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.

UNLABELLED

PURPOSE AND DESIGN OF STUDY: Asymmetric-induced changes of the renogram under angiotensin-converting enzyme inhibition (ACE-i), i.e. lateralization, is probably the most distinctive finding for the detection of haemodynamically significant renal artery stenosis (RAS) in compensated kidney, since bilateral and symmetric patterns are non-specific. In the Consensus statement of diagnostic criteria of renovascular hypertension with captopril renography (Am J Hypertens 1991; 4: 749-755S) ACE-i-induced asymmetry of renograms for the left and right kidney was viewed as vitally important. However, detection of change in split function is a reliable parameter only when using a glomerular tracer, i.e. 99mTc-DTPA. No indication regarding a more widely used tubular tracer such as 99mTc-mercaptoacetyltriglycine (99mTc-MAG3) has been given.

METHODS AND RESULTS

The theoretical contralateral curve, called 'expected renogram', was calculated frame by frame from renal curves obtained under ACE-i and one of two baseline curves. The expected renogram was compared with the recorded ipsilateral curve. More than +/- 2 SD difference between expected and recorded renograms was assumed as suggestive of monolateral or bilateral RAS. Twenty-nine patients with angiographically proven RAS (bilateral in 12) and 20 patients without arteriographic evidence of stenosis were evaluated by postcaptopril/baseline 99mTc-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-out (75%) time, and monolateral or bilateral residual cortical activity > 10%, but asymmetrical, i.e. with > 5% change in split function. Compared to the standard evaluation, the use of the expected renogram for the diagnosis of RAS improved the specificity from 70 to 95% (P < 0.03) without loss of sensitivity (79.3%). Follow-up data after revascularization were available in 18 scintigraphically positive and six scintigraphically negative patients with RAS. The sensitivity of the expected renogram method referring to short-term (1 month) patient outcome following revascularization was 88.8%. The beneficial effects on blood pressure response persisted in 77% of the these patients at 18 months. Notably, 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.

CONCLUSIONS

The high specificity of the expected renogram method reduces the number of unnecessary invasive procedures. This is a critical point for a low-prevalence disease such as renovascular hypertension.