Combination of vacuum erection device and PDE5 inhibitors as salvage therapy in PDE5 inhibitor nonresponders with erectile dysfunction

Princeton IV consensus guidelines: PDE5 inhibitors and cardiac health

BACKGROUND

In 1999, 1 year after the approval of the first oral phosphodiesterase type 5 (PDE5) inhibitor for the treatment of erectile dysfunction (ED), the first Princeton Consensus Conference was held to address the clinical management of men with ED who also had cardiovascular disease. These issues were readdressed in the second and third conferences. In the 13 years since the last Princeton Consensus Conference, the experience with PDE5 inhibitors is more robust, and recent new data have emerged regarding not only safety and drug-drug interactions, but also a potential cardioprotective effect of these drugs.

AIM

In March 2023, an interdisciplinary group of scientists and practitioners met for the fourth Princeton Consensus Guidelines at the Huntington Medical Research Institutes in Pasadena, California, to readdress the cardiovascular workup of men presenting with ED as well as the approach to treatment of ED in men with known cardiovascular disease.

METHOD

A series of lectures from experts in the field followed by Delphi-type discussions were developed to reach consensus.

OUTCOMES

Consensus was reached regarding a number of issues related to erectile dysfunction and the interaction with cardiovascular health and phosphodiesterase-5 inhibitors.

RESULTS

An algorithm based on recent recommendations of the American College of Cardiology and American Heart Association, including the use of computed tomography coronary artery calcium scoring, was integrated into the evaluation of men presenting with ED. Additionally, the issue of nitrate use was further considered in an algorithm regarding the treatment of ED patients with coronary artery disease. Other topics included the psychological effect of ED and the benefits of treating it; the mechanism of action of the PDE5 inhibitors; drug-drug interactions; optimizing use of a PDE5 inhibitors; rare adverse events; potential cardiovascular benefits observed in recent retrospective studies; adulteration of dietary supplements with PDE5 inhibitors; the pros and cons of over-the-counter PDE5 inhibitors; non-PDE5 inhibitor therapy for ED including restorative therapies such as stem cells, platelet-rich plasma, and shock therapy; other non-PDE5 inhibitor therapies, including injection therapy and penile prostheses; the issue of safety and effectiveness of PDE5 inhibitors in women; and recommendations for future studies in the field of sexual dysfunction and PDE5 inhibitor use were discussed.

CLINICAL IMPLICATIONS

Algorithms and tables were developed to help guide the clinician in dealing with the interaction of ED and cardiovascular risk and disease.

STRENGTHS AND LIMITATIONS

Strengths include the expertise of the participants and consensus recommendations. Limitations included that participants were from the United States only for this particular meeting.

CONCLUSION

The issue of the intersection between cardiovascular health and sexual health remains an important topic with new studies suggesting the cardiovascular safety of PDE5 inhibitors.

Combination therapy with topical alprostadil and phosphodiesterase-5 inhibitors after failure of oral therapy in patients with erectile dysfunction: a prospective, two-arm, open-label, non-randomized study

