To evaluate mirabegron's effect on ventricular arrhythmia control. The study will be conducted in ambulatory patients with ventricular tachycardia (VT), organic heart diseases, and an implantable cardioverter-defibrillator (ICD). The investigators will perform a pilot study involving 20 patients. Each will receive 50 mg of mirabegron. All will have neuECG recordings made before and 2 months after mirabegron. The data will be analyzed to test the proposed hypothesis.

Objectives:

Primary objective: To evaluate if mirabegron can reduce the VT burden. Secondary objective: To test the hypothesis that mirabegron can reduce the average skin sympathetic nerve activity (aSKNA).

Endpoints: The primary endpoint is the burden of VT detected by ICD. The secondary endpoint is the average skin sympathetic nerve activity, symptoms, and quality of life (QOL) questionnaires.

Study Population: This is a pilot study in patients with an ICD and, on average, > 2 episodes of VT per month over the past 2 months despite guideline-recommended medical therapy (GRMT).

Phase: Phase 2.

Description of Sites/Facilities Enrolling Participants: The investigators will enroll patients in the cardiac device clinic at the Smidt Heart Institute, Cedars-Sinai Medical Center. Dr. Ashkan Ehdaie (co-investigator) directs the clinic, which routinely follows up on patients with ICDs.

Description of Study Intervention: The investigators will give the patients 50 mg/day of mirabegron orally for three months.

Study Duration: One-year.

Participant Duration: Approximately three months. The primary endpoint takes 2 months to complete. The investigators will call the patient at 3 months to determine if there are any complications. The patient will then exit the study.

Inclusion Criteria:

• In order to be eligible to participate in this study, an individual must meet all the following criteria:

  1. Provision of signed and dated informed consent form.

  2. Age > 18 years old.

  3. Documented VT on ICD.

     1. with > 2 episodes of VT per month (on average) over the past 2 months.
     2. despite guideline-recommended medical therapy (GRMT).

Exclusion Criteria:

• An individual who meets any of the following criteria will be excluded from participation in this study:

  1. Patients who are pacemaker-dependent because the pacing artifacts will complicate skin sympathetic nerve activity (SKNA) analysis.
  2. Clinically unstable (for example, acute myocardial infarction, decompensated heart failure, undergoing cancer chemotherapy, and other acute illness requiring hospitalization)
  3. Uncontrolled hypertension (systolic blood pressure ≥180 mm Hg or diastolic blood pressure ≥110 mm Hg, or both)25
  4. Active thyrotoxicosis
  5. Any experimental medication concomitantly or within 4 weeks of participation in the study
  6. Currently participating in a different clinical trial
  7. Severe renal impairment (CrCl < 30 ml/min)
  8. Hepatic disease (Child-Pugh Class C)
  9. Pregnant
  10. Breastfeeding
  11. Cannot speak, write, and answer questions in English
  12. Does not have the capacity to consent
  13. Severe renal impairment (CrCl < 30 ml/min)
  14. Hepatic disease (Child-Pugh Class C)
  15. Pregnant
  16. Breastfeeding
  17. Cannot speak, write, and answer questions in English
  18. Does not have the capacity to consent
  19. Patients who are known to be allergic to mirabegron or skin patch electrodes
  20. Patients taking codeine, oxycodone, thioridazine, flecainide, propafenone, and digoxin. (see explanation below)

This study is supported by the American Heart Association (AHA). The AHA does not mandate IPD for studies cited in guidelines