Renal nerve stimulation: complete versus incomplete renal sympathetic denervation.

PURPOSE: Blood pressure (BP) reduction after renal sympathetic denervation (RDN) is highly variable. Renal nerve stimulation (RNS) can localize sympathetic nerves. The RNS trial aimed to investigate the medium-term BP-lowering effects of the use of RNS during RDN, and explore if RNS can check the completeness of the denervation. MATERIAL AND METHODS: Forty-four treatment-resistant hypertensive patients were included in the prospective, single-center RNS trial. The primary study endpoint was change in 24-h BP at 6- to 12-month follow-up after RDN. The secondary study endpoints were the acute procedural RNS-induced BP response before and after RDN; number of antihypertensive drugs at follow-up; and the correlation between the RNS-induced BP increase before versus after RDN (delta [Δ] RNS-induced BP). RESULTS: Before RDN, the RNS-induced systolic BP rise was 43(±21) mmHg, and decreased to 9(±12) mmHg after RDN (p < 0.001). Mean 24-h systolic/diastolic BP decreased from 147(±12)/82(±11) mmHg at baseline to 135(±11)/76(±10) mmHg (p < 0.001/<0.001) at follow-up (10 [6-12] months), with 1 antihypertensive drug less compared to baseline. The Δ RNS-induced BP and the 24-h BP decrease at follow-up were correlated for systolic (R = 0.44, p = 0.004) and diastolic (R = 0.48, p = 0.003) BP. Patients with ≤0 mmHg residual RNS-induced BP response after RDN had a significant lower mean 24-h systolic BP at follow-up compared to the patients with >0 mmHg residual RNS-induced BP response (126 ± 4 mmHg versus 135 ± 10 mmHg, p = 0.04). 83% of the patients with ≤0 mmHg residual RNS-induced BP response had normal 24-h BP at follow-up, compared to 33% in the patients with >0 mmHg residual RNS-induced BP response (p = 0.023). CONCLUSION: The use of RNS during RDN leads to clinically significant and sustained lowering of 24-h BP with fewer antihypertensive drugs at follow-up. RNS-induced BP changes were correlated with 24-h BP changes at follow-up. Moreover, patients with complete denervation had significant lower BP compared to the patients with incomplete denervation.

Renal sympathetic denervation induces changes in heart rate variability and is associated with a lower sympathetic tone.

BACKGROUND: Renal nerve stimulation (RNS) is used to localize sympathetic nerve tissue for selective renal nerve sympathetic denervation (RDN). Examination of heart rate variability (HRV) provides a way to assess the state of the autonomic nervous system. The current study aimed to examine the acute changes in HRV caused by RNS before and after RDN. METHODS AND RESULTS: 30 patients with hypertension referred for RDN were included. RNS was performed under general anesthesia before and after RDN. Heart rate (HR) and blood pressure (BP) were continuously monitored. HRV characteristics were assessed 1 min before and after RNS and RDN. RNS before RDN elicited a maximum increase in systolic BP of 45 (± 22) mmHg which was attenuated to 13 (± 12) mmHg (p < 0.001) after RDN. RNS before RDN decreased the sinus cycle length from 1210 (± 201) ms to 1170 (± 203) ms (p = 0.03), after RDN this effect was blunted (p = 0.59). The LF/HF ratio in response to RNS changed from ∆ + 0.448 (± 0.550) before RDN to ∆ - 0.656 (± 0.252) after RDN (p = 0.02). Selecting patients off beta-blockade (n = 11), the RNS-induced changes in HRV components before versus after RDN were more pronounced (LF/HF ratio ∆ + 0.900 ± 1.171 versus ∆ - 0.828 ± 0.519, p = 0.01), whereas changes in HRV parameters in patients on beta-blockade (n = 19) were no longer significant. In patients with diabetes mellitus (n = 7), RNS induced no changes in HRV parameters (LF/HF ratio ∆ - 0.039 ± 0.103 versus ∆ - 0.460 ± 0.491, p = 0.92). CONCLUSION: RNS induces changes in HRV suggesting increased sympathetic activity. Conversely, after RDN, the RNS-induced changes in HRV suggesting a lower sympathetic autonomic balance. These changes were most pronounced in beta-blocker naïve patients and not present in patients with diabetes mellitus. These findings could support RNS-guided RDN to optimize results.

Changes in arterial pressure hemodynamics in response to renal nerve stimulation both before and after renal denervation.