Phosphodiesterase type 5 inhibitors (PDE5Is) are the first-line therapeutic option for erectile dysfunction (ED), while second-line therapy includes the alprostadil. Due to the different pharmacodynamic mechanism of PDE5Is and alprostadil, a synergistic action is conceivable when they are administered in combination. The aim of present study was to evaluate the efficacy and safety of combination therapy with PDE5I and topical alprostadil in patients with ED non-responders to PDE5I alone. We designed a prospective, two-arm, open-label, non-randomized study. Patients over 18 years old, with a stable sexual relationship for at least 6 months, and ED non-responders to PDE5I monotherapy were included in the study. At baseline the variables assessed were 5-item version of the International Index of Erectile Function (IIEF-5), and Sexual Encounter Profile Questions 2 and 3 (SEP-2 and SEP-3). In addition, all subjects underwent penile dynamic duplex ultrasonography. All patients were assigned to the monotherapy group (Group A) or combination therapy group (Group B) based on their preference. Topical alprostadil 300 μg/100 mg (Virirec®) was the treatment assigned to Group A, while the combination therapy with the last PDE5I taken (at the maximum recommended dose) plus topical alprostadil 300 μg/100 mg (Virirec®) was assigned to Group B. After 3 months from assignment to groups were evaluated IIEF-5, SEP-2 and SEP-3 regarding the last sexual intercourse, and Global Assessment Questionnaire-Questions 1 and 2 (GAQ-1 and GAQ-2). All adverse events (AEs) that occurred during the study period were recorded. A total of 170 patients were included in the study (72 in Group A and 98 in Group B). Fifty-two patients were previously treated with sildenafil 100 mg (30.6%), 6 with vardenafil 20 mg (3.5%), 56 with tadalafil 20 mg (32.9%), and 56 with avanafil 200 mg (32.9%). No significant differences among the study groups were found at baseline (p > 0.05). The mean IIEF-5 score increased significantly in Group B after treatment compared to baseline (12.4 ± 3.4 vs. 17.1 ± 4.5; p < 0.001), conversely patients in Group A showed no significant increase (12.2 ± 2.5 vs. 12.7 ± 3.1; p = 0.148). The number of affirmative responses to SEP-2 was significantly higher after treatment compared to baseline only in Group B (57 vs. 78; p < 0.001). The number of affirmative responses to SEP-3 was significantly higher after treatment compared to baseline in both groups (p < 0.001). The number of affirmative responses to GAQ-Q1 and GAQ-Q2 was significantly higher in Group B compared to Group A (p < 0.001). A total of 59 (34.7%) patients experienced AEs. They were mild, self-limited, and did not cause discontinuation of treatment. No episode of priapism was recorded. No statistically significant difference was recorded between the AEs of the two groups, except for facial flushing that was reported only in Group B (p = 0.021). The combination therapy with topical alprostadil and PDE5I seems to be more effective than topical alprostadil alone without worsening the safety of the treatment.

Indications and characteristics of penile traction and vacuum erection devices

A variety of devices are available for the management of patients with erectile dysfunction, Peyronie's disease, penile dysmorphophobia, for support before and after penile prosthesis insertion, and after radical prostatectomy. Traction devices include, but are not limited to, Penimaster PRO (MSP Concept, Berlin, Germany), Andropenis and Andropeyronie (Andromedical, Madrid, Spain), and the Restorex (PathRight Medical, Plymouth, USA). The other type of devices are vacuum devices such the Osbon ErecAid (Timm Medical, MN, USA). Different devices are optimal for different clinical applications, and robust and contemporary clinical data show a variety of strengths and weaknesses for each device. Research currently favours the use of traction devices for improvement of penile curvature and erectile function in patients with Peyronie's disease compared with vacuum devices; Penimaster Pro and Restorex have been shown to be associated with the best outcomes in this indication. Vacuum devices are favoured for treatment of erectile dysfunction and penile length loss after radical prostatectomy; the Osbon ErecAid is the most well-studied device for this indication. Research into other uses of vacuum and traction devices, such as for penile dysmorphophobia or before and after penile prosthesis, is very limited. Compliance, cost and availability remain substantial challenges, and further high-quality evidence is required to clarify the role of traction devices in urology and sexual medicine.

Erectile dysfunction and diabetes: A melting pot of circumstances and treatments

Diabetes mellitus (DM), a chronic metabolic disease characterised by elevated levels of blood glucose, is among the most common chronic diseases. The incidence and prevalence of DM have been increasing over the years. The complications of DM represent a serious health problem. The long-term complications include macroangiopathy, microangiopathy and neuropathy as well as sexual dysfunction (SD) in both men and women. Erectile dysfunction (ED) has been considered the most important SD in men with DM. The prevalence of ED is approximately 3.5-fold higher in men with DM than in those without DM. Common risk factors for the development of DM and its complications include sedentary lifestyle, overweight/obesity and increased caloric consumption. Although lifestyle changes may help improve sexual function, specific treatments are often needed. This study aims to review the definition and prevalence of ED in DM, the impact of DM complications and DM treatment on ED and, finally, the current and emerging therapies for ED in patients with DM.

The Efficacy of Li-ESWT Combined With VED in Diabetic ED Patients Unresponsive to PDE5is: A Single-Center, Randomized Clinical Trial

INTRODUCTION

Phosphodiesterase type 5-inhibitors (PDE5is) are the first-line treatment for patients with diabetes mellitus-induced erectile dysfunction (DMED), however, some patients are non-responser to PDE5is. We performed a perspective, randomized, comparative study to explore the efficacy of low intensity extracorporeal shock wave treatment (Li-ESWT) combined with vacuum erectile device (VED) in the treatment of DMED patients who were unresponsive to PDE5is.

