Characteristics of Patients Undergoing Atrial Fibrillation Ablation: Trends Over a Seven-Year Period 1999?2005

Participation of women in clinical studies of atrial fibrillation in the Northern Netherlands

INTRODUCTION

Concerns exist of women underrepresentation in atrial fibrillation (AF) studies, potentially limiting the generalisability of study findings to women with AF. We assessed the participation of women in AF clinical studies performed at a tertiary care centre in the Northern Netherlands.

METHODS

Eight AF clinical studies with screening logs were available for analysis. To identify sex-specific differences, patient inclusion and exclusion and reasons for exclusion were assessed. Participation-to-prevalence ratios (PPRs) were calculated to evaluate the representation of women in the studies relative to the AF sex distribution of the general population in the Netherlands (2019 Global Burden of Disease study).

RESULTS

We included 1739 screened patients with AF in the analysis, of whom 722 (41.5%) were women. Of the patients screened, 161 (9%) were enrolled. Median age of screened patients was 69 years (interquartile range (IQR): 61-77), and women were older than men (71 years; IQR: 63-79 vs 68 years; IQR: 60-75; p < 0.001). Women were not underscreened compared with men (PPR: 1.09; 95% confidence interval (CI): 1.08-1.10), disproportionally excluded (92% vs 90%; p = 0.10) or less willing to participate (17% vs 15%; p = 0.36). Women had an overall PPR of 1.05 (95% CI: 1.05-1.06) compared with the general AF population.

CONCLUSION

At our tertiary hospital in the Northern Netherlands, women appeared to be well-represented in AF studies. The current study advocates for the adoption of a more comprehensive measure of equity, such as the PPR, and screening log evaluation to improve the generalisability of study findings to the entire clinical AF population.

Same-day discharge vs. overnight stay following catheter ablation for atrial fibrillation: a comprehensive review and meta-analysis by the European Heart Rhythm Association Health Economics Committee

AIMS

Same-day discharge (SDD) after catheter ablation of atrial fibrillation (AF) may address the growing socio-economic health burden of the increasing demand for interventional AF therapies. This systematic review and meta-analysis analyses the current evidence on clinical outcomes in SDD after AF ablation compared with overnight stay (ONS).

METHODS AND RESULTS

A systematic search of the PubMed database was performed. Pre-defined endpoints were complications at short-term (24-96 h) and 30-day post-discharge, re-hospitalization, and/or emergency room (ER) visits at 30-day post-discharge, and 30-day mortality. Twenty-four studies (154 716 patients) were included. Random-effects models were applied for meta-analyses of pooled endpoint prevalence in the SDD cohort and for comparison between SDD and ONS cohorts. Pooled estimates for complications after SDD were low both for short-term [2%; 95% confidence interval (CI): 1-5%; I2: 89%) and 30-day follow-up (2%; 95% CI: 1-4%; I2: 91%). There was no significant difference in complications rates between SDD and ONS [short-term: risk ratio (RR): 1.62; 95% CI: 0.52-5.01; I2: 37%; 30 days: RR: 0.65; 95% CI: 0.42-1.00; I2: 95%). Pooled rates of re-hospitalization/ER visits after SDD were 4% (95% CI: 1-10%; I2: 96%) with no statistically significant difference between SDD and ONS (RR: 0.86; 95% CI: 0.58-1.27; I2: 61%). Pooled 30-day mortality was low after SDD (0%; 95% CI: 0-1%; I2: 33%). All studies were subject to a relevant risk of bias, mainly due to study design.

CONCLUSION

In this meta-analysis including a large contemporary cohort, SDD after AF ablation was associated with low prevalence of post-discharge complications, re-hospitalizations/ER visits and mortality, and a similar risk compared with ONS. Due to limited quality of current evidence, further prospective, randomized trials are needed to confirm safety of SDD and define patient- and procedure-related prerequisites for successful and safe SDD strategies.

