Imaging Detects Vascular Injury Arising from Catheter-Based Renal Denervation

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Patients who undergo percutaneous renal nerve ablation for treatment-resistant hypertension show signs of endothelial and vascular injury on optical coherence tomography (OCT), according to a paper published online April 25, 2013, ahead of print in the European Heart Journal.

To prevent such damage, dual antiplatelet therapy may be required during the procedure, the researchers said, but outside sources interviewed by TCTMD strongly questioned that advice.

Thomas F. Lüscher, MD, of University Hospital Zurich (Zurich, Switzerland), and colleagues evaluated 32 arteries in 16 patients who underwent renal denervation using either the Symplicity (n = 11; Medtronic, Minneapolis, MN) or EnligHTN (n = 5; St. Jude Medical, St. Paul, MN) catheter systems. No patient was on dual antiplatelet therapy. In each artery, OCT pullbacks were performed before and after the procedure, and imaging results were analyzed in a core lab by independent investigators.

Vasospasm, endothelial-intimal edema, and thrombus formation—the latter of which was seen along the entire length of the treated artery—all were more prevalent on OCT after renal denervation (table 1).

Table 1. OCT Findings

There was 1 arterial dissection with Symplicity and 2 patients had endothelial and intimal disruptions with EnligHTN (P = 0.26). Mean renal artery diameter decreased with both the Symplicity (from 5.04 ± 0.66 mm to 4.57 ± 0.88 mm; P < 0.001) and EnligHTN catheters (from 4.69 ± 0.73 mm to 4.21 ± 0.87 mm; P < 0.001). While edema and vasospasm occurred with similar frequency with the 2 systems, there was a trend toward more thrombus formation with EnligHTN vs. Symplicity (89% vs. 53%; P = 0.07) as well as significantly greater thrombus load per renal artery (4.6 ± 3.1 vs. 1.5 ± 1.8; P = 0.006).

However, researchers cautioned that the number of pullbacks excluded from analysis due to poor image quality was higher for Symplicity, limiting the ability to make direct comparisons.

Antiplatelet Drugs, More Research Justified

Having demonstrated the feasibility of OCT for this indication, “[l]arger studies with short- and long-term follow-up by OCT now need to further document the type and extent of the healing response after [renal nerve ablation] and the relation between local injury and the blood pressure response after the procedure,” Dr. Lüscher and colleagues conclude.

“Based on our findings,” they advise, “we recommend to perform OCT routinely in patients after [renal nerve ablation] and to effectively inhibit platelet activation with either acetylsalicylic acid or an ADP-receptor antagonist.”

Dr. Lüscher told TCTMD in an e-mail communication that he was surprised by the results.

“Absolutely, the lesions are certainly more pronounced than I expected,” he said, adding, “Obviously, we now need to see 1) whether these lesions disappear, say at 1 month (studies we are currently planning), and 2) whether thrombus formation can be prevented with, say, ticagrelor. Indeed, embolization of such thrombi may impair renal function due to destruction of glomeruli.”

Because renal artery stenosis after ablation has now been described, “we need to see whether there is really no problem,” he emphasized, suggesting that in addition to antiplatelet drugs, different devices or energy sources might be explored as potential prevention strategies.

Damage May Have Few Consequences

In a telephone interview with TCTMD, George L. Bakris, MD, of the University of Chicago Medical Center (Chicago, IL), said that the renal stenosis observed in the study should not come as a shock. “If anybody is surprised by that, they’d better go back and read physiology, because that’s exactly what should happen. The question is, is it clinically significant?” The current paper comes more from a vascular biology perspective than from a clinical perspective, he added.

Dr. Bakris noted that as early as 2006, before clinical trials on catheter-based renal denervation even began, “there was a lot concern and speculation that there would be acute renal artery stenosis, acute renal failure, atherothrombotic disease, and loss of control of sodium.”

However, these worries have not come about, he said, adding that dissection is extremely rare and acute renal failure has not been reported. Any renal artery issues that have arisen in clinical trials, where there are trained operators, did not translate into lasting problems, Dr. Bakris reported.

Antiplatelet Suggestion May Be Dangerous

More importantly, the assertion that all renal denervation patients should receive antiplatelet drugs is “insane,” Dr. Bakris commented. Such medications “are great if the fundamental mechanism leading to stenosis is atherosclerosis. No question about it. Here, they’re arguing that it’s a general inflammatory mechanism—and there’s some validity to that—but here it’s self-limited, it’s not progressive, and again there are no data to support that. You cannot extrapolate the data from atherosclerosis trials.”

In an e-communication, Suzanne Oparil, MD, of the University of Alabama (Birmingham, AL), agreed. “I think dual antiplatelet therapy is a terrible idea in patients who truly have resistant hypertension,” she stressed to TCTMD. “I would rather have renal artery stenosis or a small clot rather than an intracerebral bleed.”

Similar to Dr. Bakris, she noted, “I'm not really surprised by [the results] but am happy to see that the study was done. [Electrophysiology] specialists tell me that radiofrequency ablation always [results in] tissue damage—thermal burns—that's how it works.”

Long-term data are still lacking, and the OCT findings might still have clinical sequelae, Dr. Oparil added. “I guess one could worry about accelerated atherosclerosis if the endothelium is removed and about stenosis if the spasm persists, but I think there is evidence that the spasm shown in this study is an acute effect that disappears.”

When weighing these concerns, she stressed that clinicians should remember that resistant hypertension is itself dangerous.

Dr. Bakris also advised awareness on the part of clinicians. “Is [the possibility of damage] something you should be cognizant of? Yes. Is it something you should be vigilant in looking for if the clinical scenario is such that you get results that are unexplained, like blood pressure all of a sudden going up and kidney function going down? Absolutely. That should be the first thing you look for. But after that, you’re done.

“There is no way you can prevent this,” he continued. “In fact, I would argue that what they’re proposing . . . is going to increase bleeding complications rather than prevent any stenosis.”

 

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Source:
Templin C, Jaguszewski M, Ghadri JR, et al. Vascular lesions induced by renal nerve ablation as assessed by optical coherence tomography: Pre- and post-procedural comparison with the Simplicity catheter system and the EnligHTN multi-electrode renal denervation catheter. Eur Heart J. 2013;Epub ahead of print.

 

 

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