Case presentation

A 71-year-old woman with a history of hypertension, dyslipidemia, and remote tobacco abuse presents with difficult to control blood pressure despite four medications. Diagnosed with essential hypertension many years earlier, her blood pressure had been well-controlled on an angiotensin-receptor blocker (valsartan) and a diuretic (hydrochlorothiazide). Over the past 6 to 8 months, her blood pressure progressively increased with systolic pressures in the 180 mmHg range and diastolic pressures exceeding 90 mmHg despite the addition of adequate doses of beta-blocker (atenolol) and a calcium channel blocker (amlodipine). Her physical examination was notable only for a blood pressure of 160/90 mmHg. Routine laboratory studies, including renal function, were normal, with a creatinine of 1.1 mg/dL. Suspicious of renal artery stenosis, her physician ordered a magnetic resonance angiogram (MRA) of her renal arteries. This revealed a severe stenosis of the left renal artery and she was referred for renal angiography and intervention.

Catheterization

Selective right and left renal angiography was performed using a 6 French, 55 cm long internal mammary guide catheter. Selective right renal angiography uncovered a nonsignificant stenosis of the ostium (Figure 53-1 and Video 53-1). Left renal angiography confirmed the findings on MRA with a very severe eccentric stenosis of the proximal segment of the left renal artery apparent (Figure 53-2 and Video 53-2).

FIGURE 53-1 Selective right renal angiogram demonstrating a mild stenosis of the proximal segment of the right renal artery (arrow).

FIGURE 53-2 Selective left renal angiogram revealing a severe stenosis in the left renal artery (arrow).

The decision was made to perform left renal artery stenting and, after administration of a bolus followed by an infusion of bivalirudin, the operator positioned a 0.014 inch floppy-tipped guidewire in the left renal artery and performed predilatation with a 4.5 mm diameter by 15 mm long rapid exchange balloon (Figures 53-3, 53-4). After balloon predilatation, a 6.0 mm diameter by 15 mm long bare-metal stent on a rapid exchange, a 0.014 inch platform was positioned in the proximal segment of the left renal artery (Figure 53-5). The stent was deployed by inflating the balloon to 10 atmospheres of pressure. An excellent angiographic result was obtained (Figure 53-6 and Video 53-3).

FIGURE 53-3 Balloon inflation in the left renal artery.

FIGURE 53-4 Result after balloon inflation in the left renal artery.

FIGURE 53-5 Position of the stent in the left renal artery.

FIGURE 53-6 Post-stent result in the left renal artery.

Postprocedural course

She was observed overnight and hydrated with normal saline. Blood pressures remained well-controlled after the procedure and she was discharged the next morning on aspirin, clopidogrel, simvastatin, atenolol, amlodipine, furosemide, and losartan. At follow-up 1 month later, her blood pressure measured 100/60 mmHg in both arms and the amlodipine and clopidogrel were discontinued. She returned 6 months later feeling well and brought along her own record of well-controlled blood pressures. On exam, her blood pressure was 130/60 mmHg on atenolol, furosemide, and losartan. A renal ultrasound showed normal kidney size bilaterally and normal Doppler velocities in both the right and left renal arteries.

Discussion

Renal artery stenosis is the most common cause of secondary hypertension. The underlying pathophysiology of renal artery stenosis is atherosclerosis in 90% of cases and fibromuscular dysplasia in the remaining 10%.^1,2 As demonstrated in this case, most atherosclerotic renal artery lesions affect the ostium and proximal segment of the renal artery while fibromuscular dysplasia, a condition primarily seen in young females, affects the middle third of the artery.²

Diagnosis of renal artery stenosis is based on a clinical suspicion of the entity, as symptoms and physical findings are usually absent. Guidelines suggest screening for renal artery stenosis in patients with: 1) onset of hypertension either before age 30 or after age 55; 2) accelerated, malignant, or resistant hypertension; 3) new or worsening renal insufficiency after initiation of angiotensin-converting enzyme inhibitor or angiotensin receptor blocker therapy; 4) unexplained renal atrophy; or 5) unexpected pulmonary edema.² Several imaging methods are useful for diagnostic screening including duplex ultrasound, CTA, or MRA, with angiography reserved for patients with abnormal screening tests.

Treatment of renal artery stenosis includes medical therapy, stenting, and surgical revascularization. At present, the data supporting renal artery stenting over optimal medical therapy are limited.³ Trials comparing medical therapy to renal artery revascularization are difficult to design and implement. First, the hemodynamic significance of renal artery lesions is often unclear, particularly in the presence of moderate stenoses,^4,5 and this may create a heterogenous group of patients in any given study depending on their inclusion criteria. Second, there has not been clear consensus on the need for adjunctive pharmacology or embolic protection.⁶ Third, there is a large selection bias involved in these trials, as many physicians believe they “know the answer” already and are reluctant to enroll patients in a trial in which their patient may be randomized to medical therapy instead of receiving a stent; thus the studies may consist mostly of moderate lesions, as the most severe lesions may not be enrolled. Finally, a variety of endpoints may be used, including blood pressure control, renal function, quality of life and cardiovascular mortality.

Initially, the only available randomized controlled studies consisted of a small number of patients treated with balloon angioplasty rather than stenting, and relied on study endpoints of unclear relevance.³ These studies showed no difference in blood pressure control between patients treated with balloon angioplasty and those treated with medical therapy; however, these studies did find that the balloon angioplasty group required less antihypertensive drugs to achieve that control. Given the fact that renal artery stenting, with high procedural success rates and low rates of restenosis, is clearly superior to balloon angioplasty, it was believed that the results of these trials would be different with stenting.

A recently published randomized controlled trial of medical therapy versus stenting for renal artery stenosis in over 800 patients found no clinical benefit from revascularization in terms of renal function, blood pressure, and cardiovascular events but several procedural complications in the revascularization group.⁷ Additional, large-scale randomized controlled trials designed to compare renal artery stenting to optimal medical therapy are underway and their results are highly anticipated. The study design, primary endpoints, and results of these trials will likely be exhaustively debated over the years.

Until we have the evidence from these trials, current guidelines recommend renal artery stenting for significant renal artery stenosis in the following clinical settings²:

There are several important technical issues in the performance of renal artery stenting. Most operators currently use 0.014 or 0.018 inch guidewire-compatible balloons and stents. Guide catheter placement is often straightforward but may be challenging in the presence of iliac or aortic tortuosity or if the renal artery originates at a steep angle from the aorta. One of the most challenging aspects for the operator relates to the ostial involvement of the disease. It is sometimes difficult for the operator to accurately image the ostium and be highly confident that the stent covers this segment adequately. Most operators like to have the end of the stent protrude slightly into the aorta to ensure the ostium is covered.

Complications of renal artery stenting include spasm, renal artery occlusion and loss of the kidney, renal parenchymal hemorrhage from guidewire perforation, dissection, renal artery perforation, distal embolization, and renal failure. Fortunately, these are rare in skilled hands and the procedural success rates exceed 95%. Restenosis after stenting is low (5% to 15%) and primarily relates to the diameter of the stent.