Women and atrial fibrillation

Atrial fibrillation (AF) remains a growing problem in the United States and worldwide, imposing a high individual and health system burden, including increased resource consumption due to repeated hospitalizations, stroke, dementia, heart failure, and death. This comprehensive review summarizes the most recent data on sex-related differences in risks associated with AF. Women with AF have increased risk of stroke and death compared to men, and possible reasons for this disparity are explored. Women also continue to have worse symptoms and quality of life, and poorer outcomes with stroke prevention, as well as with rate and rhythm control management strategies. Many current rhythm control treatment strategies for AF, including cardioversion and ablation, are used less frequently in women as compared to men, whereas women are more likely to be treated with rate control strategies or antiarrhythmic drugs. Sex differences should be considered in treating women with AF to improve outcomes and women and men should be offered the same interventions for AF. We need to improve the evidence base to understand if variation in utilization of rate and rhythm control management between men and women represents health inequities or appropriate clinical judgement.

Temporal trends in atrial fibrillation recurrence rates after ablation between 2005 and 2014: a nationwide Danish cohort study

Aims

During the last decade, ablation has increasingly been used in rhythm control management of patients with atrial fibrillation (AF). Over time, experience and techniques have improved and indications for ablation have expanded. The purpose of this study was to investigate whether the recurrence rate of AF following ablation has improved during last decade.

Methods and results

Through Danish nationwide registers, all patients with first-time AF ablation, between 2005 and 2014 in Denmark were identified. Recurrent AF after ablation was identified with 1 year follow-up. A total of 5425 patients undergoing first-time ablation were included. While patient median age increased over time the median AF duration prior to ablation decreased. The rates of recurrent AF decreased from 45% in 2005-2006 to 31% 2013-2014 with the relative risk of recurrent AF almost halved with an odds ratio of 0.57 [95% confidence intervals (95% CI) 0.47-0.68] in 2013-2014 compared with patients undergoing ablation in 2005-2006. Female gender, hypertension, AF duration >2 years, and cardioversion within 1 year prior to ablation were all associated with an increased risk of recurrent AF.

Conclusion

One year risk of recurrent AF following first-time ablation has almost halved from 2006 to 2014. Hypertension, female sex, cardioversion 1 year prior to ablation, and AF duration for more than 2 years all increased the associated risk of recurrent AF.

Acute Stroke After Upper Endoscopy in a Patient With a Suspected Atrioesophageal Fistula

Atrioesophageal fistula (AEF) is a rare complication of atrial fibrillation ablation. We present a man with sepsis and frank hematemesis 3 weeks after atrial fibrillation ablation. Thoracic computed tomography showed no definitive evidence of AEF. He underwent esophagogastroduodenoscopy and subsequently developed an embolic stroke. In the operating room, he was found to have AEF. This case highlights the importance of maintaining a high index of suspicion for AEF because of its nonspecific presentation and difficulty in diagnosing with imaging or endoscopy. Once AEF is suspected, esophagogastroduodenoscopy should be avoided because of the risk of precipitating embolic events.

Women with atrial fibrillation and type 2 diabetes have a higher incidence of hospitalization and undergo ablation or pacemaker implantation less frequently than men

BACKGROUND

We reviewed trends from 2004 to 2013 in the incidence and outcomes for atrial fibrillation (AF) in Spanish patients with type 2 diabetes mellitus (T2DM) comparing women and men.

METHODS

We used national hospital discharge data including all T2DM patients discharged from the hospital after AF. Patients with AF in the primary diagnosis field were selected. Discharges were grouped by sex. Incidence was calculated overall and stratified by sex. We analyzed diagnostic and therapeutic procedures, patient comorbidities, CHA2DS2-VASc score, length of hospital stay, readmission rates and in-hospital mortality (IHM).

RESULTS

We identified a total of 214,457 admissions for AF. Patients with T2DM accounted for 21.1% (19,505 men and 25,954 women). Women with T2DM had a significantly higher incidence of AF compared to men over the study period (IRR 1.33;95%CI 1.31-1.35). Women were significantly older (77.24±8.69years) than men (72.62±10.28years), had higher prevalences of obesity and hypertension, and higher CHA2DS2-VASc score. Women less frequently underwent ablation (3.21% vs. 1.54%; p<0.001) and received an implanted pacemaker (14.3% vs. 8.16%; p<0.001) than men. Crude IHM was 2.81% for women and 2.48% for men (p=0.030). Sex was not associated with a higher IHM after multivariable adjustment.

CONCLUSIONS

Our study demonstrates an increase in hospitalization for AF in diabetic women. Women were older, had a higher comorbidity index and had CHAD2DS2-VASc score than men. Women with AF and T2DM undergo ablation or pacemaker implantation less frequently than their male counterparts. After multivariable adjustment sex did not predict mortality during admissions for AF.