METHODS

One hundred and five eligible patients were randomly divided into three groups: group A (VED), group B (Li-ESWT) and group C (VED plus Li-ESWT). Follow-up was conducted at 4 weeks, 8 weeks and 12 weeks after the end of treatment. The erectile function was estimated by the international index of erectile function-erectile function domain (IIEF-EF), erection hardness score (EHS), sexual encounter profile questions 2 and 3 (SEP2 and SEP3) and global assessment question 1 and 2 (GAQ1 and GAQ2) before and after treatment. The changes of five points in IIEF-EF were calculated as the minimal clinical important difference (MCID), which was considered as the main index of efficacy.

RESULTS

The MCID was achieved in 14.7%, 14.7% and 17.6% patients in group A at the follow up on 4 weeks, 8 weeks and 12 weeks, respectively (36.4%, 39.4% and 36.4% in group B; 36.4%, 51.5%, and 66.7% in group C). There were significant differences in the percentage of MCID cases between group A and group C at the follow up on 12 weeks (P<0.001), as well as that between group B and group C (P=0.014). Additionally, comparison in MCID within group C showed that there were significant differences between 4 weeks and 12 weeks follow-up (P=0.014).

CONCLUSION

Our findings indicated the combined therapy Li-ESWT and VED was more beneficial to shift turn PDE5is non-responders to responders for moderate patients with DMED than VED or Li-ESWT monotherapy. Moreover, this study provided evidence that patients with DMED who failed after taking oral PDE5is could attempt to opt for an alternative physicotherapy (Li-ESWT or VED) prior to more invasive alternatives.

Considerations for prescribing pharmacotherapy for the treatment of erectile dysfunction

Introduction: The effectiveness of phosphodiesterase type 5 inhibitors (PDE5i) in treating erectile dysfunction (ED) creates a new field of both medical practice and pharmaceutical manufacturing. Both paved the way for emerging minimally invasive therapies to restore male sexual function. However, what is the best drug to achieve the optimum outcome is still a challenging question to be answered.Areas covered: The general viewpoint of matching the pharmacotherapeutic characteristics with the patient's medical, social, and psychological variables, in order to balance between efficacy and safety. Several studies had investigated considerations for preference and long-term adherence for PDE5i. However, a thorough investigation of considerations for prescribing ED pharmacotherapy is still lacking in the literature. This is the aim of this manuscript.Expert opinion: Several issues should be considered in the planning of ED management such as the patient's and partner's expectations, etiologic considerations, performance status, safety, adverse effects, ease of administration, compliance, bad experiences with previous treatment, availability, cost, social factors, satisfaction, and finally, regimen considerations. Addressing the patient's and partner's individual needs help to tailoring treatment in order to minimize compromises and optimize gains.

Practical Approaches to Treat ED in PDE5i Nonresponders

Erectile dysfunction (ED) is a common sexual disorder in adult males and one of the most important factors affecting their quality of life and that of their partners. Although PDE5 inhibitors (PDE5is) are the first choice for improving erectile function, there is a substantial proportion of ED patients, termed PDE5i nonresponders, who do not respond to PDE5is. Because of the lack of effective therapies, these patients always have serious social and psychological problems due to ED, which should be addressed. Here, we review the available literature about ED and PDE5is and propose several strategies for mitigating ED in PDE5i nonresponders.

Non-invasive Management Options for Erectile Dysfunction When a Phosphodiesterase Type 5 Inhibitor Fails

