Validation of a prediction rule for renal artery stenosis

Design of a clinical risk calculator for major clinical outcomes in patients with atherosclerotic renovascular disease

BACKGROUND

Risk stratification in atherosclerotic renovascular disease (ARVD) can influence treatment decisions and facilitate patient selection for revascularization. In this study, we aim to use variables with the best predictive value to design a risk calculator that can assist clinicians with risk stratification and outcome prediction.

METHODS

Patients with a radiological diagnosis of ARVD referred to our tertiary renal centre were recruited into this prospective cohort study between 1986 and 2014. Primary clinical endpoints included: death, progression to end-stage kidney disease and cardiovascular events (CVE). A stepwise regression model was used to select variables with the most significant hazard ratio for each clinical endpoint. The risk calculator was designed using Hypertext Markup Language. Survival and CVE-free survival were estimated at 1, 5 and 10 years.

RESULTS

In total, 872 patients were recruited into the Salford ARVD study with a median follow-up period of 54.9 months (interquartile range 20.2-96.0). Only models predicting death and CVE showed good performance (C-index >0.80). Survival probabilities obtained from the risk calculator show that most patients with ARVD have reduced long-term survival. Revascularization improved outcomes in patients with higher baseline estimated glomerular filtration rate and lower proteinuria but not in those with co-existing comorbidities and higher levels of baseline proteinuria.

CONCLUSIONS

Although this risk calculator requires further independent validation in other ARVD cohorts, this study shows that a small number of easily obtained variables can help predict clinical outcomes and encourage a patient-specific therapeutic approach.

Renal artery stenosis: optimizing diagnosis and treatment

Renal artery stenosis (RAS) is the most commonly caused by atherosclerosis, with fibromuscular dysplasia being the most frequent among other less common etiologies. A high index of suspicion based on clinical features is essential for diagnosis. Revascularization strategies are currently a topic of discussion and debate. When revascularization is deemed appropriate, atherosclerotic RAS is most often treated with stent placement, whereas patients with fibromuscular dysplasia are usually treated with balloon angioplasty. Ongoing randomized trials should help to better define the optimal management of RAS.

[Renal artery fibromuscular dysplasia]

Fibromuscular dysplasia (FMD) encompasses a heterogeneous group of idiopathic, segmental, nonatherosclerotic diseases of the musculature of arterial walls, leading to the narrowing of small and medium-sized arteries. The most common locations of FMD are renal arteries and carotid arteries. The diagnosis of FMD is made on the "string of beads" appearance of the arteries. The French Health Authority recommends performing a CT scan or an MRA to assess the diagnosis of FMD. A recent meta-analysis showed the cure rates using current definitions of hypertension cure are only 36% and 54% after angioplasty and surgery, respectively.

Renovascular hypertension: an update

Renovascular hypertension, the most common remediable cause of elevated blood pressure, is a controversial topic, but most authorities agree on several principles. The absolute risk of renovascular hypertension for a specific patient can be estimated using only clinical information, thereby sparing many patients further expensive and potentially dangerous evaluations. Patients with a high absolute risk of renovascular hypertension should have angiography only if they are willing to undergo revascularization if warranted. A screening test (captopril renography, Doppler ultrasonography, magnetic resonance angiography, or computed tomography) is recommended for those with an intermediate absolute risk. Angioplasty should be offered to patients with fibromuscular dysplasia. Whether intensive medical therapy (including an angiotensin-converting enzyme inhibitor or angiotensin II receptor blocker) for atherosclerotic renovascular hypertension is improved by angioplasty plus stent placement may be answered by ongoing studies, the largest of which may be the National Institutes of Health-funded Cardiovascular Outcomes in Renal Atherosclerotic Lesions (CORAL) trial.

Systemic hypertension

Hypertension is a growing public health problem worldwide. Only 37% of American hypertensives currently have their blood pressures controlled. Hypertension is traditionally diagnosed in the medical office, but both home and ambulatory blood pressure monitoring can help. Lifestyle modifications are recommended for everyone who has higher than "normal" blood pressure (<120/80 mm Hg). Voluminous clinical trial data support beginning drug therapy with low-dose chlorthalidone, unless the patient has a specific indication for a different drug. Additional drugs (typically in the sequence, angiotensin converting-enzyme inhibitor or angiotensin receptor blocker, calcium antagonist, beta-blocker, alpha-blocker, aldosterone antagonist, direct vasodilator, and centrally acting alpha(2)-agonist) can be added to achieve the blood pressure goal (usually <140/90 mm Hg, but <130/80 mm Hg for diabetics and those with chronic kidney disease). Special circumstances exist for treatment of hypertension in pregnancy, in childhood, in the elderly, and in both extremes of blood pressure (pre-hypertension or hypertensive emergencies).