Gender, Race, and Health Insurance Status in Patients Undergoing Catheter Ablation for Atrial Fibrillation

Catheter ablation for atrial fibrillation (AF) has emerged as a popular procedure. The purpose of this study was to examine whether there exist differences or disparities in ablation utilization across gender, socioeconomic class, insurance, or race. Using the Nationwide Inpatient Sample (2000 to 2012), we identified adults hospitalized with a principal diagnosis of AF by ICD 9 code 427.31 who had catheter ablation (ICD 9 code-37.34). We stratified patients by race, insurance status, age, gender, and hospital characteristics. A hierarchical multivariate mixed-effect model was created to identify the independent predictors of AF ablation. Among an estimated total of 3,508,122 patients (extrapolated from 20% Nationwide Inpatient Sample) hospitalized with a diagnosis of AF in the United States from the year 2000 to 2012, 102,469 patients (2.9%) underwent catheter ablations. The number of ablations was increased by 940%, from 1,439 in 2000 to 15,090 in 2012. There were significant differences according to gender, race, and health insurance status, which persisted even after adjustment for other risk factors. Female gender (0.83 [95% CI 0.79 to 0.87; p <0.001]), black (0.49 [95% CI 0.44 to 0.55; p <0.001]), and Hispanic race (0.64 [95% CI 0.56 to 0.72; p <0.001]) were associated with lower likelihoods of undergoing an AF ablation. Medicare (0.93, 0.88 to 0.98, <0.001) or Medicaid (0.67, 0.59 to 0.76, <0.001) coverage and uninsured patients (0.55, 0.49 to 0.62, <0.001) also had lower rates of AF ablation compared to patients with private insurance. In conclusion we found differences in utilization of catheter ablation for AF based on gender, race, and insurance status that persisted over time.

Management of Atrio-Esophageal Fistula Following Left Atrial Ablation

Currently, no guidelines have been established for the treatment of atrio-esophageal fistula (AEF) secondary to left atrial ablation therapy. After comprehensive literature review, we aim to make suggestions on the management of this complex complication and also present a case series. We performed a review of the existing literature on AEF in the setting of atrial ablation. Using keywords atrial fibrillation, atrial ablation, fistula formation, atrio-esophageal fistula, complications, interventions, and prognosis, a search was made using the medical databases PUBMED and MEDLINE for reports in English from 2000 to April 2015. A statistical analysis was performed to compare the three different intervention arms: medical management, stent placement and surgical intervention. The results of our systematic review confirm the high mortality rate associated with AEF following left atrial ablation and the necessity to diagnose atrio-esophageal injury in a timely manner. The mortality rates of this complication are 96% with medical management alone, 100% with stent placement, and 33 % with surgical intervention. Atrio-esophageal injury and subsequent AEF is an infrequent but potentially fatal complication of atrial ablation. Early, prompt, and definitive surgical intervention is the treatment of choice.

Atrioesophageal fistula following ablation procedures for atrial fibrillation: systematic review of case reports

BACKGROUND

Atrioesophageal fistula (AEF) is a rare but serious adverse event of atrial fibrillation (AF) ablation.

OBJECTIVE

To identify the clinical characteristics of AEF following ablation procedures for AF and determine the associated mortality.

METHODS

A systematic review of observational cases of AEF following ablation procedures for AF was performed following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement protocol.

RESULTS

53 cases were identified. Mean age was 54±13 years; 73% (39/53) of cases occurred in males. Mean interval between procedure and presentation was 20±12 days, ranging from 2 to 60 days. AEF was observed in 12 patients who underwent surgical radiofrequency ablation (RFA) and in 41 patients with percutaneous RFA. Fever was the most common presenting symptom (n=44) followed by neurological deficits (n=27) and haematemesis (n=19). CT of the chest (n=27) was the preferred diagnostic test. Patients who did not receive a primary esophageal repair were more likely to have a deadly outcome (34% vs 83%; p<0.05). No difference in mortality rate was found between patients who underwent surgical RFA when compared with percutaneous RFA (58% vs 56%; p=0.579). No association was found between onset of symptoms and mortality (19±10 vs 23±14 days; p=0.355).