BACKGROUND: Renal nerve denervation (RDN) is developed as a potential treatment for hypertension. Recently, we reported the use of renal nerve stimulation (RNS) to localize sympathetic nerve tissue for subsequent selective RDN. The effects of RNS on arterial pressure dynamics remain unknown. The current study aimed to describe the acute changes in arterial pressure dynamics response to RNS before and after RDN. METHODS AND RESULTS: Twenty six patients with drug-resistant hypertension referred for RDN were included. RNS was performed under general anesthesia before and after RDN. We continuously monitored heart rate (HR) and invasive femoral blood pressure (BP). Augmentation pressure (AP) and index (Aix), pulse pressure (PP), time to reflected wave, maximum systolic BP and dicrotic notch were calculated. Systolic and diastolic BP at site of maximum response significantly increased in response to RNS (120 ± 16/62 ± 9 to 150 ± 22/75 ± 15 mmHg) (p < 0.001/< 0.001), whereas after RDN no RNS-induced BP change was observed (p > 0.10). RNS increased Aix (29 ± 11 to 32 ± 13%, p = 0.005), PP (59 ± 14 to 75 ± 17 mmHg, p < 0.001), time to reflected wave (63 ± 18 to 71 ± 25 ms, p = 0.004) and time to maximum systolic pressure (167 ± 36 to 181 ± 46 ms, p = 0.004) before RDN, whereas no changes were observed after RDN (p > 0.18). All changes were BP dependent. RNS had no influence on HR or the time to dicrotic notch (p > 0.12).   CONCLUSION: RNS induces temporary rises in Aix, PP, time to maximum systolic pressure and time to reflected wave. These changes are BP dependent and were completely blunted after RDN.

Renal nerve stimulation identifies aorticorenal innervation and prevents inadvertent ablation of vagal nerves during renal denervation.

PURPOSE: Recently we reported the use of renal nerve stimulation (RNS) during renal denervation (RDN) procedures. RNS induced changes in blood pressure (BP) and heart rate are not fully delineated yet. We hypothesized that electrical stimulation of the sympathetic nerve tissue in the renal artery would lead to an increase in BP and vagal stimulation would cause a decrease in BP. We report the different patterns of BP and heart rate responses elicited by RNS prior to RDN. METHODS: 35 patients with drug-resistant hypertension were included. RNS was performed under general anesthesia at four sites in the right and left renal arteries, both before and immediately after RDN. RNS-induced BP and heart rate changes were monitored. RESULTS: A total of 289 RNS sites in 35 patients were analyzed. An increase in systolic BP of >10 mmHg was regarded as a positive BP response to RNS. This pattern of response was observed in 180 sites (62%). 86 RNS sites (30%) showed an indifferent response with BP changes ≤10 mmHg. At 13 sites (4.5%) RNS elicited a decrease in BP up to -8 mmHg. However, 10 RNS sites (3.5%) showed a pronounced vagal response with hypotension and sinus cycle lengths ranging between 4224-10272 milliseconds. These sites were distributed among two patients. CONCLUSION: RNS identified sympathetic and parasympathetic nerve tissue in the renal arteries. RNS can be potentially used to map nerve bundles and guide selective ablation of sympathetic nerve fibers and prevent inadvertent ablation of parasympathetic nerve tissue during RDN.

Renal Nerve Stimulation as Procedural End Point for Renal Sympathetic Denervation.

PURPOSE OF REVIEW: Renal sympathetic denervation (RDN) as treatment option for hypertension has a strong rationale; however, variable effects on blood pressure (BP) have been reported ranging from non-response to marked reductions in BP. The absence of a procedural end point for RDN is one of the potential factors associated with the variable response. Studies have suggested the use of renal nerve stimulation (RNS) to adequately address this issue. This review aims to provide an overview of the clinical and experimental data available regarding the effects of RNS in the setting of RDN. RECENT FINDINGS: Animal studies have shown that high-frequency electrical stimulation of the sympathetic nerves in the adventitia of the renal arteries elicits an increase in BP and leads to an increased norepinephrine spillover as a marker of increased sympathetic activity and these effects of stimulation were attenuated or blunted after RDN. In a human feasibility study using RNS both before and after RDN, similar BP responses were observed. Moreover, in patients with resistant hypertension, RNS-induced changes in BP appeared to be correlated with 24-h BP response after RDN. These data suggest that RNS is a useful tool to identify renal sympathetic nerve fibers in patients with treatment-resistant hypertension undergoing RDN, and to predict the likely effectiveness of RDN treatments. In acute procedural settings both in animal and human models, RNS elicits increase in BP and HR before RDN and these effects are blunted after RDN. Up to now, there is preliminary evidence that the RNS-induced BP changes predict 24-h ABPM outcome at follow-up in patients with resistant hypertension. Of note, studies are small sized and results of large trials comparing conventional RDN to RNS-guided RDN are warranted.

