AVS Is a 'Choke Point' for Aldosteronism Assessment in Hypertension

Mitchel L. Zoler, PhD

October 13, 2020

At a time when new evidence strongly suggests that roughly a fifth of patients with hypertension have primary aldosteronism as the cause, other recent findings suggest that many of these possibly tens of millions of patients with aldosterone-driven high blood pressure may as a consequence need an expensive and not widely available diagnostic test – adrenal vein sampling – to determine whether they are candidates for a definitive surgical cure to their aldosteronism.

Some endocrinologists worry the worldwide infrastructure for running adrenal vein sampling (AVS) isn't close to being in place to deliver on this looming need for patients with primary aldosteronism (PA), especially given the burgeoning numbers now being cited for PA prevalence.

"The system could be overwhelmed," warned Robert M. Carey, MD, a cardiovascular endocrinologist and professor of medicine at the University of Virginia in Charlottesville. "Right now, adrenal vein sampling [AVS] is the gold standard," for distinguishing unilateral and bilateral excess aldosterone secretion, "but not every radiologist can do AVS. Until we find a surrogate biomarker that can distinguish unilateral and bilateral PA" many patients will need AVS, Carey said in an interview.

Dr Jun Yang

"AVS is important for accurate lateralization of aldosterone excess in patients, but it may not be feasible for all patients with PA to undergo AVS. If the prevalence of PA truly is on the order of 15% [of all patients with hypertension] then health systems would be stretched to offer all of them AVS, which is technically challenging and requires dedicated training and is therefore limited to expert centers," commented Jun Yang, MBBS, a cardiovascular endocrinologist at the Hudson Institute of Medical Research and a hypertension researcher at Monash University, both in Melbourne. "At Monash, our interventional radiologists have increased their [AVS] success rate from 40% to more than 90% during the past 10 years, and our waiting list for patients scheduled for AVS is now 3-4 months long," Yang said in an interview.

Finding a unilateral adrenal nodule as the cause of PA means that surgical removal is an option, a step that often fully resolves the PA and normalizes blood pressure. Patients with a bilateral source of the aldosterone are not candidates for surgical cure and must be managed with medical treatment, usually a mineralocorticoid receptor antagonist such as spironolactone that can neutralize or at least reduce the impact of hyperaldosteronism.

AVS Finds Unilateral Adenomas When Imaging Can't

The evidence that raised concerns about the reliability of imaging as an easier and noninvasive means to identify hypertensive patients with PA and a unilateral adrenal nodule that makes them candidates for surgical removal to resolve their PA and hypertension came out in May 2020 in a review of 174 PA patients who underwent AVS at a single center in Calgary, Alta., during 2006-2018.

The review included 366 patients with PA referred to the University of Calgary for assessment, of whom 179 had no adrenal nodule visible with either CT or MRI imaging, with 174 of these patients also undergoing successful AVS. The procedure revealed 70 patients (40%) had unilateral aldosterone secretion (Can J Cardiol. 2020 May 16. doi: 10.1016/j.cjca.2020.05.013).

In an editorial about this report that appeared a few weeks later, Ross D. Feldman, MD, a hypertension-management researcher and professor of medicine at the University of Manitoba in Winnipeg, Man., said the finding was "amazing," and "confirms that lateralization of aldosterone secretion in a patient with PA but without an identifiable mass on that side is not a zebra," but instead a presentation that "occurs in almost half of patients with PA and no discernible adenoma on the side that lateralizes." (Can J Cardiol. 2020 Jul 3. doi: 10.1016/j.cjca.2020.06.022).

Although this was just one center's experience, the authors are not alone in making this finding, although prior reports seem to have been largely forgotten or ignored until now.

"The discordance between AVS and adrenal imaging has been documented by numerous groups, and in our own experience [in Melbourne] around 40% of patients with unilateral aldosterone excess do not have a distinct unilateral adenoma on CT," said Yang.

"Here's the problem," summed up Feldman in an interview. "Nearly half of patients with hyperaldosteronism don't localize based on a CT or MRI, so you have to do AVS, but AVS is not generally available; it's only at tertiary centers; and you have to do a lot of them," to do them well. "It's a half-day procedure, and you have to hit the correct adrenal vein."

AVS for Millions?

Compounding the challenge is the other bit of bombshell news recently dropped on the endocrinology and hypertension communities: PA may be much more prevalent than previously suspected, occurring in roughly 20% of patients with hypertension, according to study results that also came out in 2020 (Ann Int Med. 2020 Jul 7;173[1]:10-20).

The upshot, according to Feldman and others, is that researchers will need to find reliable criteria besides imaging for identifying PA patients with an increased likelihood of having a lateralized source for their excess aldosterone production. That's "the only hope," said Feldman, "so we won't have to do AVS on 20 million Americans."

Unfortunately, the path toward a successful screen to winnow down candidates for AVS has been long and not especially fruitful, with efforts dating back at least 50 years, and with one of the most recent efforts at stratifying PA patients by certain laboratory measures getting dismissed as producing a benefit that "might not be substantial," wrote Michael Stowasser, MBBS, in a published commentary (J Hypertension. 2020 Jul;38[7]:1259-61).

In contrast to Feldman, Stowasser was more optimistic about the prospects for avoiding an immediate crisis in AVS assessment of PA patients, mostly because so few patients with PA are now identified by clinicians. Given the poor record clinicians have historically rung up diagnosing PA, "it would seem unlikely that we are going to be flooded with AVS requests any time soon," he wrote. There is also reason to hope that increased demand for AVS will help broaden availability, and innovative testing methods promise to speed up the procedure, said Stowasser, a professor of medicine at the University of Queensland in Brisbane, Australia and director of the Endocrine Hypertension Research Centre at Greenslopes and Princess Alexandra Hospitals in Brisbane, in an interview.

But regardless of whether AVS testing becomes more available or streamlined, recent events suggest there will be little way to avoid eventually having to run millions of these diagnostic procedures.

Patients with PA "who decide they will not want surgery do not need AVS. For all other patients with PA, you need AVS. The medical system will just have to respond," Carey concluded.

Carey, Yang, Feldman, and Stowasser had no relevant disclosures.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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