CONCLUSIONS

AEF following ablation procedures for AF is a serious complication with high mortality rates. Presenting symptoms most often include a triad of fever, neurological deficit and/or haematemesis within 60 days of procedure. The preferred diagnostic test is CT of the chest. The treatments of choice is surgical repair.

Comparative safety of periablation anticoagulation strategies for atrial fibrillation: data from a large multicenter study

BACKGROUND

There are a variety of periprocedural anticoagulation strategies for atrial fibrillation (AF) ablation, including the use of dabigatran. It is unclear which strategy is superior.

OBJECTIVE

To compare the safety and efficacy of anticoagulation with uninterrupted warfarin, dabigatran, and warfarin with heparin bridging in patients undergoing ablation of AF at four experienced centers.

METHODS AND RESULTS

In this retrospective analysis, 882 patients (mean age: 61 ± 11 years) underwent ablation of AF using uninterrupted warfarin (n = 276), dabigatran (n = 374), or warfarin with heparin bridging (n = 232) for periprocedural anticoagulation. The rate of total complications was 23/276 (8.3%) in the uninterrupted warfarin group, 30/374 (8.0%) in the dabigatran group, and 29/232 (12.5%) in the bridged group (P = 0.15). Major complications were more frequent in the uninterrupted warfarin group 12/276 (4.3%) compared with 3/374 (0.8%) in dabigatran and 6/232 (2.6%) in the bridged group (P = 0.01). The most common major complication was the need for transfusion or occurrence of major bleeding. Minor complications did not differ among the three groups. On multivariate analysis, female gender (odds ratio [OR] 1.93, confidence interval [CI] 1.16-3.19, P = 0.011), bridging heparin (OR 2.13, CI 1.100-3.941, P = 0.016), use of triple antithrombotic therapy (OR 1.77, CI 1.05-2.98, P = 0.033), and prior myocardial infarction (OR 2.40, CI 1.01-5.67, P = 0.046) independently predicted total complications.

CONCLUSIONS

When comparing the use of uninterrupted warfarin, dabigatran, and warfarin with heparin bridging in patients undergoing catheter ablation of AF, dabigatran was not associated with increased risk, major complications were more common in the uninterrupted warfarin group, and after adjustment, warfarin with bridging increased total complications.

Trends in utilization of management strategies for newly diagnosed atrial fibrillation patients in the United States: 1999 to 2008

OBJECTIVE

To describe the trend in atrial fibrillation (AF) treatment strategies in newly diagnosed AF patients between 1999 and 2008.

METHODS

The study was a retrospective cohort study of commercial health plans claims data. Newly diagnosed adult AF patients with ≥1 claim for an AF-related intervention within 12 months of diagnosis were identified. Based on initial treatment, patients were classified into pharmacotherapy or nonpharmacotherapy groups. Pharmacotherapy group was subcategorized into rate-control or rhythm-control groups. Linear regression to assess linear trend and multinomial logistic regression to evaluate factors associated with treatment choice were conducted.

RESULTS

Three thousand ninety-four newly diagnosed AF patients were identified. Eighty percent of these patients were initiated on pharmacotherapy with the majority (84%) receiving rate-control medications only. Relative distribution of the 3 treatment groups remained similar over the study period. However, within the rate-control group, the use of beta blockers increased significantly (P < .001). Treatment with nonpharmacotherapy over rate-control medications was higher in males but lower in patients aged ≥80 (relative risk ratio [RRR]: 1.67, 95% confidence interval [CI]: 1.27-2.20 and RRR: 0.48, 95% CI: 0.30-0.77, respectively). Having stroke and congestive heart failure significantly affected the treatment choice between nonpharmacotherapy and rate-control medications.

CONCLUSION

Medication therapy, especially rate-control strategies, remains the preferred initial therapy of choice.