Treatment of atrial fibrillation in patients with enhanced sympathetic tone by pulmonary vein isolation or pulmonary vein isolation and renal artery denervation: clinical background and study design : The ASAF trial: ablation of sympathetic atrial fibrillation.

BACKGROUND: Hypertension is an important, modifiable risk factor for the development of atrial fibrillation (AF). Even after pulmonary vein isolation (PVI), 20-40% experience recurrent AF. Animal studies have shown that renal denervation (RDN) reduces AF inducibility. One clinical study with important limitations suggested that RDN additional to PVI could reduce recurrent AF. OBJECTIVE: The goal of this multicenter randomized controlled study is to investigate whether RDN added to PVI reduces AF recurrence. METHODS: The main end point is the time until first AF recurrence according to EHRA guidelines after a blanking period of 3 months. Assuming a 12-month accrual period and 12 months of follow-up, a power of 0.80, a two-sided alpha of 0.05 and an expected drop-out of 10% per group, 69 patients per group are required. We plan to randomize a total of 138 hypertensive patients with AF and signs of sympathetic overdrive in a 1:1 fashion. Patients should use at least two antihypertensive drugs. Sympathetic overdrive includes obesity, exercise-induced excessive blood pressure (BP) increase, significant white coat hypertension, hospital admission or fever induced AF, tachycardia induced AF and diabetes mellitus. The interventional group will undergo PVI + RDN and the control group will undergo PVI. RESULTS: Patients will have follow-up for 1 year, and continuous loop monitoring is advocated. CONCLUSION: This randomized, controlled study will elucidate if RDN on top of PVI reduces AF recurrence.

Blood pressure response to renal denervation is correlated with baseline blood pressure variability: a patient-level meta-analysis.

BACKGROUND: Sympathetic tone is one of the main determinants of blood pressure (BP) variability and treatment-resistant hypertension. The aim of our study was to assess changes in BP variability after renal denervation (RDN). In addition, on an exploratory basis, we investigated whether baseline BP variability predicted the BP changes after RDN. METHODS: We analyzed 24-h BP recordings obtained at baseline and 6 months after RDN in 167 treatment-resistant hypertension patients (40% women; age, 56.7 years; mean 24-h BP, 152/90 mmHg) recruited at 11 expert centers. BP variability was assessed by weighted SD [SD over time weighted for the time interval between consecutive readings (SDiw)], average real variability (ARV), coefficient of variation, and variability independent of the mean (VIM). RESULTS: Mean office and 24-h BP fell by 15.4/6.6 and 5.5/3.7 mmHg, respectively (P < 0.001). In multivariable-adjusted analyses, systolic/diastolic SDiw and VIM for 24-h SBP/DBP decreased by 1.18/0.63 mmHg (P ≤ 0.01) and 0.86/0.42 mmHg (P ≤ 0.05), respectively, whereas no significant changes in ARV or coefficient of variation occurred. Furthermore, baseline SDiw (P = 0.0006), ARV (P = 0.01), and VIM (P = 0.04) predicted the decrease in 24-h DBP but not 24-h SBP after RDN. CONCLUSION: RDN was associated with a decrease in BP variability independent of the BP level, suggesting that responders may derive benefits from the reduction in BP variability as well. Furthermore, baseline DBP variability estimates significantly correlated with mean DBP decrease after RDN. If confirmed in younger patients with less arterial damage, in the absence of the confounding effect of drugs and drug adherence, baseline BP variability may prove a good predictor of BP response to RDN.

Renal vascular calcification and response to renal nerve denervation in resistant hypertension.

Renal sympathetic nerve denervation (RDN) is accepted as a treatment option for patients with resistant hypertension. However, results on decline in ambulatory blood pressure (BP) measurement (ABPM) are conflicting. The high rate of nonresponders may be related to increased systemic vascular stiffness rather than sympathetic overdrive. A single center, prospective registry including 26 patients with treatment resistant hypertension who underwent RDN at the Isala Hospital in the Netherlands. Renal perivascular calcium scores were obtained from noncontrast computed tomography scans. Patients were divided into 3 groups based on their calcium scores (group I: low 0-50, group II: intermediate 50-1000, and group III: high >1000). The primary end point was change in 24-hour ABPM at 6 months follow-up post-RDN compared to baseline. Seven patients had low calcium scores (group I), 13 patients intermediate (group II), and 6 patients had high calcium scores (group III). The groups differed significantly at baseline in age and baseline diastolic 24-hour ABPM. At 6-month follow-up, no difference in 24-hour systolic ABPM response was observed between the 3 groups; a systolic ABPM decline of respectively -9 ±â€Š12, -6 ±â€Š12, -12 ±â€Š10 mm Hg was found. Also the decline in diastolic ambulatory and office systolic and diastolic BP was not significantly different between the 3 groups at follow-up. Our preliminary data showed that the extent of renal perivascular calcification is not associated with the ABPM response to RDN in patients with resistant hypertension.

