% change in split function. Compar ed to the standard evaluation, the use of the expected renogram for th e diagnosis of RAS improved the specificity from 70 to 95% (P<0.03) wi thout loss of sensitivity (79.3%). Follow-up data after revascularizat ion were available in 18 scintigraphically positive and six scintigrap hically negative patients with RAS. The sensitivity of the expected re nogram method referring to short-term (1 month) patient outcome follow ing revascularization was 88.8%. The beneficial effects on blood press ure response persisted in 77% of the these patients at 18 months. Nota bly, four of six scintigraphically negative patients with RAS did not show any short-term benefit from revascularization and the improvement in blood pressure values lasted for 18 months in only one case. Concl usions. The high specificity of the expected renogram method reduces t he number of unnecessary invasive procedures. This is a critical point for a low-prevalence disease such as renovascular hypertension.