Gender and Racial Characteristics of Patients Referred to a Tertiary Atrial Fibrillation Center

Atrial Fibrillation Centers (AFCs) are becoming increasingly common and are often developed at institutions to provide comprehensive evaluation and management for patients with atrial fibrillation (AF) including catheter and surgical ablation. Studies have shown that women and racial minority patients are less likely to be offered aggressive or invasive therapies. The University of Virginia (UVA) AFC was opened in 2004. We analyzed data collected during initial visits to our AFC from 2004-2008 to determine the gender and racial characteristics of a tertiary AFC population. Multivariable regression analysis was used to compare clinical characteristics. There were a total of 1664 consecutive initial patient visits. Cardiologists referred 61% and primary care physicians referred 37% of patients. Twice as many men were referred as women (570 vs. 1094; P<0.0001). Women were older (68.0±11.9 vs. 62.4±13.0 years; P<0.0001) and more symptomatic with palpitations (80% vs. 73%; P=0.008), but otherwise were not substantially different from men. Our referring physicians treated the majority of both men and women with anticoagulant and rate-controlling medications. African American patients accounted for 2.8% of AFC initial visits. In contrast, they accounted for 7.4% of patients seen for a primary diagnosis of AF at all other UVA outpatient clinics (P<0.0001). In conclusion, the demographics of a tertiary AFC are different than those of the general population. Women and racial minority patients are underrepresented, and the women have few comorbidities and symptoms than the known epidemiology would lead us to expect.

Total costs and atrial fibrillation ablation success or failure in Medicare-aged patients in the United States

INTRODUCTION

This retrospective cohort study compared the direct medical costs of successful versus unsuccessful catheter ablation in Medicare-aged patients with atrial fibrillation (AF), using medical claims data.

METHODS

AF patients with > or = 12 months of continuous medical/pharmacy coverage pre- and postablation were identified from the MarketScan Medicare database (January 2003 to December 2006). For study inclusion, patients were required to have > or = 2 AF inpatient/outpatient visits within 6 months and to have received antiarrhythmic drug therapy within 12 months prior to the index ablation. Ablation success was defined as the absence of antiarrhythmic drug therapy 6-12 months postablation.

RESULTS

Of 135 patients identified (67% men, mean age 73 years), ablation was successful in 69 (51.1%); most patients (96%) underwent a single procedure. Patients with successful ablation discontinued antiarrhythmic drug treatment after (mean) 54 days. Use of rate-control and anticoagulant drugs decreased after successful ablation, from 87% to 67% and from 86% to 64% of patients, respectively. Among failed ablation patients, 74% versus 70% received rate-control drugs, and 88% versus 82% received anticoagulants pre- versus postablation. Mean +/- SD per-patient procedural costs were $13,655+/-$12,761 for successful compared with $17,294+/-$26,502 (P=0.21) for failed ablation, while AF-related medical costs over 12 months postablation were $2394+/-$642 and $2703+/-$1706, respectively (P<0.001). Overall costs tended to be lower for successful ($16,049+/-$12,536) than for failed ($19,997+/-$13,958) AF ablation (P=0.07). These findings are subject to the limitations imposed by a retrospective database analysis and a small sample size.

CONCLUSION

Outside the clinical-trial setting, catheter ablation for second-line treatment of AF proved unsuccessful in half of Medicare-aged patients. Direct medical costs did not differ significantly between patients with failed and successful ablations. The high rate and costs of AF ablation failure in the Medicare-aged population reinforce the need for better understanding of prognostic factors for ablation outcome.

Introduction of an expert system for the discrimination of local pulmonary vein and atrial far field signals

BACKGROUND

Discrimination of local and far field potentials during sinus rhythm and atrial fibrillation (AF) is essential for successful pulmonary vein (PV) isolation. We sought to introduce an expert system for the classification of electrophysiologic PV signals.

METHODS

For the expert system database, we analyzed ablation procedures of 50 patients with paroxysmal and persistent AF. Standard circumferential catheters and bipolar recordings were required. In a prospective trial, the expert system was compared with the performing electrophysiologists' classifications of potentials during 15 procedures. A total of 1,343 recordings of local PV and far field signals were validated by the sudden disappearance of local potentials during ablation, the presence of dissociated PV activity, and pacing maneuvers. A fast Fourier transform was applied to the individual potentials. Analysis continued in the amplitude and phase representation.

RESULTS

Four parameters significant (p < 0.001) for classification were identified and entered a logistic regression model. Overall sensitivity and specificity of the model was 87% with minor, nonsignificant variations for individual PVs and different underlying rhythms. Concordance with ad hoc electrophysiologists' classification of local potentials was 70%, which increased during post hoc analysis to 86% since classification of 14% of the potentials had to be revised. For these potentials, the expert system correctly predicted their local origin in 86%.

