New Method Predicts Stent Responders

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An angiogram of a renal stent treating stenosis at the ostium of a renal artery.
An angiogram of a renal stent treating stenosis at the ostium of a renal artery.
Renal frame count can indicate likelihood of successful outcomes in patients with renal hypertension.

ORLANDO—The clinical success of renal stenting for the treatment of renovascular hypertension can be predicted on the basis of renal frame count in the catheterization lab, according to research presented here at the American College of Cardiology annual meeting.

While renal stenting can lower BP in patients who are refractory to medical treatment, there has been no reliable means of predicting who will respond to this intervention, said Ehtisham Mahmud, MD, of the University of California at San Diego School of Medicine.  

Current predictors of response appear unreliable. A resistive index (RI) greater than 0.8 is felt to identify nonresponders. However, in a study by White et al, response was similar among groups with RI less than 0.7, 0.7-0.8, and greater than 0.8 (Circulation. 2006;113:1464-1473).

In another study by the same investigators, brain natriuretic peptide (BNP) proved more predictive, as clinical response after stenting correlated with BNP greater than 80 pg/mL and BNP decrease of greater than 30%. A study has also found that fractional flow reserve lower than 0.80 is associated with BP improvement after stenting.

“We undertook our study to find angiographic parameters that could be used in the cath lab to identify patients who will respond to stenting,” Dr. Mahmud said.

Dr. Mahmud and colleagues evaluated quantitative measures of renal perfusion—renal frame count and renal blush grade (RBG)—which are impaired in the presence of renal artery stenosis and which improve to near-normal levels after renal stenting.  

“We took a similar concept—coronary frame count—and modified these measures for the renal setting,” he said.

The investigators quantitatively determined renal frame count, which is the number of angiographic frames acquired from the initial contrast opacification of the renal artery to opacification of the cortical vessel. Image acquisition was done at 30 frames per second.

RBG was a semiquantitative measure taken at the 60th frame (two seconds), scored as follows:

  • RBG 0: no parenchymal blush/contrast opacification of cortical vessels
  • RBG 1: minimal parenchymal blush/contrast opacification of cortical vessels
  • RBG 2: complete parenchymal blush/contrast opacification of cortical vessels
  • RBG 3: hyperemic parenchymal blush/brisk clearance of contrast from cortical vessels

Renal frame counts and RBG were measured in 24 consecutive hypertensive patients before and after renal stenting. Subjects had BP greater than 140/90 mm Hg despite two or more BP medications and renal artery stenosis greater than 70%. Results were compared with those from a control group of 17 hypertensive patients without renal artery stenosis whose BP was greater than 140/90 despite two or more medications.

In the control group, mean renal frame count was determined to be 20.1 and mean RBG was 2.33. This group did not receive stents. 

In the study group, the mean baseline renal frame count was 26.6, which fell to 21.4 after stenting. Mean RBG was 1.6, increasing to 2.1 after stenting, Dr. Mahmud reported.

“Both improvements in renal blush grade and the decrease in renal frame counts were statistically significant,” he noted.

At six months, both systolic BP (SBP) and diastolic BP (DBP) were significantly reduced. Mean SBP fell from 150.6 mm Hg at baseline to 128.6 mm Hg, while DBP fell from 77.2 mm Hg to 68.3 mm Hg.

“We found that 60% of patients were responders, and they experienced almost a 40-mm Hg reduction in SBP, while nonresponders averaged a 5-mm Hg reduction,” he said, “and we could differentiate these groups by our metrics. The reduction in renal frame count was significantly associated with improvements in blood pressure.”

Responders experienced a mean renal frame count reduction of seven frames after stenting, whereas nonresponders had virtually no reduction. A reduction of more than four frames was associated with a clinical improvement in 78% of patients by six months, Dr. Mahmud reported.

While weakly powered for prediction, a baseline renal frame count of more than 25 was also associated with BP reduction in 75% of patients. RBG, however, proved to be of no value in predicting clinical response.

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