Cath Lab Digest

Renal artery stenosis is the most common secondary cause of hypertension (HTN). It affects 5% of the 50 million people with HTN in the United States. Renovascular disease leads to malignant HTN in 10–45% of patients. In patients older than 50 years, it is responsible for 5–15% of the renal failure population, and 10–20% of the end-stage renal disease population. The prevalence of RAS, greater than 60%, has been reported to be 6.8% in patients older than 65 years of age.¹

Percutaneous transluminal renal angioplasty (PTRA) was introduced as an alternative to surgery by Gruentzig in 1978.² Until the early 1990’s, surgical renal artery revascularization was primarily performed for RAS. In 1993, secondary patency, reduction in blood pressure and improvement in renal function were found to be similar with surgery or PTRA.³ PTRA was associated with a decreased number of complications. Currently, surgical revascularization is rarely performed solely for RAS.

In 1998, PTRA was demonstrated to provide a significant decrease in systolic pressure as compared to medical therapy in patients with bilateral RAS.⁴ In patients with unilateral RAS, PTRA, with stenting if necessary, has been associated with the need for fewer medications to provide a similar reduction of blood pressure compared to medical therapy.⁵ The Dutch RAS interventional cooperative trial randomized patients with greater than 50% stenosis and diastolic hypertension despite treatment with 2 anti-hypertensive medications to medical therapy versus PTRA without stenting. By 3 months, 44% of the medical group had failed medical therapy and crossed over to the intervention group. At 3 and 12 months, the extent of blood pressure lowering was similar. However, the number and dose of antihypertensive medications was lower in the PTRA group.⁶ Recent data from the RENAISSANCE trial demonstrated a significant improvement in systolic hypertension 9 months after percutaneous transluminal renal angioplasty and stenting (PTRAS).⁷

In a non-randomized study, PTRA improved renal function in 41–43% of patients.⁸ Harden reported improvement or stabilization of renal function in 69% of stented renal arteries.⁹ In 2000, Watson demonstrated that renal artery stent placement was associated with a positive slope of the reciprocal of serum creatinine 72% of the time and a less negative slope 78% of the time.¹⁰

The effect of renal artery angioplasty on renal function was elegantly demonstrated by La Batide-Alanore in 2001. After following 32 patients who underwent PTRA for a mean of 6 months, split renal function was derived using captopril renal scintography. The renal function of the treated kidney was found to improve significantly after PTRA.¹¹ This suggests that PTRA improves the renal function in patients with unilateral RAS.

Plaque recoil with angioplasty alone leads to restenosis and limits patency. In 1999, 85 patients with greater than 50% RAS were randomized to treatment with PTRA versus PTRAS. PTRAS was associated with a significant improvement in primary and secondary patency rates and reduced restenosis without an increase in complications.¹² In a meta-analysis of 14 studies involving 678 patients, RAS was associated with a 98% technical success rate. Hypertension was cured in 20% and improved in 49%. In patients with renal impairment, renal function was improved in 30% and stabilized in 38%.¹³ Most recently, Rocha-Singh, et al. reported results of the first prospective RAS trial in which the results were monitored by an independent core laboratory. Renal artery stenting for failed PTRA was associated with a significant lowering of systolic and diastolic blood pressure and a reduction in the number of antihypertensive agents.¹⁴

Indications for Renal Artery Revascularization
Reductions greater than 60% are associated with a significant trans-lesional gradient.¹⁵ In a comparison of pressure gradient to renal artery vessel diameter, a vessel stenosis of approximately 50% corresponded to a 20 mm Hg pressure gradient. Beyond this severity of stenosis, there was a rapid increase in trans-lesional pressure gradients.¹⁶

Translesional pressure gradients are often measured using end-hole catheters. This technique may overestimate the gradient secondary to pressure damping. To measure pressure gradients associated with RAS, 0.014” pressure wires may be used.¹⁶ Pressure wires have been used in combination with papavarine to evaluate renal artery fractional flow reserve (FFR) in arteries with moderate (50–90%) stenosis. Subramanian, et al. demonstrated that maximal hyperemia can be achieved with papavarine, and that baseline pressure gradients correlated with FFR. They found a poor correlation between the visual angiographic estimation and hemodynamic measures of lesion severity. Furthermore, the visually estimated lesion severity was 74.9% ± 11.5%, while the quantitative vascular angiographic lesion severity was 56.6% ± 10.8%.¹⁷

These results suggest that interventionalists may overestimate renal artery lesion severity. This may lead to interventions on hemodynamically insignificant stenosis. Percutaneous renal artery revascularization should be reserved for patients with an angiographic RAS severity of 70% or greater, and a translesional gradient of greater than 20 mmHg. It is our recommendation that the hemodynamic significance of a lesion’s severity, using either renal arterial duplex or pressure wire, be confirmed prior to proceeding with intervention. This may decrease the number of PTRAS procedures performed without associated clinical benefit.