Renal denervation beyond the bifurcation: The effect of distal ablation placement on safety and blood pressure.

Renal denervation may be more effective if performed distal in the renal artery because of smaller distances between the lumen and perivascular nerves. The authors reviewed the angiographic results of 97 patients and compared blood pressure reduction in relation to the location of the denervation. No significant differences in blood pressure reduction or complications were found between patient groups divided according to their spatial distribution of the ablations (proximal to the bifurcation in both arteries, distal to the bifurcation in one artery and distal in the other artery, or distal to the bifurcation in both arteries), but systolic ambulatory blood pressure reduction was significantly related to the number of distal ablations. No differences in adverse events were observed. In conclusion, we found no reason to believe that renal denervation distal to the bifurcation poses additional risks over the currently advised approach of proximal denervation, but improved efficacy remains to be conclusively established.

Renal Nerve Stimulation-Induced Blood Pressure Changes Predict Ambulatory Blood Pressure Response After Renal Denervation.

Blood pressure (BP) response to renal denervation (RDN) is highly variable and its effectiveness debated. A procedural end point for RDN may improve consistency of response. The objective of the current analysis was to look for the association between renal nerve stimulation (RNS)-induced BP increase before and after RDN and changes in ambulatory BP monitoring (ABPM) after RDN. Fourteen patients with drug-resistant hypertension referred for RDN were included. RNS was performed under general anesthesia at 4 sites in the right and left renal arteries, both before and immediately after RDN. RNS-induced BP changes were monitored and correlated to changes in ambulatory BP at a follow-up of 3 to 6 months after RDN. RNS resulted in a systolic BP increase of 50±27 mm Hg before RDN and systolic BP increase of 13±16 mm Hg after RDN (P<0.001). Average systolic ABPM was 153±11 mm Hg before RDN and decreased to 137±10 mm Hg at 3- to 6-month follow-up (P=0.003). Changes in RNS-induced BP increase before versus immediately after RDN and changes in ABPM before versus 3 to 6 months after RDN were correlated, both for systolic BP (R=0.77, P=0.001) and diastolic BP (R=0.79, P=0.001). RNS-induced maximum BP increase before RDN had a correlation of R=0.61 (P=0.020) for systolic and R=0.71 (P=0.004) for diastolic ABPM changes. RNS-induced BP changes before versus after RDN were correlated with changes in 24-hour ABPM 3 to 6 months after RDN. RNS should be tested as an acute end point to assess the efficacy of RDN and predict BP response to RDN.

Persistent Increase in Blood Pressure After Renal Nerve Stimulation in Accessory Renal Arteries After Sympathetic Renal Denervation.

Blood pressure response to renal denervation is highly variable, and the proportion of responders is disappointing. This may be partly because of accessory renal arteries too small for denervation, causing incomplete ablation. Renal nerve stimulation before and after renal denervation is a promising approach to assess completeness of renal denervation and may predict blood pressure response to renal denervation. The objective of the current study was to assess renal nerve stimulation-induced blood pressure increase before and after renal sympathetic denervation in main and accessory renal arteries of anaesthetized patients with drug-resistant hypertension. The study included 21 patients. Nine patients had at least 1 accessory renal artery in which renal denervation was not feasible. Renal nerve stimulation was performed in the main arteries of all patients and in accessory renal arteries of 6 of 9 patients with accessory arteries, both before and after renal sympathetic denervation. Renal nerve stimulation before renal denervation elicited a substantial increase in systolic blood pressure, both in main (25.6±2.9 mm Hg; P<0.001) and accessory (24.3±7.4 mm Hg; P=0.047) renal arteries. After renal denervation, renal nerve stimulation-induced systolic blood pressure increase was blunted in the main renal arteries (Δ systolic blood pressure, 8.6±3.7 mm Hg; P=0.020), but not in the nondenervated renal accessory renal arteries (Δ systolic blood pressure, 27.1±7.6 mm Hg; P=0.917). This residual source of renal sympathetic tone may result in persistent hypertension after ablation and partly account for the large response variability.