Device Features
The OneShot™ renal denervation system is
a balloon mounted, irrigated, radiofrequency ablation catheter system. There is a single spiral shaped electrode that delivers a single ablation per renal artery. The catheter is an over-the-wire 0.014” compatible system with a low-pressure balloon that inflates to 1 atm. There are 3 balloon sizes 5mm, 6mm and 7mm that can treat 4-5, 5.1-6 and 6.1-7mm renal arteries respectively. The device requires a ‘landing zone’ of at least 20mm. OneShot™ catheters are compatible with a range of sheaths and guiding catheters from 6-8Fr (sheath compatibility 6-7Fr and guiding catheter compatibility 7-8Fr).
The
irrigated technology cools the non-treated region of the artery via 8 small holes in the balloon adjacent to the ablation strip. In cardiac ablation irrigated ablation technology has been shown to produce a deeper and wider ablation zone compared to non-irrigated technologies1-4 and has also been shown to reduce the potential for char and thrombus formation on the ablation electrode and tissue3,4. There is less theoretical risk of distal embolization of char/thrombus into the kidneys in renal artery denervation with irrigated systems.
The generator has a touch screen interface and menu and is relatively straightforward to use once one is familiar with the process, however the user interface could be aesthetically improved. This process of setting up the irrigation and tubing as well as flushing the catheter does require some practice and is slightly more complicated than some of the other CE marked devices however it is easy to master. The generator also incorporates the saline irrigation pump and has several in-built safety shut off features such as balloon over pressure, radiofrequency/impedance monitoring and catheter fault detection.
Before use, the balloon catheter is flushed and air purged out of the balloon via a function of the generator. Once an 0.014” wire is placed into the renal artery the OneShot™ catheter is advanced over the wire and contrast is injected to assess positioning in the renal artery
(fig 1). The balloon catheter tracks fairly easily over the wire and is the catheter shaft is not too rigid reduces the chances of the wire dislodging and ‘flicking’ out of the renal artery into the aorta. Once in place the balloon is inflated via the generator and the irrigation begins. A test injection of contrast through the sheath or guiding catheter determines if there is good apposition of the balloon and electrode against the renal artery wall. This is determined by assessing for occlusion of the renal artery evident by absence of contrast flow beyond the balloon
(fig 2). The kidney remains perfused by the saline irrigation and there is no complete stasis of blood in the renal artery. A 2 minute single ablation is then performed the procedure is repeated in the contralateral renal artery. The total ablation time of 4 minutes is significantly quicker than the total ablation time required for the current generation
Medtronic Symplicity™ (18-24 minutes) and
St Jude Medical EnligHTN™ (24 minutes) systems.
Results:
There are
promising results from the first in man results from the RHAS (feasibility study to evaluation the Maya* Renal Hypertension Ablation System for chronic hypertension). The study examined 9 patients with systolic bp ≥160mmHg (≥150mmHg if diabetic) on 2 or more antihypertensive medications. The renal arteries were between 4-7mm in diameter with a 20mm ‘landing zone’. The primary objective was the ability to insert the device into each renal artery and deliver low level radiofrequency energy and the secondary objectives were safety and efficacy in reducing systolic blood pressure at follow up.
9 patients underwent renal artery denervation with a primary technical success rate of 89% (8/9) with a generator calibration error leading to the single failure. The generator was reprogrammed and the patient’s case was then successfully completed.
Median total procedure time was 35 minutes (27-138). The average systolic blood pressure (SBP) at baseline was 185.7 ± 18.7 and diastolic blood pressure (DBP) 91.3 ± 14.5mmHg. At 30 days average SBP was 155.6 ± 18.8 and DBP 86.2 ± 14.0 (p=0.004), 3 months SBP 154.4 ± 19.6 and DBP 83.3 ± 15.8 (p=0.006) and at 6 months 143.7 ± 13.3 and DBP 76.0 ± 18.0mmHg (p=0.006).
The Rapid-1 trial has recently completed enrolling. This is a 50 patient international multicentre, single arm study with primary endpoints of 1) acute procedural and long term safety, 2) office SBP reduction at 6 months (compared to baseline) and 3) response rate at 6 months (reduction of SBP>10mmHg). Results are expected later this year.
Conclusion:
Overall the Covidien Oneshot™ renal denervation system is easy to use and the technique required for use is similar to other renal artery interventions and arterial angioplasty. The balloon catheter tracks easily over a 0.014” guide wires once placed into the renal artery. The process of setting up the irrigation, preparing the tubing and flushing the catheter does require practice however this is easy to master. Ablation times are quick compared to most of the other current generation CE marked devices. The results of the Rapid-1 trial are expected later this year.
References
1Petersen HH and Chen X. Temperature-Controlled Irrigated Tip Radiofrequency Catheter Ablation: Comparison of In Vivo and In Vitro Lesion Dimensions for Standard Catheter and Irrigated Tip Catheter with Minimal Infusion Rate. Pacing and Clinical Electrophysiology. 1998; 23(1): 8-17.
2Weiss C, Antz M, Eick O, Eshagzaiy K, Meinertz T and Willems S. Radiofrequency Catheter Ablation Using Cooled Electrodes: Impact of Irrigation Flow Rate and Catheter Contact Pressure on Lesion Dimensions. Pacing and Clinical Electrophysiology. 2002; 25(4): 463-469.
3Wittkampf FHM and Nakagawa H. Radiofrequency Catheter Ablation: Lessons on Lesions. Pacing and Clinical Electrophysiology. 2006; 29:1285-1297.
4Yokoyama K, Nakagawa H, Wittkampf FH, Lazzara R and Jackman WM. Comparison of Electrode Cooling Between Internal and Open Irrigation in Radiofrequency Ablation Lesion Depth and Incidence of Thrombus and Steam Pop. Circulation 2006;113:11-19.
*Maya medical was acquired by Covidien in April 2010