Phosphodiesterase type 5 inhibitors (PDE5Is) are the drug of choice for medical management of erectile dysfunction (ED). On-demand PDE5Is have an overall efficacy of 60-70% for ED; 30-35% of patients fail to respond to a PDE5I, and 30-50% of non-responders can be salvaged with detailed counseling on proper use and physician follow-up to ensure that the patient has been prescribed an appropriate and full PDE5I clinical trial. True non-responders may be offered intracavernosal injections of erectogenic drugs, intraurethral alprostadil, or surgical insertion of a penile prosthesis. Such options are not discreet and are associated with more adverse effects than PDE5Is. Thus patients may request additional non-invasive medical management options. This review describes published literature on patients who failed to respond to an on-demand PDE5I regimen and were treated with a non-invasive PDEI-based regimen, including switching from one PDE5I to another; increasing the dose of PDE5I above the labeled dosage range; using two PDE5Is concurrently; using a daily PDE5I regimen; or combining a PDE5I with a testosterone supplement, α-adrenergic antagonist, intraurethral or intracavernosal alprostadil, vacuum erection device, or low-intensity shock wave therapy. The limitations of published clinical trials do not allow for sufficient evidence to recommend one option over another. Therefore, in PDE5I-refractory patients, the choice of a specific next step should be individualized based on the preference of the patient and his sexual partner, the advantages and disadvantages of the various options, the concurrent medical illnesses and medications of the patient, and the patient's response to treatment.

Efficacy of vacuum erectile devices (VEDs) after radical prostatectomy: the initial Irish experience of a dedicated VED clinic

Controversy exists regarding optimal penile rehabilitation program following radical prostatectomy (RP). Vacuum erectile devices (VEDs) have become an important component of penile rehabilitation protocols. The aim of this study was to assess the efficacy and patient satisfaction of a dedicated VED clinic. A voluntary telephone questionnaire was performed of all patients who attended a VED clinic to date in two university teaching hospitals. Patient demographics, histopathological characteristics and functional status (International Index of Erectile Function (IIEF) scores) were obtained from a retrospective review of a prospectively maintained database. Sixty-five men attended the dedicated VED clinic in the two university teaching hospitals. Forty-men (76.3%) men purchased a VED following the dedicated clinic. There was significant differences noted between the mean preoperative and the 3-month postoperative IIEF scores (22.08±3.16 vs 11.3±3.08, P=0.0001) and between the 3-month postoperative IIEF score and the post-VED use IIEF score (11.3±3.08 vs 16.74±2.62, P=0.0001). Despite VED use, there was a significant reduction in erectile function from presurgery status (22.08±3.16 vs 16.74±2.62, P=0.0001). All patients reported that the dedicated VED was helpful and would recommend it to other patients. Our study demonstrates that, despite a reduction in erectile function after RP, successful erections are attainable with a VED. There is potential and need for the development of a standard penile rehabilitation program and treatment of ED after RP internationally.

Safety and efficacy of intraurethral alprostadil in patients with erectile dysfunction refractory to treatment using phosphodiesterase-5 inhibitors

INTRODUCTION

Phosphodiesterase-5 inhibitors (PDE5i) are the first choice for treating erectile dysfunction (ED) but are not always effective. The aim of this study was to present our experience in treating patients with ED, refractory to treatment with PDE5i, using intraurethral alprostadil (MUSE).

MATERIAL AND METHODS

We conducted a review of 82 patients with ED and no response to PDE5i, from March 2013 to October 2014. Forty-seven patients (57%) had hypertension (AHT), 24 (29%) had diabetes (DM) and 20 (24%) had AHT and DM. Additionally, 19 (23%) had undergone radical prostatic (RP) surgery. The patients were evaluated after the treatment was applied and at 4 weeks using the following validated questionnaires: International Index of Erectile Function (IIEF-5/SHIM), Global Assessment Questionnaire (GAQ), Sexual Encounter Profile (SEP) and Erectile Dysfunction Inventory of Treatment Satisfaction (EDITS).

RESULTS

The mean patient age was 60.5 years (40-80), and the mean follow-up was 11.3 months (1-20). Sixty-eight percent of the treated patients responded to MUSE(®) (74% in the AHT group, 65% in the AHT+DM group, 62.5% in the DM group and 58% in the RP group). The mean IIEF-5 score was 11.7±4.7, which increased to 18.6±4.9 after MUSE was administered (P=.027). The mean EDITS score at 4 weeks was 61.6 (6-81.9). The most common adverse effect was urethral burning, which occurred in 24 patients (29%). There were no cases of urinary tract infection, syncope or priapism.

CONCLUSIONS

Intraurethral alprostadil is an effective treatment and has a broad safety profile for treating patients with erectile dysfunction refractory to oral treatment with PDE5i.