CONCLUSION

An expert system for the evaluation of electrophysiologic signals based on morphology analysis using the Fourier transform is feasible. The ease of use and online availability facilitate a widespread use for AF ablation procedures.

Atrial fibrillation: mechanistic insights and treatment options

Atrial fibrillation (AF) remains the most common clinically encountered arrhythmia. Unlike supraventricular arrhythmias that use a defined mechanism, AF involves a wide spectrum of arrhythmias from lone AF to paroxysmal to chronic AF. AF is an arrhythmia that may develop in several ways. Mechanical remodeling manifests as decreased atrial contractility and increased atrial compliance which leads to a stretch of the atrial myocardium. Atrial remodeling may also increase in atrial fibrosis which can slow conduction velocity and can shorten the refractory period in atria with long-standing AF. It is still unclear whether initiation of AF activates direct inflammatory effects or whether the presence of a pre-existing systemic inflammatory state promotes further persistence of AF. Currently, the patient population undergoing AF ablation has greatly expanded. Patients are older and have larger left atrial size and are more likely to have persistent/permanent AF. It is likely that AF comprises a spectrum of disease with no single mechanism adequate enough to comprehensively explain AF and its variability. The management of patients with AF involves elements of anticoagulation, rate control and rhythm control and such treatment strategies are not necessarily mutually exclusive of each other.

Trends in catheter ablation for atrial fibrillation in the United States

BACKGROUND

There are few data on the use of catheter ablation for atrial fibrillation (AF) in the United States. We analyzed data from the National Hospital Discharge Survey (NHDS) to examine trends in the rate of catheter ablation for hospitalized patients with AF over a 15-year period.

OBJECTIVE

To examine rates of catheter ablation in patients with AF over time.

DESIGN

All adult patients in the NHDS with an International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) code for AF from the years 1990 to 2005 were identified and assessed for the presence of a cardiac catheter ablation procedure code. Clinical characteristics associated with ablation were identified and multivariable logistic regression used to determine trends in the rate of ablation therapy over time.

RESULTS

We identified 269,471 adults with AF. The rate of catheter ablation in AF patients increased from 0.06% in 1990 to 0.79% in 2005 (P < 0.001 for trend). Compared to those not undergoing ablation, ablated patients were younger (mean age 66 versus 76 years; P < 0.001), more likely to be male (57% versus 43%; P < 0.001), have private insurance (22% versus 11%; P < 0.001), and have a none of the following stroke risk factors: congestive heart failure, hypertension, age >75 years, diabetes mellitus, or stroke/transient ischemic attack (37% versus 16%; P < 0.001). Catheter ablation in AF patients increased by 15% per year over the time period (95% confidence interval [CI], 13%-16%) and across all age groups, including in patients age > or =80 years (0.0% in 1990 and 0.26% in 2005; P < 0.001 for trend).

CONCLUSIONS

The rate of catheter ablation in patients with AF is increasing significantly over time, even in the oldest patients. Medicine.

Rational patient selection for catheter ablation of atrial fibrillation

During the past decade, catheter ablation of atrial fibrillation has been progressively used for the treatment of drug-refractory patients. As experience and technique have evolved, patient selection criteria have been modified to include a wider range of patients. Patients with paroxysmal, persistent, and longstanding persistent atrial fibrillation can be treated with catheter ablation. Catheter ablation is an option for many patients, including older patients (septuagenarians and octogenarians), those with enlarged left atrium, and those with cardiomyopathy. Results and safety are satisfactory and often superior to medical treatment. In patients with structural heart disease, multiple ablative procedures may be required to achieve cure. Ongoing clinical research will provide further insight into future criteria for patient selection.

Catheter ablation of atrial fibrillation: for whom and how?

Catheter ablation is the treatment of choice for certain patients with drug-refractory paroxysmal or even persistent atrial fibrillation. Several techniques are used with a similar success rate of approximately 70% over 6 to 12 months of follow-up. Pulmonary vein isolation by conventional antral or electroanatomic circumferential ablation is mainly used in patients with paroxysmal atrial fibrillation. Electrogram-guided and combined approaches are also used, particularly in patients with persistent atrial fibrillation, whereas new methods such as autonomic denervation are under investigation.