Landmarks in erectile function recovery after radical prostatectomy

The description of the nerve-sparing technique of radical prostatectomy by Walsh was one of the major breakthroughs in the surgical treatment of prostate cancer in the 20(th) century. However, despite this advance and consequent technological refinements to nerve-sparing surgery, a large proportion of men still suffer from erectile dysfunction (ED) as a complication of prostatectomy. A plethora of therapeutic approaches have been proposed to optimize erectile function recovery in these patients. Several preclinical and translational studies have shown benefits of therapies including PDE5 inhibitor (PDE5I) treatment, immunomodulation, neurotrophic factor administration, and regenerative techniques, such as stem cell therapy, in animal models. However, most of these approaches have either failed to translate to clinical use or have yet to be studied in human subjects. Penile rehabilitation with PDE5Is is currently the most commonly used clinical strategy, in spite of the absence of solid clinical evidence to support its use.

Combined sildenafil with vacuum erection device therapy in the management of diabetic men with erectile dysfunction after failure of first-line sildenafil monotherapy

OBJECTIVE

To evaluate the efficacy and safety of combination therapy of sildenafil plus vacuum erection devices in men with type 2 diabetes mellitus with moderate to severe erectile dysfunction who are dissatisfied with the results of using sildenafil alone.

METHODS

The study included 66 diabetes mellitus patients presenting erectile dysfunction for at least 6 months and dissatisfied with the use of 100 mg sildenafil monotherapy. The patients were randomized in two groups. Those in group A (n = 33) were instructed to use a vacuum erection device only, whereas those in group B (n = 33) were treated with combination therapy, including sildenafil 100 mg and a vacuum erection device. Erectile function was evaluated subjectively using the International Index of Erectile Function, Sexual Encounter Profile questionnaire questions 2 and 3 at visit 1 (baseline; study entry), visit 2 (4 weeks after baseline), and visit 3 (12 weeks after baseline; study end).

RESULTS

There were no significant differences in average patient age, duration of diabetes, duration of erectile dysfunction, baseline International Index of Erectile Function scores, hypertension, blood testosterone, smoking and alcohol consumption between two groups. Mean International Index of Erectile Function scores were significantly higher for group B at the 1-month (14.86 ± 2.17 vs 12.41 ± 2.63; P < 0.0001) and 3-months (17.53 ± 2.95 vs 14.29 ± 2.81; P < 0.0001) visits. Men in group B had better successful penetration (73.3% vs 46.6%) and successful intercourse (70% vs 46.6%) at 3 months compared with group A.

CONCLUSION

Combined use of sildenafil and vacuum erection device therapy significantly enhances erectile function, and it is well tolerated by diabetes mellitus patients not responding to first-line sildenafil alone.

Treatment strategies for diabetic patients suffering from erectile dysfunction: an update

INTRODUCTION

Erectile dysfunction (ED) is one of the most common complications of diabetes. The complex pathophysiology of this disease makes it difficult to create clinical treatments tailored specifically for diabetic patients.

AREAS COVERED

This article will provide an update of both medical and surgical treatment approaches for diabetic ED, as well as discuss established treatments that are the cornerstone of this field.

EXPERT OPINION

Currently, PDE type 5 inhibitors represent the first-line treatment for all patients with ED. In the interim since this article's first publication several new PDE5 inhibitors have come to market. Several others that were previously on the market are now available for daily dosing. Analysis of both testosterone level and hemoglobin A1c is an essential part of treatment. Intracavernosal injections and vacuum constriction devices remain safe, and are highly effective treatment options. The implantable penile prosthesis remains a safe, and definitive treatment modality for those patients with refractory ED. Over the coming years as the understanding of the underlying causes of diabetic ED continues, the development of new, noninvasive, but effective medical treatments will lead to even more options for the treatment of this difficult disease.

The resurgence of the vacuum erection device (VED) for treatment of erectile dysfunction

INTRODUCTION

Vacuum erection devices (VEDs) have been approved in the United States since 1982 and offer a viable alternative to oral phosphodiesterase type 5 inhibitors (PDE5i), injections and transurethral suppositories. Studies have demonstrated efficacy in erectile dysfunction (ED) associated with a variety of conditions. More recently, this modality has been evaluated in initial phosphodiesterase inhibitor nonresponders as well as for post-prostatectomy penile rehabilitation.

AIM

This article provides a detailed overview of the history of VEDs, a review of the literature, and a concise description of their new applications in modern urological practice.

METHODS

A retrospective review of publications relevant to the field of VEDs.

MAIN OUTCOME MEASURES

Review of the historical milestones, evolution, and modern utilization of VEDs in modern urological protocols.

RESULTS

Studies have demonstrated efficacy in ED associated with a variety of conditions. Early penile rehabilitation after surgery for prostate cancer with the VED appears to improve erectile function and penile length. Adverse events are transient and not serious.

CONCLUSIONS

The VED has continued to show efficacy for treatment of ED due to various etiologies and should be considered an attractive second-line therapy. In select cases such post-prostatectomy penile rehabilitation, as well as in men who cannot use a PDE5i, the vacuum device should be considered first-line treatment.

Rehabilitation of the cavernous smooth muscle in patients with organic erectile dysfunction

This study aimed at assessing the effect of regular use of intracorporeal injection (ICI), sildenafil citrate and vacuum constriction device (VCD) on cavernous smooth muscle and erectile activity. One hundred and sixty-five patients with organic erectile dysfunction were investigated for 3 months. The patient and his partner were classified prospectively after proper counselling: group I (n = 56) received ICI twice per week; group II (n = 55) received sildenafil 100 mg twice per week; and group III (n = 54) used VCD twice per week. Duplex ultrasound was carried out before and after treatment, and then, the patients were followed up for a month to assess the resumption of unaided erection. The results showed that there was significant improvement in mean peak systolic velocity (PSV) and mean cavernosal artery diameter (CAD) at the end of the treatment in all groups, being higher in the ICI group than in the other two groups. Also, the percentage of patients who resumed unaided intercourse were higher in the ICI group compared with the other two groups (17.9%, 9.1% and 3.7% respectively). It is concluded that repeated regular use of ICI, sildenafil or VCD by patients with organic erectile dysfunction has a positive impact on their cavernous blood flow and erectile activity.

Combination therapy for erectile dysfunction: an update review

The introduction of oral phosphodiesterase-5 inhibitors (PDE5Is) in the late 1990s and early 2000s revolutionized the field of sexual medicine and PDE5Is are currently first-line monotherapy for erectile dysfunction (ED). However, a significant proportion of patients with complex ED will be therapeutic non-responders to PDE5I monotherapy. Combination therapy has recently been adopted for more refractory cases of ED, but a critical evaluation of current combination therapies is lacking. A thorough PubMed and Cochrane Library search was conducted focusing on the effectiveness of combination therapies for ED in therapeutic non-responders to PDE5I therapy. Journal articles spanning the time period between January 1990 and December 2010 were reviewed. Criteria included all pertinent review articles, randomized controlled trials, cohort studies and retrospective analyses. References from retrieved articles were also manually scanned for additional relevant publications. Published combination therapies include PDE5I plus vacuum erectile device (VED), intraurethral medication, intracavernosal injection (ICI), androgen supplement, α-blocker or miscellaneous combinations. Based on this review, some of these combination treatments appeared to be quite effective in preliminary testing. Caution must be advised, however, as the majority of combination therapy articles in the last decade have numerous limitations including study biases and small subject size. Regardless of limitations, present combination therapy research provides a solid foundation for future studies in complex ED management.

Vacuum therapy in erectile dysfunction--science and clinical evidence

Vacuum therapy (VT) utilizes negative pressure to distend the corporal sinusoids and to increase the blood inflow to the penis. Depending on its purpose, VT could be used as vacuum constriction device (VCD), with the aid of an external constricting ring which is placed at the base of penis to prevent blood outflow, maintaining the erection for sexual intercourse. Also, as a vacuum erectile device (VED), without the application of a constriction ring, just increases blood oxygenation to the corpora cavernosa and for other purposes. The emerging of phosphodiesterase 5 inhibitors (PDE(5)I) for the treatment of erectile dysfunction (ED) eclipsed VCD as therapeutic choice for ED; however, widespread usage of VED as part of penile rehabilitation after radical prostatectomy and other purposes rekindle the interest for VT. The underlying hypothesis is that the artificial induction of erections shortly after surgery facilitates tissue oxygenation, reducing cavernosal fibrosis in the absence of nocturnal erections, and potentially increases the likelihood of preserving erectile function. Due to its ability to draw blood into the penis regardless of nerve disturbance, VED has become the centerpiece of penile rehabilitation protocols. Herein, we reviewed the history, mechanism, application, side effects and future direction of VT in ED.